Abstract
Groundwater chemical evolution is the key to ensuring the sustainability of local society and economy development. In this study, four river sections and 59 groundwater wells are investigated in the Longgang River (L.R.) basin in South China. Comprehensive hydrochemical analysis methods are adopted to determine the dominant factors controlling the chemical evolution of the local phreatic groundwater and the potential impact of human activities on groundwater quality. The results indicate that the ionic composition of the local phreatic groundwater is dominated by Ca2+ (0.9–93.8 mg/L), HCO3− (4.4–280.0 mg/L), and SO42− (1.0–91.0 mg/L). Ca–Mg–HCO3, Ca–Na–HCO3, and Na–Ca–HCO3 are the major groundwater hydrochemical facies. Water–rock interactions, such as the dissolution of calcite and dolomite, are the primary source of the major ions in the local groundwater. Cation-exchange reaction has its effects on the contents of Ca2+, Mg2+, and Na+. Ammonia concentration of the sampling sections in the L.R. increases from 0.03 to 2.01 mg/L along the flow direction. Groundwater nitrate in the regions of the farmland is attributed to the lowest level of the groundwater quality standards of China, while the same test results are obtained for heavy metals in the industrial park and landfill, suggesting a negative impact of the anthropogenic activities on the local phreatic groundwater quality.
1 Introduction
Groundwater is the most important source of freshwater throughout the world, and one-third of the world’s population relies on groundwater supply [1,2,3]. Unfortunately, rapid urbanization and increasing population have accelerated the consumption of groundwater resources and caused deterioration in groundwater quality [4,5,6], which raises concern about the drinking water safety worldwide, especially in the developing countries such as India, Pakistan, and China [7,8,9]. Therefore, understanding the chemical composition of groundwater will aid in the development and management of groundwater for various uses [6,10,11].
Groundwater chemical evolution is largely dominated by the natural factors (topography and landforms, stratum, lithology, meteorological conditions, water–rock interaction, etc.) and the anthropogenic activities (agricultural irrigation, exploitation for domestic water supply and industrial manufacturing, etc.) [12,13,14]. A significant number of studies have been conducted on this topic owing to the importance of the domestic water supply. For instance, studies focused on the anthropogenic activities resulting in groundwater pollution of nitrate/heavy metals [15,16,17,18,19,20,21]; groundwater geochemical assessment using geostatistical and geographic information system approaches [22,23,24]; and groundwater salinization related to pumping and irrigation [25,26]. However, the regions with highly developed river net (such as the South China) generally consider the surface water (the rivers and the reservoirs) as the domestic water supply source; thus, the prevention of surface water pollution in such regions is emphasized, while the attention paid to the groundwater is not enough [27,28]. For instance, Shenzhen, considered one of the most developed cities in China (1,997 km2, 12.5 million population, and GDP 2.24 trillion CNY in 2017) [29], did not conduct the basic status survey of the groundwater quality until 2013 [30], and the research focused on groundwater chemical evolution in basin scale has not yet been reported. Despite the importance of the groundwater resource, groundwater hydrological information and the geochemical behavior of the groundwater system are of great significance to assess the groundwater sustainability as well as local water environment [31,32,33,34,35]. So it is necessary to identify the dominant factors that control the groundwater chemical evolution in such regions.
In the context of current needs, geochemical survey was conducted in the L.R. basin in Shenzhen, South China, and the specific objectives of this study were to (1) investigate the geochemical evolution of groundwater in the L.R. basin using the hydrochemical analysis methods; (2) evaluate the local water quality status and the predominant factors of natural and anthropogenic activities on the groundwater chemistry; and (3) identify the impact of the potential pollution sources on the groundwater quality. Taking the L.R. basin as an example, the results of this study partly reveal the negative impacts of urbanization on the local water quality and groundwater chemical evolution, which will be beneficial to promote the groundwater management for sustainable development in such rapidly urbanizing areas.
2 Study area description
The L.R. basin is located in the northeastern region of Shenzhen, South China, extending between 22°34′N to 22°49′N latitude and 114°09′E to 114°26′E longitude (Figure 1), the area and population of which are c. 302 km2 and 1.18 million, respectively. The Shenzhen Water Resources Bulletin 2017 indicates that the total water consumption of the L.R. basin is c. 27,367 × 104 m3 and the consumption of groundwater is c. 65 × 104 m3 [36]. The climate of the study area is typically subtropical monsoon, with the average monthly temperature varying from 15.4°C in January to 28.9°C in July (1981–2010) [37]. According to the meteorological data collected at the Qinglinjing Weather Station from 1960 to 1997, the average annual precipitation of the L.R. basin is c. 1,733.8 mm, ranging from 979 to 2,467 mm, and approximately 80% of the precipitation occurs during April and September [37]. The length and the river bed gradient is c. 36.3 km and 2.8‰, with 11 first tributaries distributed in arborescent pattern, and the flow direction is roughly from southwest to northeast.

Geographical location of the L.R. basin.
The NE–SW Lianhuashan Fault Zone and E–W Gaoyao–Huilai fault zone dominate the geological process of the L.R. basin, and the stratum of the study area mainly consists of sediments and igneous rocks, such as the quaternary sediments that distribute in the middle of the basin and the carboniferous sandstones that distribute in the northeast and the southern basin (Figure 2a). The hydrogeological division of the L.R. basin is complex owing to the strong geological activities; quaternary sediments are mainly distributed in the middle part of the basin, while carboniferous sandstones are distributed in the west and south of the middle part. Silurian granites, cretaceous sandstones, and conglomerates are distributed in the north and south of the basin in a scattered manner. Precipitation is the major recharge source of the local phreatic groundwater, which is exploited for the needs of distributed agricultural irrigation, industrial manufacturing, and domestic use in the study area. According to the boreholes work conducted in 2014 and 2015, the phreatic groundwater in the study area mainly flows from northeast to southwest, the aquifer of which is composed of variable materials such as silt clay, sandy clay, and weathered granite, and the thickness of the phreatic aquifer ranges from 2.6 to 6.8 m, with the water table depth varying from 1.0 to 6.8 m (Figure 2b and c).

Geological map (a) and borehole profile of the L.R. basin (b and c).
3 Materials and methods
To reveal the hydrogeochemical characteristics, rainwater, river water, and groundwater were sampled in the L.R. basin in 2015. In this study, a total of 59 groundwater samples were collected from different sampling sites (12 wells in the farmland for agricultural supply and 47 wells in the construction land for domestic use and groundwater quality monitoring, Figure 1). The selection of sampling locations was based on the field conditions and followed the technical specifications for environmental monitoring of groundwater of China [38]. The river samples were collected from four river sections once per month (numbered from 1 to 4, from the upstream to the downstream), and the rainwater samples were collected from the Longgang Weather Monitoring Station. The river water and groundwater samples were collected using high-density polyethylene containers and transported to the State Environmental Protection Key Laboratory of Drinking Water Source Management and Technology (Shenzhen) for test. The sampling number and frequency, the test parameters, and the methods used are summarized in Table 1. Test procedures followed the standard examination methods for drinking water of China [39]. Ion balance check was conducted to assess the reliability of the hydrochemical data; 72% (18/25) of the calculated charge balance errors of the samples were found to be less than ±10% (44% were less than 5%), which was an acceptable uncertainty for the hydrochemical analysis in this study. (Seven samples with charge balance errors larger than 10% were excluded from the hydrogeochemical analysis.)
Sampling and test information in this study
Cluster | Number of the sampling sites | Sampling frequency | Number of the samples | Test parameters | Number of the tested samples | Test method and instruments |
---|---|---|---|---|---|---|
Rainwater | 1 | 1/month | 12 | pH, EC, ammonia | 12 | Electrode method (PB-10, China) for pH; electrical conductivity meter (DDS-307W, China) for EC; spectrophotometer (Hach DR1900, USA) for ammonia |
River water | 4 | 1/month | 48 | pH, DO, EC, Eh, TDS | 48 | On-site portable instrument (YSIproplus, USA) |
Ammonia | 48 | Spectrophotometer (Hach DR1900, USA) for ammonia | ||||
Groundwater | 59 | 1/year | 59 | pH, DO, EC, Eh, TDS | 59 | On-site portable instrument (YSIproplus, USA) |
Na, K, Ca, Mg, Cl, SO4, HCO3 | 25 (12 wells in the farmland and 13 in the construction land) | Inductively coupled plasma atomic emission spectrometry (Integra XL, GBC, Australia) for Na, K, Ca, Mg; ion chromatography (IC-90, Dinoex, USA) for Cl, SO4, HCO3; acid–base titration for HCO3 | ||||
Ammonia, nitrate, fluoride, Pb, Hg, Zn, Cu, Cd, Ni | 59 | Spectrophotometer (Hach DR1900, USA) for ammonia, nitrate, fluoride; inductively coupled plasma atomic emission spectrometry (Integra XL, GBC, Australia) for Pb, Hg, Zn, Cu, Cd, and Ni |
4 Results and discussion
4.1 General hydrochemistry
The statistical values of pH, dissolved oxygen (DO), electric potential (Eh), electrical conductivity (EC), total dissolved solid (TDS) of the local phreatic groundwater are shown in Figure 3a. According to the test results, the pH and DO range from 3.95 (outlier) to 7.76 and from 1.75 to 8.85 mg/L, respectively, with the average value of 6.55 and 5.13 mg/L, indicating slightly acidic and aerobic conditions of the local phreatic groundwater. The TDS ranges from 16 to 2,070 mg/L (outlier), and the average value is 380 mg/L; the Eh and EC range from 280 to 729 mV and from 42.7 to 944.0 µS/cm, respectively. The outliers of the pH and TDS are attributed to the grade 5 of the standard of groundwater quality (on a scale of one to five to measure the quality of groundwater, one means good and five means poor [40]), indicating that the phreatic groundwater in some regions of the study area is of poor quality and is not potable.

Field monitoring parameters (a) and the major component concentration (b) of the phreatic groundwater in the study area.
4.2 Hydrochemical facies
The ionic composition of the phreatic groundwater of the study area is dominated by Ca2+ (0.9–93.8 mg/L, average value 29.4 mg/L), HCO3− (4.4–280.0 mg/L, average value 89.9 mg/L), and SO42− (1.0–91.0 mg/L, average value 22.9 mg/L); the concentrations of Na+ (2.0–37.9 mg/L, average value 10.5 mg/L), K+ (0.3–10.7 mg/L, average value 2.8 mg/L), Mg2+ (0.2–14.8 mg/L, average value 4.8 mg/L), and Cl− (2.0–47.9 mg/L, average value 16.5 mg/L) are relatively low (Figure 3b). The geochemical evolution of groundwater can be identified by plotting the concentrations of major cations and anions in the Piper trilinear diagram [41]. According to the distribution of the points in the plots (Figure 4), there is no obvious variance in groundwater types between the samples collected from the wells in the farmland and the construction land. Overall, 94% of the (17/18) samples are lumped in the zones A and D of the lower left triangle, indicating that calcium type and sodium type dominate the groundwater type of the study area. About half of the samples are located in the zone E of the lower right triangle, 17% (3/18) of the samples are located in the zone B, and the rest are located in the zones F and G, which reveals that bicarbonate type groundwater and non-type groundwater are predominant and the rest are sulfate type and chloride type. Meanwhile, c. 55% (10/18) of the samples are distributed in the zone 5, indicating that the bicarbonate type is most common in groundwater chemistry of the phreatic aquifer in the study area. Therefore, the hydrochemical facies in the phreatic groundwater of the study area can be classified into a variety of water types including Ca–Mg–HCO3, Ca–Na–HCO3, Na–Ca–HCO3, Na–HCO3, and Na–SO4–Cl types.

Piper plots of the phreatic groundwater of the study area.
4.3 Natural factors affecting groundwater chemistry
The geochemical evolution of groundwater is largely determined by natural factors such as the lithology, the stratum structure, and the hydrogeological conditions [23,34,35]; thus, the water–rock interactions would probably dominate the ionic components in groundwater. The Gibbs diagram and Gaillardet diagram are intuitional tools being widely used to discuss the origin of groundwater ions and the dominant factors that control the components of groundwater [34,42,43,44,45]. According to the study results illustrated in Figure 5, the plots of the samples are mainly distributed in the middle part of the diagram (the rock dominance zone), indicating that the rock weathering (water–rock interaction) controls the chemical evolution of the local phreatic groundwater. Most of the plots are lumped in the diagram with Na+/(Na+ + Ca2+) ranging from 0.1 to 0.5 (Figure 5a) and Cl−/(Cl− + HCO3−) ranging from 0.1 to 0.6 (Figure 5b), indicating that Ca+ and HCO3− are the predominant components of the phreatic groundwater in the study area. The plots of the samples collected from the farmland are distributed in the relatively upper part of the diagram than those of the samples collected from the construction land, suggesting higher TDS of the phreatic groundwater in the farmland. Evaporation is a vital factor controlling the chemical evolution of phreatic groundwater [13,14]. The transpiration of the crops may result in a larger evaporation discharge in the farmland than in the construction land. Besides, groundwater abstraction and irrigation in the farmland may accelerate the groundwater flow and the dissolution of the soil/aquifer minerals, leading to a relatively higher phreatic groundwater TDS in the farmland.

(a and b) Gibbs diagram of the phreatic groundwater of the study area.
Moreover, the dominant factors of groundwater chemistry can be revealed by the ratios of the milligram equivalent concentration of major components (abbreviated as rX). For instance, the rNa/rCl of seawater is c. 0.85–0.87; the rNa/rCl of groundwater predominated by the dissolution of halite is c. 1; and the rNa/rCl of groundwater affected by the precipitation or strong water–rock interactions (and cation exchange) is probably larger than 1 or smaller than 0.85, respectively [46]. The rNa/rCl of the phreatic groundwater samples in this study ranges from 0.59 to 3.77, with an average value of 1.21 (Figure 6a), indicating that the major components of the local groundwater are probably dominated by multiple interactions; besides, the average rNa/rCl of the samples collected from the construction land is 1.48, indicating that the groundwater evolution of the construction land is probably predominated by water–rock interactions and precipitation, and it is in agreement with the results revealed by the Gibbs diagram. The rSO4/rCl ranges from 12.03 to 200.30, with an average value of 84.06 (Figure 6b), indicating a relative oxidation condition of the phreatic groundwater.

(a and b) Statistical results of the milligram equivalent concentration of Na+, SO42− vs Cl−.
According to the study on the dissolved loads of 60 world’s largest rivers, a calculated model based on the Na+ normalized molar ratios was proposed by Gaillardet et al. [44,45] to discuss the possible origin of the river major component by the data plots on three end-members: weathering of evaporites, silicates, and carbonates. In Figure 7, the plots of the phreatic groundwater samples in this study are mainly distributed on the diagonal of the Gaillardet diagram. Most of the plots of the samples collected from the construction land are lumped between the silicates weathering zone and the evaporites zone, while the plots of the farmland are located toward the zone between silicates and carbonates weathering, indicating that silicates weathering and combined reactions would control the local groundwater major component.

Gaillardet diagram of the phreatic groundwater of the study area.
As mentioned in Section 2, the phreatic aquifer of the study area is composed of the sediments such as quartz, calcite, dolomite, albite, halite, and gypsum; therefore, the dissolution of these minerals can be a possible source of the major groundwater ions; moreover, the possible interactions can be revealed by the milligram equivalent concentration of the major ions in the local phreatic groundwater, and the interactions are summarized as equations (1)–(7). Equations (1) and (2) represent the dissolution of albite and calciclase, which may probably be the source of the local phreatic groundwater major components. Theoretically, if the major ions of groundwater originate from the weathering of carbonates (dissolution of calcite and dolomite [equations (3) and (4)]) or dissolution of evaporites (such as halite [equation (5)]), the

(a–d) Scatterplots of the milligram equivalent concentration of the major ions in the local phreatic groundwater.

(a) The cation-exchange line and (b) the CAI of the local phreatic groundwater.
4.4 Anthropogenic activities affecting groundwater chemistry
The L.R. basin is highly developed with c. 301 km2 land supporting nearly 1.18 million populations [37]. According to the remote sensing image interpretation data of the basin in 2014 [37], the construction land occupies c. 44% of the whole area of the basin, while the farmland occupies c. 14%; thus, the anthropogenic activities, for instance, the exploitation of groundwater for irrigation/domestic use and the pollution caused by industrial manufacturing and production, may affect local water environment. The river sampling results indicate that ammonia, considered the most common water pollutant indicator caused by anthropogenic activities such as the sewage discharge [56,57,58], is the major pollutant in the L.R., and its average concentration of river sections 1–4 increases from 0.03 to 1.12, 1.31, and 2.01 mg/L (Figure 10a) along the river flow direction, suggesting the anthropogenic pollution tendency of the L.R. Meanwhile, the concentration of ammonia in the phreatic groundwater of the study area ranges from 0.01 mg/L (nine samples lower than the detection limit) to 14.20 mg/L; 28.8% (17 of 59) of the samples are attributed to the lowest level of the standard for groundwater quality of P. R. China [40] (Level-5, ammonia-N; Table 2), 14 of which were sampled from the construction land (Figure 10a), reflecting the influence of anthropogenic activities. Nitrate, a ubiquitous contaminant of natural water resources that is mainly caused by agricultural activities such as the application of fertilizer and manure [16,34,59], varies within a large range from 0.01 to 102.00 mg/L (nitrate-N) in the local phreatic groundwater; 23.7% (14 of 59) of the samples are attributed to the lowest level of the standard for groundwater quality of P. R. China [40] (Level-5), 10 of which were sampled from the farmland (Figure 10b). The test results of Pb, Hg, Zn, Cu, Cd, and Ni indicate that the local phreatic groundwater is slightly polluted by heavy metals; 8.5% (5/59) of the sampling sites show detected concentrations attributing to Level-5 [40] (3 for Pb and 2 for Ni; Figure 10c and d), while the test results of other samples are superior to Level-3. It should be noted that the high levels of ammonia, nitrate, and heavy metals are mainly concentrated in the same regions such as the well nos. 4–7, 42–46, and 54–59 (Figure 10), suggesting a point-source pollution trend. Field investigation indicates that the regions of the groundwater sampling well nos. 4–7 and 54–59 have a landfill and an industrial park, which would be the potential pollution source of the regional phreatic groundwater.
![Figure 10 The groundwater test results of ammonia (a), nitrate (b), Hg, Cd, Cu (c), and Ni, Zn, Pb (d) of the study area (the white, orange, and red dots in Figure 10(a) and (b) indicate the test results under the standard of the groundwater quality of P. R. China [40] for Level-3, Level-4, and Level-5, respectively).](/document/doi/10.1515/geo-2020-0039/asset/graphic/j_geo-2020-0039_fig_010.jpg)
The groundwater test results of ammonia (a), nitrate (b), Hg, Cd, Cu (c), and Ni, Zn, Pb (d) of the study area (the white, orange, and red dots in Figure 10(a) and (b) indicate the test results under the standard of the groundwater quality of P. R. China [40] for Level-3, Level-4, and Level-5, respectively).
The environment quality standards for surface water and the standard for groundwater quality of P. R. China (ammonia, nitrate, Ni, and Pb) [40,63]
Standards | Surface water (GB 3838-2002) | ||||
---|---|---|---|---|---|
Category/uses | Chemicals (mg/L) | ||||
Ammonia | Nitrate | Ni | Pb | ||
Level-1 | Headstream water; National Nature Reserve | ≤0.15 | ≤10 (surface water source protection zone of the centralized drinking water sources) | ≤0.02 (surface water source protection zone of the centralized drinking water sources) | ≤0.01 |
Level-2 | Surface water source protection zone 1 of the centralized drinking water sources; cherish aquatic habitats, spawning grounds of fishes and shrimps, feeding grounds of the larva fishes, etc. | ≤0.5 | ≤0.01 | ||
Level-3 | Surface water source protection zone 2 of the centralized drinking water sources; wintering grounds and migration channels of fishes and shrimps, aquaculture area, swimming area, etc. | ≤1 | ≤0.05 | ||
Level-4 | General industrial water area; recreational water area that is not directly in contact with the human body | ≤1.5 | ≤0.05 | ||
Level-5 | Agricultural water area; general landscape requirement water area | ≤2.0 | ≤0.1 |
Standards | Groundwater (GB 14848-2017) | ||||
---|---|---|---|---|---|
Category/uses | Chemicals (mg/L) | ||||
Ammonia | Nitrate | Ni | Pb | ||
Level-1 | Various uses | ≤0.02 | ≤2 | ≤0.002 | ≤0.005 |
Level-2 | Various uses | ≤0.1 | ≤5 | ≤0.002 | ≤0.005 |
Level-3 | The centralized drinking water sources; industrial uses and agricultural uses | ≤0.5 | ≤20 | ≤0.02 | ≤0.01 |
Level-4 | Agricultural uses; certain industrial uses; potable water after treatment | ≤1.5 | ≤30 | ≤0.1 | ≤0.1 |
Level-5 | Not suitable as drinking water sources, selected for other uses with different purposes | >1.5 | >30 | >0.1 | >0.1 |
The sampling and analysis results indicate that the chemical composition of the local phreatic groundwater is affected by both natural and anthropogenic processes; however, it is still difficult to precisely evaluate the process contributions for each sample because the major compounds in groundwater could come from either source [6,58]. Studies used the indicative features of some specific ions such as the concentration level and distribution characters to reveal the origin of groundwater components; in particular, fluoride and nitrate compositions can be important indicators of natural versus anthropogenic sources, respectively [6,16,58]. Batch experiments on the dissolution of granite and biotite conducted by Chae et al. [58,60] indicated that F-bearing biotite may be the primary source of high fluoride concentrations in groundwater; thus, fluoride in the local groundwater may probably have originated from the natural water–rock interactions. However, the concentrations of fluoride display an inverse relationship on the Piper plots compared with nitrate, which largely originates from the diffuse (non-point) sources relating to agricultural and domestic practices, as well as the point sources such as sewage effluent [58] as discussed before. Figure 11 shows that the hydrochemical facies of the samples with high concentrations of fluoride is mainly Ca–Mg–HCO3, while nitrate is enriched in the Ca–SO4–Cl type of groundwater, suggesting different origins of fluoride and nitrate in the local groundwater. In fact, the human activities as mentioned above influence the natural groundwater quality, generally leading to increased chloride, sulfate, and nitrate [58,61,62]; thus, the Ca–SO4–Cl type of groundwater represents the anthropogenic contamination in the local phreatic groundwater, and this result is in agreement with the research conducted by Kim et al. [58] in a bedrock aquifer in South Korea.

Piper plots of the phreatic groundwater of the study area with relative concentrations of (a) fluoride and (b) nitrate (blue and red dots, respectively).
4.5 Conceptual model of the chemical evolution of the local phreatic groundwater
Precipitation and river leakage are the primary recharge sources of the phreatic groundwater; thus, the chemical characters of the groundwater are undoubtedly related to the rainwater and river water [6,56,58]. Figure 12 shows the test results of pH, EC, and ammonia concentration in rainwater, river water, and groundwater, suggesting that all of the average values of these parameters in the groundwater are within the average values in the rainwater and river water. For instance, the average values of pH in the rainwater and river water are 5.88 and 7.30, and it is 6.55 in the groundwater (Figure 12a), while the average values of EC and ammonia are 14.1, 492.7, and 357.7 µS/cm (Figure 12b) and 0.68, 2.45, and 1.03 mg/L in the rainwater, river water, and groundwater (Figure 12c), respectively. Though buffered by the vadose zone, weakly acid precipitation recharging the phreatic groundwater would probably affect its acid–alkali condition, which may further accelerate the dissolution of calcite and dolomite, which would be a possible reason for the relatively high concentrations of Ca2+ in the local groundwater. EC is a rough parameter that reveals the dissolved solid concentration of the water samples; increased average values of the river water samples compared with the rainwater and groundwater suggest chemical substance imports into the L.R.; approximate tendency of the test results of ammonia indicates that the water quality of the L.R. is affected by human activities which may potentially be one of the pollution sources of the local phreatic groundwater.

The test results of pH (a), EC (b), and ammonia concentration (c) in rainwater, river water, and groundwater.
Despite the lack of isotope sampling and test results which can reveal the groundwater supply source precisely, a conceptual model (Figure 13) that generalizes the hydrochemical evolution and potential pollution sources of local phreatic groundwater is built according to the study results mentioned above. The precipitation is the major freshwater supply source of the L.R. and local groundwater, with construction land and farmland occupying c. 58% of the whole area of the L.R. basin; human activities play a vital role in local water environment. The L.R. flows from southwest to northeast with increasing concentration of ammonia, suggesting the river water quality is influenced by anthropogenic pollution such as the sewage effluence, which may potentially affect the groundwater quality through surface water–groundwater interchange; meanwhile, the infiltration and leakage of the point source such as the industrial park and the landfill may increase the pollution risk of the local groundwater, as proved by the distribution of the high concentration of ammonia and heavy metals at sampling sites; agricultural activities including fertilizer and manure application result in non-point-source pollution of groundwater as illustrated in Figure 10b. The high nitrate concentration at sampling sites is mainly distributed in the farmland (the middle regions of the L.R. basin); moreover, pumping groundwater for irrigation enhances the leaching/infiltration of soil–water and accelerates the groundwater flow which further promotes the water–rock interactions, possibly leading to the dissolution of the soluble rocks and an increase in Ca2+ and HCO3− in groundwater. In general, both natural and anthropogenic factors dominate the phreatic groundwater geochemical evolution of the L.R. basin; the lithology, hydrogeological conditions, and water–rock interactions determine the hydrochemical facies, while pollution due to the effluent discharged into the L.R. from industrial manufacturing activities as well as the consumption of fertilizer leads to the deterioration in the local phreatic groundwater quality indirectly. The results presented herein will facilitate the development of plans to sustainably use and protect local groundwater. Moreover, further studies to identify the factors dominating the groundwater quality are warranted.

Conceptual model of the chemical evolution of the local phreatic groundwater affected by natural and anthropogenic factors.
5 Conclusions
With slightly acidic and aerobic conditions, Ca2+, HCO3−, and SO42− dominate the chemical components of the phreatic groundwater of the L.R. basin, and Ca–Mg–HCO3, Ca–Na–HCO3, Na–Ca–HCO3, Na–HCO3, and Na–SO4–Cl are the major hydrochemical facies.
Water–rock interactions such as the dissolution of calcite and dolomite are the primary source of the major ions in the local groundwater, and cation-exchange reaction has its effects on the levels of Ca2+, Mg2+, and Na+.
Anthropogenic factors play a vital role in the chemical evolution of the local river water and groundwater; the pollution discharge such as the sewage effluence results in the marked increase in the concentration of ammonia in the L.R. along the flow direction.
Different land-use types represented by industrial manufacturing and agricultural activities in the L.R. basin are related to the deterioration in the local groundwater quality, indicating high concentrations of nitrate and heavy metals in the groundwater of the farmland and the construction land.
To ensure local water environment safety, the supervision of the point sources such as the industrial park and the landfill site in the L.R. basin should be emphasized and the application of fertilizer and manure should be restricted further.
Acknowledgments
This work was financially supported by the Major Science and Technology Program for Water Pollution Control and Treatment of China (Grant No. 2015ZX07206-006), the National Natural Science Foundation of China (NSFC) (Grant No. 41702276), and Shenzhen Basic Research Plan (JCYJ20160429191638556). The authors are grateful to the editors and the anonymous reviewers for their constructive comments and suggested revisions.
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- Regular Articles
- The simulation approach to the interpretation of archival aerial photographs
- The application of137Cs and210Pbexmethods in soil erosion research of Titel loess plateau, Vojvodina, Northern Serbia
- Provenance and tectonic significance of the Zhongwunongshan Group from the Zhongwunongshan Structural Belt in China: insights from zircon geochronology
- Analysis, Assessment and Early Warning of Mudflow Disasters along the Shigatse Section of the China–Nepal Highway
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- The significance of karst areas in European national parks and geoparks
- Geochronology, trace elements and Hf isotopic geochemistry of zircons from Swat orthogneisses, Northern Pakistan
- Regional-scale drought monitor using synthesized index based on remote sensing in northeast China
- Application of combined electrical resistivity tomography and seismic reflection method to explore hidden active faults in Pingwu, Sichuan, China
- Impact of interpolation techniques on the accuracy of large-scale digital elevation model
- Natural and human-induced factors controlling the phreatic groundwater geochemistry of the Longgang River basin, South China
- Land use/land cover assessment as related to soil and irrigation water salinity over an oasis in arid environment
- Effect of tillage, slope, and rainfall on soil surface microtopography quantified by geostatistical and fractal indices during sheet erosion
- Validation of the number of tie vectors in post-processing using the method of frequency in a centric cube
- An integrated petrophysical-based wedge modeling and thin bed AVO analysis for improved reservoir characterization of Zhujiang Formation, Huizhou sub-basin, China: A case study
- A grain size auto-classification of Baikouquan Formation, Mahu Depression, Junggar Basin, China
- Dynamics of mid-channel bars in the Middle Vistula River in response to ferry crossing abutment construction
- Estimation of permeability and saturation based on imaginary component of complex resistivity spectra: A laboratory study
- Distribution characteristics of typical geological relics in the Western Sichuan Plateau
- Inconsistency distribution patterns of different remote sensing land-cover data from the perspective of ecological zoning
- A new methodological approach (QEMSCAN®) in the mineralogical study of Polish loess: Guidelines for further research
- Displacement and deformation study of engineering structures with the use of modern laser technologies
- Virtual resolution enhancement: A new enhancement tool for seismic data
- Aeromagnetic mapping of fault architecture along Lagos–Ore axis, southwestern Nigeria
- Deformation and failure mechanism of full seam chamber with extra-large section and its control technology
- Plastic failure zone characteristics and stability control technology of roadway in the fault area under non-uniformly high geostress: A case study from Yuandian Coal Mine in Northern Anhui Province, China
- Comparison of swarm intelligence algorithms for optimized band selection of hyperspectral remote sensing image
- Soil carbon stock and nutrient characteristics of Senna siamea grove in the semi-deciduous forest zone of Ghana
- Carbonatites from the Southern Brazilian platform: I
- Seismicity, focal mechanism, and stress tensor analysis of the Simav region, western Turkey
- Application of simulated annealing algorithm for 3D coordinate transformation problem solution
- Application of the terrestrial laser scanner in the monitoring of earth structures
- The Cretaceous igneous rocks in southeastern Guangxi and their implication for tectonic environment in southwestern South China Block
- Pore-scale gas–water flow in rock: Visualization experiment and simulation
- Assessment of surface parameters of VDW foundation piles using geodetic measurement techniques
- Spatial distribution and risk assessment of toxic metals in agricultural soils from endemic nasopharyngeal carcinoma region in South China
- An ABC-optimized fuzzy ELECTRE approach for assessing petroleum potential at the petroleum system level
- Microscopic mechanism of sandstone hydration in Yungang Grottoes, China
- Importance of traditional landscapes in Slovenia for conservation of endangered butterfly
- Landscape pattern and economic factors’ effect on prediction accuracy of cellular automata-Markov chain model on county scale
- The influence of river training on the location of erosion and accumulation zones (Kłodzko County, South West Poland)
- Multi-temporal survey of diaphragm wall with terrestrial laser scanning method
- Functionality and reliability of horizontal control net (Poland)
- Strata behavior and control strategy of backfilling collaborate with caving fully-mechanized mining
- The use of classical methods and neural networks in deformation studies of hydrotechnical objects
- Ice-crevasse sedimentation in the eastern part of the Głubczyce Plateau (S Poland) during the final stage of the Drenthian Glaciation
- Structure of end moraines and dynamics of the recession phase of the Warta Stadial ice sheet, Kłodawa Upland, Central Poland
- Mineralogy, mineral chemistry and thermobarometry of post-mineralization dykes of the Sungun Cu–Mo porphyry deposit (Northwest Iran)
- Main problems of the research on the Palaeolithic of Halych-Dnister region (Ukraine)
- Application of isometric transformation and robust estimation to compare the measurement results of steel pipe spools
- Hybrid machine learning hydrological model for flood forecast purpose
- Rainfall thresholds of shallow landslides in Wuyuan County of Jiangxi Province, China
- Dynamic simulation for the process of mining subsidence based on cellular automata model
- Developing large-scale international ecological networks based on least-cost path analysis – a case study of Altai mountains
- Seismic characteristics of polygonal fault systems in the Great South Basin, New Zealand
- New approach of clustering of late Pleni-Weichselian loess deposits (L1LL1) in Poland
- Implementation of virtual reference points in registering scanning images of tall structures
- Constraints of nonseismic geophysical data on the deep geological structure of the Benxi iron-ore district, Liaoning, China
- Mechanical analysis of basic roof fracture mechanism and feature in coal mining with partial gangue backfilling
- The violent ground motion before the Jiuzhaigou earthquake Ms7.0
- Landslide site delineation from geometric signatures derived with the Hilbert–Huang transform for cases in Southern Taiwan
- Hydrological process simulation in Manas River Basin using CMADS
- LA-ICP-MS U–Pb ages of detrital zircons from Middle Jurassic sedimentary rocks in southwestern Fujian: Sedimentary provenance and its geological significance
- Analysis of pore throat characteristics of tight sandstone reservoirs
- Effects of igneous intrusions on source rock in the early diagenetic stage: A case study on Beipiao Formation in Jinyang Basin, Northeast China
- Applying floodplain geomorphology to flood management (The Lower Vistula River upstream from Plock, Poland)
- Effect of photogrammetric RPAS flight parameters on plani-altimetric accuracy of DTM
- Morphodynamic conditions of heavy metal concentration in deposits of the Vistula River valley near Kępa Gostecka (central Poland)
- Accuracy and functional assessment of an original low-cost fibre-based inclinometer designed for structural monitoring
- The impacts of diagenetic facies on reservoir quality in tight sandstones
- Application of electrical resistivity imaging to detection of hidden geological structures in a single roadway
- Comparison between electrical resistivity tomography and tunnel seismic prediction 303 methods for detecting the water zone ahead of the tunnel face: A case study
- The genesis model of carbonate cementation in the tight oil reservoir: A case of Chang 6 oil layers of the Upper Triassic Yanchang Formation in the western Jiyuan area, Ordos Basin, China
- Disintegration characteristics in granite residual soil and their relationship with the collapsing gully in South China
- Analysis of surface deformation and driving forces in Lanzhou
- Geochemical characteristics of produced water from coalbed methane wells and its influence on productivity in Laochang Coalfield, China
- A combination of genetic inversion and seismic frequency attributes to delineate reservoir targets in offshore northern Orange Basin, South Africa
- Explore the application of high-resolution nighttime light remote sensing images in nighttime marine ship detection: A case study of LJ1-01 data
- DTM-based analysis of the spatial distribution of topolineaments
- Spatiotemporal variation and climatic response of water level of major lakes in China, Mongolia, and Russia
- The Cretaceous stratigraphy, Songliao Basin, Northeast China: Constrains from drillings and geophysics
- Canal of St. Bartholomew in Seča/Sezza: Social construction of the seascape
- A modelling resin material and its application in rock-failure study: Samples with two 3D internal fracture surfaces
- Utilization of marble piece wastes as base materials
- Slope stability evaluation using backpropagation neural networks and multivariate adaptive regression splines
- Rigidity of “Warsaw clay” from the Poznań Formation determined by in situ tests
- Numerical simulation for the effects of waves and grain size on deltaic processes and morphologies
- Impact of tourism activities on water pollution in the West Lake Basin (Hangzhou, China)
- Fracture characteristics from outcrops and its meaning to gas accumulation in the Jiyuan Basin, Henan Province, China
- Impact evaluation and driving type identification of human factors on rural human settlement environment: Taking Gansu Province, China as an example
- Identification of the spatial distributions, pollution levels, sources, and health risk of heavy metals in surface dusts from Korla, NW China
- Petrography and geochemistry of clastic sedimentary rocks as evidence for the provenance of the Jurassic stratum in the Daqingshan area
- Super-resolution reconstruction of a digital elevation model based on a deep residual network
- Seismic prediction of lithofacies heterogeneity in paleogene hetaoyuan shale play, Biyang depression, China
- Cultural landscape of the Gorica Hills in the nineteenth century: Franciscean land cadastre reports as the source for clarification of the classification of cultivable land types
- Analysis and prediction of LUCC change in Huang-Huai-Hai river basin
- Hydrochemical differences between river water and groundwater in Suzhou, Northern Anhui Province, China
- The relationship between heat flow and seismicity in global tectonically active zones
- Modeling of Landslide susceptibility in a part of Abay Basin, northwestern Ethiopia
- M-GAM method in function of tourism potential assessment: Case study of the Sokobanja basin in eastern Serbia
- Dehydration and stabilization of unconsolidated laminated lake sediments using gypsum for the preparation of thin sections
- Agriculture and land use in the North of Russia: Case study of Karelia and Yakutia
- Textural characteristics, mode of transportation and depositional environment of the Cretaceous sandstone in the Bredasdorp Basin, off the south coast of South Africa: Evidence from grain size analysis
- One-dimensional constrained inversion study of TEM and application in coal goafs’ detection
- The spatial distribution of retail outlets in Urumqi: The application of points of interest
- Aptian–Albian deposits of the Ait Ourir basin (High Atlas, Morocco): New additional data on their paleoenvironment, sedimentology, and palaeogeography
- Traditional agricultural landscapes in Uskopaljska valley (Bosnia and Herzegovina)
- A detection method for reservoir waterbodies vector data based on EGADS
- Modelling and mapping of the COVID-19 trajectory and pandemic paths at global scale: A geographer’s perspective
- Effect of organic maturity on shale gas genesis and pores development: A case study on marine shale in the upper Yangtze region, South China
- Gravel roundness quantitative analysis for sedimentary microfacies of fan delta deposition, Baikouquan Formation, Mahu Depression, Northwestern China
- Features of terraces and the incision rate along the lower reaches of the Yarlung Zangbo River east of Namche Barwa: Constraints on tectonic uplift
- Application of laser scanning technology for structure gauge measurement
- Calibration of the depth invariant algorithm to monitor the tidal action of Rabigh City at the Red Sea Coast, Saudi Arabia
- Evolution of the Bystrzyca River valley during Middle Pleistocene Interglacial (Sudetic Foreland, south-western Poland)
- A 3D numerical analysis of the compaction effects on the behavior of panel-type MSE walls
- Landscape dynamics at borderlands: analysing land use changes from Southern Slovenia
- Effects of oil viscosity on waterflooding: A case study of high water-cut sandstone oilfield in Kazakhstan
- Special Issue: Alkaline-Carbonatitic magmatism
- Carbonatites from the southern Brazilian Platform: A review. II: Isotopic evidences
- Review Article
- Technology and innovation: Changing concept of rural tourism – A systematic review