EFFECTS OF VANADIUM ON FRESH-WATER PHYTOPLANKTON PHOTOSYNTHESIS

In six of the seven lakes studied, addition of vanadium at concentrati ons in the 2 to 165 x 10(-7) M range decreased photosynthetic rates of phytoplankton in six lakes. The depression was not a result of photos ynthate loss. The response of phytoplankton photosynthesis to vanadium addition was assessed as the slope of photosynthetic rate (as percent of control) plotted against added vanadium concentration. We then use d univariate and multivariate statistics to determine whether the resp onse to vanadium (''slope'') was influenced by phosphorus availability (estimated by P-32-turnover-time), phytoplankton biomass, and proport ions of six taxonomic groups (as % of total phytoplankton biomass): Ch lorophyta, Bacillariophyta, Chrysophyta, Pyrrophyta, Cryptophyta, and Cyanobacteria. Simple correlation analysis revealed that only biomass and cyanobacteria were significantly correlated (p < 0.05) with the re sponse to vanadium. To reduce redundancy among the eight ecological va riables, we conducted a principal component analysis using data from t he 22 experiments. The first two principal components accounted for 59 % of the variance in the original variables. PC1 loaded highly and pos itively on biomass and cyanobacteria, and negatively on Bacillariophyt a and Chrysophyta. PC2 loaded positively on Cryptophyta and Pyrrophyta . Only PC1 was significantly correlated (p < 0.05) with the response t o vanadium (''slope''). We conclude that lakes characterised by high p hytoplankton biomass, high proportion of cyanobacteria, and low propor tion of Bacillariophyta and Chrysophyta, are most vulnerable to inhibi tion of photosynthesis by vanadium. In the surface waters studied, dis solved vanadium at concentrations above the detection limit of 5.0 x 1 0(-8) M was found only in the inshore areas of Lake Erie and in Hamilt on Harbour, Lake Ontario.