Comparison of Zygnematacean (Chlorophyta) Algae in the Metaphyton of Two Acidic Lakes

In 1986, Plastic Lake (pH≈5.6), acidified by acidic precipitation, and L.302S (pH≈5.0), experimentally acidified by addition of H2SO4, showed similar patterns of unattached benthic growth (metaphyton) of filamentous green algae. The mid to late summer build-up of metaphyton was extensive in both lakes, affecting nearly 100% of the lake perimeters, being concentrated in a shallow band 0.5–1.0 m deep in L.302S and 0.4–2.7 m deep in Plastic Lake. Distribution was negatively related to depth and bottom slope but independent of type of substratum. The areal density of metaphyton in the 0–2 m depth zone of Plastic Lake was estimated to be 1.2 g dry weight (dw)∙m−2. The productivity of metaphyton standardized by biomass was inversely related to the concentration of algae incubated. Over a common range of incubation concentrations primary production rates were similar in L.302S and Plastic Lake (≈1.6 μg C (mg dw)−1∙h−1) despite differences in the composition of the communities, predominately Mougeotia sp. and Spirogyra sp. in L.302S, and Zygogonium tunetanum Gauthier-Lievre in Plastic Lake.