A CHLORIDE BUDGET FOR ONONDAGA LAKE*, NEW YORK, U.S.A. STEVEN W. EFFLER Upstate Freshwater Institute, Inc., Syracuse, NY13214, U.S.A.P.O. Box506 and CHARLES T. DRISCOLL Department of Civil Engineering, Syracuse University, Syracuse, N Y 13210, U.S.A. (Received August 30, 1984; revised March 1, 1985) Abstract. A C1 budget is presented for a 12 yr period (1970-1981) for C1 enriched (approximate volume- weighted average concentration of 1500 mg C1 L - i ) Onondaga Lake, New York. The budget utilizes continuous discharge and lake and stream water chemistry data, collected at an interval of approximately 2 weeks, over the 12 yr study period. Budget calculations are supplemented by high frequency water chemistry data from the lake and the tributary carrying the major portion of the loading. More than 85 of the external load of C1 (approximately 9 x 108kgyr -1) to the lake originates from an alkali manufacturer. Export of C1 from the lake was highly correlated to outflow from the lake (R = 0.915, for a resolution of 1 too). A good balance between estimated external loads and lake export was obtained (within 7%) for the 12 yr period, indicating that lake concentrations are consistent with external loading of this conservative substance. The results of this analysis contradict previous calculations that indicated 40 to 50% of the C1 in the lake originated from natural internal sources. 1. Introduction Chloride concentration in freshwaters is usually of interest as an indicator of the general level of pollution (Wetzel, 1975), and as a hydraulic tracer, based on its chemically conservative nature. At the concentrations commonly observed in most freshwaters (mean concentration of 8 mg C1 L- 1 in the river waters of the world (Wetzel, 1975)) the ecological effects of C1 have been described as subtle (Stoermer, 1978) and not well established (Sonzogni et al., 1983). Onondaga Lake, New York, contrasts most other lakes by its unusually high concentrations of C1; 1500 mg C1 L- 1 is a typical volume- weighted concentration (Eflter et al., 1981). Chloride is of interest in Onondaga Lake not only because of its impact on the lake and adjoing systems, but also because of the uncertainty of its origin, as natural sources of C1 to the lake have been described as significant (USEPA, 1974). Presented here is a C1 budget for Onondaga Lake for a 12 yr period (1970-1981) that is aimed at apportioning the external loads of C1 to the lake, and evaluating the hypothesis that natural sources contribute significantly to the C1 content of the lake. * Contribution No. 38 of the Upstate Freshwater Institute, Inc. Water, Air, and Soil Pollution 27 (1986) 29-44. © 1986 by D. Reidel Publishing Company.