Prior to this study, indirect ground-water discharge was not explicitly considered in estimates of Great Lakes Basin water supply. Instead, it was incorporated into the streamflow component of the supply. Surface runoff is a short-term component of flow that results from precipitation moving overland to a stream without percolating into an aquifer. These results were extended to the entire basin by assuming that the average ground-water component of streamflow estimated for the ungaged streams is about the same as that estimated for gaged streams in the basin. Wetland functions have been shown to include storm and floodwater retention, shoreline protection, and water-quality improvement.
Wetlands also provide wildlife habitat.
More than one-third of endangered species in the United States are associated with wetlands even though wetlands comprise less than five percent of the landscape. Although the effects of these losses are beginning to be understood, more study is needed to improve our knowledge about the role of these important wetland systems. Wetland hydrology is widely recognized as the primary effect on wetland ecology, development, and persistence. An understanding of the hydrology is essential to identify and quantify wetland functions and processes. For example, ground-water flow has been shown to be important for the physical and chemical environment of other aquatic systems because the amount of dissolved solids carried by ground water is typically much higher than that carried by surface water.