Tracing the origin of fine-grained fluvial sediment using radionuclides with management implications

Abstract This paper reports a study of the origin of fine-grained river sediments and their potential impact to a reservoir that supplies drinking water. Excess sediment may affect water quality and decrease the storage capacity of the reservoir. Three sediment cores were taken in 2011 from the Rockaway River in New Jersey that leads into the reservoir to determine the sources of the sediment and propose remediation actions. The coring sites spanned an area upstream in the watershed to just above the reservoir, and the sites varied in land use. Sediment was analyzed in one to two centimeter intervals to determine the radionuclide activity of excess 210 Pb and 137 Cs. The sediment activity level at two of the sites (the ones farthest up- and downstream) show predominantly low levels of excess 210 Pb and 137 Cs, suggesting that the sediment is coming from deeper sources such as river channel widening/lateral migration and hillslope failures and/or legacy sediment sources. The sediment from site 2 exhibited higher activity of excess 210 Pb, suggesting more surficial sources of sediment or relatively recent sediments and likely tied to widespread urbanization. The different radionuclide profiles between the cores suggest spatial variation in the sediments’ sources, with the sources varying between surficial and deeper ones. Establishing the origin of this sediment would help to derive management solutions to lessen sediment delivery, stabilize and/or remove legacy sediment supplies to minimize downstream impacts.