NUTRIENT SLUG ON A DECLINING TRANSECT OF A GRAVEL-HILL PRAIRIE, WINNEBAGO COUNTY

Tallgrass prairies have been reintroduced to some urban areas of the Midwest, partially in an effort to capture runoff and pollution. This project tests the effects of an urban prairie in northern Illinois by analyzing shallow soil samples. The Harlem Hills Prairie in Winnebago County, Illinois, is a 53-acre gravel-hill prairie surrounded by residential and light commercial neighborhoods. The study area lies down-gradient of residential condominiums, and it is assumed that nutrients and pavement runoff are washed into this system from several directions. Five, 6-8 inch cores were taken from the prairie along a 159 m transect, decreasing in elevation from 257 m to 247 m. Soil pH varied from 6.4-7.4. Potassium concentrations peaked at 176 ppm, about 66.5 m down-gradient from the turf lawns, with an average value on the study area of 122.4 ppm. Phosphorus levels, peaked at 17 ppm, about 104.2 m down-gradient from the turf lawns, with an average value of 5.4 ppm. Nitrogen tests are forthcoming. Preliminary results suggest a slug of nutrients between 66.5 and 104.2 m from the prairie boundary. This slug may have been transported by surface runoff and subsequent infiltration. The fact that the most down-gradient samples have lower nutrients reflects eventual capture of the nutrients by the prairie system. Complicating factors, including variable near-surface hydrogeological and microbial properties of the soils and variable vegetation, require further study.