2007 BES Annual Meeting Presentation and Poster Abstracts
An empirical analysis of stream chemical loads in headwater reaches in Baltimore County, MD
Co-Authors: Monica Lipscomb Smith, Lawrence E. Band, and Peter Groffman
Abstract: This study investigates the effects of small catchment land cover (4 to 100 hectares) on the chemistry of urban stream according to antecedent conditions and precipitation events. Monthly discharge measurements and stream chemistry "grab samples" were collected from headwater streams for WY-2007 and analyzed for nitrate-N, sulfate and chloride loads. The concentrations of sulfate and nitrate-N of the most upstream sites are highly variable and independent of discharge compared to the relatively stable downstream concentrations with highly fluctuating discharge. Catchments with septic input, the Baisman Run catchments, had very high downstream chemical loads, despite minimal development and high percent forest cover. Peaks in all chemical loads followed major storm events. While nitrate-N and sulfate increases appear to follow a seasonal trend at all sites, the peaks in nitrate and sulfate loads in Dead Run 5 may also exhibit a cyclical flushing effect. The cyclical flushing effect suggests that both nitrate and sulfate are created and stored in the relatively dry stream banks of the highly urbanized Dead Run and are flushed out during major storm events. The chloride level in Dead Run is much higher than Baisman Run at each site, peaking at a concentration akin to brackish water (544 mg/L) after a winter storm; in this case, the conductivity was 5x pre-snow conditions. Land cover and land use characteristics, including percent land cover, population, median age of parcels, and median flow length of parcels were determined for each site’s contributing area to evaluate their effects on chemical loads. Preliminary analysis of samples collected between August, 2006 and March, 2007 is presented in this poster.