Periphyton assemblages as indicators of recovery in acidified Canadian Shield lakes

Abstract

Periphyton is very responsive to abiotic changes within recovering acidified shield lakes. We conducted a survey of acidified shield lakes to assess epilithic periphyton assemblages as indicators of natural recovery. Canonical correspondence and regression analyses both showed that dissolved inorganic carbon (DIC) was the best predictor of taxonomic composition, biomass accrual, and species richness in lakes of low alkalinity. Dissolved organic carbon (DOC) was also a significant predictor of taxonomic composition, and biomass accrual (desmids, filamentous green algae, and total). Constrained indicator species analysis identified Actinotaenium cucurbita, Cylindrocystis brebissonii, Eunotia bactriana, Fragilaria acidobiontica, Homoeothrix juliana, Tetmemorus laevis, and Zygogonium ericetorum as indicators of high-acidity (pH <5.0), clearwater lakes with low (<0.3 mg/L) DIC concentrations. Achnanthes minutissima, Cymbella microcephala, and Gomphonema acuminatum were indicative of low-acidity (pH >5.6) lakes with higher DIC concentrations (>0.6 mg/L) and positive buffering capacities. Our findings suggest that periphyton in recovering acidified shield lakes are stimulated by increasing DIC and DOC concentrations. Increases in DIC availability might enhance recolonization by diatoms in clearwater lakes, while increases in DOC concentrations may favour desmids and filamentous zygnematacean taxa, especially in naturally acidic brown-water lakes.