THE EFFECT OF PH ON THE RELEASE OF PHOSPHORUS FROM POTOMAC ESTUARY SEDIMENTS - IMPLICATIONS FOR BLUE-GREEN-ALGAL BLOOMS

The recurrence of a blue-green algal bloom (Microcystis aeruginosa) in the fresh-water tidal portion of the Potomac estuary in 1983 was related to the enhanced release of phosphorus from benthic sediments. The release of phosphorus was measured from Potomac estuary sediment cores incubated with water at pH levels encompassing the range outside (pH 7-8) and inside (pH 9·5-10·5) the 1983 bloom area. Phosphate release under aerobic conditions increased as a function of overlying water pH: between pH 8 and 9 the sediment-water phosphate flux was low; beginning with an overlying water pH of 9·5, the phosphate flux markedly increased. The increased release of phosphate at high pH is probably a result of solubilization of iron and aluminium phosphate complexes. Phosphorus release rates from the sediments at high pH (pH 9·5-10·5) are similar to the phosphorus source needed to account for the excess phosphorus measured in the bloom area and required to support the phytoplankton production. © 1991.