Longitudinal and seasonal development of planktonio chlorophyllain the Rideau River, Ontario

Abstract

Planktonic chlorophyll a (chl-a) concentrations in the Rideau River, Ontario showed longitudinal and seasonal variation and ranged from 2 to 19 μg∙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 chl-a concentration. Downstream there were reaches of net increase in chl-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 chl-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 (R2 = 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.