Centre for Northern Studies (CEN), Takuvik Joint International Laboratory, and Department of Chemistry, Université Laval, Quebec City, QC, Canada.
Department of Geography and Environmental Studies, Wilfrid Laurier University, Waterloo, ON, Canada.
Environ Pollut. 2021 Nov 1;288:117723. doi: 10.1016/j.envpol.2021.117723. Epub 2021 Jul 6.
Lake sediments are widely used as environmental archives to reconstruct past changes in contaminants deposition, provided that they remain immobile after deposition. Arsenic (As) is a redox-sensitive element that may be redistributed in the sediments during early diagenesis, for instance along with iron and manganese, and thus depth profiles of As might not provide a reliable, unaltered record of past deposition. Here, we use inverse diagenetic modelling to calculate fluxes of As across the sediment-water interface and interpret As sedimentary records in eight lakes along a 80 km transect from the Giant and Con mines, Northwest Territories, Canada. The sediment cores were dated using Pb methods and analyzed for solid-phase and porewater As, Fe, Mn and organic C concentrations. We reconstructed the history of As deposition by correcting for the varying mobility patterns and calculated contemporary As deposition fluxes. Correction for diagenesis was substantial for three of the eight lakes, suggesting that lakes with lower sedimentation rates, which allows longer residence of As within the reactive zones defined by the model, enhance the influence of diagenesis. Results show that solid phase As peaks coincides with the period of high emissions from past gold ore roasting activities. Results also show that sediments sustained present-day As fluxes to the water column of study lakes within 50 km of the mines, while sediment in study lakes further than 50 km acted as As sinks instead.
湖泊沉积物广泛应用于环境档案中，以重建过去污染物沉积的变化，前提是它们在沉积后保持不动。砷（As）是一种氧化还原敏感的元素，在早期成岩作用过程中可能与铁和锰一起在沉积物中重新分配，因此 As 的深度分布可能无法提供过去沉积的可靠、未改变的记录。在这里，我们使用反成岩模型来计算穿过沉积物-水界面的 As 通量，并解释来自加拿大西北地区 Giant 和 Con 矿 80 公里横截线上的八个湖泊的 As 沉积记录。使用 Pb 方法对沉积物岩芯进行定年，并分析固相和孔隙水 As、Fe、Mn 和有机 C 浓度。我们通过校正不同的迁移模式来重建 As 沉积的历史，并计算了当代 As 沉积通量。对于八个湖泊中的三个，成岩作用的校正非常重要，这表明对于那些沉降速率较低的湖泊，由于 As 在模型定义的反应区的停留时间更长，成岩作用的影响更大。结果表明，固相 As 峰值与过去金矿烘烤活动高排放时期相吻合。结果还表明，在距离矿山 50 公里范围内的研究湖泊中，沉积物维持了当前 As 通量向水柱的输送，而距离矿山超过 50 公里的研究湖泊中的沉积物则充当了 As 汇。
