Hydrochemical characteristics and karst carbon sink effect of border polje river in subtropical monsoon region: A case study of the Qingbo River in Mashan County, Guangxi

doi:10.13745/j.esf.sf.2024.2.14

Abstract

Abstract:

The concurrent occurrence of rainfall and heat in the subtropical monsoon climate promotes the formation of karst carbon sinks. Border poljes, recharged by allogenic water, are regions with strong carbonate rock dissolution in karst areas. Studying the hydrochemical characteristics of different water types in these regions helps deepen the understanding of karst carbon sequestration processes. This paper employs statistical methods, Piper diagrams, Gibbs diagrams, and major ion ratios to analyze the hydrochemical characteristics, origins, and carbon sink effects of rivers in a typical subtropical border polje. The results show that: (1) The main types of river water in the border polje are allogenic water, surface rivers recharged by allogenic water, karst underground rivers recharged by allogenic water, and karst groundwater. The total ion concentration shows an increasing trend. The average concentration of Ca²⁺ in karst groundwater is 91.06 mg/L, which is 2.3, 4.3, and 12.4 times that of underground rivers recharged by allogenic water, surface water recharged by allogenic water, and allogenic water, respectively. (2) After the allogenic water enters the karst area, the concentrations of Ca²⁺ and $\mathrm{HCO}_{3}^{-}$ gradually increase, and the calcite saturation index shifts positively. In the context of an accelerated water cycle due to heavy rainfall in the subtropical monsoon region, the reaction time of allogenic water with carbonate rocks is insufficient after entering the karst area to strengthen erosion. Whether it is direct infiltration of allogenic water, or karst underground rivers or surface water recharged by allogenic water, it has significant potential for increasing the carbon sink.

Key words: border polje, hydrochemistry, karst carbon sink, allogenic water, increase sinks

CLC Number:

P592
P595

ZHANG Chunlai, YANG Hui, HUANG Fen, QIU Cheng, ZHU Tongbin. Hydrochemical characteristics and karst carbon sink effect of border polje river in subtropical monsoon region: A case study of the Qingbo River in Mashan County, Guangxi[J]. Earth Science Frontiers, 2024, 31(5): 377-386.

Figures/Tables 9

Fig.1 Hydrogeological map and sampling location of the study area. Wag, Was, Wk, and Wa represents karst underground river water recharged by allogenic water, surface water in karst area recharged by allogenic water, karst underground water and allogenic water respectively.

Table 1 Statistical table of hydrochemical characteristics of different types of water samples in Qingbo River Basin of Mashan County

分组	统计量		离子浓度/(mg·L^-1)																TZ⁺/ (meq·L^-1)		TZ^-/ (meq·L^-1)		TDS浓度/ (mg·L^-1)		Ec/ (mS·cm^-1)		pH
分组	统计量		Ca²⁺		Mg²⁺		Na⁺		K⁺		$HCO 3 -$		$SO 4 2 -$		Cl^-		$NO 3 -$		TZ⁺/ (meq·L^-1)		TZ^-/ (meq·L^-1)		TDS浓度/ (mg·L^-1)		Ec/ (mS·cm^-1)		pH
外源水 Wa(n=6)	极小值		6.13		1.24		1.94		0.64		29.91		3.35		1.79		1.69		0.52		0.61		46.73		46.49		7.18
	极大值		13.34		1.92		3.19		1.18		48.02		4.24		2.50		3.83		0.91		0.93		64.29		89.16		8.29
	均值		9.38		1.52		2.43		0.89		39.75		3.69		2.04		3.09		0.72		0.79		56.25		66.83		7.54
	标准差		2.82		0.27		0.48		0.19		6.75		0.36		0.26		0.74		0.16		0.12		7.10		15.34		0.39
外源水补给地下河水 Wag(n=8)	极小值	39.84		1.12		1.83		1.10		123.58		4.71		3.02		0.03		2.24		2.21		130.18		214.90		7.52
	极大值	57.38		2.42		2.25		1.39		169.24		5.75		3.57		4.71		3.10		2.98		171.42		312.00		8.09
	均值	47.33		1.93		2.02		1.20		146.19		5.10		3.18		1.26		2.65		2.59		149.83		263.67		7.82
	标准差	6.33		0.43		0.16		0.10		16.38		0.37		0.18		1.78		0.31		0.28		14.78		33.99		0.17
外源水补给地表水 Was(n=11)	极小值	15.00		1.14		1.68		0.94		51.95		3.71		2.29		0.03		1.01		0.99		68.20		69.35		7.00
	极大值	71.44		1.82		3.08		1.68		215.68		7.13		3.87		5.12		3.84		3.79		210.97		367.00		8.05
	均值	38.62		1.57		2.26		1.16		119.65		4.90		3.04		2.46		2.19		2.15		127.48		204.55		7.56
	标准差	22.39		0.20		0.40		0.23		63.65		1.25		0.57		1.63		1.11		1.08		55.39		110.12		0.28
岩溶地下水 Wk(n=7)	极小值	81.26		0.51		0.67		0.28		241.66		6.24		2.42		2.35		4.28		4.16		230.52		391.80		7.15
	极大值	99.69		3.77		1.74		0.63		294.40		7.79		5.76		15.12		5.20		5.08		276.00		563.20		7.60
	均值	91.06		2.05		1.16		0.42		270.99		7.07		3.48		7.32		4.79		4.69		257.76		468.03		7.41
	标准差	7.21		1.28		0.40		0.11		24.58		0.63		1.23		4.77		0.36		0.40		18.80		55.57		0.18

Table 1 Statistical table of hydrochemical characteristics of different types of water samples in Qingbo River Basin of Mashan County

分组	统计量		离子浓度/(mg·L^-1)																TZ⁺/ (meq·L^-1)		TZ^-/ (meq·L^-1)		TDS浓度/ (mg·L^-1)		Ec/ (mS·cm^-1)		pH
分组	统计量		Ca²⁺		Mg²⁺		Na⁺		K⁺		$HCO 3 -$		$SO 4 2 -$		Cl^-		$NO 3 -$		TZ⁺/ (meq·L^-1)		TZ^-/ (meq·L^-1)		TDS浓度/ (mg·L^-1)		Ec/ (mS·cm^-1)		pH
外源水 Wa(n=6)	极小值		6.13		1.24		1.94		0.64		29.91		3.35		1.79		1.69		0.52		0.61		46.73		46.49		7.18
	极大值		13.34		1.92		3.19		1.18		48.02		4.24		2.50		3.83		0.91		0.93		64.29		89.16		8.29
	均值		9.38		1.52		2.43		0.89		39.75		3.69		2.04		3.09		0.72		0.79		56.25		66.83		7.54
	标准差		2.82		0.27		0.48		0.19		6.75		0.36		0.26		0.74		0.16		0.12		7.10		15.34		0.39
外源水补给地下河水 Wag(n=8)	极小值	39.84		1.12		1.83		1.10		123.58		4.71		3.02		0.03		2.24		2.21		130.18		214.90		7.52
	极大值	57.38		2.42		2.25		1.39		169.24		5.75		3.57		4.71		3.10		2.98		171.42		312.00		8.09
	均值	47.33		1.93		2.02		1.20		146.19		5.10		3.18		1.26		2.65		2.59		149.83		263.67		7.82
	标准差	6.33		0.43		0.16		0.10		16.38		0.37		0.18		1.78		0.31		0.28		14.78		33.99		0.17
外源水补给地表水 Was(n=11)	极小值	15.00		1.14		1.68		0.94		51.95		3.71		2.29		0.03		1.01		0.99		68.20		69.35		7.00
	极大值	71.44		1.82		3.08		1.68		215.68		7.13		3.87		5.12		3.84		3.79		210.97		367.00		8.05
	均值	38.62		1.57		2.26		1.16		119.65		4.90		3.04		2.46		2.19		2.15		127.48		204.55		7.56
	标准差	22.39		0.20		0.40		0.23		63.65		1.25		0.57		1.63		1.11		1.08		55.39		110.12		0.28
岩溶地下水 Wk(n=7)	极小值	81.26		0.51		0.67		0.28		241.66		6.24		2.42		2.35		4.28		4.16		230.52		391.80		7.15
	极大值	99.69		3.77		1.74		0.63		294.40		7.79		5.76		15.12		5.20		5.08		276.00		563.20		7.60
	均值	91.06		2.05		1.16		0.42		270.99		7.07		3.48		7.32		4.79		4.69		257.76		468.03		7.41
	标准差	7.21		1.28		0.40		0.11		24.58		0.63		1.23		4.77		0.36		0.40		18.80		55.57		0.18

Fig.2 Piper diagram of different types of water samples in Qingbo River, Mashan County

Fig.3 Durov diagram of different types of water samples in Qingbo River, Mashan County

Fig.4 Gibbs diagram of different water samples in Qingbo River Basin, Mashan County. Green dot with black circle is allogenic water (Wa); Green dots are karst underground river water recharged by allogenic water (Wag); Green cycle is surface water recharged by allogenic water (Was); Blue triangles are karst water (Wk).

Fig.5 Ratio of ionic millimolar concentration of various types of samples in Qingbo River Basin of Mashan County

Fig.6 Relationship between [Ca2+] and [ HCO 3 -] (a) and between [Mg2+]/[Ca2+] and TDS (b)

Fig.7 Variation characteristics of main ions in surface/underground river water in karst area recharged by allogenic water

Fig.8 Saturation index (SIc) of different hydrochemical types of calcite and its relationship with TDS

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