Response of Phytoplankton in Acidic Lakes in Ontario to Whole-Lake Neutralization

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Abstract
Changes in phytoplankton community composition were examined in two acidic lakes in Ontario, Bowland and Trout Lakes, to determine whether neutralization (and subsequent stocking with lake trout (Salvelinus namaycush) in the case of Bowland Lake) would reverse acidic characteristics. Miskokway Lake was monitored as an untreated reference lake. Analysis of community percentage similarity showed that year-to-year variability in phytoplankton community structure would have been low in the absence of neutralization. While changes in phytoplankton biovolumes or chlorophyll a concentrations after neutralization were not significant, there were several taxonomic changes: (1) the shift in the Bowland Lake phytoplankton community away from dominance by the cyanophyte, Rhabdoderma, and (2) the dominance of the prymnesiophyte Chrysochromulina breviturrita in the Bowland Lake phytoplankton community in 1985 2 yr after neutralization. It is likely that the major phytoplankton taxonomic changes were direct responses to chemical changes. These results suggest that structural changes (taxonomic) maintained stability of the phytoplankton communities under chemical stress (in terms of standing crop).