NUTRIENT REGENERATION BY THE ZEBRA MUSSEL (DREISSENA-POLYMORPHA)

Changes in suspended seston and soluble nutrients were examined as a f unction of zebra mussel (Dreissena polymorpha) density in flow-through sediment-water microcosms to determine impacts on nutrient recycling. Overall, zebra mussels removed >70% of the suspended seston and >80% of the total chlorophyll a input to the microcosms. Declines in organi c nitrogen in microcosms were accompanied by density-dependent increas es in nitrate-nitrite nitrogen. We suggest that micro nora associated with the sediments in the microcosms were transforming ammonium nitrog en, which is an excretory product of zebra mussels, into nitrate nitro gen. Declines in total phosphorus in the microcosms also coincided wit h density-dependent increases in the concentration of soluble reactive phosphorus and its rate of regeneration, suggesting enhanced nutrient cycling via excretion. Calculated rates of soluble phosphorus regener ation due to zebra mussel activity ranged from 0.3 to 2.5 mg m(-2) d(- 1) at mussel densities ranging between 170 to 1300 individuals m(-2) p hosphorus regeneration by zebra mussels could have important implicati ons for the phosphorus economy of many lakes and rivers which have bee n invaded by this organism.