Citation:

Charles, D. EFFECTS OF ACIDIC DEPOSITION ON NORTH AMERICAN LAKES: PALAEOLIMNOLOGICAL EVIDENCE FORM DIATOMS AND CHRYSOPHYTES. U.S. Environmental Protection Agency, Washington, D.C., EPA/600/J-94/082 (NTIS PB94144706), 1990.

Description:

Analysis of sediment diatom and chrysophyte assemblages is the best technique currently available for inferring past lakewater pH trends, and use of the approach for assessing the ecological effects of acidic deposition is increasing rapidly. s of August 1989, sediment core inferred pH data existed for at least 150 lakes in North America, and cores from about 100 more lakes are being analyzed. quations for inferring past pH are based on at least 15-20 calibration data sets involving about 700 lakes. aleolimnology studies indicate that recent acidification has been caused by acidic deposition in the Adirondack Mountains (New York), northern New England, Ontario, Quebec, and the Canadian Atlantic provinces. nferred pH decreases are commonly as much as 0.5-1.0 pH units. ith the exception of one lake, no acidification trends were observed in regions currently receiving low deposition of strong acids (e.g. Rocky Mountains and Sierra Nevada in the western United States) . Slight or no trends towards decreasing pH were observed in study lakes receiving moderately acidic deposition (Upper Midwest and northern Florida) . The amount of inferred acidification (increase in- H+ concentration) correlates with the amount of S and N loading and the ability of watersheds and lakes to neutralize acid inputs, and is generally consistent with current lake acidification theory. n most cases, the primary cause of recent acidification (post -1850) is acidic deposition, as opposed to land use changes or natural processes, though these may be contributing factors. cid loading has decreased in some regions since 1970 (e.g., northeastern United States).

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