Dissertations / Theses on the topic 'Heterogeneity in phytoplankton stoichiometry'

O reservatório Paiva Castro é o último reservatório de uma série de cinco barragens em cascata, que formam o Sistema Cantareira, um dos principais sistemas de abastecimento de água na Grande São Paulo. Sua biomonitoramento é uma ferramenta importante para compreender o estado ecológico do reservatório, bem como para avaliar as situações que estão causando mudanças na qualidade e quantidade da água. No presente estudo, com base em características físicas e químicos da água e atributos ecológicos do fitoplâncton e zooplâncton, verificou-se a existência de compartimentação (heterogeneidade espacial horizontal) e heterogeneidade temporal no Reservatório Paiva Castro. Foram realizadas duas coletas, uma na estação seca (maio e junho) e outra na estação chuvosa (novembro e dezembro) em 2014. O ano 2014 teve um período de seca atípica, o que desencadeou o problema da crise da água que afetou a dinâmica dos reservatórios na Região Metropolitana de São Paulo. As amostras foram coletadas em 9 pontos ao longo Reservatório Paiva Castro. As variáveis temperatura, pH, condutividade e oxigénio dissolvido foram medidos in situ com sonda multiparamétrica. A matéria suspensa, os nutrientes e pigmentos foram medidos no laboratório. Amostras de plâncton foram coletadas na zona fótica com a boca da rede na profundidade da zona eufótica. O reservatório foi classificado como oligotrófico durante a seca e mesotrófico na estação chuvosa; no entanto, os parâmetros físicos e químicos estavam de acordo com CONAMA 357. Dois compartimentos foram identificados através da análise de variáveis limnológicas (profundidade, sólidos suspensos totais e nutrientes) e das comunidades de fitoplâncton e zooplâncton: a zona afetada pela entrada rio Juqueri e b) a zona de transição que integra o canal de barragem e compartimentos. A densidade e biovolume/biomassa também aumentaram nesse sentido. A heterogeneidade temporal foi ainda mais evidenciado pelas características químicas e físicas, do que pelas comunidades planctônicas. Em relação ao fitoplâncton, o Bacillariophyceae e Chlorophyceae apresentou a maior densidade, Cryptophyceae e Dinophyceae o maior biovolume. As espécies Choricystis minor, Cylindrospermopsis c.f. raciborskii e Peridinium umbonatum foram espécies com maior densidade e Cryptomonas c.f. erosa e Peridinium umbonatum foram as espécies com maior biovolume. A disponibilidade de nutrientes (nitrogênio e fósforo) e concentração de matéria em suspensão na coluna de água foram, provavelmente, as variáveis que mais influenciaram a densidade e biovolume do fitoplâncton. Para o zooplâncton, a maior riqueza de espécies foi registrada na estação seca, no entanto, que os valores mais altos de biomassa e densidade do zooplâncton foram registrados durante a estação chuvosa. Rotíferos teve a maior riqueza e densidade, mas estiveram pouco representados na biomassa. Cladóceros tiveram a maior biomassa na estação chuvosa, mas os copépodos representados por formas jovens (copépodos náuplios e copepoditos), tiveram as maiores biomassa na estação seca, e os cladóceros foram o grupo representativo desse atributo. O rotífero Kellicottia Bostoniensis foi a espécie representante da densidade biomassa de zooplâncton. Conochilus unicornis, Gastropus hyptopus, Asplachna priodonta, Bosminopsis deitersi, Bosmina hagmanni foram as espécies com maior densidade e biomassa. As concentrações de material em suspensão na coluna de água, a disponibilidade de alimento (clorofila a) e o tempo de residência foram, provavelmente, as variáveis que influenciaram a estrutura da comunidade de zooplâncton. De acordo com os resultados, o reservatório Paiva Castro é compartimentado e influenciado pelas características e eventos que ocorrem nos reservatórios a montante
The Paiva Castro reservoir is the last reservoir of a series of five dams in cascade, which form the Cantareira System, one of the main water supply systems in the Greater São Paulo. Its biomonitoring is an important tool to understand the reservoir ecological status, as well as to evaluate situations that are causing changes in the water quality and quantity. In the present study, based on physical and chemical water characteristics and on phytoplankton and zooplankton ecological attributes it was found the existence of compartmentalization (horizontal spatial heterogeneity) and temporal heterogeneity in Paiva Castro reservoir. Two samplings were performed, one during the dry season (May and June) and the other one in the rainy season (November and December) on 2014. The year 2014 was a period of atypical drought, which triggered the problem of water crisis affecting the reservoirs dynamics on the Metropolitan Region of São Paulo. The samples were collected at 9 points along Paiva Castro reservoir. Were analysed the variables: temperature, pH, conductivity and dissolved oxygen were measured in situ with multiparameter probe and nutrients, suspended matter and pigments on the laboratory. Plankton samples were collected in the photic zone with the mouth of the network in the depth of the photic zone; Reservoir was classified as oligotrophic during dry and mesotrophic on the rainy season; however, the physical and chemical parameters were in accordance with CONAMA 357. Two compartments were identified through the analysis of limnological variables (depth, total suspended solids and nutrients) and the planktonica communities whose density and biovolume / biomass for phytoplankton and zooplankton increased upstream-downstream direction: the zone affected by the river input Juqueri and b) the transition zone integrating the channel and compartments dam. Chemical and physical characteristics rather than the planktonic communities further evidenced the temporal heterogeneity. Regarding the phytoplankton, the Bacillariophyceae and Chlorophyceae showed the highest density, Cryptophyceae and Dinophyceae the largest biovolume. The Choricystis minor species Cylindrospermopsis c.f. raciborskii and Peridinium umbonatum were species with the highest density and Cryptomonas c.f. erosa and Peridinium umbonatum were the species with the largest biovolume. The availability of nutrients (nitrogen and phosphorus) and suspended matter concentrations in the water column were probably the variables that most influence the density and biovolume of the phytoplankton community. For the zooplankton, the largest richness was recorded in the dry season, however, that the highest density and zooplankton biomass were recorded during the rainy season. Rotifers had the largest richness and density, but were under represented in biomass. Cladocerans had the highest biomass in the rainy season, but the copepods represented by young forms (copepod nauplii and copepodites), had the greatest biomass in the dry season, and the cladocerans the representative group of this attribute. The rotifer Kellicottia bostoniensis was representative specie of the zooplankton density and biomass. Conochilus unicornis, Gastropus hyptopus, Asplachna priodonta, Bosminopsis deitersi, Bosmina hagmanni were the species with the highest density and biomass. The suspended material concentrations in the water column, the food availability (chlorophyll a) and the residence time were probably the variables that influence the zooplankton community structure. According to the results, the Paiva Castro reservoir is compartmentalized and influenced by the characteristics and events that happen in the upstream reservoirs

Anthropogenic activities are increasing inorganic nitrogen (N) loadings to lakes in the northern hemisphere. In many boreal lakes phytoplankton are N limited, wherefore enhanced N input may affect the productivity of pelagic food webs. Simultaneously, global change causes increased inflows of terrestrial dissolved organic carbon (DOC) to boreal lakes. Between clear and humic lakes, whole lake primary and consumer production naturally differs. However, research is inconclusive as to what controls pelagic production in these lakes. Further, it is unclear how DOC affects the response of the pelagic food web to enhanced inorganic N availability. The overarching goal of this thesis was to study the effects of inorganic N and organic C for pelagic food webs in boreal lakes. In the thesis, I first identified the main drivers of pelagic production during summer in eight non-manipulated Swedish boreal lakes with naturally low or high DOC. Then I investigated how increased N availability affects the pelagic food chain, and how the response differs with DOC. Therefore, whole lake inorganic N fertilization experiments were conducted in six Swedish boreal lakes across a DOC gradient (low, medium, high) divided into three lake pairs (control, N enriched) with one reference and two impact years. In each lake, I also investigated the response of zooplankton growth using in situ mesocosm experiments excluding planktivores. I found that humic boreal lakes had lower phytoplankton production and biomass than clear water lakes. Further, phytoplankton community composition and food quality differed with DOC. However, high DOC did not reduce pelagic energy mobilization or zooplankton biomass, but promoted a higher dominance of cladoceran relative to copepod species. N addition clearly enhanced phytoplankton biomass and production in the experimental lakes. However, this stimulating N effect decreased with DOC as caused by light limitation. Further, the newly available phytoplankton energy derived from N addition was not efficiently transferred to zooplankton, which indicates a mismatch between producer energy supply and consumer energy use. Indeed, the mesocosm experiment revealed that decreased food quality of phytoplankton in response to N addition resulted in reduced food web performance, especially in clearer lakes. In humic lakes, zooplankton production and food web efficiency were clearly more resilient to N addition. In summary, my thesis suggests that any change in the landscape that enhances inorganic N availability will especially affect pelagic food webs in clear water lakes. In contrast, brownification will result in more lakes being resilient to eutrophication caused by enhanced N deposition.

Understanding hydrodynamic and biogeochemical processes in lakes is fundamentally important to the management of phytoplankton population and the improvement of water quality. Physical processes such as wind-driven surface mixing, thermal stratification and differential heating and cooling can affect the distribution of water, phytoplankton and sediments and the availability of nutrients and light. These lake processes, which are highly variable in space and time, affect phytoplankton dynamics in the field. This study aims to determine the spatial and temporal variability of phytoplankton and processes that either contribute to or override the variability in the artificially mixed Myponga Reservoir, South Australia. A sediment survey showed that sediments underlying deep water were richer in organic matter, carbon, nitrogen and phosphorus than the sediments underlying shallow water. This may lead to different nutrient release rates between the shallow and deep areas. Both sediment resuspension and anoxic sediment nutrient release were important internal sources of nutrient to support phytoplankton growth in summer when external nutrient supplies were limited by low rainfall in the catchment. An analysis of historical water temperature data revealed the development of micro-stratification at the sediment-water interface in summer, especially during a heatwave (air temperature > 40ºC for several consecutive days). Prolonged micro-stratification could potentially induce anoxic layers at the sediment surface, resulting in the release of nutrients. A risk assessment was conducted to predict the release of phosphorus from anoxic sediments and to evaluate the potential impact of cyanobacterial population (Anabaena circinalis) and the release of secondary metabolites (e.g. saxitoxin and geosmin). Spatial variability of surface mixed layer depths exists between the side-arm and main basin. A simple light model based on the relationships of surface mixed layer depth, daily light dose and phytoplankton growth rate, was developed to estimate the potential variation of phytoplankton population in the two different light habitats (the main basin and side-arm). The model showed that phytoplankton abundance in the main basin was lower than in the side-arm. However, differential heating drove a large basin-scale convection, which circulated the water between the side-arm and main basin within hours. This circulation overrode the time scale of days for the light-dependent growth effect between the two sites and hence there was no observable change in phytoplankton community structure. Although no spatial variability of phytoplankton was observed at community level, significant variations of phytoplankton cellular content and stoichiometry were detected. Higher carbon cellular content in the side-arm than in the main basin was probably due to a greater exposure to light (shallower surface mixed layer in the side-arm) for photosynthesis. In the situation where nutrients were scare, higher phosphorus cellular content was found in the side-arm than in the main basin; this was possibly due to a greater exposure to resuspended nutrients from the lake bottom (shallower water in the side-arm). There was also a strong seasonal pattern in phytoplankton cellular content and stoichiometry between summer and early winter of 2009. The carbon content of phytoplankton increased over time, while the phosphorus content decreased. After the first heavy rain event (70 mm over a four-day period) in early May, carbon cellular content decreased, while phosphorus cellular content increased. These changes in phytoplankton contents were most likely related to the bio-availability of phosphorus in water. This study reviews many complex, interactive processes driving the variability of lake physics and chemistry. The variability can yield rapid biological responses at physiological and cellular levels (e.g. Fv:Fm and cellular content), but does not necessarily appear at community levels (e.g. phytoplankton biomass, diversity). Often, conventional monitoring in lakes and reservoirs overlooks the subtle variability of phytoplankton dynamics. The relative scaling among physical, chemical and biological processes, therefore, is important to adequately describe the spatial and temporal variability in lakes and reservoirs.
Thesis (Ph.D.) -- University of Adelaide, School of Earth and Environmental Sciences, 2011

An increasing number of contemporary studies in aquatic ecology emphasize the im- portance of highly unsaturated fatty acids (HUFAs) at the plant-animal interface. Studies have demonstrated a wide range of fatty acid profiles in primary producers, forcing her- bivorous zooplankton to differentially retain fatty acids to meet somatic requirements. Herbivores also vary in their somatic fatty acid profiles; cladocerans collect Eicosapen- taenoic Acid (EPA), copepods prefer Docosahexaenoic Acid (DHA). Fatty acid internal reserves can be broken down to meet structural needs (i.e. phospholipid synthesis), fuel reproduction and may play a role in cold weather adaptation. Several authors have noted increases in HUFA concentration with lowering ambient temperatures. Cladoceran membranes form a gel at lower temperatures, while copepod membranes remain fluid and allow active overwintering. Both fish and crustaceans accumulate high concentrations of HUFAs during periods of rapid growth, but colimitation with elemental resources may exist. Recent modeling results suggest food webs with high quality (nutritional and biochemical) primary producers can attain inverted biomass distributions with efficient energy transfer between trophic levels. The adoption rate for this material into man- agement studies remains low, and while other sectors of the scientific community thrive on the potential of HUFAs, planktonic food-web studies are choosing traditional view points over forward thinking. Bearing in mind the emerging hypotheses on the critical factors that drive the energy flow in the plant-animal interface, my dissertation will at- tempt to address the following general questions: What are the distinct signatures of food quality and food quantity on planktonic food web dynamics? How do nutritional and biochemical factors affect the flow of energy at the plant-animal interface? What is our current understanding of the role of highly unsaturated fatty acids (HUFAs) in aquatic food webs? To what extent can the current generation of plankton models reproduce the lower food web patterns when explicitly accounting for HUFAs? Is the integration of the HUFA role into water quality management models feasible? Explicitly accounting for HUFAs requires integrating factors of animal physiology with macro-ecology: what are the ramifications? Finally, what are the evolutionary aspects of animals coping with food quality?

Spatial distribution and seasonal succesion of phytoplankton along the longitudinal axis of a eutrophic Římov reservoir was investigated in 2007. Inflow, transitional and lacustrine zones were distinquished in the reservoir according to physical, chemical and biological parameters. Using a functional group concept, typical phytoplankton assemblages were found.

This thesis deals with factors structuring phytoplankton flagellates. The aim of the thesis was to investigate the role of microhabitats in spatio-temporal differentiation of lentic communities of these flagellates, which has not been rigorously examined to date. The study was conducted during 2010-2013 in the shallow littoral sites of Horní rybník, Rybníčky u Podbořánek Nature Reserve. Phytoplankton flagellates showed cyclic seasonal dynamics, which was reflected by significantly different community structure and species richness during the season. In contrast, silica-scaled chrysophytes showed a non- cyclic seasonal dynamics. The impact of the season was strongly correlated with the impact of fluctuating environmental factors - pH, conductivity and temperature. Gradient of interrelated environmental factors between the northern and southern shore together with microhabitat - substrate type played the major role and accounted for 64.4 - 75.8 % variability in the data. Microhabitat type (plankton, metaphyton, epipelon) significantly affected species richness and community structure also in the course of the season. A large number of species was assessed to prefer a certain type of microhabitat. These preferences were observed at both species and generic levels, and even at the level of the main taxonomic...