Tracing Find Sediment Transport in Fluvial Systems Using Fallout Radionuclides

尽管我们了解沉积物和与沉积物结合的污染物的粗略路径，但我们对它们通过排水网络和到达接收体的过境时间知之甚少。该项目的目标是开发一种创新但广泛适用的工具，以研究景观中细颗粒泥沙的侵蚀机制和细颗粒悬浮物在河道中的运移特征。具体地说，我们的目标是回答以下问题：悬浮泥沙的来源(是来自片面侵蚀、细沟侵蚀、岸边侵蚀还是底层沉积物的再悬浮？)；来自分水岭的细粒泥沙的输送比例(即从景观中被侵蚀并输送到接收水域的泥沙的比例，或者仅部分输送到景观或河床中的比例)；从土壤覆盖的景观中新输送的悬浮泥沙与从河床重新悬浮的悬浮泥沙的比例；细颗粒的传输距离；颗粒的停留时间；以及来自分水岭的细颗粒的流量。我们将使用我们开发的一项新技术，使用放射性放射性沉降物(7Be、137Cs和210Pb)作为径流悬浮的细沉积物的示踪剂。为期两年的研究将集中在怀俄明州和蒙大拿州的黄石河流域。在第一年中，我们将讨论积雪、土壤、海底沉积物和悬浮沉积物的示踪动力学和放射性核素特征的表征。在第二年，我们将描述融雪过程中900公里范围内细小沉积物的来源和输送情况。实验设计包括：收集降水、土芯、漫滩沉积物、沟底沉积物和在排水网络中不同位置的悬浮沉积物样本；利用伽马能谱测量天然存在的短期(7Be)和长期(137Cs-210Pb)放射性核素沉降物以及吸附在沉积物上的其他重要放射性核素标记(214Bi、40K)；跟踪1950年从研究区域高地和源区释放的尾矿的运动；分析颗粒大小和浓度；建立波浪运动和质量平衡模型。

Despite our understanding of the gross paths taken by sediments and sediment-bound pollutants, we have a poor knowledge of the transit time for their passage through the drainage network and to receiving bodies. The goal of this project is to develop an innovative but broadly applicable tool to investigate the erosion mechanisms of fine sediment from the landscape and the transport characteristics of fine suspended particulates in channels. Specifically, we aim to answer questions on the source of the suspended sediment (Is it from sheet erosion, rill erosion, bank erosion, or resuspension of bottom sediments?); the delivery ratios of fine sediment from the watershed (i.e., the proportion of sediment that is eroded from the landscape and delivered to the receiving waters or the proportion that is transported only part way and resides on the landscape or in the streambed); the proportions of suspended sediment that is newly delivered from the soil mantled landscape versus resuspended from the bed; the transit distance of fine particulates; the residence time of particulates; and the flux of fines from the watershed. We will employ a novel technique we have developed that uses fallout radionuclides (7Be, 137Cs, and 210Pb) as tracers of fine sediments suspended by streamflow.The two-year study will be focused in the Yellowstone River watershed in Wyoming and Montana. During the first year we will address the kinetics of the tracing and the characterization of the radionuclide signature of the snowpack, soils, bottom sediment, and suspended sediment. During the second year we will characterize the sources and transport of fine sediment over a distance 900 km during a snowmelt-driven hydrograph. The experimental design includes collection of precipitation, soil cores, floodplain sediment, channel bottom sediment, and suspended sediment samples at various locations in the drainage networks; gama spectroscopy of samples for naturally occurring short-lived (7Be) and lonaer-lived (137Cs 210Pb) fallout radionuclides and other important radionuclide tags (214Bi, 40K) that adsorb to sediment providing tracers of sediment movement over different time scales; tracing the movement of mine tailings that were released from an upland source area in the study area in 1950; analyses of particle sizes and concentrations; and wave kinematic and mass balance modeling.