Collaborative Research: Hydrology and Geochemistry of Prairie Pothole Lake Sedimentary Pore Waters: Implications for the Attenuation of Pesticides

Intellectual Merit: Prairie pothole lakes (PPLs also referred to as wetlands) are important hydrologic features in the glacial till of the Upper Midwest. The hydrology and climate of the region coupled with the composition of the till have developed water chemistries unique to PPLs, including extremely high levels of sulfate. Results of a pilot project funded by NSF showed that sulfate undergoes reduction in the sediments to produce reduced sulfur species in the mM levels. Our data demonstrated that unaltered PPL pore waters sampled from lakes P1 and P8 in the Cottonwood Lakes Area abiotically and rapidly degraded chloroacetanilide and nitroaromatic pesticides (which are heavily used in row crop agriculture in the region). Additionally, we found dissolved organic matter levels in the 100s of mg/L-C in the pore waters, which are among the highest measured for lacustrine systems. This proposal expands upon our previous work to understand the linkages between hydrology, the evolution of the unique biogeochemical composition of PPL pore waters, and its ability to attenuate agricultural pesticides. We hypothesize that changes in the local hydrology in response to drought, evapotranspiration, and precipitation can influence the composition and abundance of chemical species capable of attenuating pesticides. Our specific hypotheses are: 1). During periods of drought, evapotranspiration is an important driver of groundwater flow out of PPLs; 2). Extensive precipitation creates water table mounds that can reverse hydraulic gradients and cause groundwater to flow back into wetlands; 3). The biogeochemical composition of PPLs is influenced by these local and seasonally varying hydrologic processes; 4). Overland flow is capable of transporting both pesticides and other chemical constituents to PPLs; and 5). PPL pore water constituents are capable of attenuating other classes of commonly used pesticides beyond those studied in the pilot project.

Prairie pothole lakes are a critical hydrological and ecological feature of national and international importance (e.g., groundwater recharge, habitats for waterfowl and other fauna, etc.). Their unique water chemistry makes them an important means for mitigating the effects of pesticides used in this extensively farmed region. Our research could influence how these lakes are managed in the future, especially with respect to the intractable problem of nonpoint source agricultural pollution. The proposed research will support three graduate students who will be responsible for conducting the research and aiding our USGS colleagues. The students will coordinate research and sampling events between the collaborating universities and the USGS laboratories. Research results will be broadly disseminated through conferences, journal publications, and informal town hall meetings with local stakeholders. Outreach to high school students from underrepresented groups in science and engineering will occur through activities oriented non-residential summer camps. Further, we propose to recruit a high school teacher to accompany us on our sampling trips and share these experiences through electronic journals and in his/her classroom. This outreach initiative is based upon the NSF funded ARCUS TREC model.