Geochemistry of the dissolved loads during high-flow season of rivers in the southeastern coastal region of China: anthropogenic impact on chemical weathering and carbon sequestration

[摘要] The southeastern coastal region is one of the most developed and populated areas in China. Meanwhile, it has been severely impacted by acid rain over many years. The chemical compositions and carbon isotope compositions of dissolved inorganic carbon ( δ¹³ C _DIC) in river water in the high-flow season were investigated to estimate the chemical weathering and associated atmospheric CO₂ consumption rates as well as the acid-deposition disturbance. Mass balance calculations indicated that the dissolved loads of major rivers in the Southeast Coastal River Basin (SECRB) were contributed to by atmospheric (14.3 %, 6.6 %–23.4 %), anthropogenic (15.7 %, 0 %–41.1 %), silicate weathering (39.5 %, 17.8 %–74.0 %) and carbonate weathering inputs (30.6 %, 3.9 %–62.0 %). The silicate and carbonate chemical weathering rates for these river watersheds were 14.2–35.8 and 1.8–52.1 t km ⁻² a ⁻¹ , respectively. The associated mean CO₂ consumption rate by silicate weathering for the whole SECRB was 191×10³ mol km ⁻² a ⁻¹ . The chemical and δ¹³ C _DIC evidence indicated that sulfuric and nitric acid (mainly from acid deposition) were significantly involved in the chemical weathering of rocks. There was an overestimation of CO₂ consumption at 0.19×10¹² g C a ⁻¹ if sulfuric and nitric acid were ignored, which accounted for about 33.6 % of the total CO₂ consumption by silicate weathering in the SECRB. This study quantitatively highlights the role of acid deposition in chemical weathering, suggesting that the anthropogenic impact should be seriously considered in estimations of chemical weathering and associated CO₂ consumption.

[学科分类] 地球化学与岩石