Influence of Tillage System on Water Quality and Quantity in Prairie Pothole Wetlands

Since zero tlllage (ZT) requires more herbicide and fertilizer use than conventional tillage (CT) and may improve water infiltration into soil, the system may negatively impact prairie pothole wetlands.In this paper, the hydrology and water quality of pothole wetlands tn zero tillage and conventional tillage systems were compared by monitoring three wetlands (ZT-L, ZT2 and CT) from 1995 to 7997, ar'd during a runoff-producing summer storm in 1998.Wetland water levels were recorded during snowmelt runoff and throughout the unfrozen period.Water samples from the wetlands were analyzed for total P, ortho R NOr-NO3, NFI3 and a suite of commonly-used herbicides.In each year of the study, similar snow accumulations generated more runoff per unit area from the ZT basins than the CT basin.Water levels were similar in the three wetlands in the spring of 1995, but by 7997 the water depths were less in the ZT wetlands than in the CT wetland.Despite greater fertllizer use in the ZT basins, we did not observe a consistent effect of tillage system on available N and P in the surface soil.Phosphorus concentrations were generaily higher in the ZT than the CT wetlands during snowmelt but there was no consistent effect of tillage on NOr-NO, or NH, concentrations in the wetlands.The herbicides found in all three wetlands included those that were applied during the study and some that were not.At least one herbicide was detected in trace amounts in approximately 750/o of samples from the wetlands. REsUME