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Applied Wetlands Science and Technology - Chapter 5

Avoiding and Minimizing Impacts to Wetlands Donald M. Kent and Kevin McManus - Ước tính gần đây về mức độ các vùng đất ngập nước toàn cầu khoảng 5-8,6 triệu ha (Mitsch, 1995). Tăng bằng chứng cho thấy rằng mức độ lịch sử của vùng đất ngập nước toàn cầu lớn hơn nhiều. Ví dụ, tại Nhật Bản, 45% các bãi triều có bị phá hủy từ năm 1945 (Hollis và đồ giường, 1994). Miền bắc Hy Lạp đã bị mất 94% vùng đầm lầy của nó kể từ năm 1930. Tại Hoa Kỳ ở giáp ranh ước tính có khoảng 47 triệu ha. | Kent Donald M. et al Avoiding and Minimizing Impacts to Wetlands Applied Wetlands Science and Technology Editor Donald M. Kent Boca Raton CRC Press LLC 2001 CHAPTER 5 Avoiding and Minimizing Impacts to Wetlands Donald M. Kent and Kevin McManus CONTENTS Planning Design and Construction Design Construction Erosion and Sedimentation Nitrogen Loading Planning Guidelines Estimating Nitrogen Loads Stormwater Runoff Planning and Nonstructural Practices Structural BMPs Pretreatment Detention Basins Retention Ponds Vegetated Treatment Infiltration Filtration References Recent estimates of the extent of global wetlands range from 5 to 8.6 million ha Mitsch 1995 . Increasing evidence suggests that the historic extent of global wetlands was substantially greater. For example in Japan 45 percent of tidal flats have been destroyed since 1945 Hollis and Bedding 1994 . Northern Greece has lost 2001 CRC Press LLC 94 percent of its marshland since 1930. In the conterminous United States an estimated 47 million ha of wetlands have been lost over the last 200 years an average rate of 235 000 ha per year U.S. Office of Technology Assessment 1984 Dahl 1990 Hollis and Bedding 1994 . This rate of loss appears to have decreased dramatically in recent years to about 32 000 ha per year coincident with recognition of the importance of wetlands and a no net loss government policy Heimlich and Melanson 1995 . Wetland losses are attributed to filling and draining primarily in support of development and agricultural activities. An unknown number of wetlands not filled or drained have been otherwise impacted by changes in watersheds or adjacent land uses. Alterations to wetland plant communities lead to increased erosion and sedimentation. Construction of buildings parking lots and other impervious surfaces increases the quantity and decreases the quality of surface runoff to wetlands. Septic systems and fertilizers increase the concentration of nitrogen in groundwater flow to wetlands. Activities