2008 Joint Meeting of The Geological Society of America, Soil Science Society of America, American Society of Agronomy, Crop Science Society of America, Gulf Coast Association of Geological Societies with the Gulf Coast Section of SEPM

Paper No. 6
Presentation Time: 8:00 AM-4:45 PM

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

COOK, Robert D. and CUPILLARI, Thomas G., Natural Sciences, Keystone College, La Plume, PA 18440, robert.cook@keystone.edu

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.