Distribution and relationship of radionucides to streambed gravels in a small watershed

In White Oak Creek watershed in eastern Tennessee, the radionuclides 60Co, 90Sr, and 137Cs were retained by streambed gravels on different sites: 60Co was associated with manganese in the hydrous oxide coatings on rocks and minerals; 90Sr occurred primarily as an exchangeable cation although small amounts were held in a nonexchangeable form; and 137Cs was held very selectively, presumably by illite in shale fragments composing the sediment. The distribution of radionucides on sediments was size dependent: the 0.85-3.35 mm fine-gravel fraction was higher in radionucide concentration than the sand fraction. An areal survey of radionuclide concentrations on streambed gravels from throughout the watershed, located numerous contamination sources. These radonuclide concentrations, when combined with both distribution coefficients of radionuclides between gravel and water and drainage area, were used to rank subsections of the watershed by their relative contribution to the overall contamination of the watershed. For 90Sr, this ranking procedure agreed with the measured discharges of subsections of the watershed which are routinely monitored