Hydrochemical characteristics and evolution of groundwater in the Dachaidan area, Qaidam Basin

doi:10.13745/j.esf.sf.2020.6.40

Abstract

Abstract:

Groundwater plays an important role in the ecological environmental protection in arid and semi-arid areas. The Dachaidan Lake in the northern margin of the Qaidam Basin is located in the arid, ecologically sensitive northwestern region. For sustainable use of groundwater in this region, it is crucial to understand its hydrochemical evolutionary characteristics. In this study, we collected 28 representative water samples from this area and analyzed the distribution characteristics of groundwater chemical types by using mathematical statistics, Piper chart, Gibbs chart, ion ratio, saturation index and reverse hydrogeochemical simulation; we also discussed the water-rock interaction in the groundwater hydrochemical evolutionary process. The main results are: (1) From the piedmont alluvial fan to the Dachaidan Lake, the hydrochemical type changed from HCO₃·Cl·SO₄-Na·Ca to SO₄·Cl-Ca·Na and Cl-Na while TDS increased from 1 to 380 g/L or more. (2) The gibbs diagram, major ion ratio and saturation index showed the hydrochemical characteristics of groundwater in the study area were mainly controlled by the water-rock interaction and evaporation-crystallization effect, with halite, gypsum and feldspar dissolution and calcite and dolomite deposition along the groundwater flow path. The relationship between chlor-alkali index and [(Na⁺+K⁺)-Cl^-] or [(Ca²⁺+Mg²⁺)-( $HCO 3 -$ + $SO 4 2 -$ )] showed the cation exchange also affected the chemical composition of groundwater in the area. (3) Through reverse hydrogeochemical simulation, the main water-rock effect of the groundwater runoff process revealed by qualitative analysis was quantitatively verified.

Key words: groundwater, hydrochemical characteristics, evolution law, Dachaidan Lake, Qaidam Basin

CLC Number:

P641.3

ZHANG Jingtao, SHI Zheming, WANG Guangcai, JIANG Jun, YANG Bingchao. Hydrochemical characteristics and evolution of groundwater in the Dachaidan area, Qaidam Basin[J]. Earth Science Frontiers, 2021, 28(4): 194-205.

Figures/Tables 10

Fig.1 Topographic map showing the study area location and distribution of sampling sites

Fig.2 Groundwater contour map of the study area

Fig.3 Hydrogeological profile of the study area

Table 1 Results of statistical analysis of hydrogeochemical compositions of piedmont spring and groundwater in the alluvial-proluvial plain

水样类型	野外编号	ρ_B/(mg•L^-1)									pH值
水样类型	野外编号	K⁺	Na⁺	Ca²⁺	Mg²⁺	Cl^-	$SO 4 2 -$	$HCO 3 -$	$NO 3 -$	TDS	pH值
山区泉水	W142	13.5	141	66.7	35.6	147	183	276	—	838	8.48
冲洪积平原潜水	TK1-1	4.57	96.2	59.4	20.5	136	131	144	1.11	508	8.12
	TK2-1	2.98	55.1	31.9	6.94	49.4	50.9	132	0.64	280	8.20
	W67	3.97	122	20.1	17.5	111	139	97.8	0.86	536	8.76
	W137	5.37	356	58.2	29.2	422	337	80.0	—	1 194	7.78
冲洪积平原承压水	TK1-2	4.37	75.0	52.8	15.5	102	87.1	150	0.88	398	8.13
冲洪积平原承压水	TK2-2	3.97	35.6	33.8	10.5	47.8	30.1	141	0.79	228	8.25
冲洪积平原前缘潜水	W7	6.16	126	239	43.8	150	712	198	—	1 408	7.89
	W150	10.5	681	659	23.4	671	2 214	193	—	4 840	7.88
	W164	11.5	586	641	53.6	507	2 310	136	—	3 810	7.83
	W152	101	5 713	313	482	8 827	2 695	652	—	18 940	7.92
细土平原泉水	W9	6.16	85.1	94.0	37.5	132	260	184	—	806	7.86
	W20	5.76	81.1	61.8	29.7	131	144	178	—	660	8.00
	W83	4.57	67.7	45.8	17.5	91.8	78.9	166	—	432	8.19
	W84	4.77	69.5	54.6	16.6	93.6	73.2	204	—	438	7.65
	W43	5.17	65.8	51.4	18.5	84.7	77.0	204	—	530	7.78
	W54	3.97	109	49.0	18.0	136	110	169	0.73	532	8.30
	W89	3.58	56.8	39.4	14.1	67.1	57.8	163	—	366	8.12
盐沼平原地下水	W169	13.3	264	58.2	47.5	404	250	172	—	1 344	8.14
	W176	25.0	633	177	102	932	789	308	—	3 032	8.08
	W177	6 357	109 100	361	15 943	173 010	67 376	1.0	—	383 640	8.65
河水	W13	4.37	58.6	71.5	28.3	49.4	231	157	—	570	8.34
	W57	2.58	97.4	73.9	23.9	115	189	181	1.15	652	8.48
	W58	4.57	122	120	39.9	141	390	172	—	970	8.37
	W10	4.57	73.3	61.0	24.8	106	141	163	—	548	8.38
	W44	8.15	126	69.1	54.1	150	120	441	—	826	8.40
	W178	6.95	150	69.9	38.0	185	110	358	0.81	850	8.48
湖水	W90	735	39 425	482	2 643	68 851	6 545	335	—	122 840	8.48

Table 1 Results of statistical analysis of hydrogeochemical compositions of piedmont spring and groundwater in the alluvial-proluvial plain

水样类型	野外编号	ρ_B/(mg•L^-1)									pH值
水样类型	野外编号	K⁺	Na⁺	Ca²⁺	Mg²⁺	Cl^-	$SO 4 2 -$	$HCO 3 -$	$NO 3 -$	TDS	pH值
山区泉水	W142	13.5	141	66.7	35.6	147	183	276	—	838	8.48
冲洪积平原潜水	TK1-1	4.57	96.2	59.4	20.5	136	131	144	1.11	508	8.12
	TK2-1	2.98	55.1	31.9	6.94	49.4	50.9	132	0.64	280	8.20
	W67	3.97	122	20.1	17.5	111	139	97.8	0.86	536	8.76
	W137	5.37	356	58.2	29.2	422	337	80.0	—	1 194	7.78
冲洪积平原承压水	TK1-2	4.37	75.0	52.8	15.5	102	87.1	150	0.88	398	8.13
冲洪积平原承压水	TK2-2	3.97	35.6	33.8	10.5	47.8	30.1	141	0.79	228	8.25
冲洪积平原前缘潜水	W7	6.16	126	239	43.8	150	712	198	—	1 408	7.89
	W150	10.5	681	659	23.4	671	2 214	193	—	4 840	7.88
	W164	11.5	586	641	53.6	507	2 310	136	—	3 810	7.83
	W152	101	5 713	313	482	8 827	2 695	652	—	18 940	7.92
细土平原泉水	W9	6.16	85.1	94.0	37.5	132	260	184	—	806	7.86
	W20	5.76	81.1	61.8	29.7	131	144	178	—	660	8.00
	W83	4.57	67.7	45.8	17.5	91.8	78.9	166	—	432	8.19
	W84	4.77	69.5	54.6	16.6	93.6	73.2	204	—	438	7.65
	W43	5.17	65.8	51.4	18.5	84.7	77.0	204	—	530	7.78
	W54	3.97	109	49.0	18.0	136	110	169	0.73	532	8.30
	W89	3.58	56.8	39.4	14.1	67.1	57.8	163	—	366	8.12
盐沼平原地下水	W169	13.3	264	58.2	47.5	404	250	172	—	1 344	8.14
	W176	25.0	633	177	102	932	789	308	—	3 032	8.08
	W177	6 357	109 100	361	15 943	173 010	67 376	1.0	—	383 640	8.65
河水	W13	4.37	58.6	71.5	28.3	49.4	231	157	—	570	8.34
	W57	2.58	97.4	73.9	23.9	115	189	181	1.15	652	8.48
	W58	4.57	122	120	39.9	141	390	172	—	970	8.37
	W10	4.57	73.3	61.0	24.8	106	141	163	—	548	8.38
	W44	8.15	126	69.1	54.1	150	120	441	—	826	8.40
	W178	6.95	150	69.9	38.0	185	110	358	0.81	850	8.48
湖水	W90	735	39 425	482	2 643	68 851	6 545	335	—	122 840	8.48

Fig.4 Piper diagram of groundwater and surface water from various sources in the study area

Fig.5 Gibbs diagram of groundwater

Fig.6 Correlations of major ions in groundwater

Fig.7 Plots of saturation index vs. ion concentration for the major minerals and ions in groundwater in the study area

Table 2 List of saturation indices of major minerals in the study area

主要矿物及气体	主要矿物饱和指数
主要矿物及气体	极小值	极大值	均值	标准差
SI(方解石)	-0.33	1.58	0.68	0.45
SI(白云石)	-0.86	5.21	1.15	1.28
SI(岩盐)	-7.31	0.47	-5.80	1.78
SI(石膏)	-2.32	0.48	-1.28	0.73
SI(钠长石)	-12.68	1.99	-6.11	3.36
SI(钙长石)	-11.88	-2.29	-7.21	2.26
SI(钾长石)	-11.53	2.65	-4.98	3.29
SI(绿泥石)	-9.67	24.13	3.26	12.79
SI(石英)	-4.45	-1.06	-2.55	0.98
SI(伊利石)	-17.84	2.78	-6.37	5.75
SI(高岭石)	-13.77	2.58	-3.21	5.54
SI(蒙脱石)	-21.37	0.02	-7.49	7.15
SI CO₂(g)	-10.38	-2.29	-5.03	3.24

Table 3 Results of the reverse hydrogeochemical simulation

矿物相	化学式	摩尔浓度变化/(mmol•L^-1)
矿物相	化学式	W142→W137	W137→W176
方解石	CaCO₃	-1.255	-7.245
白云石	CaMg(CO₃)₂	-0.336	5.886
岩盐	NaCl	7.976	13.130
石膏	CaSO₄·2H₂O	1.701	4.313
CO₂(g)	CO₂	-1.684	*
NaX	NaX	0.809	0.356
CaX₂	CaX₂	-0.405	-0.178
钠长石	NaAlSi₃O₈	0.000 1	0.280
钙长石	CaAl₂Si₂O₈	*	0.420
石英	SiO₂	0.001	*
绿泥石	Mg₅Al₂Si₃O₁₀(OH)₆	*	-0.560

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