COMPARISON OF FOSSIL PIGMENTS WITH 20 YEARS OF PHYTOPLANKTON DATA FROM EUTROPHIC LAKE-227, EXPERIMENTAL LAKES AREA, ONTARIO

Fossil pigments from annually laminated sediments were calibrated with coeval phytoplankton data (1970-1989) from experimentally eutrophied Fake 227 in the Experimental Lakes Area, Ontario. Concentrations of ubiquitous pigments (beta-carotene, pheophytin a) were correlated to total algal biomass standing crop (r = 0.56-0.65; P < 0.01) during the ice-free seasons, but not to carbon fixation or water-column chlorophyll (Chi). Indicator pigments were correlated to ice-free season algal biomass for cyanobacteria (echinenone, aphanizophyll) and chlorophytes (lutein-zeaxanthin, pheophytin b)(r = 0.53-0.55, P < 0.05), weakly correlated for cryptophytes (alloxanthin, alpha-carotene; r = 0.32-0.40, P < 0.10), but were uncorrelated for chrysophytes and diatoms (fucoxanthin, Chl c) or dinoflagellates (peredinin). Premanipulation concentrations of fossil pigments (nmol pigment .(g organic matter)(-1)) from green algae and filamentous cyanobacteria (myxoxanthophyll) increased 4- to 10-fold in response to eutrophication of Lake 227. N-2-fixing cyanobacteria (recorded as aphanizophyll) replaced chlorophytes after the nitrogen additions decreased threefold in 1975. In contrast, accumulation rates of pigments (nmol pigment . m(-2) . yr(-1)) were rarely correlated with algal standing crop or production and were less satisfactory than fossil concentrations for the purpose of detecting changes in phytoplankton community composition.