Nitrogen Effects on Lakes

Our research demonstrates that the structure and function of lake ecosystems is regulated on annual to millennial time scales by the influx of N from external sources, including atmospheric deposition, biological fixation of N2, migratory fishes, terrestrial DOM, forestry, agriculture, and urban pollution. Significantly, industrial N has polluted even remote polar lakes for over 120 years, thereby defining the onset of the Anthropocene. We show for the first time that early lake productivity and ontogeny is regulated by influx of N, not phosphorus (P), in sharp contrast to many modern freshwaters. As well, we uniquely find that N and other subsidies from marine salmon regulates algal beta-diversity, predation regimes, productivity, and basic N biogeochemistry of natal lake ecosystems. Finally, our experimental, LTER and fossil research has resulted in a new paradigm for lake eutrophication by demonstrating for the first time that pollution of P-rich lakes with urea and other forms of N increases production and toxicity of cyanobacteria by up to 500% on diverse temporal and spatial scales. This work resulted in legislation to regulate lake pollution with N, including the 2011 Save Lake Winnipeg Act.