Impacts of Freshwater Wetlands A Landscape Perspective on Water Quality:


In this article, we suggest that a landscape approach might be useful in evaluating the effects of cumulative impacts on freshwater wetlands. The reason for using this approach is that most watersheds contain more than one wetland, and effects on water quality depend on the types of wetlands and their position in the landscape. Riparian areas that border uplands appear to be important sites for nitrogen processing and retention of large sediment particles. Fine particles associated with high concentrations of phosphorus are retained in downstream wetlands, where flow rates are slowed and where the surface water passes through plant litter. Riverine systems also may play an important role in processing nutrients, primarily during flooding events. Lacustrine wetlands appear to have the least impact on water quality, due to the small ratio of vegetated surface to open water. Examples are given of changes that occurred when the hydrology of a Maryland floodplain was altered. There is little doubt that freshwater wetlands can significantly improve water quality and, with few exceptions, most have been shown to perform that function (Kelly and Harwell 1985, Nixon and Lee 1988). However, numerous questions about the relationship between wetlands and water quality are still unanswered because many types of freshwater wetlands have not been adequately studied (LaBaugh 1986, Nixon and Lee 1988). Most water quality research projects have been short term and have not included input -output analyses (Whigham and Bayley 1979, Howard-Williams 1985, Nixon and Lee 1988), especially for hydrologic variables (Carter 1986, LaBaugh 1986). The need for long-term studies and detailed input -output analyses has been recognized over and over again in recent reviews of the freshwater wetland literature (Kadlec and Kadlec 1979, Whigham and Bayley 1979, Zedler and Kentula 1985, LaBaugh 1986, Nixon and Lee 1979, Richardson 1988), and has been documented in recommendations to the National Science Foundation (NSF) and many other federal agencies (Larson and Loucks 1978, Clark and Clark 1979). To date the Long-Term Ecological Research Program (LTER), funded by NSF, is the only national program devoted to long-term ecological research, and wetland ecosystem research is the main focus of only two sites. Unfortunately, institutional support of long-term wetlands research has not moved very far from the initial pronouncements made in the late


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