A special algorithm has been applied to the Landsat 7 image to illuminate the changes in low-density residential land use which exemplify sprawl. There is a link between impervious surfaces within a watershed, (here we see a subset of the Chesapeake Bay watershed area) and the water quality within the watershed. In general, once 10-15 % of an area is covered by impervious surfaces, increased sediments and chemical pollutants in runoff have a measurable effect on water quality. When 15-25% of a watershed is paved or impervious to drainage, increased runoff leads to reduced oxygen levels and impaired stream life. When more then 25% of surfaces are paved, many types of stream life die from the concentrated runoff and sediments.
GCMD keywords can be found on the Internet with the following citation:
Olsen, L.M., G. Major, K. Shein, J. Scialdone, S. Ritz, T. Stevens, M. Morahan, A. Aleman, R. Vogel, S. Leicester, H. Weir, M. Meaux, S. Grebas, C.Solomon, M. Holland, T. Northcutt, R. A. Restrepo, R. Bilodeau, 2013. NASA/Global Change Master Directory (GCMD) Earth Science Keywords. Version 8.0.0.0.0