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.
The semi-arid climate and flat relief result in large endorheic (interior) drainage basins across the Canadian prairies. Due to hydrologic / climate variability and agricultural land-use lakes are highly sensitive to desiccation, salinization and eutrophication. Decadal-scale analyses of water quality and food-web composition of 20 prairie lakes indicated that 1) water availability is largely dependent on winter precipitation, 2) food-web composition is predominantly determined during drought intervals, and 3) controls of fish assemblages have changed from elevated salinity to winter kill due to recent changes in land-use intensity. Current research is evaluating the potential impacts of future climate change to help develop adaptive management practices.
The fast pace and unprecedented scale of development of the oil sands industry in western Canada has raised concerns of potential acidification and eutrophication of aquatic systems. Especially vulnerable are downwind boreal Shield lakes in north-west Saskatchewan, one of the most acid-sensitive and nutrient-poor regions in Canada. First results based on large-scale lake surveys showed that zooplankton communities in many lakes show signs of acid stress. To assess if the observed acid-stress is caused by the recent development of oil sands or a natural phenomenon, we have been conducting paleo-limnological investigations, which will reconstruct changes in biological and chemical parameters over the last ~100 years.
This theme investigates how lakes regulate climatic processes and how, in turn, climate influences lakes and society. Our prairie LTER program reveals that climate warming since 1990 has increased lake pH by 1.5 units and stimulated CO2 capture by lakes to rates equivalent to 50% of provincial agricultural emissions. Further, we show that influx of energy (E) increases spatial synchrony of lake properties, whereas the influx of mass (m) reduces temporal coherence, particularly that of aquatic food webs. Our whole-lake experiments, surveys, and stable isotope analyses reveal that variation in jet stream position, and consequently winter precipitation, is the main climatic mechanism structuring central Canadian lakes, despite chemical and food-web effects of E exchange during summer. Finally, we are developing a series of paleo-climate reconstructions to forecast the risks of droughts on the Canadian Prairies. These conditional probability analyses estimate that the risk of severe (1930s) droughts is as high as 45% by 2030 AD, with expected losses of $650 billion. This information is being used by crop insurance, agricultural and hydroelectric corporations in all Prairie Provinces to evaluate their susceptibility to climate extremes.
Application of basic ecological knowledge is essential to sustain ecosystems and their services. Here we use our novel limnological and statistical approaches to quantify causes of environmental degradation in diverse aquatic ecosystems, including First Nation’s territories, coastal estuaries, prairie lakes, northern freshwater deltas, salmon nurseries, high latitude ecosystems, alpine lakes, and iconic sites worldwide (e.g., Winnipeg, Windermere, Neagh, Champlain, Great Salt, Vattern, Kinneret, Okeechobee). In all cases, we balance novel scientific discovery with clear management recommendations to initiate legislative change and enable sustainable management (see above). Our leadership has resulted in the Energy-mass (Em) flux framework, a new conceptual paradigm adopted by 15 international research groups to quantify the unique and interactive effects of humans and climate on lakes, and formally unify limnology and paleoecology.