Species Diversity of Microbial Communities in a Northern Temperate Humic Lake

Species richness and species diversity of bacterioplankton, phytoplankton and protoplankton were examined in Crystal Bog, a humic lake in northern Wisconsin, as part of an NSF sponsored Microbial Observatory Program. Crystal Bog is part of the North Temperate Lakes Long‐Term Ecological Research site. Automated ribosomal intergenic spacer analysis (ARISA) was used to assess bacterial diversity. Phytoplankton and protoplankton were enumerated in a settling chamber with an inverted microscope. Four distinct phases in the ice‐free season of the bog can be recognized based on microbial populations. The first phase extends from ice‐out until about the first week of April. During this phase three species of dinoflagellates come to dominate the phytoplankton, with Glenodinium quadridens representing 60% of total phytoplankton biovolume. By mid‐April the spring dinoflagellate blooms collapse. The second phase is a period of instability as a series of species dominates the phytoplankton. In mid‐July dinoflagellates again dominate the third phase, and Peridinium limbatum alone represents 90% of the bog phytoplankton. The fourth phase is a stable period as P. limbatum slowly declines in late summer and fall. A strong correlation was found between bacterial and phytoplankton diversity (Shannon–Weaver Index) in this bog, suggesting the two microbial communities are linked. The protoplankton, however, were relatively uniform throughout the ice‐free period. The ice‐covered period may be treated as a fifth phase. When snow accumulates over the ice‐covered bog, light penetration is blocked and photosynthesis shut off. Heterotrophic protozoa assume dominance in the plankton.