LTREB: Response of a Reservoir Ecosystem to Declining Subsidies of Nutrients and Detritus

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Intellectual Merit. The proposed LTREB research will use long-term data to test hypotheses about how reservoir ecosystems respond to reduced nutrient and detritus (sediment) subsidies. Nutrient and sediment subsidies to the study site, Acton Lake, are declining because of changes in agricultural practices in the lake's agricultural watershed. These include a marked increase in conservation tillage and a reduction in phosphorus fertilizers. These changes appear to bedriving decreases in concentrations and loads of phosphorus and suspended sediments in Acton Lake's inflow streams, based on an 8-year trend. In Acton Lake, concentrations of suspended inorganic sediment have declined, and biomass of phytoplankton has increased, over this period. We hypothesize that reductions in detritus input will induce a decline in the population density of an important detritivorous fish, the gizzard shad, leading to further changes in the ecosystem. In addition, we hypothesize that phytoplankton and zooplankton species composition will change such that taxa typical of high productivity (eutrophic) habitats will decline and those typical of mesotrophic conditions will increase. This research will be unique in that it will consist of a long-term study on interactive effects of multiple ecosystem subsidies: 1) nutrient subsidies from watersheds, 2) detritus subsidies from watersheds, and 3) nutrient subsidies via detritivorous fish. The proposed research is also unique because it integrates watersheds, streams, and a reservoir ecosystem. Although there are many studies of eutrophication and recovery in natural lakes, we know little about how reservoirs respond to reduced nutrient subsidies. Because nutrient and sediment exports are declining in many agricultural watersheds in the US and globally, this research will shed light on how these understudied ecosystems respond to a widespread and common influence.Broader Impacts. The proposed research will have several educational, environmental and societal impacts. Undergraduates will do summer research through a variety of programs including an REU Site Program. Primary school teachers will be recruited along with graduate students and postdocs, as well. Data will be shared and collaborations continued with state and federal agencies. This research will facilitate decision-making in regards to watershed management, alternative agricultural practices (hence socio-economic influences on farmers), water quality, and fisheries management.