Relationship of water quality of Hudson River, New York, during peak discharges to geologic characteristics of contributing subbasins

Water samples from two Hudson River floods in 1977--one originating mainly in shale subbasins that produce high sediment loads, the other in soil-poor, crystalline rock terrane that yields little sediment--were analyzed to evaluate the relationship of iron, manganese, lead, phosphorus, and polychlorinated biphenyls (PCB's) to suspended-sediment concentration. During the flood of high sediment discharge, ratios for all substances studied except PCB 's reflected their concentration within the basin regolith. During the flood of smaller magnitude, from the low-sediment crystalline terrane, however, only the ratio for iron correlated with predicted concentrations in the basin, which suggests that the chemical constituents studied were contributed principally from other sources, possibly anthropogenic sources. High lead concentrations in the low-sediment flood were derived from an unidentified, basinwide source whose contribution was relatively insignificant during the flood from the shale area. (USGS)