Project: Ecosystem-scale responses of coupled carbon and nutrient cycles to dramatic shifts in benthic communities: The Upper Great Lakes

NSF Award Abstract:
This project will study the effects of invasive zebra and quagga mussels on the biology and chemistry of the Great Lakes. These mussels have caused unprecedented changes to lake ecosystems, including large shifts in water quality, altered fisheries and diminished recreational opportunities. The mechanisms by which the invasion has affected ecologically important aspects of lake chemistry remain uncertain, making it difficult to predict future changes. This project will quantify how mussels affect sediment and water nutrient chemistry in Lakes Michigan and Huron. Important missing data on altered chemical exchange between sediments and water will be collected to quantify the processes controlling nutrient cycles in the Great Lakes as water moves to the coastal ocean. Development of improved numerical models from this work will allow evaluation of other freshwater and marine systems affected by similar mussel invasions and other stressors. The project will train a post-doctoral researcher and several graduate and undergraduate students in highly interdisciplinary research. Educators and the public at large will be served through creation of freely available, online multimedia content, as well as outreach events at the Duluth Great Lakes Aquarium, the Shedd Aquarium in Chicago, and the Discovery World Science Museum in Milwaukee.

Benthic communities can have large impacts on benthic-pelagic chemical exchanges, but the ecosystem-scale effects of benthos on coupled transformations of carbon, nitrogen, and phosphorus (C-N-P) are rarely addressed and virtually unquantified in freshwaters. The recent invasion of the Laurentian Great Lakes, the world's largest freshwater ecosystem, by dreissenid (zebra and quagga) mussels coincided with massive changes to ecology and water chemistry. Consequences of the invasion include a large and unexplained decline in phosphorus levels, enigmatic reversal of past trends in nitrate levels, and the near-disappearance of native bioturbating Diporeia amphipods. Modeling suggests that nutrient fluxes from sediments could have been strongly affected by shifts in benthic community. Mechanisms explaining these changes, however, remain obscure and thus hamper model predictions of future ecosystem trajectories. Researchers from the Large Lakes Observatory - University of Minnesota Duluth will determine the effects of established dreissenid populations on sediment geochemistry and nutrient dynamics in the Great Lakes by conducting detailed studies in dreissenid-invaded Lakes Michigan and Huron and dreissenid-free Lake Superior. A team of biologists and geochemists will (1) obtain field data to characterize sediment geochemistry of C-N-P, asses rates of biogeochemical processes, and dreissenid effects on chemical and physical properties of sediments, (2) conduct lab experiments to determine how functional traits of sessile dreissenids vs. burrowing Diporeia affect sediment characteristics and chemical fluxes, and (3) use reactive-transport and mass-balance models to understand the whole-lake geochemistry of carbon and nutrients in dreissenid-invaded lakes. This work will advance understanding of the ecology of the great lakes and generally improve models of sediment - water column interactions in aquatic ecosystems.