Richness of aquatic macrophyte floras of soft water lakes of differing pH and trace metal content in Ontario, Canada

Abstract

The richness of the aquatic macrophyte floras, i.e., the total number of species, was assessed in 39 soft water lakes in central Ontario, Canada. The Cu and Ni concentrations and pH of the lakes ranged from 1 to 360 mg m −3, 2 to 3700 mg m −3 and 3.9 to 7.0, respectively. Two non-exclusive subsets of the data were examined to determine firstly, if floral richness was related to lake pH in lakes with low Cu and Ni levels (Data Set I) and secondly, if floral richness in acidic (pH ⩽ 5.3) lakes was related to levels of various trace metals (Data Set II). Charophytes were not found in lakes with pH < 5.2. In Data Set I, there was no relationship between the richness of tracheophytes and pH, and there was a negative relationship between pH and bryophyte richness. Unlike phytoplankton, zooplankton, benthic macroinvertebrates and fish, there was no decrease in total species richness in lakes of pH < 5.5, as long as trace metal levels were low. Examination of Data Set II indicated tracheophyte richness of acidic lakes was negatively correlated with Cu and Ni levels. Biological surveys of metal-contaminated acidic lakes are, therefore, not of use for predicting the effects of acid deposition alone on aquatic macrophytes.