Abstract
In the context of climate change, the input of acid substances into rivers, caused by human activities in the process of industrial and agricultural development, has significantly disrupted river systems and has had a profound impact on the carbon cycle. The hydrochemical composition and which main sources of the Lianjiang River (LR), a subtropical karst river in northern Guangdong Province, South China, were analyzed in January 2018. The objective was to explicate the influence on the deficit proportion of CO2 consumption, resulting from carbonate chemical weathering (CCW), driven by nitric acid (HNO3) and sulfuric acid (H2SO4), which is affected by exogenous acids from the industrial regions in north of the Nanling Mountains and the Pearl River Delta. The response of the riverine carbonate system to exogenous acid-related weathering was also discussed. HCO3− and Ca2+, respectively, accounted for 84.97% of the total anions and 78.71% of the total cations in the surface runoff of the LR, which was characterized as typical karst water. CCW was the most important material source of river dissolved loads in the LR, followed by human activities and silicate chemical weathering (SCW). Dissolved inorganic carbon (DIC), derived from CCW induced by carbonic acid (H2CO3), had the largest contribution to the total amount of DIC in the LR (76.79%), and those from CCW induced by anthropogenic acids (HNO3 and H2SO4) and SCW contributed 13.56% and 9.64% to the total DIC, respectively. The deficit proportion of CO2 consumption associated with CCW resulting from sulfuric acid and nitric acid (13.56%), was slightly lower than that of the Guizhou Plateau in rainy and pre-rainy seasons (15.67% and 14.17%, respectively). The deficit percentage of CO2 uptake associated with CCW induced by sulfuric acid and nitric acid, accounted for 38.44% of the total CO2 consumption related to natural CCW and 18.84% of the anthropogenic acids from external areas. DIC derived from CCW induced by human activities, had a significant positive correlation with the total alkalinity, SIc and pCO2 in river water, indicating that the carbonate system of the LR was also driven by exogenous acids, with the exception of carbonic acid. More attention should be paid to the effects of human activities on the chemical weathering and riverine carbonate system in the karst drainage basin.
Highlights
A river system is one of the most important transport channels of material and energy to the ocean in a drainage basin, which records the environment evolution processes of the river basin.Chemical weathering processes in a drainage basin can be reflected by the river hydrochemical characteristics [1,2], which is the main part of the mass exchange between the ocean and the continent.It is generally recognized that silicate chemical weathering (SCW) induced by carbonic acid is a net depletion process of the atmospheric/soil CO2
dissolved inorganic carbon (DIC) derived from chemical weathering (CCW) induced by human activities, had a significant positive correlation with the total alkalinity, SIc and pCO2 in river water, indicating that the carbonate system of the Lianjiang River (LR) was driven by exogenous acids, with the exception of carbonic acid
The CO2 consumed by carbonate chemical weathering (CCW) associated with carbonic acid will return to the atmosphere with the precipitation of carbonate minerals on a geological time scale (>1 Ma)
Summary
A river system is one of the most important transport channels of material and energy to the ocean in a drainage basin, which records the environment evolution processes of the river basin.Chemical weathering processes in a drainage basin can be reflected by the river hydrochemical characteristics [1,2], which is the main part of the mass exchange between the ocean and the continent.It is generally recognized that silicate chemical weathering (SCW) induced by carbonic acid is a net depletion process of the atmospheric/soil CO2. Chemical weathering processes in a drainage basin can be reflected by the river hydrochemical characteristics [1,2], which is the main part of the mass exchange between the ocean and the continent. The CO2 consumed by carbonate chemical weathering (CCW) associated with carbonic acid will return to the atmosphere with the precipitation of carbonate minerals on a geological time scale (>1 Ma). CCW only affects global climate change on a short time scale [3]. The CO2 consumption associated with CCW have controlled climate change over a short time scale, and dominated long-term climate change, since the emergence of aquatic photosynthetic organisms [7,8,9]
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