LONGITUDINAL AND SEASONAL DEVELOPMENT OF PLANKTONIC CHLOROPHYLL-A IN THE RIDEAU RIVER, ONTARIO

Planktonic chlorophyll a (chi-a) concentrations in the Rideau River, Ontario showed longitudinal and seasonal variation and ranged from 2 to 19 mu g . L(-1). Chlorophyll a concentrations in the river were not simply a reflection of the concentrations in the headwaters. On movement from the lentic headwaters into the lotic river waters there was usually a significant decrease in chi-a concentration. Downstream there were reaches of net increase in chi-a (sources), reaches of no change in concentration, and reaches of net decrease (sinks). Increases in concentration only occurred over reaches with retention times of 72 h or longer. No increases in chi-a concentration occurred over a reach with a retention time less than 50 h. Chlorophyll a concentration was not significantly correlated with discharge. Chlorophyll a concentration was positively related to total phosphorus concentration (R(2) = 0.15, p = 0.016). About 50% of the variation in chl-a concentration could be accounted for by a combination of total phosphorus, nitrate, and soluble reactive phosphorus concentrations.