Watershed

A watershed is a geographic area in which water moves toward a common water body, shaped by local geography and topography, networks of streams, rivers, and groundwater aquifers, and the land use decisions of individual property owners. The Monongahela River watershed lies within the Allegheny/Pittsburgh Plateau section of the Appalachian Plateau, where much of the terrain is rough, steeply sloped, and deeply eroded, with stream valleys cut into a highly dissected plateau underlain by sedimentary rocks including sandstone, shale, coal, and limestone dating from 416 million to 251 million years ago. These rocks are commonly fractured and folded but also flat-lying, and bituminous coal, including the extensively mined Pittsburgh seam, underlies most of the river. Historically, the watershed was well suited for wetlands, but because of steep topography and decades of developmental flood plain growth, large expanses of wetlands are generally not found there today; wetlands usually occur on islands and embayments and along shorelines and tributary mouths, with most located in the southern part of the watershed in West Virginia, where around 37 square miles of wetland and nearly 60 square miles of open water remain. The watershed lies in what is currently classified as the Appalachian mixed mesophytic forest and supports at least 250 species of birds, 47 species of mammals, and 51 species of amphibians and reptiles, with species diversity and suitable habitat increasing with distance from Pittsburgh. Four endangered and three threatened species live within the watershed, including the Indiana bat in Greene County. Vegetation is dominated by oak, beech, and hemlock in forested areas, with white oak-hickory forests in uplands and willow, beech, and maple hardwoods in lowlands; native vegetation remains predominant in rugged or inaccessible areas, while narrow bands persist along the water's edge even in heavily developed industrial stretches. The watershed's streams provide diverse habitats, from cold, nutrient-poor mountain streams that support trout and other cold-water fish along with aquatic invertebrates to warmer western streams with a greater diversity of fish species, while the Monongahela River basin as a whole supports a relatively modest fish fauna that is somewhat indistinct from adjacent basins.

Pennsylvania · United States