Dentre as ameaças causadas pealas mudanças climáticas, é esperado um aumento na frequência e na magnitude de eventos climáticos extremos. Portanto, é de vital importância identificar características da comunidade que confiram estabilidade aos processos ecossistêmicos. Por meio de três experimentos buscamos explorar essas intrincadas relações entre alguns aspectos da biodiversidade e a estabilidade ecológica. No primeiro estudo, comparamos a produtividade primária antes e depois de uma inundação em comunidades sintéticas com diferentes valores de riqueza de espécies, diversidade e composição funcional. No segundo experimento, investigamos como alterações na intensidade de chuvas (simuladas por meio de interceptadores) afetaram os atributos funcionais, diversidade e processos ecossistêmicos de um campo nativo sob diferentes frequências de desfolhação. O terceiro estudo, consistiu em um experimento com manipulação da riqueza de espécies por meio de remoções, onde analisamos o efeito da diversidade de espécies na estabilidade nos níveis de organização de comunidade (colonizações e extinções) e ecossistema (variação na produtividade primária). Atributos funcionais e outras características da comunidade (riqueza e composição) afetaram e foram afetadas pelos distúrbios. A relação diversidade-estabilidade apresentou diferentes tendências dependendo da natureza e intensidade do distúrbio. O aumento dos recursos após a inundação favoreceu comunidades mais ricas e aquelas contendo atributos relacionados à aquisição de recursos. Além disso, a frequência de desfolhação não afetou a resposta da vegetação à manipulação de chuva. Estabilidade apresentou tendências opostas dependendo do nível de organização ecológica considerado. Maior substituição 63 de espécies em comunidades mais ricas correspondeu a uma maior estabilidade em 64 processos ecossistêmicos. / Climate change is expected to increase the frequency and magnitude of extreme weather events. It is therefore of major importance to identify the community attributes that confer stability in ecosystem processes facing such events. By means of three experiment-based studies, we aimed to explore how plant community aspects affect ecological stability. In the first study, we compared data on biomass productivity before and after a major flood in synthetic plant communities with different values of species richness, functional diversity and community weighted means of functional traits on different measures of stability. In the second experiment, we investigate how changes in rainfall (simulated by rainout-shelters) alter functional traits and diversity and ecosystem processes of a natural grassland under different defoliation frequencies. The third study consisted on a biodiversity experiment in which we manipulated species richness by removals for studying the effects of species diversity on the stability at the community (colonization and extinction) and ecosystem levels (variation in primary productivity). Functional traits and other community features (richness, composition) affected and were affected by the disturbances. Diversity-stability relationships presented different trends depending on the disturbance nature and intensity. Resource inputs following the flood favoured rich communities and the ones characterized by traits related to resource acquisition. Also, defoliation frequency did not affect the way vegetation responded to rainfall manipulation. Stability showed opposite trends when evaluated at different levels of ecological organization. Higher turnover in rich communities corresponded to increased stability in ecosystem processes.

Thesis (S.M.)--Joint Program in Biological Oceanography (Massachusetts Institute of Technology, Dept. of Biology; and the Woods Hole Oceanographic Institution), 2008. / "February 2008." / Includes bibliographical references (p. 133). / I build on the deterministic phytoplankton growth model of Sosik et al. by introducing process error, which simulates real variation in population growth and inaccuracies in the structure of the matrix model. Adding a stochastic component allows me to use maximum likelihood methods of parameter estimation. I lay out the method used to calculate parameter estimates, confidence intervals, and estimated population growth rates, then use a simplified three-stage model to test the efficacy of this method with simulated observations. I repeat similar tests with the full model based on Sosik et al., then test this model with a set of data from a laboratory culture whose population growth rate was independently determined. In general, the parameter estimates I obtain for simulated data are better the lower the levels of stochasticity. Despite large confidence intervals around some model parameter estimates, the estimated population growth rates have relatively small confidence intervals. The parameter estimates I obtained for the laboratory data fell in a region of the parameter space that in general contains parameter sets that are difficult to estimate, although the estimated population growth rate was close to the independently determined value. / by Lorraine Thomas. / S.M.

Thesis (Ph.D.)--McMaster University, 2006. / Supervisor: Patricia Chow-Fraser. Includes bibliographical references.

<p>This thesis describes a multi-parameter biogeochemical investigation in a shallow hyper-eutrophic freshwater coastal lake, Zeekoevlei, in South Africa. The predominance of autochthonous algal-derived organic matter in lake sediments is indicated by low C/N, high H/C ratios and δ13Corganic values. Seepage from a nearby waste water treatment plant, rapid urbanization, raw sewage input and heavily fertilized farming in the catchments have caused enhanced productivity and is reflected by the changes in TOC concentrations, δ15N values, terrestrial to aquatic (n-alkane) ratio (TAR) and low carbon preference index (CPI) values. Eutrophic conditions were initiated in the lake with the start of recreational activities in early 1900s. Construction of dams and pondweed eradication in mid-1900s caused the transformation of the lake towards a hyper-eutrophic water body. Moreover, the aquatic macrophyte n-alkane proxy (Paq) values indicate the slow takeover by floating macrophytes after the eradication of submerged pondweeds in 1951. Low δ15N values and appearance of zeaxanthin indicate initiation of cyanobacterial bloom in the lake following pondweed eradication. Furthermore, the lake experienced intense cyanobacterial bloom after 1983 dredging. Although, cyanobacterial domination has decreased in recent years, hyper-eutrophic condition persists in the lake.</p><p>Chemical weathering process supplies major fraction of trace metals, whereas fertilizers, agricultural wastes, sewage effluents and road runoff constitute the anthropogenic fraction. Low industrialization in the catchments causes low metal pollution in waters. In addition, high pH and metal scavenging by planktons result low dissolved trace metal concentrations. Adsorption by CaCO3 and planktonic assimilation control trace metal and phosphorus (P) sedimentation. Lake sediments have low P retention capacity and P is released from surface sediments by wind-induced resuspension.</p>

This thesis describes a multi-parameter biogeochemical investigation in a shallow hyper-eutrophic freshwater coastal lake, Zeekoevlei, in South Africa. The predominance of autochthonous algal-derived organic matter in lake sediments is indicated by low C/N, high H/C ratios and δ13Corganic values. Seepage from a nearby waste water treatment plant, rapid urbanization, raw sewage input and heavily fertilized farming in the catchments have caused enhanced productivity and is reflected by the changes in TOC concentrations, δ15N values, terrestrial to aquatic (n-alkane) ratio (TAR) and low carbon preference index (CPI) values. Eutrophic conditions were initiated in the lake with the start of recreational activities in early 1900s. Construction of dams and pondweed eradication in mid-1900s caused the transformation of the lake towards a hyper-eutrophic water body. Moreover, the aquatic macrophyte n-alkane proxy (Paq) values indicate the slow takeover by floating macrophytes after the eradication of submerged pondweeds in 1951. Low δ15N values and appearance of zeaxanthin indicate initiation of cyanobacterial bloom in the lake following pondweed eradication. Furthermore, the lake experienced intense cyanobacterial bloom after 1983 dredging. Although, cyanobacterial domination has decreased in recent years, hyper-eutrophic condition persists in the lake. Chemical weathering process supplies major fraction of trace metals, whereas fertilizers, agricultural wastes, sewage effluents and road runoff constitute the anthropogenic fraction. Low industrialization in the catchments causes low metal pollution in waters. In addition, high pH and metal scavenging by planktons result low dissolved trace metal concentrations. Adsorption by CaCO3 and planktonic assimilation control trace metal and phosphorus (P) sedimentation. Lake sediments have low P retention capacity and P is released from surface sediments by wind-induced resuspension.

Graduation date: 1992

Warming induced changes in Arctic vegetation have to date been studied through observational and experimental field studies, leaving significant uncertainty about the representativeness of selected field sites as well as how these field scale findings scale up to the entire pan-Arctic. The purposes of this thesis were therefore to 1) analyze remotely-sensed/modeled temperature, Normalized Difference Vegeta- tion Indices (NDVI) and plant Net Primary Productivity (NPP) to assess coarse- scale changes (1982–2006) in vegetation; and 2) compare field, remote sensing and model outputs to estimate limitations, challenges and disagreements between data formats. The following data sources were used: • Advanced Very High Resolution Radiometer Polar Pathfinder Extended (APP- x, temperature & albedo) • Moderate Resolution Imaging Spectroradiometer (MODIS, Normalized Dif- ference Vegetation Index (NDVI) & Enhanced Vegetation Index (EVI) ) • Landsat Enhanced Thematic Mapper (Landsat ETM, NDVI) • Global Inventory Modeling and Mapping Studies (GIMMS, NDVI) • Global Productivity Efficiency Model (GloPEM, Net Primary Productivity (NPP)) Over the pan-Arctic (1982-2007), increases in temperature, total annual NPP and maximum annual NDVI were observed. Increases in NDVI and NPP were found to be closely related to increases in temperature according to non-parametric Sen’ slope and Mann Kendall tau tests. Variations in phenology were largely non- significant but related to increases in growing season temperature. Snow melt onset and spring onset correspond closely. MODIS, Landsat and GIMMS NDVI data sets agree well, and MODIS EVI and NDVI are very similar for spring and summer at Fosheim Peninsula. GloPEM NPP and field estimates of NPP are poorly correlated, whereas GIMMS NDVI and GloPEM NPP are well correlated, indicating a need for better calibration of model NPP to field data. In summary, increases in pan-Arctic biological productivity indicators were ob- served, and were found to be closely related to recent circumpolar warming. How- ever, these changes appear to be focused in regions from which recent field studies have found significant ecological changes (Alaska), and coarse resolution remote sensing estimates of ecological changes have been less marked in other regions. Dis- crepancies between results from model, field data and remote sensing, as well as central questions remaining about the impact of increases in productivity on soil- vegetation-atmosphere feedbacks, indicate a clear need for continued research into warming induced changes in pan-Arctic vegetation.

Warming induced changes in Arctic vegetation have to date been studied through observational and experimental field studies, leaving significant uncertainty about the representativeness of selected field sites as well as how these field scale findings scale up to the entire pan-Arctic. The purposes of this thesis were therefore to 1) analyze remotely-sensed/modeled temperature, Normalized Difference Vegeta- tion Indices (NDVI) and plant Net Primary Productivity (NPP) to assess coarse- scale changes (1982–2006) in vegetation; and 2) compare field, remote sensing and model outputs to estimate limitations, challenges and disagreements between data formats. The following data sources were used: • Advanced Very High Resolution Radiometer Polar Pathfinder Extended (APP- x, temperature & albedo) • Moderate Resolution Imaging Spectroradiometer (MODIS, Normalized Dif- ference Vegetation Index (NDVI) & Enhanced Vegetation Index (EVI) ) • Landsat Enhanced Thematic Mapper (Landsat ETM, NDVI) • Global Inventory Modeling and Mapping Studies (GIMMS, NDVI) • Global Productivity Efficiency Model (GloPEM, Net Primary Productivity (NPP)) Over the pan-Arctic (1982-2007), increases in temperature, total annual NPP and maximum annual NDVI were observed. Increases in NDVI and NPP were found to be closely related to increases in temperature according to non-parametric Sen’ slope and Mann Kendall tau tests. Variations in phenology were largely non- significant but related to increases in growing season temperature. Snow melt onset and spring onset correspond closely. MODIS, Landsat and GIMMS NDVI data sets agree well, and MODIS EVI and NDVI are very similar for spring and summer at Fosheim Peninsula. GloPEM NPP and field estimates of NPP are poorly correlated, whereas GIMMS NDVI and GloPEM NPP are well correlated, indicating a need for better calibration of model NPP to field data. In summary, increases in pan-Arctic biological productivity indicators were ob- served, and were found to be closely related to recent circumpolar warming. How- ever, these changes appear to be focused in regions from which recent field studies have found significant ecological changes (Alaska), and coarse resolution remote sensing estimates of ecological changes have been less marked in other regions. Dis- crepancies between results from model, field data and remote sensing, as well as central questions remaining about the impact of increases in productivity on soil- vegetation-atmosphere feedbacks, indicate a clear need for continued research into warming induced changes in pan-Arctic vegetation.

Temporal and spatial variations in the Sea of Marmara based on monthly averages of chlorophyll a, which is the major indicator of phytoplankton biomass and primary production, recorded by SeaWiFS and MODIS-Aqua sensors at nearly 100 stations have been analyzed for the period of 1997-2007. Majority of phytoplankton blooms occur during the winter and spring seasons, followed by a smaller secondary bloom during the fall season. The majority of high magnitude blooms occur at the Eastern part of the Sea which may be attributed to an increase in the amount of discharge of water contaminated with nutrients originating on land where the industries are located. The correlations between monthly averages of sea surface temperature (SST) and corresponding chlorophyll a values are statistically significant (inverse) at 1% level, where r= -0.53 and the equation of the fitted model is: Chlorophyll a = 7.09199 &ndash / 0.215402* SST This correlation is expected because a relative decrease in SST is an indicative of upwelling and vertical mixing which are the primary processes for the formation of phytoplankton blooms. We have also found that monthly averages of chlorophyll a recorded by SeaWiFS and MODIS-Aqua are nearly identical and either data set can be used in place of the other.

Thesis (Ph. D.)--University of Washington, 2003. / Vita. Includes bibliographical references (leaves 125-140).