The transport and mass balance of fallout radionuclides in Brotherswater, Cumbria (UK)
The transport and mass balance of fallout radionuclides in Brotherswater, Cumbria (UK)
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DOI：
10.1007/s10933-019-00095-z
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发表时间：
2019-12-01
影响因子：
2.1
通讯作者：
Warburton, J.
中科院分区：
文献类型：
--
作者：
Appleby, P. G.;Semertzidou, P.;Warburton, J.
本文研究了大气沉积的放射性核素Pb-210和Cs-137在湖泊沉积物记录中的作用。兄弟水对这一问题特别感兴趣，因为其大的集水区/湖泊面积比和较短的水停留时间可能会放大这些过程的影响，无论是从集水区还是通过水柱。兄弟水也是独一无二的，因为它是早期两项多核心研究的地点，与本研究一起，跨度为40年。对土壤岩心、悬浮沉积物和沉积物岩心进行了降尘放射性核素测量，并将结果与早期研究的结果结合起来，建立了兄弟水中铅-210和铯-137的质量平衡。结果表明，流域输入占入湖铅-210的63%。此外，进入水柱的铅-210只有47%被输送到沉积物记录中。相比之下，在附近的Blelham Tarn进行的一项较早前的研究中，流域相对较小，但水的停留时间较长，研究表明，47%的铅-210输入是通过流域输送的，其中75%被输送到沉积物记录。这两个地点的结果表明，铅-210主要以平均粒度为3-4微米的细颗粒物的形式运移。它们从水柱中去除的相对较慢的速度使它们能够相对均匀地在整个湖泊中运移，这可能有助于解释这样一个事实，即尽管迁移过程复杂，但简单的铅-210测年模型相对可靠。Cs-137的质量平衡计算比较复杂，因为有可变的尘埃记录。对输入溪流和水柱中Cs-137的测量表明，在上一次重大沉降物(切尔诺贝利)发生30年后，集水区的输入仍然很重要。模拟结果显示，集水区的投入推迟了武器试验沉降物进入湖泊的高峰日期，尽管推迟的时间不超过2年。虽然这里介绍的结果主要涉及放射性尘埃及其测年可靠性，但它们也对利用沉积物档案重建其他大气沉积物质，如痕量金属或持久性有机污染物的历史记录有影响。
This paper investigates the role of intervening transport processes on lake sediment records of the atmospherically deposited radionuclides Pb-210 and Cs-137. Brotherswater is of particular interest to this issue in that its large catchment/lake area ratio and short water residence time are likely to amplify the influence of these processes, both from the catchment and through the water column. Brotherswater is also unique in being the site of two earlier multicore studies that, together with the present study, span a period of 4 decades. Measurements of fallout radionuclides were made on soil cores, suspended sediments and sediment cores, and the results combined with those from earlier studies to construct mass balances for Pb-210 and Cs-137 in Brotherswater. The results showed that catchment inputs accounted for 63% of Pb-210 entering the lake. Further, just 47% of Pb-210 entering the water column was delivered to the sediment record. For comparison, in an earlier study at nearby Blelham Tarn with a relatively smaller catchment but longer water residence time it was shown that 47% of Pb-210 inputs were delivered via the catchment, 75% of which were delivered to the sediment record. Results from both sites suggest that Pb-210 is predominantly transported on fine particulates with a mean particle size of 3-4 mu m. Their relatively slow removal from the water column allows them to be transported relatively uniformly throughout the lake and may help account for the fact that simple Pb-210 dating models are relatively reliable in spite of the complexities of the transport processes. Mass balance calculations for Cs-137 are more complicated because of the variable fallout record. Measurements of Cs-137 in the input stream and water column showed that catchment inputs are still significant 30 years after the last significant fallout (Chernobyl). Modelled results showed that catchment inputs delayed the date of peak inputs of weapons test fallout to the lake though by no more than 2 years. Although the results presented here are primarily concerned with fallout radionuclides and their reliability for dating, they also have implications for the use of sediment archives in reconstructing historical records of other atmospherically deposited substances such as trace metals or persistent organic pollutants.