J. Magner, M. Gernes, M. Jacobson, K. Brooks, D. Engstrom 2
In the fall of 1987, a drained sixty acre agricultural field receiving runoff from over 3,200 acres, became a restored prairie pothole wetland with the installation of a ditch block weir. The objectives of this study included: the assessment water quality - loads in/out of the wetland, processes influencing phosphorus retention, and the rate of macrophyte re-establishment. Stream flow and complete water chemistry (26 parameters), including the stable isotopes of hydrogen and oxygen were measured to evaluate water quality and track hydrologic pathways of water movement in and out of the wetland. Transects were established from the edge of the wetland through the emergent vegetation zone. Vegetation sampling results suggest an early successional community dominated by mudflat species in the seasonally flooded mudflats. Perennial sedge and bullrush species occurred less than five percent of the time. Cattails dominated a narrow zone at the edge of the seasonal low levels. Submergent and floating vegetation beds have not established well within the semi-permanent pool. Sediment cores were recovered from a grid of 20 sampling stations to assess sediment deposition and total phosphorus and P-fractions. Wetland sediments were never more than two cm thick and in most cases were one cm or less. The estimated annual phosphorus retention was 25-75 kg/year. The restored wetland retained all of its watershed runoff nutrients and sediment during the first four years of restoration. Water years 1992 through 1994 were climatically normal to slightly above normal precipitation. Annual average wetland loads for 1992-1994 resulted in reductions for TSS, nitrate-nitrogen and both total and ortho phosphorus of 86 percent, 63 percent and 27 percent, respectively. However, specific runoff events varied with P exports occurring in the spring. Results indicate that the restored wetland remains physically and biochemically in transition. The most dominant factor influencing wetland redevelopment and affecting wetland water quality was the hydrology driven by climatic variability.
