Dissolved oxygen declines in the Hudson River associated with the invasion of the zebra mussel (Dreissena polymorpha)

Dissolved oxygen (DO) declines have serious implications for the health of aquatic systems. These declines ari often attributed to changes in organic or nutrient loading but are not generally attributed to species invasions. We use an Ii-year record of DO in the tidal Hudson River to describe the timing and spatial extent of the DO decline as compared to the timing and spatial extent of the zebra mussel establishment in the river. Furthermore, the system attributes that interact with zebra mussel respiration to moderate DO declines are explored using physical and biological budgets. Concurrent with the establishment of the zebra mussel, mean summertime DO declined from 8.3 to 7.3 mg L-1. Because of moderate hydrologic inputs and atmospheric exchange, system respiration would have to increase by only about 0.5 g of O-2 m(-2) d(-1) to have caused this decline. Independently estimated zebra mussel respiration (1.1 g of O-2 m(-2) d(-1)) is about double this required respiration. Increased macrophyte photosynthesis, due to increased light penetration after the zebra mussel invasion, may have moderated the effect of zebra mussels on DO.