ZEBRA MUSSEL (DREISSENA-POLYMORPHA) POPULATIONS IN THE SENECA RIVER, NEW-YORK - IMPACT ON OXYGEN RESOURCES

The character and cause of a major depletion in dissolved oxygen (DO) observed in a 16-km reach of the Seneca River, New York, in the summer of 1993 was evaluated. The decline in oxygen concentrations was attri buted to a recent severe infestation by the invading zebra mussel. Zeb ra mussel densities of 33 000-61 000 individuals m(-2) were found in a 1.4-km section, across which an average (n = 3) depletion in DO conce ntration of about 1.7 mg L(-1) was observed. The estimated areal respi ration rate for the zebra mussel population in this section (34 g m(-2 ) d(-1)) nearly matched the areal sink calculated independently from D O budget calculations (44 g m(-2) d(-1)). The zebra mussels also cause d substantial decreases in phytoplankton biomass and increases in wate r clarity over the study reach. Loss in waste assimilative capacity is expected to occur in other alkaline hardwater rivers and streams with rock substrate in North America as the zebra mussel invasion spreads.