Hydro-Ecologic Responses to Land Use in Small Urbanizing Watersheds Within the Chesapeake Bay Watershed

Glenn Moglen, Karen Nelson, Margaret Palmer, et al. (2005)

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Urbanization in the Chesapeake Bay watershed is having dramatic impacts on the streams and rivers that feed the Bay. Increasing imperviousness has led to higher peak flows and lower base flows. The movement of pollutants and other materials to receiving waters has increased and stream water temperatures have risen. These changes alter the structure and functioning of reivers, streams, and associated riparian corridors and result in changes in ecosystem services.

We define a hydrologic disturbance index that indicates varying degrees of disturbance on a reach-by-reach basis, dependent on the aggregate amount of urbanization upstream of each reach. For current conditions this index is more variable than for future conditions, because current land use in the study watershed is more variable, containing mixtures of urban, agricultural, and forested land. In contrast, future land use is projected to be more uniformly urban, leading to a less variable but greater overall degree of hydrologic disturbance.

Two effects of urbanization on fish are explored through ecological modeling: effects of streambed disturbance on food availability and effects of stream temperature on spawning. We tabulate food availability as a function of bed-mobility for 30 different fish species. We show that additional stress occurs with additional urbanization of the watershed. We show that the urban-related increase in stream temperatures may cause several warm-water species to gain opportunities to spawn in some cases. However, combining food availability and spawning day availability into a single index reveals highly stressful conditions for all fish species under the fully developed scenario.