EFFECT OF REDUCED SALINITY INPUT ON RIVER STRATIFICATION AND DISSOLVED-OXYGEN

Changes in the occurrence, character, and longitudinal extent of salin ity (S) stratification, and related impacts on dissolved oxygen (DO), in the Seneca and Oswego Rivers, NY, in response to the abatement of i onic pollution of inflowing Onondaga Lake, is documented. The analysis is based on vertical profiles of specific conductance and DO collecte d over a 20 km reach of the river system for several years before and after the closure of the source of the ionic pollution, a soda ash man ufacturing facility. The S difference between the lake and the Seneca River decreased from about 2.6 to 0.7 parts per thousand (parts per th ousand) following the closure; more than 50% of the continuing differe nce is associated with lingering ionic waste loading from soda ash pro duction. The occurrence and longitudinal range of the S stratification phenomenon was, and continues to be, highly dependent on river flow. It is most strongly manifested when river flow is low. The occurrence, magnitude, and longtitudinal extent of S stratification have decrease d, and vertical exchange between the stratified layers has increased, since the closure, thereby ameliorating the coupled negative impact on the river's oxygen resources. However, under low flow conditions (e.g ., probability of occurrence equal to 15%) S stratification continues to extent > 2 km upstream and > 8 km downstream of the point of entry of Onondaga Lake into the Seneca River. Severe DO depletion in the low el river layer, representing violations of New York water quality stan dards, continues to occur where S stratification prevails. Elimination of the continuing ionic waste inputs from soda ash production would f urther limit the stratification phenomenon and improve the river's DO problem.