摘要：Human activities have resulted in the loss of about half of the original 221 million acres of wetlands in the conterminous 48 states. Federal laws, policies, and programs have had major impacts on the nation's wetland resources. Initially, they encouraged and subsidized the draining and filling of wetlands, the flooding of wetlands behind dams, and the diversion and alteration of streamflows to riparian wetlands. More recently, federal policies have been directed to conserving and preventing further net losses. The focus of this study is on the impacts of federal policies on riparian wetlands, i.e., those formed at the interface of rivers and streams and uplands and that require occasional flooding to maintain the health of their ecosystems. The study identifies the trends in wetland acreage, describes the principal federal policies and programs impacting riparian wetlands, summarizes what is currently known or can be deduced from existing research about the impacts of these policies and programs on riparian wetlands, identifies key knowledge gaps, and suggests priorities for additional research. The policies that once directly and indirectly encouraged drainage of wetlands as well as water use and development practices harmful to wetlands have for the most part been abandoned. In some cases they have been replaced by new policies designed to protect the remaining wetlands and to encourage wetland restoration and creation. From the mid-1950s to the early 1990s conversion of wetlands to agriculture accounted for some 70 percent of total conversions. From 1982 to 1992, however, agriculture actually contributed a small net increase in the number of wetland acres. Changes in federal agricultural policies played a major role in this turn around. Overall, net wetland losses have been slowed but not ended since a "no net loss" policy was established in 1989. Several lines of research could contribute to the design and implementation of policies to achieve the "no net loss" goal. Research is needed to understand how farmers' incentives to convert wetlands to agricultural uses would be affected should Swampbuster become toothless as farm subsidies are eliminated or agricultural prices rise. And, if this analysis suggests wetland losses to agriculture would likely accelerate, alternative market-based and regulatory strategies for curbing these losses should be examined. As wetlands are lost to development and other pressures, achieving the no net loss goal requires that these losses be compensated. Research on the physical characteristics and the ability of different wetlands to provide social values such as fish and wildlife habitat, retention of flood waters, and water quality improvements would provide a better basis for determining how much society should invest in protecting, enhancing, restoring, or creating wetlands and whether these investments adequately compensate for the functions of lost wetlands. Research also is needed to determine how mitigation banking might be made more efficient and effective in ensuring social values are adequately compensated when wetlands are lost.
