Relationships Among Land-Use, In-Stream Stressors, and Biological Condition in Prince George's County, MD

Changes in land use / land cover have been repeatedly shown to be strongly associated with overall ecological degradation of streams. As natural areas are developed, there is a resulting change in the hydrologic characteristics. The development activities that alter natural ecosystem structure and function are considered stressors of that ecosystem. The intermediate linkages and complex mechanisms that relate these stressors, which are produced by the landscape features (sources), have not been as well illustrated. Diagnostic analyses performed in this study illustrate linkages not only between the sources of stressors and the stressors themselves, but also between the stressors and the biological response variables (benthic macroinvertebrates and fish). Prince George's County, for the past five years, has conducted a biological monitoring program that covered every subwatershed in the County. Using the database developed by this monitoring program of more than 255 sites, stepwise multiple regression was performed. Results demonstrated that the strongest source-stressors associations were between medium and high density residential and commercial and industrial land use as the sources, and reduced overall physical complexity of the stream habitat (i.e., decreased availability of gravel substrate, diminished cover, reduced channel sinuosity, and reduced pool variability and substrate), as the stressors. The biological response variables that had the strongest association with these stressors were the benthic macroinvertebrate and fish indexes of biotic integrity (B-IBI and F-IBI), the Ephemeroptera-Plecoptera-Trichoptera (EPT) Index, Beck's Biotic Index, % Dominant Fish Species, and % generalists, omnivores, and invertivores (%GOI). These results have been used as the basis for developing the County's Green Infrastructure Plan and the decision making tool for reviewing new development proposals. The purposes of this paper are to present the results of these findings and to recommend solutions that can enhance the likelihood of desirable biological changes. The management recommendations are to reduce, eliminate, or buffer the most likely sources causing production of the stressors.