Heterogeneous spatial and temporal cyanobacterial distributions in Missisquoi Bay, Lake Champlain: An analysis of a 9 year data set

A 9 year phytoplankton, water quality and meteorological database was analysed to determine changes in cyanobacterial community composition and abundance at 4 sites in Missisquoi Bay from 2000 to 2008, and possible environmental factors underlying changes. Exponential summer growth of cyanobacteria to in excess of 80% of the August phytoplanktonic biomass occurred in most years except 2000 and 2007. Considerable spatial heterogeneity was observed in cyanobacterial abundance, with biomass exceeding 100,000 mg/m3 at eastern sampling sites on the bay. Microcystis spp. were generally dominant from 2001 to 2005, and the cyanotoxin microcystin was frequently detected during Microcystis blooms. Aphanizomenon and Dolichospermum species were more common from 2006 onwards; however sometimes completely different taxa were dominant at different sampling sites on the same day. Highest total phosphorus concentrations occurred on the eastern side of the bay, while total nitrogen concentrations were mostly low at all sites, and molar TN:TP ratios were generally < 20. Cyanobacterial biomass was at times significantly correlated with water quality attributes such as turbidity, nutrients and water temperature. Some correlations were also found with meteorological measures including maximum and minimum air temperature and wind speed. However, the correlations were often too weak (ρ < 0.50) to be indicative of major relationships between the cyanobacteria and environmental factors. Likewise multivariate analyses indicated no strong relationships between community composition and abundance with the environmental attributes measured, and much of the spatial and temporal heterogeneity in the cyanobacterial blooms observed in Missisquoi Bay remains unexplained.