Derby, Nathan Erik, M.S., Department of Soil Science, College of Agriculture, North Dakota State University, April 1997. Depression-focused Recharge and Solute Transport to a Shallow Aquifer in Southeastern North Dakota. Major Professor: Dr. Raymond E. Knighton.

Agriculture has been named as a non-point source of ground water contamination for many years. With the advent of Best Management Practices (BMPs) and site-specific, variable rate technology, more emphasis is being placed on field variability. One area that needs to be investigated further is the spatial variability of ground water recharge and contamination relative to ground surface topography. A tracer study was initiated on a pre-existing BMP research site to monitor solute through the vadose zone into the ground water to verify findings on ground water and leachate quality that have been monitored at the site since 1990. The quarter section research site contains primarily fine sandy loam soils with a shallow water table. Granular potassium chloride (KCl) was surface applied to two areas overlying subsurface drains and to one area instrumented with soil solution samplers and monitoring wells. One of the subsurface drain tracer plots was located on level ground while the other two sites were in small topographic depressions. The applied chloride was found to move rapidly to the shallow ground water under the depressional areas after infiltration of spring snowmelt because of the compounding effects of increased water available for infiltration in the depression and nearness of the water table to the soil surface. Excessive rainfall events were also responsible for the rapid transfer of the applied chloride tracer. The plot situated on level ground did not contribute significantly to ground water contamination from the applied chloride. The findings of this study indicate that, under certain conditions, it may be necessary to manage fertilizer and pesticide applications within a field based on topography. These locations can then be integrated into a site-specific farming plan, and chemical applications can be managed to reduce the potential for ground water contamination.