Impact of the 1993 Flood on the Distribution of Organic Contaminants in Bed Sediments of the Upper Mississippi River

The 1500 km Upper Mississippi River (UMR) consists of 29 navigation pools and can be divided into the upper reach (pools 1−4), the middle reach (pools 5−13), and the lower reach (pools 14−26). Comparison of composite bed sediment samples collected from the downstream third of 24 pools before and after the 1993 UMR flood provides field-scale data on the effect of the flood on sediment organic compound distributions. The sediments were analyzed for organic carbon, coprostanol, polynuclear aromatic hydrocarbons including pyrene, linear alkylbenzenesulfonates, polychlorinated biphenyls (PCBs), and organochlorine pesticides. Most of the target compounds were detected in all of the sediment samples, although concentrations were generally <1 mg/kg. The highest concentrations typically occurred in the upper reach, an urbanized area on a relatively small river. Pool 4 (Lake Pepin) is an efficient sediment trap, and concentrations of the compounds below pool 4 were substantially lower than those in pools 2−4. Diffe...