Effects of Acid Rain on the Chemistry of Western Adirondack Streams In 2003-2005

Gregory B. Lawrence USGS, Troy, NY
Karen M. Roy New York State Dept. of Environ. Cons
Barry P. Baldigo USGS, Troy, NY
Howard A. Simonin New York State Dept. of Environ. Cons
Susan B. Capone Adirondack Lakes Survey Coop., Ray Brook, NY
James W. Sutherland, P.O. Box 2641, Nantucket, MA
Sandra A. Nierzwicki-Bauer Darrin Fresh Water Inst. and Dept. of Biology, Rensselaer Polytechnic Inst., Troy, NY
Charles W. Boylen Darrin Fresh Water Inst. and Dept. of Biology, Rensselaer Polytechnic Inst.,Troy, NY

A focus on lake chemistry has resulted in an incomplete picture of acidic deposition effects on surface waters in the Adirondack region of New York. Relatively little information is available on streams in this region, although they are more prone to acidification, particularly during high flows. An assessment of streams was therefore undertaken in the Oswegatchie and Black River drainages; an area of 4585 km2 in the western part of the Adirondack region of New York. Streams with lakes or ponds that affected more than 25 percent of their drainage area, or required more than 1 hour of hiking to reach were excluded. Of the 565 streams that met these criteria, 200 were randomly selected for sampling. Sampling surveys were conducted on 3 to 4 consecutive days, twice during spring snowmelt (March 29-April 1, 2004 and March 29-31, 2005), twice during summer base flows (August 25-29, 2003 and August 16-18, 2004) and once during fall storms (October 27-30, 2003).

Acidification was assessed with the newly developed base-cation surplus (BCS) and acidneutralizing capacity by Gran titration (ANCG). The BCS was more effective for ascribing acidic deposition effects than ANCG, because it related more closely to concentrations of inorganic Al. The percentage of streams with a BCS value < 0 µeq L-1, averaged for the five surveys, was 38 percent, compared with 18 percent with ANCG < 0 µeq L-1. The BCS percentage is consistent with the finding that 31 percent of streams (averaged for all surveys) had a concentration of inorganic Al > 2.0 µmol L-1, the level above which is toxic to brook trout, a relatively acid-tolerant fish species. These results demonstrated that the criterion for acidification of ANCG < 0 is not suitable for the protection of aquatic biota.

During elevated flows in March 2004, 56 % were acidified based on the criterion of BCS < 0 .µeq L-1, whereas during low flows in August 2003, 12% were acidified. The total length of stream reaches estimated to be prone to acidification within the study area was 718 km, although a remaining 3085 km were not assessed because of inaccessibility.