| Like many rivers around the world, the Rideau River is under pressure from a number of human induced activities resulting in a loss of species and habitat. In order to prioritise conservation efforts, it is necessary to understand what type of habitats will support the widest range of species. This study examines which physical and chemical factors exert the strongest influence on the diversity and community composition of aquatic macrophytes in the Rideau River. Macrophyte species were surveyed at 33 sites on the Rideau River, Ontario, in six 1 m2 quadrats aligned in a belt transect perpendicular to shore along a depth gradient of 0.5 m to 2.0 m. Regression analysis showed species richness and Shannon diversity were significantly related to water velocity, transect length, slope, and organic content. Multiple regression provided a model whereby 70% of species richness was explained by organic content, transect length, water velocity and chlorophyll a, and 77% of Shannon diversity was explained by organic content and water velocity. Mantel tests showed only chlorophyll a was weakly correlated with species composition. Canonical correlation analysis showed floating and floating-leaved species to favour habitats with low water velocity. No other significant patterns were found. It appears that while species diversity can be predicted from physical environmental variables, species composition cannot. |
