Seawater Intrusion Research Articles

Land subsidence is a natural hazard that is causing serious damage to the Mekong Delta (VMD) of Vietnam, with subsidence rates of up to 5 cm per year in densely populated cities such as Ca Mau, increasing the risk of salinity intrusion and tidal flooding. These ground movements not only amplify the impacts of sea level rise but also threaten infrastructure, agricultural sustainability, and long - term climate resilience. While traditional monitoring methods such as GNSS and land leveling surveys are highly accurate, they are often spatially inadequate and cost - in effective for regional - scale applications. In this context, remote sensing technologies, specifically Interferometric Synthetic Aperture Radar (InSAR) techniques such as Persistent Scatter Interferometry (PSI), have emerged as powerful tools for understanding surface deformation patterns over large areas. Integrating InSAR - derived observations with machine learning (ML) techniques offers new opportunities for predictive modeling of subsidence phenomena. Ensemble algorithms such as Random Forest (RF) and Extreme Gradient Boosting (XGBoost) have demonstrated robust performance in identifying spatially distributed land deformation susceptibility, especially when applied to high - dimensional geospatial data. In this study, we evaluate the predictive performance of three distinct methods - MAF (Moving Average Filter), RF, and XGBoost - for predicting land subsidence in Ca Mau using PSI - based displacement data. A dataset of 5,000 deformation monitoring points from Sentinel - 1 imagery from 2014 to 2019 is used to train and evaluate the models. Among these models, XGBoost demonstrated the best performance with the lowest RMSE (4.67) and MAE (3.23), and the highest R² (0.9869), significantly outperforming both RF and MAF. These findings highlight the robustness of machine learning approaches, particularly XGBoost, in predicting land subsidence and supporting sustainable land use planning and climate adaptation strategies in vulnerable deltaic environments.

Impact of geochemical iron and sulfur redox cycling on arsenic release along a salinity gradient: Sea level rise implications.

The Huangshui River Basin is located in the transition zone between the Loess Plateau and the Qinghai–Tibet Plateau, characterized by a fragile hydrological and ecological environment. Groundwater serves as a vital water source for local economic development and human livelihood. With the acceleration of urbanisation and climate change, groundwater resources face challenges such as pollution and over-exploitation. This study employs an improved DRASTIC model, tailored to the characteristics of the groundwater system in the Huangshui River Valley of the upper Yellow River, to integrate groundwater resources, groundwater environment, and ecological environment systems. Improving the DRASTIC model for groundwater vulnerability assessment. A two-tiered evaluation system with nine indicator parameters was proposed, including six groundwater quality vulnerability indicators and five groundwater quantity vulnerability indicators. Fuzzy analytic hierarchy process and entropy weight method were used to determine the weights, and Geographic Information System (GIS) spatial analysis was employed to evaluate groundwater vulnerability in the Huangshui River basin in 2006 and 2021. The results indicate that the proportion of areas with high groundwater quality vulnerability increased from 10.7% in 2006 to 31.57% in 2021, while the proportion of areas with high groundwater quantity vulnerability decreased from 22.33% to 14.02%. Overall, groundwater quality vulnerability in the Huangshui River basin is increasing, while groundwater quantity vulnerability is decreasing. Based on the evaluation results of water quality and quantity vulnerability, protection zoning maps for water quality and quantity were compiled, and preventive measures and recommendations for water quality and quantity protection zones were proposed. Human activities have a significant impact on groundwater vulnerability, with land use types and groundwater extraction coefficients having the highest weights. This study provides a scientific basis for the protection and sustainable use of groundwater in the Huangshui River basin.

This study developed a novel Water Quality Index (WQI) using Kernel Principal Component Analysis (PCA) to assess groundwater quality (GWQ) in the coastal aquifers of Al-Qatif, Saudi Arabia. A total of 39 groundwater samples were collected from shallow and deep wells and analyzed for key physicochemical parameters. Six kernel types were tested, and the polynomial kernel was found to be most effective in preserving variance and reducing dimensionality. The Kernel PCA-based WQI classified wells into ‘Very Bad,’ ‘Bad,’ and ‘Medium’ categories, with scores such as W3 (WQI = 25.51, “Very Bad”), W31 (WQI = 46.7, “Bad”), and W38 (WQI = 56.75, “Medium”). Salinity and EC presented poor Sub-Index (SI) scores, reflecting the impact of seawater intrusion and over-extraction, while pH consistently showed high SI values (100), indicating natural buffering. By integrating non-linear dimensionality reduction, the proposed framework enhances traditional WQIs and facilitates more targeted and transparent groundwater decision-making. This includes identifying priority wells for remediation and supporting sustainable abstraction policies. The findings offer insight into sustainable water management in arid and semi-arid regions that are confronting groundwater degradation.

Sea level rise is having major impacts on estuaries due to salinity intrusion. These changes in stress profiles have ripple effects in ecosystems, including altering the invasibility of these wetlands depending on the salt tolerance of the invading species. Alternanthera philoxeroides Mart. (Griseb.) (alligator weed), native to South America and long recognized as one of the world’s worst freshwater aquatic weeds, recently invaded tidal wetlands in California’s San Francisco Bay–Delta Estuary. Generally considered a freshwater-limited glycophyte, observations suggested this invasive macrophyte may have some degree of salinity tolerance, though its degree of tolerance and capacity to spread with increased salinity intrusion were unknown. In two full-factorial greenhouse experiments, we assessed responses of emergent (soil-rooted) and free-floating growth forms of A. philoxeroides to four salinity concentrations (freshwater to euhaline) at the whole-plant (growth, biomass production and allocation, fitness), physiological, and biochemical levels. We also conducted a third experiment exploring the recovery potential of free-floating A. philoxeroides in freshwater following extended exposure to mesohaline to euhaline aqueous salinity. Although sensitivity of A. philoxeroides to increasing salinity was documented, the survival of both growth forms in the full range of salinity treatments was notable and unexpected. Our results indicate A. philoxeroides is a facultative halophyte well adapted to oligohaline–mesohaline salinity levels. Results also revealed the invasive weed’s multiple strategies to survive salinity-induced physiological stress, supporting its survival even at elevated polyhaline to euhaline conditions. The macrophyte expressed functional trait responses spanning stress tolerance, avoidance, and escape strategies that may sustain its spread as estuarine salinity intrusion increases with sea level rise.

The long-term sustainability of food production and the usage of agricultural land are seriously threatened by soil salinization. To combat the salinization, the salt-tolerant cyanobacteria can be a potent candidate. However, it is not yet clear how these microbes work to remediate saline soil. Salinity is a global problem, mainly caused by higher evaporation rate, low rainfall, seawater intrusion into freshwater, overuse of chemical fertilizers, etc. This study examined the effect of various salt concentrations on Desertifilum salkalinema SSAU 7 (SSAU 7), which is isolated from the river Ganges, Prayagraj, India. This study examined the tolerance of microbes by analysing the chlorophyll-a, carotenoid, carbohydrate, and photosynthetic activity. It also includes the activity of trehalose and antioxidants, for the mechanism involved in the tolerance and providing new insights that will help the development of cyanobacteria bio-stimulants capable of ameliorating the adverse effects of salinity. The findings revealed that the strain SSAU 7 has the ability to survive up to 20 gL-1 salt concentrations efficiently. The study showed that the halotolerant cyanobacterium can not only survive at high salt concentration but also it can help in Cicer arietinum (chickpea) plant growth by secreting Indole acetic acid. With increased germination percentage of seed, stem, and root length, SSAU 7 clearly had a good impact on plant growth. These results highlight how cyanobacteria enormously combat salt stress efficiently and can also promote the production of crops while reducing the negative impact of agrochemicals on the environment.

This study investigates groundwater salinization in a section of a coastal aquifer in Rio Grande do Norte, Brazil, using frequency-domain electromagnetic (FDEM) measurements. With the global expansion of shrimp farming in ecologically sensitive coastal regions, there is an urgent need to assess associated risks and promote sustainable management practices. A key concern is the prolonged flooding of shrimp ponds, which accelerates saltwater infiltration into surrounding areas. To better delineate salinization plumes, we analyzed direct groundwater salinity measurements from 14 wells combined with 315 subsurface apparent conductivity measurements obtained using the FDEM method. Correlating these datasets improved the accuracy of salinity mapping, as evidenced by reduced variance in kriging interpolation. By integrating hydrogeological, hydrogeochemical, and geophysical approaches, this study provides a comprehensive characterization of groundwater salinity in the study area. Hydrogeological investigations delineated aquifer properties and flow dynamics; hydrogeochemical analyses identified salinity levels and water quality indicators; and geophysical surveys provided spatially extensive conductivity measurements essential for detecting and mapping saline intrusions. The combined insights from these methodologies enable a more precise assessment of salinity sources and support the development of more effective groundwater management strategies. Our findings demonstrate the effectiveness of integrating geophysical surveys with hydrogeological and hydrogeochemical data, confirming that shrimp farm ponds are a significant source of groundwater contamination. This combined methodology offers a low-impact, cost-effective approach that can be applied to other coastal regions facing similar environmental challenges.

Context Coastal freshwater wetlands and their associated communities are at an increased risk of salinity exposure because of a variety of contemporary and historical anthropogenic stressors. Salinization shifts the community structure of aquatic organisms, such as macroinvertebrates, leading to decreases in functional ecological integrity. These salinity-driven changes to communities have the potential to alter macroinvertebrate-mediated processes such as detrital decomposition. Aims Our study aimed to examine the relationship among salinity exposure, leaf decomposition and mortality of a common freshwater macroinvertebrate (isopod: genus Caecidotea). Methods Using an in-laboratory microcosm approach, we exposed tanks of isopods and detrital leaf material to varying salinity levels for 23 days, after which isopod mortality and decomposition of detrital material were measured. Key results We found that increases in salinity increased isopod mortality, but had no effect on leaf disc decomposition. Conclusions These findings demonstrated the negative effect of increased salinity on a common freshwater macroinvertebrate. Additional studies regarding the response of non-isopod decomposers, such as bacteria and fungi, are needed to provide a more complete understanding of the effects of salinity intrusion in at-risk freshwater habitats. Implications As we expect salinization to increase in the future, it is important to understand how organisms and the processes they contribute to and rely on will be affected. The detrital decomposition process and aquatic macroinvertebrates are key foundations of aquatic food webs, and significant bottom-up changes could have drastic implications for ecosystems.

Freshwater aquaculture in the Indian Sundarbans has witnessed significant growth over the past four decades, largely driven by declining agricultural viability due to increasing soil salinization, erratic rainfall, and rising demand for fish protein. This study aims to assess the spatial and temporal expansion of freshwater aquaculture from 1985 to 2024 and evaluate its production outcomes and livelihood implications. Employing a mixed-methods approach, the analysis integrates remote sensing data (Landsat and Sentinel-2 imagery), supervised and unsupervised land use classification, and field surveys involving 350 fish-farming households. Results indicate a 96.9% increase in aquaculture area-from 80.54 km2 in 1985 to 860.96 km2 in 2024-with growth concentrated in Pathar Pratima, Gosaba, and Basanti blocks. The majority (82.12%) of ponds are small-scale, yielding an average household production of 87kg and generating ₹13,918 annually, with a mean productivity of 120kg/ha/year. Labeo rohita and Labeo catla are the dominant cultured species. Despite expansion, key challenges include seed and feed shortages, salinity intrusion, and inadequate infrastructure. Government interventions such as MGNREGS and the Jal Dharo Jal Bharo scheme have facilitated water management and pond development. The findings underscore the need for strategic ecological planning and policy support to ensure the sustainability and climate resilience of freshwater aquaculture in this vulnerable coastal ecosystem.

This study examines the impacts of climate change on fisheries and aquaculture in Bangladesh, one of the most climate-vulnerable countries in the world. The fisheries and aquaculture sectors contribute significantly to the national GDP and support the livelihoods of 12% of the total population. Using a Critical Literature Review (CLR) approach, peer-reviewed articles, government reports, and official datasets published between 2006 and 2025 were reviewed across databases such as Scopus, Web of Science, FAO, and the Bangladesh Department of Fisheries (DoF). The analysis identifies major climate drivers, including rising temperature, erratic rainfall, salinity intrusion, sea-level rise, floods, droughts, cyclones, and extreme events, and reviews their differentiated impacts on key components of the sector: inland capture fisheries, marine fisheries, and aquaculture systems. For inland capture fisheries, the review highlights habitat degradation, biodiversity loss, and disrupted fish migration and breeding cycles. In aquaculture, particularly in coastal systems, this study reviews the challenges posed by disease outbreaks, water quality deterioration, and disruptions in seed supply, affecting species such as carp, tilapia, pangasius, and shrimp. Coastal aquaculture is also particularly vulnerable to cyclones, tidal surges, and saline water intrusion, with documented economic losses from events such as Cyclones Yaas, Bulbul, Amphan, and Remal. The study synthesizes key findings related to climate-resilient aquaculture practices, monitoring frameworks, ecosystem-based approaches, and community-based adaptation strategies. It underscores the need for targeted interventions, especially in coastal areas facing increasing salinity levels and frequent storms. This study calls for collective action through policy interventions, research and development, and the promotion of climate-smart technologies to enhance resilience and sustain fisheries and aquaculture in the context of a rapidly changing climate.

Saline intrusion in Niger Delta coastal aquifers, drivers, hydrogeological dynamics and mitigation strategies

Abstract Carbon and biodiversity offset markets have been proposed to finance management solutions for introduced ungulates across northern Australian coastal wetlands. However, few studies have quantified how ungulate removal may affect ecosystem services important to local Indigenous communities, especially considering coincident saltwater intrusion. Using a mixed‐method, two‐eyed seeing approach, we deployed Yolŋu Knowledge and Western scientific assessments to understand the effects of introduced ungulates and saltwater intrusion on a coastal floodplain fringe in the Laynhapuy Indigenous Protected Area, northern Australia. Collectively, dirramu (male) Yolŋu knowledge holders described the socio‐ecological impacts of introduced ungulates, including declines in bush foods, räkay (Eleocharis dulcis) sedgeland and Melaleuca forest, and how this affected their well‐being, culture, songlines and floodplain carbon stores. They noted the interactions between introduced ungulates and saltwater intrusion as channel incision, mangrove encroachment and soil damage. The miyalk (women) attributed ungulate invasion to declines in räkay corm abundance, size and harvestability, with some suggestion that salinity also affected corm size. Using existing ungulate exclusion plots, quantitative Western scientific assessments of above‐ground carbon stocks, forest tree structure and räkay corms largely aligned with the Yolŋu knowledge; however, the Western science did not detect interactions between saltwater intrusion and ungulates, only different significant main effects. In the ungulate exclusion plot array, above‐ground carbon was significantly higher in the healthy Melaleuca forest upper zone (74 ± 14.39 Mg C ha−1), compared with the mid (32.8 ± 20.91 Mg C ha−1) and lower (7.2 ± 0.84 Mg C ha−1) elevation zones where Melaleuca dieback occurred, suggesting a salinity effect. Feral ungulate exclusion resulted in greater understorey carbon in the upper (healthy Melaleuca forest) and lower (räkay sedgeland) zones. The two‐eyed seeing approach allowed for the collection of quantitative carbon and ecological data alongside locally meaningful Indigenous eco‐cultural perspectives. Nuanced understanding of the impacts of introduced ungulates and saltwater intrusion on regulating and cultural ecosystem services highlighted the potential for ecological, cultural and socio‐economic outcomes from proposed market‐based solutions to managing introduced ungulates on coastal floodplains of northern Australia. Read the free Plain Language Summary for this article on the Journal blog.

Salinity intrusion, exacerbated by climate change and anthropogenic activities, poses a significant global threat to agricultural productivity, particularly in coastal and deltaic regions. Rice, a staple crop critical for food security and economic stability in many developing nations, is highly susceptible to salt stress, which reduces yields and threatens livelihoods. In the Vietnamese Mekong Delta (VMD), a key rice-producing region, recurrent drought-induced salinity events have caused substantial damage to agriculture, and the economic well-being of millions of residents. These events highlight the urgent need for sustainable solutions to maintain rice production under adverse environmental conditions. Plant-Growth-Promoting Rhizobacteria (PGPR) have emerged as a promising eco-friendly approach to enhance plant salt tolerance, offering potential to mitigate salinity stress in rice crops. Here we review the role of PGPR in alleviating salinity stress in rice farming in the VMD, highlighting its potential as a sustainable agricultural approach. The review synthesizes existing research to assess the causes of salinity intrusion, the efficacy of PGPR, and the limitations of current studies in this region. The major points are the following: 1) Saline intrusion in the VMD is driven by multiple factors, including sea-level rise, land subsidence, upstream dams’ operation, and excessive sand mining, which exacerbate agricultural challenges; 2) PGPR enhance rice salt tolerance through mechanisms such as osmotic regulation, improved nutrient uptake, and activation of stress-responsive genes, as evidenced in controlled and field studies; 3) Research in Vietnam is constrained by a lack of long-term investigations and a reliance on publications in Vietnamese-language scientific journals, which may limit international attention and rigorous peer-review processes, necessitating further studies to support scalability and adoption by VMD farmers, and also enlarge international collaboration in this important field of study.

Seawater intrusion into coastal river systems poses increasing challenges for freshwater availability and estuarine ecosystem integrity, especially under evolving climatic and anthropogenic pressures. This study presents a multidisciplinary investigation of marine intrusion dynamics within the Magra River estuary (Northwest Italy), integrating field monitoring, isotopic tracing (δ18O; δD), and multivariate statistical modeling. Over an 18-month period, 11 fixed stations were monitored across six seasonal campaigns, yielding a comprehensive dataset of water electrical conductivity (EC) and stable isotope measurements from fresh water to salty water. EC and oxygen isotopic ratios displayed strong spatial and temporal coherence (R2 = 0.99), confirming their combined effectiveness in identifying intrusion patterns. The mass-balance model based on δ18O revealed that marine water fractions exceeded 50% in the lower estuary for up to eight months annually, reaching as far as 8.5 km inland during dry periods. Complementary δD measurements provided additional insight into water origin and fractionation processes, revealing a slight excess relative to the local meteoric water line (LMWL), indicative of evaporative enrichment during anomalously warm periods. Multivariate regression models (PLS, Ridge, LASSO, and Elastic Net) identified river discharge as the primary limiting factor of intrusion, while wind intensity emerged as a key promoting variable, particularly when aligned with the valley axis. Tidal effects were marginal under standard conditions, except during anomalous events such as tidal surges. The results demonstrate that marine intrusion is governed by complex and interacting environmental drivers. Combined isotopic and machine learning approaches can offer high-resolution insights for environmental monitoring, early-warning systems, and adaptive resource management under climate-change scenarios.

Abstract Soil salinity is a major ecological challenge that affects agricultural productivity, posed significant challenges on the ecological system, especially in the deltaic region vulnerable to human alterations and sea level rise. Assessing agricultural areas impacted by soil salinity change is very important to support decision-makers or planners in sustainable land use planning. To overcome limitations in current spatial extrapolation methods for a reliable prediction of salinity trends across extensive river deltas, an advanced synthesis approach was developed with the use of machine learning (ML) particularly appropriate to account for a multitude of factors representing land cover conditions, processes, and interactions. This study aims to: (i) address the extrapolation challenge in ML-based soil salinity mapping, and (ii) predict land cover changes due to soil salinity. The Mekong River Delta (MRD) and Red River Delta (RRD) were selected as case studies. A hybrid ML approach and land change modeler were used to analyze 39 contributing factors. To resolve the spatial extrapolation issue in soil salinity monitoring, we used 109 salinity-affected locations in the MRD and 72 in the RRD. Land cover data from 2000 and 2023, along with salinity maps, were used to project the 2050 land cover. Multiple ML models were used to cross-verify and obtain robust results. All models achieved R 2 scores above 0.85, with the best model exceeding 0.93, demonstrating high predictive performance. Among the models, XGR-particle swarm optimization achieved the highest accuracy (R 2 = 0.939), followed closely by XGR-fennec fox optimization, XGR-coati optimization algorithm (R 2 = 0.932), and XGR-osprey optimization algorithm (R 2 = 0.921), respectively, highlighting the robustness of optimization-enhanced XGBoost models. Future projections show that cropland will decline from 67% of the area (in 2000) to 64% (2023) and about 60% (2050) under the influence of salinity, with approximately 41 km2 of cropland converted to aquaculture by 2050, mostly in high-salinity coastal zones. This study develops a powerful synthesis framework to address the problem of spatial extrapolation challenges related to natural hazard mapping in general and soil salinity mapping in particular, based on ML and on accurate prediction of land cover/land use change under effects of soil salinity in the context of climate change. Results from the synthesis approach help accurately identify areas affected by salinity intrusion, useful for the development of effective solutions in space and time towards the goal of sustainable development.

Understanding the fluid storage and production mechanisms in sedimentary rocks is vital for optimising natural gas extraction and subsurface resource management. This study applies high-resolution X-ray computed tomography (≈15 μm) to digitise rock samples from onshore Cyprus, producing digital rock models from DICOM images. The workflow, including digitisation, numerical simulation of natural gas flow, and experimental validation, demonstrates strong agreement between digital and laboratory-measured porosity, confirming the methods’ reliability. Synthetic sand packs generated via particle-based modelling provide further insight into the gas storage mechanisms. A linear porosity–permeability relationship was observed, with porosity increasing from 0 to 35% and permeability from 0 to 3.34 mD. Permeability proved critical for production, as a rise from 1.5 to 3 mD nearly doubled the gas flow rate (14 to 30 fm3/s). Grain morphology also influenced gas storage. Increasing roundness enhanced porosity from 0.30 to 0.41, boosting stored gas volume by 47.6% to 42 fm3. Although based on Cyprus retrieved samples, the methodology is applicable to sedimentary formations elsewhere. The findings have implications for enhanced oil recovery, CO2 sequestration, hydrogen storage, and groundwater extraction. This work highlights digital rock physics as a scalable technology for investigating transport behaviour in porous media and improving characterisation of complex sedimentary reservoirs.

For socioeconomic development, groundwater is a vital resource, especially in areas with limited water supplies. This study assesses groundwater potential zones (GWPZs) in two distinct Nigerian regions, the inland crystalline basement complex of Ile-Ife and the coastal sedimentary basin of Ilaje using integrated geospatial techniques. The novelty of this research lies in its direct comparative analysis of these two disparate hydrogeological and anthropogenic contexts, which fills a critical gap in the existing literature. The study utilized Remote Sensing, GIS, and the Analytical Hierarchy Process (AHP), including a sensitivity analysis to improve methodological robustness. For GWPZ delineation, nine key thematic layers, including geology, land use/land cover, NDWI, NDVI, drainage density, lineament density, rainfall, DEM, and slope, were processed and weighted using AHP. Significant differences were found in the results. Ilaje had a higher percentage of highly available GWPZs (6.15%) than Ile-Ife (4.00%), which was indicative of fundamental variations in hydrogeological, geomorphological, and hydrological controls. Importantly, the results highlight how these differences call for tailored management approaches; Ile-Ife's resources are being depleted by increasing urbanization, while Ilaje's potential is accompanied by serious risks of pollution and saltwater intrusion. This research demonstrates that a “one-size-fits-all’’ approach to groundwater management is untenable in diverse environments and offers fresh empirical insights for both hydrogeological theory and practical policy formulation. It is important to note that the resulting GWPZ maps, based on secondary data, should be interpreted as preliminary indicators requiring future validation through borehole logs and pump test data.

Hydrodynamics primarily drive fluoride migration in coastal aquifers under seawater intrusion.

Heterogeneous saltwater intrusion patterns and drivers among multiple outlets in a complex estuary.

Microbial community dynamics across salinity gradients in coastal aquifers: Linking hydrogeochemical variability to prokaryotic diversity in a seawater-intruded aquifer of the Pearl River Delta, China.