Fayetteville Green Lake, New York, U.S.A.: VIII. Mass balance for 137Cs in water, varved and non-varved sediments

A mass balance for 137Cs was done in Fayetteville Green Lake. 43% of total 137Cs input was found in shallow-water (0–18 m) sediments, 16% was found in deep-water varved sediments, > 9% was found in the water column, and ∼ 32% remained to be carried away by lake outflow. Shallow-water sedimentary 137Cs must be resuspended and/or dissolved to maintain current levels of 137Cs in the water column, and current fluxes of 137Cs to deep-water varved sediments. 137Cs activities in individual varve-year samples from 1946 to 1976 followed closely the pattern of published bomb-fallout records, but the varves contained only 28–34% of cumulative unit-area fallout for this area. In order to preserve the yearly record of 137Cs sedimentation, the pore-water diffusion coefficient for 137Cs must be < 5 · 10 −11 cm 2 s −1. Bioturbation and physical mixing of these sediments does not occur. Some of the cores of shallow-water sediments accumulated 137Cs in amounts greater than was supplied by fallout to the lake surface area. This may be due to: (1) horizontal transport of surface-water 137Cs to shallow-water sediments for direct absorption; (2) bioconcentration by benthic algae and mosses, or (3) localized “funnelling” of sediments.