Impacts of a Soda Ash Facility on Onondaga Lake and the Seneca River, NY

Abstract

ABSTRACT A synthesis of the impacts of the operation (1884–1986) of a soda ash (Na2CO3) manufacturing facility on Onondaga Lake, NY, its tributaries, and adjoining portions of the river that receives the lake's outflow is presented, based on long-term programs of monitoring, process studies, and mathematical modeling. The lake was used as a source of cooling water and for the disposal of ionic (Cl− Na+, and Ca2+) waste, related solids and spent cooling water. At peak production the facility discharged ~1.3 × 106 metric tons of ionic waste to the lake annually. The soda ash facility had a profound impact on these ecosystems, by severely altering their structure and function. Portions of the two largest tributaries to the lake have been degraded from solids deposition associated with solution mining for NaCl (process reactant) and precipitation of Ca2+ waste (as CaCO3). The cooling water operation recycled phosphorus enriched hypolimnetic waters to the epilimnion. Ionic waste impacts on the lake and river included: (1) high salinity (S~3%o), (2) plunging inflows made dense by high S, that altered fundamental features of the lake's stratification regime and exacerbated the problem of severe dissolved oxygen (DO) depletion, (3) S-based density stratification and severe DO depletion over a 14 km reach of the river downstream of the lake, and (4) high levels of CaCO3 precipitation that reduced clarity, increased net sedimentation in pelagic areas, altered the character of near-shore sediments, and reduced alkalinity and pH. These impacts on the lake's chemistry and physical properties had profound effects on biological communities, including: (1) altered composition, (2) reduced richness and diversity, (3) limited macrophyte occurrence, (4) enhanced phytoplankton production, and (5) limited effectiveness of zooplankton grazing, thereby preventing intervals of high clarity. Closure of the facility resulted in dramatic improvements in water quality and ecological characteristics of these systems. Further improvement is expected as residual ionic waste loads decrease.