河流泥沙输移过程中矿物风化的碳汇效应初探——以长江干流为例

本文首先提出了河流泥沙输移过程中泥沙中的钙镁矿物溶蚀消耗水体中的CO2并具有碳汇功能的观点。基于前人长江干流从源头到入海口和支流2003~2007年期间4次河流悬移质泥沙的化学元素组成和矿物组成资料，分析悬移质中CaO、MgO含量和方解石、白云石含量变化特征，定量计算了这些取样点悬移质泥沙的CO2总碳汇能力和非永久性、永久性碳汇能力，分析了不同碳汇能力沿程变化规律及其原因。碳汇计算结果表明：寸滩—大通河段1956~2000年期间泥沙输移过程中钙镁矿物溶蚀产生的总碳汇量、非永久性和永久性碳汇量分别为2572万t/a、1700万t/a和872万t/a。由于输沙量减少，寸滩站—大通站河段的总碳汇量、非永久性和永久性碳汇量2006~2019年期间较1956~2000年期间相应分别减少了1852万t、1224万t和872万t。三峡水库年均淤积量1. 145亿t，损失总碳汇量675. 6万t，相当于三峡电站减排二氧化碳8580万t的7. 9%。全球河流入海年输沙量126. 1亿t，以寸滩- 吴淞口河段碳汇功能0. 060 t/t计，总碳汇量7. 57亿t相当于全球岩石风化碳汇总量10. 56亿t CO2的71. 6%。河流泥沙输移过程中钙镁矿物溶蚀的碳汇量具有重要的作用，其溶蚀速率大于原地风化。

A preliminary study on the inorganic carbon sink function of mineral weathering during sediment transport in the Yangtze River mainstream

This study proposed that the dissolution of calcium and magnesium minerals in river sediment could sequester CO2 and function as a carbon sink. Based on the published literature, the contents of CaO, MgO, calcite and dolomite in suspended sediment collected from 25 sampling points in the mainstream and 13 sampling points in the tributaries of the Yangtze River in 4 sampling campaigns during 2003~2007 were used to calculate the total inorganic carbon sink (TCS) capacity and nonsubstantial and substantial inorganic carbon sink (NSCS and SCS) capacities of suspended sediment along the river. Results showed that the TCS, NSCS and SCS caused by weathering of Ca and Mg minerals at Cuntan- Datong section were 2. 57×107 tons, 1. 70×107 tons and 0. 87×107 tons per year during the period of 1956~2000. Due to the reduction of sediment yield, the annual TCS, NSCS and SCS of the Cuntan- Datong section during 2006~2019 decreased by 18. 52×106 tons, 12. 24×106 tons and 8. 72×106 tons, respectively, compared to the period before 2002. The average annual sedimentation of the Three Gorges Reservoir (TGR) was 114. 5×106 tons, and the related TCS loss was 6. 76×106 tons, which were equivalent to 7. 9% of the 85. 8×106 tons of CO2 emissions reduced by the clean energy production of the Three Gorges Hydropower Station. The annual TCS of global rivers was estimated as 757×106 tons (the SCS was more than one quarter of the TCS), which is equivalent to 71.6% of the TCS by global rock weathering with 1.06×109 tons of sequestered CO2. The dissolution rate of calcium and magnesium minerals for offsite rock weathering was higher than that for in situ rock weathering.