Patterns of Epipelic Algal Abundance with Depth, Trophic Status, and Acidity in Poorly Buffered New Hampshire Lakes

Abstract

The biovolume and species composition of algae on sediments in 20 poorly buffered New Hampshire lakes were surveyed in autumn to delineate patterns of community structure and composition with acidity and trophic status of lakes, and along depth gradients within lakes. Patterns of total algal biovolume on sediments were not strongly related to these habitat conditions because of masking by algae that probably settled from the plankton onto sediments. Biovolumes of "benthic" algae generally decreased with depth; however, weak and positive correlations between biovolumes of some benthic algal taxa and depth indicated that benthic algae had adapted to low light conditions and were perhaps facultatively heterotrophic. Decreases in diatom and increases in blue-green algal biovolumes with total phosphorus and chlorophyll a concentrations in lake water indicated that blue-green algae were better adapted for sequestering nutrients in low light environments. The variability in patterns of algal biovolume with acid neutralizing capacity (ANC) and pH indicated that algae had adapted well to different levels of ANC and pH. Biovolumes of blue-greens were negatively correlated with ANC, primarily because of the high biovolumes of various blue-green algae that occurred sporadically in lakes with ANC between 0 and 20 μeg/L and pH between 5.8 and 6.0. Diatom biovolumes generally increased with ANC and pH; however, biovolumes of several species of diatoms, including a Pinnularia, were greatest in low ANC and pH lakes. In general, Eunotia biovolumes decreased and Navicula and Pinnularia biovolumes increased with ANC and pH.