Water quality of urban freshwater ecosystems is widely impaired by eutrophication, with little recent improvement and much potential for further degradation due to urban expansion and intensification. Despite the degradation of water quality in urban streams and lakes and adjacent coastal areas, relatively little is known about the relative importance of specific nutrient sources and the processes that regulate their movement across highly modified land-water interfaces. To better understand the nutrient sources and cycles that affect aquatic ecosystems, we are examining nutrient movement through urban drainage networks in the Twin Cities of Minnesota. This research relies on collaboration with the Capitol Region Watershed District, and is supported by the Institute on the Environment and the MN Water Resources Center. See http://environment.umn.edu/grant/improving-urban-vegetation-for-water-quality/ for more information.
Stream and River Ecosystem Dynamics
Aquatic ecosystems are influenced by both external inputs of water and materials from surrounding watersheds, and by internal cycling. In past and present projects, we are working to understand 1) how interactions between landscapes and stream channels affect watershed nutrient cycles and food webs dynamics and 2) the interactions of physical and biological drivers in determining the ecological processes throughout stream networks. Currently research, much of it based at UC Berkeley's Angelo Coast Range Reserve, examines regulation of productivity and food web structure in streams, the role of nitrogen fixation in stream ecosystems, and the influence resource stoichiometry on the dynamics of heterotrophic and autotrophic food webs. A new project examines interactions of climate change and land use on watershed ecology and biogeochemistry (more information). We are also interested in applications of food web research toward assessing impacts of invasive species, and understanding effects of climate and land use change on river ecosystems. Collaborators include Anika Bratt and Drs. Michael Limm (Holy Names College), Efi Foufoula (UMN), Mary Power (UC Berkeley), John Schade (St. Olaf College), and Jill Welter (St. Catherines University).
Nutrient Cycling in Lakes
Lakes are increasingly recognized as playing important roles in local to global scale biogeochemical cycles. Despite increased attention to the role of lakes in cycling of carbon, nitrogen, and phosphorus, much less is known about the factors that regulate their functioning in these element cycles. Our work seeks to understand the factors that influence nitrogen cycling rates, with a focus on the influence of effects of alternations to carbon and phosphorus availability. Current projects funded by NSF and Minnesota Seagrant are focused on the Laurentian Great Lakes, with intensive investigations of Lake Superior and Erie, and near shore areas that may function as hotspots for nitrogen cycling. Collaborators include Drs. George Bullerjahn (BGSU), Gaston Small (University of St. Thomas), Michael McKay (BGSU), Emily Stanley (UW Madision), and Robert Sterner (UMN).
Mercury in Aquatic Ecosystems
Mercury contamination in aquatic ecosystems is widespread globally but controls over its bioaccumulation and transformation in ecosystems are poorly known. Our research seeks to provide new information regarding the controls of mercury cycling in streams and watersheds. In projects in California and Minnesota, we are examining environmental factors important in determining mercury concentrations in stream biota. Specifically, we are studying how factors associated with stream size (e.g. organic carbon sources, productivity, food web structure) and watershed land use mediate the production of methylmercury and subsequent transfer to stream biota. Collaborators in this research include Drs. Martin Tsui (U Michigan), Sue Eggert, Stephen Sebestyen (both at USFS in Grand Rapids MN), Joel Blum (U Michigan), and Ed Nater (UMN).