ABSTRACT

Despite several decades of research on eutrophication in lakes, changes in reservoir plankton communities are poorly understood. The current study examined spatial patterns and dynamics of algae and zooplankton in an oligo-mesotrophic main-stem reservoir, Bull Shoals Lake, Missouri-Arkansas, which is currently threatened from rapid development in upstream reservoirs. Eighteen sites were sampled during one week in summer and the seasonal dynamics of algae and zooplankton were followed at two of these sites. The lake showed strong spatial patterning in transparency, concentrations of phosphorus and chlorophyll-a, and densities of algae and zooplankton. Algal composition also varied substantially among sites, with cyanobacteria most abundant in up-reservoir and tributary sites. Although cyanobacteria were most abundant in late summer, appreciable densities were found throughout the year. Zooplankton were dominated by rotifers and cladocerans, which showed large oscillations in density over time. Abundance peaks occurred earlier in an up-reservoir than in a down-reservoir site, with a time delay of about a month for algae and four months for zooplankton. The plankton composition was consistent with the oligo-mesotrophic status of Bull Shoals Lake, but high densities of cyanobacteria at some tributary sites and in upstream reservoirs indicate localized enrichment and the threat of eutrophication in this clear Ozark lake.