Radionuclides (⁷Be, ²¹⁰Pb and ¹³⁷Cs) as tracers for soil and sediment erosion in New Jersey stream watersheds

The water quality in U.S. rivers and streams has been steadily improving with stricter environmental regulations over the last several decades. These regulations have identified and diminished point-source pollution, but non-point source pollution remains both problematic andelusive. For example, excess fine-grained sediment from non-point sources in fluvial systems is one of the main pollutants currently in streamsand lakes and can impair water quality, biologic habitat, recreational opportunities, and the aesthetic properties of the stream. One barrier to controlling sediment load is that it is often difficult to determine whether the source of sediment is widespread from shallow surficial erosion from overland flow occurring in the watershed or from the erosion of vertical channel bank material. However, these two sources of sediment can be distinguished using ⁷Be, ²¹⁰Pb and ¹³⁷Csa. To assess how successful these established methods are at identifying the source of the fine-grained sediment within streams, we selected two watersheds in New Jersey with different land uses. One watershed is mostly urbanized while the other site is dominated by agriculture. We sampled upland soils, channel bank materials, and in-stream channel sediments and analyzed them forradionuclide activity to identify the relative contributions of these materials from the watershed and channel banks. This preliminary study indicates spatial variations in210Pb and 137Cs activities within and between thesetwo types of watersheds. While sediment 210Pb depletionwas found in the channel areas, excess 210Pb accumulation was found in the upland. In the urban watershed, excess 210Pb was accumulated in the bank area but depleted in surface soil in the upland. This research includes new information for improving stream and watershed management programs.