Summary:

There is growing concern about nitrate contamination in groundwater and surface water across much of Minnesota. The problem is especially pronounced in southeastern Minnesota. This presentation will summarize efforts by the Minnesota Geological Survey to understand geologic controls on nitrate transport in the Paleozoic bedrock-dominated landscape of southeastern Minnesota. One important outcome of our research is that variability in the correlation between agricultural land use (percent row crop) and baseflow nitrate concentrations can be accounted for by varying proportions of dilution from older, less-impacted water relative to more locally sourced, younger, nitrate-enriched water from largely unconfined, shallow aquifers. Our results also showed that the response time of baseflow nitrate concentrations to changes at the land surface is also dependent on hydrogeologic setting in a similar manner. For example, in some geologic settings where baseflow is derived from deep, confined aquifers, changes at the land surface may take decades to be manifested in water chemistry.  Future nitrate studies should consider these relationships. For example, efforts to evaluate the surface and groundwater response to current changes in agricultural practices should aim to monitor springs, streams, and wells positioned in hydrogeologic settings favoring short lag time responses.

Biography:

Tony Runkel is Chief Geologist of the Minnesota Geological Survey, and adjunct professor in the Department of Earth Sciences; both are units of the University of Minnesota. Beyond his responsibilities as Chief Geologist, he conducts research that targets geologic controls on groundwater flow, especially the transport of contaminants. Recent emphasis has been on fractured rock hydrogeology. Tony grew up in southeastern Minnesota, and holds a B.A. in Geology from the University of Minnesota, an M.S. from the University of Montana, and a Ph.D. from the University of Texas at Austin.