THE HYDRYGEOLOGICAL EFFECTS OF ALTERING LAND USE ALONG WOLF CREEK

Wolf Creek flows primarily through agricultural areas before flowing through a recently developed urbanized area. As the stream enters the urbanized area, the waters flow through a golf course before flowing through a low-density housing subdivision. As the creek exits the subdivision, the land is undeveloped and a riparian corridor exists next to the stream. To investigate the influence of the development on stream, Wolf Creek is being studied at five locations throughout the watershed where discharge, stream substrate, and chemical data are being collected. Despite the drought conditions, early data indicates that nitrate decreases in concentration downstream. Measured concentrations of nitrate in the headwater region are up to 120 mg/L NO₃ ^- and at the farthest down gradient location are as low as 55 mg/L NO₃ ^-; samples from all five locations are consistently above the Maximum Contaminant Level for nitrate. The decrease in concentration is likely due to the increase of ground water discharge (regional ground water has a nitrate concentration below 30 mg/L) to the stream, removal by either plant uptake or denitrification, or a combination of both processes. Chloride data suggest that dilution is not the primary cause in decreased nitrate concentrations downstream; however, to confirm nitrate is lost from the system, a mass balance calculation will be performed. The current data indicate that urbanization does not compound the nitrate problem but may facilitate the removal of nitrate from the system. One complication in studying the role of urbanization in Wolf Creek is that a drainage tile introduces soil water and redirects storm runoff from a city outside of the drainage basin into Wolf Creek downstream of the headwaters, but upstream of the subdivision. During baseflow, the input from the drainage tile is minimal relative to the overall flow of the system. No data are currently available for storm event input from the drainage tile, but will be collected to assess the influence of the drainage tile on the system. Overall, these data will hopefully clarify the effects of drainage tiles, agricultural areas, and proximate developing areas.