Abstract
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 study, "the contents and chemical and mineral compositions of the suspended particulate materials in the Yangtze River and their geological environmental implications” by Ding Tiping, 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. Due to the reduction in the sediment yield, the 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 and SCS losses were 6.76 × 106 tons and 2.29 × 106 tons, respectively, which were equivalent to 7.9 and 2.7 percent of the 85.8 × 106 tons of CO2 emissions reduced by the clean energy production of the Three Gorges Hydropower Station. The 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 collision and erosion of river sediment caused by turbulence in the processes of sediment transport (off-site rock weathering) could promote the dissolution of minerals. Therefore, it is reasonable that the dissolution rate of calcium and magnesium minerals for offsite rock weathering was much higher than that for in situ rock weathering.
Highlights
This study proposed that the dissolution of calcium and magnesium minerals in river sediment could sequester CO2 and function as a carbon sink
Due to the dramatic terrain changes in the upper reaches of the Yangtze River, strong gravity erosion and physical weathering, the CaO + MgO and calcite + dolomite contents were high in the mainstream section of the Jinsha River above Yibin and decreased from the headwater to the estuary, which clearly illustrated the dissolution of calcium-magnesium silicate and carbonate minerals during the process of sediment transport in the river
The collision and abrasion of river sediments combined with stirring and mixing could promote the dissolution of minerals during sediment transport processes
Summary
This study proposed that the dissolution of calcium and magnesium minerals in river sediment could sequester CO2 and function as a carbon sink. The chemical equations for Ca–Mg ions in calcium and magnesium silicates to consume and release C O2 during the weathering and deposition processes are expressed as follows: Ca−Mg 2SiO4 + 4CO2 + 4H2O → Ca−Mg 2(HCO3)4 + H4SiO4. In Eq (2), the CO2 deposited via (Ca–Mg)CO3 is a substantial carbon sink (SCS), and the CO2 that is released is a nonsubstantial carbon sink (NSCS). The chemical equation of absorbing and releasing CO2 by the Ca–Mg carbonate compounds during the weathering and deposition processes is expressed as follows. The CO2 consumed by carbonate weathering is a nonsubstantial carbon sink (NSCS), and it is released after entering the sea through rivers
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