Linking hydrology with biogeochemistry using stable isotopes to understand the consequences of ecosystem disturbance

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Understanding how pollutants move through the environment and are transformed within it is important to developing plans for mitigating pollutant effects. Some pollutants, including heavy metals, strongly bind to soil and other solids in the environment. Despite this affinity, these pollutants continue to move into aquatic ecosystems when soils are flushed by rainstorms or melting snow. Linking the movement of water and chemical reactions in the environment together at appropriate spatial and temporal scales is difficult, but critical to providing the process information necessary to deal with changing levels of pollution and possible alterations to the environment (climate change, logging). Recent advances in techniques involving enriched stable (non-radioactive) isotopes should provide a means for linking these processes. The pollutant to be studied in this research program is mercury, a toxic metal. Mercury is particularly dangerous because it can undergo biogeochemical transformations in the environment that form methylmercury, a potent neurotoxin that accumulates in fish and wildlife. The consumption of fish is the primary pathway for human exposure. Through a number of controlled laboratory and field experiments using stable isotopes, this research will first investigate and develop a model of how mercury moves between ecosystem compartments such as forests and wetlands. It will then investigate the spatial and temporal variability of this movement and its effects on the production of methylmercury. This information will be used to directly test how logging affects the movement and transformation of mercury in watersheds. Together, this knowledge will lead to more predictive possibilities from models, an improved understanding of how land-use changes affect mercury cycling, and an opportunity to develop effective strategies for preventing further methylmercury pollution in watersheds.