Seasonal influence of calcium magnesium acetate on microbial processes in 10 northern Californian lakes

Abstract

Conventional road salt has long been responsible for corrosive effects on cars and highway structures, as well as some undesirable impacts on terrestrial and aquatic ecosystems. This has resulted in investigations of a variety of alternative deicing compounds. Early studies in northern California demonstrated the formation of a salt-stabilized chemocline in Putt's Lake along Interstate 80 in the Sierra Nevada. Current studies on natural populations of algae and bacteria indicate that calcium magnesium acetate (CMA) appears to be a good alternative to sodium chloride. Bioassays of 10 northern Californian lakes were conducted in situ with various concentrations of CMA. During the summer, eight out of the 10 lakes showed no significant response in algal biomass with the CMA concentrations. Bioassays done during the late spring and early winter showed only slight deviations from these results. Temperature, prevailing weather conditions, and standing stock of microbial populations appear to be the dominant factors in determining whether or not an algal response was evident in these seasonal CMA bioassays. In a series of laboratory bioassays with natural microbial communities from Castle Lake, CMA had no significant effects on primary production or the uptake of acetate by bacteria. A significant increase in phosphorus uptake by the “algal” fraction (> 3 μm) in lakewater occurred at CMA concentrations of 10 ppm. This increase in P-uptake was attributed to bacteria that were associated with detrital particles in the water. At the same time we observed a significant decrease in algal biomass. Within the scope of this investigation, CMA appeared to have minimal effects on phytoplankton biomass other than the observed stimulation of P-uptake which may be due to competition between the natural bacterial and algal populations.