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HAVE U.S. SURFACE WATERS RESPONDED TO THE 1990 CLEAN AIR ACT AMENDMENTS?
Citation:
Kahl, J. S., J L. Stoddard, R. Haeuber, S G. Paulsen, R. Birnbaum, A. T. Herlihy, F. A. Deviney, D. R. DeWalle, J. H. Kellogg, P. S. Murdoch, K. Roy, W. Sharpe, N. S. Urquhart, J. R. Webb, AND K. E. Webster. HAVE U.S. SURFACE WATERS RESPONDED TO THE 1990 CLEAN AIR ACT AMENDMENTS? ENVIRONMENTAL SCIENCE AND TECHNOLOGY. American Chemical Society, Washington, DC, 38(24):484A-490A, (2004).
Description:
Title IV of the 1990 Clean Air Act Amendments (CAAA) set target reductions for sulfur and nitrogen emissions from industrial sources as a means of reducing the acidity in deposition. One of the intended effects of the reductions was to decrease the acidity of low alkalinity waters and thereby improve their biological condition. Consistent trends in indicators of recovery across a regional population of streams or lakes provides the strongest evidence that acidic deposition controls are working.
Researchers at the Western Ecology Division, along with cooperators from the University of Maine, Syracuse University, Penn State, University of Virginia, Oregon State University, the U.S. Geological Survey and the state of Vermont, assessed data from the U.S. EPA TIME (Temporally Integrated Monitoring of Ecosystems) and LTM (Long-Term Monitoring) projects for the period since the enactment of the CAAA in 1990. Regions included in the report are New England, Adirondack Mountains, Northern Appalachian Plateau, the Ridge and Blue Ridge provinces, and the Upper Midwest.
All regions except the Ridge and Blue Ridge provinces showed significant declines in sulfate concentrations in surface waters, with rates ranging from -1.5 to -3 eq/L/year. These declines were consistent with the decline in sulfate in precipitation. Nitrate concentrations decreased in two regions with the highest ambient nitrate concentration (Adirondacks, Northern Appalachian Plateau), but were relatively unchanged in regions with low concentrations. Dissolved Organic Carbon (DOC) increased in each region, potentially contributing natural organic acidity to offset the recovery from decreased acidity and sulfate in deposition.
Acid neutralizing capacity (ANC) is a key indicator of recovery, as it reflects the capacity of watersheds to buffer inputs of acidity. Increasing values of either ANC, pH, or both, are expected to result from decreasing deposition of sulfur and nitrogen from the atmosphere. ANC increased in three of the regions (Adirondacks, Northern Appalachian Plateau and Upper Midwest) at a rate of +1 to +2 eq/L/year, despite a decline in base cations (calcium and magnesium) in each region. The decline in base cations offsets some of the decline in sulfate, and thus limits the increase in ANC or pH. In the Adirondacks, surface water ANC and pH both increased significantly in the 1990s, and toxic aluminum concentrations declined slightly. Regional surface water ANC did not change significantly in New England or in the Ridge/Blue Ridge.
Modest increases in ANC have reduced the number of acidic lakes and stream segments in some regions. Current data estimate that there 150 Adirondack lakes with ANC less than 0, or 8.1% of the population, compared to 13% (240 lakes) in the early 1990s. In the Upper Midwest, an estimated 80 of 250 lakes that were acidic in mid-1980s are no longer acidic. TIME surveys of streams in the northern Appalachian Plateau region estimated that 5,014 kilometers of streams (ca. 12%) were acidic in 1993-94. Approximately 3,393 kilometers of streams, or 7.9%, remain acidic in this region at the present time. In these three regions, approximately one-third of formerly acidic surface waters are no longer acidic, although still with very low ANC. There was little evidence of a regional change in the acidity status of New England or the Ridge/Blue Ridge regions, and the numbers of acidic waters in these regions remain relatively unchanged.