Macrophyte Community Dynamics in Lake Simcoe’s Fringe Wetlands: Potential use as Biological Indicators of Water Quality

Abstract

Indices have been developed using macrophytes and water quality parameters to detect the impact of anthropogenic disturbance on coastal wetlands of the Great Lakes, but such an index does not currently exist for Lake Simcoe. As wetland macrophytes are influenced by water quality, any impairment in wetland quality should be reflected by taxonomic composition, biomass and dynamics of the macrophyte community. This study investigates the potential use of macrophytes as a tool for monitoring water quality by examining the dynamics (species richness, density, diversity, and above-ground biomass) in emergent macrophyte communities in fringe wetlands around Lake Simcoe exposed to contrasting degrees of disturbance. Macrophytes and limnologic data were collected from six wetlands over four seasons from 2013 – 2014. The macrophytes were identified to species and limnologic data was quantified to reflect the water quality, which was measured as a proxy for site disturbance. Wetlands in this study correspond to a wide range of environmental conditions, ranging from very clear and nutrient poor oligotrophic conditions (e.g., TP =11.25 µg/L, TN = 345.25 µg/L, CHL a =1.37 mg·m-3) to turbid and eutrophic wetlands (e.g., TP = 47.25 µg/L, TN = 2285 µg/L, CHL a = 3.26 mg·m-3. Overall, the limnologic parameters indicated that water quality reflected the degree of anthropogenic degradation influencing the wetland. Taxonomic composition and population dynamics reflected the water quality. The least disturbed site was dominated by native Scirpus acutus and Scirpus pungens, which are mostly intolerant of environmental degradation, as well as the cosmopolitan Sparganium eurycarpum, found in all sites and tolerant of many different conditions. The moderately disturbed sites were dominated by both intolerant and tolerant species, including Scirpus acutus, Leersia oryzoides, Eleocharis smallii, Typha x glauca, Typha angustifolia, and Sparganium eurycarpum. The highly disturbed sites were also dominated by Sparganium eurycarpum, and species that are considered to be invasive, aggressive, and/or very tolerant of degradation, including Typha x glauca, Typha angustifolia, Phragmites australis, and Calamagrostis canadensis. These species are indicator species of wetland integrity and their relationship with the limnologic parameters as determined by ordination demonstrated responses that were consistent with the literature. Thus this study validates that macrophytes could be used as an indicator of water quality changes in this study area.