THE EFFECT OF INCREMENTAL PH RECOVERY ON THE LAKE-223 PHYTOPLANKTON COMMUNITY

Experimental acidification of Lake 223 from pH 6.7 to 5.1 caused drama tic effects on the phytoplankton community, similar to those recorded for systems anthropogenically affected. Species diversity decreased, b iomass increased, and dominance shifted from chrysophytes to dinoflage llates. Increasing the pH from 5.0 to 5.8 stimulated very little recov ery response. Biomass and composition remained unaltered, but species diversity increased as pH increased. Elevating pH above 6 stimulated a strong recovery of the Lake 223 phytoplankton community. Species dive rsity continued to increase as pH increased. Although chrysophyte biom ass increased, total biomass began to decrease to pre-acidification le vels because of declined abundances of cyanobacteria, dinoflagellates, chlorophytes, and cryptophytes. The size structure of the phytoplankt on began to resemble more closely that seen in communities of referenc e lakes.