Linking biodiversity across ecosystem boundaries

Terrestrial ecosystems are rapidly changing to meet the food and energy demands of a large and growing human population. Nearly half of the global terrestrial landscape is dedicated to agriculture and urban areas, contributing to biodiversity loss and alterations to global biogeochemical cycles. This simplification of our landscapes alters the quality and quantity of exported carbon and nutrients. Resultant shifts in the composition of these subsidies can affect community structure and the functional diversity of downstream aquatic ecosystems. In collaboration with Jim Cotner and Cody Sheik at the University of Minnesota, we investigate the effects of terrestrial biodiversity loss and chemical diversity of exported subsidies on downstream biodiversity and function of microbial communities. 


Effects of eutrophication on lake carbon cycling

Lakes are generally considered net sources of carbon dioxide to the atmosphere, but only a handful of studies have investigated CO2 flux in eutrophic and hypereutrophic lakes with autochthonous organic carbon pools. Using a combination of high frequency sensor measurements and optical organic matter characterization, we investigate the source and magnitude of inorganic carbon flux across trophic gradients. As more lakes become impacted by expanding agriculture and urbanization, understanding how eutrophic systems process, store, and export carbon will be critical to evaluating the role of lakes in global carbon cycles. 


Carbon concentrating mechanisms and harmful blooms

Harmful blooms are increasing in frequency and intensity worldwide. These trends are attributable to a perfect storm of climate change processes, land use alteration, and nutrient inputs. Clear links exist between ambient nutrient concentrations and bloom occurrence, but drivers of the specific timing and duration of these events remain unresolved. Several groups of phytoplankton including cyanobacteria are able to actively transport bicarbonate across their cell membrane when CO2 concentrations are limiting. This may provide a competitive advantage maintaining bloom biomass when CO2 is depleted. Using stable carbon isoptope analysis in 16 agriculturally eutrophic lakes, we found that CCMs appear to be triggered when water column CO2 drops below atmospheric equilibrium.  This mechanism not only maintains bloom biomass, but appears to sustain an influx of atmospheric CO2 to lake surface waters.