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10 RESTORATION OF AQUATIC ECOSYSTEMS these projects actually achieve the benefits (e.g., flood protection, fish and wildlife enhancement) for which they were designed at costs that were projected. The committee also recommends that a national river and stream restoration target of 400,000 miles of river-riparian ecosystems be restored within the next 20 years. This target represents only about 12 percent of the total 3.2 million miles of U.S. rivers and streams, and is recommended because it is comparable to the miles of streams and rivers affected by point source and urban runoff (EPA, 1990). WETLANDS Historically, the most destructive alterations to wetlands have been physical, often eliminating the topographic and hydrologic character- istics that support the wetland ecosystem. Their position in the land- scape, whether as isolated wetlands or floodplains contiguous with rivers and streams, gives wetlands a major role in storage of flood- water and abatement of flooding. When wetlands are converted to systems that are intolerant of flooding (drained agricultural lands, filled developed lands), their storage capacity decreases and down- stream flooding- occurs. Wetlands have properties of both aquatic and terrestrial ecosystems. Their most widely valued function is pro- viding habitat for fish, birds, and other wildlife, which contributes to the maintenance of biodiversity. Controversy exists as to whether or not certain wetland systems can be restored. The arguments are particularly important when wetland restoration is undertaken with the promise that because full restoration of a degraded site is possible, other natural wetlands can be destroyed without any net loss of wetland habitat. Wetland resto- ration should not be used to mitigate avbidable destruction of other wetlands until it can be scientifically demonstrated that the replace- ment ecosystems are of equal or better functioning. Funding priority should be given to programs for restoration of damaged wetlands over wetlands creation .because of the superior chances of success. An exception would be cases in which restoration is part of a mitiga- tion agreement that would result in a net loss of acreage. Wetlands restored in regulatory contexts often receive little man- agement after initial restoration because private and public landown- ers, who are not motivated to provide such management, may move on or have no legal obligation for such management. Similarly, the responsible federal agencies do not have staff to assess the adequacy of restoration projects and do not monitor or require monitoring of permit mitigation conditions for sufficient time periods (10 years or