TRIBUTARY WATER-QUALITY FEEDBACK FROM THE SPREAD OF ZEBRA MUSSELS - OSWEGO RIVER, NEW-YORK

Dramatic changes in the water quality of the Oswego River system, incl uding Oswego Harbor, since the early 1990s brought about by zebra muss el (Dreissena polymorpha) infestation are documented. The analysis is based on summertime (June to September) water quality monitoring of th e Oswego Harbor (1981 and 1993), the mouth of the Oswego River (1983 t o 1993), and three upstream sites in the Oswego River system (1990, 19 91, and 1994), and two benthic surveys conducted along a 70 km reach o f the system to the mouth of the Oswego River in 1994. It is estimated that water in the Oswego River was filtered more than entice over thi s length by the mussels in 1994 (at median flow) before it reached Osw ego Harbor. The zebra mussel infestation converted the Oswego River an d the harbor from a turbid (low clarity), phytoplankton-rich, nutrient -depleted system, to a system with distinctly greater clarity, reduced phytoplankton concentrations, enriched in soluble reactive phosphorus . Most of this impact was attributable to dense zebra mussel populatio ns (e.g., similar to 30,000 indiv/m(2)) in a 5 km river section, locat ed > 60 km upstream of Oswego Harbor. These changes in tributary water quality represent a form of feedback associated with the spread of th e zebra mussel from the Laurentain Great Lakes. Increased attached alg ae growth in the Great Lakes proximate to the inflow of infested tribu taries is a reasonable expectation in response to the more available f orm of the phosphorous load.