ASSESSMENT OF DAM SEDIMENT FOR METAL CONTAMINATION IN A HISTORICALLY INDUSTRIALIZED NEW ENGLAND CITY

Many New England cities have known environmental contamination due to the heavily-industrialized history of the region. Fitchburg, Massachusetts is a historically industrialized city in Central Massachusetts situated along the North Nashua River. Within the North Nashua River watershed in the Fitchburg area there are >20 dams, many of which were built in the late 1800’s and are now abandoned with no plans for removal. Since dams often trap years of accumulated sediment behind them, they serve as a sink for both geogenically-derived metals from mineral weathering in addition to anthropogenically-derived metals from industrial and urbanization activities in the watershed. Therefore, sediment core sampling enables characterization of the spatial and temporal distribution of metal contamination within a watershed and helps to identify some of the potential sources of current and historical metal inputs to the fluvial system. Sediment cores were collected from eight dams within the North Nashua River watershed along an upstream to downstream gradient. Sediment grab samples were collected from the upper headwaters of the watershed where cores could not be obtained. All cores and grab samples were processed and digested according to the US EPA 3050B method, then analyzed with an inductively coupled plasma mass spectrometer (ICP-MS). Metal concentrations and enrichment factors were calculated for 12 elements and metals, then interpolated throughout the watershed using GIS to identify potential hot spots of metal contamination. Maximum sediment concentrations for As, Cd, and Cr were 44, 38, and 82 ppm, respectively, and maximum concentrations for Cu, Pb, and Zn were 351, 250, and 440 ppm, respectively. Considering enrichment, As, Cd, and Pb tended to have the highest enrichment across the watershed, whereas Cu and Zn had lower levels of enrichment. Initial interpolation maps indicate co-occurrence of As, Cr, and Pb enrichment in the mainstem (non-headwater) region of the watershed. Further statistical and mapping analyses will be conducted to analyze linkages between the spatial distribution of metal concentrations and possible watershed factors contributing to metal contamination in the North Nashua River watershed.