Comparative ecology of marine and freshwater phytoplankton

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/109932/1/lno1988334part20776.pd

Environmental control of phytoplankton cell size

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/109847/1/lno19741920361.pd

Late Pleistocene-Holocene chemical stratigraphy and paleolimnology of the Rift Valley lakes of central Africa

The interaction of climate and geology in Central Africa during Late Pleistocene and Holocene is examined. The study is based on sedimentological and limnological work on the main lakes of the Western Branch of the East African Rift Valley, particularly Lake Kivu, Changes in sediment chemistry, mineralogy and diatom assemblage provide a detailed histogram of lake level oscillations. Calculations indicate that the drop in lake level could be as high as 600 m for Tanganyika and 400 m for Kivu, Fluctuations in water levels.are the means for reconstruction of climatic events in tropical Africa of the last 15,000 years. Paleoclimatic comparison between tropical and temperate zones reveals that pluvial times coincide with the prominent interstadials in Europe, e.g. Bølling, Allerød, Climatic Optimum, and reversely, cool and dry periods in equatorial Africa with ice ages in the Northern Hemisphere. The African climatic sequence of pluvials and interpluvials is accompanied by corresponding periods of hydrothermal activity and quiescence. This may suggest that rain water exercises control on hydrothermal. activities.Prepared for the National Science Foundation under Grants GA-30641 and GA-35334

Hypothesized resource relationships among African planktonic diatoms

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/109870/1/lno19863161169.pd

Changing ecology of Lake Victoria cichlids and their environment: evidence from C13 and N15 analyses

Eutrophication is an increasing global threat to freshwater ecosystems. East Africa’s Lake Victoria has suffered from severe eutrophication in the past decades which is partly responsible for the dramatic decline in haplochromine cichlid species diversity. However, some zooplanktivorous and detritivorous haplochromine species recovered and shifted their diet towards macro invertebrates and fish. We used four formalin preserved cichlid species caught over the past 35 years to investigate whether stable isotopes of these fish are reflecting the dietary changes, habitat differences and if these isotopes can be used as indicators of eutrophication. We found that d15N signatures mainly reflected dietary shifts to larger prey in all four haplochromine species. Shifts in d13C signatures likely represented habitat differences and dietary changes. In addition, a shift to remarkably heavy d13C signatures in 2011 was found for all four species which might infer increased primary production and thus eutrophication although more research is needed to confirm this hypothesis. The observed temporal changes confirm previous findings that preserved specimens can be used to trace historical changes in fish ecology and the aquatic environment. This highlights the need for continued sampling as this information could be of essence for reconstructing and predicting the effects of environmental changes

Alternative Pest Control Methods for Homeowners

This fact sheet explains how using a comprehensive, or integrated pest management approach, will help home gardeners reduce their reliance on pesticides for pest control

Як уникнути підйому рівня води?

East Africa’s Lake Victoria provides resources and services to millions of people on the lake’s shores and abroad. In particular, the lake’s fisheries are an important source of protein, employment, and international economic connections for the whole region. Nonetheless, stock dynamics are poorly understood and currently unpredictable. Furthermore, fishery dynamics are intricately connected to other supporting services of the lake as well as to lakeshore societies and economies. Much research has been carried out piecemeal on different aspects of Lake Victoria’s system; e.g., societies, biodiversity, fisheries, and eutrophication. However, to disentangle drivers and dynamics of change in this complex system, we need to put these pieces together and analyze the system as a whole. We did so by first building a qualitative model of the lake’s social-ecological system. We then investigated the model system through a qualitative loop analysis, and finally examined effects of changes on the system state and structure. The model and its contextual analysis allowed us to investigate system-wide chain reactions resulting from disturbances. Importantly, we built a tool that can be used to analyze the cascading effects of management options and establish the requirements for their success. We found that high connectedness of the system at the exploitation level, through fisheries having multiple target stocks, can increase the stocks’ vulnerability to exploitation but reduce society’s vulnerability to variability in individual stocks. We describe how there are multiple pathways to any change in the system, which makes it difficult to identify the root cause of changes but also broadens the management toolkit. Also, we illustrate how nutrient enrichment is not a self-regulating process, and that explicit management is necessary to halt or reverse eutrophication. This model is simple and usable to assess system-wide effects of management policies, and can serve as a paving stone for future quantitative analyses of system dynamics at local scales

Bioaccumulation and biomagnification of mercury in African lakes: The importance of trophic status

Despite the global prevalence of both mercury (Hg) contamination and anthropogenic eutrophication, relatively little is known about the behavior of Hg in eutrophic and hypereutrophic systems or the effects of lake trophic status on Hg uptake and trophodynamics. In the current study we explore Hg trophodynamics at 8 tropical East African study sites ranging from mesotrophic to hypereutrophic, in order to assess the influence of lake trophic status on Hg uptake and biomagnification. Comprehensive water, plankton and fish samples were collected for analysis of total mercury (THg) and stable carbon and nitrogen isotopic ratios. We found evidence that uptake of THg into phytoplankton tended to be lower in higher productivity systems. THg concentrations in fish were generally low, and THg trophic magnification factors (TMFs; representing the average increase in contaminant concentrations from one trophic level to the next) ranged from 1.9 to 5.6. Furthermore TMFs were significantly lower in hypereutrophic lakes than in meso- and eutrophic lakes, and were negatively related to chlorophyll a concentrations both across our study lakes, and across African lakes for which literature data were available. These observations suggest that THg concentrations were strongly influenced by trophic status, with year-round high phytoplankton and fish growth rates reducing the potential for high THg in fish in these productive tropical lakes.publishedVersio