SEDIMENT ACCUMULATION RATES IN CONOWINGO RESERVOIR AS DETERMINED BY MAN-MADE AND NATURAL RADIONUCLIDES

The Susquehanna River is the major contributor to sediment loadings in the Chesapeake Bay. Because many environmental contaminants are associated with suspended particulates, the degree of particle retention within the reservoirs of the lower Susquehanna River is an important consideration in evaluating contaminant loadings to the Chesapeake Bay. Profiles of weapons-test Cs-137, nuclear power plant-related Cs-134 and Cs-137, and naturally-derived Pb-210 were used to estimate rates of sediment accretion in the Conowingo Reservoir, an impoundment of the Susquehanna River along the Maryland-Pennsylvania border. Net accretion rates ranged from about 2 cm yr-1 downstream of a nuclear power plant cooling discharge to a high of about 7 cm yr-1 at the mount of an incoming creek. Slight, but consistent, increases in the annual rate of accretion since the creation of the reservoir in 1928 are apparent. The current net average annual sediment load retained by the reservoir is estimated to be 0.4 x 10(6) to 1.5 x 10(6) metric tons yr-1. The retained sediment load represents about 8-23% of the long-time average sediment input to the reservoir.