天津平原区浅层地下水水化学特征及碳酸盐风化碳汇研究

doi:10.13745/j.esf.sf.2022.1.39

摘要/Abstract

摘要：

大气 CO₂浓度在控制全球气候变化方面具有至关重要的作用,研究碳循环、CO₂收支平衡和精确评估是制定区域CO₂减排策略和寻找新的碳汇途径最重要的组成部分。碳酸盐风化碳汇是全球碳循环研究的一个重要方向。为此,本研究以天津平原区浅层地下水为研究对象,通过对地下水调查及水样的采集与分析,运用水化学分析方法分析了地下水水化学特征,并估算了地下水总储存量、DIC储量和碳酸盐风化碳汇量。研究结果表明:浅层地下水化学场自北部山前平原向南部冲积平原和滨海平原,呈现出自北而南和由北西向南东的水平水化学分带规律,地下水由低浓度的淡水、微咸水变为高浓度咸水,沿此方向水化学类型由HCO₃-Ca·Na·Mg→Cl·SO₄-Na→Cl·HCO₃-Na→Cl-Na型转变;淡水区、微咸水区和咸水区面积分别为733、3 034和6 564 km²。地下水水化学组分中Ca²⁺、Mg²⁺和 $HCO 3 -$ 主要来源于碳酸盐的溶解作用。研究区浅层地下水总储存量为2 241 640万m³,总DIC储量为8.13×10⁶ t,总碳汇量为4.11×10⁶ t。研究区浅层地下水淡水区、微咸水区和咸水区地下水储存量分别为157 799万、6 245 936万和1 459 247万 m³,DIC浓度分别为19200、19200和19342 mg/L,DIC储量分别为0.67×10⁶、1.65×10⁶和0.58×10⁶ t,碳汇量分别为0.22×10⁶、0.90×10⁶和2.98×10⁶ t。沿地下水流向,DIC、储量和碳汇量的空间分布均呈现出由低到高的趋势。

关键词: 天津平原区, 浅层地下水, 水化学特征, 无机碳, 碳酸盐风化碳汇

Abstract:

Atmospheric CO₂ concentration plays a crucial role in controlling global climate change. Understanding the carbon cycle and CO₂ balance with an accurate assessment of atmospheric CO₂ is key to formulating regional CO₂ reduction strategies and identifying new carbon sink pathways. Carbonate weathering-related carbon sink is an important subject of global carbon cycle research. This study analyzed the shallow groundwater hydrochemical characteristics, and estimated the total groundwater storage, DIC storage in groundwater, and carbonate weathering-related carbon sink capacity of groundwater in the Tianjin plain area. From the northern piedmont plain to southern alluvial plain and coastal plain, a N-S and NW-SW horizontal hydrochemical zoning pattern in shallow groundwater was apparent, as groundwater types varied from freshwater and brackish water with low TDS to brackish water with high TDS, and water hydrochemical types changed accordingly from HCO₃-Ca·Na·Mg → Cl·SO₄-Na → Cl·HCO₃-Na → Cl-Na. The areas of freshwater, brackish water and saline water were 733, 3034 and 6564 km², respectively, where Ca²⁺, Mg²⁺, and $HCO 3 -$ in groundwater were mainly derived from the dissolution of carbonate. In the study area, the total shallow groundwater storage was 22416 million m³; the total DIC storage was 8.13×10⁶ t; and the total carbon sink capacity was 4.11×10⁶ t. In the freshwater, brackish water, and brackish water zones of the study area, the shallow groundwater storages were 1578 million, 62459 million and 14592 million m³, respectively; the DIC concentration ranged from 19 to 200 mg/L, 19 to 200 mg/L, and 19 to 342 mg/L, respectively; the DIC storages were 0.67×10⁶ t, 1.65×10⁶ t and 0.58×10⁶ t, respectively; and the carbon sink capacities were 0.22×10⁶ t, 0.90×10⁶ t and 2.98×10⁶ t, respectively. Groundwater storage, DIC storage, and carbon sink capacity increased along the groundwater flow direction across the study area.

Key words: Tianjin plain area, shallow groundwater, hydrochemical characteristics, inorganic carbon, carbonate weathering-related carbon sink

中图分类号:

P641.3

李海明, 李梦娣, 肖瀚, 刘学娜. 天津平原区浅层地下水水化学特征及碳酸盐风化碳汇研究[J]. 地学前缘, 2022, 29(3): 167-178.

LI Haiming, LI Mengdi, XIAO Han, LIU Xuena. Hydrochemical characteristics of shallow groundwater and carbon sequestration in the Tianjin Plain[J]. Earth Science Frontiers, 2022, 29(3): 167-178.

图/表 16

图1 天津平原区地下水采样点图

Fig.1 Groundwater sampling points in the study area

表1 研究区地下水水化学指标的统计分析

Table 1 Statistical analysis of groundwater chemical indexes in the study area

组分	样本量	组分浓度/(mg·L^-1)			组分浓度标准差/ (mg·L^-1)	变异系数/%
组分	样本量	极大值	极小值	均值	组分浓度标准差/ (mg·L^-1)	变异系数/%
TDS	50	63 000.00	557.00	7 836.59	11 584.12	147.82
K⁺	50	284.00	0.62	30.90	55.28	178.89
Na⁺	50	11 522.00	63.00	1 541.19	2 248.71	145.91
Ca²⁺	50	1 370.00	30.50	226.05	254.88	112.75
Mg²⁺	50	1 494.00	23.70	215.14	279.27	129.81
$HCO 3 -$	50	1 740.00	97.00	596.21	260.01	43.61
Cl^-	50	21 053.00	56.00	2 556.05	4 366.12	170.82
$SO 4 2 -$	50	4 230.00	75.00	694.69	810.89	116.73
$CO 3 2 -$	50	N.D.	N.D.	N.D.
pH值	50	9.44	7.02	7.64	0.40	5.22

表1 研究区地下水水化学指标的统计分析

Table 1 Statistical analysis of groundwater chemical indexes in the study area

组分	样本量	组分浓度/(mg·L^-1)			组分浓度标准差/ (mg·L^-1)	变异系数/%
组分	样本量	极大值	极小值	均值	组分浓度标准差/ (mg·L^-1)	变异系数/%
TDS	50	63 000.00	557.00	7 836.59	11 584.12	147.82
K⁺	50	284.00	0.62	30.90	55.28	178.89
Na⁺	50	11 522.00	63.00	1 541.19	2 248.71	145.91
Ca²⁺	50	1 370.00	30.50	226.05	254.88	112.75
Mg²⁺	50	1 494.00	23.70	215.14	279.27	129.81
$HCO 3 -$	50	1 740.00	97.00	596.21	260.01	43.61
Cl^-	50	21 053.00	56.00	2 556.05	4 366.12	170.82
$SO 4 2 -$	50	4 230.00	75.00	694.69	810.89	116.73
$CO 3 2 -$	50	N.D.	N.D.	N.D.
pH值	50	9.44	7.02	7.64	0.40	5.22

图2 研究区地下水水化学类型

Fig.2 Groundwater hydrochemical types in the study area

图3 地下水化学类型空间分布

Fig.3 Spatial distributions of groundwater hydrochemical types

图4 不同含盐量下Ca2+和 HCO 3 -的比例关系

Fig.4 Proportional relationships between Ca2+ and HCO 3 - at sampling points for different groundwater salinities

图5 不同含盐量下(Ca2++Mg2+)与 HCO 3 -的比例关系

Fig.5 Proportional relationships between (Ca2+ + Mg2+) and HCO 3 - at sampling points for different groundwater salinities

图6 不同含盐量下(Ca2++Mg2+)与( HCO 3 -+ SO 4 2 -)的比例关系

Fig.6 Proportional relationships between (Ca2+ + Mg2+) and ( HCO 3 - + SO 4 2 - ) at sampling points for different groundwater salinities

图7 不同水化学类型下Ca2+和 HCO 3 -的比例关系

Fig.7 Proportional relationships between Ca2+ and HCO 3 - at sampling points for different groundwater hydrochemical types

图8 不同水化学类型下(Ca2++Mg2+)与 HCO 3 -的比例关系

Fig.8 Proportional relationships between (Ca2+ + Mg2+) and HCO 3 - at sampling points for different groundwater hydrochemical types

图9 不同水化学类型下(Ca2++Mg2+)与( HCO 3 -+ SO 4 2 -)的比例关系

Fig.9 Proportional relationships between (Ca2+ + Mg2+) and ( HCO 3 - + SO 4 2 - ) at sampling points for different groundwater hydrochemical types

图10 研究区浅层地下水含水层厚度的变化

Fig.10 Variation of shallow groundwater aquifer thickness in the study area

图11 地下水中无机碳(DIC)浓度的变化

Fig.11 Variation of inorganic carbon (DIC) content in groundwater across the study area

图12 研究区浅层地下水DIC储量的变化

Fig.12 Variation of DIC storage in shallow groundwater across the study area

表2 浅层地下水DIC储量估算

Table 2 Estimation of DIC storage in shallow groundwater

单位面积DIC储量/(g·m^-2)	分布范围			碳储量
单位面积DIC储量/(g·m^-2)	面积/km²	占比/%		储量/t	占比/%
<500	1 427.92	13.82	0.36×10⁶		4.39
500<1 000	7 091.81	68.65	5.32×10⁶		65.47
1 000<1 500	1 533.59	14.84	1.92×10⁶		23.60
1 5002 000	165.07	1.60	0.29×10⁶		3.56
>2 000	112.64	1.09	0.24×10⁶		2.98
总计	10 331.03	100	8.13×10⁶		100

图13 浅层地下水碳酸盐风化碳汇量的变化

Fig.13 Variation of carbonate weathering-related carbon sink capacity of shallow groundwater across the study area

表3 浅层地下水碳汇量估算

Table 3 Estimation of carbon sink capacity of shallow groundwater

单位面积碳汇量/(g·m^-2)	分布范围			碳汇量
单位面积碳汇量/(g·m^-2)	面积/m²	占比/%		碳汇/t	占比/%
<300	3 198.68	30.96	0.58×10⁶		14.03
300<600	6 222.48	60.23	2.80×10⁶		68.21
600900	753.57	7.29	0.57×10⁶		13.77
>900	156.31	1.51	0.16×10⁶		4.00
总计	10 331.03	100	4.11×10⁶		100

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