INCREASE IN THE ABUNDANCE OF CLADOCERA AT PH 5.1 IN EXPERIMENTALLY-ACIDIFIED LAKE-223, EXPERIMENTAL LAKES AREA, ONTARIO

Lake 223 in the Experimental Lakes Area, northwestern Ontario was experimentally-acidified with H//2SO//4 form 1976 to the present. Cladocerans increased in absolute and relative abundance and in total biomass when the pH of Lake 223 was lowered from 6. 7 to 5. 1. The changes in cladoceran species composition with acidification are largely consistent with known responses of these species to low pH. The increase in importance of cladocerans in 1981 to 1983 was at the expense of copepods. It was hypothesized to be caused by the decline in predation by small fish during 1981 to 1983 as acidification reduced minnow populations and inhibited reproduction in trout and sucker.