Macrophyte biomass and water quality in Ontario rivers

Abstract

An empirical survey of macrophyte biomass collected from 38 stations along 28 rivers in southwestern Ontario was conducted in 1999 and 2000 to quantify the relationship between biomass and instream nutrients and dissolved ions. Multiple regression models showed that mean and maximum biomass were weakly but significantly related to the nutrients N and P; these variables explained ∼27% of the variability in biomass across stations. Models developed with 1999 data were improved with the addition of measurements of total residue, which is correlated to ionic concentrations and turbidity, providing a rough indication of instream light availability. However, validation of the models with an independent data set, collected in 2000, showed that the nutrient-only models were the most robust across data sets. We detected a significant lack of fit in all of the models developed, indicating the independent variables used were not best at explaining variability in macrophyte biomass. Although our study yielded only weak predictions of biomass in rivers, the robustness of the models based on nutrients among data sets suggests that nutrient-abatement programs, focussed primarily on N, may be successful in reducing nuisance macrophyte biomass.