Effects of Conservative Ions on Algal Assemblages.

Abstract

Laboratory and field studies were undertaken to examine the effects of increased conservative ion concentrations on various algal assemblages. In a uni-algal experiment, Cyclotella meneghiniana exhibited growth rates greater than 1 division per day for NaCl concentrations ranging from 18 to 4000 mg(.)l('-1). However, growth rates were slightly greater at the higher NaCl treatments. Morphological differences were also found between the lower and higher NaCl treatments. A competition experiment between a diatom and a bluegreen alga was conducted along an increasing NaCl and KCl concentration gradient. High potassium concentrations exhibited an adverse effect upon growth of the diatom Synedra filiformis v. exilis. It washed out of the competition flasks at KCl-35, KCl-65 and KCl-130 after 29 days. Increased sodium concentrations also inhibited growth of Synedra in the NaCl competition flasks, but to not as great an extent as did potassium. A bioassay experiment was also conducted on the effects of increased NaCl and KCl concentrations on a natural phytoplankton assemblage from Lake Superior. Potassium strongly inhibited diatom growth at K('+) concentrations as low as 8 mg(.)l('-1). Ankistrodesmus gracilis gradually increased its abundances as KCl concentrations rose, while diatom abundances steadily declined. At KCl-128, A. gracilis composed 89% of the total assemblage, while the total diatom component only comprised 2% of the assemblage. In the NaCl treatments, increased salinity appeared to have only a secondary effect upon phytoplankton community composition and development. Species interactions and phosphate additions seemed to be more important factors. A field study was also undertaken to determine the effects of salt loadings to a lake in southeastern Michigan. A sediment core was obtained to monitor changes in the diatom assemblage over a 30 year period. A 9-year lag was found from the initiation of salt storage adjacent to the lake until noticeable affects were exhibited by the diatom component. The initial response appeared to be a decline in diatom diversity followed by an increase in halophilic taxa.