Institute of Earth Sciences, China University of Geosciences (Beijing), Beijing, 100083, China.
Institute of Earth Sciences, China University of Geosciences (Beijing), Beijing, 100083, China.
Environ Res. 2022 Sep;212(Pt B):113330. doi: 10.1016/j.envres.2022.113330. Epub 2022 Apr 19.
Sr/Sr of river water are of great significance in constraining oceanic strontium (Sr) record and terrestrial climate change due to the connection of continental weathering and the adjacent ocean. This work presents the geochemical characteristics of dissolved Sr and hydrochemistry, and estimates chemical weathering rate together with elemental Sr flux during the flood season of the Mun River, the largest tributary of Mekong River. Hydrochemistry analysis indicates the dominance of Cl and HCO for major anions with the average of 34.6 and 43.0 mg/L, respectively, and Na and Ca together dominated the cationic composition with the average of 22.9 and 10.5 mg/L, respectively. The ion concentrations during flood season were lower than that in dry season, implying tremendous river runoff due to extreme rainfall. The dissolved Sr ranges 6.1-237.5 μg/L with higher contents in the upper Mun. Sr contents in flood season are lower and less fluctuated than that in dry season, whereas the divergence between up and downstream becomes larger. Sr/Sr ranges 0.7100-0.7597, slightly higher than global average. Elemental molar ratio analysis partly corroborates the inference from correlation analysis, but Sr/Sr does not correlate with Na/Ca, indicating additional influence except for the weathering of evaporites and silicates. Comparing to regional wastewater and rainwater, the lower reaches exhibits superimposed impact of agricultural inputs on weathering to dissolved loads, especially in downstream with more tributary convergence. Extreme rainfall during flood season and extensive agricultural production activities may interfere in altering riverine solutes. Silicate weathering rate and CO consumption rate are calculated as well as the yearly Sr in excess to the Mekong River and finally to the Pacific Ocean with a Sr flux of 1.98 × 10 tons/year, indicating significant influence on seawater strontium isotope evolution in the long run. Together with tropical climate and high-intensity precipitation, the accelerated chemical weathering process seems inevitable. Therefore, the impact of agricultural interference in the pan-Mekong River basin needs more systematic and multi-angle research to provide a comprehensive insight on better watershed management under tropical climatic conditions.
由于大陆风化作用与毗邻海洋的联系，河水 Sr/Sr 在约束海洋锶记录和陆地气候变化方面具有重要意义。本工作介绍了芒河（湄公河最大支流）洪水季节溶解 Sr 的地球化学特征和水化学，并估算了化学风化速率和元素 Sr 通量。水化学分析表明，主要阴离子以 Cl 和 HCO 为主，平均值分别为 34.6 和 43.0mg/L，阳离子以 Na 和 Ca 为主，平均值分别为 22.9 和 10.5mg/L。洪水季节的离子浓度低于旱季，这意味着由于极端降雨，河水径流量巨大。溶解 Sr 的范围为 6.1-237.5μg/L，上游芒河的含量较高。洪水季节的 Sr 含量低于旱季，且波动较小，而上、下游之间的差异则增大。Sr/Sr 范围为 0.7100-0.7597，略高于全球平均值。元素摩尔比分析部分证实了相关分析的推断，但 Sr/Sr 与 Na/Ca 不相关，表明除了蒸发盐和硅酸盐风化外，还有其他因素的影响。与区域污水和雨水相比，下游地区显示出农业投入对风化溶解负荷的叠加影响，特别是在支流汇聚较多的下游地区。洪水季节的极端降雨和广泛的农业生产活动可能会干扰河流溶质的变化。计算了硅酸盐风化速率和 CO 消耗速率，以及每年向湄公河和最终向太平洋输入的多余 Sr 通量为 1.98×10 吨/年，这表明从长远来看，这对海水锶同位素演化具有重要影响。再加上热带气候和高强度降水，加速的化学风化过程似乎不可避免。因此，需要对整个湄公河流域的农业干扰影响进行更系统和多角度的研究，以便在热带气候条件下对流域进行更好的管理。
