The Watershed Approach in the Baltimore Ecosystem Study

In the Baltimore Ecosystem Study (BES), we are conducting long-term watershed studies to provide a basis for comparison of urban ecosystems with other ecosystem types within the LTER netowrk and to help understand how urban watersheds respond to changes like new sewage systems and climate change. Every week since October 1998, BES scientists have sampled a network of stream sites including forested and agricultural reference sites as well as a range of urban and suburban sites.  Stream gauging stations were built and maintained by the US Geological Survey. Both filtered (nitrate, phosphate, chloride, sulfate by ion chromatography) and unfiltered (total nitrogen, total phosphorus by persulfate digestion followed by analysis.  Urban and suburban watersheds consistently have nitrate concentrations that are higher than forested watersheds, but lower than agricultural watersheds.  Suburban watershed input/output budgets for nitrogen have shown surprisingly high retention which has led to detailed analysis of sources and sinks in these watersheds. Home lawns, thought to be major sources of N in suburban watersheds, have more complex coupled carbon and N dynamics than previously thought, and are likely the site of much N retention.  Riparian zones, thought to be an important sink for N in many watersheds, have turned out be N sources in urban watersheds due to hydrologic changes that disconnect streams from their surrounding landscape. In-stream retention, thought to be an important sink for N in forested watersheds is reduced by structural degradation caused by urban runoff.  These studies suggest that; 1) urban watersheds are significant sources of nitrogen and phosphorus to Chesapeake Bay, but are not as high as agricultural watersheds, 2) there is significant potential for nitrogen retention in urban watersheds that needs to be understood and managed to improve the environmental performance of these watersheds and 3) there are some surprising “sinks” (e.g., lawns) and “sources” (e.g. riparian zones) of nitrogen in urban watersheds.

Related Materials and Graphics: 

BES Watershed poster.pdf