Aquatic epiphytes as bioindicators of wetland health: a study from the Simcoe County wetlands

Abstract

Aquatic microscopic epiphytes are increasingly recognized as sensitive bioindicators of aquatic ecosystem health, yet significant knowledge gaps remain regarding their indicator potential within Canadian wetlands. This study investigates the variability and environmental responsiveness of epiphytic communities to water quality changes as well as effects of the host species and structure. Two common macrophytes were used in this study - Typha angustifolia (alive and dead samples) and Nymphaea odorata. Four wetlands were studied, all from within the Lake Simcoe watershed (Ontario, Canada) - Langman’s Marsh, Lagoon City, Holland Marsh, and Victoria Point. Three major gaps motivated this research: the scarcity of Canadian based epiphyte bioindicator research, the limited use of multi-genera epiphyte assemblages as bioindicators rather than single taxa, and the lack of understanding of host - epiphyte relationships in Canadian wetlands. Epiphyte samples were collected seasonally (Summer 2021, Fall 2021, Spring 2022). Standardized scraping, centrifugation, and microscopic analyses with a haemocytometer, were used to quantify epiphyte density, species richness, and diversity. Measurements were taken of phytoplankton communities, water chemistry (e.g., nutrients, DOC, chlorophyll-a), and in-situ parameters (e.g., DO, pH, conductivity) were obtained to evaluate and compare wetland health. Statistical analyses - including Shannon diversity indices, data transformations, and diagnostic modelling - were used to assess spatial and temporal patterns and to determine relationships between epiphyte assemblages, macrophyte hosts, seasons, and wetland conditions. Across sites and seasons, epiphyte communities demonstrated clear, measurable variation associated with macrophyte type, season, and wetland characteristics. Preliminary findings indicate that (1) epiphyte assemblages respond sensitively to environmental gradients, supporting their use as indicators of wetland health in Canadian wetlands; (2) host macrophytes influence epiphyte density and composition, with notable differences between senescent and alive macrophytes; and (3) wetlands with higher anthropogenic stressors exhibited distinct epiphyte community structures compared with less impacted sites. Importantly, several key genera - such as Navicula spp., Nitzschia spp., Eunotia spp., Cymbella spp., and Gomphonema spp., occurred across all wetlands, but their relative abundances differentiated stressed systems from healthier ones: wetlands where Navicula spp. and Nitzschia spp. dominated reflected nutrient pressure, whereas sites where these taxa coexisted alongside diverse, well-represented assemblages indicated more stable ecological conditions. Overall, this research provides a multi-wetland, multi-host assessment of aquatic microscopic epiphytes within the Lake Simcoe region and offers strong evidence supporting their utility as bioindicators in Canadian freshwater wetlands. The findings expand baseline ecological knowledge and contribute a valuable framework for future monitoring and conservation initiatives.