Changes in epilithon and epiphyton associated with experimental acidification of a lake to pH 5

The algal taxonomy and community metabolism of epilithon and epiphyton in a lake experimentally acidified to pH 5 were compared with those in a nearby neutral lake to interpret the effect of acidification on periphyton. Acidification altered the algal community structure. Acidified periphyton had fewer filamentous cyanobacteria, whereas green algae (especially Mougeotia ) were relatively more abundant. Periphytic metabolism also differed substantially. Rates of dark respiration were higher and compensation irradiances were greater in all acidified benthic communities. Photosynthesis was C limited and enhanced by experimentally increasing turbulence to simulate rates of water movement in the shallow littoral zone. These findings are consistent with the hypothesis that the filamentous green algae of acid lakes can take up CO 2 faster than the adnate algae usually dominant in neutral lakes, thus (partially) overcoming the C limitation found in acidified lakes.