Temporal and spacial distribution of planktonic diatoms in Red Rock Reservoir, Iowa

An intensive water quality and diatom taxonomy study was conducted over a 16 month period from June, 1978 through September, 1979, on Red Rock Reservoir located on the Des Moines River, Iowa. The purpose of the study was to examine the distribution of planktonic diatoms within Red Rock Reservoir and to determine what factors were most important in controlling their distribution. Numerous water quality parameters were monitored on a weekly basis at sampling stations upstream of and within the reservoir. In addition, 10 intensive transect studies were performed during the period in order to determine the instantaneous status of the reservoir in terms of water quality and phytoplankton distribution;Although hydrologic conditions during this period were sub-optimal in terms of supporting abundant phytoplankton populations, definite temporal and spacial distribution patterns were noted. The factors which were found to be most important in controlling the distribution of planktonic diatoms included retention time, light availability, and sedimentation. Other factors found to be important during certain periods included zooplankton grazing, light availability, nutrient availability and thermal stratification;Dominant diatom taxa noted during the study period included Cyclotella meneghiniania, Melosira granulata, M. granulata var. angustissima, Stephanodiscus astraea, S. astraea var. minutula and Asterionella formosa. During a given study, longitudinal differences in species composition were most evident;Evidence was found which suggests that changes in reservoir operation leading to significantly longer retention times or the establishment of permanent thermal stratification could lead to a shift in phytoplankton species compositions. This shift would in all likelihood be away from a diatom dominated phytoplankton to one dominated by green and/or blue-green algae