Twin Cities WRS Seminar
Individual and Interactive Effects of Climate Change and Nutrient Pollution on Aquatic Ecosystems
Agricultural intensification and climate change are two of the primary causes of impaired waterbodies in North America. At the global scale, fertilizer use has led to a twofold increase in nitrogen and a fourfold increase in phosphorus available for primary producers in the environment. Large storm events transport greater than 80% of the annual phosphorus load from watersheds into lakes, and more frequent and intense storms associated with climate change will likely increase phosphorus run-off. Across North America, 40% of lakes are in the “most disturbed” category based on phosphorus pollution (data from the Environmental Protection Agency’s National Lake Assessment), while 80% of waterbodies in the northern great plains are “most disturbed”. As a result of these eutrophic conditions, lake phytoplankton communities are increasingly dominated by cyanobacteria. Cyanobacteria are a major concern for eutrophication management because they produce toxins and they are poor food resources for lake food webs. In fact, 20% of lakes in the northern great plains have cyanobacterial toxin concentrations greater than the drinking water limit established by the World Health Organization. The goal of my research is to identify what conditions lead to abundant cyanobacteria and elevated cyanobacterial toxins. I found that a climate-land use interaction was an important predictor of
phytoplankton community composition; low ratios of nitrogen to phosphorus lead to more nitrogen-fixing cyanobacteria but not communities dominated by cyanobacteria. Also, in a series of prairie lakes, I found that cyanobacterial toxins are increasing in concentration and are detectable for a greater proportion of the summer. These trends coincided with increasing summer temperatures and shorter ice duration. The combined effects of climate change and agricultural intensification are changing nutrient loads, nutrient ratios, and water temperate contributing to the global expansion of harmful algal blooms.