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Article

Key Factors Dominating the Groundwater Chemical Composition in a Grain Production Base: A Case Study of Muling–Xingkai Plain, Northeast China

by
Chen Su
1,2,
Zhuang Li
3,
Wenzhong Wang
1,2,*,
Zhongshuang Cheng
1,2,
Zhaoxian Zheng
1,2 and
Zongyu Chen
1,2
1
Institute of Hydrogeology and Environmental Geology, Chinese Academy of Geological Sciences, Shijiazhuang 050061, China
2
Key Laboratory of Groundwater Sciences and Engineering, Ministry of Natural Resources, Shijiazhuang 050061, China
3
Shandong Geological Environment Monitoring Station, Jinan 250014, China
*
Author to whom correspondence should be addressed.
Water 2022, 14(14), 2222; https://doi.org/10.3390/w14142222
Submission received: 30 May 2022 / Revised: 10 July 2022 / Accepted: 12 July 2022 / Published: 14 July 2022
(This article belongs to the Special Issue Groundwater Chemistry and Quality in Coastal Aquifers)
Browse Figures
Versions Notes

Abstract

:
Groundwater quality in the Muling–Xingkai Plain (MXP) is closely related to food security and human health. The chemical composition of groundwater in MXP has attracted great attention. A total of 168 groundwater samples were collected in MXP, and principal component analysis, chemical ion analysis and stable isotopic analysis were used to explore key factors affecting the chemical composition and hydrochemical evolution process of groundwater. Results show sources of chemical ions in groundwater are silicate minerals, carbonate minerals and domestic sewage. Domestic sewage is responsible for groundwater with high levels of Cl−, SO42− and NO3−, but a reduction environment can lead to groundwater with a high level of NH4+ due to nitrification. Human activity and soil media together influence groundwater chemical composition. Groundwater with a high level of chemical ions is mainly collected from wells near river channels, where coarse-textured soils are overlying aquifers. The black soil far away from river channels can retard the infiltration of wastewater. Agricultural activities do not directly lead to deterioration of groundwater qualities, and agricultural non-point-source pollution does not occur in MXP. Nearly 70% of the population in MXP is living in the southern plain, where the influence of sewage on groundwater chemical composition is obvious. Thus, shallow groundwater far away from river channels is the best choice for irrigation. Some measures should be implemented to control the discharge of domestic sewage for the protection of groundwater. In addition, it is necessary to avoid the transformation of the redox environment of groundwater in the northern plain.

1. Introduction

Groundwater is one of the most valuable natural resources in the world, and it can support nearly all kinds of human activities [1,2,3,4,5]. Generally, the development and utilization of groundwater resources are closely related to the chemical composition and qualities of groundwater. The chemical composition of groundwater can be influenced by natural processes (such as hydrogeological conditions, redox conditions and interaction of groundwater with minerals) and human activities (e.g., exploitation, sewage discharge and fertilizer application). Many important physicochemical and ecological processes are disrupted by changes in groundwater qualities, and even the rational utilization of groundwater resources is influenced by high levels of chemical ions [6,7,8]. It is necessary to ensure the safety of groundwater quality. The issues of groundwater chemical characteristics and their dominating factors have attracted more attention in the world. Relevant studies have been conducted in coastal areas, arid or semi-arid areas, karst areas and even rapidly urbanized areas [9,10,11,12]. At present, agricultural activities have become a critical cause and a source of groundwater pollution. Irrigation return flow water with chemical pollutants can lead to the groundwater and surface water being unsuitable or less valuable for other water uses [13,14,15,16]. Therefore, groundwater chemical characteristics under the influence of human activities in agricultural areas have become a research focus [17,18,19,20,21]. It is of great significance to identify the key factors influencing the chemical composition and hydrochemical evolution process of groundwater for rational utilization of water resources and food security in agricultural areas [22,23,24].
Muling–Xingkai Plain (MXP) is one of the biggest and most important grain production bases in NE China, where plants and crops grow in rich, dark soil. A great deal of pesticides and fertilizer is frequently applied, which could lead to deterioration of water quality. However, black soils with weak infiltration capacity can retard the infiltration of irrigation water and other surface water. Human activities coupled with special soil conditions result in a complex chemical evolution process of groundwater in MXP. Previous studies showed that agricultural activities have influenced groundwater qualities in local areas [25]. Recent studies show domestic sewage in residential zones is the source of contamination of groundwater [26,27]. Food security and human health in MXP are closely related to groundwater qualities. It is necessary to perform a thorough analysis to understand the chemical characteristics of groundwater and to distinguish the main factors affecting the chemical composition of groundwater in MXP.
Chemical ion analysis and multivariate statistical analysis have been widely applied to assess hydrochemical processes and geochemical evolution in complex systems [28,29,30]. These methods coupled with isotopic analysis were effectively applied to delineate the hydrochemical evolution process and to distinguish the source of chemical ions in groundwater [31,32,33,34]. Generally, correlation among chemical variables is the basis of chemical ion analysis [35]. Multivariate analysis is mainly applied to classify samples and to further identify the principal components. These methods are effective ways to distinguish the key factors influencing groundwater chemical composition [36,37].
The chemical evolution process of groundwater and dominant factors affecting chemical composition under the anthropogenic influence and special soil conditions are investigated using chemical ion analysis and multivariate statistical analysis in MXP. The aims are to (1) show the chemical composition of groundwater, (2) identify the chemical evolution process of groundwater, (3) distinguish various factors affecting the chemical composition of groundwater and (4) provide some implications for the protection of groundwater. The results will be beneficial for groundwater resource management in agricultural areas with similar geological or hydrogeological conditions.

2. Description of Study Area

2.1. Geographical Conditions

MXP occupies an area of about 10,000 km2 in NE China, extending between longitudes of 131°30′–133°40′ E and latitudes of 45°05′–46°17′ N. Wandashan Mountain is found along the north side and west side of the study area. The east and south boundaries of the study area are Wusuli River and Xingkai Lake, respectively. Abuqing River, Qihulin River and Muling River are three major rivers (Figure 1), and rivers flow through the plain from west to east. The annual average air temperature is 1.9 degrees centigrade, and the temperature is highest in July (21 °C) and lowest in January (−21 °C). Mean annual rainfall is 540–680 mm, with June to September accounting for about 70% of it.

2.2. Hydrogeological Setting

Four hydrogeologic subdivisions are divided based on rivers and lakes in the plain. Abuqin zone (Z1) and Qihulin zone (Z2) are located in the northern plain, and Muling zone (Z3) and Xingkai zone (Z4) are distributed in the middle and southern part (Figure 1).
Aquifers principally consist of Quaternary alluvial and lacustrine deposits and Neogene sediments. The thickness of the aquifer is 50–200 m, and the depth to groundwater is 2–20 m. Phreatic aquifers are widely overlain by thick black clay layers with small infiltration coefficients, especially the aquifer in Z4. Sandy sediments are mainly distributed along river channels. Groundwater flows from west to east, similar to the flow direction of rivers in MXP.
Recharge sources of groundwater are atmospheric precipitation, surface water and irrigation water. Groundwater is principally discharged by evaporation, artificial extraction and lateral outflow into river channels.

2.3. Land Uses and Human Activities

Large areas of natural grasslands and wetlands in the MXP have been exploited and turned into croplands since 1950s. In addition, large areas of gardens and woodland were turned into croplands, and many dry farmlands distributed in piedmont zones were turned into rice fields recently. The farmlands are widely distributed in MXP.
Groundwater is the main irrigation water in Z1, Z2 and Z3. Rice fields in Z4 are mainly irrigated by surface water abstracted from Xingkai Lake. A large amount of agricultural effluents has seeped underground, which may lead to a change in groundwater quality. Meanwhile, the quality and yield of crops may be influenced by groundwater quality. Mishan city and Hulin city are located in Z3, and villages are distributed widely in MXP. Domestic sewage in the rural area is discharged into leak channels, and it poses a threat to groundwater quality.

3. Materials and Methods

This study was conducted based on 164 groundwater samples collected in 2016–2018, and the numbers of samples in Z1, Z2, Z3 and Z4 are 17, 54, 71 and 22, respectively (Figure 1). Samples were filtrated by using 0.45 μm filter membranes and then stored under a temperature of 4 °C. Field parameters pH, temperature (T), electrical conductivity (EC) and redox potential (Eh) were measured on-site.
All analyses were carried out at the Institute of Hydrogeology and Environmental Geology, Chinese Academy of Geological Sciences. Analyses for total concentrations of four major cations (K+, Na+, Ca2+, Mg2+) were measured by inductively coupled plasma mass spectrometry. NO3−, Cl−, Br− and SO42− analyses of water samples were measured by spectrophotometry. HCO3− was measured by acid–base titration. Total dissolved solids (TDS) were measured gravimetrically. The relative error was less than 3% for all analyzed elements.
In this study, chemical ion analysis was carried out based on the molar ratio or milliequivalent ratio among chemical ions. It can suggest the source of the chemical ions, water–rock interaction and even the influence of human activities. Principal component analysis (PCA) was applied to analyze possible processes influencing the chemical composition of groundwater using the IBM SPSS program (version 19, 2010, SPSS Inc. Chicago, IL, USA). Parameters Eh and EC were eliminated for samples in Z1, Z2 and Z3 due to more than 50% of data values being missing (Table 1). In addition, nearly half of the samples were below the detection limit value for NH4+, and the values were replaced by 0.5 times the detection limit. Rotation of principal components was carried out in PCA, and the expressions “strong”, “moderate”, and “weak” were applied to describe the factor loading values of >0.75, 0.75–0.50 and 0.50–0.30, respectively [38].

4. Results and Discussion

4.1. Chemical Characteristics

4.1.1. General Chemistry

The descriptive statistics of groundwater chemistry data in four zones are presented in Table 1 and Figure 2. pH is predominantly slightly acidic to near neutral with TDS 64.7–1179 mg/L, and ionic composition is dominated by Ca2+ (6.01–191.4 mg·L−1), Na+ (3.75–96.68 mg·L−1) and HCO3− (18.23–642 mg·L−1). The order of abundance of cations is Ca2+ > Na+ > Mg2+ > K+ > NH4+, and anions follow the order of HCO3− > SO42− > Cl− > NO3−. The differences in chemical ion concentrations in the four zones are obvious. Samples in Z1 have the lowest levels of Ca2+, Mg2+, Na+, K+, Cl− and SO42− but the highest level of HCO3−. The ion concentrations of samples in Z4 are highest, except NH4+. Concentrations of chemical ions in Z2 are nearly identical to those in Z3, except NO3− and NH4+. Nearly all of the chemical parameters in the four zones are characterized by a high coefficient of variation. The groundwater chemical composition is influenced by multiple factors.

4.1.2. Groundwater Types

With respect to cations, most samples are scattered in zone B in the lower-left triangle, indicating a mixed type. Only a few samples in Z3 and Z4 are Ca-type (Figure 3). With respect to anions, most groundwater samples are plotted in zone E in the lower-right triangle. Most groundwater samples are HCO3-type.
As shown in the central diamond plot in Figure 3, more than half of the samples are scattered in zone 1, which indicates that alkaline earth elements and bicarbonate are the most common in groundwater chemistry. A large number of samples in Z1 and Z2 are scattered in zone 1, but more than half of the samples in Z3 and Z4 are scattered in zone 4. Zone 4 means samples are mixed chemical types. The chemical composition of samples in the southern part of MXP is significantly influenced by multiple factors.
The water type of groundwater samples in MXP is predominantly Ca-HCO3. However, samples with water types of Ca·Mg·Na-HCO3, Ca·Mg-HCO3, Ca·Mg-HCO3·SO4 and Ca·Na-HCO3 are widely distributed in the study area. At present, some samples are characterized by the water type of SO4, even NO3, which hardly occurred before 1963 [27]. The chemical composition of groundwater in MXP is influenced by human activities.

4.2. Hydrochemical Evolution Process

4.2.1. Chemical Ion Analysis

(1)
Gibbs Plot
Gibbs diagram can be used to detect the primary formation mechanism of the water chemistry [39]. The weight ratios of Na+/(Na++Ca2+) and Cl−/(Cl−+HCO3−) of most samples are less than 0.5, with TDS 200–500 mg/L (Figure 4). Rock dissolution is the predominant mechanism controlling the groundwater chemistry [40]. However, many groundwater samples do not fall in the banana-shaped area in the Gibbs diagram (Figure 4). The chemical composition is influenced by other factors, such as human activities and cation exchange reactions. Samples in and out of the banana-shaped area are defined as the “general samples” and the “special samples” in this paper, respectively. Only a few special samples were collected from wells in Z1 and Z2 (Table 2), suggesting the slight effect of external factors on the chemical compositions of groundwater in the northern plain.
(2)
Mixing diagram
A mixing diagram can be used to analyze the origin of chemical ions produced by the dissolution of different minerals [41]. Na+ normalized molar ratios are usually depicted in the diagram based on three representative lithologies (Figure 5).
Most general samples are close to the end-member of silicate and end-member of carbonatites (Figure 5) but far away from the end-member of evaporite. Chemical compositions of general samples are dominated by silicate dissolution and carbonate dissolution to different degrees [42]. The special samples lie close to the end-member of evaporates, suggesting the major contribution of evaporite (NaCl) dissolution to chemical composition.
Generally, a natural source of chloride in groundwater far from seas is the weathering of chloride-bearing evaporate deposits. However, mineralogical analysis on samples of rock debris and water-bearing units shows the compositions are quartz (52%), plagioclase (21%), clay mineral (16%), potassium feldspar (10%) and carbonates (1%). Halite and gypsum minerals are not the main components of rock and stratum. The study area is far away from the coastline, so the source of Cl− is not seawater. The chemical composition of special samples may be influenced by other factors. Cl− is one of the major anthropogenic components in groundwater [43]. Human activities are severely influencing the chemical composition of groundwater in local areas.
(3)
Ionic ratios
The specific hydrogeochemical processes can be further shown by milliequivalent ratios of chemical parameters. Sediments in MXP are characterized by sand and fine clay with adsorbed Na+. Therefore, Ca2+ and Mg2+ in the groundwater can exchange with Na+ absorbed on the surface of clay minerals as shown in Equation (1).
2Na (Clay) + (Ca2+ + Mg2+) (Groundwater) ↔ (Ca + Mg) (Clay) + 2Na+ (Groundwater)
Does cation exchange lead to the special samples falling out of the banana-shaped area in the Gibbs diagram? As shown in Figure 6a, the special samples are not linearly related. The cation exchange process of Na+ for Ca2+ in aquifers is not shown. The general samples lie along the 1:1 line, indicating the occurrence of the cation exchange process. However, concentrations of ρ(Na+ + K+ − Cl−) only vary from 0 to 1 meq/L. Cation exchange processes do not predominate the concentrations of Ca2+, Mg2+ and Na+ in groundwater.
Sources of Ca2+ and Mg2+ can be inferred from milliequivalent ratios of ρ(Ca2+ + Mg2+)/ρ(HCO3− + SO42−) (Figure 6d). Nearly all the general samples lie under the 1:1 line, so the dissolution of silicate minerals is controlling the concentration of Ca2+, Mg2+ and HCO3− in groundwater [44]. In addition, the dissolution process of silicate minerals also can be shown by the ratios of ρ(SO42− + Cl−)/ρHCO3− and ρ(Na+ + K+)/ρCl− (Figure 6b,c). The dissolution of silicate minerals is a key geochemical process controlling chemical composition in groundwater. Special samples in Figure 6, especially the special samples in Z3 and Z4, are far away from general samples. Groundwater qualities in the southern plain have been seriously affected by human activities.

4.2.2. Stable Isotope Analysis

The combined utilization of stable isotopes and chemical parameters can identify possible groundwater contamination. When rock–water interaction controls the concentration of chemical ions in groundwater, continued dissolution of rocks can elevate the concentration of related ions in groundwater with a slight fluctuation in the stable isotopic value, for the low isotopic fraction. In addition, a linear relationship will exist between the chemical ion concentration and the stable isotopic value under the effect of evaporation [45]. When some chemical ions increase sharply without dissolution of related minerals, but stable isotopic values of groundwater stay rather constant, the wastewater from human activities may be the principal cause of the high level of related chemical ions.
Figure 7 illustrates the relationships between the concentration of chemical variables (Cl−, SO42−, NO3−, Na+, Mg2+ and Ca2+) and the δ18O value of groundwater. The elevation of chemical ions for most general samples results from evaporation and mineral dissolution. However, concentrations of chemical ions for special samples increase sharply with little modifications in stable isotopic values, especially for Cl−, SO42− and NO3−. Major anthropogenic components in the groundwater include Cl− and NO3−, as well as SO42−. The chemical composition of special samples is influenced severely by human activities. The result of stable isotope analysis is consistent with the results discussed above.

4.2.3. PCA

PCA is used to further discuss the key factors dominating the chemical composition of groundwater in four zones, and the results are shown in Table 3.
(1)
Z1
The chemical composition of groundwater samples in Z1 is controlled by a three-factor model, and the cumulative variance of the three PCs is 87.81%. PC1 comprises strong loading of Ca2+, TDS, Mg2+, HCO3−, Na+ and PH, and TDS values increase with the concentrations of HCO3−, Ca2+, Na+ and Mg2+. Water–rock interactions are responsible for their occurrence. Based on the chemical analysis mentioned above, the dissolution of silicate and carbonate minerals is responsible for the chemical composition of groundwater.
Potassic fertilizers and urea fertilizers are widely applied in MXP. When the topsoil with high permeability occurs in farmlands, a clear correlation between K+ and NH4+ will be indicated in groundwater. Thus, PC3 is the indication of agricultural activities.
Potential sources of Cl− in groundwater include natural sources (dissolution of minerals), agricultural chemicals, animal waste and septic effluent. In PC2, no clear correlation is observed between Cl− and K+. Thus, fertilizer is not the main source of Cl−. In addition, a high level of Cl− cannot result from the dissolution of minerals as discussed above. Cl− and NO3− are the major components of domestic sewage [43]. Previous studies showed that the discharge of domestic sewage in MXP had resulted in a high level of NO3−. Chemical parameters Cl− and NO3− associated with factor 2 imply the influence process of domestic sewage.
(2)
Z2
A three-factor model can be used to explain the chemical composition of groundwater samples in Z2, and the cumulative variance of three PCs is 79.83%. As in the analysis of Z1, PC1 is the indication of water–rock interaction. PC2 with high positive loading of Cl− and SO42− and moderate loading of NO3− indicates that domestic sewage is responsible for groundwater chemistry. PC3 with moderate positive loading of NH4+ and K+ suggests groundwater quality is affected by agricultural production.
(3)
Z3
Groundwater chemistry in Z3 is controlled by a three-factor model, and the cumulative variance of the three PCs is 88.74%.
PC1 comprises strong loading of TDS, Na+, Ca2+, Mg2+, SO42+, Cl− and NO3− and moderate loading of K+. The strong correlations among TDS, Na+, Ca2+, Mg2+ and K+ show that water–rock interaction is responsible for chemical composition. However, strong correlations among NO3−, Cl− and SO42− are mainly caused by human activities. The TDS value is increased with concentrations of SO42−, Cl− and NO3−, which suggests that infiltration of domestic sewage is responsible for its high concentrations in groundwater. Thus, the chemical compositions of groundwater are dominated by water–rock interaction and domestic sewage.
PC2, which comprises strong loading of PH and HCO3− and positive loading of Ca2+ and Mg2+, indicates the slight dissolution process of carbonate minerals [7].
PC3, which only comprises strong loading of NH4+ and weak loading of NO3−, indicates reduction conditions.
(4)
Z4
Groundwater chemical composition in Z4 is controlled by a two-factor model, and the cumulative variance of the two PCs is 83.08%.
PC1, which comprises strong loading of TDS, K+, Na+, Ca2+, Mg2+, SO42+, Cl−, HCO3− and EC, implies water–rock interactions are responsible for chemical composition.
Halite and gypsum minerals are not the main constituents of rock and stratum. Chlorine-bearing fertilizers are not applied frequently. Thus, the high concentration of Cl− and SO42− cannot be attributed to the dissolution of minerals. Domestic wastewater is the main source of Cl− and SO4. PC1 indicates that water–rock interaction and domestic sewage control groundwater chemical composition.
PC2 comprises strong positive loading of PH and NH4+ and negative loading of NO3− and EH. Redox conditions may dominate the content of NH4+ and NO3−. Other ions do not show a significant correlation with NH4+ and NO3−, which implies that organic matter decomposition is dominating the concentration of nitrogen species. PC2 can be regarded as “natural reduction conditions”. Large areas of natural grasslands and wetlands were exploited and turned into croplands in the last few decades in MXP. Abundant herbaceous plants were buried underground. The organic matter decomposition has produced plenty of NH3-N. Thus, redox conditions can influence the content of nitrogen species.

4.3. Factors Dominating the Groundwater Chemical Characteristics

As the discussion above mentioned, water–rock interaction, infiltration of domestic sewage, agricultural activities and redox conditions are the main factors dominating the chemical composition of groundwater in MXP (Figure 8).
Agricultural activities only slightly influence the chemical composition of groundwater in the northern plain (Z1 and Z2). The redox environment of groundwater in the southern plain (Z3 and Z4) is a key factor influencing the concentration of NO3− and NH4+. The thick silt layer overlaying aquifers can lead to a reduction condition. Organic matter decomposition can produce plenty of NH3-N. A high level of NO3− is closely related to nitrification.
Nearly all the special samples were collected from wells near river channels, where coarse-textured sediments are overlying aquifers (Figure 9). Coarse-textured sediments mainly consist of sand and gravel, and they can allow water to infiltrate downwards easily. Most villages in MXP lack sewage disposal systems, and domestic sewage is discharged into a seepage pit directly. Thus, the discharge of domestic sewage in the rural areas near the rivers often leads to abnormal groundwater types.
Most of the plants grow in rich, black soil in MXP. Black soils can deter or retard the downward infiltration of water. Thus, agricultural activities do not influence the chemical composition of groundwater significantly due to the weak permeability of black soil. The dissolution of silicate minerals and carbonate minerals is the original source of groundwater. It is the most important factor dominating the chemical composition of groundwater in MXP. The saturation index (SI) data show that calcite, dolomite, gypsum and halite are in an unsaturated state (Table 4). The dissolution of minerals is the critical factor dominating the chemical composition of groundwater.
Domestic sewage from rural areas near rivers is a significant factor affecting the chemical composition of groundwater in local areas. Nearly 70% of the population in MXP is living in the southern plain. That is why most of the special samples are located in Z3 and Z4.
Though MXP is an important grain production base in China, agricultural activities do not lead to the deterioration of groundwater quality. Thick black soil layers deter the infiltration of wastewater. Soil media are an important natural factor influencing the chemical composition.

5. Suggestions for Groundwater Management

Agricultural activities do not directly lead to deterioration of groundwater qualities, and agricultural non-point-source pollution does not occur in MXP. However, the discharge of domestic sewage has led to the abnormity of groundwater quality near river channels. Therefore, shallow groundwater far away from river channels and residential zones can be used as irrigation water based on food safety and human health.
The sampling depth of special samples usually ranges from 4 to 30 m. Chemical compositions of deep groundwater with a depth of more than 80 m are relatively stable (Figure 10), and major chemical ion concentrations hardly exceed the drinking water standard. Deep groundwater is the best choice for water supply.
Nitrification has led to the transformation of NH4+ into NO3−. Thus, samples in Z3 and Z4 are characterized by a low level of NH4+. However, samples in Z1 and Z2 are characterized by a high level of NH4+. Human activities, such as digging many wells and overpumping, can increase dissolved oxygen in groundwater and accelerate nitrification. Such activities may increase the concentration of NO3− in groundwater.
To avoid the deterioration of groundwater quality and protect groundwater resources, local governmental should (1) construct sewage disposal systems immediately in rural areas, (2) supervise the indiscriminate discharge of various wastewaters, (3) impose control on the construction of wells and groundwater pumping and (4) protect the thick black soil layer to retard the infiltration of wastewater.

6. Conclusions

(1)
Dissolution of silicate minerals and carbonate minerals is the most important factor dominating the chemical composition of groundwater in MXP. Groundwater in MXP is predominantly Ca-HCO3 in composition. Human activities have significantly influenced the chemical composition of groundwater in the residential zone near rivers. Thus, the NO3 type and SO4 type exist.
(2)
Agricultural activities only slightly influence the chemical composition of groundwater in the northern plain, and human activities have significantly influenced the chemical composition of groundwater in the southern area. Groundwater in the southern plain is characterized by a high level of NH4+, which is related to the decomposition of organic matters in a reduction condition. The samples in the northern plain are characterized by a high level of NH4+, and it is necessary to avoid the transformation of a reduction condition into an oxidation environment.
(3)
Due to the widespread distribution of thick black soils in MXP, agricultural non-point-source pollution does not occur. The discharge of domestic sewage mainly influenced the chemical composition of shallow groundwater. So, deep groundwater with a depth of more than 80 m is the best choice for water supply. In addition, shallow groundwater far away from river channels should be used as irrigation water.
(4)
Government agencies should adopt some strategies to protect groundwater resources. These strategies include regulating the amount and type of fertilizers applied to farmland, constructing sewage disposal systems in rural areas, and strengthening the supervision of the discharge of wastewater and construction of deep wells.

Author Contributions

Methodology, C.S.; software, C.S. and Z.C. (Zhongshuang Cheng); validation, C.S. and Z.L.; formal analysis, W.W. and C.S.; investigation, C.S., Z.Z. and Z.L.; data curation, Z.C. (Zhongshuang Cheng); writing—original draft preparation, C.S. and W.W.; writing—review and editing, C.S. and W.W.; visualization, Z.L. and C.S.; supervision, Z.C. (Zongyu Chen); project administration, C.S. and Z.C. (Zhongshuang Cheng); funding acquisition, C.S. All authors have read and agreed to the published version of the manuscript.

Funding

This study was financially supported by the National Natural Science Foundation of China (Grant No. 41602268) and China Geological Survey’s project (Grant No. DD20160311).

Institutional Review Board Statement

Not applicable.

Informed Consent Statement

Not applicable.

Data Availability Statement

The data presented in this study are available on request from the corresponding author.

Conflicts of Interest

The authors declare no conflict of interest.

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Water 14 02222 g001 550
Figure 1. Study area and sampled sites.
Figure 1. Study area and sampled sites.
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Figure 2. Concentration of chemical parameters in four zones.
Figure 2. Concentration of chemical parameters in four zones.
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Figure 3. Piper third-line diagram of groundwater samples in MXP.
Figure 3. Piper third-line diagram of groundwater samples in MXP.
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Figure 4. Gibbs plot of water samples in MXP: total dissolved solids (TDS) as a function of weight ratios of (a) (Cl/Cl+HCO3) and (b) Na/(Na+Ca).
Figure 4. Gibbs plot of water samples in MXP: total dissolved solids (TDS) as a function of weight ratios of (a) (Cl/Cl+HCO3) and (b) Na/(Na+Ca).
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Figure 5. Bivariate diagrams of (a) (HCO3/Na) versus (Ca/Na), (b) (Mg/Na) versus (Ca/Na).
Figure 5. Bivariate diagrams of (a) (HCO3/Na) versus (Ca/Na), (b) (Mg/Na) versus (Ca/Na).
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Figure 6. Bivariate diagrams of (a) (Ca+Mg-HCO3-SO4) versus (Na+K-Cl), (b) (Na+K) versus Cl, (c) (SO4+Cl) versus HCO3, (d) (Ca+Mg) versus (HCO3+SO4).
Figure 6. Bivariate diagrams of (a) (Ca+Mg-HCO3-SO4) versus (Na+K-Cl), (b) (Na+K) versus Cl, (c) (SO4+Cl) versus HCO3, (d) (Ca+Mg) versus (HCO3+SO4).
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Figure 7. Variations of (a) SO4, (b) NO3, (c) Cl, (d) Mg, (e) Na, (f) Ca with the δ18O value of groundwater.
Figure 7. Variations of (a) SO4, (b) NO3, (c) Cl, (d) Mg, (e) Na, (f) Ca with the δ18O value of groundwater.
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Figure 8. Factors dominating the groundwater chemical characteristics in different zones in MXP.
Figure 8. Factors dominating the groundwater chemical characteristics in different zones in MXP.
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Figure 9. The distribution of the special samples in four zones.
Figure 9. The distribution of the special samples in four zones.
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Figure 10. Variations of (a) NO3, (b) SO42−, (c) Cl with sampling depth (well depth).
Figure 10. Variations of (a) NO3, (b) SO42−, (c) Cl with sampling depth (well depth).
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Table
Table 1. Statistics of groundwater chemistry data in four zones of Muling–Xingkai Plain (MXP).
Table 1. Statistics of groundwater chemistry data in four zones of Muling–Xingkai Plain (MXP).
ParameterUnitZ1 (n = 17)Z2 (n = 54)Z3 (n = 75)Z4 (n = 22)
Min.Max.MeanSDCV (%)Min.Max.MeanSDCV (%)Min.Max.MeanSDCV (%)Min.Max.MeanSDCV (%)
PHStandard5.87 7.806.630.5286.09 7.60 6.74 0.3865.92 7.466.740.3156.387.156.770.233
TDSmg·L−164.70442.40195.4893.354884.59746.10243.40122.945190.05 1179.00248.20154.1362106.001154.00278.58208.1175
K+mg·L−10.52 2.611.450.60410.22 49.693.09 7.502430.33 22.92 2.873.961380.4842.574.298.54199
Na+mg·L−15.40 52.17 17.3711.46668.42 63.7920.2712.36613.75 96.68 20.0713.32666.2179.0527.5016.1759
Ca2+mg·L−16.01 79.08 29.8717.575910.07120.4038.8725.36658.79 167.2036.1722.156112.65191.4038.0936.0595
Mg2+mg·L−12.78 29.10 11.847.34624.37 44.2612.817.89624.27 55.84 12.448.14653.7281.3513.9015.36111
Cl−mg·L−1--64.93 7.7615.411980.35 59.7211.5114.91129 -- 184.3020.0329.041450.35308.9037.0966.53179
SO42−mg·L−11.61 28.21 6.906.24901.62 74.1822.9121.07921.70 181.3024.2431.561301.64125.8023.5933.24141
HCO3−mg·L−118.23504.40174.93125.427233.63642.00183.49115.476324.46354.60133.9372.415466.03550.30153.16104.0668
NH4+mg·L−10.02 7.701.532.521650.01 7.001.00 1.63163 0.02 5.300.661.311980.023.900.691.27185
NO3−mg·L−11.75 104.309.5823.832490.20 147.709.74 24.17248 1.75 399.0032.6168.662111.7895.6821.2429.95141
ECms·cm−1 0.132.050.500.4080
Ehmv −164.00135.0010.5880.16758
Note: SD: standard deviation; CV: coefficient of variation; --: below detectable limit.
Table
Table 2. The number of the special samples in four zones.
Table 2. The number of the special samples in four zones.
ZonesTotal SamplesNumber of Special SamplesC (%)
Z117317.65
Z254916.67
Z3711622.53
Z4221045.45
Note: C: ratio of the number of special samples to total samples.
Table
Table 3. Principal component loading for groundwater samples in four zones.
Table 3. Principal component loading for groundwater samples in four zones.
Chemical ParameterZ1Z2Z3Z4
PC1PC2PC3PC1PC2PC3PC1PC2PC3PC1PC2
PH0.820−0.390−0.0370.860−0.272−0.301−0.1150.957−0.0840.2280.775
TDS0.9650.1400.1310.8190.5590.0360.995−0.0110.0290.996−0.040
K+−0.210−0.1080.9130.4820.4480.5890.684−0.2110.0160.9430.213
Na+0.8450.136−0.2710.771−0.0690.2150.935−0.069−0.0440.881−0.253
Ca2+0.9690.0000.1080.7770.563−0.1110.9430.1850.0960.9820.049
Mg2+0.952−0.033−0.0030.7790.576−0.0460.9220.2280.0680.9780.063
HCO3−0.920−0.3500.1360.9690.1140.180−0.0150.7600.4200.7830.587
SO42−−0.4280.128−0.624−0.0750.8260.0260.866−0.331−0.2730.823−0.140
Cl−−0.1170.953−0.2340.1290.8040.0180.861−0.212−0.2320.944−0.235
NH4+0.016−0.0910.8920.0370.0190.700−0.068−0.0030.979−0.0120.669
NO3−0.0190.976−0.0600.1770.566−0.0420.896−0.253−0.4760.262−0.835
EC 0.981−0.014
Eh 0.127−0.812
Eigenvalue5.252.212.204.442.901.446.391.851.537.862.94
Explained variance (%)47.7420.0919.9840.3826.4013.0558.0616.8013.8860.4522.63
Cumulative % of variance47.7467.8387.8140.3866.7779.8358.0674.8688.7460.4583.08
Table
Table 4. Saturation index of groundwater samples in four zones.
Table 4. Saturation index of groundwater samples in four zones.
Saturation
Index		Z1Z2Z3Z4
MaxMinMeanMaxMinMeanMaxMinMeanMaxMinMean
SI (Calcite)0.37−3.34−1.950.26−2.49−1.250.08−2.79−1.560.44−1.78−1.45
SI (Dolomite)0.58−5.52−2.240.29−5.2−2.64−0.15−4.52−3.020.75−3.84−2.56
SI (Gypsum)2.61−3.75−3.23−0.61−3.65−2.74−1.91−3.56−2.75−1.31−3.85−2.85
SI (Halite)−7.25−9.62−8.35−7.29−9.68−8.89−6.91−9.54−8.51−6.23−9.7−8.88
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Su, C.; Li, Z.; Wang, W.; Cheng, Z.; Zheng, Z.; Chen, Z. Key Factors Dominating the Groundwater Chemical Composition in a Grain Production Base: A Case Study of Muling–Xingkai Plain, Northeast China. Water 2022, 14, 2222. https://doi.org/10.3390/w14142222

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Su C, Li Z, Wang W, Cheng Z, Zheng Z, Chen Z. Key Factors Dominating the Groundwater Chemical Composition in a Grain Production Base: A Case Study of Muling–Xingkai Plain, Northeast China. Water. 2022; 14(14):2222. https://doi.org/10.3390/w14142222

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Su, Chen, Zhuang Li, Wenzhong Wang, Zhongshuang Cheng, Zhaoxian Zheng, and Zongyu Chen. 2022. "Key Factors Dominating the Groundwater Chemical Composition in a Grain Production Base: A Case Study of Muling–Xingkai Plain, Northeast China" Water 14, no. 14: 2222. https://doi.org/10.3390/w14142222

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