Origin of Stream Bed Sediments in Northwest New Jersey: Factors of Land Use and Source Determined by Trace Element Analysis

Streams in northern New Jersey span a broad range of environments and land covers, including urban, agriculture, wetlands, and forest. Stream sediments receive input from these environments, and indicate pulses or stages of land use change, or stability. In this project, we use trace elements, including rare earth elements, to fingerprint sediment sources and differentiate between land use as well as immediate sources of sediment, such as stream banks, floodplains, uplands, or urban inputs. Samples of stream bed, stream bank, floodplain sediments, and urban and upland soils were obtained from eight locations in the Flat Brook, Rockaway River, and Wallkill River watersheds in Sussex and Morris counties in New Jersey. Samples were prepared for trace element analysis with inductively coupled plasma mass spectrometry (ICPMS). Element content was compared to land use, sediment source, and a stream stability index (the Rapid Geomorphic Assessment, RGA). Several elements (V, Cr, Ni, Sr, Pb) were statistically significant at distinguishing between land use. Zr and W were able to distinguish sediment source (i.e. floodplain, bank, upland, etc.) with statistical confidence. Related to stream and bank stability, the RGA showed significant positive correlation with Cr and Co content (increasing Cr and Co with increasing instability), indicating these elements as good proxy indicators for bank erosion. Ongoing studies of element ratios, combined with Cs-136 and Pb-210 activity levels by gamma detector, will further refine the sediment characterization, with an eventual goal of approximating a sediment budget across different land uses and identifying hot spots that deliver disproportionately high amounts of sediment.; Increase in Co content corresponds to an increase in channel and bank instability, indicated by increasing RGA value.