长江干流水化学成因与风化过程CO2消耗通量解析

长江流域面积巨大,岩性多变,加之三峡大坝等重大水利工程的影响,干流河水的水化学成因存在较大争议。此外,以往研究中流域矿物风化过程的碳汇通量估算一般基于阳离子来源分析,但该算法通常涉及多种矿物端元的参数选取,结果具有不确定性。本次研究对长江干流水化学的时空演变进行了整体分析,并基于上游河水样品HCO₃~-含量的校正与计算,提出了一种计算矿物风化过程碳汇通量的新方法。研究结果表明,蒸发盐溶解、循环盐作用、矿物风化及硫酸盐溶解是控制长江干流河水离子组成的主要水文地球化学作用,而人类活动主要影响了离海距离3 000 km以内河水NO₃~-含量;长江上游干流硅酸盐风化消耗CO₂速率为1.16×10~5 mol/(km~2·a),碳酸盐风化消耗CO₂速率为4.75×10~5 mol/(km~2·a)。本研究有助于加深对长江干流主要水文地球化学作用的认识,丰富和完善碳循环研究理论。

Hydrochemical origins and weathering-controlled CO2 consumption rates in the mainstream of the Yangtze River

Because river water in the Yangtze River watershed with a huge area is influenced by variable lithologies and large-scale water projects such as the Three Gorges Dam,the hydrochemical origins of the main stream are still controversial.Furthermore,previous estimations on the carbon sink in the watershed caused by mineral weathering are mostly based on the mass-balance calculations of cations,but this method generally involves the selection of parameters of various mineral end-members,which causes the uncertainty of results.In this study,the temporal and spatial evolutions of hydrochemistry of the main stream are determined,and a new method for the determination of CO₂ consumption rates during mineral weathering processes are proposed based on the mass-balance calculations of HCO₃^- of the upper reaches.The results show that dissolution of evaporites,circulating salts,minerals weathering and sulfate dissolution are the main hydrogeochemical reactions controlling the ionic compositions of river water of the mainstream of the Yangtze River,while human activities mainly control the contents of in the river water within 3000 km from the estuary.The CO₂consumption rates of silicate weathering and carbonate weathering in the upper reaches of the Yangtze River are 1.16×10⁵mol/(km²·a)and 4.75×10⁵mol/(km²·a),respectively.This study may provide a better understanding of the major hydrochemical processes,enriches and promotes the theory of carbon cycle.