Institute of Surface-Earth System Science, School of Earth System Science, Tianjin University, Tianjin 300072, China.
School of Earth Science and Resources, Chang'an University, Xi'an 710054, China.
Sci Total Environ. 2021 Mar 15;760:143416. doi: 10.1016/j.scitotenv.2020.143416. Epub 2020 Nov 17.
High levels of dissolved arsenic (As) have been reported in many rivers running though the Tibetan Plateau (TP), the "Water Tower of Asia". However, the source, spatiotemporal variations, and geochemical behavior of dissolved As in these rivers remain poorly understood. In this study, hot spring, river water, and suspended particulate material samples collected from the Yarlung Tsangpo River (YTR) (upper reaches of the Brahmaputra River) system in 2017 and 2018 were analyzed. Spatial results shown that the upper reaches of YTR (Zone I) have comparatively high levels of dissolved As ([As]: mean 31.7 μg/L; 4.7-81.6 μg/L; n = 16), while the tributaries of the lower reaches (Zone II) have relatively low levels (mean 0.54 μg/L; 0.11-1.3 μg/L; n = 7). Seasonal results shown that the high [As] (6.1-22.4 μg/L) were found in September to June and low [As] (1.4-3.7 μg/L) were observed in July to August. Geothermal water is suspected as the main source of the elevated As levels in YTR due to the extremely high [As] in hot springs (1.13-9.76 mg/L) and abundance of geothermal systems throughout TP. However, the seasonal results suggested that weathering of As-containing rocks and minerals is also a key factor affecting the [As] in the river water in July to August (wet-season). Natural attenuation of As in main channel is dominated by dilution process due to the lower As concentrations in tributaries, but mostly occurred by both dilution and adsorption (or co-precipitation) processes in tributaries. This work highlights that the weathering process may have an important contribution to the dissolved As in the river waters in wet-season, and the geochemical behavior of As is largely transported conservatively in the main channel and relative non-conservatively in the tributaries in YTR system.
已报道许多流经亚洲水塔——青藏高原的河流中溶解态砷（As）含量较高。然而，这些河流中溶解态 As 的来源、时空变化及地球化学行为仍不清楚。本研究于 2017 年和 2018 年采集了雅鲁藏布江（YTR）（雅鲁藏布江上游）水系的温泉、河水和悬浮颗粒物样品，对其进行了分析。空间结果表明，YTR 上游（区 I）的溶解态 As 含量较高[As]（平均值为 31.7μg/L；4.7-81.6μg/L；n=16），而下游支流（区 II）的含量相对较低[As]（平均值为 0.54μg/L；0.11-1.3μg/L；n=7）。季节结果表明，高[As]（6.1-22.4μg/L）出现在 9 月至 6 月，低[As]（1.4-3.7μg/L）出现在 7 月至 8 月。由于温泉中极高的[As]（1.13-9.76mg/L）和青藏高原上丰富的地热系统，温泉水被怀疑是导致 YTR 中 As 含量升高的主要来源。然而，季节结果表明，7 月至 8 月（雨季）含 As 岩石和矿物的风化也是影响河水[As]的关键因素。由于支流中 As 浓度较低，主河道中 As 的自然衰减主要通过稀释过程进行，但在支流中主要通过稀释和吸附（或共沉淀）过程进行。本研究强调，风化过程可能对雨季河水中溶解态 As 有重要贡献，且 As 的地球化学行为在 YTR 水系主河道中主要呈保守运移，在支流中呈非保守运移。
