Periphyton as an early indicator of perturbation in recreational lakes

We looked for empirical relationships between periphyton biomass and recreational development in the Laurentian lakes of Quebec (Canada). We compared the response of periphyton (as chlorophyll a) on rocks and sediments with that of phytoplankton. Epilithon and epipelon biomass increased significantly with lake recreational development (as percentage of cleared land within a 50 m riparian strip) but. was not related with open-water phosphorus concentration. In contrast, phytoplankton was related to open-water phosphorus but did not increase along the gradient of lake development. Periphyton stoichiometric composition also changed with increasing take development. High C:P and C:N ratios were found in pristine lakes, whereas lower periphyton molar ratios, which approached the optimal stoichiometric composition for benthic microalgae, were observed in the most developed lakes. Our findings suggest that periphyton, positioned near the land-water interface, has access to land-derived nutrients before they are diluted in the open water. Therefore, periphyton on all substrata is the first community to respond to increased inputs resulting from lake recreational development. The measurement of littoral algal biomass and chemical composition may represent a better tool for early detection of lake perturbation than classic methods based on pelagic characteristics.