Collaborative research: Regulation of lake productivity by terrestrial dissolved organic matter

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Lakes are economically and culturally important components of the landscape. Microscopic algae and aquatic plants strongly influence the benefits that humans derive from lakes, because they influence water quality and are the foundation of the food web supporting species important to commercial, recreational, and subsistence fisheries. The abundance and growth rate of algae contribute to lake productivity, and lake productivity is affected by inputs of natural and human-derived nutrients, primarily phosphorus and nitrogen. Lake productivity is also influenced by inputs of organic molecules from the watershed which compete with algae for light and, at high concentrations, can result in tea-colored water. Inputs of nutrients and organic molecules from the watershed vary substantially from lake to lake and change through time as well. The researchers will study the implications of watershed inputs for lake water quality, food webs, and other benefits humans derive from lakes. Their research will experimentally test and refine a mathematical model of lake productivity and ultimately predict the response of lakes to watershed inputs of nutrients and organic molecules that vary across the landscape and through time. The project will support the training of six undergraduate students, including students from Puerto Rico and Native American populations. These students will conduct independent research projects as part of a ten-week field ecology program. The researchers will use replicated mesocosm experiments, a comparative study across broad natural gradients, and a whole-lake manipulation to test hypotheses drawn from their mathematical model of lake productivity. First, predicted counteracting effects of terrestrially-derived organic carbon and nutrients will be evaluated using replicated mesocosms subjected to supplies of these elements in varied ratios. Second, the project will use a comparative survey of lake food web productivity to test predictions for how lake size alters the effect of terrestrial organic carbon and nutrients. Third, the researchers will embrace the full complexity of natural ecosystems in a whole-lake manipulation of terrestrial organic carbon and nutrient inputs. Finally, following refinement of the mathematical model of lake productivity based on experimental results, the researchers will use a global meta-analysis to test the general applicability of the mathematical model.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.