Collaborative LTREB Proposal: Will increases in dissolved organic matter accelerate a shift in trophic status through anoxia-driven positive feedbacks in an oligotrophic lake?

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Lakes provide many services to society, such as clean drinking water and productive fisheries. Many lakes, however, are now experiencing increased input of carbon and nutrients, warming temperatures, and declining ice cover, which may reduce water quality or cause blooms of potentially harmful algae. Specifically, many lakes across the United States are experiencing increased browning due to high loading of organic matter leached from land plants. Browning reduces water clarity and interferes with drinking water management practices. In addition, it can cause other changes that may lead to rapid long-term declines in water quality. This research will test the hypothesis that browning may reduce oxygen concentrations in lakes. Low oxygen can cause nutrient release from lake sediments that may increase algae blooms, leading to lake eutrophication. Understanding the effects of browning will increase knowledge of lake ecosystems, and improve forecasts of how lakes will change as their surrounding environments change. This research will also train graduate and undergraduate students, and will lead to better public understanding of threats to lake water quality.Ecological tipping points are of vital interest as anthropogenic activities rapidly transform natural ecosystems. Changes in dissolved organic matter (DOM) represent one important potential driver of tipping points in aquatic ecosystems. This project will investigate whether increases in terrestrial DOM loading can push clear-water oligotrophic lakes beyond a critical tipping point by stimulating hypolimnetic anoxia and sediment DOM and phosphorus release, which may initiate a positive feedback loop of decreasing water clarity, stronger thermal stratification, and enhanced hypolimnetic anoxia. This feedback loop accelerates ecological change and ultimately may shift lake trophic status toward greener, mesotrophic to eutrophic as well as browner, dystrophic conditions. This project will extend a long-term data set of water quality variables sampled since the late 1980s in two lakes in or near the Lacawac Sanctuary and Biological Field Station, located in northeastern Pennsylvania. Complementing these long-term observations, experiments and modeling will be carried out to understand feedbacks associated with browning and enhancing understanding of broader patterns of change in inland water bodies. The project will support a regional lake monitoring network in Pennsylvania and closely interface with GLEON, the Global Lake Ecological Observatory Network.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.