Monday, August 6, 2007

PS 2-18: Missing streams in the mid-Atlantic US: Insights from aerial-photography calibrated satellite remote sensing

Andrew J. Elmore and Sujay Kaushal. University of Maryland Center for Environmental Science

Headwater streams provide important ecosystem services such as drinking water, habitat for aquatic life, and biological uptake and increased processing of nutrients, which can reduce delivery of nitrogen and phosphorus to downstream coastal waters. Despite their known importance to humans, many streams have become "missing" from developing landscapes due to coverage by impervious surfaces or direct conversion to storm drains, contributing to habitat degradation and loss of ecosystem services. Much of the existing work has focused on understanding the consequences of riparian buffer degradation, but not the extent to which streams have become completely removed from the land surface. We measured the occurrence of stream channel fill-in within the Gunpowder-Patapsco watershed in eastern Maryland for streams with catchments ranging from 10 ha to 106 ha. Our methods involved identifying where streams should be from a 10m DEM, and then calibrating a 30m impervious surface product using high-resolution air photography to build a stream channel classification. The fraction of missing streams was 25% for small, sometimes intermittent, streams that are currently not protected by federal regulations. Missing stream length decreased to 12% for large streams, and averaged 21% for all streams. For streams draining densely urbanized environments, the data suggest a non-linearity at a catchment size of 259 ha (1 mi2), which coincides with the minimum stream size to fall under Federal Emergency Management Agency (FEMA) regulations. Our results are some of the first depicting the spatial pattern and extent of natural stream channel destruction in the Chesapeake Bay region.