Groundwater Salinity Distribution Research Articles

Geochemistry of Arsenic and Salinity-Contaminated Groundwater and Mineralogy of Sediments in the Coastal Aquifers of Southwest Bangladesh

This study aimed to develop a geochemical database by thoroughly analyzing groundwater and sediments from coastal aquifers of southwest Bangladesh. Moreover, we investigated the source of sediment deposition and the mechanisms behind the presence of arsenic and salinity in groundwater. The seasonal distribution patterns of arsenic among the shallow and deep coastal aquifers were found to be 45.12 µg/l and 20.65 µg/l during dry and wet seasons, respectively. Moreover, the groundwater salinity distribution ranged from 3262.88 mg/l to 1930.88 mg/l during the dry and wet seasons. Cored sediment samples showed fine to medium sands of 92%, with silt and clay particles. The petrographic study of authigenic and heavy minerals revealed that the mineral grains were subangular to angular, indicating their textural immaturity of coastal sediments. The reactivity of goethite (FeOOH) and siderite (FeCO3) minerals suggests that the aquifers were subjected to slightly oxidized to moderately reducing conditions, with ORP values ranging from +50.40 mv to −149.5 mv. Such redox conditions could potentially result in the enrichment and mobility of arsenic in the groundwater. Although arsenic concentrations in deep aquifers are relatively low, higher salinity values are found in both shallow and intermediate coastal aquifers.

Nitrate fate in coastal unconfined aquifers influenced by preferential flows

This study examined the influence of preferential flow on pore water flows and marine nitrogen transport reaction in variable saturation and variable density coastal aquifers. The 2-D unconfined aquifer model established was based on the software COMSOL by coupling the dynamic and chemical processes together. The results showed that preferential flow affects groundwater flow and salinity distribution, leading to a more complicated mixing process. The preferential flow resulted in an increase in mixing zone area and the upper saline plume area of 10.33 and 2.62 m2, respectively, a decrease in saltwater wedge area of 7.22 m2, and an increase in nitrate (NO3-) removal efficiency from 7.9% to 8.97%. The NO3- removal efficiency increases progressively with the depth (h) and quantity (n) of preferential flows; however, it decreases after a certain quantity. Further quantitative analysis revealed an increase in the intensity of nitrification and dissolved oxygen inflow flux with preferential flow depth and quantity increase. This phenomenon usually occurs on coasts where biological caves are abundant. The results also offer significant implications for designing engineering measures to mitigate saltwater intrusion and are significant to prevent groundwater quality deterioration in coastal zones.

Impacts of groundwater dynamics around a macro-tidal river on agricultural soil salinity

Estuaries are vulnerable to oceanic and atmospheric climate change. Much of the research investigating climate change impacts on estuaries is focused on saltwater intrusion within surface water due to drought and rising sea levels, with implications for ecosystems and humans. Groundwater and soil near estuaries may also be influenced, as estuary salinity and hydraulic head changes can impact soils and aquifers not previously at risk of salinization. This study was conducted to address knowledge gaps related to present and future groundwater salinity distribution in a groundwater system connected to a macro-tidal estuary. The studied estuary experiences a tidal bore due to its hydraulic connection to the Bay of Fundy in Nova Scotia, Canada. A parcel of agricultural land adjacent to the estuary was selected to assess the groundwater response to episodic fluctuations in estuary water levels and salinity. Groundwater monitoring and electromagnetic surveys were conducted to map soil and groundwater salinity patterns. A numerical model of groundwater flow and solute transport informed by field data was used to investigate how varying estuary salinity due to droughts and sea-level rise could impact groundwater salinity. Results showed that, in contrast to salt wedges observed along marine coasts, the saline groundwater existed as a plume immediately around the estuary. Model simulations showed that short-term droughts had an insignificant impact on the adjacent groundwater salinity. However, permanent increases in salinity caused by sea-level rise increased the plume volume by 86 %, or an additional ∼11 m horizontally and ∼ 4.5 m vertically. Our results suggest that increased river salinity in this setting would not result in widespread salinization of porewater and agricultural soils, but more extensive salinization may be experienced in permeable aquifers or along more saline estuarine zones. Findings may inform land management decisions in regions exposed to increased salinity in the future.

Hydrogeochemical characterization and assessment of factors controlling groundwater salinity in the Chamwino granitic complex, central Tanzania

Chamwino district, central Tanzania is a semi-arid granitic complex province, where groundwater is the major source of water for domestic and other uses. However, groundwater in the area is affected by salinity, thus, lowering the availability of potable water for various uses, decrease in crop production, taste less, wastage of soap, and abnormal pain. Due to this, this study sought to characterize groundwater using hydrogeochemical facies and signatures in order to identify the factors influencing the distribution of salt water in the Chamwino Granitic Complex. A total of 141 groundwater samples were collected from wells spatially distributed within the study area from January 2023 to April 2023, (a season of relatively low rainfall). All samples were subjected to in situ analyses of physicochemical parameters pH, temperature (T), total dissolved solids (TDS), electrical conductivity (EC), and salinity using a multi-parameter water analyzer and analyses of major ions (Ca2+, Mg2+, K+, Na+, Cl−, SO42−, HCO3−, and NO3−). The study revealed that the dominant cations in the groundwater are Na+ > Ca2+ > Mg2+, and the anions are Cl− > HCO3− > SO42. Five geological formations (granodiorite, tonalitic orthogenesis, migmatite, tonalite, and alluvium) were identified, and each is characterized by its unique groundwater facie. In the areas that are dominated with granodiorite, the major hydrogeochemical facies were Ca–HCO3, Na–Cl, Ca–Na–HCO3, Ca–Mg–Cl, and Ca–Cl water types; tonalitic orthogenesis was dominated by Ca–HCO3, Na–Cl, Ca–Mg–Cl, and Ca–Cl water types; migmatite was dominated by Ca–HCO3, Na–Cl, Ca–Mg–Cl, and Ca–Cl water types; tonalite was dominated by Na–Cl, Ca–Mg–Cl, and Ca–Cl water types; and alluvium was dominated by Na–Cl and Ca–Mg–Cl and Ca–Cl water types. The common hydrogeochemical facies in all five geological units are Na–Cl, Ca–Mg–Cl, and Ca–Cl water types. It is revealed that the groundwater in the study area is alkaline in nature and slightly saline with salinity level between 0.2 mg/L (fresh water) and 2.8 mg/L (brackish water) with mean 1.07 mg/L (of 141 samples). The factors controlling groundwater salinity distribution are mainly rock-water interaction and ion exchange reactions. Groundwater salinity in the study area is largely attributed to the abundance of Na+, Ca2+, Cl− and SO42−. Abundance of Na+ and Ca2+ is the results of both, weathering of feldspar minerals particularly plagioclase (Na–Ca feldspars) which are the major mineral in granites, and evaporation crystallization cycles of evaporates in semi-arid areas such as Chamwino. Also, such evaporation crystallization cycles account for the abundance of Cl− and SO42− especially in areas dominated by alluvium. However, anthropogenic activities as evidenced by elevated nitrate up to 212.6 mg/L in congested areas are also likely to contribute in area) to the elevated Cl− and SO42−. In other geological units such as tonalitic orthogneiss, migmatite and granodiorite, there was an ostensible mixing of saline water with fresh water from local recharge as indicated by the abundance of HCO3− ions. Nonetheless, the hydrogeochemical characterization of groundwater in the Chamwino granitic complex suggests that there is little possibility for groundwater to evolve to a carbonate water type (fresh water) because the groundwater salinity is mainly geogenic, unless artificial recharge through rainwater harvesting is applied.

Analyzing Spatial Groundwater Salinity Using Multivariate Analysis and Multiple Linear Regression Models

The increase in the amount of groundwater withdrawal will inevitably pose a threat of seawater intrusion. The purpose of this research was to identify the distribution of shallow groundwater salinity in North Jakarta, West Jakarta and Central Jakarta and to develop a regional model of shallow groundwater salinity distribution. The data used in this study was that of the groundwater quality monitoring, obtained from the Regional Environment Status Book (SLHD), published by The Environment office of Greater Jakarta released in 2022, involving a total of 121 sample points in North Jakarta, West Jakarta, and Central Jakarta. The primary data was taken at 6 (six) sampling locations for model validation purposes. The study began with data grouping, using the Hierarchical Cluster Analysis (HCA) method. The results of identifying the highest distribution of salinity are in cluster 3 (three). A model was subsequently developed, after removing the outliers, with multiple linear analysis methods using the variable the distance from the coastline (X1), well depth (X2) and hardness (X3), to determine the influence of EC, TDS and salinity distribution in shallow groundwater. The results obtained are as follows; EC Models: YEC3 = -1.879+ (1.19.X1) + (5.08.X3). TDS models: YTDS3 = -2.211.30 + (0.81.X1) + (101.41.X2) + (4.07.X3). Salinity models: Ysalinity3 = -0.07+ (6.75×10-5.X1) + (2.4×10-4.X3). Model verification results for R2EC3 = 0.70; R2TDS3 = 0.92; R2salinity3 = 0.88. Validation results produce 21.14% for EC, 8.21% for TDS, and 22.87% for Salinity. This needs further research by increasing the number of primary samples.

Groundwater Salinity Across India: Predicting Occurrences and Controls by Field-Observations and Machine Learning Modeling.

Elevated groundwater salinity is unsuitable for drinking and harmful to crop production. Thus, it is crucial to determine groundwater salinity distribution, especially where drinking and agricultural water requirements are largely supported by groundwater. This study used field observation (n = 20,994)-based machine learning models to determine the probabilistic distribution of elevated groundwater salinity (electrical conductivity as a proxy, >2000 μS/cm) at 1 km2 across parts of India for near groundwater-table conditions. The final predictions were made by using the best-performing random forest model. The validation performance also demonstrated the robustness of the model (with 77% accuracy). About 29% of the study area (including 25% of entire cropland areas) was estimated to have elevated salinity, dominantly in northwestern and peninsular India. Also, parts of the northwestern and southeastern coasts, adjoining the Arabian Sea and the Bay of Bengal, were assessed with elevated salinity. The climate was delineated as the dominant factor influencing groundwater salinity occurrence, followed by distance from the coast, geology (lithology), and depth of groundwater. Consequently, ∼330 million people, including ∼109 million coastal populations, were estimated to be potentially exposed to elevated groundwater salinity through groundwater-sourced drinking water, thus substantially limiting clean water access.

Understanding groundwater use and vulnerability of rural communities in the Mekong Delta: The case of Tra Vinh province, Vietnam

Groundwater has been increasingly used for water supply to sustain local livelihood and socio-economic development in the Vietnam Mekong Delta (VMD). Yet, intensive groundwater use raises concerns on sustainability as available fresh groundwater is finite with little or limited natural recharge in the area on one hand and, on the other hand, groundwater levels have been decreasing, with induced land subsistence, increased flooding and inundation, and exacerbated salinity intrusion. This study aimed to develop understanding of groundwater use and vulnerability of rural communities in the VMD. It was motivated by both the significance and little knowledge of decentralized groundwater use of small capacity by rural communities that is not monitored and managed. In this study, we designed and conducted a structured survey in selected rural communities to collect information related to water supply and groundwater use for domestic purposes and agriculture. Combining survey data and information from different sources, our analysis found that: 1) groundwater plays a varying role in domestic water use, with a heterogeneous pattern consistent with the spatial distribution of groundwater salinity; 2) local dependence on groundwater increases spatially from inland towards coastal areas; 3) poor households in coastal areas are of high vulnerability to groundwater limitations imposed by salinity or resource depletion for domestic use; 4) groundwater use in agriculture appears to be complementary to available fresh surface water, non-essential while exhibiting a spatial pattern corresponding to groundwater salinity or availability; and 5) there is indication of groundwater depletion associated with groundwater use in agriculture. The study revealed locally developed water use behavior adapting to local water conditions and wealth level, with fresh groundwater being of strategic importance, particularly to domestic water use and poor households in coastal areas. The findings fill the knowledge gap in the literature while providing relevant information for welfare improving management decision making on groundwater in the VMD.

A 3D-numerical simulation of groundwater flow and salinity in a rice field adjacent to a marine shrimp farm

Rice plants are impacted by high soil salinity, which causes dehydration, stunted growth, and eventual death. It is critical to comprehend the groundwater flow behavior and salinity distribution in a rice field. Thailand’s Samut Sakhon Province features territory that borders the ocean where rice and shrimp are grown. Because of this, the goal of the current study is to perform a 3D analysis of the groundwater flow and soil salinity in a rice field next to a shrimp farm. Darcy’s law was used to estimate the flow of groundwater, and a dispersion model was used to examine the salinity of the soil. The governing equations of a three-dimensional domain were solved by running a finite element method in COMSOL Multiphysicsë software. The results and the numerical simulations agreed closely with those from previous studies. Within the marine shrimp farm pressure, flow velocity, and salinity concentration were highest at the topsoil surface, decreasing with depth. Furthermore, the results were higher near the left edge of the shrimp farm, falling when measurements were taken closer to the right border with the rice field. The gradients of both velocity and salinity were maximal at the topsoil surface, reducing towards the lowest depths. Flows from left to right and from bottom to top in the rice field created a semi-circular zone. We also examined salinity concentrations at the topsoil surface and in the region at a depth of not more than 5 meters. This may help selection of cultivars that are suitable for planting in such areas. The salinity concentration here was found to be rather low, with electrical conductivity of between 0 dS/m and 2.08 dS/m, which tends to support results from previous research.

Temporal and spatial distribution patterns of upper saline plumes and seawater-groundwater exchange under tidal effect

Under tidal influence, an active exchange process occurs between seawater and groundwater in the coastal aquifer system. However, in-situ studies and research on the temporal and spatial distribution patterns of upper saline plumes (USPs) and seawater-groundwater exchange process are lacking. In this study, we selected the Shilaoren beach in Qingdao as the study area, and used pseudo-3D electrical resistivity tomography (ERT) and hydrogeological measurement methods to monitor the spatial distribution of groundwater salinity and the seawater and groundwater exchange process. We found that during the ebbing tide, USPs were divided into several smaller USPs driven by groundwater discharge. Subsequently, during the flooding tide, high-salinity seawater recharge was observed, and several smaller USPs gradually aggregated into a complete USP. In coastal aquifers, the exchange of seawater and groundwater not only occurs through the beach surface and seepage face, but also includes high-permeability underground channels. Seawater and groundwater exchange occurs more rapidly through these underground channels randomly distributed at depth, which also leads to spatial differences in the seawater and groundwater exchange process. Additionally, affected by underground channels, the groundwater discharge flux shows spatial heterogeneity. In areas with underground channels, the groundwater discharge flux significantly increases. Therefore, the non-seepage face area has a similar groundwater discharge flux to the main groundwater discharge area, namely, the seepage face. In the intertidal zone of the study area (70 × 60 m), the total groundwater discharge flux through the seepage face is 3407.6 m3, and no significant difference is observed in the groundwater discharge flux at various parts of the seepage face. In the non-seepage face area, the groundwater discharge is highly spatially heterogeneous; the total groundwater discharge flux is 3252.0 m3, and approximately 60% of this occurs through densely developed underground channels.

Combined effect of subsurface dam and layered heterogeneity on groundwater flow and salinity distribution in stratified coastal aquifers

Combined effect of subsurface dam and layered heterogeneity on groundwater flow and salinity distribution in stratified coastal aquifers

Influences of paleoclimatic environment and hydrogeochemical evolution on groundwater salinity in an arid inland plain in northwestern China

Highly saline groundwater limits the availability of freshwater resources, especially in arid/semi-arid inland areas with a growing demand but a scarcity of water resources. Understanding the spatial distribution of groundwater salinity and the factors that control their variability is vital for the scientific management of water resources in these areas. Integrated hydrogeochemistry and environmental isotopes (δD, δ18O, 3H, 14C) were used to study the distribution and evolution of fresh and saline groundwater in the Aksu Plain and its links to the paleo-climatic environment since the Late Pleistocene. The results indicated that the sources of groundwater was meteoric water from the Tianshan Mountains. Modern groundwater was found in the piedmont plain and shallow groundwater adjacent to the surface water. The paleo-atmospheric precipitation replenished the deep confined groundwater during the Last Glacial Period. There was no correlation between groundwater salinity and depth. Along the flow path, groundwater salinity has no increasing trend. We found that the paleoclimatic environment and water-rock interaction jointly determine the distribution of groundwater salinity, while evaporation had a slight effect based on the isotopic composition. The long residence time (8–19 ka) and evaporites in sediments (such as halite and gypsum) could provide the conditions for sufficient water-rock interactions, leading to the formation of brackish/saline groundwater. Conversely, the fresh, deep, confined groundwater corresponds to paleo-recharge conditions during the humid Last Glacial Period (21–24.5 ka). Surface water infiltration reduces the salinity of shallow groundwater, but the influence is limited. This study presents a mode that combines hydrogeochemical evolution and paleoclimatic environments to better assess groundwater salinity in the arid inland region.

Dynamics of upstream saltwater intrusion driven by tidal river in coastal aquifers

For the coastal aquifers, recent research have shown that the tidal has a significant effect on saltwater intrusion in the near-shore aquifer. However, it is currently unclear how the tidal river contributes to the groundwater flow and salinity distribution in the upstream aquifer of the estuary. This study examined the effects of a tidal river on the dynamic characteristics of groundwater flow and salt transport in a tidal river-coastal aquifer system using field monitoring data and numerical simulations. It was found that changes in tidal-river level led to the reversal of groundwater flow. For a tidal cycle, the maximum area of seawater intrusion is about 41.16 km2 at the end of the high tide stage. Then the area gradually decreased to 39.02 km2 at the end of the low tide stage. More than 2 km2 area variation can be observed in a tidal cycle. Compared to the low tide stage, the area of SWI increased by 5 % at high tide stage. The SWI region was also spreading landward from the tidal river. In addition, we quantified the water exchange and salt flux between the tidal river and aquifer. When the tidal fell below the level of the riverbed, the water exchange rate was stabilized at about −1.6 m/h. The negative value indicated that the river was recharged by the groundwater. With the increasing of tidal water level, the water exchange rate gradually changes from negative to positive and reached the maximum value of 3.2 m/h at the beginning of the falling tide stage. The presence of a physical river dam can amplify the difference in water level between high and low tides, thereby enhancing the influence of a tidal river on water exchange and salt flux. The findings lay the foundation for gaining a comprehensive understanding of the tidal river on groundwater flow and salt transport in upstream aquifers.

Assessing the impact of groundwater abstractions on aquifer depletion in the Cauvery Delta, India

Many of the world’s deltas are highly productive areas for agriculture as well as important places of socio-economic development but are currently under stress. This study assesses the impacts of stresses on groundwater pumping, changing cropping patterns, and saltwater intrusion on groundwater resources in the Cauvery Delta in Tamil Nadu, India. A transient groundwater flow model of the delta was constructed for this assessment. The historical changes in groundwater resources in response to decreasing irrigation canal flows and increasing groundwater abstractions were assessed for the past 30 years. Furthermore, the model was used to formulate and analyze future sustainable groundwater development scenarios. Farmers’ narratives about a drying delta, as they experience water scarcity and quality issues most closely, were ascertained in the research. Farmers have abandoned many shallow wells in their fields. The model simulation shows groundwater levels are decreasing and aquifer storage depleting. Furthermore, salinization has increased, with continuous declining groundwater levels in the deep aquifer from 1990 to 2019. A more robust hydro-chemical assessment and further modeling of seawater intrusion are needed to better assess the sources and distribution of groundwater salinity. The pathway for future sustainability requires enhancing groundwater recharge in the shallow aquifer and controlling groundwater abstraction in the deep aquifers.

Spatial Distribution of Groundwater Salinity In The Coastal Area of Aceh Besar District

Abstract: Utilization of groundwater sources is still an alternative for people living in the coastal areas of Aceh Besar District. If the use of groundwater is carried out continuously, it will have a negative impact on the quality and quantity of groundwater. So the purpose of this study was to determine the distribution of groundwater salinity in the coastal areas of Aceh Besar District. The sample points were determined based on the random sampling method in grids. Sample testing for groundwater salinity was carried out directly in the field according to the planned location. The data obtained was inputted into Microsoft excel and mapping of groundwater salinity distribution using the Inverse Distance Weight (IDW) method with Argis software. A correlation test was performed with Pearson Product Moment. Based on the measurement results, 20 sample points of high salinity were measured. The distribution of salinity values also has a relationship with coastal distance, where the distribution of salinity in general, the farther the groundwater is from the coast, the lower the salinity value, and the closer the groundwater to the coast, the higher the salinity.Abstrak: Pemanfaatan sumber air tanah masih menjadi alternatif bagi masyarakat yang tinggal di wilayah pesisir Kabupaten Aceh Besar. Jika pemanfaatan air tanah dilakukan secara terus-menerus akan berdampak negatif secara kualitas dan kuantitas air tanah. Sehingga tujuan penelitian ini adalah untuk mengetahui sebaran salinitas air tanah di wilayah pesisir Kabupaten Aceh Besar. Titik sampel ditentukan berdasarkan metode random sampling in grids. Pengujian sampel untuk salinitas air tanah dilakukan langsung di lapangan sesuai dengan lokasi yang telah direncanakan. Data yang diperoleh diinput ke dalam Microsoft excel dan pemetaan distribusi salinitas air tanah menggunakan metode Inverse Distance Weight (IDW) dengan perangkat lunak Argis. Uji korelasi dilakukan dengan Pearson Product Moment. Berdasarkan hasil pengukuran, nilai salinitas yang tinggi terukur sebanyak 20 titik sampel. Nilai salinitas tinggi pada umumnya dipengaruhi oleh intrusi air asin terhadap air tawar. Faktor sebaran salinitas air tanah terjadi akibat intrusi, penggunaan lahan yang dekat dengan tambak dan muara sungai, faktor sebaran salinitas juga dipengaruhi oleh kepadatan penduduk. Sebaran nilai salinitas juga memiliki hubungan dengan jarak pantai, dimana sebaran salinitas secara umum, semakin jauh air tanah dengan jarak pantai maka nilai salinitasnya semakin rendah, dan semakin dekat air tanah dengan jarak pantai maka salinitasnya semakin tinggi.

Impact of climate change on groundwater recharge and salinity distribution in the Vientiane basin, Lao PDR

Abstract Groundwater is widely used for domestic, agricultural, and industrial purposes in the Vientiane basin. The trend of groundwater use is increasing but the usage of the mentioned groundwater is without proper study and monitoring. Six climatic scenarios from three General Circulation Models (GCMs) under Representative Concentration Pathways (RCPs) 4.5 and 8.5 were used to project rainfall and temperature in the future (2021–2050) periods. The numerical models HELP3, MODFLOW, and MT3D were used for groundwater recharge estimation, groundwater potential, and salinity distribution, respectively. The study found that during the following 30 years (2050), rainfall is expected to rise by 16, 17.52, and 49.93% for the MPI-ESM-MR, MIROC5, and CNRM-CM5 (under RCPs 4.5 and 8.5), respectively. Groundwater recharge is estimated to rise from baseline throughout all future climate conditions. Climate change's impact on salinity distribution in depth aquifers, the area with the water with the TDS between 500 and 1,500 mg/l will tend to decrease, whereas the freshwater (TDS <500 mg/l) area will tend to increase. Annual groundwater replenishment is expected to increase from current levels in all future climate scenarios in the range of 334–401 MCM/year or approximately 22.7–47.5%.

Study of Groundwater Salinity Distribution in Coastal Areas, Adimulyo Sub-district, Kebumen Regency, Central Java

Groundwater salinization occurs in Adimulyo Sub-district, Kebumen Regency due to human activities. A very slow river flow, due to its small hydraulic gradient towards the estuary area. Reduced groundwater due to increased uptake by human activities causes intrusive river water which results in brackish groundwater. The data analysis carried out in the study was based on the primary data of the sample whose groundwater salinity was measured, showing the influence of the salt solution at a certain level which indicates a level of salinity with a negative chloride ion content. The salinity value belongs to the type of brackish water. Electrical Conductivity Groundwater shows the nature of conducting electricity from water. The highest groundwater salinity is in the area of Adimulyo Sub-district, Kebumen Regency, the middle part, which ranges from 4.45 "° - 10.15 "°. There are other factors besides the distance of the area from the coastline, namely brackish river water (estuary), and the large amount of groundwater withdrawal by residents which can increase the absorption of brackish river water (estuary) into groundwater. In the northern part of Adimulyo Sub-district, Kebumen Regency is an area that has the lowest groundwater salinity, which ranges from 0.12 "° - 2.50 "°. As for the area of Adimulyo Sub-district, Kebumen Regency, the South has medium groundwater salinity, which ranges from 0.80 "° - 2.87 "°.

Computational assessment of groundwater salinity distribution within coastal multi-aquifers of Bangladesh

The rising salinity trend in the country’s coastal groundwater has reached an alarming rate due to unplanned use of groundwater in agriculture and seawater seeping into the underground due to sea-level rise caused by global warming. Therefore, assessing salinity is crucial for the status of safe groundwater in coastal aquifers. In this research, a rigorous hybrid neurocomputing approach comprised of an Adaptive Neuro-Fuzzy Inference System (ANFIS) hybridized with a new meta-heuristic optimization algorithm, namely Aquila optimization (AO) and the Boruta-Random forest feature selection (FS) was developed for estimating the salinity of multi-aquifers in coastal regions of Bangladesh. In this regard, 539 data samples, including ten water quality indices, were collected to provide the predictive model. Moreover, the individual ANFIS, Slime Mould Algorithm (SMA), and Ant Colony Optimization for Continuous Domains (ACOR) coupled with ANFIS (i.e., ANFIS-SMA and ANFIS-ACOR) and LASSO regression (Lasso-Reg) schemes were examined to compare with the primary model. Several goodness-of-fit indices, such as correlation coefficient (R), the root mean squared error (RMSE), and Kling-Gupta efficiency (KGE) were used to validate the robustness of the predictive models. Here, the Boruta-Random Forest (B-RF), as a new robust tree-based FS, was adopted to identify the most significant candidate inputs and effective input combinations to reduce the computational cost and time of the modeling. The outcomes of four selected input combinations ascertained that the ANFIS-OA regarding the best accuracy in terms of (R = 0.9450, RMSE = 1.1253 ppm, and KGE = 0.9146) outperformed the ANFIS-SMA (R = 0.9406, RMSE = 1.1534 ppm, and KGE = 0.8793), ANFIS-ACOR (R = 0.9402, RMSE = 1.1388 ppm, and KGE = 0.8653), Lasso-Reg (R = 0.9358), and ANFIS (R = 0.9306) models. Besides, the first candidate input combination (C1) by three inputs, including Cl− (mg/l), Mg2+ (mg/l), Na+ (mg/l), yielded the best accuracy among all alternatives, implying the role importance of (B-RF) feature selection. Finally, the spatial salinity distribution assessment in the study area ascertained the high predictability potential of the ANFIS-OA hybrid with B-RF feature selection compared to other paradigms. The most important novelty of this research is using a robust framework comprised of the non-linear data filtering technique and a new hybrid neuro-computing approach, which can be considered as a reliable tool to assess water salinity in coastal aquifers.

Pemetaan Salinitas Sumur Dangkal Berdasarkan Jumlah Konsentrasi Garam Di Kecamatan Tebing Tinggi Dan Tebing Tinggi Barat Kabupaten Kepulauan Meranti

This study was conducted to analyze the salinity of shallow well water so as to get an overview of the distribution of groundwater salinity at the research location. The research location is in the Selatpanjang City area, precisely in the Tebing Tinggi District and part of the Tebing Tinggi Barat District, Meranti Islands Regency. The research site is surrounded by the sea and rivers. Many people in the research location live in coastal areas. In coastal areas or near bodies of water, tidal water can enter up to the ground level and even onto roads. This situation makes people think that their groundwater is polluted due to tidal water entering the mainland. This research can provide information to the government and the community at the research site regarding the distribution of groundwater salinity that has occurred. The data analysis used is the interpolation method by creating a mapping using the ArcGIS application. Data analysis can be done after getting the data from the salinity measurement in the field. The water quality test parameters reviewed in this study were the salinity value of shallow wells water measured with a refractometer and marked the coordinates of the sample using the Avenza Maps application. In this study, 57 shallow wells were taken randomly. The results of field measurements show that based on salt concentration, shallow well water is classified as dubious and dangerous.

Seawater Intrusion-Retreat Processes and Groundwater Evolution in Intruded Coastal Aquifers with Land Reclamation: A Case Study of Eastern Jiangsu, China

Abstract The hydrogeochemical analysis and numerical simulation were conducted to explore the impact of land reclamation on submarine groundwater discharge and groundwater evolution in the seawater intrusion-retreat processes in eastern Jiangsu, China. The hydrogeochemical results indicated that the origin of salt in most groundwater is saltwater mixing, and weathering-dissolution of minerals enriches the salt in fresh groundwater. The evolution path of coastal groundwater in Jiangsu is Ca-Na-HCO3-Cl → Ca-Na-Cl-HCO3 → Na-Ca-Cl-HCO3 → Na-Mg-HCO3 → Na-Mg-HCO3-Cl → Na-Cl-HCO3 → Na-Cl, and the difference in groundwater evolution in different regions is obvious. The numerical simulation revealed that the land reclamation has blocked groundwater exchange and restrained the seawater intrusion. The sensitive analysis indicated that the permeability and the slope of the land reclamation have dominated the salinity distribution. And the aquifer heterogeneity promotes groundwater evolution and leads to the irregular salinity distribution of the groundwater. Moreover, the groundwater evolution in the shallow aquifer with the land reclamation shows that the residual seawater is gradually desalinating and discharged into the sea. The land reclamation is salinized by saltwater discharge and seawater intrusion together and then subsides into a stable saltwater wedge. The groundwater salinity distribution in Jiangsu is not fit seawater intrusion, which is caused by the coastline changes due to anthropogenic land reclamation and natural activities.

The three-dimensional groundwater salinity distribution and fresh groundwater volumes in the Mekong Delta, Vietnam, inferred from geostatistical analyses

Abstract. Over the last decades, economic developments in the Vietnamese Mekong Delta have led to a sharp increase in groundwater pumping for domestic, agricultural and industrial use. This has resulted in alarming rates of land subsidence and groundwater salinization. Effective groundwater management, including strategies to work towards sustainable groundwater use, requires knowledge about the current groundwater salinity distribution, in particular the available volumes of fresh groundwater. At the moment, no comprehensive dataset of the spatial distribution of fresh groundwater is available. To create a 3D model of total dissolved solids (TDS), an existing geological model of the spatial distribution and thickness of the aquifers and aquitards is updated. Next, maps of drainable porosity for each aquifer are interpolated based on the sedimentological description of the borehole data. Measured TDS in groundwater, inferred TDS from resistivity measurements in boreholes and soft incomplete data (derived from measurements in boreholes and data from domestic wells) are combined in an indicator kriging routine to obtain the full probability distribution of TDS for each (x,y,z) location. This statistical distribution of TDS combined with drainable porosity yields estimates of the volume of fresh groundwater (TDS < 1 g L−1) in each aquifer. Uncertainty estimates of these volumes follow from a Monte Carlo analysis (sequential indicator simulation). Results yield an estimated fresh groundwater volume for the Mekong Delta of 867 billion cubic metres with an uncertainty range of 830–900 billion cubic metres, which is somewhat higher than previous assessments of fresh groundwater volumes. The resulting dataset can for instance be used in groundwater flow and salt transport modelling as well as aquifer storage and recovery projects to support informed groundwater management decisions, e.g. to prevent further salinization of the Mekong Delta groundwater system and land subsidence, and is available at https://doi.org/10.5281/zenodo.4441776 (Gunnink et al., 2021).