Effects of acidity and doc on phytoplankton community structure and production in three acid lakes (Nova Scotia)

Abstract

Phytoplankton community structure varied between the three lakes and between years within lakes. The Beaverskin Lake phytoplankton community was dominated by cyanophytes and chlorophytes in the summer and chrysophytes in the winter. Kejimkujik Lake was dominated by bacillariophytes in the summer of 1979 but no single group dominated in 1980 or 1981. Pebbleloggitch Lake phytoplankton consisted mainly of chlorophytes in 1979 but low biomass and no dominant groups characterized this lake during the growing season of 1980. Daily integral planktonic primary production measured simultaneously in the three lakes showed that in both years annual planktonic primary production was highest in the clear water lake, Beaverskin Lake, which also had lower dissolved organic carbon (DOC) concentration compared to the two dystrophic lakes. In the clear water lake annual production was similar between years but in the two colored lakes annual production was 40% higher in the second year. The observed increases in annual production between years in the colored lakes were largely due to changes in euphotic depth resulting from variations in hydrology and DOC export from the lake catchments. Lower discharges in the colored lakes in 1980 were accompanied by significantly lower in lake DOC concentrations, water color, light extinction coefficients and increased euphotic depth. Similar changes in discharge accompanied by lower DOC concentration in the clear water lake did not produce significant changes in water color, light extinction coefficient nor annual production between years. Rates of primary production at light optimum (P-max) were consistently higher in the most colored, acidic lake indicating that relatively high rates of autotrophic production will occur under acidic conditions if nutrient supply is maintained.