WATER QUALITY MONITORING FROM 1988 TO 1991 AT THE IOWA ACADEMY OF SCIENCE'S PARISH FARM, GRUNDY COUNTY, IOWA

B.K. Nations and G.R. Hallberg


Iowa Department of Natural Resources, Geological Survey Bureau, 109 Trowbridge Hall, Iowa City, IA 52242-1319
Journal of the Iowa Academy of Science, in press

ABSTRACT


In May 1988 water sampling was initiated to evaluate the water quality in relation to management practices at Parish Farm, which is owned by Iowa Academy of Science. Initial results showed tile line effluent to have high levels of nitrate-nitrogen. Twelve monitoring wells were installed over a one year period to analyze shallow groundwater at the farm. The wells, tile lines, and surface water, were sampled monthly, through October, 1991, and the water analyzed for nitrate-N and some pesticides. Nitrate-N concentrations varied according to landuse and management of adjacent areas. Greater nitrate-N concentrations were detected from row-cropped areas than in the restored wildlife-vegetation buffer strip and prairie areas. The greatest concentrations (up to 79 mg/L) were associated with greater amounts of corn in the cropping sequence. Concentrations of pesticides were dependent on various factors such as chemical properties, season, hydrologic events, and patterns of use. Atrazine was the pesticide most often detected and was present in 46% of the samples. Seven agricultural pesticides used on the farm were detected in water samples with a maximum detected concentration of 6.9 g/L (for alachlor). Pesticide and high nitrate-N concentrations were detected in wells beneath the restored natural vegetation buffer areas; probably as a result of groundwater transport from application areas upgradient. The data suggest that the buffer strips were not effective at removing nitrate-N or pesticides from the groundwater flowing through these areas. Nitrate-N concentrations were high (often over 25 mg/L) during the study, in spite of improved N management on the farm. The high concentrations may be due to mobilization of excess residual nitrate-N that accumulated during the dry years prior to the monitoring.