Institute of Ecosystem Studies

2008 BES Annual Meeting Presentation and Poster Abstracts

The influence of land cover elements on nitrogen and water flux in small urban watersheds.
McConaghie, James
Co-Authors: James McConaghie, Monica Lipscomb-Smith, Weiqi Zhou, Peter Groffman, Lawrence Band, Mary Cadenasso
Abstract: Aquatic systems in urban areas may receive enhanced nutrient inputs from the surrounding landscape. The Chesapeake Bay has been impaired by terrestrial nitrogen input, including that from urban areas. Watershed structure is hypothesized to influence nitrogen flux into aquatic systems, and in urban areas, impervious surfaces and vegetation may control these inputs. It has been hypothesized that increased impervious surface cover increases discharge to urban streams, and is correlated with increased nitrogen flux. On the other hand, vegetation slows water flow and retains nutrients on the landscape. Therefore, increases in vegetation cover are expected to decrease discharge and nutrient flux to the streams. To evaluate these hypotheses, we selected 12 sub-basins of the Baisman Run and Gwynns Falls watersheds that range from 4 to 30 ha. These sub-basins differ in land cover, and high-resolution aerial imagery was used to calculate percentage of buildings, coarse vegetation (trees and shrubs), fine vegetation (herbs and grasses), pavement, and bare soils. Water quality data was collected from each stream for 18 months. We used correlation and multi-linear regression models to determine which land cover variables or combinations of variables best predict water quality. Results indicate that building and pavement were the most important predictors of nitrogen concentration and flux, but, contrary to the hypothesis, the correlation between nitrogen flux and buildings and pavement was negative. An understanding of the relationship between landscape structure and nutrient flow will help to elucidate mechanisms of material flow and may inform better management of nutrients in urban systems.