DRY-WEIGHT DEPOSITION IN POLLUTED ONONDAGA LAKE, NEW-YORK, USA

Short and long-term trends in dry weight deposition rates are document ed for polluted Onondaga Lake, NY, based on analyses of sediment trap collections made below the epilimnion at a single deep-water location in ten years over the 1980-1992 period using cylindrical traps. Additi onally, comparisons of dry weight rates obtained with two different di ameter (4.0 and 7.6 cm) traps of the same aspect ratio (6), at four di fferent depths below the epilimnion, and from the lake's two basins, i n 1993, are presented to establish the representativeness of the long- term data. The near equivalence of fluxes determined with the differen t size traps and cumulative deposition rates measured over the range o f deployment depths, and the minor differences in flux observed for th e two basins, supports the representativeness of long-term data in qua ntifying deposition rates for the pelagic zone of the lake. Short-term variations in downward flux have been common in the lake over the per iod of monitoring. The summer-average dry weight deposition rate decre ased systematically (by about 45%) following the closure (in 1986) of a soda ash facility that caused enhanced rates of calcium carbonate de position; from an average of 23.2 to 12.8 g m(-2) d(-1). These dry wei ght deposition rates are high compared to values reported in the liter ature for other lakes, and are responsible for the lake's high rate of net sedimentation.