Imprints of seawater intrusion on groundwater quality of coastal region of Pudukkottai district, India: An integrated approach

Mohamed Tharik; Sai Saraswathi Vijayaraghavalu

doi:10.4491/eer.2024.065

Environ Eng Res > Volume 30(2); 2025 > Article

Tharik and Vijayaraghavalu: Imprints of seawater intrusion on groundwater quality of coastal region of Pudukkottai district, India: An integrated approach

Research

Environmental Engineering Research 2025; 30(2): 240065.

Published online: April 30, 2025

DOI: https://doi.org/10.4491/eer.2024.065

Imprints of seawater intrusion on groundwater quality of coastal region of Pudukkottai district, India: An integrated approach

Mohamed Tharik, Sai Saraswathi Vijayaraghavalu^†

Department of Chemistry, School of Advanced Sciences, Vellore Institute of Technology, Vellore 632-014, India

^†Corresponding author, E-mail: v.saisaraswathi@vit.ac.in, Tel: +91 89037 61281, ORCID: 0000-0002-8788-3541

Received February 4, 2024 Revised May 24, 2024 Accepted September 4, 2024

This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/3.0/) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract

Climate change and groundwater overexploitation endanger the sustainability of groundwater in India, particularly in the coastal region of Tamil Nadu. The increasing population, agricultural and industrial development, raised the demand for groundwater in the Coastal area of Pudukottai District, Tamil Nadu. Seawater intrusion establishes a challenging environment for freshwater management in coastal areas. A total of 64 groundwater samples were collected from different places, including borewells and open wells. The seawater intrusion is evaluated using the statistical method and physiochemical analysis such as water indices, ionic ratio and hydrochemical facies. As per the results of the groundwater quality index, 93% of the samples were not suitable for drinking as the examined parameter exceeded the Indian Standards. Piper’s diagram classify the Coastal groundwater into mixed Ca²⁺-Na⁺-HCO₃ ⁻, Na⁺ - HCO₃ ⁻ and Na⁺-Cl⁻ type as the dominant. As per the seawater mixing index, 78% of the groundwater samples were affected by seawater intrusion. Further, the results of the ionic ratio (Na⁺/Cl⁻, Mg²⁺/Cl⁻, Ca²⁺/Mg²⁺, Ca²⁺/SO4, Ca²⁺/HCO₃ ⁻) identify the salinization influence in the groundwater. The thematic maps created with the QGIS platform effectively to define the area of seawater intrusion. This study contributes to establishing a firm basis for decision-makers to enhance coastal groundwater management.

Keywords: Groundwater, Hydrochemical facies, Ionic ratio, Pudukottai District Seawater Intrusion, Seawater Mixing Index

Graphical Abstract

Keywords: Groundwater, Hydrochemical facies, Ionic ratio, Pudukottai District Seawater Intrusion, Seawater Mixing Index

Introduction

Globally, coastal aquifers play a significant role in freshwater supply for residential and industrial purpose [1, 2] In the coastal aquifers, fresh groundwater and seawater have an equilibrium naturally, balancing oceanic and terrestrial hydrological system [2]. However, recent research evidenced number of factors can disrupt this natural equilibrium, resulting in the freshwater-seawater interface to shift inland, a phenomenon known as “Seawater Intrusion” [2, 3]. This phenomenon reduces groundwater quality in many coastal areas across the world [1, 4–6]. Due to the changes in the rate at which freshwater recharges these coastal aquifers, the encroaching seawater will encounter a zone of dispersion where freshwater and saltwater mix and develop an interface, according to the Ghyben-Herzberg relationship theory. This interface moves forward and backwards naturally [7].

Natural and anthropogenic activities are the two main causes of seawater intrusion. It was accepted that future sea level rise would result from climate change [8, 9]. Human activities also have an impact on this natural process, which affects the interface of freshwater and seawater, collapsing the equilibrium balance [2]. Anthropogenically, seawater intrusion may occur as a result of increased groundwater demand in many coastal regions caused by population growth, economic development, expanding agriculture, and excessive utilization of groundwater in coastal aquifers [10–12]. It is essential to understand the extent to which seawater influences groundwater in order to avoid deterioration of coastal aquifers. Seawater intrusion not only affects the social and financial systems, but it also degrades the whole coastal environment of the affected region [5].

Previous studies have used hydrochemical analyses, isotope makers, flow pattern definition, and groundwater salinization process identification to characterize the behavior of saline groundwater flow [13–15]. The application includes understanding the movement of the freshwater-saltwater interface and the interactions between the surrounding freshwater and the saline water bodies in various coastal aquifers. Increased concentrations of essential groundwater ions such as Na⁺, Mg²⁺, Cl⁻, and SO₄ ²⁻ along the coastline, as well as high levels of Total Dissolved Solids (TDS) and Electric Conductivity (EC), can be indications of seawater intrusion [2, 16–17]. Therefore, integrating data from various sources with hydrogeological and chemical information may significantly improve our understanding of seawater intrusion mechanisms [18]. Numerous studies have successfully assessed seawater intrusion in coastal aquifers using groundwater geochemistry [1, 19–24].

The research area located an eastern part of Pudukkottai District of Tamil Nadu in South India. In general, the coastal area faces numerous problems in maintaining groundwater quality due to overexploitation, salt production, aquaculture, agricultural activity, and overexploitation of groundwater through deep borewells, which may disrupt the freshwater-seawater interface. Understanding the interaction of groundwater and seawater is important in this area for water resource management and determining the level of seawater intrusion.

There is limited knowledge in the study area about the status of seawater intrusion in the coastal aquifers. Therefore, the purpose of this article has been to understand the degree of salinization of freshwater resources as a result of rapid urbanization and agricultural activity, as well as to classify and summarize the changing hydrochemistry of aquifers. Hence, the assessment of seawater intrusion in the study area is currently performed using conventional hydrogeochemical approaches such as i) Groundwater Quality Index (GQI) [25, 26], ii) Hydrochemical facies such as Piper trilinear diagram [27], Gibbs diagram [28] and Stiff diagram [29], iii) Geospatial analysis of ionic ratio like enrichment of Ca, Na⁺/Cl⁻ (Jones Ratio), Mg²⁺/Cl⁻, Ca²⁺/Mg²⁺, Ca²⁺/SO₄ ²⁻, Ca²⁺/HCO₃ ⁻ [17], iv) Seawater Mixing Index (SMI) [30], v) Statistical analysis such as principal component analysis and Pearson correlation matrix [31]. Therefore, this is an integrated approach to quantify the degree of seawater intrusion in the coastal region of the Pudukottai District, India.

Materials and Methods

2.1. Study Area

Pudukkottai, the central district of Tamil Nadu, is between 9°50′ and 10°40′ North latitude and between 78°25′ and 79°15′ East longitude. The district covers 4644 km² and has a 42 km coastline. The district is bounded to the east by the Bay of Bengal, to the south by the Sivagangai District, to the north by the Tiruchirappalli District, to the northeast by the Thanjavur District, and to the south by the Ramanathapuram District. According to the 2011 census, the total population of the Pudukkottai district is 16.18 lakhs. The population density is 348 people per square kilometer [32]. The study area has a mean annual precipitation of approximately 900 mm and a tropical maritime and monsoon climate. Silt and clay deposits (Quaternary Sediments) were found in the study area [33]. The district faces low soil fertility and extreme alkalinity issues in some locations due to salt production, aquaculture and seawater intrusion [32, 34]. The geographical location of the study area is shown in Fig. 1.

2.2. Groundwater Sampling Strategy

To assess seawater intrusion in the Pudukkottai District, 64 samples were collected from open wells (n=20) and borewells (n=44) in the study sites using line-transect and random sampling methods during pre-monsoon (August 2023) according to the standard protocol (APHA 2017) [35]. The samples were collected every 1 km from the seashore to inland for 10 km in all possible sources, and 4 transects were laid towards the seashore for every 10 km length. The sampling locations were marked with Notecam GPS Ver. 5.15.4. The depth of the collected samples ranges from 3 to 12 m for open well and 150 to 460 m for borewells. Plastic 250 ml polypropylene bottles were used to collect the water samples. The plastic bottles were washed using distilled water and air dried. The collected groundwater samples were stored in a portable cooler box in the field after being filtered via Whatman 42 filter paper (pore size 2.5 μm). They were kept at 4–5°C in the chemical laboratory until they could be examined. Total Dissolved Solids (TDS), Electric Conductivity (EC), and Hydrogen Ion Concentration (pH) were measured in situ using the portable pH meter (model: Testr 10) and TDS & EC meter. The salinity was determined using a refractometer - Labart EBR 80. The chemical analysis was carried out in the Environmental chemistry laboratory, Vellore Institute of Technology, India, using standard analytical procedures (APHA 2017) [35].

2.3. Hydro-geochemistry

Total Hardness (TH), Total Alkalinity (TA), bicarbonate (HCO₃ ⁻), chlorine (Cl⁻), carbonate (CO₃ ²⁻), sulphate (SO₄ ²⁻), nitrate (NO₃ ⁻), sodium ions (Na⁺), potassium (K⁺), calcium (Ca²⁺), and magnesium (Mg²⁺) were among the groundwater parameters that were studied. TH was calculated using the EDTA titration method, and TA was determined by titrating with standard sulfuric acid. The concentrations of Na⁺, Ca²⁺, and K⁺ were determined using a Systronics flame photometer model 129. SO₄ ²⁻ and NO₃ ⁻ were determined using a UV spectrophotometer. Chloride was measured by argentometric titration, and Dissolved O₂ was analyzed by Winkler’s method [36, 37].

2.4. Groundwater Quality Index (GQI)

According to a review of the literature, the GQI is one of the most reliable indices for measuring groundwater quality and preliminary characterization of intrusive zones. The GQI weights all of the major parameters that influence human health [30]. The GQI was computed using the hydrochemical parameters pH, Na⁺, K⁺, Ca²⁺, Mg²⁺, Cl⁻, HCO^{3 −}, SO₄ ²⁻, NO₃ ⁻, and TDS (Table S1). The methodology was adapted from the approaches described in [18, 38–40]. Further, the GQI was classified into five categories: i) excellent water (GQI <50), ii) good water (50 ≤ GQI < 100), iii) poor water (100 ≤ GQI < 200), iv) very poor water (200 ≤ GQI < 300), and v) water is unfit for human consumption (GQI ≤ 300) [18, 41]. The GQI was calculated using the weighted arithmetic method developed by Brown et al. [42], as follows:

(1)

G Q I = \frac{Σ_{i = 1}^{n} W_{i} Q_{i}}{Σ_{i = 1}^{n} W_{i}}

where n=number of parameters, W_i = unit weight of ith parameter, Q_i = quality rating of the ith parameter the calculated unit weight (W_i) of each parameter shown in Table S2.

The various parameters of water quality define unit weights (Wi) that are inversely proportional to the recommended standards.

(2)

W_{i} = K / S_{n}

where K is a proportional constant, S_n is the ith parameter’s standard value, and W_i is the ith parameter’s unit weight.

The following equation is used to compute the value of K, which is assumed to be ‘1’ in this case:

(3)

K = 1 / Σ (\frac{1}{s_{n}})

The following equation is used to calculate the value of quality rating (Q_i), according to Brown et al. [42]:

(4)

Q_{i} = 100 [(V_{o} - V_{i}) / (S_{n} - V_{i})]

where V_i is the ideal value of the ith parameter for pure water, S_n is the standard allowable value, and V_o is the observed value of the ith parameter in the given sample.

All ideal values (V_i) for drinking water are set to zero, except for pH and dissolved oxygen [40]. The ideal pH and DO values (V_i) are 7 and 14.6, respectively. The pH and DO limits are 8.5 and 5, respectively.

2.5. Hydrochemical Facies Method

Gibbs, Piper and Stiff diagram were used to estimate the hydrochemical facies of groundwater and evaluate the mixing of ground and seawater. TDS, major anions and cations were used to understand the interaction of ions and their dominate type. The hydrochemical facies diagrams were performed in Originpro 2024 [18].

2.6. Seawater Mixing Index (SMI)

SMI was proposed by Park et al. [43] is used to estimate the quantitative mixing of groundwater and seawater. This index is based on the concentration of four major ionic constituents in seawater such as Na⁺, Mg²⁺, Cl⁻ and SO₄ ²⁻ as follows:

(5)

S M I = a \times \frac{C_{N a}}{T_{N a}} + b \times \frac{C_{M g}}{T_{M g}} + c \times \frac{C_{C l}}{T_{C l}} + d \times \frac{C_{S O 4}}{T_{S O 4}}

where the relative concentrations of ions in seawater Na⁺, Mg²⁺, Cl⁻, and SO₄ ²⁻ are indicated by the constants a, b, c, and d (a = 0.31, b = 0.04, c = 0.57, and d = 0.08), respectively [2, 18]. Relative threshold (T) values for particular ions were computed to understand cumulative probability curves, as illustrated in Fig. S1, where C is the measured ion concentration in the sample [11].

2.7. Statistical Analysis Method

The Principal Component Analysis (PCA) and Pearson correlation was used to find significance and similarities in the behavior of various parameters [2]. Through multivariate pattern decomposition, PCA helps in the classification of the original data [18]. The PCA and Pearson correlation analysis was done using Origin Pro 2024.

Results and Discussion

In the coastal region of Pudukottai district, water quality investigations of groundwater samples are given in Table S1. TDS was the primary parameter used to determine the quality of the water; readings for all groundwater samples ranged from 49 to 8799 mg/L. TDS = 2000 mg/L is the maximum allowable limit, and 30% (n = 19) of the samples surpassed it. The source of pollutants influencing groundwater quality in the study area could be inferred using a wide range of different hydrochemical parameters. A high Clconcentration (2556 mg/L) could be used to observe groundwater contamination [25]. An extremely high concentration of Na⁺ (950.7 mg/L) and Ca²⁺ (1310 mg/L) indicates seawater intrusion and dissolution of minerals [18]. Potassium concentrations in the study area are high, ranging from 1.07 mg/L to 150.48 mg/L, which could be caused by potash feldspar weathering [44].

3.1. Groundwater Quality Index (GQI)

Estimated GQI using equation (1) indicates 93% of the groundwater samples is unsuitable for the drinking purposes and 7% of the samples are very poor in the study area. The GQI ranges from 193.9 to 2399.6, indicating extreme salinization in the groundwater samples. GQI is extremely high due to the concentrations of TDS, TH, potassium (K⁺), calcium (Ca²⁺), and bicarbonate (HCO₃ ⁻) [22, 24, 40].

3.2. Hydrochemical Facies

In Fig. 2, the main ions are represented on a piper trilinear diagram. The two triangles and one diamond in the diagram stand for the main cation and anion types that determine the characteristics of groundwater respectively. Six different types of groundwater are classified by the piper diagram: mixed Ca²⁺-Mg²⁺-HCO₃ ⁻ type, mixed Ca²⁺-Na⁺- HCO₃ ⁻ type, Na⁺-Cl⁻ type, Na⁺-HCO₃ ⁻ type, Ca²⁺-Mg²⁺ type, and Ca²⁺-Cl⁻ type. The intensive evaluation of the diagram reflects that 61% of the samples falls under mixed Ca²⁺-Na⁺-HCO₃ ⁻ type, 22% of the samples under Na⁺-HCO₃ ⁻ type, 5% of the samples under mixed Ca²⁺-Mg²⁺-Cl⁻ type and 6% of the groundwater samples under Ca²⁺-mg²⁺ and Na⁺-Cl⁻ type. Moreover, 89% of samples fall under Na⁺ or K⁺ type in cations and 92% of the groundwater samples under HCO₃ ⁻ type in anions. A high dominance of mixed Ca²⁺-Na⁺-HCO₃ ⁻ type in the piper diagram indicates freshening of ion exchange in the groundwater (Fig. 2). The concentration of Na⁺-HCO^{3 −} represents marine depositional conditions in the aquifers of the sampling sites [45, 46]. However, the concentration of Na⁺-Cl⁻ and mixed Ca²⁺-Mg²⁺-Cl⁻ type indicates influence of seawater mixing on few groundwater samples in the study area [2].

Stiff diagram is known as pattern diagram. It is commonly used to represent chemical analysis of water samples. The anion concentration (in meq/L) are plotted to the right of the vertical zero axis, while the cations concentrations (in meq/L) are plotted to the left. The water type was determined based on the highest concentration of cations and anions as shown in stiff diagram (Fig. 3). The detailed evaluation of stiff diagram shows that Ca²⁺-Cl⁻ and Ca²⁺-HCO₃ ⁻ type contributing 23.4% each, 21.9% of groundwater samples under Mg²⁺-Cl⁻, 20.3% of samples falls under Mg²⁺-HCO₃ ⁻, 6.3% and 4.7% of samples under Na⁺-Cl⁻ and Na⁺-HCO₃ ⁻ respectively (Fig. 3). As a result, a stiff diagram proves by the dominance of Mg²⁺-Cl⁻, Ca²⁺-Cl⁻ and Ca²⁺-HCO₃ ⁻ indicates that high salinity and hardness on the groundwater samples in the study sites.

3.2.1. Controlling mechanism of groundwater chemistry

A Gibbs plot is used to determine the various processes which influence the chemistry of groundwater [44]. Fig. 4. indicates that the groundwater in the Coastal area of Pudukkottai district is primarily controlled by evaporation. TDS vs. Na⁺/(Na⁺+K⁺+Ca²⁺) (Fig. 4a) and TDS vs. Cl⁻(HCO3⁻+Cl⁻) (Fig. 4b) on the Gibbs diagram are helps to comprehend the probable source of salination in the research area. The two graphs indicate that almost 90% of the samples fall into the categories of evaporation precipitation and seawater mixing, which indicates the role these two processes have in regulating the hydrochemistry of the aquifers in the research area (Fig. 4). Meanwhile, none of the samples were controlled by precipitation dominance mechanism.

3.3. Identification of Seawater Intrusion

3.3.1. Seawater mixing index

The SMI was calculated using equation (5). Fig. S1 shows the essential parameter’s threshold value (T) which includes Na⁺, Mg²⁺, Cl⁻ and SO₄ ²⁻. The range of SMI values in the study area are 0.22 to 15.61. Fig. 5a. Shows the spatial distribution of SMI values of Coastal groundwater. The spatial analysis is plotted against the sampling points and the degree of seawater mixing (SMI Values) (Fig. 5a). The SMI >1 represents the influence of seawater mixing in the groundwater and SMI <1 indicates the fresh groundwater [2, 30, 47]. Significant seawater influence was found in 78% of the water samples (N = 50), while fresh groundwater was found in 22% of the samples (N = 14) (Fig. 5b). In the coastal region of Pudukottai district, seawater has a significant influence on groundwater, as indicated by the magnitude of SMI. Similarly, Sivaranjani et al. [11] found that seawater mixing affected 95% of the region in Karaikal Coast, Tamil Nadu. Multiple research studies indicate that seawater intrusion in the coastal regions of India is primarily caused by excessive utilization of groundwater resources and tidal activities [48,49].

3.3.2. Spatial analysis of ionic ratio to understand the seawater intrusion

The possible salination sources are classified based on distinct geochemistry and commonly used ionic ratios associated with hydrogeochemical processes [18]. Ionic ratios of groundwater have been used to estimate seawater intrusion in the coastal region [16, 17]. The amount of Cl⁻ concentration in groundwater indicates the occurrence of pollution and seawater intrusion [17].

To differentiate between seawater intrusion and other sources of saltwater, the Jones ratio (JR) is used. JR=Na⁺/Cl⁻ is the ratio used for calculation [23]. If the ratio is greater than 1, it indicates that domestic wastewater has contaminated the groundwater; if it is less than 0.86, it indicates that seawater has contaminated the groundwater. Almost 74% of groundwater samples (n=47) have an (Na⁺/Cl⁻) less than 0.86 indicates the influence of seawater in the study area and remaining samples (n=8) have an (Na⁺/Cl⁻) greater than 1 represents the salination of aquifers due to leaching of wastewater (Fig. 6a). Mg²⁺/Cl⁻ can be considered as indication of process of salinization [44]. About 67% of the samples have an (Mg²⁺/Cl⁻)>0.5, which reflects the seawater intrusion (Fig. 6d). According to Sudaryanto and Naily [17], the enrichment of Ca²⁺ is the principal ion can also be used as an indicator of seawater intrusion. About 77% of groundwater samples were found to be impacted by seawater intrusion with a ratio >1 based on the analysis of Ca²⁺ enrichment (Fig. 6e).

Generally, seawater contamination is indicated by an ionic ratio of Ca²⁺/Mg²⁺ > 1, which suggests that Ca²⁺ dominates in groundwater and Mg²⁺ dominates in seawater [17]. About 74% of samples (n=47) have an (Ca²⁺/Mg²⁺)>1 represent seawater intrusion (Fig. 6c). The ionic ratio Ca²⁺/SO₄ ²⁻ and Ca²⁺/HCO₃ ⁻ are also considered as an indicator of seawater intrusion if this ratio greater than 1. About 90% of the samples (n=58) and 21% of groundwater samples (n=14) have an ionic ratio (Ca²⁺/SO4²⁻)>1 and (Ca²⁺/HCO₃ ⁻)> 1 respectively, which indicates the imprints of seawater in the coastal groundwater (Fig. 6b). The issue of salinization is primarily related to natural recharge processes, whereas local factors like excessive use of groundwater are largely responsible for seawater intrusion. Therefore, the intensive analysis of ionic ratios such as Na⁺/Cl⁻, Mg²⁺/Cl, Ca²⁺/Mg²⁺, enrichment of Ca²⁺ and Ca²⁺/SO4²⁻ are strongly indicates that around 65% of the groundwater samples in the Pudukottai district influenced by the seawater (Fig. 7).

3.4. Statistical Analysis

3.4.1. Principal component analysis

The Principal Component Analysis (PCA) plot is intended to identify correlations, patterns, and water with extreme chemical compositions, as well as for more statistical modelling [2]. The impact of seawater on groundwater has been evaluated using the PCA method [50, 51]. The number of latent factors is determined by their eigenvalues and the internal model validation error [52]. Two Principal Components (PC) in the analysis shows 63% of the overall variance (Fig. 8), and the individual variance of two PCs 46.7% in PC1 and 16.3% in PC2 respectively. The primary contributing factors in seawater include TDS (0.35), EC (0.35), TH (0.32), Cl⁻ (0.31), Ca²⁺ (0.30), Na⁺ (0.29), Mg²⁺ (0.29), and So₄ ²⁻ (0.29), all of which have higher positive loading on PC1. The term “Seawater Salination Factor” refers to this kind of highest positive loading of major ions and hydrochemical parameters, which represents the traces of saltwater intrusion on groundwater [18, 31]. TA, HCO₃ ⁻ and CO₃ ²⁻ have been positively loaded in the PC2 which comprises 16.3% in the total variance.

3.4.2. Pearson correlation matrix

A Pearson correlation analysis was conducted on 17 parameters such as calcium, magnesium, sodium, potassium, sulphate, chloride, carbonate, bicarbonate, nitrate, DO, turbidity, TH, TA, pH, TDS, EC and salinity (%) (Table S3). The study area’s occurrence of seawater intrusion is indicated by the high positive correlation that TDS showed with Cl⁻ (0.91), TH (0.88), Na⁺ (0.83), Ca²⁺ (0.81), and Mg²⁺ (0.80) and the moderate positive correlation with SO₄ ⁻ (0.74). Table S3 shows a significant positive correlation between GQI and K⁺ (0.94). There is a substantial positive correlation between the salinity of the groundwater samples and Cl⁻ (0.94), TDS and EC (0.88), and TH (0.834), indicating saltwater contamination in the groundwater. A high correlation between Na⁺ and Cl⁻ (0.72) indicates the presence of saltwater in the coastal aquifer and implies that seawater intrusion in the study area [53].

Conclusions

Integrated hydrogeochemical and statistical techniques assessed seawater intrusion in the study area. This study established baseline information for seawater intrusion analysis in this coast. Based on the findings, the hydrochemical facies, major ion concentrations, TDS, Sodium, and chloride concentrations in this geochemical study indicate the influence of seawater intrusion in the study area. GQI values ranged from 193 to 2399, with 93% of the samples being unsuitable for drinking. The hydrochemical facies analysis in the study area clearly showed mixed Ca²⁺-Na⁺⁻ HCO₃ ⁻> Na⁺-HCO₃ ⁻ > Na⁺-Cl⁻ > Ca²⁺-Mg²⁺ > Ca²⁺-Mg⁺-Cl⁻ groundwater facies by piper diagram. Stiff diagram demonstrates Ca²⁺-Cl⁻> Ca²⁺- HCO₃ ⁻> Mg²⁺-Cl⁻ > Mg²⁺- HCO₃ ⁻ > Na⁺-Cl⁻ > Na⁺- HCO₃ ⁻ indicating the salinization on the groundwater. Gibbs diagram represents that evaporation is the controlling mechanism in the study area which can increase the salinity level on the groundwater. Major ionic ratios such as the Jones ratio (Na⁺/Cl⁻), Mg²⁺/Cl⁻, Ca²⁺/SO₄ ²⁻, Ca²⁺/Mg²⁺, Ca²⁺/HCO₃ ⁻, and Ca²⁺ enrichment reflect the influence of seawater on groundwater in the Pudukkottai District’s coastal areas. According to the SMI index calculation, seawater intruded into 78% of the groundwater samples in the study area. SMI Index revealed around 402 km² of study area is affected by seawater. From the principal component analysis, it was concluded that the salinization process is taking place in the study area which was explained by first component (46.7%) in the total variance. Component 2 was responsible of 14.3% of the overall variance. The Groundwater quality of study area is constantly deteriorating due to salinization caused by overexploitation of groundwater for agriculture, salt production and aquaculture. This first systematic approach addressed the research gaps existing in this study area. The intensity of seawater intrusion in the coastal area of the Pudukottai district may assist policy makers, researchers to create suitable strategies and management planning to ensure safe drinking water for locals. Indeed, limiting deep borewells, regulating salt production and aquaculture activities, and continuously monitoring the salinization process will result in better conservation and management of water resources in this coastal area.

4.1. Management Recommendations

The most significant issue facing seawater intrusion management in the Pudukkottai district due to overexploitation of groundwater resources and lack of awareness among the locals. Therefore, the implementation of awareness programs on seawater intrusion, investigation on mechanisms, and management strategies are highly required. There are few recommendations given below.

Establishing a modern monitoring system comprised of inspection wells with several screens at different depths, as well as sensors and automatic database storage systems, to monitor saltwater inland progress.
Rainwater harvesting and artificial groundwater recharge schemes should be prioritized to avoid future deterioration of groundwater.
Regulating salt production and aquaculture activities in the study area may help to improve the quality of groundwater.
Expanding the development of canals, ponds and lakes to reduce the overexploitation of groundwater resources for agricultural activities through boreholes.
Regulating and monitoring private water suppliers.

Supplementary Information

eer-2024-065-supplementary.pdf

Notes

Conflict-of-Interest Statement

The authors declare that they have no conflict of interest.

Author Contribution

M.T (PhD Student) conducted the research, investigation progress and wrote the original draft. S.S.V (Associate Professor), conceptualization, data validation, supervision the research progress, reviewed and edited the final manuscript. The authors reviewed and accepted the research article for final publication.

References

1. Senthilkumar S, Vinodh K, Babu GJ, Gowtham B, Arulprakasam V. Integrated seawater intrusion study of coastal region of Thiruvallur district, Tamil Nadu, South India. Appl Water Sci. 2019;9(5)124. https://doi.org/10.1007/s13201-019-1005-x

2. Jeen SW, Kang J, Jung H, Lee J. Review of Seawater Intrusion in Western Coastal Regions of South Korea. Water. 2021;13(6)761. https://doi.org/10.3390/w13060761

3. Werner AD, Bakker M, Post VEA, Vandenbohede A, Lu C, Ashtiani BA, Simmons CT, Barry DA. Seawater intrusion processes, investigation and management: Recent advances and future challenges. Adv. Water Resour. 2013;51:3–26. https://doi.org/10.1016/j.advwatres.2012.03.004

4. Najib S, Fadili A, Mehdi K, Riss J, Makan A. Contribution of hydrochemical and geoelectrical approaches to investigate salinization process and seawater intrusion in the coastal aquifers of Chaouia, Morocco. J. Contam. Hydrol. 2017;198:24–36. https://doi.org/10.1016/j.jconhyd.2017.01.003

5. Amores MJ, Verones F, Raptis C, et al. Biodiversity Impacts from Salinity Increase in a Coastal Wetland. Environ Sci Technol. 2013;47(12)6384–6392. https://doi.org/10.1021/es3045423

6. Xaza A, Mapoma HWT, Abiye TA, Clarke S, Kanyerere T. Investigating Seawater Intrusion in Republic of South Africa’s Heuningnes, Cape Agulhas Using Hydrogeochemistry and Seawater Fraction Techniques. Water. 2023;15(11)2141. https://doi.org/10.3390/w15112141

7. Dunlop G, Palanichamy J, Kokkat A, James EJ, Palani S. Simulation of saltwater intrusion into coastal aquifer of Nagapattinam in the lower cauvery basin using SEAWAT. Groundw. Sustain. Dev. 2019;8:294–301. https://doi.org/10.1016/j.gsd.2018.11.014

8. Werner AD, Simmons CT. Impact of Sea-Level Rise on Sea Water Intrusion in Coastal Aquifers. Ground Water. 2009;47(2)197–204. https://doi.org/10.1111/j.1745-6584.2008.00535.x

9. Mahmoodzadeh D, Karamouz M. Seawater intrusion in heterogeneous coastal aquifers under flooding events. J. Hydrol. 2019;568:1118–1130. http://dx.doi.org/10.1016/j.jhydrol.2018.11.012

10. Costall AR, Harris BD, Teo B, Schaa R, Wagner FM, Pigois JP. Groundwater Throughflow and Seawater Intrusion in High Quality Coastal Aquifers. Sci. Rep. 2020;10(1)9866. https://doi.org/10.1038/s41598-020-66516-6

11. Sivaranjani S, Ellappan V, Karthick LA. Appraisal of Seawater Mixing Index in Coastal Aquifer of Karaikal, Southern India Using Geospatial Technology. J. Geol. Soc. India. 2019;94:641–644. https://doi.org/10.1007/s12594-019-1371-x

12. Bourjila A, Dimane F, Ghalit M, et al. Mapping the spatiotemporal evolution of seawater intrusion in the Moroccan coastal aquifer of Ghiss-Nekor using GIS-based modeling. Water Cycle. 2023;4:104–19. https://doi.org/10.1016/j.watcyc.2023.05.002

13. Diédhiou M, Ndoye S, Celle H, Faye S, Wohnlich S, LeCoustumer P. Hydrogeochemical Appraisal of Groundwater Quality and Its Suitability for Drinking and Irrigation Purposes in the West Central Senegal. Water. 2023;15(9)1772. https://doi.org/10.3390/w15091772

14. Kumar P, Kumar A, Singh CK, Saraswat C, Avtar R, Ramanathan AL, Herath S. Hydrogeochemical Evolution and Appraisal of Groundwater Quality in Panna District, Central India. Expo Health. 2016;8(1)19–30. https://doi.org/10.1007/s12403-015-0179-1

15. Seddique AA, Masuda H, Anma R, Bhattacharya P, Yokoo Y, Shimizu Y. Hydrogeochemical and isotopic signatures for the identification of seawater intrusion in the paleobeach aquifer of Cox’s Bazar city and its surrounding area, south-east Bangladesh. Groundw. Sustain. Dev. 2019;9:100215. http://dx.doi.org/10.1016/j.gsd.2019.100215

16. Abdalla F. Ionic ratios as tracers to assess seawater intrusion and to identify salinity sources in Jazan coastal aquifer, Saudi Arabia. Arab J Geosci. 2016;9(1)40. https://doi.org/10.1007/s12517-015-2065-3

17. Sudaryanto , Naily W. Ratio of Major Ions in Groundwater to Determine Saltwater Intrusion in Coastal Areas. IOP Conf. Ser.: Earth Environ. Sci. 2018;118:012021. https://doi.org/10.1088/1755-1315/118/1/012021

18. Bhagat C, Puri M, Mohapatra PK, Kumar M. Imprints of seawater intrusion on groundwater quality and evolution in the coastal districts of south Gujarat, India. Case Stud. Chem. Environ. Eng. 2021;3:100101. https://doi.org/10.1016/j.cscee.2021.100101

19. Senthilkumar S, Balasubramanian N, Gowtham B, Lawrence JF. Geochemical signatures of groundwater in the coastal aquifers of Thiruvallur district, south India. Appl. Water Sci. 2017;7:263–274. https://doi.org/10.1007/s13201-014-0242-2

20. Naik PK, Dehury BN, Tiwari AN. Groundwater Pollution Around an Industrial Area in the Coastal Stretch of Maharashtra State, India. Environ. Monit. Assess. 2007;132:207–233. https://doi.org/10.1007/s10661-006-9529-6

21. Pujari PR, Soni AK. Sea water intrusion studies near Kovaya limestone mine, Saurashtra coast, India. Environ. Monit. Assess. 2009;154:93–109. https://doi.org/10.1007/s10661-008-0380-9

22. Tomaszkiewicz M, Abou Najm M, ElFadel M. Development of a groundwater quality index for seawater intrusion in coastal aquifers. Environ. Model. Softw. 2014;57:13–26. https://doi.org/10.1016/j.envsoft.2014.03.010

23. Trabelsi N, Triki I, Hentati I, Zairi M. Aquifer vulnerability and seawater intrusion risk using GALDIT, GQISWI and GIS: case of a coastal aquifer in Tunisia. Environ. Earth Sci. 2016;75:669. https://doi.org/10.1007/s12665-016-5459-y

24. Piyathilake IDUH, Ranaweera LV, Udayakumara EPN, Gunatilake SK, Dissanayake CB. Assessing groundwater quality using the Water Quality Index (WQI) and GIS in the Uva Province, Sri Lanka. Appl. Water Sci. 2022;12:72. https://doi.org/10.1007/s13201-022-01600-y

25. Kumar S, Rajesh V, Khan N. Evaluation of groundwater quality in Ramanathapuram district, using water quality index (WQI). Model. Earth Syst. Environ. 2022;8:35–45. https://doi.org/10.1007/s40808-020-01025-z

26. Aladejana JA, Kalin RM, Sentenac P, Hassan I. Groundwater quality index as a hydrochemical tool for monitoring saltwater intrusion into coastal freshwater aquifer of Eastern Dahomey Basin, Southwestern Nigeria. Groundw. Sustain. Dev. 2021;13:100568. https://doi.org/10.1016/j.gsd.2021.100568

27. Teng WC, Fong KL, Shenkar D, Wilson JA, Foo DCY. Piper diagram – A novel visualisation tool for process design. Chem. Eng. Res. Des. 2016;112:132–145. https://doi.org/10.1016/j.cherd.2016.06.002

28. Gibbs RJ. Mechanisms Controlling World Water Chemistry. Sci. 1970;170(3962)1088–1090. https://doi.org/10.1126/science.170.3962.1088

29. Hounsinou SP. Presentation and use of a new diagram to determine the facies and the origins of water: The 3rd Parfait-Hounsinou diagram. Heliyon. 2023. 97e17688. https://doi.org/10.1016/j.heliyon.2023.e17688

30. Chaudhari AN, Mehta DJ, Sharma ND. Coupled effect of seawater intrusion on groundwater quality: study of South-West zone of Surat city. Water Supply. 2022. 2221716–1734. https://doi.org/10.2166/ws.2021.323

31. Das N, Mondal P, Ghosh R, Sutradhar S. Groundwater quality assessment using multivariate statistical technique and hydro-chemical facies in Birbhum District, West Bengal, India. SN Appl. Sci. 2019;1:825. https://doi.org/10.1007/s42452-019-0841-5

32. Muthulakshmi R. Geo-spatial analysis of irrigation water quality of Pudukkottai district. Appl. Water Sci. 2020;10:82. https://doi.org/10.1007/s13201-020-1167-6

33. Government of India. Pudukottai District Survey Report for Gravel, Red Earth, Earth, Pebble [Internet]. Ministry of Environment, Forest and Climate Change. Government of India; 2019. [cited 08 January 2024]. Available from: https://tnmines.tn.gov.in/pdf/dsr/6.pdf

34. National Water Mission. Ground Water Resources Pudukottai District [Internet]. National Water Mission; 2019. [cited 09 January 2024]. Available from: https://nwm.gov.in/

35. Baird R, Bridgewater L. Standard methods for the examination of water and wastewater. 23rd edWashington DC: American Public Health Association; 2017.

36. Swain PK, Biswal T. Assessment of groundwater quality in terms of water quality index (WQI) and fluoride contamination of Nuapada District, Odisha, India. Appl. Water Sci. 2023;13:218. https://doi.org/10.1007/s13201-023-02030-0

37. Xaza A, Mapoma HWT, Abiye TA, Clarke S, Kanyerere T. Investigating Seawater Intrusion in Republic of South Africa’s Heuningnes, Cape Agulhas Using Hydrogeochemistry and Seawater Fraction Techniques. Water. 2023;15(11)2141. https://doi.org/10.3390/w15112141

38. WHO. Guidelines for drinking-water quality [Internet]. World Health Organization; 2004. [cited 15 January 2024]. Available from: https://www.who.int/publications/i/item/9789241549950

39. Singh A, Patel AK, Kumar M. Mitigating the Risk of Arsenic and Fluoride Contamination of Groundwater Through a Multi-model Framework of Statistical Assessment and Natural Remediation Techniques. Kumar M, Snow D, Honda R, editorsEmerging Issues in the Water Environment during Anthropocene Springer Transactions in Civil and Environmental Engineering. Springer; Singapore: 2020. p. 285–300. https://doi.org/10.1007/978-981-32-9771-5_15

40. Ram A, Tiwari SK, Pandey HK, Chaurasia AK, Singh S, Singh YV. Groundwater quality assessment using water quality index (WQI) under GIS framework. Appl. Water Sci. 2021;11:46. https://doi.org/10.1007/s13201-021-01376-7

41. Yidana SM, Yakubo BB, Akabzaa TM. Analysis of groundwater quality using multivariate and spatial analyses in the Keta basin, Ghana. J Afr Earth Sci. 2010;58(2)220–234. https://doi.org/10.1016/j.jafrearsci.2010.03.003

42. Brown RM, Mccleiland NJ, Deiniger RA, O’Connor MF. Water quality index-crossing the physical barrier. In : International Conference on Water Pollution Research; 18–24 June 1972; Jerusalem. p. 787–797.

43. Park SC, Yun ST, Chae GT, et al. Regional hydrochemical study on salinization of coastal aquifers, western coastal area of South Korea. J. Hydrol. 2005;313:182–194. https://doi.org/10.1016/j.jhydrol.2005.03.001

44. Kumar PJS, Jegathambal P, Babu B, Kokkat A, James EJ. A hydrogeochemical appraisal and multivariate statistical analysis of seawater intrusion in point calimere wetland, lower Cauvery region, India. Groundw. Sustain. Dev. 2020;11:100392. https://doi.org/10.1016/j.gsd.2020.100392

45. Putranto TT, Ginting RS. Determining groundwater facies and water quality index in Tanah Bumbu Regency/South Borneo Indonesia. E3S Web Conf. 2020;202:04007. https://doi.org/10.1051/e3sconf/202020204007

46. Sidibé AM, Lin X, Koné S. Assessing Groundwater Mineralization Process, Quality, and Isotopic Recharge Origin in the Sahel Region in Africa. Water. 2019;11(4)789. https://doi.org/10.3390/w11040789

47. Putra DBE, Hadian MSD, Alam BYCSSS, et al. Geochemistry of groundwater and saltwater intrusion in a coastal region of an island in Malacca Strait, Indonesia. Environ. Eng. Res. 2021. 2621–8. https://doi.org/10.4491/eer.2020.006

48. Prusty P, Farooq SH. Seawater intrusion in the coastal aquifers of India - A review. HydroResearch. 2020;3:61–74. https://doi.org/10.1016/j.hydres.2020.06.001

49. Siddha S, Sahu P. Status of seawater intrusion in coastal aquifer of Gujarat, India: a review. SN Appl. Sci. 2020;2:1726. https://doi.org/10.1007/s42452-020-03510-7

50. Mondal NC, Singh VP, Singh VS, Saxena VK. Determining the interaction between groundwater and saline water through groundwater major ions chemistry. J. Hydrol. 2010;388:100–111. https://doi.org/10.1016/j.jhydrol.2010.04.032

51. Adadzi P, Allwright A, Fourie F. Multivariate and Geostatistical Analyses of Groundwater Quality for Acid Rock Drainage at Waste Rock and Tailings Storage Site. J. Ecol. Eng. 2022. 2312203–216. https://doi.org/10.12911/22998993/153091

52. Benkov I, Varbanov M, Venelinov T, Tsakovski S. Principal Component Analysis and the Water Quality Index—A Powerful Tool for Surface Water Quality Assessment: A Case Study on Struma River Catchment, Bulgaria. Water. 2023;15(10)1961;https://doi.org/10.3390/w15101961

53. Maurya P, Kumari R, Mukherjee S. Hydrochemistry in integration with stable isotopes (δ18O and δD) to assess seawater intrusion in coastal aquifers of Kachchh district, Gujarat, India. J. Geochem. Explor. 2019;196:42–56. https://doi.org/10.1016/j.gexplo.2018.09.013

Fig. 1

Location map of the study area with groundwater sampling points.

Fig. 2

Piper trilinear diagram of groundwater samples.

Fig. 3

Stiff diagram of all individual groundwater samples.

Fig. 4

Gibbs plot showing controlling mechanism of groundwater chemistry.

Fig. 5

Spatial distribution map and Radial bar plot shows Seawater Mixing Index (SMI) of all the sampling locations.

Fig. 6

Spatial distribution maps of major ionic ratios (a. Jones ratio (Na⁺/Cl⁻), b. Ratio of Ca²⁺/SO₄ ²⁻ and Ca²⁺/HCO₃ ⁻, c. ratio of Ca²⁺/Mg²⁺, d. ratio of Mg²⁺/Cl⁻, e. enrichment of Ca²⁺).

Fig. 7

Calculated ionic ratio of groundwater samples.

Fig. 8

Biplot diagram of Principal Component Analysis for the groundwater samples.