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Grid-Nesting is a common method of local refinement when using structured quadrilateral grid in estuarine models. Nevertheless, various issues need to be improved, such as the Courant-Friedrichs-Lewy (CFL) limitations of external gravity wave and information exchange between two-way nesting grids. Based on the material conservation law, a novel scheme with Implicit, Grid-Nesting Elevation Solution (IGNES) and matched Nesting Boundary Flux Conservation Interpolation (NBFCI) was developed in this paper. The unstructured quadrilateral grid, finite-differencing, estuarine and coastal ocean model (UFDECOM) was update to UFDECOM-i. The gravity wave propagation experiment shows that the IGNES can relax the CFL limitations. Compared to traditional i-j two-direction strip refinement, the new scheme has higher computational efficiency. When the root-mean-square-error of elevation and current velocity increases by less than 0.05% and 0.2%, the calculation time is reduced by 40%. When simulating vortex motion, it overcomes the problem of simulation collapse caused by errors in nested boundaries. When simulating material transport, NBFCI scheme has smaller errors at the nesting boundary compared to quadratic interpolation, the high-order spatial interpolation at the middle temporal level (HSMIT) parabolic interpolation, upwind Advection-Equivalent interpolation, and HSIMT Advection-Equivalent interpolation scheme. The simulation results of the severe saltwater intrusion in the Changjiang Estuary in the late summer and early autumn of 2022 demonstrate that the UFDECOM-i with NBFCI and IGNES has higher computational efficiency and accuracy. [ABSTRACT FROM AUTHOR]

This paper presents a new approach to the spatiotemporal design of groundwater quality monitoring networks for coastal aquifers. A fusion model combines the outputs of several developed simulation models to make estimates more accurate. A modified GALDIT method is used to incorporate the aquifer vulnerability to saltwater intrusion. The value of information (VOI) theory is applied to determine sufficient monitoring wells. The groundwater quality monitoring network is designed by employing a robust decision-making (RDM) approach under different management strategies and economic considerations. This approach incorporates the deep uncertainties of some critical variables, including water level and total dissolved solids (TDS) concentration at the coastline and pumping flow rates of agricultural wells. The new methodology is implemented in the coastal Qom-Kahak aquifer, Iran. The results illustrate that the combination model has significantly improved evaluation criteria compared to individual prediction models. The fusion model results indicate that thirty monitoring wells would be ideal. The RDM-based analyses in the Qom-Kahak aquifer showed that an optimal network with 30 monitoring wells outperforms the current network regarding various criteria, such as VOI and variance of estimation error. The new well configuration also demonstrates a suitable spatial distribution. Given that the current sampling frequencies are unsuitable for areas with varying vulnerabilities, we recommend sampling every 3 months in areas with moderate vulnerabilities and once every three seasons in areas with low vulnerabilities, based on the information transfer index. Finally, a management strategy in which the pumping rate should be less than 60% of the current rate is suggested to prevent saltwater intrusion into the aquifer. [ABSTRACT FROM AUTHOR]

Saltwater intrusion (SWI) is a well‐studied phenomenon that threatens the freshwater supplies of coastal communities around the world. The development and advancement of numerical models has led to improved assessment of the risk of salinization. However, these studies often fail to include the impact of surface waters as potential sources of aquifer salinity and how they may impact SWI. Based on field‐collected data, we developed a regional, variable‐density groundwater model using SEAWAT for east Dover, Delaware. In this location, major users of groundwater from the surficial aquifer are the City of Dover and irrigation for agriculture. Our model includes salinized marshland and tidal streams, along with irrigation and municipal pumping wells. Model scenarios were run for 100 years and included changes in pumping rates and sea‐level rise (SLR). We examined how these drivers of SWI affect the extent and location of salinization in the surficial aquifer by evaluating differences in chloride concentration near surface waters and the subsurface freshwater‐saltwater interface. We found the presence of the marsh inverts the typical freshwater‐saltwater wedge interface and that the edge of the interface did not migrate farther inland. Additionally, we found that tidal streams are the dominant pathways of SWI at our site with salinization from streams being exacerbated by SLR. Our results also show that spatial distribution of pumping affects both the magnitude and extent of salinization, with an increase in concentrated pumping leading to more intensive salinization than a more widely distributed increase of the same total pumping volume. Key Points: Presence of a saltmarsh inverts the freshwater‐saltwater interface in our study locationTidal streams contribute substantially to salinization of inland groundwaterConcentrated pumping led to more intensive salinization than widespread pumping [ABSTRACT FROM AUTHOR]

Saltwater intrusion is a common issue in the Yangtze River estuary (YRE), significantly affecting the nearshore ecological environment and human activities. Using 20 years of runoff data, a high-resolution Finite-Volume Coastal Ocean Model (FVCOM) is constructed to simulate the lower reaches and estuary of the Yangtze River. This model is employed to analyze full-depth current and salinity characteristics and to explore the influence of factors such as runoff, wind, tides, and riverbank morphology on saltwater intrusion in the YRE. The model's accuracy is validated by comparing its output with current speed and salinity observations and comparing long-term salinity variations with reanalysis data. The comparison shows that the model well reproduces the saltwater intrusion in the YRE. Over the long term, the salinity pattern exhibits a "high–low–high" variation. Analyzing the vertical structure of the intrusion, it is observed that during summer, surface waters are heated, resulting in stronger stratification, weaker mixing, and a more pronounced saltwater intrusion in the YRE. Using power spectrum and correlation analyses, runoff is identified as the factor having the greatest impact on saltwater intrusion, followed by meridional wind and changes in riverbank morphology. This study of the variations in long-term saltwater intrusion has important reference value for the protection of freshwater resources in the YRE. [ABSTRACT FROM AUTHOR]

Salt-sensitive trees in coastal wetlands are dying as forests transition to marsh and open water at a rapid pace. Forested wetlands are experiencing repeated saltwater exposure due to the frequency and severity of climatic events, sea-level rise, and human infrastructure expansion. Understanding the diverse responses of trees to saltwater exposure can help identify taxa that may provide early warning signals of salinity stress in forests at broader scales. To isolate the impacts of saltwater exposure on trees, we performed an experiment to investigate the leaf-level physiology of six tree species when exposed to oligohaline and mesohaline treatments. We found that species exposed to 3–6 parts per thousand (ppt) salinity had idiosyncratic responses of plant performance that were species-specific. Saltwater exposure impacted leaf photochemistry and caused early senescence in Acer rubrum, the most salt-sensitive species tested, but did not cause any impacts on plant water use in treatments with <6 ppt. Interestingly, leaf spectral reflectance was correlated with the operating efficiency of photosystem II (PSII) photochemistry in A. rubrum leaves before leaf physiological processes were impacted by salinity treatments. Our results suggest that the timing and frequency of saltwater intrusion events are likely to be more detrimental to wetland tree performance than salinity concentrations. [ABSTRACT FROM AUTHOR]

The shallow Vrana Lake in Dalmatia, Croatia, is directly connected to the Adriatic Sea by the Prosika canal (0.85 km), constructed in the eighteenth century. The aim of this research was to examine the impacts of salinization on long-term changes in littoral macro-crustacean (Malacostraca) populations and assemblages in Vrana Lake and connecting canals. Benthic macroinvertebrates were sampled at seven sites during the period 2011–2020 (14 months) using a hand net (25 × 25 cm, 500 µm). During the study period, saltwater intrusions (strongest in 2012) through the Prosika Canal and site V4 caused increased salinization, resulting in a shift from normal oligohaline (0.5–5 PSU) to mesohaline (5–18 PSU) salinity. Out of a total of 18 macro-crustacean taxa identified, five widespread species—amphipods Echinogammarus stocki and Gammarus aequicauda, isopods Lekanesphaera hookeri and Proasellus coxalis, and decapod Palaemon antennarius constituted 91.6% of collected specimens (26,986). The first three brackish/marine species were significantly positively correlated with the average salinity 12 and 24 months before sampling. They disappeared or had very low abundance during the second low salinity phase (< 1–2 PSU), when freshwater/oligohaline P. coxalis and P. antennarius were the dominant macro-crustaceans. Two years of low salinity were needed for a strong population decline or disappearance of three brackish/marine species. Salinization is a major stressor in the Vrana Lake basin, and measures for its active control are urgently needed. The use of tested macro-crustacean metrics is recommended for future ecological monitoring as it could provide fast information about the effects of water management on aquatic biodiversity. [ABSTRACT FROM AUTHOR]

Desalination plants employing feed water sourced from saline groundwater (SGW) are a feasible approach to tackle freshwater scarcity and seawater intrusion (SWI). Available studies lacked comprehensive analysis quantifying the impact of pumping from a coastal aquifer, on changes in solute transport mechanism. This study investigates the impact of different rates of SGW pumping on the solute transport in a coastal aquifer. A regional-scale model resembling the Upper Floridan aquifer was modelled using SEAWAT to quantify SWI variables. The study found that the length of intrusion of toe (Ltoe), width of mixing zone (WMZ) and residual salt mass (RSM) varied with dispersivity values. The ratio of saltwater to freshwater influx was unaffected by dispersivity values. Significant decrease in the toe-length occurred when the pumping rate was highest and the dispersivity was lowest. The WMZ was found to be the most sensitive SWI variable towards varying dispersivity, with 65% difference for higher pumping rates. The mid-bottom region was experiencing substantial modifications, leading to an inclined response at increased pumping rates, which suggested that the diluting process was primarily taking place in the bottom portion. This study gives insight into saline wedge movement in a coastal aquifer system which will benefit in the design of SGW well system for desalination plants. [ABSTRACT FROM AUTHOR]

Saltwater intrusion occurs frequently in the Yangtze Estuary during winter, when the river discharges are low along with strong wind and waves. However, the influence of wind and waves on saltwater intrusion in the Yangtze Estuary remains unclear. This study uses a coupled wind‐wave‐current numerical model based on Delft3D to investigate the impacts of wind and waves on saltwater intrusion in the Yangtze Estuary. The results show that the strong northerly wind alone enhances saltwater intrusion in the estuary by inducing a counterclockwise circulation and reducing the stratification. However, with the combined effect from wind and waves, it is found that stratification is reduced in the outer North Channel, but enhanced in the inner North Channel, which results in an increase of salt transport in the estuary by approximately 40%. The results highlight the fact that saltwater intrusion in the Yangtze Estuary could be significantly underestimated without considering waves. Plain Language Summary: The effect of wind on saltwater intrusion in estuaries has been widely reported. However, strong wind can generate strong waves, but relatively few studies explore the combined effect of wind and waves on saltwater intrusion. This study uses a strong wind event that occurred in the Yangtze Estuary in 2014 with a coupled computer model to demonstrate such an effect. We found that the peak salt transport can be significantly underestimated without considering waves, as they play an important role in salt transport during strong wind events. Therefore, it is necessary to consider the combined influence from wind and waves in studying saltwater intrusion in estuaries to ensure the safety of the freshwater supply. Key Points: Strong northerly winds have considerable effects on the saltwater intrusion in the Yangtze EstuaryCombined wind and waves effects further increase the estuarine salt transportWave radiation stress enhances the stratification in the North Channel under northerly winds [ABSTRACT FROM AUTHOR]

Saltwater intrusion along rivers is a complex process controlled by multiple factors and thus fluctuates with a highly nonlinear nature and time-varying characteristics. It is challenging to monitor saltwater intrusion. The objective of this study was to clarify the spatial-temporal variation of saltwater intrusion and its potential impact on agriculture in the Po River Delta (Italy). 2006 was the most severe year of saltwater intrusion in the period we considered. 2022 was even worse, but the data are still under processing. In this study, the Hilbert-Huang transform (HHT) and rescaled range (R/S) were used to identify the multi-time scales and change trends of the salinity and discharge in 2006. After that, the time-dependent intrinsic correlation (TDIC) was used to depict intrinsic relationships between salinity and discharge at different time scales. The results showed that discharge and salinity exhibited behaviours of positive long-range correlation during different periods. The temporal series of salinity and discharge was decomposed into six intrinsic mode functions (IMF) and residuals based on the ensemble empirical mode decomposition (EEMD). The sum of variance contribution rates of IMF1 (4 days), IMF2 (10 days), and IMF3 (12.1 days) of salinity was more than 75%. All measured TDICs have highlighted strong correlations between salinity and discharge. Furthermore, we used spatial interpolation techniques to map salinity data along rivers. This allowed the investigation of dynamic changes in saltwater intrusion patterns during periods of severe drought. Outcomes show a significant negative correlation between salinity and normalized difference vegetation index (NDVI), indicating that the study area's agricultural greening was affected by saltwater intrusion.

Accurate prediction of estuarine salinity can effectively mitigate the adverse effects of saltwater intrusion and help ensure the safety of water resources in estuarine regions. Presently, diverse data-driven models, mainly neural network models, have been employed to predict tidal estuarine salinity and obtained considerable achievements. Due to the nonlinear and nonstationary features of estuarine salinity sequences, this paper proposed a multi-factor salinity prediction model using an enhanced Long Short-Term Memory (LSTM) network. To improve prediction accuracy, input variables of the model were determined through Grey Relational Analysis (GRA) combined with estuarine dynamic analysis, and hyperparameters for the LSTM model were optimized using a multi-strategy Improved Sparrow Search Algorithm (ISSA). The proposed ISSA-LSTM model was applied to predict salinity at the Cangqian and Qibao stations in the Qiantang Estuary of China, based on measured data from 2011–2012. The model performance is evaluated by mean absolute error (MAE), mean absolute percentage error (MAPE), root mean square error (RMSE), and Nash-Sutcliffe efficiency (NSE). The results show that compared to other models including Back Propagation neural network (BP), Gate Recurrent Unit (GRU), and LSTM model, the new model has smaller errors and higher prediction accuracy, with NSE improved by 8–32% and other metrics (MAP, MAPE, RMSE) improved by 15–67%. Meanwhile, compared with LSTM optimized with the original SSA (SSA-LSTM), MAE, MAPE, and RMSE values of the new model decreased by 13–16%, 15–16%, and 11–13%, and NSE value increased by 5–6%, indicating that the ISSA has a better hyperparameter optimization ability than the original SSA. Thus, the model provides a practical solution for the rapid and precise prediction of estuarine salinity. [ABSTRACT FROM AUTHOR]

Around 40% of the world's population depends on coastal aquifers for freshwater supply but natural and anthropogenic drivers threaten groundwater availability. Of these drivers, saltwater intrusion (SWI) is one of the most critical and is increasingly affecting coastal areas worldwide. Interest in coastal aquifers has significantly increased, as demonstrated by the growing number of publications in which researchers describe various approaches to illuminate the importance of coastal aquifers, specifically with regard to SWI. The state of research and knowledge of the coastal SWI issue has been reviewed herein. The review includes a discussion of select geophysical and field methods and tools which can inform the numerical modeling of coastal aquifers. MODFLOW was identified as the most often used numerical modeling platform. Further, while many research sites, particularly in the United States, were identified where field studies and geophysical methods, mostly geoelectric ones, added important value to the numerical modeling of the SWI process in the coastal zone, in some regions of the world, data scarcity was identified as the main challenge. Overall, numerical modeling, combined with geophysical methods, is a valuable tool for studying SWI and managing coastal water resources. [ABSTRACT FROM AUTHOR]

Fresh coastal groundwater is a valuable water resource of global significance, but its quality is threatened by saltwater intrusion. Excessive groundwater abstraction, sea‐level rise (SLR), land subsidence and other climate‐related factors are expected to accelerate this process in the future. The objective of this study is to (a) quantify the impact of projected climate change and (b) explore the role of individual hydrogeological boundaries on groundwater salinization of low‐lying coastal groundwater systems until 2100 CE. We employ numerical density‐dependent groundwater flow and salt transport modeling for this purpose, using Northwestern Germany as a case. Separate model variants are constructed and forced with climate data, that is, projected SLR and groundwater recharge, as well as likely ranges of other hydrogeological boundaries, including land subsidence, abstraction rates and drain levels. We find that autonomous salinization in the marsh areas, resulting from non‐equilibrium of the present‐day groundwater salinity distribution with current boundary conditions, is responsible for >50% of the salinization increase until 2100 CE. Sea‐level rise, land subsidence and drain levels are the other major factors controlling salinization. We further show that salinization of the water resources is a potential threat to coastal water users, including water suppliers and the agrarian sector, as well as coastal ecosystems. Regional‐scale uplifting of drain levels is identified as an efficient measure to mitigate salinization of deep and shallow groundwater in the future. The presented modeling approach highlights the consequences of climate change and anthropogenic impacts for coastal salinization, supporting the timely development of mitigation strategies. Plain Language Summary: Our study focuses on fresh groundwater near coastlines, which is crucial for drinking water, agriculture, and natural ecosystems, but is at risk of becoming salty due to mixing with saline groundwater. We investigate how climate change, including sea‐level rise, changing groundwater recharge and subsiding land surfaces, might make this problem worse by 2100 CE. Northwestern Germany, located at the North Sea, is used as a case, and numerical groundwater models are employed to simulate the groundwater development in the study area. We find that the current groundwater salinity distribution is not at equilibrium with present‐day boundary conditions, which is a primary reason for an expected salinity increase by 2100 CE. Rising sea‐levels and the design of the marsh drainage system are other key factors. We show that raising mainland drainage levels would be an effective way to reduce future salinization in both deep and shallow groundwater. The methods applied in this study could help other coastal areas to understand the implications of future groundwater salinization. Key Points: We show that autonomous salinization is a key process driving salinization of low‐lying coastal groundwater systemsWe find that sea‐level rise and land subsidence are other major factors amplifying future groundwater salinizationWe describe how salinization of coastal fresh groundwater impacts different water users [ABSTRACT FROM AUTHOR]

Saltwater intrusion in a coastal region is one of the major issues facing the agricultural, domestic, and industrial sectors. Groundwater withdrawal for an increasing population and agricultural and industrial demands are the main reasons for saltwater intrusion into coastal aquifers. Saltwater intrusion into freshwater aquifers directly affects a population's health, economy, and social development. This study explores an innovative approach to modeling saltwater intrusion into freshwater using a prey–predator model. Freshwater is analogized as the prey and saltwater as the predator, providing a unique perspective on understanding this phenomenon. The present model was formulated using a balance of freshwater and saltwater and is applicable to coastal aquifers. An amount of freshwater withdrawal such that the volume of saltwater does not produce adverse impacts is predicted graphically. Based on a certain simulation, the current model suggests that if the withdrawal rate drops to 50%, freshwater is projected to surpass saltwater dominance for about 90 years. The model has been validated through a benchmark saltwater intrusion problem. [ABSTRACT FROM AUTHOR]

Saltwater intrusion (SWI) is a critical concern affecting coastal groundwater sources due to natural and anthropogenic activities. The health of coastal aquifers is deteriorated by excessive SWI, mainly caused by the disturbance of the freshwater–saltwater equilibrium due to the escalating population, climate change, and the rising demand for freshwater resources for human activities. Therefore, gaining insight into the dynamics of SWI is crucial, particularly concerning the various factors that influence the intrusion mechanism. The present study focuses on the experimental simulation of saltwater in freshwater aquifers, considering boundary conditions and density-dependent effects. Two geological scenarios within coastal environments were investigated: First, a uniform, homogeneous case consisting of only sand, and second, a heterogeneous case in which layers of sand, clay, and sand mixed with pebbles are used. During the experiment, DC resistivity sounding data, as part of a widely recognized geophysical method, were collected and subsequently inverted to determine the depth of the freshwater–saltwater interface (FSWI). A finite element analysis was employed to generate numerical models based on experimental feedback. Further, for validation purposes, electrical resistivity tomography (ERT) data were collected from two distinct locations: near the seacoast and an aquaculture area. The ERT results show the presence of salinity intrusion in the study area, attributed mainly to groundwater overpumping and fish farming practices. The experimental findings indicate that the advancement of saltwater is affected by the geological properties of the media they traverse. The porosity (ϕ) and permeability (k) of the geological layer play a crucial role during the passage of saltwater flux into freshwater aquifers. The FSWI deviated along the clay boundary and hindered the easy passage of saltwater into surrounding layers. The alignment of experimental, numerical, and geophysical data suggests that this integrated approach could be valuable for studying SWI and can be applied in different geological settings, including tidal flats and alluvial plains. [ABSTRACT FROM AUTHOR]

Saltwater intrusion poses severe threats to rice farming in Vietnam. Farmers can adapt by producing other crops or switching to other production models. This study evaluates the impact of implementing different saltwater-intrusion-adaptation strategies on farmers' livelihoods by applying propensity score matching to cross-sectional survey data for 414 farmers in the Central Coastal region of Vietnam. We consider both economic and social indicators and find that there is considerable heterogeneity in the outcomes. With the exception of switching to new rice varieties, all adaptation strategies considered in the study significantly increase saline-land productivity, mainly as a result of higher revenues. Moreover, for these strategies, food security is found to be significantly higher, whereas life satisfaction is only higher for those farm households that cultivate vegetables, shrimp, or lotus-fish. Adopting new rice varieties is found to significantly decrease saline-land productivity, whereas the social impacts are not significant. [ABSTRACT FROM AUTHOR]

Tidal freshwater forests are usually located at or above the level of mean high water. Some Louisiana coastal forests are below mean high water, especially bald cypress (Taxodium distichum (L.) Rich.) forests because flooding has increased due to the combined effects of global sea level rise and local subsidence. In addition, constructed channels from the coast inland act as conduits for saltwater. As a result, saltwater intrusion affects the productivity of Louisiana's coastal bald cypress forests. To study the long-term effects of hydrology and salinity on the health of these systems, we fitted dendrometer bands on selected trees to record basal area increment as a measure of growth in permanent forest productivity plots established within six bald cypress stands. Three stands were in freshwater sites with low salinity rooting zone groundwater (0.1–1.3 ppt), while the other three had higher salinity rooting zone groundwater (0.2–4.9 ppt). Water level was logged continuously, and salinity was measured monthly to quarterly on the surface and in groundwater wells. Higher groundwater salinity levels were related to decreased bald cypress radial growth, while higher freshwater flooding increased radial growth. With these data, coastal managers can model rates of bald cypress forest change as a function of salinity and flooding. [ABSTRACT FROM AUTHOR]

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Groundwater is widely regarded as being among the freshwater natural resources with the lowest levels of contamination. Nevertheless, the saltwater intrusion has resulted in the contamination of groundwater in coastal regions with lower elevation. The rationale of the present work is to investigate the chemistry of groundwater, to identify the various facies of groundwater, to identify the processes that influence groundwater chemistry and saltwater intrusion, and to evaluate the groundwater's aptness for use in drinking and farming. In order to gain an understanding of the groundwater quality as well as the salinization process that occurs in coastal aquifers as a result of hydrogeochemical processes, a total of 108 groundwater samples (54 each in pre- and post-monsoon) were taken and analyzed for several physiochemical parameters in the southern part of the Puri district in the Indian state of Odisha. The data has undergone analysis and examination to identify the factors (such as hydrological facies, potential solute source in water, and salinization process) that contribute to groundwater salinity. The result showed the chemistry controlling processes of rock-water interaction as per Gibbs diagram. The majority of shallow aquifers exhibit the Na-Cl type of facies as per the Piper plot. A total of 37% pre-monsoon and 33% post-monsoon samples having Na+/Cl− ratio below the threshold of 0.86 indicating the influence of saltwater intrusion. In both seasons, it was observed that 74% of the samples exhibited a Na+ concentration that exceeded the permissible limit set by the World Health Organization (WHO) for drinking purposes. The findings indicate that most groundwater failed to pass safe drinking water and irrigation standards due to saltwater intrusion. Consequently, the monitoring of coastal aquifer quality has become imperative in order to ensure the sustainability of aquifers and the development of groundwater resources. This is because coastal aquifers are highly vulnerable to saltwater intrusion, primarily as a result of the extensive extraction of groundwater for diverse purposes. [ABSTRACT FROM AUTHOR]

This study analyzes the factors that influence the choice of saltwater intrusion adaptation strategies of farmers living in Vietnam's Central Coastal region, using a multinomial choice model fitted to data from a cross-sectional survey of 414 farmers. The adaptation strategies identified include cultivating new varieties of rice or switching to papyrus planting, vegetable planting, shrimp production, or lotus--fish production. The results reveal that family size decreases the likelihood of applying new varieties of rice and plant papyrus but increases the probability of applying shrimp production. The level of education of the household's head negatively impacts the probability of switching to new varieties of rice and shrimp production but positively affects the odds of implementing papyrus and vegetable production. The older, more experienced farmers are more likely to cultivate new varieties of rice. Regarding the farm's characteristics, the higher the percentage of salted land and the less serious the saltwater intrusion level, the higher the probability of switching to shrimp or lotus--fish production. Access to information from the local authorities, taking part in training courses, and being a member of Vietnamese Women Union all promote adaptation to saltwater intrusion. From a policy perspective, we recommend that the government develop official media channels to promote saltwater intrusion adaptation, organize more training courses for farmers, support the activities of the Woman Union, and relax constraints on accessing public credit. [ABSTRACT FROM AUTHOR]

Rising sea levels lead to the migration of salt marshes into coastal forests, thereby shifting both ecosystem composition and function. In this study, we investigate leaf litter decomposition, a critical component of forest carbon cycling, across the marsh-forest boundary with a focus on the potential influence of environmental gradients (i.e., temperature, light, moisture, salinity, and oxygen) on decomposition rates. To examine litter decomposition across these potentially competing co-occurring environmental gradients, we deployed litterbags within distinct forest health communities along the marsh-forest continuum and monitored decomposition rates over 6 months. Our results revealed that while the burial depth of litter enhanced decomposition within any individual forest zone by approximately 60% (decay rate = 0.272 ± 0.029 yr−1 (surface), 0.450 ± 0.039 yr−1 (buried)), we observed limited changes in decomposition rates across the marsh-forest boundary with only slightly enhanced decomposition in mid-forest soils that are being newly impacted by saltwater intrusion and shrub encroachment. The absence of linear changes in decomposition rates indicates non-linear interactions between the observed environmental gradients that maintain a consistent net rate of decomposition across the marsh-forest boundary. However, despite similar decomposition rates across the boundary, the accumulated soil litter layer disappears because leaf litter influx decreases from the absence of mature trees. Our finding that environmental gradients counteract expected decomposition trends could inform carbon-climate model projections and may be indicative of decomposition dynamics present in other transitioning ecosystem boundaries. [ABSTRACT FROM AUTHOR]

During summer and fall 2023, Louisiana experienced a historic local drought while dry conditions elsewhere in the central US withheld vital runoff from the Mississippi River, leading to below‐normal discharge into the Gulf of Mexico. Thus, by late October 2023, Louisiana was gripped by two super‐imposed water crises: a severe local drought and saltwater contamination in the Mississippi River channel. This study frames the development of the water emergency through the lens of flash drought using the Evaporative Demand Drought Index (EDDI). The EDDI shows south Louisiana experience a flash drought during June 2023, while the Mississippi River basin was subsequently characterized by large expanses of high‐percentile EDDI in August‐September 2023 shortly before the saltwater intrusion episode along the lower Mississippi River. Over the last 15 years, MRB‐wide EDDI percentile has oscillated between years‐long elevated and depressed states, accounting for 23.7% of the monthly discharge anomaly near New Orleans. Plain Language Summary: In 2023, Louisiana experienced one of its driest and hottest summers on record. While drought developed across the state, rain shortfalls further north led to low water levels in the Mississippi River, a major navigation corridor and drinking water source for the state. As river levels fell, seawater moved into the channel, threatening to contaminate the water supply with salt. The statewide drought, particularly in coastal Louisiana, is shown to have developed rapidly during June 2023 through a process called flash drought. Meanwhile, high evaporation rates and low rainfall upriver exacerbated Louisiana's water shortage by limiting runoff into the Mississippi River. Over the last 15 years, evaporative demand over the Mississippi River watershed varies closely with river discharge near New Orleans, and even corresponds to river conditions more closely than rainfall itself. Key Points: Louisiana experienced 5 months of exceptional evaporative demand and low precipitation, including a flash drought during June 2023Historically low flows on the lower Mississippi River in fall 2023 were accompanied by several episodes of high evaporative demand upbasinBasin‐wide high evaporative demand coincides with low discharge near New Orleans, with a trend toward this combination since the 2019 flood [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

The paleochannels in coastal areas may be the priority channels for saltwater intrusion, and identifying paleochannels is important for revealing the pollution mechanisms of coastal zone aquifers and protecting groundwater resources. The use of electrical methods to identify paleochannels has become common. Still, the highly dynamic hydrological characteristics of saltwater intrusion area and the differences in the conductive properties of saltwater and freshwater increase the uncertainty of the interpretation process. This study combined groundwater numerical simulation data, hydrochemical data and stratigraphic data to construct an electrical model of the paleochannel, which provides a reference for the interpretation of paleochannel using ERT data. The paleochannel electrical model constructed by combining multiple sources of data reflects the spatial heterogeneity of resistivity values of paleochannel in different seasons and at varying levels of saltwater intrusion, making the identification of paleochannel in saltwater intrusion areas more accurate. The results show that the paleochannel shows high resistivity anomalies relative to the background stratigraphy in brackish water areas, and low resistivity anomalies relative to the background stratigraphy in freshwater areas. Combining the paleochannel forward model with ERT data can effectively identify the paleochannel in saltwater intrusion areas. [ABSTRACT FROM AUTHOR]

Copyright of Advances in Earth Science (1001-8166) is the property of Advances in Earth Science Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

"Ghost cypress"—standing trees killed by increased salinity—indicate sea-level rise (SLR) effects along lower reaches of many coastal plain rivers. Mature cypress can survive indefinitely in permanently flooded sites, but experience mortality at salinities as low as 2 to 3 ppt. Thus, ghost trees in permanently inundated sites can indicate mortality due to increased salinity. Ghost cypress were mapped along the margins of the Neuse River estuary and fluvial-estuarine transition zone (FETZ), along with co-indicators of salinity as a potential cause of death. The distribution was compared with other indicators of upstream propagation of SLR effects; all occurred within a 25 km river reach. Many ghost cypress are consistent with SLR-driven mortality, but in the upper FETZ the co-indicators argue against it, and throughout the study area some ghost cypress lack co-indicators of salinity effects and may have been killed by other factors. The upstream limit of ghost cypress with co-indicators suggesting possible SLR-driven mortality, and the downstream limit of Nyssa aquatica and N. biflora, whose habitats and niches overlap almost entirely with Taxodium except for less salinity tolerance, occur downstream of other indicators of the leading edge of SLR. The furthest upstream is the hydraulic impact of backwater effects on river flow. Downstream, other effects are encountered: a transition from occasionally to frequently flooded wetlands, sedimentary burial of Pleistocene alluvial terraces, and a shift from dominantly mineral floodplain soils to Histosols. The ecological indicators of cypress and tupelo are furthest downstream. Hydraulic (backwater) effects are the leading edge of SLR impacts on the Neuse, trailed by geomorphological, sedimentological, and pedological indicators. Though biota often respond more rapidly to changes than landforms and soils, ecological indicators such as ghost cypress and forest-to-marsh transitions that are salinity dependent are the downstream-most sentinels of sea-level encroachment in rivers. [ABSTRACT FROM AUTHOR]

Understanding the subsurface is of prime importance for many geological and hydrogeological applications. Geophysical methods offer an economical alternative for investigating the subsurface compared to costly borehole investigations. However, geophysical results are commonly obtained through deterministic inversion of data whose solution is non-unique. Alternatively, stochastic inversions investigate the full uncertainty range of the obtained models, yet are computationally more expensive. In this research, we investigate the robustness of the recently introduced Bayesian evidential learning in one dimension (BEL1D) for the stochastic inversion of time-domain electromagnetic data (TDEM). First, we analyse the impact of the accuracy of the numerical forward solver on the posterior distribution, and derive a compromise between accuracy and computational time. We also introduce a threshold-rejection method based on the data misfit after the first iteration, circumventing the need for further BEL1D iterations. Moreover, we analyse the impact of the prior-model space on the results. We apply the new BEL1D with a threshold approach on field data collected in the Luy River catchment (Vietnam) to delineate saltwater intrusions. Our results show that the proper selection of time and space discretization is essential for limiting the computational cost while maintaining the accuracy of the posterior estimation. The selection of the prior distribution has a direct impact on fitting the observed data and is crucial for a realistic uncertainty quantification. The application of BEL1D for stochastic TDEM inversion is an efficient approach, as it allows us to estimate the uncertainty at a limited cost. [ABSTRACT FROM AUTHOR]

Groundwater is one of the most important sources of drinking, industrial, and agricultural water in arid and semi-arid regions, where the occurrence of droughts, rapid population growth, and the corresponding increase in water demand threaten groundwater resources. Over-exploitation and mismanagement of groundwater resources result in environmental problems such as subsidence and saltwater intrusion in coastal aquifers. The risk of saltwater intrusion threatens the Urmia aquifer due to the proximity of the aquifer to Lake Urmia and severe groundwater decline. This study evaluates the vulnerability of saltwater intrusion by the GALDIT framework. The results show the conservative vulnerability index with low efficiency, where vulnerable areas are limited to a narrow strip near the coastline. Fuzzy membership functions were employed within the GALDIT framework to increase efficiency. The results of the modified GALDIT resolve the weakness of presenting conservative results in the basic GALDIT framework. [ABSTRACT FROM AUTHOR]

Estuarine reservoirs are critical for freshwater supply and security, especially for regions facing water scarcity challenges due to climate change and population growth. Conventional methods for assessing drought severity or monitoring reservoir water level and storage are often limited by data availability, accessibility and quality. We present an approach for monitoring estuarine reservoir water levels, storage and extreme drought via satellite remote sensing and waterline detection. Based on the CoastSat algorithm, Landsat-8 and Sentinel-2 images from 2013 to 2022 were adopted to extract the waterline of Qingcaosha Reservoir, the largest estuarine reservoir in the world and a key source of freshwater for Shanghai, China. This study confirmed the accuracy of the satellite-extracted results through two main methods: (1) calculating the angle of the central shoal slope in the reservoir using the extracted waterline data and measured water levels and (2) inverting the time series of water levels for comparison with measured data. The correlation coefficient of the estimated water level reached ~0.86, and the root mean square error (RMSE) of the estimated shoal slope was ~0.2°, indicating that the approach had high accuracy and reliability. We analyzed the temporal and spatial patterns of waterline changes and identified two dates (21 February 2014 and 15 October 2022) when the reservoir reached the lowest water levels, coinciding with periods of severe saltwater intrusions in the estuary. The extreme drought occurrences in the Qingcaosha Reservoir were firstly documented through the utilization of remote sensing data. The results also indicate a strong resilience of the Qingcaosha Reservoir and demonstrate that the feasibility and utility of using satellite remote sensing and waterline detection for estuarine reservoir storage can provide timely and accurate information for water resource assessment, management and planning. [ABSTRACT FROM AUTHOR]

The Pearl River Estuary (PRE) frequently experiences the impacts of typhoons, storm surges, and saltwater intrusion. While previous research has mainly focused on saltwater intrusion during the dry season, there is limited research on saltwater intrusion caused by storm surges in the PRE. In this study, we systematically investigate the effects of ten typical autumnal typhoons and associated storm surges on saltwater intrusion in the Modaomen Waterway using in situ data of water level, river discharge, and chloride concentrations from 2006 to 2022. We introduce the concept of Storm surge-Induced Salinity Augmentation (SISA) and analyze its characteristics and primary influencing factors. Our findings reveal that SISA primarily occurs in autumn, with reduced upstream river discharge and the dominance of high-salinity water in the estuary. SISA occurs immediately after storm surges and grows rapidly and violently, with a time lag of 2–4 h, but rapidly recedes after the typhoon passage due to heavy rainfall and high freshwater discharge. Typhoons with a westward trajectory have a greater influence, and the southeastern winds outside the estuary during typhoon events are the primary factors determining the intensity of SISA. Pre-typhoon river discharge affects the range and duration of saltwater intrusion. Moreover, the coupling effect of extreme river dryness, spring tide, and storm surges significantly enhances saltwater intrusion. Further research is needed to quantify the spatiotemporal characteristics of SISA accurately. [ABSTRACT FROM AUTHOR]

Copyright of Pearl River is the property of Pearl River Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Abstract Fresh coastal groundwater is a valuable water resource of global significance, but its quality is threatened by saltwater intrusion. Excessive groundwater abstraction, sea‐level rise (SLR), land subsidence and other climate‐related factors are expected to accelerate this process in the future. The objective of this study is to (a) quantify the impact of projected climate change and (b) explore the role of individual hydrogeological boundaries on groundwater salinization of low‐lying coastal groundwater systems until 2100 CE. We employ numerical density‐dependent groundwater flow and salt transport modeling for this purpose, using Northwestern Germany as a case. Separate model variants are constructed and forced with climate data, that is, projected SLR and groundwater recharge, as well as likely ranges of other hydrogeological boundaries, including land subsidence, abstraction rates and drain levels. We find that autonomous salinization in the marsh areas, resulting from non‐equilibrium of the present‐day groundwater salinity distribution with current boundary conditions, is responsible for >50% of the salinization increase until 2100 CE. Sea‐level rise, land subsidence and drain levels are the other major factors controlling salinization. We further show that salinization of the water resources is a potential threat to coastal water users, including water suppliers and the agrarian sector, as well as coastal ecosystems. Regional‐scale uplifting of drain levels is identified as an efficient measure to mitigate salinization of deep and shallow groundwater in the future. The presented modeling approach highlights the consequences of climate change and anthropogenic impacts for coastal salinization, supporting the timely development of mitigation strategies.

This study investigates groundwater resources in the El-Omayed area on the northwestern coast of Egypt. The aim is to assess the extent and severity of saltwater intrusion in the shallow aquifer system, as well as its potential impacts on groundwater resources. A combined geophysical and hydrochemical approach was adopted in this investigation. Across the study area, 32 vertical electrical soundings were conducted, along with two electrical resistivity tomography profiles. Sixteen water samples were collected, and then chemically analyzed to evaluate water quality, seawater intrusion, and source of salinity. The results of geophysical interpretation revealed the existence of a thin, shallow freshwater-bearing layer (42–95 Ω.m), predominantly situated in the central parts of the area, followed by saltwater saturated layers of (0.9–2.1 Ω.m) affected by the Mediterranean Sea invasion. The eastern portion of the aquifer also recorded a relatively high seawater intrusion. As evidenced by the actual data gathered from drilled wells, the study area can be divided into three distinct zones: fresh, brackish, and saltwater zones. The study identified the most suitable sites to establish new groundwater wells, in addition to identifying the source of salinity through the investigation of the geochemical properties of water samples.

Saltwater intrusion is a common issue in the Yangtze River estuary (YRE), significantly affecting the nearshore ecological environment and human activities. Using 20 years of runoff data, a high-resolution Finite-Volume Coastal Ocean Model (FVCOM) is constructed to simulate the lower reaches and estuary of the Yangtze River. This model is employed to analyze full-depth current and salinity characteristics and to explore the influence of factors such as runoff, wind, tides, and riverbank morphology on saltwater intrusion in the YRE. The model’s accuracy is validated by comparing its output with current speed and salinity observations and comparing long-term salinity variations with reanalysis data. The comparison shows that the model well reproduces the saltwater intrusion in the YRE. Over the long term, the salinity pattern exhibits a “high–low–high” variation. Analyzing the vertical structure of the intrusion, it is observed that during summer, surface waters are heated, resulting in stronger stratification, weaker mixing, and a more pronounced saltwater intrusion in the YRE. Using power spectrum and correlation analyses, runoff is identified as the factor having the greatest impact on saltwater intrusion, followed by meridional wind and changes in riverbank morphology. This study of the variations in long-term saltwater intrusion has important reference value for the protection of freshwater resources in the YRE.

Salt-sensitive trees in coastal wetlands are dying as forests transition to marsh and open water at a rapid pace. Forested wetlands are experiencing repeated saltwater exposure due to the frequency and severity of climatic events, sea-level rise, and human infrastructure expansion. Understanding the diverse responses of trees to saltwater exposure can help identify taxa that may provide early warning signals of salinity stress in forests at broader scales. To isolate the impacts of saltwater exposure on trees, we performed an experiment to investigate the leaf-level physiology of six tree species when exposed to oligohaline and mesohaline treatments. We found that species exposed to 3–6 parts per thousand (ppt) salinity had idiosyncratic responses of plant performance that were species-specific. Saltwater exposure impacted leaf photochemistry and caused early senescence in Acer rubrum, the most salt-sensitive species tested, but did not cause any impacts on plant water use in treatments with A. rubrum leaves before leaf physiological processes were impacted by salinity treatments. Our results suggest that the timing and frequency of saltwater intrusion events are likely to be more detrimental to wetland tree performance than salinity concentrations.

The overexploitation of coastal aquifers is one of the important reasons for the salinity of groundwater due to seawater intrusion (SWI). This study assesses the hydrochemical changes of the Ghaemshahr-Juybar (GH.-J.) plain. For this purpose, specific statistical methods, modified Piper diagram groundwater quality indicators ( GQI Piper mix and GQI Piper dom ), groundwater quality index specific to seawater intrusion ( GQI SWI ), and hydrochemical facies evolution diagram (HFE-D) along with GIS (Geographic Information System) techniques were applied to identify the spatiotemporal changes of salinity in coastal multilayer alluvial aquifer. The results show that the chemical composition in the GH.-J. aquifer is basically controlled by three main factors: (1) Caspian SWI and fossil saltwater penetration from an underlying layer, (2) reverse cation exchange process, and (3) feeding by domestic sewage, agricultural activities, and use of nitrate chemical fertilizers. The investigation of the hydrogeochemical facies evolution process shows that due to the reduction of extraction from wells, saltwater infiltration has significantly decreased. Therefore, according to the geological and lithological conditions of the aquifer and exposure to seawater, it is possible to prevent the entry of saltwater from the confined aquifer into the unconfined aquifer and the saltwater intrusion by developing well optimal operation policies in order to control withdrawal from semi-deep wells and the elimination of deep wells. This practical approach to managing the salinity of coastal aquifers is suitable for the allocating groundwater resources and for use in the development of aquifer simulation models. [ABSTRACT FROM AUTHOR]

This study explores the impact of a novel approach on the levels of SWI (saltwater intrusion) and NO3− (nitrate) contamination. Some numerical simulations were conducted utilizing a coupled model that incorporates variably saturation and density, as well as convection diffusion reaction within a sandy coastal aquifer. We verified the reliability of the model for SWI based on comparison lab experiments and for chemical reactions based on a comparison of previous in situ observations. Cutoff walls and subsurface dams cannot simultaneously control SWI and reduce NO3− contamination. A novel approach that combines subsurface dams and permeable CH2O (organic carbon) walls (PC-Wall) is proposed. Subsurface dams are utilized to prevent SWI, while PC-Walls are employed to mitigate NO3− pollution. Results demonstrate that the construction of a PC-Wall with a concentration of 1.0 mM facilitated a transition from nitrification (Ni)-dominated to denitrification (Dn)-dominated. An increase in CH2O concentration to 1.0 mM caused a significant 1942.5 % rise in mDn (the mass of NO3− removed through Dn). Increment of the distance between the PC-Wall and the ocean from 35 to 45 m could result in a 103.7 % mDn increase and reduce mN (the compound mass of NO3− remaining in the aquifer) by 11.7 %. The study offers a detailed comprehension of the intricate hydrodynamics of SWI and NO3− pollution. In addition, it provides design guidance for engineering to mitigate contamination by NO3− and controlling SWI, thus fostering the management of groundwater quality. [ABSTRACT FROM AUTHOR]

The main purpose of the present research is to propose a comprehensive attitude of the salinity in groundwater resources of Iran using 116 papers in the assessment of groundwater quality in different areas of the country. The conducted study contains the measurement of the values of physicochemical parameters of which electrical conductivity (EC), as the fundamental parameter for salinity determination of groundwater, was considered mostly, and by comparing it with standards, as well as employing the Wilcox diagram, the quality of water was assessed for drinking and agricultural purposes, respectively. Study of the previous papers revealed that in only the west and northwest of the country, the groundwater quality was suitable for drinking, and in the majority of provinces, EC values exceeded the recommended limits. The highest EC level was seen in central provinces which led to the aggravation of groundwater and the largest proportion of salinity, putting the quality of water in an unsuitable class for drinking. Additionally, the assessment of groundwater quality for irrigation uses using the Wilcox diagram showed high and very high salinity rates in most areas of the study area. Northwestern provinces relatively had the lowest level putting in C3–S1 class, while central areas reached the highest with C4–S4 classification. Deficiency of rainfall, high rate of groundwater exploitation, and the intrusion of saltwater from Salt Lake were the principal reasons for groundwater deterioration in central parts of the study area. [ABSTRACT FROM AUTHOR]

Small island countries like Vanuatu are facing the brunt of climate change, sea level rise (SLR), tropical cyclones, and limited or declining access to freshwater. The Tagabe coastal aquifer in Port Vila (the capital of Vanuatu) shows the presence of salinity, indicating saltwater intrusion (SWI). This study aims to develop and evaluate effective SWI management strategies for Tagabe coastal aquifer. To manage SWI, the numerical simulation model for the study area was developed using the SEAWAT code. The flow model was developed using MODFLOW and the transport model was developed using MT3DMS. Whereby SEAWAT solved flow and transport equations simultaneously. The model was calibrated, and different scenarios were evaluated for the management of SWI. The SLR was also considered in the model simulations. The results indicated that increased population, pumping rates, and SLR affect the SWI rates. To manage the SWI, we introduced hydraulic barriers like barrier wells and injection wells which effectively managed SWI in Tagabe coastal aquifer. The results from this study are significantly important whereby, the water managers, site owners, and governing bodies can use the management strategies presented in this study to create policies and regulations for managing SWI rates in Port Vila. Additionally, the water industry, private businesses, and investors who wish to extract groundwater from the Tagabe can use this study as a reference for daily or yearly freshwater production rates without the risk of SWI. [ABSTRACT FROM AUTHOR]

Land-use planning plays an important role in agricultural development. However, the tools used to support planners in proposing land-use planning solutions are lacking, especially when considering saltwater intrusion conditions in coastal regions. In this study, optimization is applied by analyzing land use in developing solutions for agricultural land-use planning, wherein a multi-objective optimization model is developed to optimize land-use area, including land-use allocation, and taking into account socioeconomic and environmental factors. The model was applied to three districts of Soc Trang province, Vietnam (Long Phu, My Xuyen, and Tran De), representing three ecological regions of salt water, brackish water, and fresh water in the Mekong Delta of Vietnam. The results are shown for the implementation of two multi-objective optimization scenarios (in terms of profit, labor, environment benefits, and risk reduction) as follows: (i) multi-objective optimization of agricultural land use until 2030 under normal conditions; (ii) optimizing agricultural land use until 2030 under climate change conditions similar to the 2016 drought and saltwater intrusion phenomenon in the Mekong Delta. The results demonstrate that the second scenario is the preferred option for implementing land-use planning thanks to the balance between good profits and minimizing economic and environmental risk. Land allocation was carried out by taking into account the factors of household economics, the influence of adjacent production types, local traffic, and canal systems to allocate areas toward ensuring optimal land use. This process, involving a combination of land-use optimization and spatial allocation, can help planners to improve the quality of agricultural land-use planning. [ABSTRACT FROM AUTHOR]

Ghost forests consisting of dead trees adjacent to marshes are striking indicators of climate change, and marsh migration into retreating coastal forests is a primary mechanism for marsh survival in the face of global sea‐level rise. Models of coastal transgression typically assume inundation of a static topography and instantaneous conversion of forest to marsh with rising seas. In contrast, here we use four decades of satellite observations to show that many low‐elevation forests along the US mid‐Atlantic coast have survived despite undergoing relative sea‐level rise rates (RSLRR) that are among the fastest on Earth. Lateral forest retreat rates were strongly mediated by topography and seawater salinity, but not directly explained by spatial variability in RSLRR, climate, or disturbance. The elevation of coastal tree lines shifted upslope at rates correlated with, but far less than, contemporary RSLRR. Together, these findings suggest a multi‐decadal lag between RSLRR and land conversion that implies coastal ecosystem resistance. Predictions based on instantaneous conversion of uplands to wetlands may therefore overestimate future land conversion in ways that challenge the timing of greenhouse gas fluxes and marsh creation, but also imply that the full effects of historical sea‐level rise have yet to be realized. [ABSTRACT FROM AUTHOR]

The shallow buried paleochannel zone is a critical conduit for groundwater transportation, and exploring the location of the paleochannels is of great significance for evaluating and preventing the intrusion of saltwater. Electrical resistivity tomography (ERT) is used to describe the distribution and morphology of paleochannels. However, the resistivity characteristics of the paleochannels are strongly affected by the resistivity properties of the groundwater within the paleochannels in the study area, especially in the saltwater intrusion area. The difference in groundwater resistivity will interfere with the identification of the paleochannel. In this study, the extent of saltwater intrusion was determined using stratified monitoring wells, and four ERT detection profiles were provided in the direction of saltwater intrusion. Based on the groundwater data and ERT results, the distribution and morphological characteristics of the paleochannels were circled by the quantitative relationship between resistivity data and geochemical data established by Archie's law and Waxman's law (petrophysical relationship). Backcalculations were also carried out through petrophysical relationship as a medium to convert resistivity values into porosity values and calculate the water-rich capacity of the paleochannels based on Darcy's law. The results show that the paleochannel is 10–25 m deep, 50–150 m wide and 35–55 m thick, and the water-rich capacity of the paleochannel in the study area is 1.24–1.48 times greater than the background stratigraphy. Considering the electrical characteristics of groundwater in the saltwater intrusion zone is beneficial to ERT in identifying and evaluating paleochannels, and provides important support for the sustainable development and utilisation of groundwater resources within paleochannels. [ABSTRACT FROM AUTHOR]

Aquifers on small islands are at risk of salinization due to low elevations and limited adaptive capacity, and present risks will be exacerbated by climate change. Most studies addressing small‐island saltwater intrusion (SWI) have focused on homogeneous sandy islands and one or two hydraulic disturbances. We herein investigate SWI dynamics in a layered, confined island aquifer in response to multiple environmental perturbations related to climate change, with two considered in tandem. Our field and modeling work is based on an island aquifer that provides the drinking water supply for an Indigenous community in Atlantic Canada. Observation well data and electrical resistivity profiles were used to calibrate a numerical model (HydroGeoSphere) of coupled groundwater flow and salt transport. The calibrated model was used to simulate the impacts of climate change including sea‐level rise (SLR), storm surge overtopping, changing aquifer recharge, and erosion. Simulated aquifer conditions were resilient to surges because the confining layer prevented deeper saltwater leaching. However, reduced recharge and erosion resulted in saltwater wedge migration of 170 and 110 m, respectively when considered individually, and up to 295 m (i.e., into the wellfield) when considered together. Despite the confining conditions, SLR resulted in wedge migration up to 55 m as the confining pressures were not sufficient to resist wedge movement. This is the first study to harness an integrated, surface‐subsurface hydrologic model to assess effects of coastal erosion and other hydroclimatic stressors on island aquifers, highlighting that climate change can drive extensive salinization of critical groundwater resources. Plain Language Summary: Due to their limited resources and adaptive capacity, small islands are highly vulnerable to climate change impacts, including saltwater intrusion. Freshwater needs on small islands are often sourced from small aquifers that are in delicate balance between conditions in the ocean, atmosphere, and land. In this study, we investigate the movement of saltwater into the freshwater aquifer of a small island that provides drinking water resources for an Indigenous First Nation. We consider climatic changes in the ocean (sea‐level rise (SLR), storm surges, and related coastal erosion) and atmosphere (changes to net precipitation) and associated impacts to the island's fresh groundwater resources. We use field data paired with a mathematical model and demonstrate that the pressurized conditions of the layered island aquifer make it more resilient to SLR than unconfined aquifers in sandy islands are. However, the aquifer's freshwater volume is susceptible to coastal erosion and reduced precipitation, particularly when these happen at the same time. Results point to coastal erosion as a potential widespread driver of freshwater loss along eroding portions of the global coastline. Key Points: A surface‐subsurface numerical model is used to investigate climate change impacts on island groundwater resources used for water supplyThe confined aquifer is resilient to storm surges which only salinize the unpumped surficial aquifer before being flushedCoastal erosion and recharge reductions result in the most saltwater intrusion and can work in tandem to threaten future water supply [ABSTRACT FROM AUTHOR]

The saltwater intrusion occurs in many coastal areas worldwide and has become a serious menace to freshwater quality. In the Pearl River estuary, saltwater intrusion has threatened the water supply for residential, agricultural, and industrial uses in the past decades, resulting in ecological and economic losses. In this study, the observed saltwater intrusion records of 10 years (2012 ~ 2021) at 9 stations in the Modaomen waterway, the largest inlet of the Pearl River estuary, were compiled. The time duration of saltwater intrusion was analyzed rather than the traditional distance length, along with the reported annual sea level records and river discharge volumes. The annual duration of saltwater intrusion exhibits spatial variations and is inversely related to the distance from the the Pearl River estuary mouth. In the study area which is near the main estuary mouth of the Pearl River, results from a multiple linear regression show that the observed annual saltwater intrusion days near the main Pearl River estuary mouth could be quantitatively explained by the combination of river discharge (dominant) and relative sea level. This work presents an example to investigate the combined river discharge and sea level impact on saltwater intrusion with annually compiled observed data and from a time-change perspective. [ABSTRACT FROM AUTHOR]

The coastal plain aquifer down gradient of Wad Essaquia Elhamra (WEE), is the main source of groundwater in the arid region of Laayoune Essaquia El Hamra located in south of Morocco. The over-exploitation of this aquifer over the last decade for water supply, agriculture and industry led to deterioration of groundwater quality, including seawater intrusion. The objective of this study is to investigate the spatial variation of groundwater quality, and to assess the influence of sea water intrusion on the groundwater quality using hydro-chemical tools. Several measurement campaigns of physico-chemical parameters of the groundwater were performed, which shows a very high mineralization ratios versus chloride, confirming the double influence of mixing mechanisms of fresh and saline waters and the water-rock interactions. Computed seawater fraction for sampled water shows that the average mixing rate of seawater intrusion reached 10.5%, confirming the marine intrusion in the aquifer. The highest values were registered in coastal wells. In the upstream around Laayoune and the spreading area, nitrate concentrations exceed 50 mg/L which is the threshold set by the World Health Organization, revealing a high level of contamination by domestic sewage. The combination of ionic ratios and seawater fraction is a useful tool to assess marine intrusion. This study reveals that the phenomenon of marine intrusion is not the only process that dominates hydrochemistry of ground water. The high groundwater mineralization is also due to rockwater interaction associated with reverse ion exchange with clay material and anthropogenic pollutants. [ABSTRACT FROM AUTHOR]

This study investigates groundwater resources in the El-Omayed area on the northwestern coast of Egypt. The aim is to assess the extent and severity of saltwater intrusion in the shallow aquifer system, as well as its potential impacts on groundwater resources. A combined geophysical and hydrochemical approach was adopted in this investigation. Across the study area, 32 vertical electrical soundings were conducted, along with two electrical resistivity tomography profiles. Sixteen water samples were collected, and then chemically analyzed to evaluate water quality, seawater intrusion, and source of salinity. The results of geophysical interpretation revealed the existence of a thin, shallow freshwater-bearing layer (42–95 Ω.m), predominantly situated in the central parts of the area, followed by saltwater saturated layers of (0.9–2.1 Ω.m) affected by the Mediterranean Sea invasion. The eastern portion of the aquifer also recorded a relatively high seawater intrusion. As evidenced by the actual data gathered from drilled wells, the study area can be divided into three distinct zones: fresh, brackish, and saltwater zones. The study identified the most suitable sites to establish new groundwater wells, in addition to identifying the source of salinity through the investigation of the geochemical properties of water samples. [ABSTRACT FROM AUTHOR]