Seawater Intrusion Research Articles

Iron-oxidizing Betaproteobacteria and Zetaproteobacteria are generally associated with freshwater and marine environments, respectively. Despite repeated cross-environment observations of these taxa, there has been no focused exploration of the genomes of marine Gallionella (Betaproteobacteria) to understand transitions between freshwater and marine habitats. Consequently, their roles in these environments remain uncertain. Here, we present strong evidence for the co-occurrence of Gallionella and Zetaproteobacteria at deep-sea hydrothermal vents at the Arctic Mid-Ocean Ridges through metagenomic analyses. Phylogenomic analysis of Gallionella metagenome-assembled genomes (MAGs) suggests that seawater adaptation is an evolutionary event that occurred multiple times in distinct lineages. Similarly, several distinct evolutionary events for freshwater and terrestrial Mariprofundus and other Zetaproteobacteria are predicted. The presence of c-type cytochrome cyc2 iron oxidation genes in co-occurring marine Betaproteobacteria and Zetaproteobacteria implies an overlap in niches of these iron-oxidizers. Functional enrichment analyses reveal genetic differences between marine MAGs of both iron-oxidizing groups and their terrestrial aquatic counterparts linked to salinity adaptation. Though scanning electron microscopy confirms the presence of Fe(III) oxyhydroxide stalks where Gallionella and Mariprofundus co-occur, Gallionella MAGs from hydrothermal vents lack evidence of putative stalk formation genes. Mariprofundus is therefore the likely sole stalk-producing iron-oxidizer in this environment. Conversely, the discovery of putative stalk formation genes in Mariprofundus MAGs across the marine-freshwater barrier suggests that Fe(III) oxyhydroxide stalks might not be an exclusive signature for single iron-oxidizing taxa in marine and freshwater environments. Our research provides novel insights into the iron-oxidizing capacities, stalk production, environmental adaptation, and evolutionary transitions between marine and freshwater habitats for Gallionella and Zetaproteobacteria.IMPORTANCEIron-oxidizing bacteria (FeOB) play an important role in the global cycling of iron, carbon, and other metals. While it has previously been assumed that bacterial evolution does not frequently involve crossing the salinity barrier, recent studies indicate that such occurrences are more common than previously thought. Our study offers strong evidence that this also happens among FeOB, with new insights into how these bacteria adapt to the new environment, including hydrothermal vents and freshwater habitats. In addition, we emphasize the importance of accurate iron-oxidizing taxa identification through sequencing, rather than relying solely on the morphology of Fe(III) oxyhydroxides and environment. On a larger scale, microorganisms within established communities need to respond to changes in salinity due to events like seawater intrusion in coastal aquifers, and thus, our findings underscore the importance of knowledge of transitions across habitat types with different salt concentrations.

The Axarquía region in southern Spain, a hotspot of avocado and mango production in Europe, underwent an extreme water crisis in 2019-2024. Reservoir levels dropped below the 8% outlet threshold and groundwater in the main aquifer dropped to sea level in several locations, risking seawater intrusion. Socioeconomic impacts ranged from substantial crop losses to a potential long-term decline in regional economic viability. We examine the main drivers of this crisis using a coupled human and natural systems approach, combining an examination of water and land governance with analysis of time series (dam inflows and outflows, meteorological variables, reservoir, and groundwater levels) and spatial data (irrigated land use, groundwater bodies, water entitlement location, and volume). Our results show two severe meteorological droughts in close succession immediately preceding rapid declines in reservoir and groundwater reserves. Emergency measures delayed dam depletion but likely exacerbated groundwater extraction. Reservoir data disaggregating inflows, outflows, and uses (irrigation and urban) show an increasing trend in dam water use for irrigation in 2000-2022 associated with increasing irrigated area. Water management planning since 1998 reveals important inconsistencies within and between plans pointing to large uncertainties in freshwater availability and extraction and aquifer overdraft even during nondrought periods. The Axarquía case exhibits many symptoms of water crises faced by agriculturally significant regions globally. It highlights the necessity for integrated basin-scale land-water management, caps on irrigated area, flexible extraction quotas, real-time metering at all extraction points, and effective enforcement mechanisms, substantiating management lessons derived from major drought-affected regions worldwide.

Abstract Groundwater governance is a challenge in most arid and semi-arid areas of the world. In many aquifers groundwater extractions exceed natural recharge, leading to steady aquifer declines with negative consequences for the social, agricultural and ecological systems that depend on these aquifers. In this article we analyze how in the semi-arid La Mancha Eastern Aquifer, Spain, organized groundwater users -in close collaboration with knowledge institutes and water authorities- have developed a governance system that ensures aquifer sustainability. Our analysis shows that the use of tempo-spatially explicit data generated through remote sensing technologies co-evolved with the development of a user based groundwater management institution, and a state agency support framework into an effective co-governance approach for regulating groundwater use in the agricultural sector. The research highlights the importance of socio-technical co-creation for the establishment of effective groundwater governance systems that build on -and are embedded in- user-based organizations that are supported by an enabling institutional environment.

Abstract Towed and moored ADCP and salinity measurements were collected in Summer 2023 at two cross-channel transects of the 80-km-long Guadiana Estuary, at 4 km and 20 km from the mouth, during low (< 10 m3/s) river discharge conditions. The dataset indicates that the lateral structure of axial residual flows changed from vertically sheared to laterally sheared with tidal forcing. These structures resemble theoretical expectations for a density-driven or eddy viscosity-shear covariance (ESCO) circulation at neap tide and for a tidally driven circulation produced by longitudinal advection (tidal stress) at spring tide. The tidal variability of the residual flow magnitude and of the contributions of unidirectional or two-layer vertical profiles indicate that the primary driver of the residual circulation changes between neap tide and spring tide. Seawater (i.e. with salinity > 35 kg/g) intrusion was several kilometres, equivalent to ~ 1/8 of the estuary’s length. As a result, the horizontal density gradient was weakest near the mouth where the residual circulation was barotropic, produced by tidal stress at spring tide and possibly by an ESCO mechanism at neap tide. At 20 km upstream, the dominant driver switched from tidal stress at spring tide to a baroclinic (and potentially ESCO) circulation at neap tide. At this location, scaling analyses of the tidally averaged momentum equation using the densimetric tidal Froude number supported the idea of dominance of tidal stress at spring tide.

Seawater intrusion changes the chemical composition of fresh water in coastal groundwater and surface water sources, leading to the formation of additional brominated and iodinated disinfection byproducts (DBPs) in drinking water. In this study, impact of seawater intrusion on trihalomethanes (THMs) and haloacetic acids (HAAs) concentrations was assessed through mixing 0.0 to 2.0% seawater (SW) to groundwater (GW). Human exposure and risks were predicted for selected DBPs, which were then used to estimate the loss of disability-adjusted life years (DALY). The initial concentrations of bromide and iodide ions in GW without seawater were 42.5µg/L and non-detectable (ND), respectively. For 2.0% SW, the concentrations were increased up to 1100 and 2.1µg/L respectively. For 0.0% SW, averages of regulated THMs, HAAs and iodinated THMs (I-THMs) were 30.4, 27.9 and 0.13µg/L respectively while these concentrations were 106.3, 72.9 and 1.6µg/L in the samples with 2.0% SW respectively. From 0.0% to 2.0% SW, bromoform (TBM) and iodoform levels were increased up to 94.3 and 1.02µg/L respectively. For HAAs, tribromoacetic acid was increased from 2.0 to 43.7µg/L. The overall cancer risk from selected DBPs was 3.09 × 10⁻5 for 0.0% SW, while at 1.0% and 2.0% SW, the risks were 4.88 × 10⁻5 and 4.11 × 10⁻5 respectively. The loss of DALY was increased for up to 1.0%SW (77.30 at 0.0%SW and 122.0 at 1.0%SW), which was decreased to 102.8 at 2.0%SW. Future study is warranted to better control emerging DBPs in the coastal regions.

ABSTRACT Coastal cities have become the hotspots for climate migrants, leading to unplanned urbanization and further increasing the vulnerability and risk of climate change. The study assessed the vulnerability and risk index in 22 urbanizing cities in 10 coastal districts following the IPCC AR5 framework and the Analytical Hierarchy Process (AHP) approach. Field investigation, Key Informant Interviews (KIIs), and Focused Group Discussions (FGDs) identified key natural and physical stressors. The main sources of vulnerability include riverbank erosion, storm surge, salinity intrusion, waterlogging, weak infrastructure, and water scarcity. The main concern regarding natural and physical vulnerability stress is waterlogging, which is exacerbated by inadequate drainage, solid waste dumping, canal siltation, and urban planning deficiencies. Critical infrastructure, including drains, canals, sluice gates, and roads, is deteriorating, compounding risks. Climate variability, extreme heat, erratic rainfall, and drought further threaten livelihoods, agriculture, and food security. Among 22 coastal cities, Chalna, Morrelganj, Kalaroa, Char Fasson, Kuakata, Lalmohan, Burhanuddin, Paikgachha, and Patharghata are highly vulnerable, with risks projected to escalate. Adaptation priorities include securing drinking water, canal dredging, restoring connectivity, strengthening sluice gates, improving drainage, waste management, and preserving forests. The findings provide critical guidance for prioritizing the National Adaptation Plan (NAP) implementation in coastal Bangladesh.

Tidal pumping controls transport of foodborne microbial pathogens between coastal groundwater and seawater.

Rapid growth of thermophilic bacteria during a high-temperature aquifer thermal energy storage (HT-ATES) field experiment.

This study investigates saltwater intrusion (SWI) dynamics in the Biscayne aquifer, which includes two scenarios (1) simulation scenarios were developed using SEAWAT to assess the aquifer’s response to sea level rise (SLR) and tidal fluctuation-induced pressure waves at the base case (before using seawall) and (2) using seawall intervention to mitigate SWI and SLR flooding. SLR projections were modeled using boundary conditions informed by National Oceanic and Atmospheric Administration (NOAA) and The Intergovernmental Panel on Climate Change (IPCC) data, revealing progressive SWI advancement up to 8900 m intrusion under +2.62 m SLR compared to the baseline where the SWI extent was 7950 m. Tidal impacts, modeled using observed Broward County tidal ranges and an amplified sinusoidal (SIN) wave, showed intrusion length up to 8750 m for the tidal fluctuations value of +2.31 m. Seawall height requirements to manage overtopping were calculated using empirical wave run-up models, indicating a minimum design height of 7.5 m to resist a worst-case SLR of +2.62 m and maximum tide of +2.31 m. The findings underscore the importance of adaptive coastal management, integrating engineering solutions with hydrogeologic and ecological considerations.

This study investigates the effect of seawater moisture content on the resistivity of unconsolidated sand in the coastal region of Yogyakarta. Laboratory experiments were conducted using a standard ASTM G-57 soil box with samples prepared at varying percentages of seawater moisture content. The results indicate that increasing seawater content in the sediment medium leads to an exponential decrease in resistivity. A mathematical relationship was established in the form of a power function: R=1145.7MC?2.23. Resistivity values tend to stabilize when the moisture content exceeds 13%. A resistivity range of 0.8–2.8 ??m is proposed as a cut-off for identifying seawater intrusion in coastal areas. These findings provide an important contribution to the development of geoelectrical methods for monitoring seawater intrusion and evaluating groundwater quality in coastal regions, which can serve as a basis for sustainable water resource management.

Understanding regional groundwater characteristics is an important aspect for sustainability. The Indian subcontinent is one of the critical regions because of the high population and rapid developmental activities where the groundwater potential plays a crucial role in meeting the water demands for agriculture, domestic, and industrial purposes. Here we evaluate the characteristics of the major aquifer systems in the Indian subcontinent and divide these into three distinct types viz. sedimentary aquifers comprising 48%, followed by metamorphic crystalline aquifers 32% and igneous crystalline aquifers at 20%. In 2023, India extracted 241.34 BCM of groundwater though all these aquifers, representing approximately 59.26% of the nation's annual extractable groundwater resource. Severe over-exploitation of groundwater is observed in sedimentary aquifers of the Indo-Gangetic alluvial system, notably in Haryana, Punjab, Rajasthan, and Delhi, whereas significant over-exploitation in metamorphic crystalline aquifers is reported of Tamil Nadu and Karnataka, particularly in cities such as Bangalore and Chennai. Nevertheless, most assessment units are categorized as 'safe,' offering ample opportunity for sustainable groundwater development. Our review shows that 87% of India's groundwater is extracted annually primarily for irrigation purposes. We observe substantial disparities in the distribution and extraction of groundwater for irrigation across the country, exacerbated by increasing water shortages linked to rising temperatures. These findings underscore the urgent need for building efficient irrigation systems in mitigating climate-induced threats. Therefore, to align with the UN Sustainable Development Goals (SDG-6,13 and 15) and safeguard India's productive aquifer units, it is essential to implement managed aquifer recharge schemes across the country.

The study assesses the water crisis and its management in the climate-vulnerable coastal areas of Bangladesh, focusing on household, agriculture, and aquaculture water risks. Coastal areas like Assasuni (Satkhira) and Moheshkhali (Cox’s Bazar) face severe water insecurity due to salinity intrusion, seasonal variability, and inadequate infrastructure. Household water risks are linked to contamination, high costs, and the disproportionate burden on women for water collection. Rainwater harvesting, pond water, purchased water, and tubewells serve as primary sources, but their availability and quality fluctuate with the seasons, especially during cyclones and floods. In agriculture, dependence on climate-sensitive water sources leaves crop production and livestock vulnerable to salinity intrusion, erratic rainfall, and weak irrigation systems. Similarly, aquaculture in both regions faces challenges from saltwater intrusion, poor water control, and infrastructure damage, with limited institutional support for adaptation. The study identifies key water management issues, including fragmented governance, poor infrastructure maintenance, and limited access to climate-resilient technologies. Coping strategies, such as water rationing and the use of salt-tolerant species, are insufficient to address the scale of the water risks. The findings emphasize the need for integrated water resource management, better infrastructure, improved governance, and community-based solutions. Gender-sensitive interventions and strengthening institutional capacities are crucial to ensure long-term water security and resilience for the affected coastal communities.

Purpose The Vietnamese Mekong Delta (VMD), a vital agricultural region supporting millions, faces severe environmental threats from interacting anthropogenic pressures and climate change, profoundly altering its hydrology. A comprehensive, quantitative understanding of recent water level changes is lacking. This study aims to identify and quantify changes in annual flood peaks and key tidal water level characteristics (1980–2024), analyzing the combined drivers. Design/methodology/approach This paper analyzed long-term (1980–2024) daily/hourly water level records from strategic hydrometric stations. Time series analysis, including low-pass filtering and Mann–Kendall/Sen’s slope tests, identified significant changes in annual flood peaks, mean water levels (MWLs) and tidal range (TR). Findings Analysis reveals significant upstream flood peak decline (especially post-2010s, linked to hydropower). MWL decreased upstream post-2000 but rose substantially mid-delta/coastally, amplified beyond regional relative sea level rise by local factors. Most stations show marked lower low water decreases alongside significant TR increases, indicating enhanced tidal propagation and amplification, more pronounced along the Tien River than the Hau River. Originality/value This paper offers a quantitative, spatiotemporal assessment connecting flood and tidal regime changes to the interplay of multiple drivers during accelerating environmental change. It highlights escalating risks—reduced freshwater availability, increased tidal inundation, heightened salinity intrusion—providing crucial insights for developing robust water resource management and climate adaptation strategies essential for the VMD’s sustainability.

Integrating opinion dynamics and differential game modeling for sustainable groundwater management.

River inflow and seawater intrusion shape distinct phytoplankton communities in jinghai bay, a coastal bay of the Yellow Sea.

ABSTRACT Seawater intrusion into freshwater aquifers occurs mainly in coastal areas due to the excessive groundwater extraction, lowering the water table. In north-eastern Algeria, seawater intrusion exerts a significant influence on the coastal aquifers of Annaba and Guerbes, leading to highly variable and generally elevated salinity levels. Electrical conductivity in inspected regions ranges from 0.2 to 15 mS·cm−1, with an average of 1.9 mS·cm−1. Annaba aquifers have the highest conductivities in the plain areas near the Mediterranean Sea and along the rivers draining the plain. Conversely, the Guerbes aquifer displays a different pattern, with lower conductivities in the inner zones that increase along the streams toward the coast. Chemical analyses of water samples indicate that sodium chloride and calcium chloride facies are predominant. The concentrations of chemical trace elements (Sr2+, Li+, Br−) and major ions were analyzed to elucidate the salinity behavior of these coastal aquifers. The findings suggest that the mineralization of groundwater in the Annaba and Guerbes aquifers is influenced by four primary sources: dissolution–precipitation processes of aquifer rocks, the upward movement of saline deep water in fault zones, infiltration of irrigation water, and marine influences, including seawater intrusion, aerosols, and sea spray.

Decoding nutrient dynamics in coastal aquifers: Machine learning insights into submarine groundwater discharge and seawater intrusion in south India.

A hybrid approach for identifying the seasonal variation of groundwater quality, source apportionment and health risk in a coastal area driven by natural and anthropogenic factors.

Potential source of CO2 emissions to the atmosphere from groundwater use in the Republic of Korea.

Abstract Semarang City, located in the lowlands area of Central Java Province, is densely populated. This will certainly have an impact on the carrying capacity of the land as a place to live, including the need for water consumption in the form of groundwater extraction for household or industrial needs. Continuous groundwater withdrawal will result in continuous land subsidence. This study is intent to searching how much settlement were currently occurred because of soil consolidation, and how much will occur because of soil consolidation and ground water extraction. The method used in this study is to perform deep well modeling using numerical software to determine the prediction of land subsidence due to soil consolidation and groundwater extraction. The lower Semarang area in this study is divided into two zones, first zone namely the area of Semarang North West at Tugu Subdistrict, and the second zone is at East Semarang Subdistrict. The results of consolidation analysis in Tugu Subdistrict and East Semarang Subdistricts showed that without pumping, the subsidence reached 37.4 cm and 37.3 cm in 3 years or 12.5 cm/year and 12.4 cm/year, respectively. The rate of settlement without pumping is in the range of soil rate settlement measured by Abidin, et all [8]. With pumping, the settlement increased to 33.8 cm/year at Tugu Subdistrict and 38.8 cm/year at East Semarang Subdistrict. The percentage of subsidence relative to the compressible soil thickness ranged from 0.32% to 0.51% without pumping and 0.87% to 1.58% with pumping. Based on the results obtained, it appears that at the study site, the use of pumps can accelerate the consolidation process and increase the rate of land subsidence each year. Along with the development of the area in Semarang City, the use of pumps in the area can increase the rate of soil settlement. To maintain soil settlement in the long term, it is recommended that a better fresh water supply system has to be implemented, so that the use of pumps can be minimized or stopped.