Matisoff Gerald
Department of Earth, Environmental and Planetary Sciences, Case Western Reserve University, Cleveland, OH 44106-7216, USA.
J Environ Radioact. 2014 Dec;138:343-54. doi: 10.1016/j.jenvrad.2014.03.008. Epub 2014 Apr 13.
Although (137)Cs has been used extensively to study soil erosion and particle transport in the terrestrial environment, there has been much less work using excess or unsupported (210)Pb ((210)Pbxs) to study the same processes. Furthermore, since (137)Cs activities in soils are decreasing because of radioactive decay, some locations have an added complication due to the addition of Chernobyl-derived (137)Cs, and the activities of (137)Cs in the southern hemisphere are low, there is a need to develop techniques that use (210)Pbxs to provide estimates of rates of soil erosion and particle transport. This paper reviews the current status of (210)Pbxs methods to quantify soil erosion rates, to identify and partition suspended sediment source areas, and to determine the transport rates of particles in the terrestrial landscape. Soil erosion rates determined using (210)Pbxs are based on the unsupported (210)Pb ((210)Pbxs) inventory in the soil, the depth distribution of (210)Pbxs, and a mass balance calibration ('conversion model') that relates the soil inventory to the erosion rate using a 'reference site' at which neither soil erosion nor soil deposition has occurred. In this paper several different models are presented to illustrate the effects of different model assumptions such as the timing, depth and rates of the surface soil mixing on the calculated erosion rates. The suitability of model assumptions, including estimates of the depositional flux of (210)Pbxs to the soil surface and the post-depositional mobility of (210)Pb are also discussed. (210)Pb can be used as one tracer to permit sediment source area identification. This sediment 'fingerprinting' has been extended far beyond using (210)Pb as a single radioisotope to include numerous radioactive and stable tracers and has been applied to identifying the source areas of suspended sediment based on underlying rock type, land use (roads, stream banks, channel beds, cultivated or uncultivated lands, pasture lands, forested lands, construction sites, undisturbed lands) or style of erosion (sheet wash, rills, bank). The transport time of particles in the terrestrial system can be estimated using (7)Be/(210)Pbxs radionuclide ratios and from mass balance models of (210)Pbxs and/or (7)Be in streams. Watershed residence times can be calculated from the radionuclide inventory and the erosional loss rate.
尽管铯 - 137（(137)Cs）已被广泛用于研究陆地环境中的土壤侵蚀和颗粒迁移，但利用过剩或非支持态铅 - 210（(210)Pbxs）来研究相同过程的工作却少得多。此外，由于土壤中铯 - 137的活度因放射性衰变而降低，一些地区因添加了源自切尔诺贝利的铯 - 137而增加了复杂性，且南半球铯 - 137的活度较低，因此有必要开发利用(210)Pbxs来估算土壤侵蚀速率和颗粒迁移速率的技术。本文综述了利用(210)Pbxs方法来量化土壤侵蚀速率、识别和划分悬浮泥沙源区以及确定陆地景观中颗粒迁移速率的现状。利用(210)Pbxs确定的土壤侵蚀速率基于土壤中非支持态铅 - 210（(210)Pbxs）的存量、(210)Pbxs的深度分布以及一个质量平衡校准（“转换模型”），该模型使用一个既未发生土壤侵蚀也未发生土壤沉积的“参考站点”将土壤存量与侵蚀速率联系起来。本文介绍了几种不同的模型，以说明不同模型假设（如表层土壤混合的时间、深度和速率）对计算出的侵蚀速率的影响。还讨论了模型假设的适用性，包括对(210)Pbxs向土壤表面沉积通量的估计以及(210)Pb沉积后的迁移性。铅 - 210可作为一种示踪剂用于识别泥沙源区。这种泥沙“指纹识别”已远远超出将(210)Pb作为单一放射性同位素的范畴，还包括众多放射性和稳定示踪剂，并已应用于根据底层岩石类型、土地利用（道路、河岸、河床、耕地或非耕地、牧场、林地、建筑工地、未受干扰的土地）或侵蚀方式（片蚀、细沟侵蚀、岸蚀）来识别悬浮泥沙的源区。陆地系统中颗粒的迁移时间可利用铍 - 7（(7)Be）/(210)Pbxs放射性核素比值以及溪流中(210)Pbxs和/或(7)Be的质量平衡模型来估算。流域停留时间可根据放射性核素存量和侵蚀损失速率来计算。
