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 dramatic effects on the phytoplankton community, similar to those recorded for systems anthropogenically affected. Species diversity decreased, biomass increased, and dominance shifted from chrysophytes to dinoflagellates. Increasing the pH from 5.0 to 5.8 stimulated very little recovery 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 diversity continued to increase as pH increased. Although chrysophyte biomass increased, total biomass began to decrease to pre-acidification levels because of declined abundances of cyanobacteria, dinoflagellates, chlorophytes, and cryptophytes. The size structure of the phytoplankton began to resemble more closely that seen in communities of reference lakes.