Collaborative Proposal: Redox Processes in the Sedimentary Porewaters of Prairie Pothole Lakes: Implications for the Attenuation of Pesticides

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AbstractThis award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5). Prairie pothole lakes (PPL) are important hydrologic features in the glacial till of the Upper Midwest. A number of these lakes have developed unique water chemistries, including extremely high (10?s to 100?s of millimolar) levels of sulfate. Sulfate in these waters undergoes reduction in the sediments to produce reduced sulfur species that can act as both nucleophiles and reductants. In sulfate poor lakes, Fe(II) and dissolved organic matter (DOM) may also become important reductants, but this will be influenced by DOM composition. To date nothing is known about the biogeochemistry of naturally occurring reductants in PPL sediments. Given their unique water chemistry we hypothesize that both reductive and non-reductive reactions are able to abiotically transform certain heavily used agrochemicals in prairie pothole sediments. The extent to which this can occur will be determined by the presence and amount of reactive chemical species present. These species include dissolved reduced sulfur species (bisulfide and polysulfides) and to a lesser extent a combination of Fe(II) and dissolved organic matter in potholes that lack high levels of reduced sulfur. We will conduct a one year ?pilot? study in the Cottonwood Lakes of North Dakota to learn more about the abundance and reductive potential of sulfur species, Fe(II), and DOM in these systems. Sediments and water samples will be collected to screen for pesticides commonly used in the region. Porewaters will be carefully collected under anoxic conditions to quantify the concentration of the important reductants, and determine their ability to transform two commonly used herbicides trifluralin and alachlor. We will also conduct electrochemical studies to assess the speciation of the various reductants using voltammetry. The ultimate goal of this pilot-project is to demonstrate to the scientific community at large the promise that these unique aquatic ecosystems have to naturally attenuate pesticides. It will provide us with valuable background information regarding the type and amount of reactive chemical species present in sediment porewaters and their potential to transform pesticides. Once armed with this information we will be able to examine the role of these lakes within a larger hydrologic context.