Impact of ionic strength on goethite colloids co-transported with arsenite (As3+) through a saturated sand column under anoxic condition: Experiment and mathematical modeling.

The knowledge about co-transport of goethite and As3+ to investigate the effect of goethite colloids on As3+ transport under various degrees of seawater intrusion, particular extremely conditions, in groundwater environment is still limited. The main objective is to investigate the influence of seawater intrusion on the sorption, migration, and reaction of As3+and goethite colloids into sand aquifer media under anoxic conditions by using the bench-scale and reactive geochemical modeling. The research consisted of two parts as follows: 1) column transport experiments consisting of 8 columns, which were packed by using synthesis groundwater at IS of 0.5, 50, 200, and 400 mM referring to the saline of seawater system in the study area, and 2) reactive transport modeling, the mathematical model (HYDRUS-1D) was applied to describe the co-transport of As3+ and goethite. Finally, to explain the interaction of goethite and As3+, the Derjaguin-Landau-Verwey-Overbeek (DLVO) calculation was considered to support the experimental results and HYDRUS-1D model. The results of column experiments showed goethite colloids can significantly inhibit the mobility of As3+ under high IS conditions (>200 mM). The Rf of As3+ bound to goethite grows to higher sizes (47.5 and 65.0 µm for 200 and 400 mM, respectively) of goethite colloid, inhibiting As3+ migration through the sand columns. In contrast, based on Rf value, goethite colloids transport As3+ more rapidly than a solution with a lower IS (0.5 and 50 mM). The knowledge gained from this study would help to better understand the mechanisms of As3+ contamination in urbanized coastal groundwater aquifers and to assess the transport of As3+ in groundwater, which is useful for groundwater management, including the optimum pumping rate and long-term monitoring of groundwater quality.

Combined effects of aquifer heterogeneity and subsurface dam on nitrate contamination in coastal aquifers.

Subsurface dams are effective for seawater intrusion mitigation, yet they can cause upstream nitrate accumulation. This research examines the interplay between subsurface dam construction and aquifer layering on nitrate pollution in coastal settings, employing numerical models to simulate density-driven flow and reactive transport. The study reveals that while subsurface dams are adept at curbing seawater intrusion, they inadvertently broaden the nitrate accumulation zone, especially when a low-K layer is present. Heterogeneous aquifers see more pronounced nitrate accumulation from subsurface dams. This effect is pronounced as it influences dissolved organic carbon dynamics, with a notable retreat inland correlating with the expansion of the nitrate pollution plume. A critical finding is that controlling seawater intrusion via dam height adjustment within the Effective Damming Region effectively reduces nitrate levels and bolsters freshwater output. However, exceeding the critical threshold-where the dam surpasses the low-K layer's bottom-results in a substantial shift in nitrate concentration, underscoring the need for precise dam height calibration to avoid aggravating nitrate pollution. This study's innovative contribution lies in its quantification of the nuanced effects of subsurface dams in stratified aquifers, providing an empirical basis for dam design that considers the layered complexities of coastal aquifers. The insights offer a valuable framework for managing nitrate contamination, thus informing sustainable coastal groundwater management and protection strategies.

Hydrodynamic behavior of freshwater-saltwater mixing zone in the context of subsurface physical barriers.

The seawater intrusion (SWI) process lasts for decades in real world, thus the research on dynamic process of SWI is essential. The freshwater-saltwater mixing zone plays a crucial role in governing the groundwater movement and the solute transport in coastal aquifers. To date, there has been a lack of research on the hydrodynamic behavior of the mixing zone in the presence of subsurface physical barriers. In this work, we employed laboratory experiments and numerical simulations to investigate the dynamics of the mixing zone, comparing scenarios with and without subsurface physical barriers. The findings indicate that the construction of a subsurface physical barrier will not immediately slow down the seawater intrusion velocity and change the salinity distribution of mixing zone. The block effect of subsurface physical barriers with different heights or bottom opening sizes became apparent only when the wedge toe approached the physical barriers. The widening effect of increasing longitudinal dispersivity on the mixing zone width was more pronounced during the dynamic process compared to the steady state. Furthermore, the widening effect of increasing longitudinal dispersivity on the mixing zone was more significant compared to transverse dispersivity in both the SWI and subsurface dam scenarios throughout the intrusion process. However, in the cutoff wall scenarios, the widening effect of increasing transverse dispersivity became more obvious during the later intrusion period. Our conclusions provide a reference for the groundwater management in coastal aquifers. According to the current seawater intrusion situation, the local water bureau can predict the seawater intrusion velocity and the temporal changes of mixing zone after the construction of physical barriers.

Unravelling the signatures of submarine groundwater discharge and seawater intrusion along the coastal plains of Odisha, India: a multi-proxy approach.

Submarine Groundwater Discharge (SGD) and Seawater Intrusion (SWI) are two contrary hydrological processes that occur across the land-sea continuum and understanding their nature is essential for management and development of coastal groundwater resource. Present study has attempted to demarcate probable zones of SGD and SWI along highly populated Odisha coastal plains which is water stressed due to indiscriminate-exploitation of groundwater leading to salinization and fresh groundwater loss from the alluvial aquifers. A multi-proxy investigation approach including decadal groundwater level dynamics, LANDSAT derived sea surface temperature (SST) anomalies and in-situ physicochemical analysis (pH, EC, TDS, salinity and temperature) of porewater, groundwater and seawater were used to locate the SGD and SWI sites. A total of 340 samples for four seasons (85 samples i.e., 30 porewater, 30 seawater and 25 groundwater in each season) were collected and their in-situ parameters were measured at every 1-2 km gap along ~ 145 km coastline of central Odisha (excluding the estuarine region). Considering high groundwater EC values (> 3000 µS/cm), three probable SWI and low porewater salinities (< 32 ppt in pre- and < 25 ppt in post-monsoons), four probable SGD zones were identified. The identified zones were validated with observed high positive hydraulic gradient (> 10 m) at SGD and negative hydraulic gradient (< 0 m) at SWI sites along with anomalous SST (colder in pre- and warmer in post-monsoon) near probable SGD locations. This study is first of its kind along the Odisha coast and may act as initial basis for subsequent investigations on fresh-saline interaction along the coastal plains where environmental integrity supports the livelihood of coastal communities and the ecosystem.

Evaluation of spatial and temporal dynamics of seawater intrusion in coastal aquifers of southeast India: insights from hydrochemical facies analysis.

This study aims to investigate and understand the temporal and spatial movement of seawater intrusion into the coastal aquifers. Groundwater salinity increase has affected the entire eastern part of the study area and is primarily influenced by direct and reverse ion exchange reactions associated with intrusion and freshwater influx phases, which alternate over monsoons. To gain insights into the spatiotemporal dynamics of the seawater intrusion process, hydrochemical facies analysis utilizing the HFE-Diagram was employed. Additionally, the study considered the major ionic changes during both the monsoons. The HFE-Diagram analysis of hydrochemical facies revealed distinctions in the behaviour of each coastal aquifer concerning seawater intrusion-induced salinization. In PRM 2020, the data shows that approximately 65% of the samples fall under the freshening phase, while the remaining 35% were categorized as intrusion phase. Within the freshening phase, seven different hydrochemical facies were identified, including Na-Cl, Na-MixCl, MixNa-MixCl, Na-MixHCO3/MixSO4, MixNa-MixSO4, Na-HCO3, and MixCa-HCO3. In contrast, the intrusion phase had four facies: MixCaMixHCO3, MixNa-Cl, Ca-Cl, and Na-Cl. Especially, the Na-Cl facies (f1) within the freshening phase attributed for the largest percentage, contributing 30% of the samples. In POM 2021, the distribution of samples shifted slightly, with approximately 72.5% belonging to the freshening phase and 27.5% to the intrusion phase. Within the freshening phase of POM 2021, five hydrochemical facies were identified: Na-Cl, Na-MixCl, Na-MixHCO3/MixSO4, MixNa-MixSO4, and Na-HCO3. The intrusion phase of POM 2021 had three facies: MixNa-Cl, Na-Cl, and MixCa-Cl. Similar to PRM 2020, the Na-Cl facies (f1) remained the most predominant in the freshening phase, comprising 30% of the samples. The relation between total dissolved solids (TDS) and various ionic ratios, such as HCO3-/Cl-, Na+/Cl-, Ca2+/Cl-, Mg2+/Cl-, K+/Cl-, and SO42-/Cl-, clearly demonstrates the presence of seawater influence within the coastal aquifers of the study area.

Impacts of climate change and coastal salinization on the environmental risk of heavy metal contamination along the odisha coast, India.

Climate change-mediated rise in sea level and storm surges, along with indiscriminate exploitation of groundwater along populous coastal regions have led to seawater intrusion. Studies on groundwater salinization and heavy metal contamination trends are limited. Present study investigated the heavy metal contamination, associated risks and provided initial information on the impacts of groundwater salinization on heavy metals along the coastal plains of Odisha, India. Total 50 groundwater samples (25 each in post- and pre-monsoon) were collected and analysed. Concentrations of Fe (44%), Mn (44%), As (4%) and Al (4%) in post-monsoon and Fe (32%), Mn (32%), As (4%), B (8%) and Ni (16%) in pre-monsoon exceeded Bureau of Indian Standards (BIS) drinking water limits. High concentrations of heavy metals (Fe, Sr, Mn, B, Ba, Li, Ni and Co) and high EC (>3000 µS/cm) indicated that the groundwater-seawater mixing process has enhanced the leaching and ion exchange of metallic ions in central part of the study area. Multivariate statistical analysis suggested leaching process, seawater intrusion and agricultural practices as the main heavy metal sources in the groundwater. 4% of samples in post- and 16% in pre-monsoon represented high heavy metal pollution index (HPI). Pollution indices indicated the central and south-central regions are highly polluted due to saline water intrusion and high agricultural activities. Ecological risks in the groundwater systems found low (ERI <110) in both seasons. Children population found more susceptible to health risks than adults. Hazard index (HI > 1) has shown significant non-carcinogenic risks where Fe, Mn, As, B, Li and Co are the potential contributors. Incremental lifetime cancer risk (ILCR >1.0E-03) has suggested high carcinogenic risks, where As and Ni are the major contributors. The study concluded that groundwater salinization could increase the heavy metal content and associated risks. This would help policymakers to take appropriate measures for sustainable coastal groundwater management.

Assessment of groundwater salinization impact in coastal aquifers based on the shared socioeconomic pathways: An integrated modeling approach.

Seawater intrusion (SWI) has become a significant threat to human health and sustainable economic development in coastal areas with the rapid pace of climate change. Therefore, it is crucial to determine the response of SWI to climate change. However, most studies cannot reflect the direct impact of future climate change on groundwater salinity. This study first established the SWAT-MODFLOW coupled model after unifying both spatiotemporal computational units. Streamflow, groundwater level observation data, etc., were used to calibrate and validate the coupled model. And then SEAWAT model was loaded into the coupled model to form a new integrated model. Finally, precipitation of six Global Climate Models (GCMs) under two shared socioeconomic pathways (1-2.6 and 5-8.5 scenarios) was imported into the above calibrated integrated model separately to make SWI prediction from December 30, 2020, to December 30, 2030. The results show that this integrated model accurately reflected the study area's current flow and concentration field distribution. Precipitation under different ssps had little effect on future SWI, while the uncertainty of SWI prediction was mainly derived from different GCMs. This study provides important implications for exploring the occurrence and the prediction of SWI in the coastal aquifer. It has specific reference significance for the optimal management of water resources in coastal areas and the effective mitigation of SWI.

Simulation-based multi-objective optimization framework for sustainable management of coastal aquifers in semi-arid regions.

Groundwater is a strategic source of water supply, especially in arid and semi-arid coastal regions. Growing demand, along with scarce water sources, may impose intense pressure on this precious resource. This pressure will degrade water quality for future use and cause social inequality, despite supplying current needs. A novel sustainable management model for water allocation is developed to address these interconnected concerns in coastal aquifers. Three aspects of sustainable development are considered: groundwater quality with total dissolved solids (TDS) indicator for the environmental part, gross value added from water for the economic efficiency, and the Gini coefficient for social inclusion and equity. The problem is solved with a simulation-based multi-objective optimization framework using a numerical variable-density simulation code and three approved evolutionary algorithms, NSGA-II, NRGA, and MOPSO. The obtained solutions are integrated to enhance the solutions' quality by using each algorithm's strengths and dominated members' elimination. In addition, the optimization algorithms are compared. The results showed that NSGA-II is the best in terms of solutions quality, with the least number of total dominated members (20.43%) and a 95% success rate of obtained Pareto front. NRGA was supreme in finding extreme solutions, the least computational time, and diversity, with an 11.6% higher diversity value than the second competitive NSGA-II. MOPSO was the best in spacing quality indicator, followed by NSGA-II, showing their great arrangement and evenness in obtained solution space. MOPSO has the propensity for premature convergence and needs more stringent stopping criteria. The method is applied to a hypothetical aquifer. Still, the obtained Pareto fronts are determined to assist decision-makers in real-world coastal sustainable management problems by illustrating existing patterns among different objectives.

Spatio-temporal variability of seawater mixing in the coastal aquifers based on hydrogeochemical fingerprinting and statistical modeling.

This study discusses monitoring and characterization of spatial and temporal variability to comprehend groundwater salinization based on hydrogeochemical fingerprinting and statistical modeling in the coastal belt of Digha-Shankarpur-Tajpur-Mandarmani, West Bengal, India. An integrated study of hydrogeochemical, bulk magnetic susceptibility, multivariate statistical, and geochemical modeling methods is implemented. The major cationic and anionic concentrations in groundwater are in the order Na+ > Ca2+ > Mg2+ > K+ and Cl- > HCO3- > SO4- > NO3- > F- respectively. The major water types are dominated by (Ca2+ - HCO3-) followed (Ca2+ - Mg2+ - Cl-), (Ca2+ - Na+ - HCO3-), (Na+ - HCO3-), and (Na+ - Cl). The results showed that the groundwater quality continuously declined steadily from pre-monsoon 2020 to pre-monsoon 2022. The deterioration of groundwater is due to an interplay of multiple factors, i.e., water-rock interaction, including ion-exchange, seawater mixing, and anthropogenic actions. Furthermore, it is also found that the regions showing higher seawater mixing index and oversaturated with carbonate minerals are also areas where groundwater is unsuitable for irrigation. The findings are beneficial in assisting local communities and legislators in designing appropriate management and mitigation techniques to arrest seawater intrusion in coastal regions.

Effects of Seawater Intrusion on the Groundwater Quality of Multi-Layered Aquifers in Eastern Saudi Arabia.

The degradation of groundwater (GW) quality due to seawater intrusion (SWI) is a major water security issue in water-scarce regions. This study aims to delineate the impact of SWI on the GW quality of a multilayered aquifer system in the eastern coastal region of Saudi Arabia. The physical and chemical properties of the GW were determined via field investigations and laboratory analyses. Irrigation indices (electrical conductivity (EC), potential salinity (PS), sodium adsorption ratio (SAR), Na%, Kelly's ratio (KR), magnesium adsorption ratio (MAR), and permeability index (PI)) and a SWI index (fsea) were obtained to assess the suitability of GW for irrigation. K-mean clustering, correlation analysis, and principal component analysis (PCA) were used to determine the relationship between irrigation hazard indices and the degree of SWI. The tested GW samples were grouped into four clusters (C1, C2, C3, and C4), with average SWI degrees of 15%, 8%, 5%, and 2%, respectively. The results showed that the tested GW was unsuitable for irrigation due to salinity hazards. However, a noticeable increase in sodium and magnesium hazards was also observed. Moreover, increasing the degree of SWI (fsea) was associated with increasing salinity, sodium, and magnesium, with higher values observed in the GW samples in cluster C1, followed by clusters C2, C3, and C4. The correlation analysis and PCA results illustrated that the irrigation indices, including EC, PS, SAR, and MAR, were grouped with the SWI index (fsea), indicating the possibility of using them as primary irrigation indices to reflect the impact of SWI on GW quality in coastal regions. The results of this study will help guide decision-makers toward proper management practices for SWI mitigation and enhancing GW quality for irrigation.

Seawater intrusion on the west coast of Shenzhen during 1980-2020 due to the influence of anthropogenic activities.

Anthropogenic activities are considered key factors to affect the evolution of seawater intrusion (SWI) status. Understanding the relationships between anthropogenic factors and SWI development is crucial to formulate strategies that are used to mitigate groundwater salinization in coastal areas. In this study, we analyzed changes in land use on the west coast of Shenzhen, Guangdong province, China, over the recent four decades based on remote sensing data, and evaluated the SWI degrees in three historical stages during 1980-2020 based on the hydrochemistry data. Then, combining the timelines of groundwater exploitation, land use, land reclamation, and groundwater salinization, we presented the evolution of SWI affected by anthropogenic activities on the west coast of Shenzhen. It is found that the SWI can be divided into three stages: 1988-1999, a fully developing period; 2000-2009, a partly degrading period; and 2018-2020, a fully degrading period. The interface of saline and fresh groundwater paralleling with the coastline advanced 2 km inland in 20 years and took the next 20 years to retreat about 1 km. The interface advancing and retreating correspond to the excess and the prohibition of groundwater exploitation, respectively. Meanwhile, the construction and demolishment of high-position saltwater aquaculture areas, respectively, corresponded to the increase and decrease of Cl- concentrations in these areas. Besides, the correlation between seawater mixing index (SMI) values and Na+ concentrations became much lower during the desalination of groundwater, which can be considered direct evidence for the SWI retreat.

High spatial heterogeneity and low connectivity of bacterial communities along a Mediterranean subterranean estuary.

Subterranean estuaries are biogeochemically active coastal sites resulting from the underground mixing of fresh aquifer groundwater and seawater. In these systems, microbial activity can largely transform the chemical elements that may reach the sea through submarine groundwater discharge (SGD), but little is known about the microorganisms thriving in these land-sea transition zones. We present the first spatially-resolved characterization of the bacterial assemblages along a coastal aquifer in the NW Mediterranean, considering the entire subsurface salinity gradient. Combining bulk heterotrophic activity measurements, flow cytometry, microscopy and 16S rRNA gene sequencing we find large variations in prokaryotic abundances, cell size, activity and diversity at both the horizontal and vertical scales that reflect the pronounced physicochemical gradients. The parts of the transect most influenced by freshwater were characterized by smaller cells and lower prokaryotic abundances and heterotrophic production, but some activity hotspots were found at deep low-oxygen saline groundwater sites enriched in nitrite and ammonium. Diverse, heterogeneous and highly endemic communities dominated by Proteobacteria, Patescibacteria, Desulfobacterota and Bacteroidota were observed throughout the aquifer, pointing to clearly differentiated prokaryotic niches across these transition zones and little microbial connectivity between groundwater and Mediterranean seawater habitats. Finally, experimental manipulations unveiled large increases in community heterotrophic activity driven by fast growth of some rare and site-specific groundwater Proteobacteria. Our results indicate that prokaryotic communities within subterranean estuaries are highly heterogeneous in terms of biomass, activity and diversity, suggesting that their role in transforming nutrients will also vary spatially within these terrestrial-marine transition zones.

Hybridization of GALDIT method to assess actual and future coastal vulnerability to seawater intrusion.

In the recent years, the coastal aquifer of Jijel plain (North Algeria) located on the south of the Mediterranean Sea was utilized for cities growth and agricultural development of the region. Consequently, overexploitation and seawater intrusion were identified as major risks to the groundwater resource. In this work, a new approach integrating groundwater vulnerability method and numerical model for predicting the actual and future seawater is proposed. The groundwater vulnerability assessment has been performed by applying the GALDIT method using GIS and the MODFLOW model was used to simulate the actual and future groundwater level of the aquifer over the period 2020-2050. Three scenarios were simulated under water demand and climate conditions (drought, recharge) to obtain the changes in the groundwater level variation. The results of the GALDIT model application to the actual conditions (year 2020) showed that the high class of groundwater vulnerability is located in the coastal fringe and the terminal stretches of wadis where the seawater intrusion limit is located at a distance range between 840 and 1420 m from the shoreline. However, the results for predicting future groundwater vulnerability showed that the scenario which proposed the artificial recharge basins, although predicting a worrying situation compared to the actual condition, has the best figure of the groundwater vulnerability assessment and seawater intrusion despite the other two scenarios. In this case the limit in the year 2050 is located between distances of 850-1640 m from the shoreline with a forward speed of seawater intrusion of 1-8 m/year, compared to the reference year 2020. This showed that groundwater level variation and recharge were the key factors in controlling groundwater vulnerability to seawater intrusion. The presented new approach can be used to mapping the actual and future groundwater vulnerability assessment to seawater intrusion and groundwater resources management in any coastal areas worldwide.

Influence of velocity distribution conditions of coastal aquifer on nitrate contamination and seawater intrusion in the presence of subsurface physical barriers.

The velocity distribution is an important factor that affects seawater intrusion (SI) and nitrate (NO3-) pollution. However, there are few studies on the impact of subsurface physical barriers (SPBs) on the velocity distribution of the whole aquifer and the impact of velocity distribution on SI and NO3- pollution. Especially, the quantitative method of velocity distribution has not been studied. By the methods of laboratory experiments and numerical simulations, effects of the NO3- concentrations of the pollution source, hydraulic gradients (HGs), the location of the SPB and relative heights of SPBs (HP') on the SI, NO3- pollution levels and velocity in the presence of SI and SPBs were investigated. The velocity distribution was first quantified to better describe the relationships between the velocity and degrees of SI and NO3- pollution. The results showed that the HG and HP' were the main factors that affected the velocity, NO3- pollution and SI. The higher the HG, the smaller the HP', and the decreased SI inferred a more serious NO3- pollution. The influence of SPBs on NO3- pollution and SI was mainly affected by the changes in the velocity distribution in the aquifer. With increasing HGs, for the region with flow rate less than 0.5 m/d (A0.5), the smaller its distribution area is, the smaller the relative area of SI (TLs') is. With an increase in the HG or decrease in the HP', the relative area of NO3- pollution (Ns') is proportional to the distribution area where the flow velocity is greater than 1 m/d (A1). When the flow velocity distribution condition was A'1 (the relative area of A1) > A'0.5-1 (A'0.5-1 is the ratio of the area where the flow velocities are greater than 0.5 m/d and less than 1 m/d to the total area of the aquifer) > A'0.5 (the relative area of A0.5), NO3- pollution was serious; when the flow velocity distribution condition was A'0.5 > A'0.5-1 > A'1, the levels of NO3- pollution were the lowest.

Assessing the protective effect of cutoff walls on groundwater pumping against saltwater upconing in coastal aquifers.

Subsurface physical barriers are amongst the most effective methods to mitigate seawater intrusion in coastal aquifers. The main objective of this study was to examine the impact of cutoff walls on saltwater upconing using laboratory and numerical modelling experiments. Physical experiments were first completed to reproduce the saltwater upconing process in a laboratory-scale coastal aquifer model incorporating an impermeable cutoff wall. Numerical modelling was used for validation purposes and to perform additional simulations to explore the protective effect of cutoff walls against saltwater upconing. The results suggest that the cutoff wall did not substantially delay the saltwater upconing mechanism in the investigated configurations. Laboratory and numerical observations showed the existence of some residual saline water, which remained on the upper part of the aquifer on the seaward side of the wall following the retreat of the saltwater. The protective effect of cutoff walls was noticeably sensitive to the design parameters. Specifically, cutoff walls installed close to the pumping well enabled the implementation of higher pumping rates, therefore a more optimal use of the freshwater, especially for deeper wells. The results highlighted that the penetration depth of the cutoff walls may not necessarily need to exceed the depth of the pumping well to ensure effectiveness, which is of great importance from construction and economic perspectives.

Integrated Hydrogeological, Hydrochemical, and Isotopic Assessment of Seawater Intrusion into Coastal Aquifers in Al-Qatif Area, Eastern Saudi Arabia.

Seawater intrusion (SWI) is the main threat to fresh groundwater (GW) resources in coastal regions worldwide. Early identification and delineation of such threats can help decision-makers plan for suitable management measures to protect water resources for coastal communities. This study assesses seawater intrusion (SWI) and GW salinization of the shallow and deep coastal aquifers in the Al-Qatif area, in the eastern region of Saudi Arabia. Field hydrogeological and hydrochemical investigations coupled with laboratory-based hydrochemical and isotopic analyses (18O and 2H) were used in this integrated study. Hydrochemical facies diagrams, ionic ratio diagrams, and spatial distribution maps of GW physical and chemical parameters (EC, TDS, Cl-, Br-), and seawater fraction (fsw) were generated to depict the lateral extent of SWI. Hydrochemical facies diagrams were mainly used for GW salinization source identification. The results show that the shallow GW is of brackish and saline types with EC, TDS, Cl-, Br- concentration, and an increasing fsw trend seaward, indicating more influence of SWI on shallow GW wells located close to the shoreline. On the contrary, deep GW shows low fsw and EC, TDS, Cl-, and Br-, indicating less influence of SWI on GW chemistry. Moreover, the shallow GW is enriched in 18O and 2H isotopes compared with the deep GW, which reveals mixing with recent water. In conclusion, the reduction in GW abstraction in the central part of the study area raised the average GW level by three meters. Therefore, to protect the deep GW from SWI and salinity pollution, it is recommended to implement such management practices in the entire region. In addition, continuous monitoring of deep GW is recommended to provide decision-makers with sufficient data to plan for the protection of coastal freshwater resources.

Assessment and delineation of potential groundwater recharge zones in areas prone to saltwater intrusion hazard: a case from Central Iran.

Demarcation of the potential zones for groundwater artificial recharge (GAR) based on the most influential factors is an urgent need for retardation of saltwater intrusion and, thus, sustainability of groundwater resources in the arid zones. This study developed an overlay-index methodology to delineate favorable GAR zones by a linear combination of 11 influential thematic layers in ArcGIS. The proposed methodology was implemented on two coastal aquifer settings Sharif-Abad (SAA) and Qom-Kahak (QKA) aquifers adjacent to Salt Lake, Central Iran. Results indicated that 16.41% of the surface of SAA and 28.58% of QKA were identified as the high potential zone for GAR mainly located in low GW vulnerability parts. Based on the analysis of the area under the receptive operating curve (AUC), the produced GAR map has an accuracy of 0.643, and 0.611 for SAA and QKA aquifers, respectively, which relies on the acceptable limit. Finally, the quantity of water required for GAR to control the intrusion of seawater at the suitable parts of these aquifers was estimated as 25 MCM and 35 MCM, annually. The methodology adopted in this study can serve as a holistic assessment for the detection of SWI in coastal aquifers, and also a comprehensive blueprint for managers to delineate the favorable GAR zones, especially in arid regions.

Managerial sustainability indices for improving the coastal groundwater decisions by a parallel simulation-optimization model.

Seawater intrusion is one of the causes of groundwater quality degradation in coastal zones. This phenomenon is intensified by overexploitation of coastal aquifers. In this paper, optimal management strategies have been determined to prevent the advance of seawater using a parallel simulation-optimization decision model. This model has been applied to a real case study of Ajabshir aquifer located in Urmia Lake basin, Iran, for a 20-year planning horizon (2015-2034). Four categorizes of new sustainability indices (indices of protection, reliability, vulnerability, and aquifer area with a groundwater problem) as the objective functions have been examined for the first time. The developed management problems based on these four categories have been solved under two different conditions of groundwater elevation and salinity concentration. The results of 20-year period simulations indicate that by changing the extraction pattern in different regions of the aquifer (as the decision variables) based on the solution of management problems, the largest decrease in net recharge (0.065 million cubic meters) occurs in the second half of the hydrologic year (October to March) compared to the continued condition in which all factors are similar to 2014. The contribution of using indices in this study can help the local water managers to identify the high-risk areas for better planning and other coastal settings.

Statistical assessment of seasonal variation of groundwater quality in Çarsamba coastal plain, Samsun (Turkey).

Çarsamba aquifer is one of the most important coastal aquifers in Turkey. This aquifer is confronted by overexploitation due to the agricultural and industrial activities. The aim of the present study is to investigate the seasonal variations of hydrogeochemical parameters and to assess the suitability for drinking and irrigation of groundwater in the coastal aquifer of Çarsamba plain. For this purpose, in July and December of the year 2019, 33 and 30 groundwater samples respectively were taken from boreholes in the study area and for these samples, EC, pH, TDS, Na+, Ca+, K+, Mg2+, CO3-, HCO3-, Cl-, SO42-, NH4+, NO3-, and NO2- values were determined. Strong correlation was observed between Cl- and Na+ during both seasons indicating the seawater intrusion on groundwater in the study area. Principal component analysis showed that in the study area, seawater intrusion, rock-water interaction, and anthropogenic activities from agricultural areas are the main factors that impact the groundwater chemistry. Seawater intrusion is the most important factor which affects the groundwater chemistry in July while in December, the main factor is rock-water interaction. In December, NO2- and NH4+ values of most water samples exceed the authorized limits of Turkish Standard and WHO. Water quality index indicated that most of the water samples are suitable for drinking. Wilcox diagram and US salinity diagram used to evaluate the suitability of groundwater for irrigation suggested that in July, 87.87% (90% in December) (for Wilcox diagram) and 96.96% (100% in December) (for US salinity diagram) of the water samples belonged to the good to permissible class, and therefore are suitable for irrigation purpose. In addition, the EC, %Na, TH, RSC, SAR, PI, KI, and MH values of samples showed that during both seasons, most of the water samples are suitable for irrigation. However, in July, 51.52% (43.43% in December) of samples have extremely high potential salinity values, thus revealing the unsuitability of most groundwater samples for irrigation in the study area.

SWOT risk analysis towards sustainable aquifer management along the Eastern Mediterranean.

This study examines the risks of seawater intrusion (SWI) in data scarce aquifers along the Eastern Mediterranean by quantifying the interaction of the main natural, anthropogenic and climatic drivers, while also considering varying abilities of implementing adaptation and mitigation measures. For this purpose, we conducted a semi-quantitative Strengths, Weaknesses, Opportunities and Threats (SWOT) analysis representing a first attempt at integrating a complex physical process with multi layered influences in a SWOT analysis model that was tested at 26 coastal aquifers with varying levels of SWI severity. The analysis results showed alarming signs of SWI at several eastern and southeastern aquifers, particularly those underlying densely populated centers (i.e. Beirut, Lebanon; Magoza, Cyprus; Gaza, Palestine and the Nile Delta, Egypt). The analysis also highlighted adaptive capabilities that appear to be strong in Cyprus, Israel and Turkey, emerging in Egypt, and weak in Lebanon, Syria, and Palestine. The risks exhibited a strong and statistically significant positive relationship with the reported status of SWI at the tested aquifers thus providing an effective decision-making tool towards the preliminary assessment of SWI in regions with data scarcity. The study concludes with proposing a framework for sustainable aquifer management in the East Med region with emphasis on controlling SWI risks.