Spatial and Temporal Distribution of Sedimentation Using 137Cs, Lake Cottrel, Susquehanna County, Pennsylvania, USA

The areal distribution of sedimentation rates in a 22 acre glacial lake in northeastern, Pennsylvania, USA were estimated from ¹³⁷Cs activity in sediment cores. The till-dammed lake has a maximum depth of 30 feet. It is located in a 187 acre watershed at an elevation of 1651 feet (amsl). With the exception of inflow from a small inlet stream, the lake is fed by ground water discharge and overland flow. The watershed consists of forest (75%) including reverted pasture, uncultivated fields (18%), and residential development (7%). Cesium-137 activity profiles in soil and sediment cores were measured using a NaI (Tl) detector. Cesium-137 fallout from nuclear weapons testing increased significantly after ~1954 and its highest flux appears around 1964. Post-depositional modification (e.g. bioturbation and diffusion) of ¹³⁷Cs profiles in lake cores appears to have been minor. Mass accumulation rates (MAR) for the period 1964-2007 were 0.23 g cm^-2 yr^-1, 0.15 g cm^-2 yr^-1, and 0.02 g cm^-2 yr^-1, at 1 m, 4 m, and 10 m from shore. The MARs for the period 1954-1964 were 0.63 g cm^-2 yr^-1, and 0.37 g cm^-2 yr^-1, at 1 m and 10 m from shore. Post-1964 ¹³⁷Cs activity in near shore sediments was similar to the activity in surficial soils in the watershed. The total ¹³⁷Cs inventory in watershed soils was ~638 Bq/m². In lake sediments, ¹³⁷Cs inventories ranged from ~826 Bq/m² near shore (fine-medium sands) to ~1246 Bq/m² at 10 m from shore (organic rich silt and clay). Sediment focusing factors in the lake sediments, relative to watershed soils, were 1.3 and 2.0 at 1 m and 10 m from shore, respectively. Total Cu and Zn concentrations in lake sediments peak in the upper 4 cm of sediment cores. The Cu spike is from copper sulfate herbicide applications from 1990 to 2003.