The source of the sediment appears to vary both spatially and temporally. Between sites 1, 2, and 3 the radionuclide activity varies, indicating that the source also varies, possibly as a result of changes in land use as well as the local surficial geology. Additionally, the activity

varies down-core in Site 2, suggesting there are temporal variations in the sources of sediment. It is also possible that sediment is being stored along the fluvial system, although there are not broad floodplains there that indicate this is likely. Site 2, while only 1 km upstream of Site 3 (Fig. 1), had a markedly different radionuclide profile than Site SB431542 3 (Fig. 2). Site 2 is situated just upstream of the gorge that the Rockaway River has eroded through glacial till and so does not receive sediment from these sources. It is, however, just downstream of the largest area of urbanized land in the watershed (Fig. 1). Alternatively, Site 2 may contain three depositional periods, with INK128 different sediment sources. Sediment from the surface to 5 cm depth and from 7 cm to 13 cm, with its higher activity levels, could each represent

surficial sediment deposition. This was interrupted by the interval 5–7 cm, when sediment with low to no activity of 210Pb or 137Cs was deposited from deeper sources such as river channel banks or hillslopes. The sediment at Site 2 is transported toward and possibly temporarily stored at Site 3, potentially influencing the sediment signal there. However, the

actively eroding hillslope, producing deeper sediment with little to no radionuclide activity, probably overwhelms the signal from site 2. Distinguishing the sediment from site 2 and site 3, although desirable, may not be possible as they are not lithologically different. These variations in sediment sources are an important factor in mitigation efforts for this river. The entire length of the river should be analyzed and assessed for potential sediment sources. This is important because mitigation efforts would depend on the source of the sediment. In this study, there were spatial and temporal variations in the sources, making the water management efforts more complex. Further analysis and sediment RAS p21 protein activator 1 collection would also allow a sediment budget to be constructed for this river, an important step in terms of managing downstream resources such as reservoirs. The analyses and results described above provides tentative answers to the three research questions posed. First, two of the sites (1 and 3) had sediment originating from either deeper sediment sources or from sediment stored within the watershed. The other site (#2), contained sediment from surficial sources. Second, there was longitudinal variability in the radionuclide signals of the river sediment, as the sediment sources varied between the sites.