Dissertations / Theses: 'Tropical lakes'

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Hamaguchi, Satoshi, and Mitsuru Sakaizumi. "Species differentiation of fishes in tropical lakes : The Seventh MEDAKA Symposium." Laboratory of Freshwater Fish Stocks Bioscience Center Nagoya University, 1994. http://hdl.handle.net/2237/13794.

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Conroy, Jessica. "HISTORY AND DYNAMICS OF CLIMATE VARIABILITY IN THE ASIAN MONSOON REGION AND TROPICAL PACIFIC DURING THE LATE HOLOCENE." Diss., The University of Arizona, 2011. http://hdl.handle.net/10150/145432.

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Large-scale climate modes such as the El Niño/Southern Oscillation (ENSO), the Asian monsoon, and the Arctic Oscillation are responsible for much of the Earth’s climate variability. Despite the importance of these modes, we have limited understanding of how they vary on long (multidecadal to millennial) timescales due to the short length of instrumental climate records. Fortunately, climate information stored in natural archives can provide us with information on how these modes varied in the more distant past. Lake sediments are an ideal climate archive since they are continuous, have high temporal resolution, and contain many potential climate proxies. In the present study, I use lake sediment records to assess past climate and environmental changes associated with the El Niño/Southern Oscillation, the Asian monsoon, and the Arctic Oscillation. Exploring modern precipitation variability across the Asian monsoon region, I found that precipitation within this broad area is not coherent, which holds implications for paleorecords that are hypothesized to represent monsoon variability, including many lake sediment records on the Tibetan Plateau. Monsoon precipitation in the Arabian Sea is distinct from precipitation in India and China, and increased precipitation in the Arabian Sea coincides with decreased precipitation in the western North Pacific. Furthermore, only precipitation in southwestern Tibet responds to the Southwest monsoon, whereas precipitation in southeastern Tibet responds to the western North Pacific monsoon. In southwestern Tibet, I have reconstructed dust variability over the last millennium using the lake sediment record from Kiang Co. The sediment record shows a trend toward increasing dust over the 20th century, and our hypothesized dust proxy is positively correlated with the June-November Arctic Oscillation Index. A trend toward more positive Arctic Oscillation Index values as well as higher temperatures over the 20th century likely drove increased dustiness in southwestern Tibet, due the influence of temperature on glaciofluvial sediment availability in the Himalayas. Sediment trap, sediment core data, and modern measurements of local climate and lake water variables at Genovesa Crater Lake, Galápagos, indicate the lake and its sediments respond to local climate variability, with carbonate-rich sediments forming during prolonged dry periods (La Niña events), and organic-rich sediment forming during the warm season and El Niño events. The ratios of silica to calcium and strontium to calcium also reflect cool season SST. Thus, this lake sediment record has potential to provide a record of both seasonal and ENSO variability spanning the Holocene.

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Miranda, Marcela Aparecida Campos Neves. "Medidas de mitigação para controle e manejo das florações de cianobactérias em um sistema raso tropical." Universidade Federal de Juiz de Fora (UFJF), 2017. https://repositorio.ufjf.br/jspui/handle/ufjf/6500.

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Florações de cianobactérias são consequência principalmente da eutrofização de ambientes aquáticos que afeta a qualidade e compromete o uso da água para diversas finalidades. A restauração de sistemas aquáticos eutrofizados é um dos principais desafios da limnologia atual. Nosso objetivo foi identificar as principais causas do processo de eutrofização e ocorrência de florações de cianobactérias e testar a eficácia e aplicabilidade do uso combinado de coagulantes e adsorventes de P em fase sólida no controle da eutrofização e florações em um lago tropical raso. O estudo foi conduzido no lago do Museu Mariano Procópio, localizado em Juiz de Fora – MG e dividido em quatro fases. As duas primeiras fases compreendem uma análise sistêmica do lago. Na primeira, buscou-se conhecer a dinâmica da comunidade fitoplanctônica a fim de entender a dominância de cianobactéria deste sistema. Na segunda, foram avaliados os aportes de fósforo (P) para o sistema. Na terceira fase foram realizados experimentos em laboratório, para verificar a eficácia de diferentes coagulantes e lastros para remoção de cianobactérias. E na quarta fase foram realizados experimentos em mesocosmos no lago, para testar o controle da eutrofização e florações de cianobactérias. A análise sistêmica mostrou dominância de diferentes espécies de cianobactérias e que as altas concentrações de nutrientes presentes do sistema vêm principalmente de contribuição externa. O uso combinado de coagulantes e lastros foi eficiente para a remoção de biomassa de cianobactérias, porém foi dependente da espécie. Nos experimentos com mesocosmos, foi observada uma forte redução de Clorofila a (Chl a 85%) e fósforo total (TP 78%) (p <0,0010) em todos os tratamentos, porém estas reduções não se mantiveram ao longo do tempo. Para mitigar as florações de cianobactérias deste sistema, será necessário o controle das fontes externas de nutrientes e um ajuste na técnica de coagulante-lastro para manter a clorofila e o fósforo total em concentrações reduzidas por mais tempo.
Cyanobacterial Blooms are mainly a consequence of eutrophication of aquatic environments that affect the water quality and compromise the use of water for various purposes. The restoration of eutrophic aquatic systems is one of the main challenges of today's limnology. Our objective was to identify the main causes of the eutrophication process and the occurrence of cyanobacterial blooms in a shallow tropical lake, and to test the efficacy and applicability of the combined use of coagulants and adsorbents of P in solid phase for the control of eutrophication and cyanobacteria blooms in a tropical shallow system. The study was conducted in the lake of the Mariano Procópio Museum, located in Juiz de Fora - MG and divided into four phases. The first two phases comprised a systemic analysis of the lake. The first one sought to know the dynamics of the phytoplankton community and to understand the causes of the cyanobacteria dominance in this system. In the second one, the main contributions of phosphorus to the system and the general balance of P were evaluated. In the third phase, laboratory experiments were carried out to evaluate the efficacy of different coagulants and ballasts for the removal of cyanobacteria. Last, in the fourth phase experiments were carried out in mesocosmos in the lake to test the control of eutrophication and cyanobacterial blooms. The systemic analysis showed the dominance of different species of cyanobacteria and that the high concentrations of nutrients present in the system come mainly from external contribution. The combined use of coagulants and ballasts was efficient for the removal of cyanobacteria biomass, but it is dependent on the species pool. In the experiments with mesocosms, a strong reductions of chloropyll a (Chl a) 85% and total phosphorus (TP) 78% (p < 0.001) were observed in all treatments, however these reductions were not lasting. To mitigate the cyanobacterial blooms of this system, it will be necessary to control the external sources of nutrients and also an adjustment in the coagulant-ballast technique to keep Chl a l and TP in reduced concentrations for longer time.

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Rai, Ash Kumar. "Limnological Characteristics and Food Evaluation of Planktivorous Caged Fish Species in Sub-tropical Lakes Phewa, Begnas and Rupa of Pokhara Valley, Nepal." 京都大学 (Kyoto University), 2000. http://hdl.handle.net/2433/181462.

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Hales, Philip. "Inorganic geochemistry of tropical lake and swamp sediments." Thesis, University of Oxford, 1991. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.357524.

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Kitaka, Nzula. "Phosphorus supply to a shallow tropical lake and its consequences, Lake Naivasha, Kenya." Thesis, University of Leicester, 2000. http://hdl.handle.net/2381/29813.

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The ecological stability of Lake Naivasha is unpredictable, as it lies in an endorrheic basin situated in an intensive agricultural region with diversified climatic conditions. The situation is getting worse as increase in agricultural activities and hence human population continues, consequently resulting in an increase in water demand and abstraction. An investigation in phosphorus dynamics, interactions and possible sources was carried out both in the inflowing waters and the lake. During the "El Nino" rains approximately 9 times more TP was transported into the lake from the catchment mainly in particulate form (PP). The river Malewa transported almost 30 times more total phosphorus (TP) than the other two rivers. Most of the TP input arose from the middle course of the river, mainly in PP form bound in suspended solids. Watering of the livestock in the river was found to elevate the concentration of TP, PP and total suspended solids (TSS), although its influence downstream depended on discharge, intensity and frequency of disturbance. The phosphorus lake loading to the lake varied significantly between the two hydrological phases encountered with 1.41 and 0.21 g m-2 yr-1 for the "extremely" wet and "normal" wet years respectively classifying the lake as eutrophic. However the overall quotient between the mean in-lake phosphorus (P) and the inflow phosphorus (Pi) concentration from the river Malewa portrayed an equilibrium state with an overall P/Pi ratio of 0.62. The Naivasha sediments are poorly sorted with inorganic phosphorus dominance. The lake sediment has low phosphorus buffering capacity as portrayed by a low phosphorus sorption index (PSI), indicating a phosphorus source rather than sink.

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Park, Lisa Ellyn. "Assessing diversification patterns in an ancient tropical lake: Gomphocythere (Ostracoda) in Lake Tanganyika." Diss., The University of Arizona, 1995. http://hdl.handle.net/10150/187316.

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I examined the distribution of 70 morphological characters for 17 extant species of an ostracod genus, Gomphocythere, in Africa, to test hypotheses concerning character development and speciation patterns. Using heuristic searches conducted with the phylogenetic reconstruction program PAUP, I found 9 trees of 269 steps (CI = 0.45). The skewness of tree length distribution reveals significant phylogenetic structure in the data. Nodes are supported by 2 to 13 character state changes, and these character changes are sometimes reversed or paralleled elsewhere, accounting for much of the homoplasy in the reconstructions. The results suggest the presence of four new species (Gomphocythere coheni, G. downingi, G. wilsoni, G. woutersi). These species are relatively derived within the favored tree. Analyses were done to elucidate the effect of the exclusion of hard and soft part characters and the effects of differential fossil preservation on phylogenetic reconstruction. Eliminating the hard part characters caused the collapse of many branches as polytomies and decreased the agreement of the hard part trees. Excluding the soft part characters increased the number of most parsimonious trees, and decreased the resolution of the trees by creating many unresolved polytomies, but produced similar islands of stability as the complete analysis. I integrated phylogenetic and ecological data sets to examine ecological variables of substrate and depth range and their role in speciation of Gomphocythere in Lake Tanganyika. Using one-way MANOVAs on substrate distribution data, I found significant variability in the substrate distribution of (p =.001) seven species. In addition, principle components analysis and R-mode cluster analysis revealed close associations between certain species with respect to substrate ranges. Correlations exist between species and their ecological tolerances, indicating that environmental fluctuations could have had a profound effect on speciation. In addition, evidence for multiple invasions of Gomphocythere species exist from mapping endemism onto the phylogenetic tree. From this information, a model of speciation emerges in which there have been multiple invasions and subsequent radiations.

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Alin, Simone Rebecca. "Calibration and Interpretation of Holocene Paleoecological Records of Diversity from Lake Tanganyika, East Africa." Diss., The University of Arizona, 2001. http://hdl.handle.net/10150/231412.

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Lake Tanganyika is a complex, tropical ecosystem in East Africa, harboring an estimated 2,100 species. Extensive watershed deforestation threatens the biodiversity and ecological integrity of the lake. In this dissertation, ecological and paleoecological methods were employed to study the distribution of invertebrate biodiversity through space and time, with particular emphasis on linkages between biodiversity and land –use patterns. Ecological surveys of fish, mollusc, and ostracod crustacean diversity at sites in northern Lake Tanganyika representing different levels of watershed disturbance revealed a negative correlation between biodiversity and intensity of watershed disturbance. To elucidate the long -term relationship between disturbance and biodiversity, paleoecological records of invertebrates offshore from watersheds experiencing different degrees of anthropogenic disturbance were examined. Life, death, and fossil assemblages of ostracod valves were compared to assess the reliability and natural variability inherent to the paleoecological record. These comparisons indicated that paleoecological (i.e. death and fossil) assemblages reliably preserve information on species richness, abundance, and occurrence frequency at comparable -to- annual resolution. Unlike life assemblages, species composition of paleoecological assemblages reflects input of species from multiple habitat types. Ostracod paleoecological assemblages are characterized by spatiotemporal averaging that renders them representative of larger areas and longer time spans than life assemblages. Thus, paleoecological assemblages provide an efficient means of characterizing longer -term, site -average conditions. Natural variability in ostracod fossil assemblages from a sediment core representing the Late Glacial to the present indicates that abundance of individual ostracod species is highly variable. Ostracod assemblages were preserved in only the most recent 2,500 years of sediment. Species composition of ostracod assemblages reflects lake water depth. Core geochemical data indicate that the coring site may have been below the oxycline for ~2,000 years, inhibiting ostracod survival and preservation. Paleoecological, sedimentological, and stable isotope data revealed differences in biodiversity and watershed disturbance through time offshore from a pair of sites. The protected site is offshore from Gombe Stream National Park (Tanzania), the other offshore from a deforested watershed outside the park. Offshore from the deforested watershed, sedimentation rates increased, and turnover in ostracod species composition occurred during the past 50 years. Comparable changes were not observed offshore from the park.

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Du, Feu Timothy Avon. "Tropical reservoir fisheries : Lake Kainji, Nigeria: a case study." Thesis, University of Hull, 2003. http://hydra.hull.ac.uk/resources/hull:5505.

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Hubble, David S. "Controls on primary production in Lake Naivasha, a shallow tropical freshwater." Thesis, University of Leicester, 2000. http://hdl.handle.net/2381/29812.

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This study uses Lake Naivasha, Kenya as an example of a shallow tropical freshwater lake. In common with many tropical lakes it experiences fluctuating water-levels which influence its area and productivity, and is currently considered moderately eutrophic. The light regime experienced by phytoplankton in Lake Naivasha dominates other controls as it determines the potential level of primary production. Photoinhibition reduces productivity by 25% at the surface with maximum productivity at a depth of approximately 0.5m. Light attenuation reduces productivity by 50% at 1m depth with zero productivity at 5m depth. Self-shading causes a 17% loss of productivity under conditions of below average productivity, but a 46% loss when productivity is above average. Hydrological factors form a primary control as the mixing regime determines the light regime. Lake Naivasha is generally well mixed, but where temporary stratification occurs there is nutrient resupply due to sediment anoxia. Without mixing, there is a 75% loss of productivity by cell sedimentation. Low sinking rates, tropical conditions and high nutrient availability favour low Surface Area:Volume species such as Aulacoseira which is the dominant genus. Changing conditions such as increased water-column stability could favour cyanobacteria. Bottom-up controls were the most important in Lake Naivasha, reducing potential productivity by 50%. Nitrogen was found to be more limiting than phosphorus with an algal preference for ammonium over nitrate. Minor nutrients were not limiting. The main source of allochthonous nutrients was from river inflow with underflow and circulations around the lake. Top-down control by grazing imposes a 15% reduction in productivity with zooplankton preferring large 'production' cells over small 'standing-stock' cells.

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Matla, Matsoele Moses. "Helminth ichthyo-parasitic fauna of a South African Sub-Tropical Lake." Thesis, University of Limpopo (Turfloop Campus), 2012. http://hdl.handle.net/10386/822.

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Thesis (Ph.D. (Zoology)) --University of Limpopo, 2012
The diversity of the helminth parasites of fishes in a clear-water, subtropical Lake Tzaneen, in South Africa was investigated. Of the 527 fish specimens sampled approximately 9000 parasites were collected. There are 38 different parasite species discussed comprising 27 Monogenea, 3 Digenea, 4 Cestoda, 3 Nematoda and 1 Acanthocephala. Four new monogenean species are described and these are Dactylogyrus spp. 1 to 4. Three monogenean species are introduced as first records in Africa and these are Actinocleidus fusiformis (Mueller, 1934), Haplocleidus furcatus Mueller, 1937 and Acolpenteron ureteroecetes Fischthal & Allison, 1940. Fourteen monogenean and one acanthocephalan species are discussed as first geographical records for South Africa and these are Gyrodactylus rysavyi Ergens, 1973, Dactylogyrus brevicirrus Paperna, 1973, Dactylogyrus cyclocirrus Paperna, 1973, Dogielius dublicornis Paperna, 1973, Dogielius sp., Schilbetrema quadricornis Paperna & Thurston, 1968, Quadriacanthus aegypticus El Naggar & Serag, 1986, Quadriacanthus clariadis Paperna, 1961, Scutogyrus gravivaginus (Paperna & Thurston, 1969), Cichlidogyrus quaestio Douëllou, 1993, Cichlidogyrus halli Price & Kirk, 1967, Cichlidogyrus sclerosus Paperna & Thurston, 1969, Cichlidogyrus dossoui Douëllou, 1993, Cichlidogyrus tilapiae Paperna, 1960 and Acanthosentis tilapiae Baylis, 1948. Seven species are discussed as first records for their hosts and these are Cichlidogyrus dossoui, Cichlidogyrus halli and Acanthosentis tilapiae on Oreochromis mossambicus; Dactylogyrus sp. 1 on Barbus radiatus and Barbus trimaculatus; Dactylogyrus sp. 2 on Barbus unitaeniatus; Dactylogyrus sp. 3 and Dactylogyrus sp. 4 on Labeo molybdinus. Gyrodactylus rysavyi is the only species with a first site (gills) record. The other monogenean species discussed are Macrogyrodactylus clarii Gussev, 1961, Macrogyrodactylus karibae (Douellou and Chishawa, 1995), Dactylogyrus afrolongicornis afrolongicornis Paperna, 1973, Dactylogyrus allolongionchus Paperna, 1973, Dactylogyrus spinicirrus (Paperna & Thurston, 1968) and Cichlidogyrus philander (Douëllou, 1993). The digeneans discussed are Glossidium pedatum Looss, 1899 and the larvae of Diplostomum van Nordmann, 1832 and Clinostomum Leidy, 1856. The Cestodes discussed are Proteocephalus glanduligerus (Janicki, 1928) Fuhrmann, 1933, Polyonchobothrium clarias Woodland, 1925 and the larvae of Ligula intestinalis Goeze, 1782 and family Gryporhynchidae. The nematodes discussed are Procamallanus laevionchus (Wedl, 1861), Paracamallanus cyathopharynx Baylis, 1923 and larvae of Contracaecum Railliet and Henry, 1912. Monogenea were commonly found on the gills but less on the skin and in the urinary bladder. Digenea were found mainly in the eyes, brain and visceral cavity, with only one species (Glossidium pedatum) present in the intestines of Clarias gariepinus. Cestoda and Nematoda were found in the intestine and body cavity. Only one species of Acanthocephala (Acanthosentis tilapiae) was found in the intestines of Oreochromis mossambicus. No definite seasonal variations of infection and parasite affinities towards the sexes and the sizes of the hosts could be determined. The lake is oligotrophic with the water quality having no influence on the parasite diversity and species richness.
the University of Limpopo Research Office, and the National Research Foundation

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Rajmanickam, Vijayaraj, Hema Achyuthan, Christopher Eastoe, and Anjum Farooqui. "Early-Holocene to present palaeoenvironmental shifts and short climate events from the tropical wetland and lake sediments, Kukkal Lake, Southern India: Geochemistry and palynology." SAGE PUBLICATIONS LTD, 2017. http://hdl.handle.net/10150/624066.

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The Kukkal basin, Tamil Nadu, India, receives most of its rain from the southwest monsoon (SWM). A sediment core from Kukkal Lake preserves a continuous sediment record from the early-Holocene to present (9000 yr BP to present). The present lake is situated at an elevation of similar to 1887m a.s.l., in a small basin that appears to have alternated between a and wetland depositional environment. Climate proxies, including sediment texture, total organic carbon (TOC), total nitrogen (TN), C/N, pollen and geochemical composition indicate a steady progression to wetter conditions, with two stepwise changes at about 8000, and between 3200 and 1800 yr BP. The change at 8000 yr BP appears to correspond to a brief (100-150years) dry spell recorded elsewhere in India. The change at 3200-1800 yr BP consisted in a rapid intensification of the SWM, and may correlate with the initiation of the Roman Warm Period'. There is no clear evidence of changes at the times of the Medieval Warm Period' (MWP') and the Little Ice Age' (LIA'). The C/N ratio of the sediments ranges from 14.02 to 8.31, indicating that the organic matter originated from a mixture of lacustrine algae, vascular and terrestrial plants. Chemical weathering indices (Chemical Index of Alteration (CIA), Chemical Index of Weathering (CIW), and Plagioclase Index of Alteration (PIA)) are consistent with extreme silicate weathering. Pollen data show a development from savanna vegetation prior to about 8000 yr BP, followed by grassland with palms, the appearance of ferns just prior to 3200 yr BP and the establishment of the tropical humid forest between 3200 and about 1800 yr BP.

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Wang, Ning, and 王宁. "Organic carbon signatures of the middle-late quaternary lacustrine history of tropical South China." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2014. http://hdl.handle.net/10722/208631.

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In order to reconstruct a long-time tropical terrestrial record of Asian monsoon in South China, the organic carbon in a 120 m lacustrine sediments from Maar Lake Tianyang was analyzed. Results in TOC, C/N and δ13C value show two lines of variations: (1) from a deep lake environment below 42 m to a shallow lake environment of the upper 42 m, (2) environmental changes between glacial and interglacial conditions throughout the lacustrine sediment sequence. In the shallow lake stage, δ13C values change according to glacial and interglacial periods, comparable with other proxies such as pollen, TOC and magnetic susceptibility. However, variations of these proxies including δ13C values are suppressed in the deep lake sequence, a result of the exceptionally high in-situ aquatic (diatom) productivity within this tropical lake. To differentiate the internal productivity and terrigenous high plant input for the deep lake sequence, a three-end-member model (diatom, C3 and C4 land plants) was developed. The result helps extract further information from the deep lake sequence that reveals both the autochthonous productivity caused by lake-level and terrestrial changes by external forcing mechanisms. The n-alkanes indexes from 115 selected samples show distinctive distributions of various chain-length homologues. Most n-alkane indexes (e.g. Paq, CPI and ACL) show more frequent fluctuations than organic carbon records, implying other environmental alterations within the glacial and interglacial periods. Most n-alkanes indexes show a clear relationship with the palaeoclimate history, but further comparison of individual compound concentrations to other environmental indexes (pollen and δ13C values) suggests that n-C29 is a better index of tree concentration while n-C31 has alternative source from flowering trees instead of grasses. Unique appearance of hopanes in the deep lake sediments suggests high activity of methanotrophic bacteria in chemocline. The examination of GDGT concentration from 130 samples indicates pH, temperature and evolution of archaea and bacteria communities. Complications in the interpretation and correction of GDGT results are also discussed and several alternative corrections for palaeo-temperature reconstruction are provided for further investigations. According to both n-alkane and GDGT results, the sediment sequence contains mainly three different stages: the aquatic mixing community (Crenarchaeota and methanotrophic bacteria) from the bottom to 78m; the aquatic methanotrophic community (Euryarchaeota and methanotrophic bacteria); the terrestrial aerobic community (aerobic bacteria).
published_or_final_version
Earth Sciences
Doctoral
Doctor of Philosophy

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Hardy, Elsa Rodrigues. "Cycle characteristics of planktonic cladocerans in a tropical lake, Central Amazon : field and experimental work." Thesis, Royal Holloway, University of London, 1989. http://repository.royalholloway.ac.uk/items/c71f2018-fabf-4a5a-ba6a-26653ffcccf2/1/.

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This thesis is concerned with an investigation into the effects of food concentration, temperature and turbidity on the life cycle characteristics such as growth, body size, development and reproduction of species of planktonic Cladocera brought to the U.K. from a shallow turbid Lake Jacaretinga, Amazonia. The species studied were Daphnia gessneri, Moina reticulata and Diaphanosoma sarsi. Long term growth experiments were performed using both batch and continuous flow culture under controlled laboratory conditions using various combinations of temperature (22°, 27°, and 32°C),concentration of algal food Scenedesmus acutus (0.03, 0.05, 0.1, 0.25, 0.5, and 1.OmgC.1) and turbidity (10, 20, and 50 NTU). Animals were examined daily throughout their cycle from the newborn (neonate) to 3rd adult instars. The ecology of planktonic animals in Lake Jacaretinga was studied intensively during a three month period (February, March and April 1986). This period of study included two ecologically/limnologically important periods, namely, before the flooding of the River Amazon and after the river flooding, when the lake became more turbid due to suspended particles. Weekly samples of zooplankton providedinformation on the species composition and numerical density of the cladoceran populations as well as their horizontal distribution in five stations. Information was also obtained on environmental condition in the lake (temperature, dissolved oxygen concentration, Secchi disc transparency, chlorophyll-a and particulate carbon concentration). Population of Diaphanosoma sarsi, Ceriodaphnia cornuta and Daphniagessneri, decreased during the flood, and populations of Moinareticulata increased and became a dominant species. Life cycle experiments shows that growth and reproduction are greatly influenced by food concentration and turbidity. Consistent differences were found between Daphnia gessneri and Moina reticulata,being Moina reticulata more successful in survival, growth and reproduction. Application of the experimental results on the effects of food, temperature and turbidity on the life cycle characteristics of the planktonic cladocerans are used to interpret the changes in the cladoceran population in Lake Jacaretinga during this period of floading. This is a significant contribution to our knowledge since Lake Jacaretinga is one of the characteristic varzea lakes in Central Amazonia whose limnology is largely determined by the annual flooding of Amazon River.

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Lucca, José Valdecir de. "Composição, distribuição e abundância dos macroinvertebrados bentônicos da Lagoa do Caçó (MA)." Universidade de São Paulo, 2002. http://www.teses.usp.br/teses/disponiveis/18/18139/tde-04022016-101949/.

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As comunidades bentônicas são relevantes nos ecossitemas aquáticos devido ao seu papel no funcionamento dos ecossistemas e também como mercadores ou indicadores de paleocondições. Sua distinção, similarmente à de outras comunidades, estão condicionadas por fatores abióticos e pela interação entre eles, determinando a estrutura da comunidade que se estabelecerá. Pelo presente trabalho objetivou-se determinar a composição taxonômica, a abundância e a distribuição espacial da comunidade bentônica, amostrando-se em 20 pontos na lagoa do Caçó. Um total de 14 pontos foram estabelecidos na região litorânea (7 na margem esquerda e 7 na margem direita) e 6 na região limnética. A variação sazonal em parâmetros da comunidade e também das características físicas e químicas da água e do sedimento foram analisadas e relacionadas aos deslocamentos da Zona de Convergência Intertropical. A lagoa do Caçó está localizada ao Norte do Estado do Maranhão e possui aproximadamente 5 km de comprimento e largura média de 500 metros. As coletas foram realizadas em abril (período chuvoso) e novembro (período seco) de 1999. Pelos resultados obtidos, ficam evidentes as diferenças tanto na riqueza de táxons quanto na diversidade de espécies e na densidade das populações em função da sazonalidade. A diversidade, a riqueza e a densidade foram maiores no período seco do que no período chuvoso. A família Chironimidae (Diptera Insecta) foi o mais importante componente da comunidade, representando aproximadamente 50% do total da fauna bentônica da lagoa. O sedimento da Lagoa do Caçó tem baixo conteúdo de matéria orgânica, sendo classificado como mineral. A análise da composição granulométrica mostrou que o sedimento é heterogêneo, sendo arenoso na margem esquerda, predominantemente argiloso na margem direita e limo arenoso e argiloso na região limnética. Em relação às variáveis limnológicas, observaram-se microestratificações térmicas e ) químicas. Os índices tróficos aplicados permitiram classificar a lagoa do Caçó como oligotrófico. A alternância dos períodos seco e chuvoso atuou como a principal função de força condicionado as alterações nas condições físicas e químicas da água bem como na comunidade bentônica no ano de 1999. Além disso, a identificação dos Chironomidae atuais da lagoa do Caçó até o nível de gênero, e o fato deste grupo produzir remanescentes fossilizáveis os tornam bons marcadores paleolimnológicos e paleoclimáticos que podem ser utilizados para inferir sobre as condições lacustres e climáticas passadas.
Benthic communities are relevant in aquatic ecosystems due to their role in the ecosystem functioninq and also as rnarkers or indicators of paleoconditions. Their distribution, similarly to other communities, is conditioned by abiotic and biotic factors and to their interactions, which determine the structure of the community that will be established. The present work aimed to determine the taxonomic composition, the abundance and spatial distribution of the benthic community, by collecting at 20 sampling points in Caçá Lake. A total of 14 points were located in the littoral region (7 on the right margin and 7 on the left one) and 6 in the limnetic zone. Seasonal variation on community parameters and also of chemical and physical characteristics of water and sediment were analysed and related to the seasonal displacement of the Intertropical Convergence Zone. Caçó Lake is located at the North of Maranhão State and it has approximately 5 km of length and 500m mean width. Sampling was carried out in April (rainy season) and November (dry season). The results evidenced that there are differences in the richness of taxa, diversity and density of benthic species that are mainly related to the seasonality. The diversity, richness and density were higher in the dry than in the rainy period. The family Chironomidae (Diptera, Insecta) was the most important component of the community representing approximately 50% of the total benthic fauna of the lake. The sediment of Caçá Lake has low organic content being classified as a mineral one. The granulometric composition shows that the sediment is heterogeneous being sandy at the left margin, clayey in the right margin and sandy-clayey in the limnetic zone. In relation to the limnological variables, thermal and chemical (pH, dissolved oxygen and temperature) micro-stratifications were observed for both periods sampled. The trophic state indices applied have allowed to classifv Lake Caçá as an oligotrophic lake. The alternation of dry and rainy periods can be considered the main forcing function causing the changes in physical and chemical water characteristics as well on benthic community in the year 1999. The identification of the present Chironomidae at the genus level and the fact that this group does produce fossilizing remains make them good paleolimnological and paleoclimatic tracers that may be used to infer on past lake and climate conditions.

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16

Thompson, Diane M., Jessica L. Conroy, Aaron Collins, Stephan R. Hlohowskyj, Jonathan T. Overpeck, Melanie Riedinger-Whitmore, Julia E. Cole, et al. "Tropical Pacific climate variability over the last 6000 years as recorded in Bainbridge Crater Lake, Galápagos." AMER GEOPHYSICAL UNION, 2017. http://hdl.handle.net/10150/625825.

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Finely laminated sediments within Bainbridge Crater Lake, Galapagos, provide a record of El Nino-Southern Oscillation (ENSO) events over the Holocene. Despite the importance of this sediment record, hypotheses for how climate variability is preserved in the lake sediments have not been tested. Here we present results of long-term monitoring of the local climate and limnology and a revised interpretation of the sediment record. Brown-green, organic-rich, siliciclastic laminae reflect warm, wet conditions typical of El Nino events, whereas carbonate and gypsum precipitate during cool, dry La Nina events and persistent dry periods, respectively. Applying this new interpretation, we find that ENSO events of both phases were generally less frequent during the mid-Holocene (similar to 6100-4000 calendar years B.P.) relative to the last similar to 1500 calendar years. Abundant carbonate laminations between 3500 and 3000 calendar years B.P. imply that conditions in the Galapagos region were cool and dry during this period when the tropical Pacific E-W sea surface temperature (SST) gradient likely strengthened. The frequency of El Nino and La Nina events then intensified dramatically around 1750-2000 calendar years B.P., consistent with a weaker SST gradient and an increased frequency of ENSO events in other regional records. This strong interannual variability persisted until similar to 700 calendar years B.P., when ENSO-related variability at the lake decreased as the SST gradient strengthened. Persistent, dry conditions then dominated between 300 and 50 calendar years B.P. (A.D. 1650-1900, +/- similar to 100 years), whereas wetter conditions and frequent El Nino events dominated in the most recent century. Plain Language Summary Sediments accumulating at the bottom of Bainbridge Crater Lake have provided a record of Galapagos climate and the frequency of El Nino events over the past similar to 6000 years. Motivated by the importance of this lake for our understanding of climate in the tropical Pacific Ocean, we have been monitoring the link between climate, lake conditions, and the physical and chemical properties of the lake sediments since 2009. Based on this long-term monitoring, we find that the Bainbridge sediment record preserves both El Nino and La Nina events. This makes Bainbridge a particularly valuable archive of past climate, as most sediment-based records typically preserve only one or the other key phase of tropical Pacific climate.

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17

Delvalle, David. "Geochemical and mineralogical analysis of stream and lake sediments from a tropical watershed (Panama canal watershed) /." Heidelberg : [Ruprecht-Karls-Universität], 1989. http://catalogue.bnf.fr/ark:/12148/cb37428731k.

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18

Roberts, David Thomas. "Trophic Implications of Drought on a Sub-Tropical Reservoir Food Web: Lake Samsonvale (North Pine Dam)." Thesis, Griffith University, 2012. http://hdl.handle.net/10072/367026.

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This thesis provides new insights into the ecological functioning and trophic dynamics of a sub-tropical reservoir during a period of extreme hydrological variability. Australia is one of the driest continents on earth with the majority of its urban population relying on reservoirs for potable water supplies. Despite the importance of reservoirs in Australia, very little is known about the ecological functioning and trophic dynamics of these artificial ecosystems. This thesis investigates the trophic structure, dominant trophic interactions, key drivers of trophic dynamics and the influence of drought on these ecosystem features within a regionally important drinking water reservoir in South East Queensland, Lake Samsonvale (27º 16º S, 152º 56º E). Food web conceptual diagrams provide a means for describing resource-consumer relationships within an ecosystem and can highlight the importance of certain interactions between the biotic and abiotic components of the system in the flow of energy. Carbon and nitrogen are two elements that form the currency of these interactions. This study utilised stable isotopes of carbon and nitrogen to describe the food web and investigate the trophic dynamics under contrasting hydrologic conditions within Lake Samsonvale. The application of stable isotopes for describing the Lake Samsonvale food web conformed to a number of important prerequisites to successfully apply this technique. These included sufficient isotopic separation between available energy sources and between food web components such that they occupy unique carbon and nitrogen isotopic space. Secondly, isotope values of food web components were found to change in predictable ways according to the basic principles of isotope fractionation and mixing, including conservative δ13C fractionation, and trophic level δ15N enrichment. Additionally, isotopic description of diets of many Lake Samsonvale consumers conformed to literature based description of diets.
Thesis (PhD Doctorate)
Doctor of Philosophy (PhD)
Griffith School of Environment
Science, Environment, Engineering and Technology
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19

Posselt, Amanda J. "Are Nutrients the Key Driver in Prompting Dominance of Toxic Cyanobacterial Blooms in a Sub-Tropical Reservoir?" Thesis, Griffith University, 2010. http://hdl.handle.net/10072/367306.

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Toxic cyanobacteria cause major problems, both for drinking and recreation, within water systems and bulk water storages, worldwide. Many investigations have been conducted to determine how, and why, they proliferate as well as why, and when, they produce toxins. A common assumption is that cyanobacteria grow in response to an increase in water column nutrient availability, but this is an oversimplification. In a sub-tropical reservoir (L. Samsonvale, South East Queensland, Australia), the toxic cyanobacterium Cylindrospermopsis raciborskii has been dominating the phytoplankton community in the summer months for many years. The reason for this is unknown. Lake Samsonvale typically has relatively low phosphorus (P) concentrations, relatively high nitrogen (N) concentrations and C. raciborskii can grow without significant nutrient inputs from the catchment or point sources. The relatively high N concentrations in L. Samsonvale mean that it is unlikely to be a key nutrient in promoting dominance of C. raciborskii. The low phosphorus (in particular the phosphate) concentrations on the other hand may suggest a reason for C. raciborskii dominance in L. Samsonvale. Studies of a non-toxic strain of C. raciborskii originally isolated from the northern hemisphere found that a rapid phosphate uptake rate and high phosphorus storage capacity was contributing to its dominance in a phosphate-limited reservoir (Istvánovics et al. 2000). The aim of this thesis was to characterise the relationship between phosphorus and C. raciborskii in L. Samsonvale. To achieve this, three levels of investigation were used: 1. Physiological studies at the species level; 2. Manipulative experiments at the phytoplankton community level; 3. Characterisation of C. raciborskii ecology at the whole of system level. The relationship between C. raciborskii and phosphorus was studied using a multilevel approach. Knowledge gained from this allowed detailed investigation of iii the relationship between the dominance of this species within the phytoplankton community of L. Samsonvale. Using continuous culture experiments, the phosphate uptake and storage capacity of two toxic Australian strains of C. raciborskii was determined. One of these strains was isolated from the reservoir of interest, L. Samsonvale. P dependent growth rate and toxin production were also quantified. Both strains of C. raciborskii had a high maximum phosphate uptake rate (450 – 600 μmol P mg C-1 d-1) with a relative low half saturation constant (0.64 μmol P L-1). This study suggests that C. raciborskii is capable of taking full advantage of any available phosphate that may be introduced (such as run off) or regenerated within the phytoplankton/bacterial community. The P dependent growth rates were similar for both strains of C. raciborskii with a maximum growth rate at the lowest concentration of P tested (0.03 μmol P L-1). Growth rates were lower overall than in other strains of C. raciborskii. When C. raciborskii cells were starved of P, they produced much more toxin than when they were grown in a nutrient sufficient environment. This indicates that toxin production may be related to a stress response. Some phytoplankton have been shown to produce alkaline phosphatase. This enzyme cleaves phosphate from organically bound forms, targeting esters, which can be taken up and used by the cell. Since C. raciborskii appears to proliferate in phosphate limited systems, its potential to secrete this enzyme, and whether it was capable of growth with an organically bound source of phosphate, were investigated. Alkaline phosphatase activity was detected and C. raciborskii was found to be capable of multiplying in a culture media containing only an organic form of P (glucose-6- phosphate, G-6-P). However, the maximum growth rate was lower (~0.13 d-1) when cells were grown in G-6-P compared to phosphate (~0.22 d-1) The ability of C. raciborskii to use: 1. Organic P; 2. Rapidly utilise phosphate; and 3. Grow at a maximum rate at relatively low phosphate concentrations, are likely to make C. raciborskii a dominant competitor in phosphate-limited systems. iv To determine whether C. raciborskii has a competitive advantage over other phytoplankton in the P-limited system of L. Samsonvale, in situ dialysis tube bioassays were used to test the phytoplankton response to nutrient addition. The dialysis tube bioassay is a novel approach aiming to minimise the confounding problem of artificial nutrient limitation associated with traditional closed bottle bioassays. Samples of the phytoplankton population were subjected to nutrient additions at four different times over a summer period, to test whether a change in phytoplankton species composition (with particular reference to C. raciborskii) could be seen after four days. In phytoplankton communities where the proportion of C. raciborskii was equal to, or above, 50% (biovolume), a statistically significant increase in C. raciborskii dominance occurred when phosphate was added as a daily spike at either of two concentrations (0.32 and 16 μM P). However, C. raciborskii dominance decreased when phosphate was constantly added in very high concentrations or when N and P are added together. From the bioassay experiments it can be inferred that C. raciborskii has a competitive advantage in L. Samsonvale due to its ability to rapidly take up phosphate. But, when the phosphate concentration is constantly high (>6.4 μmol P L-1), C. raciborskii loses this competitive advantage. Analysis of historical data has shown that there is no correlation between periodic nutrient inputs (e.g. rainfall) and an increase in C. raciborskii dominance. The mechanisms by which C. raciborskii is accessing phosphate within L. Samsonvale were therefore examined. One theory about how C. raciborskii is accessing phosphate in L. Samsonvale is that it comes from nutrient injections in the bottom waters caused by mixing the reservoir using artificial destratification. The concentration of dissolved organic phosphorus (DOP) may also provide C. raciborskii with available phosphate. To assess these two hypotheses, the nutrient concentration and phytoplankton cell concentrations throughout the water column were measured, both before and after artificial destratification. The DOP fraction was measured over a summer. Phosphate remained v below detection limits throughout the study, therefore the role of the destratifier in injecting phosphate into the water column was difficult to determine. A difference in phytoplankton distribution was noted with C. raciborskii being found at higher concentrations lower in the water column post destratification. In contrast, the other toxic species of cyanobacteria Microcystis aeruginosa present in substantial cell concentrations significantly decreased in cell concentrations after the destratifier was turned on. DOP was found to be a significant fraction (total mean 32%) of the total P in the water column of L. Samsonvale and may therefore provide an important source of P for C. raciborskii under low phosphate conditions. This study has shown C. raciborskii has adapted to the low concentrations of P in L. Samsonvale to gain a competitive advantage. Reservoir management, particularly in relation to nutrient loads, should take this into account, as efforts to reduce P loads may not lead to a decrease in C. raciborskii cell number or phytoplankton dominance.
Thesis (PhD Doctorate)
Doctor of Philosophy (PhD)
Griffith School of Environment
Science, Environment, Engineering and Technology
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20

Dunn, Catherine. "How Unusual is Tropical Storm Irene? A Case Study of Storm Deposition in Littleville Lake, Huntington, MA." Oberlin College Honors Theses / OhioLINK, 2014. http://rave.ohiolink.edu/etdc/view?acc_num=oberlin1400777365.

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21

McGlue, Michael Matthew. "LATE QUATERNARY PALEOLIMNOLOGY IN THE SOUTHERN HEMISPHERE TROPICS." Diss., The University of Arizona, 2011. http://hdl.handle.net/10150/204064.

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Lake deposits are widespread throughout the Phanerozoic rock record and have long intrigued geologists and paleobiologists in search of natural resources or fossil biota. Low-energy lacustrine depositional environments, characterized by relatively rapid sediment influx rates and shallow zones of bioturbation, likewise produce highly-resolved archives of climate and ecosystems evolution. This dissertation describes four studies that use lake sediments for Quaternary environmental analysis. In East Africa, many decades of prior study provided the critical framework necessary for in-depth paleoenvironmental research at Lake Tanganyika (3° - 9°S). Seismic stratigraphic analysis integrated with radiocarbon-dated sediment cores from the Kalya horst and platform document a dramatic lake level lowstand prior to ~106 ka and a minor, short-lived regression during the Last Glacial Maximum (32 - 14 ka). Paleobathymetric maps reveal that Lake Tanganyika remains a large, connected water body even during episodes of extreme drought, which has implications for local and regional fauna. Over shorter timescales, geochronological, taphonomic and sedimentological analyses of shell beds around Kigoma (central Lake Tanganyika) document three distinct facies-types that are time-averaged over the latest Holocene. Lake level fluctuations associated with the termination of the Little Ice Age (~ 16th century CE) and subsequent encrustation played a key role in shell bed formation and persistence along high-energy littoral platforms, which has implications for structuring specialized communities of benthic fauna. In central South America (18° - 22°S), we studied the limnogeology of small lakes in the Puna and the Pantanal. Analyses of these sites were undertaken to: 1) ascertain how the lakes act as depositional basins; 2) assess sedimentation rates; and 3) construct limnogeological databases to guide future interpretations of ancient sediment cores. At Laguna de los Pozuelos (Argentine Puna), linear sedimentation rates approach 0.14 cm*y⁻¹ in the playa-lake center, and litho- and organo-facies development are dominantly controlled by basin hydrology, climate and biological feedbacks (both nutrient cycling and bioturbation) from waterbirds. At Lagoas Gaíva, Mandioré and Vermelha (Brazilian Pantanal), short-lived radioisotopes indicate uninterrupted depositional rates of 0.11 - 0.24 cm*y⁻¹, and hydrochemical and depositional patterns respond sensitively to changes in the seasonal flooding cycle of the Upper Paraguay River.

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22

Thompson, Diane Marie. "Variability and trends in the tropical Pacific and the El Niño-Southern Oscillation inferred from coral and lake archives." Diss., The University of Arizona, 2013. http://hdl.handle.net/10150/311122.

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The background state and changes associated with the El Niño-Southern Oscillation (ENSO) in the tropical Pacific Ocean influence climate patterns all over the world. Understanding how the tropical Pacific will be impacted by climate change is therefore critical to accurate regional climate projections. However, sparse historical data coverage and strong natural variability in the basin make it difficult to assess the response of the tropical Pacific to anthropogenic climate change. Further, climate models disagree regarding the response of the basin to continued anthropogenic forcing into the future. Building off of the limited instrumental record, high-resolution records from coral and lake sediment archives can be used to assess the response of the tropical Pacific to past climate changes and to compare and assess climate model projections. In the present study, I use high-resolution coral and lake records from the equatorial Pacific to assess climate model projections and the response of the coupled ocean-atmospheric climate system in the basin (ocean temperature, salinity, winds, precipitation) to natural and anthropogenic forcing. Using a simple model of how climate is recorded by corals, we compare historical climate data and climate model simulations with coral paleoclimate records to assess climate model projections and address uncertainties in the historical data, models and paleoclimate records. We demonstrate that this simple model is able to capture variability and trend observed in the coral records, and show that the both sea surface temperature and salinity contribute to the observed coral trend. However, we find major discrepancies in the observed and climate model simulated trends in the tropical Pacific that may be attributed to uncertainties in model simulated salinity. We then assess 20th-century variability and trends in SST and salinity in the central tropical Pacific using replicated coral δ¹⁸O and Sr/Ca records from the Republic of Kiribati and the central Line Islands. We find that the coral records from these sites display a warming and freshening trend superimposed on strong interannual and low-frequency variability. Further, we demonstrate an apparent strengthening of the E-W SST gradient across the dateline (between 173°E and 160°W) and a slight weakening of the N-S SST gradient due to enhanced warming along the equator and west of the dateline relative to other sites. However, we find no evidence of increased variability in the central Pacific, suggesting that there has not been an increase in central Pacific style ENSO events. Finally, we show that the salinity response to climate change may be very patchy within the basin. Using a new ~90 year coral Mn/Ca record from the central Pacific, we investigate variability and trends in tropical Pacific trade winds. First, we demonstrate a strong association between westerly wind anomalies and coral skeletal Mn/Ca, which recorded all of the major historical El Niño events of the 20th century. In this new long Mn/Ca record, we find a reduction in the amplitude and frequency of Mn/Ca pulses between 1893 and 1982, suggesting a decrease in westerly wind anomalies in the western equatorial Pacific Ocean. Finally, we use a sediment record from Bainbridge Crater Lake, Galápagos Archipelago to assess variability in the eastern tropical Pacific over the past ~6 thousand years. Based on results from long-term monitoring of the lake, we propose a new climate interpretation of the sediment record and find further evidence reduced mid-Holocene ENSO variability and a ramp up of ENSO variability starting around 1775 cal. years BP.

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23

Kristen, Iris. "Investigations on rainfall variability during the late Quaternary based on geochemical analyses of lake sediments from tropical and subtropical southern Africa." Phd thesis, Universität Potsdam, 2009. http://opus.kobv.de/ubp/volltexte/2009/3254/.

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This thesis presents investigations on sediments from two African lakes which have been recording changes in their surrounding environmental and climate conditions since more than 200,000 years. Focus of this work is the time of the last Glacial and the Holocene (the last ~100,000 years before present [in the following 100 kyr BP]). One important precondition for this kind of research is a good understanding of the present ecosystems in and around the lakes and of the sediment formation under modern climate conditions. Both studies therefore include investigations on the modern environment (including organisms, soils, rocks, lake water and sediments). A 90 m long sediment sequence was investigated from Lake Tswaing (north-eastern South Africa) using geochemical analyses. These investigations document alternating periods of high detrital input and low (especially autochthonous) organic matter content and periods of low detrital input, carbonatic or evaporitic sedimentation and high autochthonous organic matter content. These alternations are interpreted as changes between relatively humid and arid conditions, respectively. Before c. 75 kyr BP, they seem to follow changes in local insolation whereas afterwards they appear to be acyclic and are probably caused by changes in ocean circulation and/or in the mean position of the Inter-Tropical Convergence Zone (ITCZ). Today, these factors have main influence on precipitation in this area where rainfall occurs almost exclusively during austral summer. All modern organisms were analysed for their biomarker and bulk organic and compound-specific stable carbon isotope composition. The same investigations on sediments from the modern lake floor document the mixed input of the investigated individual organisms and reveal additional influences by methanotrophic bacteria. A comparison of modern sediment characteristics with those of sediments covering the time 14 to 2 kyr BP shows changes in the productivity of the lake and the surrounding vegetation which are best explained by changes in hydrology. More humid conditions are indicated for times older than 10 kyr BP and younger than 7.5 kyr BP, whereas arid conditions prevailed in between. These observations agree with the results from sediment composition and indications from other climate archives nearby. The second lake study deals with Lake Challa, a small, deep crater lake on the foot of Mount Kilimanjaro. In this lake form mm-scale laminated sediments which were analyses with micro-XRF scanning for changes in the element composition. By comparing these results with investigations on thin sections, results from ongoing sediment trap studies, meteorological data, and investigations on the surrounding rocks and soils, I develop a model for seasonal variability in the limnology and sedimentation of Lake Challa. The lake appears to be stratified during the warm rain seasons (October – December and March – May) during which detrital material is delivered to the lake and carbonates precipitate. On the lake floor forms a dark lamina with high contents of Fe and Ti and high Ca/Al and low Mn/Fe ratios. Diatoms bloom during the cool and windy season (June – September) when mixing down to c. 60 m depth provides easily bio-available nutrients. Contemporaneously, Fe and Mn-oxides are precipitating which cause high Mn/Fe ratios in the light diatom-rich laminae of the sediments. Trends in the Mn/Fe ratio of the sediments are interpreted to reflect changes in the intensity or duration of seasonal mixing in Lake Challa. This interpretation is supported by parallel changes in the organic matter and biogenic silica content observed in the 22 m long profile recovered from Lake Challa. This covers the time of the last 25 kyr BP. It documents a transition around 16 kyr BP from relatively well-mixed conditions with high detrital input during glacial times to stronger stratified conditions which are probably related to increasing lake levels in Challa and generally more humid conditions in East Africa. Intensified mixing is recorded for the time of the Younger Dryas and the period between 11.4 and 10.7 kyr BP. For these periods, reduced intensity of the SW monsoon and intensified NE monsoon are reported from archives of the Indian-Asian Monsoon region, arguing for the latter as a probable source for wind mixing in Lake Challa. This connection is probably also responsible for contemporaneous events in the Mn/Fe ratios of the Lake Challa sediments and in other records of northern hemisphere monsoon intensity during the Holocene and underlines the close interaction of global low latitude atmospheric circulation.
In dieser Arbeit werden Ergebnisse von Untersuchungen an den Sedimenten zweier afrikanischer Seen vorgestellt, die ein Archiv für Klimaveränderungen über einen Zeitraum von mehr als 200.000 Jahren darstellen. Der Schwerpunkt liegt in dieser Arbeit auf dem letzten Glazial und dem Holozän (ca. 100.000 Jahre vor heute [nachfolgend als 100 kyr BP bezeichnet] bis heute). Grundlegende Voraussetzung für solche Studien ist ein gutes Verständnis der Ökosysteme in und um den See, sowie des gegenwärtigen Sedimentationsgeschehens. Deswegen beinhalten beide Seestudien Untersuchungen der heutigen Organismen, Böden, Gesteine, Wasserchemie und Sedimentablagerungen. Im Tswaing-See im nordöstlichen Südafrika wurden anhand eines 90 m langen Sedimentprofils Studien zur Sedimentzusammensetzung und Untersuchungen der Zusammensetzung und Qualität des organischen Materials durchgeführt. Sie zeigen einen Wechsel zwischen Phasen hohen detritischen Eintrags, während derer v.a. kaum autochthones organisches Material im See erhalten blieb, mit Phasen geringen Eintrags und dafür karbonatischer oder evaporitischer Sedimentation, die hohe Gehalte v.a. autochthonen organischen Materials aufweisen. Diese Phasen werden als relativ feuchte bzw. trockene Perioden interpretiert und folgen bis vor ca. 75 kyr BP Schwankungen der lokalen solaren Einstrahlung. Dieser Einfluss nimmt nach 75 kyr BP ab und azyklische feuchte Phasen werden beobachtet. Mögliche Ursachen sind Veränderungen in der ozeanischen Zirkulation und Verschiebungen in der Lage der Innertropischen Konvergenzzone (ITCZ); beides sind auch heute Haupteinflussfaktoren auf die Niederschläge in der Region. Die heute lebenden Organismen des Tswaing-Kraters wurden mittels Analysen der Biomarkerzusammensetzung und der Kohlenstoffisotopie charakterisiert und ihr Einfluss auf die heutigen Seeablagerungen untersucht. Dabei konnten zusätzlich Indikatoren für die Aktivität methanotropher Bakterien nachgewiesen werden. Der Vergleich heutiger Sedimente mit denen des Zeitraumes 14 bis 2 kyr BP zeigt deutliche Veränderungen sowohl in der Zusammensetzung, als auch in der Kohlenstoffisotopie der Biomarker, die mit Veränderungen in der Hydrologie erklärt werden können. Die gefundenen Hinweise auf feuchtere Bedingungen im Zeitraum älter als 10 kyr BP, für trockenere Verhältnissen zwischen 10 und 7.5 kyr BP und für die nachfolgende Wiederzunahme an Feuchtigkeit werden durch die sedimentologischen Ergebnisse unterstützt. Objekt der zweiten Seestudie ist der Challa-See am Fuß des Kilimanjaro. Hier werden heute im mm-Maßstab laminierte Sedimente gebildet, die mit Mikro-XRF-scanning auf Veränderungen in der Elementzusammensetzung untersucht wurden. Zusammen mit Untersuchungen der Mikrofazies und im Vergleich mit ersten Ergebnissen noch laufender Sedimentfallenstudien, mit meteorologischen Daten und Analysen des Umgebungsgesteins werden die saisonalen Veränderungen in der Temperaturverteilung, der Durchmischungstiefe, dem detritischen Eintrag und der Bioproduktivität des Sees in den Sedimenten nachvollziehbar. Der See ist in den feucht-warmen Perioden von Oktober bis Dezember und von März bis Mai stratifiziert. Während dieser Zeit erfolgt der Eintrag detritischen Materials und Kalziumkarbonat fällt aus; eine dunkle Lage mit hohen Gehalten an Fe und Ti und mit hohen Ca/Al- und niedrigen Mn/Fe-Verhältnissen bildet sich am Boden des Sees. Diatomeen blühen während der kühlen, windigen Periode von Juni bis September, wenn die Durchmischung bis auf etwa 60 m Tiefe Nährstoffe verfügbar macht. Die Ausfällung von Fe- und Mn-oxiden sorgt für hohe Mn/Fe-Verhältnisse; es bildet sich eine helle Lage auf dem Sediment. Trends im Mn/Fe-Verhältnis werden als Signal für Veränderungen in der Intensität oder Dauer der saisonalen Durchmischung interpretiert. Dies wird unterstützt durch parallele Trends im Gehalt an organischem Material und an biogenem Silizium, wie durch Analysen an einem 22 m langen Bohrkern gezeigt werden kann. Nach gut durchmischten und von erhöhtem Eintrag von außen geprägten Verhältnissen während des letzten Glazials erfolgt gegen 16 kyr BP ein Übergang zu stärker stratifizierten Bedingungen. Diese korrespondieren mit einem steigenden Seespiegel und verbreiteten Hinweisen auf feuchte Bedingungen im tropischen Ostafrika. Stärkere Durchmischung herrschte während der Jüngeren Dryas und von 11.4 bis 10.7 kyr BP. Diese Perioden entsprechen Zeiten verringerter Südwest- und vermutlich verstärkter Nordostmonsunintensität im Bereich des Indisch-Asiatischen Monsuns und spiegeln eine global beobachtete südliche Verschiebung der ITCZ wider. Nach einer kurzen stabilen, feuchten Phase im frühen Holozän nimmt die Durchmischung des Sees im Verlauf des Holozän wieder zu. Abrupte Ereignisse während des Holozän scheinen im Challa-See zeitgleich mit Veränderungen der Monsunintensität der Nordhemisphäre aufzutreten und bezeugen die starke klimatische Kopplung der niederen Breiten in globalem Maßstab.

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24

Carvalho, Felipe Rust de. "Fluxo de CO2 e CH4 em uma lagoa tropical (Pantanal, Brasil) com gradiente de turbidez." Universidade Federal de Juiz de Fora, 2015. https://repositorio.ufjf.br/jspui/handle/ufjf/413.

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Ecossistemas de água doce (rios, lagos e reservatórios) desempenham um papel essencial na ciclagem de carbono nos continentes. Esses ambientes são fontes significantes de gases de efeito estufa (GEE) para a atmosfera, principalmente de gás carbônico (CO2) e metano (CH4). Apesar do aumento do número de estimativas, a dinâmica e o controle das emissões naturais de GEE em ambientes aquáticos ainda é pouco estudada, especialmente nos trópicos. O objetivo geral da dissertação foi estimar os fluxos de CO2 e CH4 em uma lagoa tropical rasa com gradiente de turbidez. O trabalho foi realizado na lagoa Sinhá Mariana (MT), uma lagoa pantaneira com a ocorrência de duas regiões hidrológicas distintas; a lagoa é ligada ao rio Mutum de águas claras, pobre em material em suspensão, e baixa turbidez e ao rio Cuiabá de águas túrbidas, que apresenta alta taxa de material em suspensão. Duas coletas foram realizadas no ambiente, caracterizando os períodos hidrológicos de águas altas e águas baixas. A variação temporal, espacial e o pulso de inundação mostraram serem fatores importantes no fluxo de CO2, que variou de -4,95 mmol m-2 d-1 a 282 mmol m-2 d-1 nos períodos amostrados e diferenças significativas foram observadas entre um período e outro, com maiores emissões no período de águas altas (142 ± 40 mmol m-2 d-1) e menores nas águas baixas (2,3 ± 11,5 mmol m-2 d-1). Além disso, os fluxos de CO2 foram significantemente m/aiores nas proximidades do rio Mutum e menores na região túrbida e intermediária da lagoa, em ambos os períodos. Diferentemente, o fluxo total de CH4, embora estimado apenas nas águas altas, registrou os maiores valores médios na região de maior turbidez da lagoa (10,9 ± 6,9 mmol m-2 d-1), seguido pela região intermediária (5,1 ± 3,9 mmol m-2 d-1) e pela região influenciada pela água clara (2,5 ± 1,4 mmol m-2 d-1). A ebulição foi o principal processo de emissão de CH4, responsável por 78% do fluxo total. O gradiente de turbidez registrado ao longo da lagoa pareceu ter sido um fator determinante na dinâmica do fluxo tanto de CO2 quanto do CH4. Os dados deste trabalho reforçam a necessidade da amostragem espacial dos fluxos de CH4 e CO2 em lagos tropical, além de reforçar que estes fluxos podem ser controlados principalmente pela turbidez e pelo pulso de inundação (CO2).
Freshwater ecosystems (lakes, rivers and reservoirs) play an essential role in carbon cycling in the continents. These environments are significant sources of greenhouse gases (GHG), especially carbon dioxide (CO2) and methane (CH4), to the atmosphere. Despite the increase in the number of estimates, the natural GHG emissions dynamics in aquatic environments is still poorly studied, especially in the tropics. The general aim of this work was to estimate the CO2 and CH4 fluxes in a shallow tropical lake with turbidity gradient. The work was conducted in the Sinhá Mariana lake (MT), a wetland lake with the occurrence of two distinct hydrological regions; the lake is connected to the Mutum river (clear water), poor in suspended material with low turbidity, and connected to the Cuiabá River (turbid waters), which features high rate of suspension material. Samples were taken for characterizing the hydrological periods of high and low water. The temporal, spatial variation and the flood pulse shoed to be important factors affecting the CO2 flux, which ranged from -4.95 mmol m-2 d-1 to 282 mmol m-2 d-1. Significant differences were observed from one period to another, with higher emissions during high waters (142 ± 40 mmol m-2 d-1) and lower in the low water (2.3 ± 11.5 mmol m-2 d-1). In addition, the CO2 flux was significantly higher near the Mutum river and lower in the turbid region, in both periods. The total CH4 flux, although estimated only in high waters, showed the highest mean rates in the higher turbidity region of the lake (10.9 ± 6.9 mmol m-2 d-1), followed by the intermediate region (5.1 ± 3.9 mmol m-2 d-1) and the area influenced by clear water (2.5 ± 1.4 mmol m-2 d-1). The ebullition flux was the main CH4 emission pathway, responsible for 78% of the total flux. The turbidity gradient observed along the lake appeared to have been a determining factor in the flux dynamics of both CO2 and CH4. This study data reinforce the need for spatial sampling of CH4 and CO2 fluxes in tropical lakes, in addition to reinforcing that these fluxes can be controlled by turbidity and by the flood pulse (CO2).

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Stephan, Ligia Roma [UNESP]. "Comunidades zooplanctônicas em ambientes lênticos tropicais: influência da predação e das características físicas locais." Universidade Estadual Paulista (UNESP), 2017. http://hdl.handle.net/11449/152217.

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Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)
Neste estudo foi avaliada a importância das características limnológicas locais e da predação por peixes na estrutura das comunidades zooplanctônicas, sendo os objetivos e resultados apresentados em dois capítulos distintos: Capítulo 1. Tem por objetivo avaliar a influência dos pulsos de inundação na estrutura funcional e taxonômica das comunidades de microcrustáceos em lagoas marginais. Para atingir o objetivo proposto, foram determinadas a estrutura funcional e taxonômica das assembleias de microcrustáceos coletadas em lagoas marginais ao Rio Turvo em três estações distintas: seca, intermediária e chuvosa. Os resultados encontrados foram comparados entre lagoas e entre estações; também foram comparadas a estrutura das asssembléias das lagoas marginais com amostras de microcrustáceos provenientes de ambientes lênticos com diferentes regimes hidrológicos. Neste estudo também foi avaliado se um período longo de estiagem pode influenciar as dinâmicas sazonais dos microcrustáceos. A estrutura das assembleias dos microcrustáceos com base na classificação funcional e taxonômica apresentaram variações entre lagoas e estações, assim como ambientes aquáticos que não sofrem influência dos pulsos de inundação apresentam uma maior uniformidade funcional. A dinâmica sazonal das assembleias foi afetada pelo período prolongado de estiagem, onde as variações na estrutura das comunidades que existem entre estações foram menos intensas no período de estiagem quando comparado ao ano chuvoso. Os resultados mostram que as características limnológicas das lagoas são influenciadas pelos pulsos de inundação e pelo regime hidrológico, bem como um período prolongado de estiagem é capaz de influenciar a dinâmica sazonal das assembléias de microcrustáceos em lagoas marginais. O estudo também mostra que há uma grande heterogeneidade funcional entre as lagoas, sugerindo que o padrão encontrado para a comunidade zooplanctônica revela mais a importância das características locais associadas ao pulso de inundação do que os efeitos deste sobre a comunidade de toda a planície. Capítulo 2. O segundo capítulo tem por objetivo avaliar se a predação por 6 peixes pode influenciar a estrutura funcional das assembleias de microcrustáceos. A influência da predação sobre a comunidade de microcrustáceos foi avaliada por meio de um experimento de mesocosmo e pela avaliação do conteúdo estomacal dos peixes provenientes das lagoas marginais ao Rio Turvo. A abundância e a estrutura funcional dos microcrustáceos foram influenciadas pela presença dos peixes e das macrófitas aquáticas no experimento, entretanto, para as análises realizadas nas lagoas marginais os resultados mostram que a predação não possui um efeito capaz de influenciar a estrutura das assembleias. Como conclusão, podemos inferir que a presença dos peixes pode ser um fator estruturador das comunidades, mas que em ambientes dinâmicos tais como as lagoas marginais, a influência exercida por alterações nas características locais pode ser um fator mais intenso na estruturação das assembleias de microcrustáceos do que a predação por peixes.
In this study, the importance of local characteristics and predation by fish in the zooplankton community structure was evaluated. The objectives and results were separated in two distinct chapters: Chapter 1. Its objective is to evaluate the influence of flood pulses on the functional and taxonomic structure of microcrustacean communities in oxbow lakes. For the proposed objective, the functional and taxonomic structure of the microcrustacean assemblages from oxbow lakes to the Rio Turvo was determined in three seasons: dry, intermediate and rainy. The results were compared between oxbow lakes and between seasons, as well as between samples from environments with different hydrological regimes. In this study, it was also evaluated if a long period of drought can influence the seasonal dynamics of microcrustaceans. The structure of the microcrustacean assemblages based on the functional and taxonomic classification showed variations between oxbow lakes and seasons; a greater functional uniformity was found on the aquatic environments not influenced by the flood pulses. The seasonal dynamics of the assemblages was affected by the prolonged period of drought, where the variations in the structure of communities between seasons were less intense in the drought year when compared to the rainy year. Our results show the influence of flood pulses on limnological characteristics and on the functional and taxonomic assemblages of microcrustaceans in the oxbow lakes; we also observed that a prolonged period of drought is able to influence the seasonal dynamics of microcrustacean assemblages in oxbow lakes. Chapter 2. The second chapter aims to assess the influence of fish predation on the functional structure of microcrustacean assemblages. The influence of fish predation was evaluated through an mesocosm experiment, and through an evaluation of fish stomach contents sampled in the marginal lakes from Turvo River. In the experiment, the abundance and functional structure of the microcrustaceans were influenced by the presence of fish and aquatic macrophytes, however, results from the oxbow lakes show that predation does not have an effect capable to incluence the structure of the microcrustaceans assemblages. As conclusion, fish predation should have a role in the 8 structure of the communities, although in dynamic environments such as oxbow lakes, the influence of the local characteristics may be a more important factor in the structuring of the microcrustacean assemblages then the fish predation.

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REY, ESPINASSE JEANNE. "Contribution a l'etude du zooplancton d'altitude et de la taxonomie des cladoceres." Toulouse 3, 1986. http://www.theses.fr/1986TOU30185.

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Etude consacree dans la premiere partie a la taxonomie et a la biogeographie des eladoceres du lac tchad et du bassin moyen de l'orenoque. Une deuxieme partie etudie le zooplancton de 9 lacs d'altitude des pyrenees (cladoceus et copepodes) notamment la repartition des especes, leur cycle evolutif regi par le facteur thermique, la dynamique des populations

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Ferreira, Gustavo Luiz. "Análise da composição da dieta de seis espécies de peixes coexistentes em um reservatório tropical (Reservatório de Ribeirão das Lajes, Piraí-RJ)." Universidade do Estado do Rio de Janeiro, 2010. http://www.bdtd.uerj.br/tde_busca/arquivo.php?codArquivo=4305.

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O presente estudo analisou o conteúdo digestório de 221 indivíduos de seis espécies de peixes, do reservatório de Ribeirão das Lajes (Piraí-RJ), sendo 44 exemplares da espécie Loricariichthys castaneus, 56 de Parauchenipterus striatulus, 46 de Metynnis maculatus, 40 de Astyanax bimaculatus, 31 de Astyanax parahybae e 4 de Rhamdia quelen. O intuito foi o de estabelecer suas dietas, através do emprego do índice de importância alimentar (IAi), verificar a existência de diferenças na alimentação entre épocas seca e chuvosa e ainda as suas relações tróficas no ambiente aquático em questão. Não foram observadas grandes alterações da dieta das espécies estudadas entre épocas do ano. Foi evidenciada uma utilização de recursos alimentares semelhantes entre as espécies, que puderam ser divididas em dois grupos: um composto por espécies de hábitos onívoros com tendência a insetivoria e que empregaram recursos alóctones em suas dietas, formado por A. bimaculatus, A. parahybae e P. striatulus e outro contendo L. castaneus, R. quelen e M. maculatus que apresentaram uma maior amplitude de itens ingeridos, sendo muitos itens associados ao substrato e alguns a coluna dágua. Existiu uma sobreposição alimentar entre as espécies onívoras, todavia a ampla disponibilidade de recursos alimentares passíveis de serem explorados pelos peixes no reservatório faz com que esta sobreposição não se converta em possível competição por alimentos. Além disso, as espécies exploraram secundariamente itens alimentares diferenciados em suas dietas.
The present study analyzed the digestive contents of 221 individuals of six fish species, from Ribeirão das Lajes reservoir (Piraí-RJ). There were 44 specimens of Loricariichthys castaneus, 56 Parauchenipterus striatulus, 46 Metynnis maculatus, 40 Astyanax bimaculatus, 31 Astyanax parahybae and 4 Rhamdia quelen. The aim was to establish their diets, through the use of alimentary importance index (IAi), to verify the existence of differences in their feeding between different seasons of the year, and their trophic relationships to their environment. There were no great alterations to the diets of the analyzed species between the seasons of the year. All species used similar food resources, which could be divided into two groups: one composed of species with omnivorous habits with tendencies to insectivory and which apply allochthonous resources in their diets, formed by A. bimaculatus, A. parahybae e P. striatulus and another one with L. castaneus, R. quelen e M. maculatus that presented larger amplitudes of ingested items, which many items were associated with the substratum and a few to the water column. There is an alimentary overlap between the omnivorous species, however the great availability of food resources, capable of being exploited by the fishes in this reservoir, probably diminishes competition for food. Moreover the species also exploited different kinds of secondary food items.

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Kristen, Iris. "Investigations on rainfall variability during the late Quaternary based on geochemical analyses of lake sediments from tropical and subtropical southern Africa." Potsdam Deutsches GeoForschungsZentrum GFZ, 2010. http://d-nb.info/1000714233/34.

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Dunn, Ryan J. K. "Biogeochemical Processes of a Sub-tropical Coastal Lagoon (Coombabah Lake, Southern Moreton Bay, Australia): With Emphasis on Organic Matter and Nutrient Dynamics." Thesis, Griffith University, 2009. http://hdl.handle.net/10072/365282.

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Coombabah Lake is a sub-tropical, semi-urbanised, shallow lagoon in southern Moreton Bay (Australia), recognised nationally and internationally as an important conservation and habitat zone. However, significant increases in urban development have occurred within the lagoon catchment in recent times, raising concerns over the sustainability of the lagoon ecosystem. This is typical of many estuarine environments which are ecologically and economically important waterways that often become surrounded by urban development and therefore experience degradation of water and sediment quality. The processes controlling the distribution of organic matter and nutrients in estuaries are especially important in understanding their chemical cycling. Consequently, the assessment and understanding of biogeochemical processes and other influential factors is essential for the effective management of estuaries. This study is a multi-disciplinary investigation of biological, physical, and biogeochemical processes occurring in the surface sediments and overlying waters of Coombabah Lake and the adjoining creek. The primary aim of this study was to investigate physico-chemical and biogeochemical processes occurring over various patial and temporal scales and improve the understanding of Coombabah Lake and similar shallow sub-tropical systems. Spatial variability of physico-chemical surface sediment variables and the sources and distribution of surface sediment organic matter were investigated to provide an understanding of the physico-chemical and ecological processes driving the lagoon system. Lagoon sediments were characterised by generally fine sediments with predominantly sandier sediments occurring within the northern region and muddier sediments occurring within the southern region. Although some sediment locations had elevated nutrient concentrations in comparison to adjacent lagoon sediments, nutrient concentrations within the lagoon were generally typical of Australian estuarine environments. Comprehensive analysis of biomarkers indicated that the lagoon received organic matter from a variety of autochthonous and allochthonous sources including terrestrial vascular plants (i.e. surrounding mangroves), diatoms, and benthic bacteria with the fringing mangroves potentially playing an important role in the lagoon food web. The intratidal variability of hydrological and physico-chemical variables were measured and the filterable nutrient and chlorophyll-a transport loads entering the lagoon determined. Instrumental measurements and hourly water collections provided the first account of intratidal variability within the system and indicated the lagoon and adjoining creek was characterised by a mixed tidal regime with cyclic and temporal variations in physico-chemical variables, suspended solids, and chl-a concentrations. Both dissolved oxygen and turbidity values exceeded regulatory guideline values for the region. Nutrient concentrations were typical of local and Australian estuarine environments and exceeded regulatory guideline values for the region. Nutrients sourced externally from the Coombabah Lake-Creek system resulted in increased transportation rates during flood events indicating a potential for increased nutrient loadings and enrichment within the lagoon and associated wetland environment...
Thesis (PhD Doctorate)
Doctor of Philosophy (PhD)
School of Engineering
Science, Environment, Engineering and Technology
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Rocha, Rinaldo José da Silva. "Decomposição de macrófitas aquáticas em dois reservatórios com diferentes estados tróficos." Universidade Federal de São Carlos, 2012. https://repositorio.ufscar.br/handle/ufscar/2078.

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The macrophytes are essential for the development and maintenance of food webs, to carbon dynamics and nutrient cycling in tropical aquatic systems. After senescence and plant death, decomposition of organic detritus depends heavily on their elemental compositions. Thus, the present study aimed to evaluate the effect of seasonality and trophic state of reservoirs and Vigário Lajes on the mass losses of detritus of Salvinia auriculata, Pistia stratiotes, Eichhornia crassipes, Sagittaria montevidensis and Brachiaria subquadripara, the influence of elemental composition of debris on the coefficients decay of carbon, nitrogen and phosphorus, and the stoichiometric ratios between these elements during the decomposition process. Over 120 days, the richest detritus in nutrients and less refractory (S. montevidensis and P. stratiotes) showed a biphasic pattern of decay and the greater decay of carbon (70-90%), phosphorus (90-96%) and nitrogen (68-94%). The poorest and refractories detritus (S. auriculata and E. crassipes) had lower rates of decay, with monophasic and biphasic patterns and lower mass loss in carbon-based (20-34%), phosphorus-based (26%), and nitrogen-based (10- 37%). As for the difference between the environments, the total mass loss of carbon was up to 70% higher during the rainy season (Sept/10 to Jan/11) and 27% higher in the dry season (may/11 to Sep/11) for detritus S. auriculata incubated in the reservoir Vigário; for the detritus of B. subquadripara total mass loss was also greater in this reservoir, reaching 58% in the rainy season and 36% during the dry season. The minor differences between the environments occurred in the mass loss of carbon detritus of S. montevidensis, (ca. 1.3% and 0.3% in rainfall in the dry season) and P. stratiotes (ca. 5.3% in the rainy season and 5.5% in the dry season). Yet these detritus showed the greatest losses of phosphorus (90-95%) and nitrogen (68-94%) in both experiments. The minor differences between the environments occurred in the mass loss of carbon detritus of S. montevidensis, (ca. 1.3% and 0.3% in the rainy season in the dry season) and P. stratiotes (ca. 5.3% and 5.5% in the rainy season in the dry season). Yet these detritus showed the greatest losses of phosphorus (90-95%) and nitrogen (68-94%) in both experiments. The ratio between carbon and nitrogen was higher in detritus of S. auriculata and E. crassipes in oligotrophic reservoir, and lower in detritus of S. montevidensis and P. stratiotes, whose mass loss coefficients (k) were higher.
As macrófitas são essenciais para o desenvolvimento e manutenção das cadeias tróficas, para a dinâmica do carbono e ciclagem de nutrientes de sistemas aquáticos tropicais. Após senescência e morte das plantas, a decomposição dos detritos orgânicos depende muito das suas composições elementares. A temperatura, a concentração de nutrientes inorgânicos no meio, as relações estequiométricas entre os organismos decompositores e os detritos podem afetar as taxas de decomposição, embora no caso da relação estequiométrica isso nem sempre ocorra. Nesse sentido, esse estudo teve como objetivo avaliar o efeito da sazonalidade e da condição de trofia dos reservatórios de Lajes e de Vigário sobre as perdas de massa dos detritos de Salvinia auriculata, Pistia stratiotes, Eichhornia crassipes, Sagittaria montevidensis e Brachiaria subquadripara; a influência da composição elementar dos detritos sobre os coeficientes de decaimento de carbono, nitrogênio e fósforo; e as relações estequiométricas entre esses elementos durante o processo de decomposição. Ao longo de 120 dias, os detritos mais ricos em nutrientes e menos refratários (S. montevidensis e P. stratiotes) apresentaram padrão bifásico de decaimento, além dos maiores decaimentos de carbono (70 a 90%), fósforo (90 a 96%) e nitrogênio (68 a 94%). Os detritos mais pobres e refratários (S. auriculata e E. crassipes) apresentaram menores coeficientes de decaimento, com padrões monofásico e bifásico e as menores perdas de massa em base de carbono (20 a 34%), de fósforo (26%) e de nitrogênio (10 a 37%). Quanto à diferença entre os ambientes, a perda de massa total de carbono foi até 70% maior no período das chuvas (set/10 a jan/11) e 27% maior no período seco (mai/11 a set/11) para detritos de S. auriculata incubados no reservatório de Vigário; para os detritos de B. subquadripara a perda de massa total também foi maior neste reservatório, chegando a 58% no período das chuvas e 36% no período seco. As menores diferenças entre os ambientes ocorreram na perda de massa de carbono dos detritos de S. montevidensis , (ca. 1,3% nas chuvas e 0,3% na seca) e de P. stratiotes (ca. 5,3% nas chuvas e 5,5% na seca) .Contudo, esses detritos apresentaram as maiores perdas de fósforo (90 a 95%) e de nitrogênio (68 a 94%) nos dois experimentos. A razão entre carbono e nitrogênio foi mais alta nos detritos de S. auriculata e E. crassipes, no ambiente oligotrófico, e mais baixa nos detritos de S. montevidensis e P. stratiotes, cujos coeficientes de perda de massa (k) foram maiores.

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França, Roberta Sebastiany. "Estudo limnológico da Lagoa dos Tropeiros, Capitólio, MG, com ênfase na comunidade de macroinvertebrados bentônicos." Universidade Federal de São Carlos, 2010. https://repositorio.ufscar.br/handle/ufscar/1664.

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The studies on the diversity and functional role of benthic macroinvertebrates in lake ecosystems can provide relevant informations regarding the functioning and the health of these freshwater ecosystems. The aim of this study was to analyze the Tropeiros Lake, located in the municipality of Capitólio (MG), performing a limnological evaluation of the ecosystem and ecological investigation on the diversity of the benthic macroinvertebrate community. Thus, changes in the taxonomical composition, abundance, diversity, biomass and the taxa participation in the trophic functional groups were analyzed. Water and sediment were sampled in October 2006 and 2007 (dry periods) and in March 2007 and 2008 (rainy periods). The results evidenced that Tropeiros Lake is a shallow environment with maximum depth of 3 m, densely colonized by macrophytes and with high water transparency. It has low concentration of nitrogen with predominance of the ammonium ion, low concentrations of phosphorus being organic phosphate the predominant compound, low pH values with water varying from neutral to slightly acid and moderate water electrical conductivity. The sediment has high clay and organic matter contents. The Discriminant Analysis separated the sampling periods, grouping the similar rainy periods but separating the dry ones. According to the trophic state index the lake was classified as oligotrophic during the rainy periods and mesotrophic during the dry periods. Benthic community was composed by 81 taxa, mainly represented by the members of the Order Diptera, especially those belonging to the families Chironomidae and Chaoboridae. The trophic guild of collectors was the most representative, with minimum abundance of 57.2%, with the taxa Chironomus sp, Goeldichironomus sp and Tanytarsus sp, followed by that of the predators, having Chaoborus and Ablabesmyia sp as the main taxa. The mean biomass determined for the macroinvertebrate community of Tropeiros Lake was 0.94 g. m-2. Except Chironomus sp, that was abundant, regarding both, numbers and biomass, a different condition was observed for the taxa as Pisidium pulchellum, Melanoides tuberculata and a Libellulidae nymph that were numerically less abundant but contributed significantly for the total biomass. Regarding the trophic guilds, predators was more representative in the periods of October 2006 and March 2007 than the collector guild, in terms of biomass. The same was observed regarding the macroinvertebrates contribution to the biomass in each trophic guild, where predators were more abundant than collectors in October 2006 and March 2007, evidencing the importance of this approach in ecological studies. The method based on K-dominance curves (ABC curves) indicated that Tropeiros Lake is under moderate perturbation according to the cumulative values of abundance and biomass. This results corroborates those obtained for lake trophic state index, based on the mean biomass when compared to environments of different trophic states and with the species composition, formed by both, group of tolerant species as well as those more sensible to adverse environmental conditions.
A diversidade e o papel funcional dos táxons que compõem a comunidade de macroinvertebrados bentônicos dos sistemas lacustres podem fornecer informações importantes sobre a saúde e funcionamento destes ecossistemas de água doce. O objetivo deste estudo foi analisar limnologicamente a Lagoa dos Tropeiros, em Capitólio (MG), e realizar um estudo ecológico da diversidade dos macroinvertebrados bentônicos, avaliando a densidade, abundância, biomassa e participação dos táxons nas guildas tróficas funcionais. Para isso foram avaliadas as mudanças na composição taxonômica, na diversidade e na ocorrência sazonal da comunidade bentônica desse sistema. As amostras de água e de sedimento foram coletadas em outubro de 2006 e de 2007 (períodos secos) e em março de 2007 e de 2008 (períodos chuvosos). Os resultados indicaram que a lagoa caracterizou-se como sendo um ambiente raso, com profundidade máxima de 3m, grande quantidade de macrófitas aquáticas, elevada transparência da água, reduzidas concentrações de compostos de nitrogênio, com predominância do íon amônio, e baixas concentrações de fósforo com predomínio de fosfato orgânico, valores de pH variando de neutros a ligeiramente ácidos, condutividade moderada e elevados teores de argila e de matéria orgânica no sedimento. A Análise Discriminante evidenciou a separação dos períodos de amostragem, sendo que os períodos chuvosos foram muito semelhantes, diferentemente do observado para os períodos secos que se diferenciaram por diferentes características ambientais. De acordo com o Índice de Estado Trófico a lagoa foi classificada como um ambiente oligotrófico durante os períodos chuvosos e mesotrófico durante os períodos de seca. A comunidade bentônica foi composta por 81 táxons, sendo representada principalmente por organismos pertencentes à ordem Diptera, especialmente das famílias Chironomidae e Chaoboridae. A guilda trófica dos coletores foi a mais representativa, com abundância mínima de 57,2%, sendo os principais representantes os táxons Chironomus sp, Goeldichironomus sp e Tanytarsus sp, seguida pelos predadores com Chaoborus sp e Ablabesmyia sp como os principais táxons. A biomassa média calculada para a comunidade de invertebrados bentônicos na lagoa foi de 0,94 g. m-2. Com exceção de Chironomus sp, que foi abundante em termos de número de indivíduos e também de biomassa, observou-se uma condição diferente para táxons como Pisidium pulchellum, Melanoides tuberculata e uma ninfa de Libellulidae os quais foram pouco abundantes numericamente, mas apresentaram uma elevada participação na composição da biomassa total. O mesmo foi observado para a participação dos macroinvertebrados em biomassa nas guildas tróficas, onde os predadores foram mais abundantes que os coletores em outubro de 2006 e março de 2007, demonstrando a importância dessa abordagem em estudos ecológicos. O método baseado em curvas de k-dominância (curvas ABC) indicou que a Lagoa dos Tropeiros encontra-se moderadamente perturbada, de acordo com os valores cumulativos de abundância de indivíduos e biomassa. Tal resultado confirma aqueles obtidos para o índice de estado trófico, para os valores de biomassa média quando comparados com ambientes de diferentes graus de trofia e com a composição das espécies presentes, formada tanto por grupos tolerantes como também por aqueles mais sensíveis às condições ambientais adversas.

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32

Kristen, Iris [Verfasser]. "Investigations on rainfall variability during the late Quaternary based on geochemical analyses of lake sediments from tropical and subtropical southern Africa / Iris Kristen. Deutsches GeoForschungsZentrum GFZ." Potsdam : Deutsches GeoForschungsZentrum GFZ, 2010. http://d-nb.info/1000714233/34.

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Guiguen, Yann. "Approches morphologique, histologique et endocrinienne des cycles reproducteurs et de l'inversion sexuelle chez un poisson hermaphrodite protandre : le loup tropical, lates calcarifer, introduit en elevage en polynesie francaise." Rennes 1, 1992. http://www.theses.fr/1992REN10133.

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A tahiti, le lates calcarifer presente une saison de reproduction annuelle et les animaux males peuvent s'inverser apres cette saison. Les caracteristiques histologiques de l'inversion sont, la degenerescence du tissu germinal male, l'apparition du tissu degenerescent male, et enfin la proliferation du tissu germinal femelle avec persistance du tissu germinal femelle. Ce processus d'inversion peut etre acheve au moins en 17 jours, et necessite une profonde reorganisation morphologique des gonades. Au niveau ultrastructural, nous avons identifie de nombreuses cellules germinales primordiales durant la phase de proliferation du tissu germinal femelle. Ces cellules aux caracteristiques indifferenciees pourraient jouer un role important dans l'ontogenese du tissu germinal femelle. Nous avons aussi mesure les concentrations des steroides sexuels plasmatiques et gonadiques, et effectue des etudes de metabolisme in vitro par des gonades a differents stades de maturation sexuelle et d'inversion. Les principaux resultats de ces etudes sont la mise en evidence d'un steroide de type strogene synthetise in vitro en grande quantite par des gonades en fin d'inversion, et par la detection de fortes concentrations gonadiques dans les gonades des le debut de l'inversion. Ceci suggere un role important des strogenes dans la regulation endocrienne de l'inversion sexuelle du lates calcarifer. Concernant le compose de type strogene, ses caracteristiques biochimiques sont identiques a celles d'un 3-ester d'stradiol. Ce steroide pourrait servir de reserve tissulaire d'stradiol 17

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Martins, Renato Tavares. "Colonização de Oligochaeta e outros macroinvertebrados durante a decomposição de Eichhornia azurea (SW.) Kunth (Pontederiaceae) e Salvinia auriculata Aubl. em um sistema lêntico na região tropical." Universidade Federal de Juiz de Fora (UFJF), 2009. https://repositorio.ufjf.br/jspui/handle/ufjf/2820.

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O presente estudo foi composto por dois experimentos, o objetivo do primeiro deles verificar a colonização de Oligochaeta ao longo da decomposição da macrófita Eichhornia azurea (Sw.) Kunth, no segundo experimento, analisou-se a estrutura faunística dos macroinvertebrados no decorrer da decomposição de E. azurea e Salvinia auriculata Aubl. O experimento 1 foi dividido em dois períodos (1º período: setembro a novembro de 2007; 2º período: fevereiro a abril de 2008), em cada um deles, 21 sacos de náilon contendo 10 g de folhas de E. azurea, foram colocados no lago, e retirados após 2, 5,8, 12, 25, 45, e 65 dias. No experimento 2 (novembro de 2007 a fevereiro de 2008), foram utilizados 60 sacos de náilon, 30 deles com 10 g de folhas de E. azurea, e os demais contendo a mesma quantidade de folhas de S. auriculata. Após 30 minutos, 2, 4, 8, 12, 24, 36, 48, 60 e 72 dias os sacos foram retirados do lago. Em ambos os experimentos, após serem retirados do lago, os sacos foram levados ao laboratório, e o material remanescente fixado em formol 4%, lavado e triado, os organismos encontrados foram identificados e conservados em álcool 70%. No experimento 1, o maior coeficiente de decomposição (K) foi observado no primeiro período (K= 0,023 d-1 ) em relação ao segundo (K= 0,018 d-1 Palavras–Chave: Chironomidae, Lago dos Manacás, macrófitas, Naididae, relação carbono:nitrogênio ), no entanto, não houve diferença significativa. Observou-se o aumento da densidade e riqueza dos Oligochaeta ao longo do estudo em ambos os períodos. Naididae foi a família dominante, estes organismos por possuírem a capacidade de se locomover na coluna d'água próximo ao substrato, mostraram-se melhores colonizadores do que Enchytraeidae e Tubificidae. No experimento 2, ao final dos 72 dias, observou-se menor biomassa total de E. azurea (2,65 g MS) em relação à S. auriculata (5,10 g MS), sendo que na primeira macrófita registrou-se a diminuição da relação carbono: nitrogênio durante o estudo, enquanto que em S. auriculata não foi observada a diminuição desta razão. Chironomidae e Naididae foram as famílias com maiores densidades, representando mais de 95% da fauna em ambas as macrófitas. Os coletores foram o grupo funcional mais abundante em E. azurea e S. auriculata, confirmando a predominância destes organismos nas folhas em decomposição na região tropical.
The present study was composed of two experiments. The first with the objective to verify the colonization of Oligochaeta during decomposition of the macrophyte Eichhornia azurea (Sw.) Kunth, while the second experiment analized the faunistic struture of the macroinvertebrates along decomposition of E. azurea and Salvinia auriculata Aubl. Experiment 1 was divided into two periods (1st period: September to November 2007; 2nd period: February to April 2008). In each period, 21 nylon bags containing 10 g of dry leaves of E. azurea, were placed in the lake, and removed at intervals of 2, 5,8, 12, 25, 45, and 65 days. In experiment 2 (November 2007 to February 2008), 60 nylon bags were used, 30 of them filled with 10 g of dry leaves of E. azurea and the others, containing the same amount of dry leaves of S. auriculata. After intervals of 30 minutes, 2, 4, 8, 12, 24, 36, 48, 60 and 72 days the bags were taken out of the lake. In both experiments, after out of the lake, the bags were taken to the laboratory, and the remanescent material was fixed in a formol solution 4%, washed and sorted. The organisms were identified and preserved in 70% alcohol. In experiment 1, the highest decomposition coefficient (K) was observed in the first period (K= 0.023 d-1) in relation to the second (K= 0.018 d-1 ), however with no significant difference. An increase of density and richness of Oligochaeta along the study was observed in both periods. Naididae was the most dominant family, represented by the genera Allonais, Chaetogaster, Dero and Pristina. These organisms, for their ability of moving themselves in the water column, near the substrate, showed to be better colonizers than Enchytraeidae and Tubificidae. In experiment 2, at the end of the 72 days, it was observed a small fraction of total biomass of E. azurea (2.65 g DM) in relation to S. auriculata (5.10 g DM), whereas in the first macrophyte it was registered a decrease of the carbon: nitrogen relationship during the study, while in S. auriculata it was not observed the decrease of this rate. Chironomidae and Naididae were the families with the higher densities, representing more than 95% of the fauna in both macrophytes. The collectors were the most abundant functional group in E. azurea and S. auriculata, attesting to the predominance of these organisms in the leaves in decomposition in the tropical region.

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Silva, Raquel Lemos da. "EvoluÃÃo morfodinÃmica e hidrolÃgica direcionada ao manejo de lagoas costeiras tropicais. Estudo de caso: lagoa das almÃcegas, Paraipaba - Trairi/Ce." Universidade Federal do CearÃ, 2007. http://www.teses.ufc.br/tde_busca/arquivo.php?codArquivo=1687.

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CoordenaÃÃo de AperfeiÃoamento de Pessoal de NÃvel Superior
A lagoa costeira, AlmÃcegas, estÃ localizada no litoral Oeste do Estado do CearÃ na divisa dos municÃpios de Trairi e Paraipaba. O principal objetivo deste trabalho foi avaliar a evoluÃÃo os processos controladores da morfologia e hidrologia da Lagoa das AlmÃcegas visando gerar informaÃÃes Ãteis ao uso e gestÃo desse recurso hÃdrico costeiro. A origem da lagoa das AlmÃcegas estÃ subordinada ao comportamento climÃtico-natural da Ãrea, bastante influenciado pela dinÃmica litorÃnea. Com a gÃnese relacionada aos processos transgressivos e regressivos do mar, e barramento do riacho pelo sistema de dunas (transporte eÃlico) e processos associado (descarga fluvial), sendo posteriormente com a construÃÃo da barragem. A metodologia utilizada para realizaÃÃo desta pesquisa baseia-se na compreensÃo da organizaÃÃo da natureza dentro do espaÃo, e a relaÃÃo que ocorre entre seus componentes. Para tanto foram realizadas analises dos parÃmetros fÃsicos e quÃmicos da Ãgua: temperatura, condutividade elÃtrica, turbidez, pH e transparÃncia. Ademais, foram coletadas amostras de subsuperfÃcie e fundo para a investigaÃÃo de material em suspensÃo. TambÃm, realizou-se a caracterizaÃÃo sedimentolÃgica, analise de matÃria orgÃnica e metaisâtraÃo (cobre, cÃdmio e zinco) no sedimento, e o estudo morfomÃtrico e levantamento batimÃtrico da lagoa. Os resultados demonstram que o sistema estudado apresentou variaÃÃo sazonal relacionada aos dois perÃodos hidrolÃgicos distintos. O perÃodo chuvoso se caracterizou por precipitaÃÃes mais intensas e menor insolaÃÃo, enquanto que o seco apresentou maior insolaÃÃo e maiores velocidades dos ventos, trazendo conseqÃÃncias diretas sobre o nÃvel dâÃgua da lagoa. A coluna dâÃgua apresentou estratificaÃÃo (tÃrmica) significativa devido principalmente Ã profundidade do sistema, Ã atuaÃÃo dos ventos e transparÃncia da coluna dâÃgua. A composiÃÃo granulomÃtrica dos sedimentos de fundo da Lagoa das AlmÃcegas resultaram em seis classes principais: areia com cascalho esparso (43,8 %), areia (25%), areia fina (6,3%), areia siltosa (6,3%), areia lamosa (6,3%), silte (6,3%) e silte arenoso (6,3%). Observa-se que as fraÃÃes grossas do sedimento, maiores que 0,063 mm, ocorrem na grande maioria das amostras, o que pode estÃ relacionado ao processo de assoreamento. A distribuiÃÃo da matÃria orgÃnica indica os diferentes graus de aeraÃÃo das diversas Ãreas do ambiente de sedimentaÃÃo. Quanto Ã morfologia a lagoa apresentando uma Ãrea de 1,3 km2, perÃmetro de 9,935 Km, largura mÃxima de 684 m e comprimento de 3,5 km, volume de 6.688.000 mÂ, profundidade mÃxima de 5,85 m, profundidade mÃdia de 2,55m. A relevÃncia do volume classifica este reservatÃrio como de capacidade de armazenamento satisfatÃrio. Em termos de ocupaÃÃo, a lagoa encontra-se com baixa ocupaÃÃo imobiliÃria, devido principalmente a pouca especulaÃÃo. Mas, as ocupaÃÃes que jÃ ocorrem na regiÃo ultrapassam os limites impostos pela lei (Ãreas de PreservaÃÃo Permanente), jÃ a ocupaÃÃo associada Ã retirada da cobertura vegetal Ã possÃvel de ser vista, e este problema pode gerar uma instabilidade das margens e conseqÃente alteraÃÃo das caracterÃsticas morfomÃtricas e fÃsicoquÃmicas da lagoa, podendo ocasionar impactos negativos, como aumento do escoamento superficial, erosÃo das margens, maior aporte de sedimentos na lagoa, assoreamento, diminuiÃÃo do volume de Ãgua, e maior concentraÃÃo de poluentes na lagoa, podendo vir a comprometer tambÃm a vida da populaÃÃo local.
The coastal lagoon, AlmÃcegas, are located in the coastal West of the State of the CearÃ in the verge of the cities of Trairi and Paraipaba. The main objective of this work was to evaluate the evolution the controlling processes of the morphology and hidrology of the Lagoon of the AlmÃcegas being aimed at to generate useful information to the use and management of this coastal hÃdrico resource. The origin of the lagoon of the AlmÃcegas is subordinated to the climatic-natural behavior of the area, sufficiently influenced for the littoral dynamics. With genesis related to the transgression and regression processes of the sea, and slide bars of the extended river for the dune system (aeolian transport) and processes associated (fluvial discharge), being later with the construction of the barrage. The methodology used for accomplishment of this research is based inside on the understanding of the organization of the nature of the space, and the relation that occurs between its components. For they had been in such a way carried through you analyze of the physical and chemical parameters of the water: temperature, electric condutividade, turbidez, pH and transparency. Furthermore, had been collected samples of deep subsurface and for the inquiry of material in suspension. Also, it was become fullfilled sedimentation characterization, analyzes of organic substance and metal-traces (it has covered, cadmium and zinc) in the sediment, and the morfomÃtrico study and batimÃtrico survey of the lagoon. The results demonstrate that the studied system presented related sazonal variation to the two distinct hidrolÃgicos periods. The rainy period if characterized for more intense precipitations and lesser insolation, whereas the dry one presented greater insolation and greaters speeds of the winds, bringing direct consequences on the water level of the lagoon. The water column presented stratification (thermal) significant had mainly to the depth of the system, to the performance of the winds and transparency of the water column. The grain sized composition of the sediments of deep of the Lagoon of the AlmÃcegas had resulted in six main classrooms: slightly gravelly sand (43.8%), sand (25%), fine sand (6.3%), muddy sand (6.3%), slightly gravelly muddy sand (6.3%), silt (6.3%) and sandy silt (6.3%). It is observed that the thick fractions of the sediment, greaters that 0,063mm, occur in the great majority of the samples, what it can is related to the silting. The distribution of the organic substance indicates the different degrees of aeration of the diverse areas of the sedimentation environment. How much to the morphology the lagoon presenting an area of 1,3km2, perimeter of 9,935Km, maximum width of 684m and length of 3,5km, Volume of 6.688.000m Â, maximum depth of 5,85m, average depth of 2,55m. The relevance of the volume classifies this reservoir as of capacity of satisfactory storage. In occupation terms, the lagoon meets with low real estate occupation, had mainly to little speculation. But, the occupations that already occur in the region exceed the limits taxes for the law (Areas of Permanent Preservation) already the occupation associated with the withdrawal of the vegetal covering are possible of being seen, and this problem can generate an instability of the edges and consequence the alteration of the morfomÃtricas characteristics and physicistchemistries of the lagoon, being able to cause negative impacts, as increase of the superficial draining, erosion of the edges, greater arrives in port of sediments in the lagoon, assoreamento, reduction of the volume of water, and greater concentration of pollutants in the lagoon, being able to come also compromising the life of the population place.

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Dile, Yihun. "Intensifying Agricultural Water Management in the Tropics : A cause of water shortage or a source of resilience?" Doctoral thesis, Stockholms universitet, Stockholm Resilience Centre, 2014. http://urn.kb.se/resolve?urn=urn:nbn:se:su:diva-102878.

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Frequent climatic shocks have presented challenges for rainfed agriculture in sub-Saharan Africa. Appropriate water management practices are among the solutions to the challenges. The role of water harvesting in achieving sustainable agricultural intensification and specified resilience was explored. Suitable areas for water harvesting in the Upper Blue Nile basin were identified. The usefulness of the Curve Number method for surface runoff estimation was evaluated, and was found to perform satisfactorily. The impact of climate change in the Lake Tana sub-basin was studied. A decision support system was developed for locating and sizing of water harvesting ponds in the SWAT model. Methodological developments enabled analysis of the implications of water harvesting intensification in a meso-scale watershed in the Lake Tana sub-basin. Results suggest that water harvesting can increase agricultural productivity, sustain ecosystems and build specified resilience, and thereby contribute to sustainable agricultural intensification. There is considerable potential for water harvesting in the Upper Blue Nile Basin. Rainfall may increase in the Lake Tana sub-basin due to climate change. Supplementary irrigation from water harvesting ponds and better nutrient application increased staple crop production by up to three-fold. Moreover, a substantial amount of cash crop was produced using dry seasonal irrigation. Water harvesting altered the streamflow regime, and reduced sediment loss from the watershed. Water harvesting can play an important role in food security. It showed potential to buffer climatic variability. In the watershed studied, water harvesting will not compromise the environmental water requirements. Instead, increased low flows, and reduced flooding and sediment loss may benefit the social-ecological systems. The adverse effects of disturbance of the natural flow variability and sediment influx to certain riverine ecosystems warrant detailed investigation.

At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 2: Manuscript. Paper 3: Manuscript. Paper 5: Epub ahead of print. Paper 6: Manuscript.

Water resources management and social-ecological resilience

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Ishak, Mohd Yusoff. "Predictive modelling of eutrophication and algal bloom formation in tropical lakes." Thesis, 2012. http://hdl.handle.net/2440/78097.

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My original contribution to knowledge is the successful application of two modelling paradigms 1) SALMO-PLUS process based model and 2) HEA data driven model to tropical lakes of different morphometry and trophic status. The application of SALMO-PLUS to tropical lakes involves utilising the SALMO-OO model structure for optimisation. This was followed by multi objective parameter optimisation on selected parameters to seek the optimum parameter values that can model the algal dynamics and state variables fluctuations in the tropical lakes to an acceptable magnitude and peaks. SALMO-PLUS is another version SALMO-OO with capability to run optimisation by means of particle swarm optimisation (PSO) method. SALMO-OO has been used as a research tool over a number of lakes with different trophic states and mixing conditions to simulate algal succession and respond to ecosystem dynamic. SALMO-OO is driven by process-based differential equations and works by utilizing a library of three phytoplankton growth and three grazing process models. Evolutionary algorithms (EA) are bio-inspired adaptive methods which mimic processes of biological evolution, natural selection and genetic variation such as cross-over and mutation to develop solutions to complex computational problems (Recknagel et al, 2006). HEA is designed for rule discovery in water quality timeseries (Cao et al., 2006b) and is capable of forecasting potential algal population dynamics and outbreaks in water bodies. The SALMO-PLUS model was applied for simulating the state variables of selected lakes (Lake Kenyir, Lake Penang, Saidenbach Reservoir, Roodeplaat Dam and South Para Reservoir). Measured data from the year 2005 and 1992 were used for Lake Penang and Lake Kenyir respectively. The HEA was applied for predicting the Chl-a and algal biovolume abundance on tropical lakes (Lake Putrajaya, Lake Penang and Lake Kenyir) in Malaysia. This study discusses the application of SALMO-PLUS and HEA towards tropical lakes eutrophication management. The results of application of SALMO-PLUS on tropical lakes are presented, simulating response of the phytoplankton community to fluctuation in nutrient loading, light availability and hydrological aspect in the water bodies. Results of applying HEA on tropical lakes are also interpreted in the context of empirical and causal knowledge on Chl-a and algal biovolumes dynamics under tropical lake water quality conditions by means of rule-based model. Results for both Lake Kenyir and Penang showed that SALMO-PLUS were able to predict annual average trends not only for chlorophyll-a but also other state variables and algal functional groups. Simulated state variables namely Chl-a, N and P showed good agreement with field observations data for both lakes. Despite the fact that this is the first time SALMO-PLUS been used for tropical lakes and the limited data availability from this region, the simulated values of biological and nutrient state variables match reasonably with measured data. Outcomes from SALMO-PLUS simulation show consistent compliance with algal community assembly obtained from other researchers. The HEA achieved reasonable accuracy in predicting timing and magnitudes of algal blooms up to 7-days-ahead. The HEA proved to be most efficient in modelling and predicting seasonal dynamics of chlorophyll-a and algal biovolumes. A sensitivity analysis conducted for Lake Penang revealed that algal abundance is not only driven by physical and chemicals characteristics of the water body but also by impact of inorganic substances in the water that contributes to high level of chemical oxygen demand in the water as well. In addition, this study has successfully implemented a new process model from Law et al. (2009) consisting algal growth, algal grazing, zooplankton growth and zooplankton mortality functions into the SALMO-OO simulation library. Combination of this new process models were tested on dataset from Lake Kenyir, Lake Penang, Saidenbach Reservoir and Roodeplaat Dam within the simulation library to discover the optimal model structures for respective water bodies. Even though the new process model was not selected in complete totality as the optimal model structure for any of the test lakes, the addition has added another alternative for water body simulation in SALMO-OO process library. Based on these forecasting results, both SALMO-PLUS and HEA have showed potential for utilisation in early warning and strategic control of algal blooms in tropical freshwater lakes. The generic nature of HEA forecast model was also observed when tested for forecasting algal biovolume for merged data of similar lake ecosystem category. Results from merged Lake Kenyir and Lake Penang data showed reasonable accuracy in predicting the timing and magnitudes of algal blooms up to 7-days-ahead. Addition of the new process model from Law et al. (2009) into the SALMO-PLUS simulation library has also expanded the alternative for lake category simulation to give a more comprehensive decision support tool for lake and reservoir management. This study has also affirmed the generality and flexibility of SALMO-PLUS for usage in tropical lakes modelling. SALMO-PLUS was observed to be capable of simulating simultaneous seasonal fluctuations in algal growth and nutrients (phosphate and nitrate) making it valuable for forecasting the impacts of various simulated scenarios for various lake management regimes.
Thesis (Ph.D.) -- University of Adelaide, School of Earth and Environmental Sciences, 2012

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Lininger, Katherine Blom. "The hydro-geomorphology of the middle Araguaia River: floodplain dynamics of the largest fluvial system draining the Brazilian Cerrado." 2013. http://hdl.handle.net/2152/21826.

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Located in central Brazil, the Araguaia River is the largest river flowing through the Cerrado, the Brazilian savanna. The thesis presented here assesses the hydro-geomorphology of the middle Araguaia River-floodplain system by characterizing flooding patterns and linking these patterns to the geomorphology of the floodplain. It also determines the response of floodplain lake morphometry and surface water connectivity to the annual flooding of the river, and describes how different floodplain geomorphologic units influence changes in open water areas in the floodplain from the dry season to the wet season. Peak discharges along the middle Araguaia River can be reduced downstream despite large increases in drainage area and the contribution of tributary inputs. After analyzing average daily discharge measurements from 1975 to 2007 along an upstream reach and a downstream reach in the middle Araguaia River, four main flooding types are characterized based on the magnitude of the peak discharge and the pattern of peak discharge reduction that occurs as the flood wave moves downstream. Short-term losses of channel discharge during the flooding peak and over the flooding season from November to May are estimated, with the downstream reach displaying more short-term channel loss compared to the upstream study reach. Differences in floodplain geomorphological characteristics between the two study reaches, including the proportions of distinct geomorphologic units (a lower elevation impeded floodplain, a unit dominated by paleomeanders, and a unit of accreted banks and islands), influence the patterns of peak reduction and channel loss. Short-term losses of channel discharge during flooding peaks are usually re-gained by the channel by the end of the flooding season, although in two years about 10% of the volume input into the downstream reach was lost from the channel over the flooding season. Using satellite imagery and an open water index, changes in lake area, perimeter, and surface water connectivity with the main channel between dry season and the wet season are determined for 32 floodplain lakes. The changes in lake morphometry and connectivity are linked to how fluvial processes formed the floodplain lakes. Spatial variations in the floodplain areas that became open water from the dry season to the wet season demonstrate that distinct floodplain geomorphologic units influence the extent and location of open water areas during flooding. Floodplain lakes that expand in area and in depth and are connected to the river channel via surface water likely provide storage areas for the channel losses and peak discharge reductions observed in some of the flooding types for the middle Araguaia River. Although there have been attempts to plan the placement of dams on the Araguaia River, the river is not impounded, allowing for the analysis of a river system with an unaltered flow regime. This thesis contributes to knowledge of a large and understudied tropical river in an ecologically sensitive region.
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Collins, Geoffrey M. "Phenotypic drivers of hypoxia tolerance in a tropical diadromous fish (Lates calcarifer)." Thesis, 2016. https://researchonline.jcu.edu.au/48866/1/48866-collins-2016-thesis.pdf.

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Increasing coastal eutrophication and rising global temperatures are placing substantial pressure on wild fish populations. In the tropics, routinely high temperatures close to the equator have the combined effects of reducing the solubility of O₂ in water, increasing metabolic rates and enhancing thermal stratification. Such conditions may be particularly pronounced in lentic freshwater environments, and have led to a suite of adaptations by tropical fish species. Inter-specific diversity in hypoxia tolerance is widely acknowledged, however, many species exist not as a single, continuous population, but rather as multiple populations that may be distributed over broad latitudinal gradients, potentially spanning thousands of kilometres. In the absence of horizontal migration and genetic mixing between populations, and with differences in prevailing environmental conditions (such as temperature and dissolved O₂), such populations may become phenotypically and even genotypically divergent over time. Performance of fish populations have been extensively investigated in the context of temperature, particularly with regard to projected temperature increases from climate change models. Despite the intrinsic relationship between temperature, O₂ and metabolism in fish, population differences in hypoxia tolerance have received little research attention to date. To address this knowledge gap, the hypoxia tolerance of geographically and genetically divergent populations of juvenile barramundi from across the distribution in northern Australia was assessed (Chapter 2). Juvenile barramundi were collected from five hatcheries across northern Australia, and were assessed for their resting O₂ consumption rate (ṀO₂) and critical O₂ level (O₂CRIT) using intermittent-flow respirometry. Measurements for all five populations were made at temperatures considered benign for this species across its distribution in Australia (26°C) and at temperatures that may be encountered during the pre-wet season (36°C). A posteriori comparisons revealed significant temperature effects for both resting ṀO₂ and O₂CRIT, but no conclusive evidence for population differences in either measure. The results from this study indicate a similar capacity for barramundi populations to regulate metabolism in response to hypoxia at typical and warm temperatures. The magnitude of temperature effects on O₂CRIT for barramundi was lower than for many other tropical and temperate fish species, indicating that barramundi retain a high capacity to regulate metabolism in hypoxic environments at high temperatures. Over long time scales (tens to hundreds of thousands of years), populations that are genetically divergent may become either locally adapted to a specified range of conditions (if conditions are constrained within a narrow range), or they may retain a large degree of physiological plasticity (if the environments they inhabit are highly variable). Further, dissolved O₂ may display high spatial and temporal variability in coastal freshwater and estuarine systems that is often overlooked in empirical studies. To assess the contribution of population-of-origin or physiological plasticity to hypoxia tolerance, juvenile barramundi (one tropical and one sub-tropical population) were exposed to daily fluctuations in dissolved O₂ (>85% to <10% saturation) for 0 (control), 8 or 16 d (Chapter 3). Fish (separate cohorts) were then assessed for either resting ṀO₂ and O₂CRIT, or haematological parameters. No changes in any parameters were detected after 8 d, however after 16 d a reduction in O₂CRIT, and increases in both haematocrit and haemoglobin were observed. No population differences were detected for any measured parameter. This study demonstrates that barramundi populations are capable of acclimating to diel-cycling hypoxic conditions following repeated exposure, and that such changes are accompanied by improvements to blood-O₂ carrying capacity. Inter-specific diversity in hypoxia tolerance of teleost fish is widely acknowledged, however the extent of intra-specific diversity in hypoxia tolerance is less well understood, due in part to the logistical and temporal constraints of measuring performance across a large number of individuals. Further, the temporal repeatability and hence the reliability of hypoxia tolerance measures have received virtually no attention in the broader scientific literature. To address these knowledge gaps, ~800 juvenile barramundi were first separated into hypoxia tolerance categories (Chapter 4) based on time to loss of equilibrium (LOE) tests: sensitive, intermediate and tolerant. Following a recovery period, fish were then assessed for growth performance, metabolic regulation under hypoxia (O₂CRIT) and repeatability of time to LOE. Further, the relationship between ṀO₂ and DO during O₂CRIT tests was assessed using non-linear regression and broken-stick regression techniques, which represents a novel approach to handling such a large empirical data set. Fish were reliably separated into different hypoxia tolerance categories, yet there were no significant category effects for any of the subsequently measured variables: growth rate, feed conversion ratio, standard metabolic rate or O₂CRIT. Non-linear regression was more robust in describing the relationship between ṀO₂ and DO than the more commonly used broken-stick regression method. Surprisingly, there was no significant relationship between two independent measures of hypoxia tolerance: time to LOE and O₂CRIT. The time to LOE test was broadly repeatable after ~100 d. This study highlights the extent of intra-specific diversity in hypoxia tolerance that can exist within fish populations. All previous assessments of hypoxia tolerance were necessarily conducted on unfed individuals to eliminate the influence of specific dynamic action (SDA) on metabolic responses. In the wild, and on commercial fish farms, metabolism of fish may be elevated above resting levels due to feeding behaviour. Digestive responses are potentially influenced by dissolved O₂ conditions, however, few studies have assessed this possibility in tropical fish. Further, no studies have assessed the effect of hypoxia tolerance phenotype on digestive metabolic responses. Therefore, barramundi were separated into hypoxia tolerance phenotypes (sensitive or tolerant) based on time to LOE tests (Chapter 5). Fish were then fed a restricted ration (2.5% of their body-mass), before being assessed for ṀO₂ under normoxic (>85% saturation) and chronic hypoxic (~35% saturation) conditions. There was no effect of hypoxia tolerance phenotype for any measured parameter, and negligible differences in a range of digestive responses (SDA magnitude, SDA duration, SDA coefficient) under normoxic or hypoxic conditions. The results from this study suggest that barramundi are capable of maintaining maximal digestive capacity even when O₂ drops to 35% saturation. The results from this thesis demonstrate that barramundi are extremely resilient to bouts of environmental hypoxia, and retain a strong tolerance to hypoxic conditions at extremely warm temperatures. The lack of population differences in hypoxia tolerance may be explained by the retention of a high degree of physiological plasticity as a strategy for responding to environmental hypoxia. The extent of phenotypic diversity in hypoxia tolerance is impressive, and the influence of this diversity on performance is still poorly understood. The homogeneity of performance between hypoxia tolerance phenotypes across two experiments and a number of measured parameters suggests that hypoxia tolerance is unrelated to several other performance metrics under either normoxic or hypoxic conditions. Future research should be directed at further exploring the relationship between phenotypic diversity in hypoxia tolerance and fitness, with an objective to more clearly elucidate the ecological consequences of trait variability.

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40

"Impact of bike lanes and sidewalk improvements in New Orleans, Louisiana." Tulane University, 2013.

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41

Moore, Randall Phillips 1965. "Biogeographic and experimental evidence for local scale dispersal limitation in central Panamanian forest birds." Thesis, 2005. http://hdl.handle.net/1957/1407.

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Graduation date: 2006
I examined the avian biogeography of the islands of Lago Gatun, Panama, in an effort to better understand the effects of forest fragmentation in this biodiverse region, and specifically to understand the importance of fragment isolation and the mechanism behind its effects on tropical bird distribution. I combined exhaustive surveys of 29 islands with an experimental release program. Analyses of these data were conducted in a hierarchical fashion to evaluate evidence for avian dispersal limitation at multiple scales. First, I assessed the potential roles of area and isolation in determining avian species richness across this series of fragments, and how these relationships may differ for edge and forest dependent birds. Next, I analyzed community structure and species distributions to determine the relative contributions of island area and isolation in creating patterns of species-specific insular occurrence. Lastly, I assessed the results of the experimental investigation to evaluate the hypothesis that dispersal limitation explains the insular distribution patterns of several tropical forest birds. Isolation is a significant predictor of avian species richness, but only after accounting for the stronger effect of area. Species-isolation relationships are different in this archipelago for birds that rely on forest and edge habitats, respectively. Species-specific distributions are significantly nested when islands are ordered by area, and by isolation once the effect of area is considered. Occurrence of most forest species is sensitive to area and isolation of the archipelago. Examination of guild structure suggests that multiple mechanisms are responsible for these occurrence patterns. There are distinct species-specific differences in ability to cross small gaps, and species which are better able to cross these gaps are more widely distributed across the archipelago than those species that negotiate the same barriers poorly. Species that performed uniformly well in release experiments were much less likely to have suffered insular extinction in the preceding 25 years than those species that showed moderate to poor experimental performance. There is strong evidence of a morphological basis for the patterns. The cumulative evidence from these analyses is the most comprehensive evidence to date of local-scale dispersal limitation in volant birds.

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McCullough, Gregory Keith. "Circulation of terrestrial runoff and its suspended load in a large tropical lake : a study of processes and effects near the mouth of the Linthipe River in Lake Malawi." 2006. http://hdl.handle.net/1993/20912.

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Balston, Jacqueline Marie. "An examination of the impacts of climate variability and climate change on the wild barramundi (Lates calcarifer): a tropical estuarine fishery of north-eastern Queensland, Australia." Thesis, 2007. https://researchonline.jcu.edu.au/2060/1/01front.pdf.

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Scope As is the case overseas, the wild fisheries of Australia are under increasing threat from the pressures of over-fishing, habitat destruction and water quality degradation. In addition, inshore fisheries that are dependant on freshwater flows to provide nutrient pulses and nursery habitats are also affected by changes in natural flow regimes as a result of water impoundment and extraction (Robins, Halliday et al. 2005). The barramundi (Lates calcarifer) is an important commercial fish species in Australia worth $8.8 million in 2004/05 (ABARE 2006), and supports valuable tourism and recreational fishing industries. Commercial catch displays a high degree of inter-annual variation; a characteristic that many fishers believe is the result of climate variability. However, apart from rainfall and freshwater flow, previous studies of the barramundi have not examined the impacts from climate in any detail, and existing management strategies do not consider natural climate variability or climate change. This study examined the effects from long-term (biannual to decadal) and short-term (inter-annual) climate variability, extreme and threshold climate events, and anthropogenic climate, change on the commercial catch of wild barramundi in north-east Queensland. The possibility of incorporating climate parameters into the management of the fishery was also examined. Methods A life cycle model of the barramundi was developed to link climate parameters with the complex developmental stages of the species from spawning in the estuary through maturation in freshwater rivers. Fisheries and climate data were extracted from a variety of sources and compiled for analysis. A gamma distributed logarithm link function model was constructed to calculate total freshwater flow for those years when records were incomplete. Correlation analysis identified significant relationships between climate parameters and catch, and forward stepwise ridge regression was used to develop a model of barramundi catch using climate parameters as predictors. The impact of threshold events was determined by non-linear analysis and the effects of extreme events on barramundi habitat were qualified against MODIS satellite imagery. A selection of climate change scenarios from a range of global climate models (GCMs), were run through the predictive model developed to determine the likely impacts of future anthropogenic climate change on the fishery. Results In the near-pristine Princess Charlotte Bay area, warm sea surface temperatures, high rainfall, increased freshwater flow and low evaporation (all measures of an extensive and productive nursery habitat) were significantly correlated with barramundi catch two years later as recorded by the CFISH logbook system. These results suggest that early barramundi survival is enhanced in these conditions. Catchability was significantly increased after high freshwater flow and rainfall events in the year of catch, a result that reinforced previous observations that mature fish in freshwater habitats are flushed into the commercial estuarine fishery. October – December rainfall and April – June flow showed non-linear asymptotic relationships and annual evaporation a quadratic relationship, with commercial catch two years later. Curves peaked at approximately 325 mm, 245 000 Ml and 2 000 mm respectively, a result that demonstrated that once these hydro-meteorological threshold events occurred, the response from the fishery was reversed and subsequent commercial barramundi catch reduced. A comparative analysis of data from the Fitzroy River area, a catchment and near shore area that has been highly modified by human intervention, showed only increased freshwater flow prior to the wet season enhanced subsequent barramundi catch. This result indicated that the anthropogenic changes to habitat either affected or masked the relationship between other climate variables and barramundi catch in the area. Total long-term barramundi landings as recorded by the Queensland Fish Board for six regions along the north-east coast of Queensland showed a near decadal cycle. Correlation analyses returned significant relationships between catch and the January – March average L-index (a measure of the latitude of the subtropical ridge) two, three and four years prior to catch, and the Quasi-biennial Oscillation (QBO) three and four years prior to catch. These results suggest that each of these cycles affects climate in the north-east Queensland region and subsequent survival of barramundi in the early life cycle stages, and provides an opportunity to estimate catch a number of years in advance. A forward stepwise ridge regression model was built to predict commercial barramundi catch in Princess Charlotte Bay. The model contained July – September rainfall and annual evaporation two years prior to catch and explained 62% of the variance in catch and had a cross validated predictive R2 of 59%. A second model also contained April – June flow in the year of catch (a measure of catchability). This second model explained 69% of the variance in catch and had a cross validated R2 of 61%, however, the improvement was not statistically significant. Using the nine global climate models in the OZCLIM program set for three initiating TAR SRES markers (A1B, A2 and B1), a suite of twelve climate change scenarios was generated for the years 2030 and 2070 for Princess Charlotte Bay. These scenarios were then run through the predictive barramundi model developed. Results indicated that due to a likely increase in annual evaporation, barramundi catch in the area will decrease for all future climate scenarios including those that show an increase in July – September rainfall. An analysis to calculate future sea surface temperatures using REEFCLIM indicated that, depending on the availability of suitable habitats, it is possible that the range of the species will extend further south by up to 800 km by the year 2070 as temperatures increase. Conclusions Results from this study indicate that a significant proportion of the variability seen in commercial barramundi catch in north-east Queensland is driven by variability in climate. Climate signals are significant at both short and long-term time frames and for some variables the impact is non-linear beyond a defined threshold. Anthropogenic changes to the fishery habitat alter or mask the relationship between climate and barramundi catch, and possibly affect the reproductive success of the species. The likely impact of future anthropogenic climate change will be a reduction in barramundi catch in areas where an increase in evaporation results in a subsequent decrease in shallow wetland habitats essential for early life cycle survival. This thesis provides supporting evidence for policy makers to improve significantly both the prediction of future barramundi catch and the sustainable management of the species by considering the impacts of climate variability and climate change on the species, and by incorporating climate variables into catch models.

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Balston, Jacqueline Marie. "An examination of the impacts of climate variability and climate change on the wild barramundi (Lates calcarifer) : a tropical estuarine fishery of north-eastern Queensland, Australia /." 2007. http://eprints.jcu.edu.au/2060.

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Kristen, Iris [Verfasser]. "Investigations on rainfall variability during the late Quaternary based on geochemical analyses of lake sediments from tropical and subtropical southern Africa / vorgelegt von Iris Kristen." 2009. http://d-nb.info/995396264/34.

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Dissertations / Theses on the topic 'Tropical lakes'

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