2000 BES Abstracts

Nitrogen and phosphorus concentrations and yields along an urban rural gradient in the Gwynns Falls watershed.

Kenneth T. Belt, Peter M. Groffman, Peter, Lawrence E. Band, Gary T. Fisher, Mark Colosimo

Weekly sampling for cations and anions was conducted in watersheds of the 17,150 ha. urbanized Gwynns Falls watershed. We discuss nitrate nitrogen (N) and phosphate phosphorus (P) concentrations and yields (mass exported per area), and water yields (runoff volume per area) along an urban-rural gradient for water year 1999.

Seasonal patterns and differences between watersheds were seen. The forested Pond Branch had the lowest mean concentrations and yields for both N and P. The mean annual N yield for the Gwynns Falls at Carroll Park was more than 60 times the yield at Pond Branch. Glyndon, a suburban watershed in the rural headwaters, had the second highest P yield but only the fifth highest N yield. Dead Run, an older moderately developed suburban watershed had the lowest N yield (except for Pond Branch), but ranked among the highest in P yield.

In the main channel of the Gwynns Falls, nitrate N concentrations tended to decrease in the downstream reaches and N yield was lower at Carroll Park than at the upstream Villa Nova and Gwynnbrook stations. This was curious, since N inputs were expected to be highest in the lower, densely populated reaches with its aging sewage infrastructure.

Water yields during an extended drought were higher at the two lower Gwynns Falls main channel stations than for those in the upper suburban and rural parts of the watershed. This was a surprise since conventional wisdom holds that urbanized watersheds have very low baseflows.