QUALITY OF GROUND WATER AND SURFACE WATER AT A PRAIRIE AND WETLAND RESTORATION SITE, NORTHWEST MINNESOTA

In 2002, the Nature Conservancy began restoring 24,000 acres of drained agricultural land to native prairie and wetlands in Polk County, Minnesota. Concurrently, the U.S. Geological Survey began studying the ground water and surface water of the restoration area to document hydrologic changes resulting from the land-use change. Synoptic samples collected in the summer of 2004 provide a snapshot of water quality before the restoration is completed and serve as a reference against which to later compare water quality influenced by the restoration. Ditches, wetlands, and wells were sampled for major ion, nutrient, herbicide, water isotope, and dissolved gas content. Well samples represent water in surficial and buried sand and gravel aquifers within glacial sediments. A subset of these sites has been monitored about monthly for nutrients since fall 2002. Waters generally are of the calcium-magnesium bicarbonate type. A few samples of both ground and surface waters have substantial sulfate concentrations. Concentrations of agriculturally-related nutrients and herbicides are highly variable across the restoration area, but appear somewhat coincident with areas of recent chemical use. Among the acetamide and triazine herbicides analyzed, acetachlor, metolachlor, and atrazine were most frequently detected, though at low concentrations. Generally, degradation products of these classes of herbicides were detected 2–3 times more frequently and at concentrations 1–2 orders of magnitude higher than the parent compounds. Alachlor ethanesulfonic acid and 2-chloro-4-isopropylamino-6-amino-s-triazine were the most frequently detected degradation products. A comparison of these data with future synoptic sampling data will demonstrate the degree to which natural attenuation improves water quality or atmospheric deposition contributes agricultural chemicals to waters in the study area.