2008 BES Annual Meeting Presentation and Poster Abstracts
The Gutter Subsidy: Tree Cover Proximal to Impervious Surfaces in the Gwynns Falls Catchment
Co-Authors: Elizabeth Bayne, Mike McGuire, Ken Belt
Abstract: Aquatic-terrestrial linkages are important to any receiving water, but nowhere is this link more crucial than in urbanized catchments because impervious surfaces and their attendant storm drainage networks effectively extend these to upland areas, effectively turning much of the landscape into an “upland riparian zone.” This extended drainage network gives rise to a “gutter subsidy” in terms of providing a vehicle for the input of exponentially greater amounts of particulate and dissolved organic matter to aquatic ecosystems. Organic matter is important as a food resource in aquatic food webs and functions in the fate and transport of pollutants such as heavy metals and organics, and may itself give rise to greater concentrations of disinfection by products in drinking water. We used 1999 aerial photography to characterize the extent of tree coverage proximal to impervious surfaces in the Gwynns Falls at Gwynnbrook catchment, one of the study sites of the US Forest Service and Baltimore Ecosystem Study LTER which drains to the Patapsco River and subsequently Baltimore Harbor and Chesapeake Bay. These were spatially joined with Lidar data using ERDAS software and high resolution surface cover classification was accomplished by assigning pixels similar in band width, height, and texture to polygons through an automated process using eCognition software. The polygons were manually classified into pervious and impervious groups, such as grass, tree, soil, asphalt, concrete, or building, based on surface appearance and polygon height. The remaining unclassified polygons were automatically assigned to groups through eCognition using information from manually selected polygons. We discuss these results and estimates of potential leaf litter inspired organic matter loads to the Gwynns Falls and the implications for both stream ecosystems and watershed management.