Dissertationen: „Nutrient cycling“

1

Ngai, Zoology. „Trophic effects on nutrient cycling“. Thesis, University of British Columbia, 2008. http://hdl.handle.net/2429/2851.

Der volle Inhalt der Quelle

Annotation:

The top-down effects of consumers and bottom-up effects of resource availability are important in determining community structure and ecological processes. I experimentally examined the roles of consumers — both detritivores and predators — and habitat context in affecting nutrient cycling using the detritus-based insect community in bromeliad leaf wells. I also investigated the role of multiple resources in limiting plant productivity using meta analyses. The insect community in bromeliads only increased nitrogen release from leaf detritus in the presence of a predator trophic level. When only detritivores were present, the flow of stable isotope-labeled nitrogen from detritus to bromeliads was statistically indistinguishable from that in bromeliads lacking insects. I suggest that emergence of adult detritivores constitutes a loss of nitrogen from bromeliad ecosystems, and that predation reduces the rate of this nutrient loss. Hence, insects facilitate nutrient uptake by the plant, but only if both predators and detritivores are present. Moreover, predators can affect nutrient cycling by influencing the spatial scale of prey turnover. This mechanism results in a pattern opposite to that predicted by classic trophic cascade theory. Increasing habitat complexity can have implications for nutrient cycling by decreasing the foraging efficiency of both predators and their prey, and by affecting the vulnerability of predators to intraguild predation. Along a natural gradient in bromeliad size, I found that, depending on the relationship between community composition and habitat size, habitat complexity interacts with the changing biotic community to either complement or counteract the impact of predators on nutrient uptake by bromeliads. In contrast to the existing emphasis on single-resource limitation of primary productivity, meta-analyses of a database of 653 studies revealed widespread limitation by multiple resources, and frequent interaction between these resources in restricting plant growth. A framework for analyzing fertilization studies is outlined, with explicit consideration of the possible role of multiple resources. I also review a range of mechanisms responsible for the various forms of resource limitation that are observed in fertilization experiments. These studies emphasize that a wider range of predator and nutrient impacts should be considered, beyond the paradigm of single resource limitation or classic trophic cascades.

APA, Harvard, Vancouver, ISO und andere Zitierweisen

2

Barthelemy, Hélène. „Herbivores influence nutrient cycling and plant nutrient uptake : insights from tundra ecosystems“. Doctoral thesis, Umeå universitet, Institutionen för ekologi, miljö och geovetenskap, 2016. http://urn.kb.se/resolve?urn=urn:nbn:se:umu:diva-120191.

Der volle Inhalt der Quelle

Annotation:

Reindeer appear to have strong positive effects on plant productivity and nutrient cycling in strongly nutrient-limited ecosystems. While the direct effects of grazing on vegetation composition have been intensively studied, much less is known about the indirect effect of grazing on plant-soil interactions. This thesis investigated the indirect effects of ungulate grazing on arctic plant communities via soil nutrient availability and plant nutrient uptake. At high density, the deposition of dung alone increased plant productivity both in nutrient rich and nutrient poor tundra habitats without causing major changes in soil possesses. Plant community responses to dung addition was slow, with a delay of at least some years. By contrast, a 15N-urea tracer study revealed that nutrients from reindeer urine could be rapidly incorporated into arctic plant tissues. Soil and microbial N pools only sequestered small proportions of the tracer. This thesis therefore suggests a strong effect of dung and urine on plant productivity by directly providing nutrient-rich resources, rather than by stimulating soil microbial activities, N mineralization and ultimately increasing soil nutrient availability. Further, defoliation alone did not induce compensatory growth, but resulted in plants with higher nutrient contents. This grazing-induced increase in plant quality could drive the high N cycling in arctic secondary grasslands by providing litter of a better quality to the belowground system and thus increase organic matter decomposition and enhance soil nutrient availability. Finally, a 15N natural abundance study revealed that intense reindeer grazing influences how plants are taking up their nutrients and thus decreased plant N partitioning among coexisting plant species. Taken together these results demonstrate the central role of dung and urine and grazing-induced changes in plant quality for plant productivity. Soil nutrient concentrations alone do not reveal nutrient availability for plants since reindeer have a strong influence on how plants are taking up their nutrients. This thesis highlights that both direct and indirect effects of reindeer grazing are strong determinants of tundra ecosystem functioning. Therefore, their complex influence on the aboveground and belowground linkages should be integrated in future work on tundra ecosystem N dynamic.

APA, Harvard, Vancouver, ISO und andere Zitierweisen

3

Heggenstaller, Andrew Howard. „Productivity and nutrient cycling in bioenergy cropping systems“. [Ames, Iowa : Iowa State University], 2008.

Den vollen Inhalt der Quelle finden

APA, Harvard, Vancouver, ISO und andere Zitierweisen

4

Lammers, Peter J. „Energy and nutrient cycling in pig production systems“. [Ames, Iowa : Iowa State University], 2009.

Den vollen Inhalt der Quelle finden

APA, Harvard, Vancouver, ISO und andere Zitierweisen

5

Jabro, Nicholas Berman. „Microcosm studies of nutrient cycling in Bahamian stromatolites“. College Park, Md.: University of Maryland, 2008. http://hdl.handle.net/1903/8594.

Der volle Inhalt der Quelle

Annotation:

Thesis (M.S.) -- University of Maryland, College Park, 2008.
Thesis research directed by: Marine, Estuarine, Environmental Sciences Graduate Program. Title from t.p. of PDF. Includes bibliographical references. Published by UMI Dissertation Services, Ann Arbor, Mich. Also available in paper.

APA, Harvard, Vancouver, ISO und andere Zitierweisen

6

Langi, Martina Agustina. „Nutrient cycling in tropical plantations and secondary rainforests /“. St. Lucia, Qld, 2001. http://www.library.uq.edu.au/pdfserve.php?image=thesisabs/absthe16357.pdf.

Der volle Inhalt der Quelle

APA, Harvard, Vancouver, ISO und andere Zitierweisen

7

McManamay, Ryan A. „The effect of resource stoichiometry on fish and macroinvertebrate nutrient excretion“. Thesis, Virginia Tech, 2007. http://hdl.handle.net/10919/30780.

Der volle Inhalt der Quelle

Annotation:

Consumer-driven nutrient cycling has been shown to be an important process in supplying inorganic nutrients to autotrophic and heterotrophic organisms in aquatic ecosystems. Theory indicates that consumer nutrient excretion is influenced primarily by an organismâ s nutrient composition; however, an organismâ s diet should also play an important role in nutrient excretion, especially if the consumer is nutrient limited. This study asks the question, how does diet influence nutrient excretion of consumers at different trophic levels? Macroinvertebrates and fish were collected from six streams and nitrogen (N) and phosphorus (P) excretion were quantified. Epilithon, leaf detritus, and seston (fine particulate organic matter in transport) were collected and analyzed for carbon (C), nitrogen (N), and phosphorus (P) content in an attempt to qualitatively assess the nutritional status of the diet of primary consumers. Macroinvertebrates were also analyzed for C, N, and P content to assess their nutritional composition in relation to their excretion and also to assess the nutritional composition of the diet of predatory insects and fish. Fish were also analyzed for C, N, and P.

Similar to theoretical predictions, fish and macroinvertebrate P excretion was negatively related to P content and the N:P excretion ratio was negatively related to the body N:P ratio. However, this relationship was driven primarily by two phosphorus rich species, mottled sculpin in the fish and crayfish in the macroinvertebrates. Some relationships did emerge between consumer excretion and diet. For example, hydropsychid caddisflies had the highest macroinvertebrate P excretion, possibly explained by the low N:P of seston. However, shredders, eating on a very low N and P diet of leaf detritus, had very low N and P excretion.

The relationship between consumers, their food, and nutrient excretion is a matter of mass balance. If the food N:P ratio is higher than that of the consumer, then the N:P excretion should be higher than the consumer N:P and the food N:P, especially if organisms are P-limited. However, N:P excretion by macroinvertebrates and fish were very similar despite large differences in diet. The majority of macroinvertebrates and fish had a lower N:P excretion ratio than the predicted N:P of their food, possibly indicating that 1) consumers were either selectively consuming more P-rich foods than the diets that I assigned them or 2) consumers are generally not N or P limited or influenced by the N or P in their diet. Mottled sculpin and crayfish were the only organisms with a higher N:P excretion than their resources and both had a higher %P than the other fish and macroinvertebrates, respectively. High N:P excretion along with high phosphorus content is indicative of P-limitation. Macroinvertebrates and fish, excluding mottled sculpin and crayfish, had a lower N:P excretion and the N:P ratio of the water column. If consumers do play a role in nutrient dynamics, then consumers could alter the relative abundance of nitrogen and phosphorus by supplying more phosphorus. However, the presence of a P-limited organism, such as mottled sclupin or crayfish, could alter the relative abundance of nitrogen and phosphorus by supplying less phosphorus.
Master of Science

APA, Harvard, Vancouver, ISO und andere Zitierweisen

8

Vaillant, Grace C. „Nutrient cycling at cattle feedlots field & laboratory study“. Thesis, Manhattan, Kan. : Kansas State University, 2007. http://hdl.handle.net/2097/318.

Der volle Inhalt der Quelle

APA, Harvard, Vancouver, ISO und andere Zitierweisen

9

Oates, Richard Hunter. „Phosphate-mineral interactions and potential consequences for nutrient cycling“. Thesis, Online version of original thesis, 2008. http://hdl.handle.net/1912/2395.

Der volle Inhalt der Quelle

APA, Harvard, Vancouver, ISO und andere Zitierweisen

10

Mitchell, Mark E. „Nutrient Cycling Dynamics and Succession in Green Roof Ecosystems“. University of Cincinnati / OhioLINK, 2017. http://rave.ohiolink.edu/etdc/view?acc_num=ucin150487303109878.

Der volle Inhalt der Quelle

APA, Harvard, Vancouver, ISO und andere Zitierweisen

11

Cottam, Nigel D. „Internal nutrient cycling in evergreen and deciduous tree species“. Thesis, University of Aberdeen, 1990. http://digitool.abdn.ac.uk/R?func=search-advanced-go&find_code1=WSN&request1=AAIU027729.

Der volle Inhalt der Quelle

Annotation:

This thesis compares the cycling of nutrients (N, P, K, Mg and Ca) within twigs and foliage, between the evergreen species Pinus sylvestris L. (Scots pine) and Picea abies (L.) Karst. (Norway spruce), and the deciduous species Quercus petraea (Matt.) Liebl. (oak) and Betula pubescens Ehrh. (birch). In addition, the role of foliage produced in previous seasons as a source of nutrients for current growth, in young stands of Scots pine and lodgepole pine (Pinus contorta Loud.), was investigated by means of defoliation experiments, where various age-classes of foliage were removed. In both evergreen and deciduous species, the main areas of overwinter storage and sources of nutrients to support current growth appear to lie outside the twig/foliage system. Patterns of leaf litter production were similar in both Scots pine, oak and birch, however the deciduous species lost a greater amount of nutrients in leaf litter than did the evergreen species. In comparisons between Scots pine and oak, it was observed that foliage production in spring and summer is much slower, and takes place over a longer period, in the Scots pine, which also maintains a greater amount of nutrients within its foliar biomass. Results from the artificial defoliation experiments, suggested that older needle fractions do not play a major role in supplying nutrients to sites of current growth, however they do appear to provide an essential source of photosynthate to support new biomass production. A mechanism is proposed, whereby evergreen species are able to reduce the level of current nutrient demands in two main ways, firstly by means of their slower more extended growing period, and secondly by maintaining lower foliar nutrient concentrations (thereby reducing nutrient losses via leaf litterfall), at the expense of maintaining a greater amount of nutrients within their biomass.

APA, Harvard, Vancouver, ISO und andere Zitierweisen

12

Bush, Timothy. „Response to environmental perturbations in microbial nutrient-cycling ecosystems“. Thesis, University of Edinburgh, 2015. http://hdl.handle.net/1842/15789.

Der volle Inhalt der Quelle

Annotation:

The habitability of Earth is dependent upon the global recycling of elements essential for life, such as nitrogen, sulfur and carbon. Nutrient-cycling by micro-organisms is vital to these biogeochemical cycles because many key steps are mediated primarily, or exclusively, by microbial life. The dynamics of these cycles are highly complex, and environmental perturbations (such as changes in the oceanic oxygen concentration) can have unexpected or catastrophic effects; often causing abrupt switches between chemical states. Despite the importance of these environmental perturbations however, few theoretical models have addressed how they affect the dynamical behaviour of nutrient-cycling microbial ecosystems. In this work, we investigate the effect of environmental perturbations on microbially-mediated nutrient cycles and assess the likelihood of "sudden transitions" between chemical states of the ecosystem occurring in a variety of ecological contexts. To do this, we first use computational modelling of microbial nutrient-cycling, using a "box model" approach. We then move on to an experimental study using the microbial sulfur cycle as a model ecosystem, with freshwater pond sediment/water microcosms. These microcosms have the advantage of retaining many of the features of the real ecosystem (such as microbial diversity, spatial structure, and abiotic interactions) while allowing the controlled manipulation of environmental perturbations. We study these microcosms using a combination of chemical measurements and high-throughput sequencing of the microbial community. Finally, we return to the computational side, and attempt to reproduce chemical data from our experiments in a mathematical model containing realistic abiotic chemical interactions.

APA, Harvard, Vancouver, ISO und andere Zitierweisen

13

Enoki, Tsutomu. „Topographic Variations of Nutrient Cycling in a Pinus Thunbergii Parl.Plantation“. Kyoto University, 1997. http://hdl.handle.net/2433/160875.

Der volle Inhalt der Quelle

Annotation:

本文データは平成22年度国立国会図書館の学位論文(博士)のデジタル化実施により作成された画像ファイルを基にpdf変換したものである
Kyoto University (京都大学)
0048
新制・課程博士
博士(農学)
甲第6616号
農博第907号
新制||農||734(附属図書館)
学位論文||H9||N2993(農学部図書室)
UT51-97-B287
京都大学大学院農学研究科林学専攻
(主査)教授岩坪五郎, 教授小﨑隆, 教授川那辺三郎
学位規則第4条第1項該当

APA, Harvard, Vancouver, ISO und andere Zitierweisen

14

Prior, Hannah. „Total nitrogen and total phosphorus cycling in riparian ecosystems“. Thesis, University of Reading, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.285963.

Der volle Inhalt der Quelle

APA, Harvard, Vancouver, ISO und andere Zitierweisen

15

Safi, Zikrullah [Verfasser]. „Nutrient cycling and nutrient use efficiency in urban and peri-urban agriculture of Kabul, Afghanistan / Zikrullah Safi“. Kassel : Universitätsbibliothek Kassel, 2011. http://d-nb.info/1012867978/34.

Der volle Inhalt der Quelle

APA, Harvard, Vancouver, ISO und andere Zitierweisen

16

Dubeux, Júnior José Carlos B. „Management strategies to improve nutrient cycling in grazed Pensacola bahiagrass pastures“. [Gainesville, Fla.] : University of Florida, 2005. http://purl.fcla.edu/fcla/etd/UFE0011202.

Der volle Inhalt der Quelle

APA, Harvard, Vancouver, ISO und andere Zitierweisen

17

Stark, S. (Sari). „Reindeer grazing and soil nutrient cycling in boreal and tundra ecosystems“. Doctoral thesis, University of Oulu, 2002. http://urn.fi/urn:isbn:9514266927.

Der volle Inhalt der Quelle

Annotation:

Abstract In northernmost Fennoscandia, grazing by reindeer (Rangifer tarandus L.) has a substantial impact on the vegetation of boreal forests and arctic-alpine tundra heaths, which are reflected in below-ground processes, such as nutrient mineralization and soil organic matter decomposition. In the present thesis, the effects of reindeer grazing on soil nutrient cycling were studied by comparing grazed situation with an ungrazed control area in ten boreal forests and six arctic-alpine tundra heaths. In boreal forests, reindeer grazing reduced microbial respiration in both the oligotrophic and mesotrophic study areas, indicating a deficiency of labile substrates for the soil microbes due to reindeer grazing. Simultaneously, there was heterogeneity in the impact on nitrogen mineralization rates as at some sites, mineralization was enhanced by grazing. The fertilization effect of urine and faeces can therefore be strong enough a factor to outweigh a reduction in quality of soil organic matter. In the oligotrophic forests, low soil moisture content in the grazed areas could sometimes limit the mineralization rates even when the potential for mineralization was enhanced by grazing. In the tundra ecosystems, there was spatial variation in the impact of grazing on microbial respiration and nitrogen mineralization. Low grazing intensity occurring outside the growing season had a retarding impact on nutrient cycling in both unfertilized, nutrient-poor and fertilized, nutrient-rich conditions. In contrast, a relatively high grazing intensity enhanced the mineralization rates in two nutrient-poor and two nutrient-rich tundra heaths. When three different grazing intensities were compared in one oceanic, nutrient-rich and one continental, nutrient-poor tundra heath, the strongest positive effect of grazing on soil nutrient cycling occurred in the heavily grazed areas. The data do not support the assumption that soil nutrient availability regulates whether herbivores enhance or retard nutrient cycling in the soil. Instead, the net effect of grazing is determined by the balance between the underlying mechanisms that may work at opposite directions. The most important of these mechanisms are the grazer-mediated impact on the decomposability of the dominant vegetation and fertilization by urine and faeces. The duration, intensity and seasonal timing of the grazing seem to be important factors that regulate whether reindeer grazing enhances or retards soil nutrient cycling in each specific area. Due to the high spatial and temporal variation in the effects of grazing observed in this study, it is not possible to generalize the overall impact of grazing. Further study is required in order to determine the exact conditions under which grazing enhances or it retards soil nutrient cycling.

APA, Harvard, Vancouver, ISO und andere Zitierweisen

18

Campbell, Jocelyn. „Relationships between cyanolichen communities and nutrient cycling in sub-boreal spruce forests“. Thesis, University of British Columbia, 2010. http://hdl.handle.net/2429/23238.

Der volle Inhalt der Quelle

Annotation:

Cyanolichens (lichens with cyanobacterial symbionts) form a distinct assemblage of epiphytes strongly associated with humid microclimatic conditions in inland British Columbia. Disparate abundance patterns in sub-boreal forests are examined in relation to the influence of overstorey tree species. A comparison of lichens on conifer saplings beneath five overstorey tree species revealed that saplings beneath Populus support a disproportionately abundant and species-rich community of cyanolichens. Cyanolichens also grew more rapidly and had lower rates of mortality beneath Populus than beneath conifer overstorey trees. That cyanolichens were observed beneath Populus in stands that were otherwise climatically unsuitable suggests that Populus facilitates cyanolichen communities by providing a factor that compensates for sub-optimal conditions. Chemical analyses of throughfall precipitation from beneath Populus, Picea, Abies, Pseudotsuga and Betula failed to explain the variation in lichen community structure. However, glucose-rich nectar, exuded from extrafloral nectaries on Populus leaves, may instead be supporting cyanolichen communities. The nectar accumulates during dry periods, is washed off during subsequent rain events, and may be intercepted and metabolized by cyanolichens on conifer saplings beneath mature Populus canopies. C-flux measurements and phospholipid fatty-acid analyses with experimental applications of ¹³C₆-labelled glucose revealed a strong physiological response to glucose and a rapid incorporation of exogenous-¹³C into cyanolichen fatty-acid tissues. Field evidence further supports this hypothesis with higher rates of cyanolichen establishment observed on Picea branches under treatment of 2% glucose solution compared to water. The exogenous C may enable cyanolichens to become established in regions that are otherwise too dry to support them by providing a source of C despite drought-induced inactivity of the cyanobacterial partner. The abundant communities of nitrogen-fixing cyanolichens in wet, mature forests and beneath Populus are important to ecosystem function. The contribution of cyanolichens to N-cycling is calculated at sites with varying lichen abundances from measured rates of lichen litter deposition, decomposition and nutrient release. Cyanolichen litter biomass represents up to 11.5% of the total N-input from aboveground litterfall and is estimated to release 2.1 kg N ha⁻¹ yr⁻¹ of newly-fixed N that would otherwise be unavailable in these mature sub-boreal forests.

APA, Harvard, Vancouver, ISO und andere Zitierweisen

19

O'Reilly, Andrew M. „Biogeochemical Cycling and Nutrient Control Strategies for Groundwater at Stormwater Infiltration Basins“. Doctoral diss., University of Central Florida, 2012. http://digital.library.ucf.edu/cdm/ref/collection/ETD/id/5360.

Der volle Inhalt der Quelle

Annotation:

Elevated concentrations of nutrients, particularly nitrate, in groundwater and springs in Florida are a growing resource management concern. Stormwater infiltration basins, which are a common stormwater management practice in the well-drained karst terrain areas of Florida, are a potentially important source of nutrients to the groundwater system because stormwater exits the basin by only evaporation or infiltration. To better understand the biogeochemical processes integrating stormwater infiltration impacts on groundwater resources in a field-scale setting, a combination of hydrologic, soil chemistry, water chemistry, dissolved and soil gas, isotope, and microbiological data was collected from 2007 through 2010 at two stormwater infiltration basins receiving runoff from predominantly residential watersheds in north-central Florida. Substantially different biogeochemical processes affecting nitrogen fate and transport were observed beneath the two stormwater infiltration basins. Differences are related to soil textural properties that deeply link hydroclimatic conditions with soil moisture variations in a humid, subtropical climate. During 2008, shallow groundwater beneath the basin with predominantly clayey soils (median 41% silt+clay content) exhibited decreases in dissolved oxygen from 3.8 to 0.1 mg/L and decreases in nitrate-nitrogen from 2.7 mg/L to less than 0.016 mg/L, followed by manganese and iron reduction, sulfate reduction, and methanogenesis. In contrast, beneath the basin with predominantly sandy soils (median 2% silt+clay content), aerobic conditions persisted from 2007 through 2009 (dissolved oxygen of 5.0–7.8 mg/L), resulting in nitrate-nitrogen of 1.3–3.3 mg/L in shallow groundwater. Soil extractable nitrate-nitrogen was significantly lower and the copper-containing nitrite reductase gene density was significantly higher beneath the clayey basin. Differences in moisture retention capacity between fine- and coarse-textured soils resulted in median volumetric gas-phase contents of 0.04 beneath the clayey basin and 0.19 beneath the sandy basin, inhibiting surface/subsurface oxygen exchange beneath the clayey basin. Subsurface biogeochemical processes at the clayey stormwater infiltration basin were further analyzed to better understand the effects of the highly variable hydrologic conditions common in humid, subtropical climates. Cyclic variations in biogeochemical processes generally coincided with wet and dry hydroclimatic conditions. Oxidizing conditions in the subsurface persisted for about one month or less at the beginning of wet periods with dissolved oxygen and nitrate showing similar temporal patterns. Reducing conditions in the subsurface evolved during prolonged flooding of the basin. At about the same time oxygen and nitrate reduction concluded, manganese, iron, and sulfate reduction began, with the onset of methanogenesis one month later. Reducing conditions persisted up to six months, continuing into subsequent dry periods until the next major oxidizing infiltration event. Evidence of denitrification in shallow groundwater at the site is supported by median nitrate-nitrogen less than 0.016 mg/L, excess nitrogen gas up to 3 mg/L progressively enriched in delta-15N during prolonged basin flooding, and isotopically heavy delta-15N and delta-18O of nitrate (up to 25 and 15 per mil, respectively). Isotopic enrichment of newly infiltrated stormwater suggests denitrification was partially completed within two days. Soil and water chemistry data suggest a biogeochemically active zone exists in the upper 1.4 m of soil, where organic carbon was the likely electron donor supplied by organic matter in soil solids or dissolved in infiltrating stormwater. The cyclic nature of reducing conditions effectively controlled the nitrogen cycle, switching nitrogen fate beneath the basin from nitrate leaching to reduction in the shallow saturated zone. Soil beneath the sandy stormwater infiltration basin was amended using biosorption activated media (BAM) to study the effectiveness of this technology in reducing inputs of nitrogen and phosphorus to groundwater. The functionalized soil amendment BAM consists of a 1.0:1.9:4.1 mixture (by volume) of tire crumb (to increase sorption capacity), silt and clay (to increase soil moisture retention), and sand (to promote sufficient infiltration), which was applied to develop an innovative best management practice (BMP) utilizing nutrient reduction and flood control sub-basins. Construction and materials costs, excluding profit and permit fees, for the innovative BMP were about $US 65 per square meter of basin bottom. Comparison of nitrate/chloride ratios for the shallow groundwater indicate that prior to using BAM, nitrate concentrations were substantially influenced by nitrification or variations in nitrate input. In contrast, for the new basin utilizing BAM, nitrate/chloride ratios indicate minor nitrification and nitrate losses with the exception of one summer sample that indicated a 45% loss. Biogeochemical indicators (denitrifier activity derived from real-time polymerase chain reaction and variations in major ions, nutrients, dissolved and soil gases, and stable isotopes) suggest nitrate losses are primarily attributable to denitrification, whereas dissimilatory nitrate reduction to ammonium and plant uptake are minor processes. Denitrification was likely occurring intermittently in anoxic microsites in the unsaturated zone, which was enhanced by increased soil moisture within the BAM layer and resultant reductions in surface/subsurface oxygen exchange that produced conditions conducive to increased denitrifier activity. Concentrations of total dissolved phosphorus and orthophosphate were reduced by more than 70% in unsaturated zone soil water, with the largest decreases in the BAM layer where sorption was the most likely mechanism for removal. Post-BAM orthophosphate/chloride ratios for shallow groundwater indicate predominantly minor increases and decreases in orthophosphate with the exception of one summer sample that indicated a 50% loss. Differences in nutrient variations between the unsaturated zone and shallow groundwater may be the result of the intensity and duration of nutrient removal processes and mixing ratios with water that had undergone little biogeochemical transformation. In order to quantify potential processes leading to observed nitrogen losses beneath the innovative BMP, an integrated infiltration basin–nitrogen reduction (IBNR) system dynamics model was developed. Based on two simulation periods, the IBNR model indicated denitrification accounted for a loss of about one-third of the total dissolved nitrogen mass inflow and was occurring predominantly in the BAM layer. The IBNR model results in combination with the field-based biogeochemical assessment demonstrated that the innovative BMP using the functionalized soil amendment BAM is a promising passive, economical, stormwater nutrient-treatment technology. Further field- and laboratory-scale research on the long-term sustainability of nutrient losses and further elucidation of causative physicochemical and biogeochemical mechanisms would contribute to improved BAM performance and green infrastructure development in the future.
ID: 031001572; System requirements: World Wide Web browser and PDF reader.; Mode of access: World Wide Web.; Adviser: Ni-Bin Chang.; Title from PDF title page (viewed August 26, 2013).; Thesis (Ph.D.)--University of Central Florida, 2012.; Includes bibliographical references (p. 246-263).
Ph.D.
Doctorate
Civil, Environmental, and Construction Engineering
Engineering and Computer Science
Civil Engineering

APA, Harvard, Vancouver, ISO und andere Zitierweisen

20

Chuyong, George Bindeh. „Nutrient cycling in ectomycorrhizal legume-dominated forest in Korup National Park, Cameroon“. Thesis, University of Stirling, 1994. http://hdl.handle.net/1893/2640.

Der volle Inhalt der Quelle

Annotation:

Patterns and rates of nutrient input to the forest floor in litterfall, throughfall and stemflow were investigated in plots of low and high abundance of ectomycorrhizal species. The aim of the study was to examine the comparative advantage of the ectomycorrhizal species in nutrient acquisition and cycling on nutrient-poor soils in Korup. Litterfall was similar in both forests with annual estimates of 9.00 and 8.33 t ha-1 yr-1 for LEM and HEM forests respectively. Litterfall distribution followed a mono-modal pattern, with peaks in the dry season in both forests and the HEM forest showing stronger seasonality. The concentrations N, K and Ca in total litterfall were higher in the LEM forest while those of P and Mg were higher in the HEM forest. The bulk of nutrients in total litterfall was in leaf litter with the reproductive fractions having the highest concentrations of nutrients. Ectomycorrhizal species showed lesser internal redistribution of nutrients than non-ectomycorrhizal species which resulted in their higher leaf litter concentrations of nutrients. Breakdown of litter was relatively faster in the LEM forest with an annual decomposition constant (KL) of 3.21 compared to 2.43 for the HEM forest. The reproductive fractions had relatively higher annual decomposition constants of 8.20 and 4.27 in the LEM and HEM forests respectively compared to the other fractions. The overall element mobility in decomposing leaf litter was similar in both forests and in the following order: Mg>K>Ca>P>N. Mineralization of N, P and K in the decomposing leaf litter was similar in both forests and higher in the HEM forest for Mg and Ca. Throughfall was 96.6% and 92.4%, and stemflow 1.5% and 2.2%, of gross rainfall in LEM and HEM forests respectively. Considerable amounts of Ca, Mg and P were brought to the forest canopy in gross rainfall (24-45% of total input through this route) with higher amounts of K and Ca leached from plant parts by the rainwater. The amounts of P, K and Ca in stemflow and throughfall were of the same magnitude in both forests with the enhancement of N slightly higher in the LEM forest and Mg in the HEM forest.

APA, Harvard, Vancouver, ISO und andere Zitierweisen

21

Laruelle, Goulven Gildas. „Quantifying nutrient cycling and retention in coastal waters at the global scale“. Doctoral thesis, Utrecht University, Utrecht, 2009. http://hdl.handle.net/2013/ULB-DIPOT:oai:dipot.ulb.ac.be:2013/282551.

Der volle Inhalt der Quelle

APA, Harvard, Vancouver, ISO und andere Zitierweisen

22

Tavakol, M. Hossien. „Production and nutrient cycling in three Scottish oak woods on contrasting soils“. Thesis, University of Stirling, 1991. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.317316.

Der volle Inhalt der Quelle

APA, Harvard, Vancouver, ISO und andere Zitierweisen

23

Brockett, Beth. „Patterns in forest soil microbial community composition across a range of regional climates in Western Canada“. Thesis, University of British Columbia, 2008. http://hdl.handle.net/2429/486.

Der volle Inhalt der Quelle

Annotation:

Soil microbial communities can be characterized by community structure and function (community composition) across a spectrum of spatial scales, and variation in soil microbial composition has been associated with a number of environmental gradients. This study investigates the structure and function of soil microbial communities under mature, undisturbed forested sites across a range of regional climates in British Columbia and Alberta, and also examines the variation in community composition within sites. Phospholipid fatty acid analysis was used to investigate the structure of soil microbial communities and total soil microbial biomass at each site. Extra-cellular enzyme assays established the functional potential of the soil microbial community at each site. Multivariate analysis of the data showed that the soil microbial communities under different forest types did significantly separate along the regional climate gradient by both community structure and function, despite high local variation in the communities. Soil moisture content and soil organic matter concentration consistently exhibited the strongest relationship with microbial community characteristics, although the functional and structural responses to the external drivers were different. Microbial community function and structure also changed with soil depth but not with time of sampling. Microbial community function was related to the regional annual average precipitation gradient. Most of the locations exhibited unique microbial community functional profiles in their soil layers; however the enzyme activities in the samples from the driest (Ponderosa Pine) and wettest (Mountain Hemlock) locations were notably different from each other and from those of the other locations, especially in the organic layers. The moist maritime-influenced Coastal Western Hemlock (CWH) forest exhibited microbial community structural characteristics which were unique from those of the other forest locations. The higher abundance of bacteria relative to fungi in the CWH forest soils may be related to the significantly higher available nitrogen concentrations at this site.

APA, Harvard, Vancouver, ISO und andere Zitierweisen

24

Sharma, Ghanashyam. „Productivity and Nutrient Cycling in and age series of Alnus-Cardamom agroforestry in the Sikkim Himalaya“. Thesis, University of North Bengal, 2001. http://hdl.handle.net/123456789/1070.

Der volle Inhalt der Quelle

APA, Harvard, Vancouver, ISO und andere Zitierweisen

25

Galli, Corina Verónica Sidagis. „Análise da função de uma várzea na ciclagem de nitrogênio“. Universidade de São Paulo, 2003. http://www.teses.usp.br/teses/disponiveis/18/18139/tde-17022016-130159/.

Der volle Inhalt der Quelle

Annotation:

Para identificar a influência de uma área de várzea do ribeirão do Feijão (São Carlos-SP) sobre a ciclagem de nitrogênio e sobre a qualidade da água superficial e subsuperficial, foram analisadas as características físicas e químicas da água e determinadas as taxas de nitrificação e desnitrificação dos sedimentos da várzea. A maior concentração dos compostos nitrogenados foi observada na água de interface subsuperficial da várzea, região mais ativa em termos de fluxos de água e materiais. As taxas de nitrificação variaram de 0,145 a 0,068 μmol N-NO3-.g-1.dia-1 e a rota metabólica predominante foi a autotrófica, na qual as bactérias utilizaram amônio como substrato. As taxas de desnitrificação tiveram um valor médio de 0,0081 nmol N2O.g-1.dia-1. Mediante um modelo de estimativa foi calculado que 70% da água que circula no Ribeirão do Feijão provém do lençol que flui sob terras secas e o restante das áreas de várzea da bacia. Foi observado que existe uma considerável redução das concentrações dos compostos nitrogenados, principalmente do amônio, desde as zonas ripárias mais distantes do curso do rio até o canal, passando pela área de várzea. O funcionamento da várzea como sistema de filtro e depuração das águas subsuperficiais que alimentam o rio foi evidenciada pelas características físicas e químicas da água do rio em relação ao uso do solo na bacia.
In order to identify the influence of a floodplain area of the Feijão stream (São Carlos-SP) on surface and subsurface water quality, the physical and chemical characteristics of the water were analyzed and the floodplain sediment\'s nitrification and denitrification rates were determined. The highest concentration of nitrogen compounds was observed at the floodplain\'s subsurface water interface it being the most active region with respect to water and solute flow. Nitrification rates varied between 0.145 and 0.068 μmol N-NO3-.g-1.day-1 and the autotrophic metabolic route dominated, in which bacteria use ammonia as a substrate. Denitrification rate average was 0.0081 nmol N2O.g-1.day-1. Through a model it was estimated that 70% of the water flowing in the Feijão stream came from the water table flowing under dry land, the remainder coming from the floodplain of the area. A significant reduction of nitrogen compound concentration, mainly ammonium, was observed between the more distant riparian zones and the river\'s channel going through the floodplain. The floodplain\'s action as a filtering system for the water reaching the river was brought out through the physical and chemical characteristics of the river water relative to land use in the catchment area.

APA, Harvard, Vancouver, ISO und andere Zitierweisen

26

Pimentel, Tania Pena. „Dinâmica do carbono em uma microbacia no extremo leste da Amazônia“. Universidade de São Paulo, 2016. http://www.teses.usp.br/teses/disponiveis/91/91131/tde-01082016-175320/.

Der volle Inhalt der Quelle

Annotation:

O presente estudo objetiva avaliar os mecanismos de transferência de carbono entre os compartimentos atmosfera, vegetação, solo e igarapé em uma microbacia da Amazônia Ocidental. Dois igarapés drenandos, respectivamente, 2927 e 66,73 ha de floresta de terra firme, foram monitorados durante um ano. A área de estudo se encontra na zona de amortecimento de uma Unidade de Conservação de Uso Sustentável denominada Floresta Estadual do Amapá (FLOTA/AP), na região central do estado de mesmo nome. Foram coletadas as águas da chuva, da precipitação interna da floresta, do escoamento de água pelo tronco, do escoamento superficial pelo solo, da solução do solo, da água subterrânea e da água do igarapé. Os solos também foram investigados em relação a suas características físico-químicas. Para calcular a entrada e saída de C do sistema, foram determinadas as concentrações do carbono orgânico e inorgânico dissolvido (COD e CID, respectivamente) na água da chuva e do igarapé, em 16 eventos de chuva. As concentrações médias de COD na água da chuva foram de 1,6± 1,52 mg L-1, resultando em um aporte de 11,43 Kg C ha-1 ano-1. Na precipitação interna os valores médios observados foram de 9,1 ± 5,99 mg L-1, o que corresponde a um fluxo de 100,71 Kg C ha-1 ano-1. No escoamento do tronco, os valores médios observados foram de 17,4 ± 8,03 mg L-1 e no escoamento superficial do solo de 14,2 ± 6,4 mg L-1. Nos compartimentos amostrados abaixo do solo, solução do solo e água do lençol, as concentrações de COD foram relativamente mais baixas. A saída de COD pelo igarapé, os fluxos foram de 0,45 Kg C ha-1 ano-1. Em relação às concentrações de CID, o aporte pela água da chuva foi de 3,66 Kg C ha-1 ano-1, passando a 10,10 Kg C ha-1 ano-1 na precipitação interna e com uma saída pelo igarapé de 0,07 Kg C ha-1 ano-1. Os resultados mostram grande variabilidade espaço-temporal e retenção de C pelo sistema, seja na fase orgânica (COD) ou inorgânica (CID), demonstrando a importância destes processos para a compreensão do funcionamento destes ecossistemas.
This study aims to evaluate carbon transfer mechanisms between the atmosphere, vegetation, soil and stream in a microbasin of eastern Amazon. Two streams, draining respectively 2917 and 66.73 ha of \"terra firme\" forests were monitored during one year. The study area is located in a Conservation Unit named Amapá State Forest (FLOTA/AP), in the central region of the Amapá State. We sample rain water, throughfall, stemflow, soil surface flow, soil solution, groundwater and stream water. Physico-chemical characteristics of soils were also evaluated. To calculate inputs and outputs of C in this system, we determined the concentrations of dissolved organic and inorganic carbon (DOC and DIC, respectively) in rain and stream water during 16 rain events. Average concentrations of DOC in rain water were 1.6± 1.52 mg L-1, resulting in an input of 11.43 Kg C ha-1 year-1. Throughfall had average concentrations of 9.1 ± 5.99 mg L-1, which increased inputs to 100.71 Kg C ha-1 year-1. Stemflow had average concentrations of 17.4 ± 8.03 mg L-1 while those of soil surface flow were 14.2 ± 6.4 mg L-1. Bellow ground DOC concentrations were relatively lower. The export of DOC in stream water was 0.45 Kg C ha-1 year-1. In relation to DIC, the input from rain water was 3.66 Kg C ha-1 year-1, increasing to 10.10 Kg C ha-1 year-1 in throughfall and exiting the micro basin through the stream with a flux of 0.07 Kg C ha-1 year-1. The results show large spatiotemporal variations and C retention within the system, either in the organic (DOC) or inorganic (DIC) phases, showing the importance of these processes for the comprehension of the functioning of these ecosystems.

APA, Harvard, Vancouver, ISO und andere Zitierweisen

27

Mettam, Colin. „Nutrient cycling and oxygen availability in ancient oceans : extinction events and evolutionary opportunities“. Thesis, University of St Andrews, 2018. http://hdl.handle.net/10023/16334.

Der volle Inhalt der Quelle

APA, Harvard, Vancouver, ISO und andere Zitierweisen

28

Bilal, Ruba Candiga. „Soil Carbon and Nutrient Cycling Across Cover Types in Southern Appalachian Hardwood Forests“. Diss., Virginia Tech, 2017. http://hdl.handle.net/10919/85625.

Der volle Inhalt der Quelle

Annotation:

Appalachian mixed hardwood stands along south facing slopes of the Ridge and Valley physiographic province were used to determine fine scale soil respiration (Rs ) and nutrient dynamics among four distinct cover types, white oak (WO, Quercus alba L.), scarlet oak (SO, Quercus coccinea Muech.), chestnut oak (CO, Quercus montana Wild.) and a pine-oak co-dominant cover (PO, Pinus spp. and Quercus spp. (primarily Pinus pungens Lamb. and Q. montana)). Null hypotheses were that: (1) Rs and its relationship to environmental drivers would not differ among the cover types, (2) water and nutrient use efficiencies (WUE and NUE) would not differ among the cover types, and (3) litter decomposition would not differ among the diverse cover types. In 0.02 ha plots, replicated four times, Rs and associated variables (e.g., soil temperature and moisture) were measured. Measurements occurred in three sub-sample locations per plot, from July 2014 - December 2015. In each plot, foliage from two trees of the dominant species were collected to determine WUE using δ¹³C isotope discrimination. Nutrient (N, P and K) content of this fresh foliage was compared with that of litterfall to determine NUE. Litterbags, collected over a one and half year period were used to determine decomposition rate constants for each dominant species. Soil temperature and moisture explained 71% of the variability in Rs. Although only slight, there were statistically significant differences in the Rs models due to cover type. At the same soil temperature, the PO cover type had the highest Rs while the SO, WO cover types had the lowest Rs. WUE, and NUE varied among cover types. SO had significantly greater WUE than the other species, including Table mountain pine, which had the highest NUE. Higher elevation cover types (i.e., PO and CO) ad greater decomposition rate constants. Among the factors driving decomposition, soil C: N ratio had the strongest correlation to decomposition. Correlations between decomposition and productivity variables of total above ground biomass, total stand biomass, and aboveground net primary production also exist. In conclusion, carbon and nutrient cycling varies across the level of cover type within the southern Appalachian hardwood forests. Future efforts to focus on carbon and nutrient dynamics in the context of land use or global change should consider these finer-scale differences.
Ph. D.

APA, Harvard, Vancouver, ISO und andere Zitierweisen

29

Altinalmazis, kondylis Andreas. „Tree diversity effects on root production, decomposition and nutrient cycling under global change“. Thesis, Bordeaux, 2021. http://www.theses.fr/2021BORD0067.

Der volle Inhalt der Quelle

Annotation:

L'hypothèse de l'assurance prévoit que les forêts composées de mélanges d'espèces d'arbres pourraient mieux résister aux conditions environnementales stressantes que les forêts composées d'une seule espèce d'arbre. La majorité des travaux antérieurs ont testé cette hypothèse en se focalisant sur la productivité et les variables de réponse associées sans prendre en compte les processus souterrains. L’objectif principal de ma thèse était d’étudier l’effet de la diversité des espèces d’arbres sur les processus souterrains impliqués dans la décomposition des racines à travers des gradients climatiques. J'ai émis l'hypothèse que le mélange d'espèces ayant des systèmes racinaires contrastés entraînerait une faible compétition souterraine, et se traduirait par la production de plus biomasse de racines fines. En outre, j'ai émis l'hypothèse que les racines ayant des caractéristiques chimiques et morphologiques contrastées dans les peuplements mixtes se décomposent plus rapidement. Dans des conditions de stress hydrique, j'ai émis l'hypothèse d'une décomposition plus lente mais d’une atténuation des mélanges d'arbres sur la décomposition en raison de l'amélioration des conditions micro-environnementales. Pour tester ces hypothèses, j'ai examiné la variation des caractéristiques fonctionnelles des racines et leurs conséquences sur les flux de C, N et P à l'échelle de l'écosystème à travers l’étude de : 1) la ségrégation verticale des racines et la biomasse des racines fines, 2) la dynamique des racines fines et les flux de nutriments associés et 3) la décomposition des racines fines et des feuilles mortes. Dans ce cadre, trois deux expériences de terrain ont été réalisé, l'une avec une expérience de plantation d'arbres de 10 ans avec du bouleau et du pin près de Bordeaux (expérience ORPHEE), la seconde le long d'un gradient latitudinal de forêts de hêtres matures dans les Alpes françaises (expérience BIOPROFOR).Les résultats obtenus montrent que les racines de bouleaux et de pins présentaient une distribution verticale similaire et une biomasse souterraine similaire de racines dans les mélanges d'arbres par rapport aux monocultures, contrairement à ma première hypothèse. Cependant, l'attribution plus importante du pin mais pas du bouleau à la croissance des racines dans les horizons du sol supérieur dans des conditions moins limitatives en eau suggère des conditions localement favorables qui peuvent conduire à une compétition asymétrique à la profondeur du sol. De plus, la production et la décomposition des racines fines étaient similaires dans les mélanges et dans les monocultures, en contradiction avec ma deuxième hypothèse. Il est intéressant de noter que les racines de bouleau, mais pas les racines de pin, ont libéré du P pendant leur décomposition, ce qui suggère un rôle important du bouleau dans le cycle du P et pour la nutrition en P des arbres sur ces sols sableux limités en P. Conformément à ma troisième hypothèse, j'ai observé une décomposition plus lente de la litière de feuilles et des racines fines en réponse à une sécheresse estivale prolongée, tout au long du gradient latitudinal dans les Alpes. Cependant, cette décomposition plus lente sous la sécheresse n'a pas été atténuée dans les peuplements forestiers à essences mixtes par rapport aux peuplements à essences uniques. Il est intéressant de noter qu’il y a une libération nette d'azote dans les racines fines en décomposition mais pas dans la litière de feuilles en décomposition, ce qui suggère un rôle distinct des racines fines dans le cycle de l'azote. En conclusion, j'ai constaté que le mélange des espèces d'arbres n'atténue pas les effets négatifs du changement climatique. Cette thèse démontre que la promotion de mélanges peut toujours être bénéfique pour au moins une des espèces d'arbres mélangées, par l'ajout d'espèces, car une espèce d'arbre peut en faciliter la nutrition minérale d’une autre par des flux souterrains de N et de P
The insurance hypothesis predicts that forests with tree species mixtures may resist better to stressful environmental conditions than forests composed of only one tree species. Most of the currently available literature tested this hypothesis for aboveground productivity and its related response variables, but less is known about belowground processes. In my PhD thesis, I studied the drivers of belowground productivity and decomposition across climatic gradients and how they are affected by tree mixtures. I hypothesized that mixing of tree species with contrasting rooting patterns and fine root morphologies, would result in a release of competitive pressure belowground, and translate into higher fine root standing biomass and increased fine root productivity. Moreover, I hypothesized that roots with contrasting chemical and morphological characteristics in mixed stands would decompose faster, which may be particularly important under nutrient-limited conditions. Under water-limiting conditions, such as during extreme summer drought, I hypothesized overall slower decomposition but an attenuating effect of tree mixtures on decomposition due to improved micro-environmental conditions, in particular for leaves, since roots decompose in a more buffered soil environment. To test these hypotheses I examined the variation in tree root functional traits (across- and within-species), and its consequences for fluxes of C, N and P at the ecosystem scale. I addressed three main objectives and associated research questions to quantify the interactive effect of tree mixtures and climate on: 1) vertical root segregation and fine root standing biomass, 2) fine root dynamics and their associated nutrient fluxes and 3) fine root- and leaf litter decomposition. I could benefit from two different field experiments for my work, one with a 10-year-old tree-plantation experiment with birch and pine close to Bordeaux (ORPHEE experiment), the second along a latitudinal gradient of mature beech forests in the French Alps (BIOPROFOR experiment).I observed that roots from the birch and pine tree-plantation showed similar vertical distribution and similar belowground root standing biomass in tree mixtures compared to monocultures, contrary to my first hypothesis. However, the greater allocation of pine but not of birch to root growth within the top soil horizons under less water-limiting conditions suggests locally favourable conditions that may lead to soil depth-specific asymmetric competition. In the same experiment, fine root production and decomposition were similar in mixtures and in monocultures, in contradiction with my second hypothesis. Moreover, I did not observe any interactive effects of tree mixtures with stand density or water availability. Interestingly though, birch roots, but not pine roots released P during root decomposition, which suggests an important role of birch in the P-cycle and for P nutrition of trees on these P-limited sandy soils. In line with my third hypothesis, I observed a slower decomposition of leaf litter and fine roots in response to reinforced and prolonged summer drought, irrespective of the position along the latitudinal gradient in the Alps. However, this slower decomposition under drought was not attenuated in forest stands with mixed tree species compared to single species stands. Compared to leaf litter, fine roots decomposed slower and released less C. Interestingly, I found a net N release in decomposing fine roots but not in decomposing leaf litter, which suggests a distinct role of fine roots in the N cycle. In conclusion, I found that mixing tree species did not attenuate negative effects of climate change. However, this thesis demonstrates that promoting mixtures can still be beneficial for at least one of the admixed tree species, through species addition (i.e., complementing one tree species with another tree species), as one tree species may facilitate another via belowground fluxes of N and P

APA, Harvard, Vancouver, ISO und andere Zitierweisen

30

West, Elizabeth Jane. „The Influence of Zooxanthellate and Non-zooxanthellate Jellyfish on Nutrient Cycling and Trophodynamics“. Thesis, Griffith University, 2009. http://hdl.handle.net/10072/366387.

Der volle Inhalt der Quelle

Annotation:

The appearance and disappearance of large numbers of medusae is a common characteristic of jellyfish populations. Blooms of jellyfish can attain very large biomasses that cover wide areas and can be short-lived, after which time the population may crash rapidly. The sheer biomass of jellyfish during bloom periods and the ‘boom and bust’ population dynamics are likely to have considerable impacts on the surrounding ecosystem. Some species of jellyfish contain symbiotic dinoflagellates called zooxanthellae. Zooxanthellae are able to assimilate nutrients from the surrounding water and transfer photosynthetic products to the host jellyfish. Zooxanthellate jellyfish are likely to acquire and recycle nutrients very differently to non-zooxanthellate species, and are therefore likely to have contrasting influences on nutrient cycling and trophodynamics. However, there are large gaps in our understanding of these processes. This thesis directly compares the role of zooxanthellate and non-zooxanthellate jellyfish on nutrient cycles and trophodynamics, by investigating these processes in zooxanthellate jellyfish, Cassiopea sp. and Phyllorhiza punctata, and the non-zooxanthellate jellyfish, Catostylus mosaicus. An important step in understanding the influence of jellyfish on ecosystem processes is to determine how nutrients are cycled within individual medusae. To do this, the exchanges of nutrients with the surrounding water were compared between zooxanthellate and non-zooxanthellate jellyfish. Experiments were done to compare the net exchanges (uptake and excretion) of organic and inorganic nitrogen and phosphorus with the surrounding water. Changes in nutrient concentrations were measured in tubs housing zooxanthellate Cassiopea sp., non-zooxanthellate C. mosaicus, and water control (no jellyfish). Experiments were repeated during the day, when photosynthesis and respiration could occur, and at night when only respiration could occur. Organic nutrients were found to comprise 25 - 43 % of the total excretion by non-zooxanthellate jellyfish. Organic nutrient excretion by blooms (506 t km-2) of non-zooxanthellate jellyfish were estimated to potentially support 62 – 120 mg C m-2 of bacterial production per day. In addition, excretion of inorganic nutrients by blooms of non-zooxanthellate jellyfish were estimated to potentially support 201- 423 mg C m-2 of primary production per day. In contrast, zooxanthellate jellyfish excreted minimal amounts of inorganic and organic nutrients or took them up from the water column. Therefore, nutrients assimilated by zooxanthellate jellyfish are likely to be retained and temporarily stored in the biomass of the population. The assimilation and retention of nitrogen were compared between zooxanthellate and non-zooxanthellate jellyfish. To do this, firstly, the assimilation and retention of nitrogen were directly compared between Cassiopea sp. and C. mosaicus. Jellyfish were labelled with isotopic nitrogen (15N) from two different sources, 15N-labelled Artemia prey and dissolved ammonium (15NH4+). The incorporation and retention of 15N was measured in the jellyfish tissues over nine days. Secondly, experiments were done to measure the influence of the availability of prey and concentrations of nutrients on the retention of nitrogen by Cassiopea sp. To do this, Cassiopea sp. were labelled with 15NH4+ and then placed in pools that had different combinations of high and low nutrient concentrations and high and low feeding regimes. The retention of 15N was measured in jellyfish over 37 days. Respiration and excretion rates were also measured for animals at the end of the experiment. Cassiopea sp. was found to assimilate nitrogen from both NH4+ and prey, and recycle this nitrogen internally. In contrast, C. mosaicus only assimilated nitrogen from prey and quickly excreted this nitrogen to the external environment, resulting in a short retention time. Cassiopea sp. retained nitrogen more than five times longer than C. mosaicus. Further, the nitrogen retention time of Cassiopea sp. was influenced by the availability of prey and dissolved nutrients, with the availability of prey having the greatest effect. Specifically, medusae exposed to low feeding retained nitrogen twice as long as medusae exposed to high feeding, which suggests that ingestion of prey by the host jellyfish is an important source of nitrogen in Cassiopea sp. Further, daily rates of photosynthesis and respiration suggest that photosynthesis by the zooxanthellae can potentially supply all of the carbon required for respiration and growth of the entire medusa. Jellyfish populations can hold considerable proportions of carbon and nutrients in an ecosystem and when a population crashes, jellyfish may sink to the benthos and decompose. An experiment was done that measured the changes in sediment oxygen demand as well as inorganic and organic nutrients during the decomposition of dead jellyfish, C. mosaicus. Fluxes were measured in tubs housing dead jellyfish over nine days as the jellyfish tissue decomposed. The decomposition of C. mosaicus resulted in a rapid leaching of organic nutrients from the dead tissues. Following this, microbial mineralisation dominated, which consumed oxygen and released dissolved inorganic nutrients. Although this release of nutrients may serve as a trophic link to pelagic primary producers, it may also lead to environmental problems associated with low oxygen concentrations depending on the size of the bloom and the degree of mixing in the system. Lastly, the influence of zooxanthellate and non-zooxanthellate jellyfish on plankton communities was compared. An in situ mesocosm experiment was done to compare the influence of C. mosaicus (non-zooxanthellate) and P. punctata (zooxanthellate). Changes in primary production and plankton assemblages were measured in mesocosms containing C. mosaicus, P. punctata, a combination of these species and compared to controls over six days. Catostylus mosaicus was found to increase chlorophyll a and productivity in the water column due to the large amount of nutrients excreted, causing a bottom-up influence on primary producers. This was in contrast to P. punctata, which were found to have little influence on chlorophyll a and production. This study provided direct experimental evidence that unlike C. mosaicus, P. punctata does not enhance primary production due to the minimal excretion of nutrients. Both P. punctata and C. mosaicus also had a large top-down predation pressure on zooplankton communities, causing significant declines in most species. This was with the exception of bivalve veligers, which were not consumed by either species, and gastropod veligers, which were not consumed by P. punctata. The major findings of this research have been integrated into a conceptual model that compares the influence of zooxanthellate and non-zooxanthellate jellyfish on nutrient cycles and trophodynamics. This model has been discussed in context to existing literature and recommendations have been made for future research. Overall this research found that zooxanthellate and non-zooxanthellate jellyfish assimilate, retain and release nutrients very differently and therefore have contrasting impacts on the nutrient cycling and trophodynamics of their surrounding ecosystem.
Thesis (PhD Doctorate)
Doctor of Philosophy (PhD)
Griffith School of Environment
Science, Environment, Engineering and Technology
Full Text

APA, Harvard, Vancouver, ISO und andere Zitierweisen

31

Andersson, Sara. „Nutrient cycling by the herbivorous insect Chrysomela tremulae : Nutrient content in leaves and frass and measurements of ingestion, egestion and exuviation rates“. Thesis, Umeå universitet, Institutionen för ekologi, miljö och geovetenskap, 2016. http://urn.kb.se/resolve?urn=urn:nbn:se:umu:diva-125632.

Der volle Inhalt der Quelle

Annotation:

Insect herbivory on forest canopies strongly affects ecosystem nutrient cycling and availability in a variety of ways, e.g. by changing the quantity, quality and timing of nutrient input to forest soils. A qualitative method for measurements of ingestion, egestion and exuviation rates of the insect Chrysomela tremulae on leaves of the hybrid Populus tremula x tremuloides were tested in this study with the aim to detect differences in relative nutrient cycling efficiencies. The assimilation efficiency (AD), efficiency of conversion of digested food (ECD) and efficiency of conversion of ingested food (ECI) increased from 1st, through 2nd and 3rd instar larvae with generally higher efficiencies for nitrogen than carbon. Effects on nutrient limitations for the insect were also tested by increasing the C:N ratio of insect diet. A carbohydrate solution was painted onto leaves which resulted in a significant increase in C:N (p<0.0001). This lead to a trend of lengthened developmental time for each ontogenetic stage, as well as higher ingestion rate and lower egestion- and exuviation rates. However, a different method of increasing the C:N ratio is recommended in future experiments since the leaves never truly absorbed the solution.

APA, Harvard, Vancouver, ISO und andere Zitierweisen

32

Meyers, Emily. „Phosphate Cycling in the Presence of Biogenic Iron Oxides and Iron-Reducing Bacteria“. Thesis, Université d'Ottawa / University of Ottawa, 2018. http://hdl.handle.net/10393/37306.

Der volle Inhalt der Quelle

Annotation:

Nutrient pollution from industrial activity is an environmental problem that persists in water bodies near urban settings, and has been a primary contributor to eutrophication, bacterial contamination, and harmful algal blooms. Biogenic iron oxides offer a potential solution to the treatment of lakes and rivers containing high concentrations of phosphate, the limiting nutrient in aquatic systems. Soluble ferrous iron can act as an electron donor for iron-oxidizing bacteria, which thrive in low-oxygen environments. This results in the formation of insoluble ferric iron minerals, ideal adsorbents for negatively charged phosphate. Conversely, iron-reducing bacteria reduce ferric iron to form ferrous iron, resulting in the formation of secondary minerals depending on the chemistry of the particular environment. This project investigates the chemical conditions at which biogenic iron oxides have the maximum adsorptive capacity, especially with respect to organic carbon content. A simplified model of natural biogenic iron oxides was synthesized by co-precipitating the mineral ferrihydrite (a common iron oxide) with the polysaccharide alginate, an analogue to bacterial exopolysaccharides. At the levels of carbon investigated, organic matter was not found to affect the adsorptive capacity of iron oxides at the C/Fe ratios analyzed. Similarly, organic matter did not appear to significantly influence the rate of reduction of ferrihydrite by the iron-reducing bacterium Shewanella putrefaciens CN32. Presence of organics did however influence rates of reduction and the mineralogy of the post-reduction precipitates. Phosphate adsorbed to iron oxides prior to microbial reduction greatly increased both the rate and the extent of ferric iron reduced, and also had an impact on the secondary minerals that formed (vivianite, green rust). An improved understanding of these conditions could contribute to a more efficient process by which iron-oxidizing bacteria are used for large-scale industrial water treatment.

APA, Harvard, Vancouver, ISO und andere Zitierweisen

33

Wilks, Melissa Kimberly. „Predation Mediated Carbon Turnover in Nutrient-Limited Cave Environments“. University of Akron / OhioLINK, 2013. http://rave.ohiolink.edu/etdc/view?acc_num=akron1384803278.

Der volle Inhalt der Quelle

APA, Harvard, Vancouver, ISO und andere Zitierweisen

34

Falconi, Claus Francois. „Complex water column nutrient dynamics in the Gulf of Trieste; freshwater nutrient discharge Vs biologicallly mediated cycling of dissolved organic matter“. Doctoral thesis, Università degli studi di Trieste, 2009. http://hdl.handle.net/10077/3172.

Der volle Inhalt der Quelle

Annotation:

2007/2008
Il Golfo di Trieste, localizzato nella parte più settentrionale ed orientale del bacino Adriatico, rappresenta un’area peculiare per le sue caratteristiche geomorfologiche, oceanografiche e biologiche. In quest’area, in particolare, insistono diverse attività economiche che vanno dalla maricoltura al turismo e pertanto i problemi legati alla qualità ambientale sono oltremodo diversificati: da un lato è importante che la trofia del sistema supporti lo sviluppo e la crescita dei molluschi allevati e dall’altro la fruizione delle acque per la balneazione richiede requisiti di qualità precisi e stabiliti dalle normative europee. Alla base di qualsiasi approccio gestionale all’ambiente marino costiero è comunque necessario conoscere la dinamica dei composti che stanno alla base della rete alimentare e che rappresentano anche importanti segnali di apporti antropici al sistema. I nutrienti, siano essi nella forma inorganica o in quella organica, regolano le dinamiche trofiche dell’ecosistema costiero e sono oltremodo concentrati in prossimità di scarichi urbani o nelle acque a bassa salinità frutto del mescolamento tra fiume e mare. Nonostante i numerosi e approfonditi studi sull’ecosistema del Golfo di Trieste, la dinamica dei nutrienti è stata poco approfondita, soprattutto in relazione alla frazione organica. La ricerca svolta nell’ambito di questo dottorato ha avuto come obiettivi principali: La valutazione delle dinamiche spaziali e temporali della concentrazione dei macronutrienti, nella forma inorganica ed organica, nelle acque del Golfo di Trieste La verifica del ruolo degli apporti fluviali e antropici sulla loro disponibilità La comprensione dell'importanza delle attività microbiche di rimineralizzazione sulla disponibilità degli stessi. Il protocollo sperimentale ha previsto l'analisi di campioni d'acqua prelevati mensilmente in 9 stazioni del Golfo, nel periodo 2004-2008. Nella stazione storica C1 il campionamento è stato intensificato per meglio valutare le dinamiche temporali esplorando la variabilità giornaliera e quella a scala oraria. Poiché il Golfo è soggetto a notevoli apporti fluviali, è stato valutato il ruolo dell’Isonzo, il fiume più importante, e, a partire dal 2006, è stato considerato anche il Timavo. Per evidenziare il ruolo degli scarichi antropici sono stati considerati i dati provenienti dal Monitoraggio delle acque costiere predisposto dalla Regione FVG (2002-2005). L’imponente lavoro analitico ha permesso di confermare la scarsa disponibilità di fosforo nelle acque del Golfo anche in periodi di limitata utilizzazione biologica. L’apporto dei fiumi arricchisce le acque delle forme particellate ma non incide sulla frazione disciolta mentre gli scarichi urbani non influenzano significativamente la disponibilità. Importante risulta, invece, il ruolo della degradazione enzimatica della sostanza organica. Sia il fitoplancton che il batterioplancton producono, infatti, notevoli quantità di fosfatasi alcalina, enzima in grado di recuperare fosforo da molecole organiche. Attraverso la produzione di enzimi, i microrganismi riescono a sopperire alla scarsa disponibilità di molecole inorganiche, più facilmente utilizzabili ma estremamente meno abbondanti. Questi risultati sono oltremodo importanti per l’organizzazione dei futuri piani di monitoraggio degli ambienti marini costieri caratterizzati da forti input di acqua dolce sia di origine antropica che fluviale. La trofia del sistema, infatti, non è sostenuta soltanto dai Sali inorganici disciolti di azoto, fosforo e silicio ma è fortemente dipendente dal pool di organico sia disciolto che particellato. L’attività degradativi dei microrganismi su queste matrici consente loro di ottenere le sotanze essenziali per la crescita e la duplicazione.
XIX Ciclo
1966

APA, Harvard, Vancouver, ISO und andere Zitierweisen

35

Arnaudin, Mary Elin. „Benefits of Dung Beetles (Coleoptera: Scarabaeidae) on Nutrient Cycling and Forage Growth in Alpaca Pastures“. Thesis, Virginia Tech, 2012. http://hdl.handle.net/10919/31419.

Der volle Inhalt der Quelle

Annotation:

Alpacas have been gaining prominence in the U.S. since the early 1980s. In pastures, dung beetle activity has been shown to enhance the degradation and incorporation of dung into the soil. The benefits of this activity have been quantified for cattle, but not for alpacas. The objectives of this study were to document the dung beetle species present in alpaca pastures, and to evaluate the impact of dung beetle activity on the growth of a common summer annual grass. In 2010 and 2011, dung beetle species present in alpaca pastures located at Virginia State University (VSU), were evaluated weekly from late May until late August. Eleven species of dung beetles were found, with Onthophagus taurus Schreber being the most dominant. In 2011, a greenhouse study was conducted at Virginia Techâ s Southern Piedmont Research Station. Treatments included a control (no dung, no beetles), dung only, dung with five pairs of O. taurus, and dung that was allowed to be colonized in alpaca pastures at VSU. The addition of O. taurus and the field colonization both significantly increased total yield over the no dung control by 10% and 14%, respectively. These results indicate that healthy and diverse dung beetle communities occur in alpaca pastures in the mid-Atlantic region, and that the presence of these beetles would likely enhance nutrient cycling and pasture growth. However, it is important to remember that dung beetles are just one component of many found in a healthy grassland ecosystem, and the functions of these components are interrelated.
Master of Science

APA, Harvard, Vancouver, ISO und andere Zitierweisen

36

NASCIMENTO, Sandra Maria do. „Distribuição, exportação e ciclagem de nutrientes minerais em Cupiúva (Tapirira guianensis Aubl.), em um fragmento manejado de mata atlântica no município de Goiana - PE“. Universidade Federal Rural de Pernambuco, 2006. http://www.tede2.ufrpe.br:8080/tede2/handle/tede2/5114.

Der volle Inhalt der Quelle

Annotation:

Submitted by Mario BC (mario@bc.ufrpe.br) on 2016-07-28T16:39:44Z No. of bitstreams: 1 Sandra Maria do Nascimento.pdf: 553060 bytes, checksum: af162526240a5bf78aa1ac5c4f3cbba7 (MD5)
Made available in DSpace on 2016-07-28T16:39:44Z (GMT). No. of bitstreams: 1 Sandra Maria do Nascimento.pdf: 553060 bytes, checksum: af162526240a5bf78aa1ac5c4f3cbba7 (MD5) Previous issue date: 2006-05-31
The Atlantic rainforest is one of the richest biomasses of the planet in terms of biodiversity, but has been compromised by considerable anthropogenic action. The present study investigated a managed fragment of the Atlantic rainforest in the city of Goiana, PE, Brazil, on the Megaó farmland, with the aim of evaluating the distribution and exportation of mineral nutrients in Tapirira guianensis Aulb. (cupiúva), a perennial, pioneering halophyte species belonging to the family Anacardiaceae. Analysis of the mineral nutrients in the vegetal biomass and litter was carried out at the Mineral Nutrition of Plant Laboratory (Chemistry Department) and the Soil Chemistry Laboratory (Agronomy Department); soil analysis was carried out at the Soil Physics and Soil Fertility Laboratories (Agronomy Department) of the Rural Federal University of Pernambuco. Macronutrient (N, P, K, Ca, Mg, S) and micronutrient (Cu, Fe, Mn, Zn) determinations were performed on the leaves, branches, bark and trunk. Pre-dried samples were submitted to nitro-perchloric digestion, with the exception of N, for which sulfuric digestion was performed. Colorimetry was used for the analytic determination of P, whereas turbidimetry was used for S; K was assessed using the flame photometric technique, and the Ca, Mg, Cu, Fe, Mn and Zn contents were determined by the atomic absorption spectrophotometric method. N concentration was determined by the Kjeldahl method. Results were submitted to variance analysis and the averages were compared through the Tukey test at 5 % probability. The concentration of nutrients in the Tapirira guianensis Aulb. biomass obeyed the following order: leaves>bark>branches>trunk. The distribution of macronutrients in the leaves, bark and branch were distributed in N>Ca>Mg>K>S>P, and in the trunk in N>Ca>S>P>Mg>K. Micronutrients followed the distribution sequence for all arboreal components: Fe>Zn>Mn. The leaves presented a greater accumulation of nutrients, despite their biomass being smaller than the remaining components. Leaf maintenance is therefore important in the management area, thereby ensuring the cycling of nutrients through litter and the adequate maintenance of the management area. The total of exported nutrients was 71 % at the time of the cutting of the tree when the trunk, bark and branches are removed from the site, which could compromise the sustainability of the site.
A mata Atlântica é um dos biomas mais ricos em biodiversidade do planeta, diversidade esta que se encontra comprometida por causa da forte ação antrópica, que entre outros problemas, produz a degradação do solo. O presente trabalho teve como área de estudo um fragmento manejado de mata Atlântica no município de Goiana – PE, na fazenda Megaó. O objetivo foi avaliar a distribuição e exportação de nutrientes minerais em Tapirira guianensis Aulb. (cupiúva), espécie perenifólia, pioneira, e heliófita, pertencente à família Anacardiaceae. As análises dos nutrientes minerais na biomassa vegetal e na serrapilheira foram realizadas no Laboratório de Nutrição Mineral de Plantas (Departamento de Química) e no Laboratório de Química do Solo (Departamento de Agronomia), e as análises do solo foram realizadas nos Laboratórios de Física do solo e Fertilidade do Solo (Departamento de Agronomia), da Universidade Federal Rural de Pernambuco. As determinações dos macronutrientes (N, P, K, Ca, Mg, S) e micronutrientes (Cu, Fe, Mn, Zn), foram realizadas nas folhas, galhos, casca e fuste. As amostras pré-secas foram submetidas à digestão nitroperclórica, com exceção do N, onde foi feita a digestão sulfúrica. A determinação analítica de P se deu por colorimetria e S por turbidimetria; K, foi avaliado através da técnica de fotometria de chama e os teores de Ca, Mg, Cu, Fe, Mn e Zn foram determinados pelo método de espectrofotometria de absorção atômica. Os teores de N foram determinados pelo método de Kjeldahl. Os resultados foram submetidos à análise de variância e as médias comparadas pelo teste de Tukey a 5 % de probabilidade. A concentração de nutrientes na biomassa da cupiúva obedeceu a seguinte ordem folhas>casca>galhos>fuste. A distribuição de macronutrientes nas folhas, casca e galho foi distribuídos em N>Ca>Mg>K>S>P e no fuste foi N>Ca>S>P>Mg>K. Os micronutrientes seguiram a seqüência de distribuição para todos os componentes arbóreos Fe>Zn>Mn. As folhas apresentaram maior concentração de nutrientes, apesar de sua biomassa ser menor que os outros componentes, sendo assim importante sua manutenção na área de manejo, garantindo a ciclagem de nutrientes via serrapilheira e a boa manutenção da área de manejo. O total de nutrientes exportados no momento do corte da árvore, em que são retirados o fuste, a casca e os galhos do sítio, é de 71 %, o que representa uma grande perda no total de nutrientes da área de manejo, e pode comprometer a sustentabilidade do sítio.

APA, Harvard, Vancouver, ISO und andere Zitierweisen

37

Bazza, Zineb. „Soil amendments from urban residuals and their effect on crop productivity and nutrient cycling“. Thesis, University of British Columbia, 2017. http://hdl.handle.net/2429/63222.

Der volle Inhalt der Quelle

Annotation:

Urban residuals have been used in agriculture to decrease disposal costs, recycle nutrients, and prevent or counteract the degradation of soils linked to the intensification of agriculture. Technological advancements continue to produce novel residuals that can be used as soil amendments, with the potential to reduce or eliminate waste. This thesis entails two studies that examine the potential to utilize new urban residuals for food production. The objectives of the first study were to look at the potential benefits and impacts, on crop productivity and nutrient cycling, of using monopotassium phosphate (MKP) fertilizers, made using the co-products of biodiesel production. The treatments in this study include MKP-M, a purified form of MKP, MKP-C, a crude MKP from biodiesel production with glycerin and MKP-C2, similar to MKP-C but with double the glycerin. There were no differences in yields in the field trial. The greenhouse trial showed higher pepper yields using MKP-C and foliar MKP-M, and higher number of fruits with foliar MKP-M and a retail MKP. Soil analyses suggest that glycerin in certain amounts can inhibit nitrification and improve nitrogen (N) uptake. In the second study, a compost like material (HTI Compost) made in 24 hours was tested to better understand the effects unstable and immature compost could have on yield, nutrient cycling and greenhouse gas (GHG) emissions. The treatments were the HTI compost, UBC farm compost (typical municipal compost), a mix of the two composts, HTI compost + bloodmeal, and no amendment. The results show the HTI treatments had similar yields to the UBC farm compost for beets, but lower yields in spinach due to reduced or delayed germination. The HTI treatments delayed soil N availability and resulted in higher GHG emissions. Emissions of carbon dioxide and methane from the HTI treatments were high in the beginning of the season when the compost was decomposing, while nitrous oxide emissions were highest later on as decomposition rates declined. These results show promising benefits for using urban residuals as soil amendments, but the management of these amendments is crucial to avoid any negative impacts on crop productivity or the environment.
Land and Food Systems, Faculty of
Graduate

APA, Harvard, Vancouver, ISO und andere Zitierweisen

38

Spears, Bryan Millar. „Benthic-pelagic nutrient cycling in shallow lakes : investigating the functional role of benthic microalgae /“. St Andrews, 2007. http://hdl.handle.net/10023/371.

Der volle Inhalt der Quelle

APA, Harvard, Vancouver, ISO und andere Zitierweisen

39

Moore, Patrick T. „Forest Recovery, Nutrient Cycling and Carbon Sequestration in a Southern Appalachian Spruce-Fir Forest“. DigitalCommons@USU, 2013. http://digitalcommons.usu.edu/etd/1519.

Der volle Inhalt der Quelle

Annotation:

In order to fully understand the magnitude of the benefits that forests provide, it is crucial to understand the full suite of ecosystem services that they offer. A southern Appalachian red spruce-Fraser fir forest was intensively analyzed using a variety of methodologies to determine the nature and quantity of some of these services. Many hypotheses exist regarding the future of these spruce-fir forests, which were heavily disturbed by the non-native balsam wooly adelgid during the 1980s. Direct measurements over the course of a decade assessed these hypotheses and indicate that this forest is recovering structure and function. The forest is accruing overstory biomass, with vegetation composition on a trajectory towards historic conditions. By using a total forest inventory of all vegetation from overstory trees to understory mosses, rates of productivity and nutrient cycling were determined. Productivity of this forest at low elevations has returned to pre-adelgid levels, while at high elevations productivity is approaching these levels. In the absence of an intact overstory, forest understory vegetation can compensate by disproportionately cycling and retaining nutrients such as nitrogen that would otherwise leach offsite. The understory of this forest provides an important service in nutrient cycling. Our ability to actively manage forests in order to manipulate levels and rates of carbon sequestration was assessed using stand data and the Forest Vegetation Simulator Growth and Yield Model. Silvicultural intervention proved effective at sequestering additional carbon over a no action alternative by the end of our simulation period. This forest provides a variety of ecosystem services and has retained its ability to recover their function after catastrophic disturbance.

APA, Harvard, Vancouver, ISO und andere Zitierweisen

40

Spears, Bryan M. „Benthic-pelagic nutrient cycling in shallow lakes : investigating the functional role of benthic microalgae“. Thesis, University of St Andrews, 2007. http://hdl.handle.net/10023/371.

Der volle Inhalt der Quelle

Annotation:

Microbes, living on the boundary between the sediment and the water-column in lakes, can play a pivotal role in governing the magnitude and frequency of nutrient cycling. The purpose of this research was to focus on the role of benthic microalgae in regulating such processes and to identify spatial and temporal characteristics in their function. Approaches included the quantification of sediment nutrient concentrations (particularly P fractionation), estimates of equilibrium phosphate concentrations (EPC0) (resuspended and undisturbed sediment estimates), and assessment of the benthic microalgal community composition, biostabilisation capacity, and its ability to regulate diffusive-nutrient flux. This thesis highlighted the importance of biological regulation of benthic/pelagic nutrient cycling, especially the role of benthic microautotrophs. Release sensitive sediment-P fractions were observed to be highly variable (both with depth and season) and correlated well with indicators of benthic photosynthesis (e.g. DO, chlorophyll, pH). Understanding the seasonality of whole-system P partitioning can enhance future lake management programmes. EPC0 estimates were significantly higher during undisturbed as opposed to disturbed sediment conditions. Epipelon constituted < 17 % of the total sediment chlorophyll signal and was highest in the clearer winter months and at intermediate depths at which a trade off between wind-induced habitat disturbance and light limitation existed. In intact core experiments, the benthic microalgal community significantly reduced the diffusive nutrient (especially PO₄-P and SiO₂) flux. NH₄ -N release was highest under light conditions at high temperatures. The mechanisms for regulation included direct uptake, photosynthetic oxygenation of the sediment surface, and regulation of nitrification/denitrification processes. Sediment stability increased with colloidal carbohydrate concentration (extruded by benthic microbes) at 4.1 m water-depth but not at 2.1 m overlying water depth, probably indicating the role of habitat disturbance in shallow areas acting to reduce epipelic production. Additionally, in an ecosystem comparison, the nature and extent of the biotic mediation of sediment stability varied between freshwater and estuarine ecosystems.

APA, Harvard, Vancouver, ISO und andere Zitierweisen

41

Wilson, Deirdre Barnetson. „Effect of nitrogen enrichment on the ecology and nutrient cycling of a lowland heath“. Thesis, Manchester Metropolitan University, 2003. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.289616.

Der volle Inhalt der Quelle

Annotation:

This study was part of an ongoing investigation into the long-term effects of nitrogen enrichment and environmental stress on lowland heath ecology and nutrient cycling. The original experimental site, 4 replicate blocks of 2m x 1m plots, was established on pioneer-phase Calluna vulgaris - Deschampsia flexuosa heathland in 1996 (Cawley, 2000). Nitrogen treatments (0, 20, 60 & 120 kg N ha" yr") have been applied on a fortnightly basis, against a background deposition of -20 kg N ha'! yr" (NOx & NHy). During 1997 the plots were split and a six-month drought versus non-drought treatment introduced (full details in Cawley, 2000). The period of environmental stress experienced by the dominant C. vulgaris canopy was extended over the following two years (1998 & 1999) by a natural outbreak of Lochmaea suturalis. Zero-tension lysimeters were installed under the non-droughted half of these plots (2001), facilitating study of increased nitrogen deposition effects upon nitrogen losses through leaching.' A second set of experimental plots were started in 2000 to enable study of germination and establishment of D. flexuosa under conditions of increased nitrogen deposition and canopy gap creation in an otherwise closed C. vulgaris canopy. This study has shown that elevated, long-term deposition of atmospheric nitrogen in combination with periods of environmental stress can contribute to significant changes in the ecology and nutrient cycling of a lowland heath. Elevated nitrogen deposition was found to induce significant increases in: tissue nitrogen content of Calluna and Hypnum sp.; litter nitrogen content; the loss of nitrogen from the system through leaching. Additionally, there were significant reductions in the C/N ratio of both vegetation and soil. This could have major implications for changes in the rates of nitrogen mineralisation and immobilisation in this nitrogen-limited ecosystem. By 2001, few effects of the 1997 drought continued to be apparent in the heathland vegetation. However differences were recorded in the nitrogen content and C/N ratio of the soil components of the droughted and nondroughted plots. Some responses were not as expected, such as the transitory increase in the Deschampsia population. The predicted outcome, based on studies of other European lowland heaths, would have been for a marked transition to a Deschampsia-dominated canopy, especially in those high nitrogen (80N & 140N) treatment plots which had been droughted in 1997. Nitrogen deposition levels in excess of the critical load for dry heathlands (10 - 20 kg N ha" yr"), in combination with Calluna canopy opening induced by environmental stress, have been associated with such transitions in vegetation on Continental heaths. An equally unexpected outcome of this study was the significant recovery of the moss layer after the cessation of drought conditions in 1997. Again, reports from other European heaths have suggested that increased nitrogen deposition would normally be associated with a loss of bryophytes and cryptograms. Elevated nitrogen inputs, at this study site, have been associated with a reduction in bryophyte species diversity. Conversely, there has been a corresponding, significant, increase in the cover of nitrophilic Hypnum species.

APA, Harvard, Vancouver, ISO und andere Zitierweisen

42

Villela, Dora Maria. „Nutrient cycling in a monodominant and other rain forest types on Maraca Island, Brazil“. Thesis, University of Stirling, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.296770.

Der volle Inhalt der Quelle

APA, Harvard, Vancouver, ISO und andere Zitierweisen

43

Hardison, Amber Kay. „Interactions between macroalgae and the sediment microbial community : nutrient cycling within shallow coastal bays /“. W&M ScholarWorks, 2009. http://web.vims.edu/library/Theses/Hardison09.pdf.

Der volle Inhalt der Quelle

APA, Harvard, Vancouver, ISO und andere Zitierweisen

44

Tutua, Shane Sarere. „Residue Management and Carbon and Nutrient Cycling in Exotic Pine Plantations of Southeast Queensland“. Thesis, Griffith University, 2009. http://hdl.handle.net/10072/366298.

Der volle Inhalt der Quelle

Annotation:

In Southeast Queensland, Australia, future wood production from exotic pines will rely heavily on second-rotation plantations. This increases the importance of sustaining soil fertility through logging or harvest residue retention for soil organic matter (SOM) maintenance in forest plantations. However, a greater understanding of harvest residues and their impact is essential to fully realise the potential of harvest residue management as an integral component of sustainable production forestry. Therefore, this study examined the nature of harvest residues, their decomposition and nutrient release dynamics, and the short- and long-term impacts of the residues on soil carbon (C), nitrogen (N) and phosphorous (P) pools, tree nutrition, growth and productivity in exotic pine plantations of Toolara State forest (26 degrees 00' South, 152 degrees 49' East), Maryborough districy, southeast Queensland.
Thesis (PhD Doctorate)
Doctor of Philosophy (PhD)
Griffith School of Environment
Science, Environment, Engineering and Technology
Full Text

APA, Harvard, Vancouver, ISO und andere Zitierweisen

45

Cole, Andrew. „The response of grassland carbon cycling to drought events and changes in nutrient availability“. Thesis, Lancaster University, 2016. http://eprints.lancs.ac.uk/86756/.

Der volle Inhalt der Quelle

Annotation:

In grasslands, climate change has the potential to disrupt a range of ecosystem services, including agricultural production, carbon (C) storage and nutrient cycling. In particular, climate change is likely to increase the frequency and severity of extreme climate events, such as drought and the subsequent rewetting event. Yet the effect of drought events will not be consistent across grassland communities, instead likely varying with grassland properties. One such property may be the level of nutrient availability, which brings about changes in plant productivity, plant community composition, and soil microbial composition and function. In this thesis, the effect of reduced precipitation on C cycling in UK species-rich grasslands is investigated in two field experiments, with varying long-term grassland restoration treatments and short-term nutrient addition, and a glasshouse experiment with reduced soil moisture. It was hypothesised that changes in plant and soil microbial communities, brought about by differences in nutrient availability, would modulate above and belowground C cycling responses to drought. This thesis found that the level of nutrient availability was important for modulating how C is cycled in response to drought in plants, soil microbial communities and whole ecosystem CO2 fluxes. For plants, the effect of drought and nutrient availability differed between functional groups, species and due to intraspecific trait variation. For soil microbial communities, the effect of drought on carbon use efficiency was modulated by short-term nutrient addition. Increased nutrient availability and drought therefore interact to determine how C is cycled and stored in plants and soil microbial communities, revealing the importance of agricultural practices in modulating whole community responses to climate change. Overall, this thesis shows the mechanisms by which drought may alter C cycling and its potential feedbacks to climate are complex, but at least in part, depend on the level of nutrient availability.

APA, Harvard, Vancouver, ISO und andere Zitierweisen

46

Aikio, S. (Sami). „Plant adaptive strategies in relation to variable resource availability, soil microbial processes and ecosystem development“. Doctoral thesis, Oulun yliopisto, 2000. http://urn.fi/urn:isbn:9514256824.

Der volle Inhalt der Quelle

Annotation:

Abstract Plants have evolved various adaptive strategies for balancing the benefits and costs of having a high affinity for resources, plasticity of growth allocation and mycorrhizal symbiosis. The relative growth rates of mycorrhizal and non-mycorrhizal plants were modelled for stable and variable nutrient availability. Mycorrhizal plants had higher growth rates at low and non-mycorrhizal plants at high nutrient availability. Variation in nutrient availability reduced the growth rate of mycorrhizal plants due to a high affinity for nutrients. However, mycorrhizal plants may be able to buffer against external fluctuations and therefore experience less environmental variation than non-mycorrhizal plants. Non-mycorrhizal plants may even benefit from variation. The optimal allocation of growth between shoot and roots depends on the availability of energy and nutrients. The optimisation model predicted that the requirement for phenotypic plasticity of shoot/root allocation is greatest in environments with low resource availability. Plants with a high affinity for resources required more plasticity in order to tolerate variation than plants with a low affinity. The model predicted a trade-off between the ability to deplete resources and the ability to tolerate resource fluctuations. Changes in the availability and ratio of resources lead to changes in the structure and composition of vegetation during primary succession. The field study of the forested phases of the land uplift island Hailuoto showed a successional change in the vegetation from the dominance of bryophytes and deciduous dwarf shrubs to dominance by lichens and evergreen dwarf shrubs. The humus layer became thinner and the availability of nutrients declined, while the C/N ratio of soil organic matter increased during succession indicating a decline in the quality of organic matter. The increased soil respiration rate indicates a successional increase in the energetic costs of decomposing organic matter. Nutrients mediate both direct and indirect trophic interactions. Indirect interactions of nutrient cycling are not explicit in continuous time models. A transformation to a discrete time model was shown to make the indirect interactions explicit as transition probabilities and allowed their dynamic contribution to be evaluated with an elasticity analysis. The importance of indirect interactions was greater in tundra than temperate forest and increased with the rate of nutrient cycling.

APA, Harvard, Vancouver, ISO und andere Zitierweisen

47

Torres, Lisette E. „Variation Among Fish Species in the Stoichiometry of Nutrient Excretion“. Miami University / OhioLINK, 2005. http://rave.ohiolink.edu/etdc/view?acc_num=miami1123178303.

Der volle Inhalt der Quelle

APA, Harvard, Vancouver, ISO und andere Zitierweisen

48

Kulesza, Stephanie Brooke. „Effects of Manure Injection on Transport and Transformation of Nutrient and Antibiotics“. Diss., Virginia Tech, 2015. http://hdl.handle.net/10919/56895.

Der volle Inhalt der Quelle

Annotation:

Overapplication of manure in sensitive watersheds is an issue of increasing environmental concern due to increased nutrient loading and antibiotic release into aquatic environments. Manure is typically surface applied, leaving nutrients and antibiotics vulnerable to loss at the soil surface. Elevated nutrient and antibiotic loading into water bodies can increase the rate of eutrophication and occurrence of antibiotic resistance genes in areas of high animal agriculture production, such as the Chesapeake Bay watershed. Manure injection is a new technology that incorporates manure into the soil with minimal disturbance, and management strategies that reduce manure loss from agricultural fields could prevent the transport of nutrients and antibiotics to sensitive waterways. However, little is known about the efficacy of dry litter injection to decrease nitrogen (N) loss when compared to surface application. Also, there are no studies that determine the effects of injection on antibiotic transport and transformation after manure application. Therefore, this project focused on changes in N cycling, orchardgrass hay yield and quality, and transport and transformation of pirlimycin and cephapirin, two common antibiotics in dairy production, when manure is injected. Subsurface injection eliminated ammonia volatilization and N loss in runoff and increased soil inorganic N when compared to surface application after volatilization, incubation, and rainfall simulation studies. Although these benefits did not translate to higher yields in orchardgrass hay, protein increased when poultry litter was injected, indicating greater N uptake. Injection of dairy manure decreased losses of pirlimycin to levels of the control when compared to surface application. Although, pirlimycin had a slower degradation rate within the injection slit compared to surface application, potentially increasing the amount of time soil microbes are exposed to antibiotics. In an incubation study, pirlimycin concentrations decreased after 7 days, but concentrations increased sharply after 14 days. This indicates that conjugates formed in the liver or digestive tract of dairy cows may revert back to the parent compound after manure application. With increased retention of nutrients and antibiotics, injection could be a best management practice used to reduce the loss of these compounds to the environment while increasing the quality of crops produced.
Ph. D.

APA, Harvard, Vancouver, ISO und andere Zitierweisen

49

Smolders, Kate Elizabeth. „Forestry and Stream Ecology: A Multi-Catchment Experiment on the Effects of Selective Harvesting“. Thesis, Griffith University, 2010. http://hdl.handle.net/10072/366199.

Der volle Inhalt der Quelle

Annotation:

In forested headwater streams, ecological processes such as carbon and nutrient cycling, the stream hydrological regime, and the structure of biological assemblages are tightly linked to the surrounding catchment. As such, headwater streams are vulnerable to disturbances within their catchments at various spatial (e.g. reach and catchment) and temporal (e.g. months to decades) scales. Forest harvesting is an example of a disturbance that has been widely linked to changes in the structure and function of biological communities, and changes in stream processes, such as leaf breakdown. This thesis explores the short term (1 year) response of benthic organic matter storage and retention, leaf litter breakdown and macroinvertebrate structural and functional assemblage composition in headwater streams to catchment-scale selective harvesting in dry-sclerophyll forest in north-eastern NSW Australia. This study used a Multiple Before-After Control-Impact (MBACI) design, with five small adjacent equivalent-sized catchments (302-770 ha), three of which were selectively harvested during a commercial forestry operation, with two left as unharvested controls. Riparian vegetation was retained in accordance with licence conditions for Forests NSW. All five streams were gauged, and since 2001 Forests NSW have been collecting data on turbidity, suspended solids, temperature, run off and stream flow. Standing stocks and composition of coarse particulate organic matter (CPOM) were quantified before and after harvesting in all five catchments, with the prediction that stocks would be significantly lower in harvested streams. Mean standing stocks in all five streams were highly variable spatially and temporally, but harvested streams did not differ significantly from control streams in standing stocks of CPOM. Composition of CPOM was consistent across all streams and proportionally dominated by leaves, then small wood and bark. These findings were remarkably similar to values reported from other Australian streams. The results indicate that in the short term (1 year) there were no detectable reductions in CPOM standing stocks or changes in CPOM composition from selective harvesting.
Thesis (PhD Doctorate)
Doctor of Philosophy (PhD)
Griffith School of Environment
Science, Environment, Engineering and Technology
Full Text

APA, Harvard, Vancouver, ISO und andere Zitierweisen

50

Haron, Khalid. „Nutrient cycling in an oil palm (Elaeis guineensis Jacq.) plantation : residues decomposition and implications for management“. Thesis, University of Exeter, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.361325.

Der volle Inhalt der Quelle

APA, Harvard, Vancouver, ISO und andere Zitierweisen

Dissertationen zum Thema „Nutrient cycling“

Geben Sie eine Quelle nach APA, MLA, Chicago, Harvard und anderen Zitierweisen an