Microbiological influences on phosphorus release from aerobic lake sediments

Abstract

The role of sediments in regulating nutrient availability in lakes and reservoirs has been the subject of many recent studies. Classical theories concerning the regulation of phosphorus release from sediments by oxidation-reduction potential neglect the potential of microorganisms to transfer large amounts of phosphorus out of sediments.

Aerobic surface sediments collected from the eutrophic Occoquan Reservoir, Virginia, were treated with ethylene oxide to reduce the populations of living organisms. These sediments served as the sole source of phosphorus in cultures inoculated with bacteria and/or blue-green algae collected from the Occoquan Reservoir. Inoculum composition was maintained for the thirty-five-day incubation period with selective inhibitors. An abiotic culture series served as a control. Cultures were harvested at five-day intervals and were analyzed for phosphorus fractions in sediment and medium, chlorophyll, bacteria in the sediments, and air dry weight of the sediments.

Short-term (less than five days) release of total and inorganic phosphorus was roughly equal for all cultures. After five days growth of algae correlated with rapid transfer of phosphorus from the sediments. A large proportion of the released phosphorus was incorporated into the algae. Cultures containing just bacteria showed only slightly higher phosphorus release rates than abiotic cultures.

Blue-green algae appear to act as a sink for phosphorus, permanently upsetting the phosphorus equilibrium between sediment and water. The sediments continuously release phosphorus to restore the equilibrium. Bacteria appear to have little effect beyond the mineralization of relatively small quantities of organic phosphorus.