Zooplankton Recovery in Chemically Recovering, Acidified Adirondack Lakes

William H. Shaw1 Paul A. Bukaveckas2, James W. Sutherland3 Charles W. Boylen4 and Sandra A. Nierzwicki-Bauer4

Microcrustaceans and rotifers were examined from 30 Adirondack lakes from 1994-2006 as part of the Acidification Effects Assessment Program (AEAP). One goal of this effort was to generate baseline data to assess recovery should water column pH of the study lakes rise, as was expected to occur as a result of the 1991 Clean Air Act Amendments. The 28 species of microcrustaceans and 53 species of rotifers displayed differential sensitivity to acidic conditions and showed direct correlations of species richness and diversity with pH that was readily apparent during 1994-1996, the most acidic period of the study. Although some chemical recovery has occurred, during the 13 year period, only 13 lakes have shown a pH increase > 0.4 units and only 3 sites exceeded pH 6.0, a critical level where community changes are believed to occur. Changes in species richness, diversity and densities of acid sensitive species were used to evaluate biotic recovery in sites exhibiting pH improvement. Acid sensitive species were identified by Detrended Correspondence Analysis (DCA). Regression analysis revealed only 3 minor improvements in community variables relative to pH or elapsed time for microcrustaceans and 5 strong and 4 weak improvements for rotifers in 9 lakes. There was 1 strong improvement for microcrustaceans alone in a 10th lake. While it is clear that some biotic recovery is occurring, overall, it appears to be insufficient to overcome individual lake variability in zooplankton species richness and community composition and the annual variation in weather and local ecological conditions.

1 Sullivan County Community College, Loch Sheldrake, New York 12759, Retired, 2 Center for Environmental Studies, Virginia Commonwealth University, Richmond, Va. 23220, 3 NYSDEC, Senior Scientist, Bolton Landing, New York 12814, Retired, 4 Darrin Freshwater Institute, Associate Director, Bolton Landing, New York 12814