Factors regulating phytoplankton and zooplankton biomass in temperate rivers

By measuring Chl a, zooplankton biomass, nutrient concentrations, and water residence time in 31 rivers in eastern Canada, we tested the following hypotheses: Chl a is positively related to nutrient concentrations and water residence time, and zooplankton biomass is positively related to Chl a and water residence time. Chl a ranged from 1.8 to 27.6 µ g liter −1 , total phosphorus (TP) from 7.3 to 212.3 µ g liter −1 , and water residence time from 3.3 to 19.4 d. There was a positive relationship between Chl a and TP ( R 2 = 0.76) and no relationship between Chl a and residence time. In contrast, zooplankton biomass was positively related to water residence time ( R 2 = 0.33). There was only a weak positive relationship between Chl a and zooplankton biomass. Mean river zooplankton biomass was low (11.3 µ g liter −1 dry mass) compared to lakes of similar Chl a concentration.