Chemical weathering in the Himalayan river basins is among the highest in the world and has received vast research attention related to past climate change. Many early estimates of chemical weathering are based on a small number of water property data that ignore those spatial and seasonal variations. Therefore, this study analyzed spatial and seasonal variations in chemical weathering in the Mekong Basin, where the geology, climate, and hydrologic cycle of the basin vary significantly from the lower to upper reaches and from dry to rainy seasons. We separately estimated the origins of dissolved elements and potential CO₂ consumption rates using the numerous chemical compositions of river water throughout the entire basin and in both seasons. The CO₂ consumption rate in the rainy season is three to five times that in the dry season that may be due to the high temperature and precipitation. Despite the low temperatures and dryness of the upper and middle basins, the CO₂ consumption rate is approximately twice that in the lower reaches; this can be attributed to active physical denudation in steep mountainous areas which increases the surface area for water–rock interactions. The total CO₂ consumption obtained by combining each season and basin was 48‒70 × 10⁹ mol/a and 148‒159 × 10⁹ mol/a for silicate and carbonate weathering, respectively, which are almost half the values of previous estimates. Our results suggest that seasonally and spatially separated evaluations are important for generating estimates of chemical weathering in large Himalayan rivers.

中文翻译：

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湄公河流域化学风化的季节和空间变化：从源头到下游

喜马拉雅河流域的化学风化是世界上最高的，并且受到与过去气候变化有关的广泛研究关注。许多关于化学风化的早期估计是基于少量的水属性数据，而忽略了那些空间和季节变化。因此，本研究分析了湄公河流域化学风化的空间和季节变化，该盆地的地质，气候和水文循环从下游到上游以及从旱季到雨季都有显着变化。我们使用整个盆地和两个季节中河水的多种化学成分分别估算了溶解元素的来源和潜在的CO ₂消耗率。一氧化碳₂雨季的消费量是干旱季节的三到五倍，这可能是由于高温和降水造成的。尽管上流域和中流域的温度较低且干燥，但CO ₂消耗率约为下游的两倍。这可以归因于陡峭山区的活跃物理剥蚀，这增加了水岩相互作用的表面积。通过每个季节和盆地的组合获得的总CO ₂消耗量为48‒70×10 ⁹  mol / a和148‒159×10 ⁹ mol / a分别对应于硅酸盐和碳酸盐的风化作用，几乎是先前估算值的一半。我们的结果表明，季节性和空间分隔的评估对于生成喜马拉雅大河中化学风化的估算非常重要。