EFFECT OF REDUCED SALINITY INPUT ON RIVER STRATIFICATION AND DISSOLVED OXYGEN

Changes in the occurrence, character, and longitudinal extent of salinity (S) stratification, and related impacts on dissolved oxygen (DO), in the Seneca and Oswego Rivers, NY, in response to the abatement of ionic pollution of inflowing Onondaga Lake, is documented. The analysis is based on vertical profiles of specific conductance and DO collected 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 manufacturing facility. The S difference between the lake and the Seneca River decreased from about 2.6 to 0.7 parts per thousand (‰) following the closure; more than 50% of the continuing difference is associated with lingering ionic waste loading from soda ash production. 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 decreased, 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 lowel river layer, representing violations of New York water quality standards, continues to occur where S stratification prevails. Elimination of the continuing ionic waste inputs from soda ash production would further limit the stratification phenomenon and improve the river's DO problem.