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Summary
Pages 1-22

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From page 1...
... However, protection of wetlands generally does not encompass riparian areas the lands bordering waterbodies such as rivers, lakes, and estuaries even though they often provide many of the same functions as wetlands. Especially in more arid regions of the country, riparian areas support the vast majority of wildlife species, they are the predominant sites of woody vegetation including trees, and they surround what are often the only available surface water supplies.
From page 2...
... Over the last several decades, federal and state programs have increasingly focused on the need for maintaining or improving water quality, ensuring the sustainability of fish and wildlife species, protecting wetlands, and reducing the impacts of flood events. Because riparian areas perform a disproportionate number of biological and physical functions on a unit area basis, their restoration can have a major influence on achieving the goals of the Clean Water Act, the Endangered Species Act, and flood damage control programs.
From page 3...
... Because the lack of a consistent definition has been identified as a major problem of federal and state programs that might manage and protect these areas, the NRC committee developed the following definition. Riparian areas are transitional between terrestrial and aquatic ecosystems and are distinguished by gradients in biophysical conditions, ecological processes, and biota.
From page 5...
... Varying flow regimes have corresponding sediment dynamics that help shape riparian areas. Although precipitation and runoff promote erosion of uplands and the transport of sediment into stream channels, riparian areas may trap some of these particles.
From page 6...
... , and in hyporheic zones. The importance of these mechanisms in controlling water quality depends on the amount of time that hillslope runoff is retained in the riparian area, on whether overland and subsurface flows concentrate and flow through only a portion of the riparian area, and on the stream order of the adjacent channel.
From page 7...
... Finally, forested riparian areas contribute wood to streams and lakes, which helps maintain their physical habitat, slows the downstream routing of sediment and organic matter, provides increased hydraulic resistance to flow, and provides a food supply to microorganisms and invertebrates. Environmental Services of Riparian Areas The fundamental ecological functions that riparian areas perform fall into three major categories: (1)
From page 8...
... Effects include changes in the hydrology of rivers and riparian areas, alteration of geomorphic structure, and the removal of riparian vegetation. Drastic declines in the acreage and condition of riparian lands in the United States over the last 100 years are testimony to these effects.
From page 9...
... Because groundwater and surface water are generally connected in floodplains, declines in groundwater level can indirectly be caused by surface water withdrawals or by the regulation of surface water flow by dam construction. Lowering groundwater levels by just one meter beneath riparian areas is sometimes sufficient to induce water stress in riparian trees, especially in the western United States.
From page 10...
... Conversion of undeveloped riparian land to agriculture has the potential to decrease infiltration and increase overland flow volumes and peak runoff rates. This results in high erosion rates that inundate riparian vegetation with sediment and limit the filtering functions of the riparian area.
From page 11...
... As vegetation is replaced by impervious surfaces (roads, buildings, parking lots) , infiltration, groundwater recharge, groundwater contributions to streams, and stream base flows all decrease, while overland flow volumes and peak runoff rates increase.
From page 12...
... For example, saltcedar has replaced cottonwood and other native riparian trees throughout much of the southwestern United States. This situation has been exacerbated by a reduction in flood flows caused by dams and by the lowering of water tables caused by water withdrawal.
From page 13...
... Although landscape studies assessing the status of riparian areas are limited, they reveal that the spatial extent of riparian forests has been substantially reduced, plant communities on floodplains have been converted to other land uses or have been replaced with developments, and the area of both woody and non-woody riparian communities has decreased. The functions of these riparian areas are greatly diminished in comparison to what occurred historically.
From page 14...
... At the national level, several Farm Bill programs provide incentives for moving intensive agricultural practices away from streams by installing riparian buffers. Fifth, privately owned riparian lands can be purchased either in fee or by easement for public management.
From page 15...
... Thus, while different and additional constraints apply to management of federal riparian lands as compared to privately owned riparian lands, the constraints are not uniform from agency to agency, nor are they even uniformly interpreted and applied within agencies. For the most part, they have been established principally by administrative action, not by legislation, and thus are subject to administrative change.
From page 16...
... Public lands should be managed to protect and restore functioning riparian areas. Federal land management agencies should promulgate regulations requiring that the values and services of riparian areas (habitat-related, hydrologic, water quality, aesthetic, recreational)
From page 17...
... There are many riparian systems where ecological restoration is achievable. However, there are also situations where permanent changes in hydrologic disturbance regimes (e.g., dams)
From page 18...
... Most IBI assessments have been limited to aquatic ecosystems. Both HGM and IBI should be revised for use in riparian areas, for example by developing indices of integrity for riparian plant communities.
From page 19...
... Riparian vegetation has evolved with and adapted to the patterns of changing flows associated with stream and river environments. Altering dam operations, removing levees, and otherwise re-creating a more natural flow regime and associated sediment dynamics are of fundamental importance for recovering riparian vegetation and the functions that it provides.
From page 20...
... For overgrazed riparian areas, the passive restoration approach is simply to exclude domestic livestock from riparian areas via fencing, herd management, or other approaches. Excluding cattle from riparian areas is the most effective tool for restoring and maintaining water quality and hydrologic function, vegetative cover and composition, and native species habitats.
From page 21...
... Even when riparian buffer zones are marginally effective for pollutant removal, they are still valuable because of the numerous habitat, flood control, groundwater recharge, and other environmental services they provide. Unless new evaluation procedures are developed that consider both the water quality and ecological functions of riparian areas, it is unlikely that riparian zone size (width and length)
From page 22...
... CONCLUSIONS Riparian areas provide essential life functions such as maintaining streamflows, cycling nutrients, filtering chemicals and other pollutants, trapping and redistributing sediments, absorbing and detaining floodwaters, maintaining fish and wildlife habitats, and supporting the food web for a wide range of biota. The future success of at least five national policy objectives protection of water quality, protection of wetlands, protection of threatened and endangered species, reduction of flood damage, and beneficial management of federal public landsdepends on the restoration of riparian areas.


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