H Chen, J. M Burke, T Mosindy, P. M Fedorak and E. E. Prepas
Journal of Plankton Research, 2009, 31(9), 993-1008. DOI: 10.1093/plankt/fbp048
Euphotic water samples were collected monthly from 16 sites in Lake of the Woods, Ontario, Canada from July to September, 2006 and 2007. Sites represented a range of inorganic nitrogen and phosphorus concentrations and mixing regimes, which was reflected in the spatial variability in phytoplankton biomass and community composition, and cyanobacterial toxin [microcystin-LR (MC-LR)] concentrations. Nutrient concentrations decreased along a south to north transect, concomitant with distance from the main river inlet at the south end of the lake. Filamentous, nitrogen-fixing Aphanizomenon spp. and Anabaena spp. were dominant at most sites: Aphanizomenon was more abundant at southern sites and Anabaena was more abundant at northern sites. MC-LR was detected at all sites at least once (maximum concentration 0.69 µg L–1). However, there was no correlation between MC-LR concentration and the biomass of Anabaena, a documented MC-LR producer. For the pooled data set, total phosphorus and ammonium concentrations were the two parameters most strongly related with MC-LR concentration. Principal components analysis was used to analyze the data set; it indicated that two factors accounted for 81% of the variability among the 12 environmental parameters tested. Factor 1 represented physicochemical characteristics and phytoplankton biomass and Factor 2 represented Anabaena and Woronichinia biomass.