The effects of multiple stressors on the biogeochemistry of lakes and their catchments: mass budgets, long-term trends and modeling

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The major objective of this proposal is to evaluate how human activities interact with each other in causing environmental change in lakes, streams and catchments. I will do this by utilizing an existing long-term database that includes climate, hydrologic, chemical and physical data measured over the past 35 years for a set of 8 lakes, 24 streams and their catchments that are located in the southern part of Canada's boreal ecozone. This environmental database is one of the most detailed and long-term records in the world. For some data types such as lake chemistry mass balances, it is the most complete dataset in existence. In addition, I will utilize shorter-term data measured over the past 3 years for several sub-catchments of the Lake Simcoe basin that are south of the boreal ecozone and that have very different chemistry. The stressors that are considered here are climate change, nutrients, acid deposition and trace metal contamination. I will use these data to test a number of hypotheses, for example, that climate factors that are controlling ecosystem acidification and recovery from acidification subsequently affect nutrient (phosphorus) levels and thus lake productivity. I will also investigate changes in dissolved organic matter cycles that may result in changes in greenhouse gas production and in trace metal availability. There will be a strong focus on developing models that will allow us to make quantitative predictions about the future state of ecosystems. I will use the available data to modify existing models of acidification to include nitrogen species and the transformations between inorganic and organic nitrogen; this refinement will allow much more accurate estimation of critical loads of acid to the Canadian environment.