Simulating Saltwater Intrusion Research Articles

Optimizing Irrigation Systems for Water Efficiency and Groundwater Sustainability in the Coastal Nile Delta

This study investigates the replacement of traditional surface irrigation methods with modern irrigation systems (MIS) including horizontal sprinkler, central pivot, surface drip, and subsurface drip aimed at improving water efficiency in the Nile Delta, Egypt. The primary objectives were to determine the optimal agricultural area for implementing MIS and to assess the effects of these systems on groundwater quantity and quality in the region. To achieve this, the LINDO software was employed to optimize land allocation for each irrigation method. At the same time, the SEAWAT code was utilized to simulate saltwater intrusion (SWI) in the Nile Delta aquifer. The transition from traditional surface irrigation to MIS resulted in significant water savings, reaching 2.15 × 10^9 m³. However, groundwater modeling indicated a decrease in groundwater levels, leading to an 8 % increase in aquifer salinity due to reduced infiltration of recharge water. These findings underscore the urgent need to revise outdated irrigation practices and enhance water management strategies in the Nile Delta to mitigate salinity issues in coastal aquifers. This research's outcomes are crucial for decision-makers and stakeholders in selecting appropriate irrigation methods, particularly in arid and semi-arid regions, to ensure sustainable water use and agricultural productivity.

The Effect of Saltwater Stress on the Performance of Cherry Tomatoes

Rising sea levels and saltwater intrusion in aquifers pose significant challenges for South Florida agriculture, leading to increased groundwater salinity and potential crop losses. Utilizing salttolerant crop species presents a potential solution for saline soils and regions with active saltwater intrusion. However, the effects of soil salinization through groundwater alone remains less studied. This research investigates the impact of short-term, below-ground saltwater stress on the growth, survival, and overall health of commonly grown cherry tomatoes (Solanum lycopersicum). The objectives of the study are to: 1) determine the impact of saline groundwater on tomato plant health and 2) compare the nutrient content of soil and tomato plant tissue exposed to varying concentrations of saline water. Established cherry tomato plants were exposed to varying concentrations of NaCl solution, simulating saltwater intrusion into groundwater. Over 28 days, plant height, leaf chlorophyll levels, and disease occurrences were monitored. It was found that the NaCl treatments did not significantly affect cherry tomato performance under the parameters of height, chlorophyll levels, or leaf nutrition when compared to the control group. This study suggests that cherry tomatoes can tolerate short-term exposure to NaCl in groundwater. Further exploration of more intense salt stress conditions from groundwater could be beneficial for utilizing this crop in areas with saline soils or polluted groundwater. Identification of salt-tolerant cherry tomato varieties can provide alternative crop options for non-arable land affected by high soil salinity.

Changes in the salt concentration distribution in surface water (seawater) due to seawater recirculation in a porous medium under tidal fluctuations

Many studies have used numerical simulations and experiments to simulate saltwater intrusion in a nearshore aquifer. Thus, it is known that seawater recirculation occurs in a porous medium just below a sloping beach, and a saltwater wedge occurs in the medium below where the slope intersects the water level at low tide. This study investigated the salt distribution in the surface water when subterranean recirculation of seawater is occurring and there is a saltwater wedge in an underlying porous medium, along with the relationships between the seawater recirculation and the tidal amplitude and beach gradient. The salt distribution in a subterranean aquifer and in surface seawater where the shore sloped gently seaward with a constant slope of 1/10 or 1/5 under tidal amplitudes of 0.5, 1.0, or 2.0 m was numerically simulated by the ASGMF method, which couples water pressure and water flow in a porous medium with those in the overlying surface water and can simulate variable-density flows and the salt concentration distribution in both the porous medium and the surface water. The results showed that the recirculation of seawater depended on the tidal amplitude, being greater when the amplitude exceeded 1.0 m, but that it was unlikely to occur when the beach gradient was steep. Thus, the aspect ratio (width to depth) of the seawater recirculation decreased as the tidal amplitude increased above 1.0 m. Furthermore, the simulated surface water level was often lower than the tidal water level; thus, the surface water level was not consistent with the tidal water level imposed at the right boundary of the simulation domain but varied slightly under the influence of water flow in the surface water and gas flow in the atmosphere. The salt concentration in the surface water was not always the same as the seawater salt concentration because a thin freshwater layer and a brackish water layer of mixed freshwater and saltwater overlay the seawater.

Integrated SWAT-MODFLOW model to study saltwater intrusion in Da Nang coastal city

This study applied an integrated surface water-groundwater (SW-GW) model, SWAT-MODFLOW to study interaction of surface and groundwater than simulate saltwater intrusion at a regional scale in Da Nang coastal city, center of Vietnam. Model components were calibrated and validated using monthly river flow data and hydraulic head data for the 2005-2020 period and showed good agreement with observed data. The results demonstrated that GW-SW exchange in the upstream areas had the most pronounced fluctuation between the wet and dry months under historical conditions. The combined potential impact is that intensive groundwater use may have more immediate effects on river flow than those of climate change, which has important implications for water resources management and supply in the future. The results showed that the total average recharge to groundwater from the rivers was varied from 12046 to 23147 m3/d relative to 50 – 74% of water resources in rain and dry season. Saltwater intrusion intrusion in 2020 is about 100 km2. In the area of Son Tra and Ngu Hanh Son districts, groundwater pumping must be reduced to zero, in some other areas, pumping rate do not exceed 250 to 1000 m3/day with distance to coastline at least 500 to 1400m depends on each area.

Cooperative microbial interactions mediate community biogeochemical responses to saltwater intrusion in wetland soils.

In freshwater wetlands, competitive and cooperative interactions between respiratory, fermentative and methanogenic microbes mediate the decomposition of organic matter. These interactions may be disrupted by saltwater intrusion disturbances that enhance the activity of sulfate-reducing bacteria (SRB), intensifying their competition with syntrophic bacteria and methanogens for electron donors. We simulated saltwater intrusion into wetland soil microcosms and examined biogeochemical and microbial responses, employing metabolic inhibitors to isolate the activity of various microbial functional groups. Sulfate additions increased total carbon dioxide production but decreased methane production. Butyrate degradation assays showed continued (but lower) levels of syntrophic metabolism despite strong demand by SRB for this key intermediate decomposition product and a shift in the methanogen community toward acetoclastic members. One month after removing SRB competition, total methane production recovered by only ∼50%. Similarly, butyrate assays showed an altered accumulation of products (including less methane), although overall rates of syntrophic butyrate breakdown largely recovered. These effects illustrate that changes in carbon mineralization following saltwater intrusion are driven by more than the oft-cited competition between SRB and methanogens for shared electron donors. Thus, the impacts of disturbances on wetland biogeochemistry are likely to persist until cooperative and competitive microbial metabolic interactions can recover fully.

Modeling variable-density flow in saturated-unsaturated porous media: An advanced numerical model

Modeling variable-density flow in unconfined aquifers is a challenging task because of the nonlinear coupling between variably saturated flow and contaminant transport. This results in a highly nonlinear system since the strongly nonlinear Richards flow equation is, in addition, coupled to the advection-dispersion transport equation by viscosity and density variation. The solution of such a nonlinear system is often subject to convergence issues and can be very expansive in terms of computational time, especially for large-scale problems. Conventional numerical algorithms based on the sequential approach and the classical finite difference or finite element methods with the first-order backward Euler time integration scheme are generally inefficient and/or do not provide satisfactory results. In this work, we develop a new efficient and accurate 2D numerical model for the transport of dense contaminants in unsaturated porous media that allows for the simulation of large-scale problems. This research describes a new model that combines advanced spatial discretization methods (mixed hybrid finite element method, discontinuous Galerkin finite element method, and multipoint flux approximation method) with higher-order time integration techniques via the method of lines (MOL). The latter allows one to adapt the time step's size and the order of the time integration to improve the computational efficiency while maintaining accuracy. The robustness and accuracy of the new model are shown by comparison against a widely used commercial code based on the standard finite element method. The applicability of the developed model to a large-scale problem is then investigated by simulating saltwater intrusion under a climate change projection and long-term pumping regimes for the Akkar coastal aquifer in Lebanon using a simplified 2D conceptual model.

Effects of Saltwater Pulses on Soil Microbial Enzymes and Organic Matter Breakdown in Freshwater and Brackish Coastal Wetlands

Coastal freshwater and brackish wetlands are exposed to pulses of saltwater during times of reduced freshwater flows (i.e., dry seasons, droughts), periodic storm surges, and increased tidal extent associated with rising seas. The effects of saltwater pulses on belowground processing rates of detrital organic matter as mediated by microbial activities are uncertain. Our objectives were to quantify whether and how pulses of saltwater (i) change soil porewater physicochemistry, (ii) change soil microbial extracellular enzyme activities, and (iii) change root litter breakdown over time in freshwater and brackish marshes. From 2014 to 2016, we simulated saltwater intrusion as monthly in situ pulsed additions of artificial seawater in experimental dosing chambers (1.4 m diameter) within freshwater and brackish marshes of Everglades National Park. At monthly intervals, we collected soil porewater chemistry, and measured microbial extracellular enzymes, elemental stoichiometric ratios, and breakdown rates (k) of incubated (0–30 cm depth) root litter and compared these responses over time. Saltwater pulses increased sulfate and nitrogen concentrations in porewater at the freshwater site. However, saltwater pulses generally decreased porewater constituents (e.g., dissolved organic carbon, dissolved nitrogen and phosphorus species) at the brackish site. One saltwater pulse increased root litter k by 1.25-fold in the brackish marsh. However, long-term (740 days) k in brackish wetlands, and both short- and long-term k in freshwater wetlands, were not affected by 24 monthly pulses of saltwater. Enzyme activities fluctuated with time and did not respond to multiple saltwater pulses. Our results suggest that detrital organic matter stocks and associated soil microbial activities are relatively resistant to single and multiple (n = 24) pulses of saltwater.

Laboratory and Numerical Investigation of Saltwater Intrusion Processes in a Circular Island Aquifer

AbstractA novel radial flow experimental system to study saltwater intrusion processes in an island aquifer is presented. The study investigated steady state and transient scenarios involving advancing and receding saltwater wedges in a circular island. The experimental results were simulated using the density‐coupled version of the MODFLOW‐USG code. The experimental data along with the model simulation results are employed to develop a new radial benchmark problem for testing density‐coupled models used for simulating saltwater intrusion processes. The experimental data for transient changes in toe position and freshwater storage level indicated an asymmetric pattern where the intrusion time scale is greater than the recession time scale. Numerical experiments were completed to further investigate this asymmetric effect and to intercompare the associated transient transport processes in circular and linear strip islands. We also analyzed the sensitivity of island geometry in controlling the freshwater storage levels under different recharge conditions. Modeling results show that for similar‐sized systems, circular islands are more efficient in storing freshwater than linear strip islands.

Phosphorus alleviation of salinity stress: effects of saltwater intrusion on an Everglades freshwater peat marsh.

Saltwater intrusion and salinization of coastal wetlands around the world are becoming a pressing issue due to sea level rise. Here, we assessed how a freshwater coastal wetland ecosystem responds to saltwater intrusion. In wetland mesocosms, we continuously exposed Cladium jamaicense Crantz (sawgrass) plants and their peat soil collected from a freshwater marsh to two factors associated with saltwater intrusion in karstic ecosystems: elevated loading of salinity and phosphorus (P) inputs. We took repeated measures using a 2 × 2 factorial experimental design (n=6) with treatments composed of elevated salinity (~9ppt), P loading (14.66μmol P/d), or a combination of both. We measured changes in water physicochemistry, ecosystem productivity, and plant biomass change over two years to assess monthly and two-year responses to saltwater intrusion. In the short-term, plants exhibited positive growth responses with simulated saltwater intrusion (salinity + P), driven by increased P availability. Despite relatively high salinity levels for a freshwater marsh (~9 ppt), gross ecosystem productivity (GEP), net ecosystem productivity (NEP), and aboveground biomass were significantly higher in the elevated salinity + P treated monoliths compared to the freshwater controls. Salinity stress became evident after extended exposure. Although still higher than freshwater controls, GEP and NEP were significantly lower in the elevated salinity + P treatment than the +P treatment after two years. However, elevated salinity decreased live root biomass regardless of whether P was added. Our results suggest that saltwater intrusion into karstic freshwater wetlands may initially act as a subsidy by stimulating aboveground primary productivity of marsh plants. However, chronic exposure to elevated salinity results in plant stress, negatively impacting belowground peat soil structure and stability through a reduction in plant roots.

Origin and Dynamics of Saltwater Intrusion in a Regional Aquifer: Combining 3‐D Saltwater Modeling With Geophysical and Geochemical Data

AbstractWorldwide, aquifers in low‐lying coastal areas are threatened by saltwater occurrence, as a result of small head gradients, high groundwater abstraction rates, and drain management of the landscape, which is likely to intensify with climate change. Numerical models can serve as tools to identify the sources of the salt and thus to increase understanding of the driving mechanisms and important parameters controlling the extent of saltwater intrusions. This way, areas vulnerable to sea level rise can be identified and managed. Challenges include unknown initial salt concentrations, heterogeneous geology, and anthropogenic alterations. In this study, hydrogeological, geophysical, and geochemical data are used to develop a numerical density‐dependent groundwater flow and transport model with the objective to understand the history of a saltwater‐affected groundwater system and its likely response to historic and future changes. The extent of the simulated saltwater intrusion compares well with Airborne Electromagnetic data that show salt water up to 20 km inland. The results reveal that the salt water originates from a combination of laterally intruding seawater and vertically infiltrating transgression water. Main features controlling the progression of the modern seawater into the coastal aquifers are high permeable, deep Miocene sand aquifers, buried valleys that provide preferential flow paths in combination with extensive Miocene clay layers that delay saltwater intrusion. Anthropogenic activity enhances the saltwater inflow from the ocean and induces transient conditions. Future scenarios show that saltwater progression due to nonstationarity leads to enhanced contamination of the deeper aquifers. Climate change affects primarily the shallow aquifer systems.

Estimating the thickness of unconsolidated coastal aquifers along the global coastline

Abstract. Knowledge of aquifer thickness is crucial for setting up numerical groundwater flow models to support groundwater resource management and control. Fresh groundwater reserves in coastal aquifers are particularly under threat of salinization and depletion as a result of climate change, sea-level rise, and excessive groundwater withdrawal under urbanization. To correctly assess the possible impacts of these pressures we need better information about subsurface conditions in coastal zones. Here, we propose a method that combines available global datasets to estimate, along the global coastline, the aquifer thickness in areas formed by unconsolidated sediments. To validate our final estimation results, we collected both borehole and literature data. Additionally, we performed a numerical modelling study to evaluate the effects of varying aquifer thickness and geological complexity on simulated saltwater intrusion. The results show that our aquifer thickness estimates can indeed be used for regional-scale groundwater flow modelling but that for local assessments additional geological information should be included. The final dataset has been made publicly available (https://doi.pangaea.de/10.1594/PANGAEA.880771).

Functional and Compositional Responses of Periphyton Mats to Simulated Saltwater Intrusion in the Southern Everglades

Periphyton plays key ecological roles in karstic, freshwater wetlands and is extremely sensitive to environmental change making it a powerful tool to detect saltwater intrusion into these vulnerable and valuable ecosystems. We conducted field mesocosm experiments in the Florida Everglades, USA to test the effects of saltwater intrusion on periphyton metabolism, nutrient content, and diatom species composition, and how these responses differ between mats from a freshwater versus a brackish marsh. Pulsed saltwater intrusion was simulated by dosing treatment chambers monthly with a brine solution for 15 months; control chambers were simultaneously dosed with site water. Periphyton from the freshwater marsh responded to a 1-ppt increase in surface water salinity with reduced productivity and decreased concentrations of total carbon, nitrogen, and phosphorus. These functional responses were accompanied by significant shifts in periphytic diatom assemblages. Periphyton mats at the brackish marsh were more functionally resilient to the saltwater treatment (~ 2 ppt above ambient), but nonetheless experienced significant shifts in diatom composition. These findings suggest that freshwater periphyton is negatively affected by small, short-term increases in salinity and that periphytic diatom assemblages, particularly at the brackish marsh, are a better metric of salinity increases compared with periphyton functional metrics due to functional redundancy. This research provides new and valuable information regarding periphyton dynamics in response to changing water sources in the southern Everglades that will allow us to extend the use of periphyton, and their diatom assemblages, as tools for environmental assessments related to saltwater intrusion.

A 3D unstructured-grid model for Chesapeake Bay: Importance of bathymetry

We extend the 3D unstructured-grid model previously developed for the Upper Chesapeake Bay to cover the entire Bay and its adjacent shelf, and assess its skill in simulating saltwater intrusion and the coastal plume. Recently developed techniques, including a flexible vertical grid system and a 2nd-order, monotone and implicit transport solver are critical in successfully capturing the baroclinic responses. Most importantly, good accuracy is achieved through an accurate representation of the underlying bathymetry, without any smoothing. The model in general exhibits a good skill for all hydrodynamic variables: the averaged root-mean-square errors (RMSE's) in the Bay are 9 cm for sub-tidal frequency elevation, 17 cm/s for 3D velocity time series, 1.5 PSU and 1.9 PSU for surface and bottom salinity respectively, 1.1 °C and 1.6 °C for surface and bottom temperature respectively. On the shelf, the average RMSE for the surface temperature is 1.4 °C. We highlight, through results from sensitivity tests, the central role played by bathymetry in this estuarine system and the detrimental effects, from a common class of bathymetry smoothers, on volumetric and tracer fluxes as well as key processes such as the channel-shoal contrast in the estuary and plume propagation in the coast.

Simulation of saltwater intrusion in a poorly karstified coastal aquifer in Lebanon (Eastern Mediterranean)

To date, there has been no agreement on the best way to simulate saltwater intrusion (SWI) in karst aquifers. An equivalent porous medium (EPM) is usually assumed without justification of its applicability. In this paper, SWI in a poorly karstified aquifer in Lebanon is simulated in various ways and compared to measurements. Time series analysis of rainfall and aquifer response is recommended to decide whether quickflow through conduits can be safely ignored. This aids in justifying the selection of the exemplified EPM model. To examine the improvement of SWI representation when discrete features (DFs) are embedded in the model domain, the results of a coupled discrete-continuum (CDC) approach (a hybrid EPM-DF approach) are compared to the EPM model. The two approaches yielded reasonable patterns of hydraulic head and groundwater salinity, which seem trustworthy enough for management purposes. The CDC model also reproduced some local anomalous chloride patterns, being more adaptable with respect to the measurements. It improved the overall accuracy of salinity predictions at wells and better represented the fresh–brackish water interface. Therefore, the CDC approach can be beneficial in modeling SWI in poorly karstified aquifers, and should be compared with the results of the EPM method to decide whether the differences in the outcome at local scale warrant its (more complicated) application. The simulation utilized the SEAWAT code since it is density dependent and public domain, and it enjoys widespread application. Including DFs necessitated manual handling because the selected code has no built-in option for such features.

A Combined Discontinuous Galerkin Method for Saltwater Intrusion Problem with Splitting Mixed Procedure

AbstractIn this paper, a new combined method is presented to simulate saltwater intrusion problem. A splitting positive definite mixed element method is used to solve the water head equation, and a symmetric discontinuous Galerkin (DG) finite element method is used to solve the concentration equation. The introduction of these two numerical methods not only makes the coefficient matrixes symmetric positive definite, but also does well with the discontinuous problem. The convergence of this method is considered and the optimal L2-norm error estimate is also derived.

Design Concept of an Automated Irrigation System for Simulating Saltwater Intrusion in a Mesocosm Experiment

Coastal wetlands make up about one third of the overall wetland area in the conterminous United Stated based on the Environmental Protection Agency 2016 [1]. Sea-level rise is expected to elevate water salinity and effect carbon sequestration, nitrogen removal, further alter plant communities and shift ecosystem function. To promote understanding of the influence of seawater intrusion into tidal freshwater wetlands, we designed a mesocosm experiment with automated irrigation system at Spring Hill, Storrs, CT, USA (41.8°N, 72.3°W). To simulate marine water intrusion, we designed an automated irrigation to work for an on-going mesocosm experiment, which is composed of 64 tanks with 4 wetland species: Carexstricta, Spartinapectinata, Typhalatifolia, Phragmitesaustralis. During low tide, solenoid valves quantify water based on the instruction of system core controller (Arduino) and water is distributed to assigned tank [2] [3]. During high tide, water is pumped up into assigned tank, salinity is varied with plant species, Carexstricta and Spartinapectinata are fresh water species, Typhalatifolia, Phragmitesaustralis are brackish water species. The manipulation core of system is an open-source microcontroller platform. The irrigation system was designed daily twice change from low tide water level to high tide water level, and same water tank should keep at constant salinity within 30 days. Staff just needs monthly visit to add sea salts, the raw material of artificial seawater. Ecosystem CO2 and CH4 gas exchanges were measured monthly from May to September 2015 using large transparent chambers that enclosed emergent plants and the soil surface; field sampling and analysis procedures followed [4]. The simulated saltwater intrusion results are expected to alter plant growth, emission of carbon dioxide, methane and other greenhouse gases, and effect interaction with coastal marsh ecosystem.

Design and Construction of an Automated Irrigation System for Simulating Saltwater Intrusion in a Tidal Freshwater Wetland

Sea-level rise is expected to cause saltwater intrusion into tidal freshwater wetlands. The resulting changes in the soil environment would likely cause shifts in plant and microbial communities and alter ecosystem functions. To simulate saltwater intrusion, we constructed a solar-powered automated irrigation system. The system consisted of holding tanks that were filled with freshwater or artificial brackish water during high tide. During low tide, the water was gravity-fed through solenoid valves and metered out to each plot. This system was controlled by an open-source microcontroller platform and built from off-the-shelf electronics at a cost of $1800. Porewater salinity in near-surface soils of the plots receiving brackish water was increased from freshwater to oligohaline levels within one month of operation and was maintained throughout the first summer of operation. This porewater manipulation led to changes in the plant community and in exchanges of carbon dioxide and methane between the marsh and atmosphere. The system has proven to be a reliable way of manipulating wetland salinity for studying changes in the physicochemical environment. With modifications, it could be used to manipulate nutrient loads, hydrology, and sediment supply in other wetland systems.

The Henry-Saltwater Intrusion Benchmark – Alternatives in Multiphysics Formulations and Solution Strategies

In a classical paper Henry set up a conceptual model for simulating saltwater intrusion into coastal aquifers. Up to now the problem has been taken up by software developers and modellers as a benchmark for codes simulating coupled flow and transport in porous media. The Henry test case has been treated using different numerical methods based on various formulations of differential equations. We compare several of these approaches using multiphysics software. We model the problem using Finite Elements, utilizing the primitive variables and the streamfunction approach, both with and without using the Oberbeck-Boussinesq assumption. We compare directly coupled solvers with segregated solver strategies. Changing finite element orders and mesh refinement, we find that models based on the streamfunction converge 2-4 times faster than runs based on primitive variables. Concerning the solution strategy, we find an advantage of Picard iterations compared to monolithic Newton iterations.

Program Profile: The Georgia Coastal Ecosystems Long Term Ecological Research Project (GCE‐LTER)

Program Profile: The <scp>G</scp>eorgia Coastal Ecosystems Long Term Ecological Research Project (GCE‐LTER)

Effects of Salinity on Denitrification and Greenhouse Gas Production from Laboratory-incubated Tidal Forest Soils

We measured ambient and potential denitrification in tidal freshwater floodplain forest (tidal forests) soils along the Altamaha, Ogeechee, and Satilla Rivers in southeast Georgia to characterize nitrogen removal from these understudied systems. Further, we measured the response of denitrification, greenhouse gas production (CO2, CH4, N2O), and the formation of reduced inorganic sulfur species following laboratory incubations simulating saltwater intrusion with salinity levels of 2 and 5. Ambient denitrification ranged from 0.03 μg N2O/g/hr in the Satilla River to 0.40 μg N2O/g/hr in the Altamaha River. Potential denitrification was two to eight times greater than ambient denitrification. Denitrification from Satilla River soils increased with salinity, while Altamaha and Ogeechee River soils were unaffected. Methane production, however, was inhibited by salinity, decreasing by 77% in the 2 treatment and 89% in the 5 treatment whereas CO2 generally increased with salinity, though exhibited a variable response between the three rivers. Formation of reduced sulfur species followed a similar trend to CO2 production. Our findings suggest that tidal forests are effective sinks for N, capable of producing anywhere from 0.032 to 1.9 μg N2O/g soil/hr. Overall, salinity increased the amount of C mineralized suggesting that low levels of salinity can alter the short-term C dynamics of tidal freshwater forests.