HYPORHEIC FUNCTION IN FORESTED VS. AGRICULTURAL STREAMS

The function of the hyporheic zone is particularly sensitive to riparian perturbations that alter channel morphology and sediment distribution. At a reach scale, channel homogenization can reduce hydrologic forces driving hyporheic exchange. At a sediment scale, infiltration of fines into the stream substrate can reduce hydraulic conductivity, further reducing hyporheic exchange. Loss of hyporheic exchange can reduce stream water contact with potential microbial habitat, subsequently decreasing the retention of biologically active solutes.

The objective of our current research is to determine how agricultural land use in southern Appalachian headwater streams affects stream function through hyporheic alteration. Ongoing field work and data analysis are designed to examine effects of agricultural land use at stream reach and sediment scales. A total of six study sites in the Appalachian mountains of southern North Carolina were selected based on riparian land use: three agricultural and three forested. The agricultural sites have no significant woody riparian vegetation and have channels noticeably straighter than the forested sites. The agricultural sites also have visually smaller sediments and more embedded substrates than the forested sites. At each site, reach scale morphologies are being measured from thalweg surveys. Substrate size distributions are being measured through gravelometry and sieve analysis of sediment samples. Hydrological and biological characteristics of the channel and hyporheic zone are being measured through concurrent additions of conservative and biologically active tracers. Hyporheic exchange and nutrient retention will be compared among the study sites to investigate the effects of land use, sediment distribution, and reach scale morphology.