Pore Water Salinity Research Articles

Environmental drivers of sediment carbon storage in temperate seagrass meadows

Seagrass meadows are productive ecosystems that contribute to climate change mitigation by accumulating ‘Blue Carbon’ in their plant biomass and sediments. However, there is wide variation in reported sediment carbon stocks (Cstocks) across different global regions and between meadows composed of different seagrass species. Therefore, understanding the drivers for sediment Cstocks variation is crucial to developing effective conservation and restoration projects for seagrass ecosystems. This study analyses the influence of environmental factors on the variation in sediment Cstocks for six intertidal seagrass meadows within the Solent region, in southern England. There were significant differences between sites for all variables, except leaf density, and concentrations of the sediment pore water nutrients. Sediment dry bulk density, mean grain size, sorting coefficient, % mud, elevation above sea level, and pore water salinity showed high levels of association with Cstocks when assessed individually. Multivariate analyses showed that sediment dry bulk density, sorting coefficient, % mud, and pore water pH and concentration of nutrients greatly influenced Cstock. Moreover, sediment characteristics acted in conjunction to explain most of the variation in Cstock among sites. Therefore, sediment characteristics should be considered as important indicators for carbon storage potential in intertidal temperate seagrass meadows.

Microbes from wastewater treated mangrove soil and their heavy metal accumulation and Zn solubilization

Abstract The present study isolated and identified six species of bacteria and fungi from the rhizosphere soil of mangroves species (Avicennia marina), treated for 60 days with artificial wastewater, and further tested for their potential in heavy metal accumulation and Zn solubilization. The wastewater treated mangrove soil had higher microbial counts, porewater salinity and nutrients (N, P, K, total organic carbon), but lower soil bulk density, pH and temperature. The predominant bacterial strains isolated from the treated soil were identified as Bacillus altitudinis, B. anthracis and B.marisflavi, and the fungal strains as Penicillium citrinum, Aspergillus quadrilineatus and Gibberella intermedia. The heavy metal accumulation was determined in those microbial strains cultured with artificial wastewater under shaker culture for seven days. The accumulation was the highest for Zn (70% over control), Cu (62%), Pb (62%) in the bacterium, B. marisflavi and for Mn (50%) in the fungus, P. citrinum. The B.marisflavi was further tested for Zn solublization in terms of pH decline, after 10 days of incubation with the insoluble Zn sources (ZnO, ZnSO4 and ZnCO3). The highest activity of 31.6% pH drop was observed with ZnO. Overall results revealed the potential of B. marisflavi in heavy metal removal and Zn solubilization.

A Darcy‐Brinkman‐Biot Approach to Modeling the Hydrology and Mechanics of Porous Media Containing Macropores and Deformable Microporous Regions

AbstractThe coupled hydrology and mechanics of soft porous materials (such as clays, hydrogels, membranes, and biofilms) is an important research area in several fields, including water and energy technologies as well as biomedical engineering. Well‐established models based on poromechanics theory exist for describing these coupled properties, but these models are not adapted to describe systems with more than one characteristic length scale, that is, systems that contain both macropores and micropores. In this paper, we expand upon the well‐known Darcy‐Brinkman formulation of fluid flow in two‐scale porous media to develop a “Darcy‐Brinkman‐Biot” formulation: a general coupled system of equations that approximates the Navier‐Stokes equations in fluid‐filled macropores and resembles the equations for poroelasticity in microporous regions. We parameterized and validated our model for systems that contain either plastic (swelling clay) or elastic microporous regions. In particular, we used our model to predict the permeability of an idealized siliciclastic sedimentary rock as a function of pore water salinity and clay content. Predicted permeability values are well described by a single parametric relation between permeability and clay volume fraction that agrees with existing experimental data sets. Our novel formulation captures the coupled hydro‐chemo‐mechanical properties of sedimentary rocks and other deformable porous media in a manner that can be readily implemented within the framework of Digital Rock Physics.

Potential geologic osmotic pressure in the Wakkanai Formation: Preliminary estimation based on the dynamic equilibrium between chemical osmosis and advection

Geologic osmotic pressure has been proposed as a cause of excess fluid pressures in argillaceous formations in which dynamic geologic processes have little effect on pressure. However, the identification of geologic osmotic pressure has rarely been attempted, thus its potential effect on groundwater systems is a longstanding question in hydrogeology. Herein we present a quantitative analysis of excess fluid pressures of unknown origin in the Wakkanai Formation, assuming osmotically generated overpressure. Potential geologic osmotic pressures are estimated from profiles of pore water salinity and rock physical properties using a one-dimensional model that describes geologic osmotic pressures in a state of dynamic equilibrium between chemical osmosis and advection. The model results indicate that the Wakkanai Formation has the requisite conditions of both salinity gradient and semipermeability to generate geologic osmotic pressures comparable to observed excess pressures, up to 230 kPa. The applicability of the dynamic equilibrium model is also confirmed by using a steady-state model with the same pore water salinity and rock physical properties data. These results suggest that chemical osmosis is a potential cause for the excess fluid pressures observed in the Wakkanai Formation.

Differential pressure dependence of the complex conductivity of sandstones

SUMMARY An experimental work is undertaken to understand the effect of the differential pressure (in the range 3–20.7 MPa) upon the complex conductivity of sedimentary rocks. We use five sandstone core samples from outcrops and a sandstone analog built from sintered glass beads. The spectra were fitted with a Cole–Cole complex conductivity model and the four Cole–Cole parameters were plotted as a function of the differential stress (in the range 3–20.7 MPa). The Cole–Cole relaxation times are analysed in terms of the evolution of the pore size with the differential pressure. Neither the relaxation time nor the Cole–Cole exponent show a strong dependence with the differential pressure indicating that the distribution of the relaxation times remains here roughly the same when the differential stress increases. More specifically, the Cole–Cole exponent does not describe the entire distribution of relaxation times, but the broadness of this distribution. Since the relaxation times are related to the pore sizes, this means that the pore sizes do not depend on the differential pressure in this case. The chargeability is essentially independent of the differential pressure and close to the upper value that can be reached in rocks without metallic particles. This also means that the conductivity of these rocks is dominated by their surface conductivity contribution considering the low pore water salinity used in this work. These results are interpreted thanks to the Stern layer polarization model. The Stern layer denotes the inner part of the electrical double layer coating the surface of the grains. The predictions of this model are mostly consistent with the data.

Effect of Salinity on Strength Behavior of Cement-treated Dredged Clay at High Initial Water Contents

This paper presents the experimental investigation into the effect of salinity on the strength behavior of cement-stabilized dredged clays as fills at high initial water contents. One source of dredged clay was dredged from Baima Lake of China. Specimens were prepared having different porewater salinities by blending the air-dried clays with NaCl solution at different salt concentrations. The prepared saline dredged clay specimens were thereafter adjusted to different initial water contents and blended with cement with different amounts. Unconfined compression tests were performed on cement-stabilized dredged clay specimens after 28-day curing. All tested specimens show strain softening behavior where the axial strain corresponding to the peak stress varies with amount of cement. Stress-strain curve for the specimen with lower salinity lies above on that of higher one. Initial water content has a negative effect on the strength of cement-treated clays while cement has a positive effect on the development of strength for cement-treated dredged clays due to the pozzolanic reactions. The presence of salt has an adverse influence on the obtaining of strength for cement-treated dredged clays because salt can inhibit cement from generating C-S-H and C-A-H. Unconfined compressive strength almost linearly decreases with the increasing salinity. A quantitative expression was presented to calculate the unconfined compressive strength for cement-treated saline dredged clays concerning the effects for initial water content, porewater salinity and amount of cement.

Crab burrows as preferential flow conduits for groundwater flow and transport in salt marshes: A modeling study

Crab burrows can act as preferential flow conduits for pore water-surface water interactions in salt marshes, but the effect of preferential flow on subsurface transport in these tidally-influenced systems is not fully understood. We used numerical models based on salt marshes of North Inlet, South Carolina, to investigate the impacts of crab burrows on porewater salinity. This modeling effort was inspired by field results from North Inlet, where prior field studies that used a combination of tension samplers and passive diffusion samplers measure salinity in crab burrows and in the adjacent sediment matrix found that the minimum salinity (28 PSU) reported by the tension samplers was larger than the maximum salinity (26 PSU) reported by passive diffusion samplers. Two kinds of numerical models were developed to investigate the effect of crab burrows on tidally-driven groundwater flow and salt transport. In the equivalent-continuum model (ECM), crab burrows were included via a shallow surface layer with hydraulic properties representing a bulk average of sediment matrix and crab burrow properties. In the preferential flow model (PFM), an independent high-permeability material was embedded in the surface muddy layer to explicitly simulate preferential flow conduits. The simulated results showed that both models can depict the effect of crab burrow on soil saturation and salt transport in salt marshes. The presence of crab burrows can greatly increase tidally-driven water exchange, improve the intensity and duration of soil aeration and enhance salt transport in salt marshes. The effect of crab burrows on groundwater flow and salt transport varied spatially from the creek bank to marsh interior. PFM models demonstrated that salinity is likely to differ between crab burrows and the sediment matrix, which supports observed differences in results between tension samplers and passive diffusion samplers. These findings may have important implications for practical pore water sampling and hydrochemical investigation in coastal wetlands.

Shrinkage property of bentonite-sand mixtures as influenced by sand content and water salinity

The shrinkage of bentonite-sand mixtures may degrade the performance of a clay barrier constructed in waste disposal facilities. In this study, changes to material properties occurring when bentonite was modified by addition of sand and exposure to different pore water salinities were considered. Paste-like bentonite-sand mixtures were free-desiccated in the laboratory. Sand addition could only reduce the volumetric shrinkage of material when the percentage of sand was larger than 30%. Changes in pore water salinity also may reduce shrinkage of the material because bentonite aggregates were flocculated by synthetic brackish groundwater based on results from particle and pore size analysis. For both effects on the bentonite, the reductions of material shrinkage can be considered theoretically by a packing phenomenon accompanied by the evolution of a mixed grain size distribution.

Water flow and solute transport due to Macrotide in a gravel beach

A combined field and numerical study of water flow and solute transport was conducted along a clean transect of a tidal gravel beach in Smith Island, Prince William Sound (PWS) that was heavily polluted after the Exxon Valdez oil spill. Water table and pore water salinity were directly measured in the field. The numerical model MARUN, validated with the field observations, was used to simulate subsurface flow and dissolved salt transport processes. Our study identified a two-layer hydraulic structure in the beach, a high-permeability upper layer and a low-permeability layer at the bottom. Numerical simulations indicated that the density gradient between the saltwater and freshwater strongly affects solute transport in the intertidal zone of the beach. A sensitivity study indicated that depth to and slope of the bedrock had major effects on solute transport in the lower layer, but minor effects in the upper layer. A deep bedrock caused the water particles travelling in the lower layer to penetrate deeper in the beach. Our study revealed high terrestrial freshwater recharge to the transect which promotes the removal of oil in two-layer beaches by maintaining the water table at or above the interface of the two layers. The study presented in this paper has strong implications on the oil persistence and associated removal strategies along the Alaskan coastline polluted with oil. Findings from this work in relation to oiled beaches include: 1) oil tends to persist at locations of small freshwater recharge and 2) Prior to oil arriving to the shoreline, one could minimize oil penetration into the beach by releasing water onto the beach at the high tide line during low tides.

Combined geophysical and analytical methods to estimate offshore freshwater extent

Offshore fresh groundwater is increasingly suggested as a potential water resource for onshore human demands. In many cases, onshore pumping already draws significant fresh groundwater from offshore. However, offshore aquifers and the extent of offshore freshwater are usually poorly characterised due to data scarcity. This study combines geophysical data, hydraulic information and a first-order mathematical analysis to investigate offshore freshwater extent in the Gambier Embayment (Australia). A large seismic data set, combined with onshore and offshore bore-log geological profiles, are used to explore the regional offshore hydro-stratigraphy. Aquifer hydraulic parameters and onshore heads are obtained from onshore investigations. A novel application of Archie’s law, geophysical data and onshore hydrochemical data provide useful insights into the salinity profiles within four offshore wells. These are compared to steady-state, sharp-interface estimates of the freshwater extent obtained from a recently developed analytical solution, albeit using simplified conceptual models. Salinities derived from resistivity measurements indicate that in the south of the study area, pore water with total dissolved solids (TDS) of 2.2 g L−1 is found up to 13.2 km offshore. Offshore pore-water salinities are more saline in the northern areas, most likely due to thinning of the offshore confining unit. The analytical solution produced freshwater-saltwater interface locations that were approximately consistent with the freshwater-saltwater stratification in two of the offshore wells, although analytical uncertainty is high. This investigation provides a leading example of offshore freshwater evaluation applying multiple techniques, demonstrating both the benefit and uncertainty of geophysical interpretation and analytical solutions of freshwater extent.

Giant tufas of Lake Van record lake-level fluctuations and climatic changes in eastern Anatolia,Turkey

Lake Van, the largest soda lake in the world, is a key area where climatic changes are recorded by well-preserved sedimentary successions. In spite of the existence of such sequences, the ancient lake levels are still under debate. Here, we present U/Th ages of tufa layers exposed along the northern margin of the lake near the town of Adilcevaz. Tufa are interpreted to form during humid and temperate climate conditions in the contact zone between the highly alkaline lake water – rich in bicarbonate and carbonate ions – and calcium-rich groundwater. These contact zones most likely appear near shore. Thus, U/Th ages and altitude of the tufa present minimum ancient lakestands. The tufas obtained in our study are dated between 112.7 and 19.3 ka. They are interpreted to record two transgressional intervals, the first starting at 1701 meters above sea level (masl) altitude at 112.7 ka reaching 1706 masl at 72.5 ka (based on three U/Th ages). The second transgression starts at the present Lake Van level of 1646 masl at 30.1 ka, reaching 1725 masl at 19.3 ka (based on 15 U/Th ages). Comparison with climate proxies reveals that the first transgression was caused by intensified precipitation accompanied by warming, while the second transgression was triggered mainly by warming that initiated melting of glaciers. The lake-level fluctuations described here are almost in line with the ones gathered from dated lake terraces but contradict lake-level reconstruction based on pore water salinity.

Integrating field and laboratory approaches for ripple development in mixed sand-clay-EPS.

The shape and size of sedimentary bedforms play a key role in the reconstruction of sedimentary processes in modern and ancient environments. Recent laboratory experiments have shown that bedforms in mixed sand–clay develop at a slower rate and often have smaller heights and wavelengths than equivalent bedforms in pure sand. This effect is generally attributed to cohesive forces that can be of physical origin, caused by electrostatic forces of attraction between clay minerals, and of biological origin, caused by ‘sticky’ extracellular polymeric substances (EPS) produced by micro‐organisms, such as microalgae (microphytobenthos) and bacteria. The present study demonstrates, for the first time, that these laboratory experiments are a suitable analogue for current ripples formed by tidal currents on a natural mixed sand–mud–EPS intertidal flat in a macrotidal estuary. Integrated hydrodynamic and bed morphological measurements, collected during a spring tide under weak wave conditions near Hilbre Island (Dee Estuary, north‐west England, UK), reveal a statistically significant decrease in current ripple wavelength for progressively higher bed mud and EPS contents, and a concurrent change from three‐dimensional linguoid to two‐dimensional straight‐crested ripple planform morphology. These results agree well with observations in laboratory flumes, but the rate of decrease of ripple wavelength as mud content increased was found to be substantially greater for the field than the laboratory. Since the formation of ripples under natural conditions is inherently more complex than in the laboratory, four additional factors that might affect current ripple development in estuaries, but which were not accounted for in laboratory experiments, were explored. These were current forcing, clay type, pore water salinity and bed EPS content. These data illustrate that clay type alone cannot explain the difference in the rate of decrease in ripple wavelength, because the bed clay contents were too low for clay type to have had a measurable effect on bedform development. Accounting for the difference in current forcing between the field and experiments, and therefore the relative stage of development with respect to equilibrium ripples, increases the difference between the ripple wavelengths. The presence of strongly cohesive EPS in the current ripples on the natural intertidal flat might explain the majority of the difference in the rate of decrease in ripple wavelength between the field and the laboratory. The effect of pore water salinity on the rate of bedform development cannot be quantified at present, but salinity is postulated herein to have had a smaller influence on the ripple wavelength than bed EPS content. The common presence of clay and EPS in many aqueous sedimentary environments implies that a re‐assessment of the role of current ripples and their primary current lamination in predicting and reconstructing flow regimes is necessary, and that models that are valid for pure sand are an inappropriate descriptor for more complex mixed sediment. This study proposes that this re‐assessment is necessary at all bed clay contents above 3%.

Bayesian joint inversion of controlled source electromagnetic and magnetotelluric data to image freshwater aquifer offshore New Jersey

SUMMARY Joint inversion of multiple electromagnetic data sets, such as controlled source electromagnetic and magnetotelluric data, has the potential to significantly reduce uncertainty in the inverted electrical resistivity when the two data sets contain complementary information about the subsurface. However, evaluating quantitatively the model uncertainty reduction is made difficult by the fact that conventional inversion methods—using gradients and model regularization—typically produce just one model, with no associated estimate of model parameter uncertainty. Bayesian inverse methods can provide quantitative estimates of inverted model parameter uncertainty by generating an ensemble of models, sampled proportional to data fit. The resulting posterior distribution represents a combination of a priori assumptions about the model parameters and information contained in field data. Bayesian inversion is therefore able to quantify the impact of jointly inverting multiple data sets by using the statistical information contained in the posterior distribution. We illustrate, for synthetic data generated from a simple 1-D model, the shape of parameter space compatible with controlled source electromagnetic and magnetotelluric data, separately and jointly. We also demonstrate that when data sets contain complementary information about the model, the region of parameter space compatible with the joint data set is less than or equal to the intersection of the regions compatible with the individual data sets. We adapt a trans-dimensional Markov chain Monte Carlo algorithm for jointly inverting multiple electromagnetic data sets for 1-D earth models and apply it to surface-towed controlled source electromagnetic and magnetotelluric data collected offshore New Jersey, USA, to evaluate the extent of a low salinity aquifer within the continental shelf. Our inversion results identify a region of high resistivity of varying depth and thickness in the upper 500 m of the continental shelf, corroborating results from a previous study that used regularized, gradient-based inversion methods. We evaluate the joint model parameter uncertainty in comparison to the uncertainty obtained from the individual data sets and demonstrate quantitatively that joint inversion offers reduced uncertainty. In addition, we show how the Bayesian model ensemble can subsequently be used to derive uncertainty estimates of pore water salinity within the low salinity aquifer.

Submarine Permafrost Map in the Arctic Modeled Using 1‐D Transient Heat Flux (SuPerMAP)

AbstractOffshore permafrost plays a role in the global climate system, but observations of permafrost thickness, state, and composition are limited to specific regions. The current global permafrost map shows potential offshore permafrost distribution based on bathymetry and global sea level rise. As a first‐order estimate, we employ a heat transfer model to calculate the subsurface temperature field. Our model uses dynamic upper boundary conditions that synthesize Earth System Model air temperature, ice mass distribution and thickness, and global sea level reconstruction and applies globally distributed geothermal heat flux as a lower boundary condition. Sea level reconstruction accounts for differences between marine and terrestrial sedimentation history. Sediment composition and pore water salinity are integrated in the model. Model runs for 450 ka for cross‐shelf transects were used to initialize the model for circumarctic modeling for the past 50 ka. Preindustrial submarine permafrost (i.e., cryotic sediment), modeled at 12.5‐km spatial resolution, lies beneath almost 2.5 ×106km2of the Arctic shelf. Our simple modeling approach results in estimates of distribution of cryotic sediment that are similar to the current global map and recent seismically delineated permafrost distributions for the Beaufort and Kara seas, suggesting that sea level is a first‐order determinant for submarine permafrost distribution. Ice content and sediment thermal conductivity are also important for determining rates of permafrost thickness change. The model provides a consistent circumarctic approach to map submarine permafrost and to estimate the dynamics of permafrost in the past.

Longitudinal Gradients in Tree Stem Greenhouse Gas Concentrations Across Six Pacific Northwest Coastal Forests

AbstractThe aim of this study was to examine the magnitude of greenhouse gas (GHG) concentrations in tree stems of Pacific Northwest, USA coastal forests and evaluate various tree and site characteristics along river‐to‐sea gradients as possible drivers of tree stem GHG variation. We measured the concentration of CH4, CO2, and N2O during summer and winter in live and dead tree stems of five species from six coastal watersheds and related this to soil porewater GHG concentrations, porewater salinity, and tree characteristics. Overall, average pCO2 and pCH4 were elevated above atmospheric concentration, and average pN2O was slightly below atmospheric concentration. Stem pCO2 was higher in the summer than the winter and was higher in angiosperm trees compared to gymnosperm trees, whereas pCH4 was significantly higher in fresh upstream compared to salt‐influenced reaches. Stem pCH4 was also positively correlated with porewater pCH4 in contrast to other GHGs. The above results suggest that tree stem pCH4 in these coastal settings was primarily controlled by soil linkages, pCO2 was primarily regulated by tree physiology, and factors controlling pN2O remain unclear.

Explanation of the Influence of Sodium Chloride Solution on Volume Deformation and Permeability of Normally Consolidated Clays.

The marine clays located in the Southeast area of China are characterized by their higher water content, higher compressibility and higher salinities. This soil is mainly composed of illite/montmorillonite interlayer minerals. Previous research has shown that the saline water significantly influences the liquid limit and other physical characteristics of the clays. As the desalination of pore water occurs as a result of freshwater or rainfalls, the physical and mechanical behaviors of the soft marine clays changes, and this can lead to potential hazards for infrastructure. Therefore, it is essential to understand the effects of chemistry variations and to predict the long-term foundation deformations. Based on previous works, the deformation behavior of artificial soils corresponding to a mixture of kaolinite and bentonite (the mass ratios of bentonite were 0%, 5%, 10% and 20%) was further discussed in a ln(1 + e)-logp’ system. The permeabilities of the samples mixed with different concentrations of sodium chloride solutions were compared based on oedometer tests. The micro-structures in the samples were investigated by SEM (scanning electronic microscopy) tests. The declining trend of a newly defined volume compression index Ccv and swelling index Csv with pore water salinity and e0/eL was observed when the initial void ratios e0 of the samples were close. The permeability coefficient k and the slopes Ck = e/logk of the mixtures increased with the ionic concentrations. Finally, the changes in volume deformations and permeabilities induced by sodium chloride solution are discussed based on ‘suction pressure’ and initial void compression at micro-level. This paper proves that the influences of salinity on the mechanical behavior of clays are mainly attributable to the interaction between diffused double layers, and these findings are helpful for improving the constitutive model of soft clays when taking pore water chemistry changes into consideration.

Effect of salinity on rheological and strength properties of cement-stabilized clay minerals

This paper presents an experimental investigation into the effect of salinity on Atterberg limits, flowability, viscosity and strength properties of cement-stabilized clay minerals. Three groups of clay minerals (illite, kaolinite and montmorillonite) were obtained. Specimens with different porewater salinities were prepared by mixing the air-dried clays with sodium chloride (NaCl) at various salt concentrations (i.e., 0%, 2% 4%, 6% and 8%). Atterberg limits test results indicated that liquid limit and plasticity index decreased insignificantly with increasing salinity for Kaolinite and illite but significantly for montmorillonite. Flow test results indicated that of all specimens of three groups of clay minerals with or without adding cement consistently increase with increasing salinity. The flow value of montmorillonite increased more significantly than kaolinite and illite. Viscosity test results indicated that all the specimens tested behave as Bingham plastic. Flow value consistently decreased with increasing dynamic viscosity or yield stress, regardless of clay mineralogy, porewater salinity and cement amount. Strength test results indicated that all cement-stabilized specimens exhibit strain softening behavior. Unconfined compressive strength for three groups of clay minerals stabilized with cement consistently decreased with increasing salinity indicating that the presence of salt had an adverse effect on the development of strength.

Salt Marsh Greenhouse Gas Fluxes and Microbial Communities Are Not Sensitive to the First Year of Precipitation Change

AbstractChanging precipitation patterns are predicted to alter ecosystem structure and function with potential carbon cycle feedbacks to climate change. Influenced by both land and sea, salt marshes are unique ecosystems and their productivity and respiration responses to precipitation change differ from those observed in terrestrial ecosystems. How salt marsh greenhouse gas fluxes and sediment microbial communities will respond to climate‐induced precipitation changes is largely unknown. We conducted 1‐year precipitation manipulation experiments in the Spartina patens (high marsh) zone of two salt marshes and quantified ecosystem functions at both and microbial community structure at one. Precipitation treatments (doubled rainfall, extreme drought, and seasonal intensification) had a significant, although transient, impact on porewater salinity following storms at both sites, but most site conditions (nutrient concentrations, sediment moisture, and temperature) were unaffected. Extreme drought led to a subtle change in microbial community structure, but most ecosystem functions (primary productivity, litter decomposition, and greenhouse gas fluxes) were not affected by precipitation changes. The absence of ecosystem function change indicates functional redundancy (under extreme drought) and resistance (under doubled precipitation and seasonal intensification) exist in the microbial community. Our findings demonstrate that salt marsh ecosystems can maintain function (including ecosystem services like carbon sequestration) under even the most extreme precipitation change scenarios, due to resistance, resilience, and functional redundancy in the underlying microbial community.

Influence of pore water salinity on the compressibility of Maryland clay

Influence of pore water salinity on the compressibility of Maryland clay

Application of VES and ERT for delineation of fresh-saline interface in alluvial aquifers of Lower Bari Doab, Pakistan

Geophysical methods are effectively used to delineate intrusion boundary between the fresh and saline aquifers because of their intrinsic capability to assess the lateral variations in the pore-water salinity. In this study, an integrated geophysical approach of vertical electrical sounding (VES) and electrical resistivity tomography (ERT) has been conducted to delineate the contaminated aquifers in the Lower Bari Doab, Pakistan. Electrical resistivity tomography (ERT) using Schlumberger array with 5 m electrode spacing was conducted along eleven profiles at three selected sites (LBD1, LBD2 and LBD3) in the investigated area. The surface geoelectrical method was performed by sixty electrical resistivity soundings using the same array with maximum current electrode spacing (AB = 150 m). The integration of formation resistivity with ten boreholes reveals four discrete subsurface layers i.e., clay having saline aquifer, clay-sand containing brackish aquifer, sand with fresh aquifer and gravel-sand containing fresh aquifer. Estimation of Dar-Zarrouk Parameters (i.e., longitudinal resistivity, transverse resistance and longitudinal conductance) from different combinations of aquifer thickness and resistivity delineated the fresh, brackish and saline water zones with specific values range through mapping and graphical analysis. Geochemical method was performed on forty wells for main cations (K+, Na+, Ca2+ and Mg2+), anions (SO42−, Cl−, HCO3– and NO3−) and other parameters (As, EC, TDS and pH) to validate the results obtained from the geophysical methods. The fresh/saline aquifers delineated by the inclusion of ERT and geoelectrical method are in good agreement with those revealed by the physicochemical analysis and the local hydrogeological data. The results suggest that the use of non-invasive geophysical methods can reduce the number of expensive boreholes to obtain an interface between the fresh and saline water for the exploitation of fresh groundwater resources in any large area of homogeneous or heterogeneous aquifers.