PREFERENTIAL MOBILIZATION OF ATMOSPHERICALLY-DEPOSITED CONTAMINANTS DURING STORMFLOW

Fine-grained particulates play an important role in contaminant sequestration and transport in fluvial systems; the large surface area to volume ratio allows for high levels of adsorption. While studies have shown the high concentration of contaminants on these particles, few have investigated their release into streams during precipitation events. This study examines how different magnitude storms mobilize sediment stored in channel margins and incorporate it into the suspended sediment load. In addition to monitoring suspended sediment concentrations, this study incorporates short-lived radionuclides Be-7 and Pb-210 as tracers for contaminants over the course of 7 storms during the summer of 2012.

Preliminary results of this study demonstrate that different magnitude storms have a different effect on the suspended sediment load. Radionuclide signatures suggest that larger storms mobilize sediment from a source not affected in smaller storms. The results also suggest that the precipitation itself may play a significant role in radionuclide activity in smaller storms, while the influence of groundwater may be more apparent in larger storms. Further work is to be done in examining the organic content of the suspended sediment load throughout the storm, as well as the varying isotopic composition of the stream water. These processes will aim to identify more positively the source of the sediment in suspension at different times during stormflow and answer the question of why the radionuclide signatures vary at these sources. These results will aid in the understanding of contaminant and sediment transport in small streams in New England.