CHANGES IN ZOOPLANKTON DURING THE EXPERIMENTAL NEUTRALIZATION AND EARLY REACIDIFICATION OF BOWLAND LAKE NEAR SUDBURY, ONTARIO

The zooplankton of Bowland Lake was sampled before and for 6 yr after neutralization of the lake from pH 4.9 to 6.9. Changes in community composition, including decreased abundance of the acidophilic rotifers Keratella taurocephala, Ploesoma lenticulare, and Gastropus stylifer and increased abundance of Keratella cochlearis, Polyarthra sp., and other species, occurred after neutralization. Two crustacean species not previously seen in Bowland Lake, Eubosmina tubicen and Epischura lacustris, became important in the zooplankton in the second and fourth years, respectively, after neutralization. Subsequently, increases in the abundances of K. taurocephala, G. stylifer, and P. lenticulare and decreases in the abundance of E. lacustris occurred during the early reacidification of the lake, when average pH declined to approximately 5.5. Temporal patterns in the total abundances of crustaceans, rotifers, and ciliates appeared linked to biological interactions, including predation by fish and larval Chaoborus, not directly to water quality changes.