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Assessing Organic Contaminant Fluxes from Contaminated Sediments Following Dam Removal in an Urbanized River
Citation:
Cantwell, Mark G., Monique M. Perron, J. Sullivan, David R. Katz, Robert M. Burgess, AND J. King. Assessing Organic Contaminant Fluxes from Contaminated Sediments Following Dam Removal in an Urbanized River. ENVIRONMENTAL MONITORING AND ASSESSMENT. Springer, New York, NY, 186(8):4841-4855, (2014).
Impact/Purpose:
Dam removal is becoming a regular activity in the effort to restore riverine habitats and ecosystems. Many locations with dams have contaminated sediments that may be susceptible to release during removal and restoration activities. This manuscript presents methods, approaches and results on monitoring the release and remobilization of previously sequestered contaminants before and after dam removal. This research was performed in the Pawtuxet River, an urbanized river in Rhode Island,USA.
Description:
In this study, methods and approaches were developed and tested to assess changes in contaminant fluxes resulting from dam removal in a riverine system. Sediment traps and passive samplers were deployed to measure particulate and dissolved PAHs and PCBs in the water column prior to and following removal of a small, low head dam in the Pawtuxet River, an urbanized river located in Cranston, RI, USA. During the study, concentrations of particulate and dissolved PAHs ranged from 21.5-103 µg/g and 68-164 ng/L, respectively. Overall, temporal trends of PAHs showed no increases in either dissolved or particulate phases following removal of the dam. Dissolved concentrations of PCBs were very low, remaining below 1.72 ng/L at all sites. Particulate PCB concentrations across sites and time showed slightly greater variability, ranging from 80-469 ng/g, but with no indication that dam removal influenced any increases. Particulate PAHs and PCBs were sampled continuously at the site located below the dam, and did not show sustained increases in concentration resulting from dam removal. The employment of passive sampling technology and sediment traps were highly effective in monitoring the concentrations and flux of contaminants moving through the river system. Variations in river flow had no effect on the concentration of contaminants in the dissolved or particulate phases, but did influence the flux rate of contaminants exiting the river. Overall, dam removal did not cause measurable sediment disturbance or increase the concentration or fluxes of dissolved or particulate PAHs and PCBs. This is due in large part to low volumes of impounded sediment residing above the dam and highly armored sediments in the river channel, which limited erosion. Results from this study will be used to improve methods and approaches that assess the short and long-term impact ecological restoration activities such as dam removal have on the release and transport of sediment-bound contaminants.
