Hydrochemical characteristics and karst carbon sink estimation under the influence of allogenic water
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The water originating from non-karst area, i.e., allogenic water (AW), has low pH and low calcite saturation. After entering the karst area, the chemical weathering of carbonate rocks would be accelerated and the karst carbon sink flux would be increased. Yufuhe River Basin, located in Ji’nan, Northern China, was selected to clarify the mechanism of the karst carbon sink and its flux under the influence of AW; both the surface water and groundwater were detected in situ and their hydrochemical characteristics were analyzed in the laboratory. To estimate the influence of AW on the karst carbon sink exactly, a modified Galy model was adopted. The results showed that the hydrochemical type of Yufuhe River Basin is HCO3·SO4–Ca, and its ions were derived mainly from carbonate rock and less from silicate rock. Water saturation model demonstrated that AW became saturated after they mixed with the karst water (KW) as indicated by dolomite saturation index (SId) and calcite saturation index (SIc). The dissolution capacity of KW and karst carbon sink flux was then enhanced. The estimation showed that the weathering rate of silicate rocks is 8.06 mm/ka, and the weathering rate of carbonate rocks is 18.51 mm/ka. When AW mixed with KW, the dissolution rate of carbonate erosion rate increased to 20.12 mm/ka. There was also a significant promoting effect of AW on the karst carbon sink. The CO2 sink rate of metamorphic rock (gneiss-dominated area) in the upper reaches of the basin is 3.87 t/km2a. In the karst area, the average CO2 sink rate of the KW is 7.51 t/km2a, while the value became 13.03 t/km2a when it mixed with AW, nearly doubled compared with KW. Based on the above analysis, the annual CO2 consumption of Yufuhe River Basin is 5500 t, contributing to an important approach of the regional CO2 sink.
KeywordsAllogenic water Karst water Karst carbon sink CO2 consumption
The work was supported by the National Natural Science Foundation of China (41571203), the National Key Research and Development Program of China (2017YFC0406104), the Geological exploration project of Shandong province (2016-79), and the China Geological Survey (DD20160305). Our great thanks to two anonymous peer reviewers for their constructive suggestions that improved the manuscript.
LZ, PL, JC and XQ conceived and designed the field investigation; PL, XS and XY performed the investigation; XS, WL and LZ analyzed the data; PL, DY and XY contributed reagents/materials/analysis tools; XS, PL and LZ wrote the paper.
Compliance with ethical standards
Conflict of interest
The authors declare no conflict of interest.
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