Flow and Transport Processes in a Riverine Peat Deposit

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The subsurface flow regime within wetlands is well understood only in very few locations, despite the large areal importance of peaty, water-saturated terrain on Earth's surface and the hydrologically strategic location of wetlands in many catchments. Ecologists have long attributed key aspects of peatland development to the interactions of hydrology, chemical transport, and plant growth. Wetlands can also play a critical, controlling role in the transport and fate of toxic chemicals. The present project is focused on such a wetland, where a deep peat deposit interacts with both a heavily contaminated river and a glacial outwash aquifer containing a former municipal wellfield. In this setting the fundamental processes of subsurface water transport through a peatland will be studied, with a focus on peat characteristics at several spatial scales and the processes that subsurface water flow and chemical transport. One working hypothesis is that, due to heterogeneity on the scale of the peat formation, rates of both water and pollutant movement through the wetland may significantly exceed the low rates commonly attributed to peat formations. Accordingly, a variety of measurements and tests will be conducted to define and assess the importance of these heterogeneities. Investigative techniques will include head and hydraulic conductivity measurements, a piezocone survey, aquifer stress/tracer tests, chemical analyses of soil and groundwater, and speciation analysis and sequential extractions of certain toxic metals.