Acid Rains Essay Research Paper Acid RainsScientific — страница 2

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on those resources. Research conducted under the auspices of the National Acid Precipitation Assessment Program (NAPAP) concluded that regions in the United States most at risk from continued acidic deposition are located along the Appalachian Mountain chain stretching from the Adirondacks to the Southern Blue Ridge. Although many surface waters in western North America are as sensitive as, or more sensitive than, aquatic systems in the East, deposition levels in the West are sufficiently low that the risk of chronic (longterm) acidification to resources in most of the West is low at present and is expected to remain low in the foreseeable future. Episodic acidification (from spring snowmelts) adversely affects some eastern surface waters. It may be affecting high-elevation

western surface waters, as well. An acid deposition standard or standards could be designed to achieve a variety of environmental protection goals. For example, the goal of a standard may be to (a) maintain specific conditions as observed at a particular point in time (e.g., conditions observed in 1984 during the National Surface Water Survey); (b) protect all systems from any harmful anthropogenic effects (i.e., return to preindustrial conditions); or (c) balance effects, costs, and other societal values. A standard can be designed to address chronic or episodic acidification and could vary by region based on the regional variability of ecological sensitivity. No guidance is provided in the statutory language regarding the degree of protection desired by a standard or standards.

Target populations of Adirondack lakes, Mid-Appalachian streams, and Southern Blue Ridge streams were selected for detailed analysis in this study because they represent areas that receive fairly high levels of acidic deposition, are sensitive to acidic deposition, have the best historical data, and have been extensively studied by scientists. Potential future impacts of acidic deposition are estimated by modeling the response of a target population of aquatic systems (lakes and streams) in these areas to various levels of deposition. Target populations are selected to represent sensitive surface waters over broad geographic regions. Individual target populations of sensitive surface waters used for various acidic deposition studies have become progressively smaller over time as

investigators have refined their work to study more intensively the acidification processes influencing the most sensitive surface waters. For example, of the total population of lakes in the eastern United States, 18,156 of these lakes potentially most sensitive to acidification were included within the target population of the National Surface Water Survey (NSWS, 1984). In turn, further refinement of sensitivity characteristics for the NSWS lakes led to targeting a total population of 3,227 lakes in the Northeast during the Direct/Delayed Response Project (DDRP, 1988) and 703 lakes in the Adirondack Mountains during the Nitrogen Bounding Study (NBS, 1994). Similar refinements also occurred for lakes and stream reaches in other regions. This approach is illustrated

diagrammatically in Exhibit I (not to scale). In this report, analyses of risks from acidic deposition to sensitive lakes and streams focuses extensively on extrapolations regarding the highly sensitive, but limited, target populations used during the NBS studies. Selecting an Acid Deposition Standard or Standards The analyses presented in this study provide model projections of direction and magnitude responses for modeled target watersheds under various sulfur and nitrogen deposition scenarios. Based on the remaining scientific uncertainties, particularly regarding the effects of nitrogen and the rate of those effects on the watershed, selection of an appropriate level or levels for a standard to achieve any particular environmental goal is very difficult. Therefore, this study

does not recommend an acid deposition standard or standards at this time. The modeling analyses in this report however, do indicate important watershed responses to emissions reductions in the Clean Air Act and provide estimates of deposition reductions that would be needed to achieve a range of environmental goals within the uncertainty of the modeling results. Impact of the CAAA on Sensitive Surface Waters Model projections from the Nitrogen Bounding Study (NBS) indicate that sulfur deposition reductions mandated by Title IV of the Clean Air Act Amendments would benefit sensitive surface waters by the year 2040. Exhibits II-IV show ranges of percent target population lakes or streams in each sensitive region projected to be chronically acidic (acid neutralizing capacity [ANC]