Steady state reach‐scale theory for radioactive tracer concentration in a simple channel/floodplain system
Steady state reach‐scale theory for radioactive tracer concentration in a simple channel/floodplain system
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简单河道/洪泛区系统中放射性示踪剂浓度的稳态到达尺度理论
DOI：
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发表时间：
2010
期刊：
影响因子：
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通讯作者：
J. Willenbring
中科院分区：
文献类型：
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作者：
J. Lauer;J. Willenbring
[1]一个稳态分析模型，提出了一个衰减的放射性示踪剂的浓度与沉积物颗粒，定期通过一个通道外洪泛区的到达尺度的变化。河漫滩被表示为一系列混合良好的沉积物水库，不断与河道交换沉积物。该模型考虑了支流输入和全流域的淤积或退化。示踪剂浓度取决于上游边界浓度、示踪剂和沉积物负荷、洪泛区几何形状以及洪泛区示踪剂产生和/或衰减的速率。该理论预测，长寿命同位素浓度的下游变化相对较小，但意味着可能会发生重大变化：（1）半衰期足够短的示踪剂（如14 C）或（2）沉积物停留时间足够长的洪泛平原，宇宙生成物或流星沉降物足以增加下游示踪剂浓度。的配置文件被证明是强烈依赖于泥沙和河漫滩的粒度分布。结果表明，下水道14 C配置文件有可能限制全新世床料负荷系统有足够的存储。该理论简明地描述了洪泛区对于改变原位产生的宇宙成因示踪剂浓度的一般重要性，并且还可以表征洪泛区对于沉降物放射性同位素的重要性（即，10 Be、210 Pb或7 Be）或有机14 C。
[1] A steady state analytical model is presented for reach-scale variation in the concentration of a decaying radioactive tracer associated with sediment particles that regularly pass through an off-channel floodplain. The floodplain is represented as a series of well-mixed sediment reservoirs that continually exchange sediment with the channel. The model allows for tributary input and valley-wide aggradation or degradation. Tracer concentration depends on the upstream boundary concentration, the tracer and sediment load, floodplain geometry, and the rates of in-floodplain tracer production and/or decay. The theory predicts relatively modest down-channel change in the concentration of long-lived isotopes but implies that significant change may occur for (1) tracers with a short-enough half-life (such as 14C) or (2) floodplains with sediment residence times that are large enough for cosmogenic production or meteoric fallout to increase tracer concentration in the down-valley direction. The profiles are shown to be strongly dependent on the grain size distributions of both the sediment load and the floodplain. The results imply that down-channel 14C profiles have the potential to constrain Holocene bed material loads in systems with sufficient storage. The theory concisely describes the general importance of a floodplain for modifying in situ produced cosmogenic tracer concentration and can also characterize floodplain importance for fallout radioisotopes (i.e., 10Be, 210Pb, or 7Be) or organic 14C.