WATER TRACING IN THE CRYSTAL CREEK WATERSHED IN MINNESOTA

The Root River Field to Stream Partnership is a multi-agency effort led by the Minnesota Dept. of Agriculture (MDA). The Partnership’s goal is to document nutrient losses by agriculture to surface water and groundwater and to apply sustainable best management practices to reduce those losses. One of the Partnership’s three study areas is the Crystal Creek Watershed (CCW) in south central Fillmore County, MN.

The CCW is located on a well-developed, highly integrated karst hydrologic system in Ordovician Galena Group carbonates. The bedrock is overlain by thin loess and glacial deposits. Groundwater is a significant receptor of the nutrient losses via infiltration through the thin soils and surface runoff into sinkholes and sinking streams. The CCW became an interesting target for water tracing research after the MDA secured landowner cooperation, instrumented a continuous-recording monitoring station at the end of Crystal Creek, and began detailed, multi-year inventories of agricultural activities in CCW. Fluorescent dye tracing from sinkholes to springs had been conducted in several of the surrounding watersheds to determine surface water-groundwater connections and map spring catchment areas, but little information was available about the CCW.

Collaboration between the MDA, the Minnesota Dept. of Natural Resources, and the University of Minnesota has conducted 14 dye traces between 2010 and 2016 in the CCW. In 10 traces at least one connection was confirmed between the sinkhole dye input and a monitored spring or creek with groundwater flow velocities up to 1.5 miles/day. The positive results, drawn as springshed maps (spring catchment maps), illustrate these connections and begin to delineate the springsheds. As expected some sinkholes outside of the surface water boundaries of the CCW feed springs on Crystal Creek. Some of the sinkholes in the CCW feed springs outside of the surface water boundaries of the CCW. These results complicate, but improve the nutrient loss calculations. Future tracing work can potentially improve our understanding of the hydrologic system under varying flow regimes. Dye traces and springshed maps have been crucial in helping elevate discussions with local watershed landowners and farmers about surface water-groundwater interactions and strategies to minimize nutrient losses.