tailieunhanh - AQUATIC EFFECTS OF ACIDIC DEPOSITION - CHAPTER 2

Cách tiếp cận thực hiện cho cuốn sách này đã được xem xét và tổng hợp kết quả quan trọng của nỗ lực nghiên cứu thủy sản hiệu ứng thực hiện hoặc hoàn thành từ năm 1990. Sự nhấn mạnh chính là kết quả trình bày trong peer-xem xét lại các ấn phẩm trong các tài liệu khoa học, mặc dù kết quả của một số báo cáo cơ quan cũng được thảo luận. Kết luận được rút ra trên cơ sở của một loạt các công cụ đánh giá, sử dụng một cách tiếp cận cân bằng chứng, như. | 2__ Background and Approach Overview Atmospheric Inputs The approach taken for this book has been to review and summarize important results of aquatic effects research efforts undertaken or completed since 1990. The major emphasis is on the results presented in peer-reviewed publications in the scientific literature although results of some agency reports are also discussed. Conclusions are drawn on the basis of a variety of assessment tools using a weight-of-evidence approach as followed by Sullivan 1990 and NAPAP 1991 . Emphasis is placed on studies conducted in regions that contain large numbers of acid-sensitive aquatic systems. Regions in which aquatic resources are either not very sensitive or are primarily influenced by environmental perturbations other than acidic deposition receive less coverage. The natural cycling of S N and C has been fundamentally altered by human activities across large areas of the earth since the last century. Both S and N have the capacity to acidify soils and surface waters. Nitrogen can also lead to eutrophication of lakes streams estuaries and near-coastal ocean ecosystems and can cause reduction in visibility. Disruptions of the carbon cycle have caused increasing concerns about global climate change. A need has therefore arisen to develop a more complete scientific understanding of key processes that regulate elemental transport of S N and C among the various environmental compartments atmosphere soils water and biomass. The term acidic deposition refers to deposition from the atmosphere to a surface of the hydrosphere lithosphere or biosphere . any portion of a watershed of one or more acid-forming precursors. The latter can include oxidized forms of S and oxidized or reduced forms of N. Such atmospheric deposition occurs in several forms the best understood of which is wet deposition or deposition as dissolved SO42- NO3- and NH4 in rain or snow. A sizable component of the acidic