Microcystins in components of twelve New Hampshire lakes of varied trophic status


Cyanobacteria toxins, called microcystins (MCs), were found in components of twelve, stratified New Hampshire (USA) lakes of varied trophic status during the summer of 1998. A sensitive ELISA method detected MC levels in whole lakewater, grazable phytoplankton fractions (\u3c30 mm), net phytoplankton (\u3e 375 µm), and isolated copepod and cladoceran (Daphnia sp.) samples. Whole lakewater (WLW) and net phytoplankton MC concentrations ranged between 9 and 165 ng MC L-1 and 0.2 and 2031 mg MC g-1-dry wt, respectively. Lakewater MC concentrations correlated with total epilimnetic phosphorus and total epilimnetic chlorophyll a concentrations and inversely with Secchi disk depth. The filter-feeding cladoceran (daphnid) and omnivorous copepod components of the zooplankton were separated and assayed independently for MCs. The cladoceran component accumulated between 7 and 2800 µg MC g-1-dry wt. in 10 of the lakes. The copepod component accumulated similar levels (4 and 2400 µg MC g-1 dry-wt.) in all lakes. Toxin accumulation by zooplankton directly correlated with lakewater and net phytoplankton MC concentrations. The highest levels were found in Silver Lake, a productive lake where Microcystis aeruginosa blooms frequently occur. It is particularly noteworthy that MC levels were also detected by ELISA methods in Russell Pond, a pristine, deep mountain lake of low productivity. The results emphasize the importance of including oligotrophic lakes and water supplies in monitoring programs for MCs to ensure the safety of animals and humans utilizing them for drinking and recreation

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