Pore Water Salinity Research Articles

Effects of the middle Holocene high sea‐level stand and climate on Amazonian mangroves

ABSTRACTThe high sea‐level stand during the mid‐Holocene is a benchmark in mangrove dynamics along the north‐east/south‐east coast of Brazil and provides a reference point for landward and seaward mangrove migrations corresponding to changes in relative sea level (RSL). However, evidence of the impacts associated with RSL fall on the northern Brazilian coast is scarce. Multi‐proxy data from the highest tidal flats of the Bragança Peninsula in northern Brazil revealed modern herbaceous areas were occupied by mangroves Rhizophora and Avicennia from ~6250 to ~5850 cal a bp, and only Avicennia between ~5850 and ~5000 cal a bp. The same tidal flats were vegetation‐free between ~5000 and ~4300 cal a bp. A combination of a high sea‐level stand (0.6 ± 0.1 m) at ~5000 cal a bp and a dry early–middle Holocene in the Amazon probably caused an increase in porewater salinity of tidal flats, which resulted in a mangrove succession from Rhizophora to Avicennia dominance. RSL fall accentuated this process, contributing to mangrove degradation between ~5000 and ~4300 cal a bp. RSL fall, and a wetter period over the past ~4300 cal a bp caused a mangrove migration from highest to lowest flats, followed by expansion of herbaceous vegetation on the highest flats.

Control of coal-bearing claystone composition by sea level and redox conditions: An example from the Upper Paleozoic of the Datong Basin, North China

In order to investigate the genesis of different types of claystones and facies-related variations in clay mineralogy, a mineralogical and geochemical investigation of the coal-bearing Upper Carboniferous Taiyuan Formation of North China was undertaken in the Wangping and Xiaoyu mines of the SE Datong Basin. This formation contains both kaolinitic and mixed-layer illite/smectite (I/S) claystones having distinctly different compositions. The former is composed of kaolinite with minor illite, quartz, calcite, and boehmite, whereas the latter consists mainly of R1 and R3 mixed-layer I/S clay and kaolinite with minor illite, siderite, quartz, dolomite, and anatase. The two types of claystone formed from the same parent materials, as shown by Al2O3/TiO2 ratios and rare earth element (REE) patterns. Paleosalinity indices (B/Ga and Sr/Ba) and redox proxies (Mo and U enrichment factors and Corg/P ratios) indicate that the kaolinitic claystones formed under freshwater, oxic-anoxic conditions, whereas the I/S claystones formed under brackish, oxic-suboxic conditions. Chemical index of alteration (CIA) values show that the kaolinitic claystones experienced more intense leaching than the I/S claystones, even though both formed in a warm and humid climate, and this result is consistent with late Carboniferous-early Permian global climate and weathering intensity. The kaolinite developed through recrystallization and alteration of terrigenous clastics and an aluminosilicate colloidal solution in a reducing, freshwater peaty swamp environment. The formation of smectite was linked to marine transgressions that altered the salinity and oxygen content of sedimentary porewaters, with subsequent deep-burial conversion of smectite to mixed-layer I/S. The frequent changes in salinity and redox conditions that caused mineralogical variations in Taiyuan Formation claystones were driven by glacio-eustatic fluctuations of the Late Paleozoic Ice Age (LPIA), which led to episodic marine incursions into the Datong Basin.

Effects of pore-water salinity on soil identification using in situ cone penetration tests

In geological surveys of coastal regions, data interpretation and site identification are usually affected by underground water (including salinity). This study aimed to investigate the effect of pore-water salinity on soil identification via in situ CPTs. Combinations of triaxial shearing, cone penetration, and vane shear tests were also performed at a laboratory scale on Lianyungang marine clay with different pore-water salinities. The results suggested that the effective friction angles and shear strength increased with the pore-water salinity. The in situ CPTs showed that the normalized tip resistances increased with an increase in pore-water salinity, whereas no significant correlation between the normalized sleeve fraction and salinities was found. The use of the conventional soil identification method (soil-behavior-type chart, i.e., SBT chart) may be effective in very low-salinity conditions despite that it does not take into account the pore-water salinity effect. The salinity investigation of Lianyungang marine clay suggests that an inhomogeneous salinity distribution significantly influences soil identification when with rich clay mineral of montmorillonite and high pore-water salinity. From the theoretical and practical analyses, an improved soil identification method considering pore-water salinity modification was proposed to avoid the misclassification of in situ soil.

Effect of porewater salinity on compression behaviors and hydraulic conductivity of soft marine clay

This study investigates the effect of porewater salinity on the compression behaviors of soft marine clay with multi-mineral compositions. A series of one-dimension compression tests were conducted with clays at different porewater salinity. The results indicate that the compression index decreases with increasing porewater salinity and can be described by a second-order polynomial equation, where the influence of porewater salinity is limited as the salinity increases to a threshold value. The normalized void indexes are taken from both ICL and EICL curves. It is believed that the compression behaviors of soft marine clay depend on the bentonite content. Hydraulic conductivity was back calculated based on empirical equations and is found to increase with increasing porewater salinity. Hydraulic conductivity is dominated by the inter-aggregated voids for soft marine clay at relatively high porewater salinity, and the influence of porewater salinity on the inter-aggregated voids of soil is limited at high salinity. A conceptual framework was presented to understand the changes in macroscopic soil behaviors with respect to the particles and pore fabrics of soil under the effect of porewater salinity.

Eco-engineering of coastal environment through saltmarsh restoration towards climate change impact mitigation and community adaptation in Bangladesh

A field research was undertaken to investigate the effects of saltmarsh restoration and some eco-engineering activities on the climate change impact mitigation and community adaptation in the coastal environment of Sonadia Island, Cox’s Bazar, Bangladesh. Two research sites viz., saltmarsh restoration site (SMRS) and impacted site (IP) were selected for this study. Amount of carbon assimilation by saltmarsh plant Porteresia coarctata at SMRS was increased from 165.17 ± 68.35 to 198.18 ± 41.32 g/m2 during the study. The highest carbon assimilation (198.18 ± 41.32 g/m2) was noticed during winter, while the highest biomass (10.47 ± 0.25 kg/m2) was measured from SMRS. Soil compactness, organic matter, organic carbon, field water capacity, plant height, plant biomass and shoot density were found to be significantly (p < 0.05 to 0.01) higher in the SMRS than that of the IS. Seasonal variations of air temperature, water temperature, water pH, water salinity, water transparency, tidal height, inundation period, wave velocity, soil temperature, soil pH, pore water salinity, sedimentation, soil texture particle density, plant height, biomass and shoot density at different significance levels (p < 0.05 to p < 0.01) were noticed throughout the study. Correlation matrix showed that the plant height, biomass and shoot density were positively correlated with sedimentation, and negatively correlated with wave velocity at different significant levels (p < 0.05 to p < 0.01). From the present study, it is evident that SMRS, which was controlled and managed with some artificial inputs not only showed the elevated levels of plant height, biomass, shoot density, sedimentation and carbon assimilation but also exhibited remarkable changes in some of the factors studied rather than impacted site (IS), the findings of which could be helpful for the protection of coastal environment as well as mitigation of climate change impact that will ultimately save the local community from natural calamities in the long run.

Diffusion of tritiated water, 137Cs+, and 125I− in compacted Ca-montmorillonite: Experimental and modeling approaches

Mechanistic understanding and predictive modeling of radionuclide diffusion in Na- and Ca-montmorillonite are essential to evaluate the long-term evolution of the bentonite barrier and their impact on radionuclide migration during geological disposal of radioactive wastes. Thus, the diffusion behavior of 137Cs+, 125I−, and tritiated water (HTO) in compacted Ca-montmorillonite was investigated as a function of porewater salinity and dry density via both experiments and models. The effective diffusion coefficient (De) followed in the order of 137Cs+ > HTO > 125I−. The De of 137Cs+ decreased with increasing salinity, whereas the dependence of De of 125I− on salinity was uncertain. The cation excess and anion exclusion effects for Ca-montmorillonite were lower than those for Na-montmorillonite. The integrated sorption and diffusion (ISD) model, assuming the homogeneous pore structure and the electrical double layer (EDL) theory for 2:1 electrolyte (CaCl2), could account for the observed trends for De in Ca-montmorillonite. The lower dependence of De on the porewater salinity in Ca-montmorillonite was caused by the reduction of the EDL thickness for divalent cations (Ca2+) in comparison with that for monovalent cations (Na+). The multipore model could improve the fit for De of 125I− at low salinity due to the reduction of interlayer pore volumes and anion exclusion effect, however, the disparity at higher densities was considerably larger. From these results, cation diffusion for compacted Ca-montmorillonite could be mainly explained by the electrostatic interactions in the homogeneous pore model; in contrast, anion diffusion was sensitive to both electrostatic interactions and heterogeneous pore structures. The proposed ISD model is an effective tool to evaluate the radionuclide diffusion and sorption behavior in both compacted Ca-montmorillonite and Na-montmorillonite.

Changes in carbon and nitrogen metabolism during seawater-induced mortality of Picea sitchensis trees.

Increasing seawater exposure is causing mortality of coastal forests, yet the physiological response associated with seawater-induced tree mortality, particularly in non-halophytes, is poorly understood. We investigated the shifts in carbon and nitrogen (N) metabolism of mature Sitka-spruce trees that were dying after an ecosystem-scale manipulation of tidal seawater exposure. Soil porewater salinity and foliar ion concentrations increased after seawater exposure and were strongly correlated with the percentage of live foliated crown (PLFC; e.g., crown 'greenness', a measure of progression to death). Co-occurring with decreasing PLFC was decreasing photosynthetic capacity, N-investment into photosynthesis, N-resorption efficiency and non-structural carbohydrate (soluble sugars and starch) concentrations, with the starch reserves depleted to near zero when PLFC dropped below 5%. Combined with declining PLFC, these changes subsequently decreased total carbon gain and thus exacerbated the carbon starvation process. This study suggests that an impairment in carbon and N metabolism during the mortality process after seawater exposure is associated with the process of carbon starvation, and provides critical knowledge necessary to predict sea-level rise impacts on coastal forests.

Drying model of a high salt content cementitious waste form: Effect of capillary forces and salt solution

A water transport model coupling capillary liquid flow with vapor diffusion is developed to describe the drying process for a cementitious waste form with high salinity porewater. Vapor-liquid equilibrium is formulated as the driving force for vapor diffusion and the model accounts for pore capillary and high salinity effects on water thermodynamic activity. Pore filling and porewater surface tension as a function of pore size distribution and water saturation have been quantified for the material. Geochemical speciation modeling is used to simulate porewater activity as a function of composition over the range of saturation. The theoretical relationship between relative humidity and water saturation generally agrees with experimental measurement, and the developed model is capable of predicting drying rates under various external relative humidity conditions. The model was developed to be incorporated into reactive transport models considering the effects of drying such as salt redistribution and efflorescence.

Application of electrical resistivity to map the stratigraphy and salinity of fluvio-deltaic aquifers: case studies from Bangladesh that reveal benefits and pitfalls

Fluvio-deltaic aquifers are the primary source of drinking water for the people of Bangladesh. Such aquifers, which comprise the Ganges-Brahmaputra-Meghna Delta, are hydrogeologically heterogeneous. Because of widespread groundwater quality issues in Bangladesh, it is crucial to know the hydrostratigraphic architecture and hydrochemistry, as some aquifer units are contaminated, whereas others are safe. Geophysical methods provide a potentially effective and noninvasive method for extensive characterization of these aquifers. This study applies and investigates the limitations of using electrical resistivity imaging (ERI) for mapping the hydrostratigraphy and salinity of an aquifer-aquitard system adjacent to the Meghna River. Some electrical resistivity (ER) sections showed excellent correlation between resistivity and grain size. These suggest that ERI is a powerful tool for mapping internal aquifer architecture and their boundaries with finer-grained aquitards which clearly appear as low-ER zones. However, in parts of some ER sections, variations in electrical properties were determined by porewater resistivity. In these cases, low ER was indicative of brine and did not indicate the presence of finer-grained materials such as silt or clay. Accordingly, the following hydrostratigraphic zones with different resistivities were detected: (1) aquifers saturated with fresh groundwater, (2) a regional silt/clay aquitard, and (3) a deeper brine-saturated formation. In addition, shallow silt/clay pockets were detected close to the river and below the vadose zone. ERI is thus a promising technique for mapping aquifers versus aquitards; however, the observations are easily confounded by porewater salinity. In such cases, borehole information and groundwater salinity measurements are necessary for ground-truthing.

Effect of Bypass-Flow on Leaching of Salts in a Cracking Soil in the Nile Delta

Salinity is a major threat to the sustainability of irrigated agriculture in arid and semi-arid regions. Leaching is the primary measure for removing excess salts from the root zone, but not all water applied to the soil surface contributes to the removal of salts. In clayey soils, bypass flow along cracks can occur without being mixed with saline pore water in the matrix. To present a field dataset to quantitatively evaluate the contribution of bypass flow to the leaching of salts, soil sampling and monitoring of groundwater and discharge from a tile drain were carried out in farmland having a cracking soil in the Nile Delta. The electrical conductivities of 1:2 extracts were measured to evaluate the salinity of the soil. The first evidence for the occurrence of significant bypass flow through cracks was the salinity of the pore water, which was nearly triple that of the shallow groundwater and outflow from drainage. Second, the difference in root zone salinity before and after paddy rice cultivation was not significant. Third, the gradient of the groundwater table was very small. in spite of the low saturated hydraulic conductivity. Fourth, the salinity of the outflow from the tile drain dropped just after irrigation or rain. These results indicated that bypass flow through cracks played a significant role in the drainage process in the soil, and that nearly half of the water bypasses through cracks in the field with a cracking soil.

Effect of evaporation on soil salinization caused by ocean surge inundation

Ocean surge inundation occurs frequently in low-lying coastal areas worldwide. While studies have been conducted to examine aquifer salinization and recovery caused by ocean surge inundation, evaporation is predominantly overlooked. Based on numerical simulations considering variably saturated, density-dependent pore-water flow and salt transport, this study examines the combined effects of evaporation and ocean surge inundation on soil salinization in coastal unconfined aquifers. The results show that evaporation enhances soil salinization caused by ocean surge inundation. Due to evaporation-induced water uptake, the downward movement of salt is weakened and the salt from the ocean surge inundation is significantly trapped in the unsaturated zone. The pore-water salinity in the shallow soil layer is increased by soil evaporation, particularly in the low-elevation area with longer seawater inundation. The sensitive analysis shows that the evaporation-enhanced soil salinization is more remarkable for silt-loam and clay-loam aquifers rather than sandy-loam aquifers. A higher mean sea level favors salt trapping in the shallow soil layer of aquifers. These results demonstrate the importance of evaporation on soil salinization caused by ocean surge inundation, and that could be considered in future studies.

Volume change behavior of reconstituted marine clay: effect of initial and leaching pore fluid salinity

Because the salinity of marine clay changes continuously in response to the migration of seawater toward land or freshwater from river to sea, the intrinsic pore fluid salinity of the clay-water system may change periodically. Recent studies indicate that pore-water salinity changes the intrinsic properties of reconstituted homoionic artificial clay. However, the effect of seawater on the intrinsic properties of marine clay is unknown. The aim of this study was to investigate changes in the compression parameters of marine clay for the leaching salinity of seawater with respect to tap water. The results show that ratio $${e}_{0}/{e}_{\mathrm{L}}$$ is more sensitive to salinity than $${e}_{100}^{*}$$ . Although the Iv − log p for all samples at different intrinsic/leaching salinities were located on the intrinsic compression line (ICL); some deviation from the ICL was observed at low-stress levels. In high-salinity reconstituted samples, the osmotic gradient caused the low-salinity water to penetrate the clusters and separate individual particles, increasing the size of intra-cluster pores and settlement during consolidation. The distance between the particles at any stress level was larger than in diffuse double layer theory because of a deviation from the assumed parallel fabric in the theory.

Carbon sequestration and storage in planted mangrove stands of Avicennia marina

This work assessed the carbon storage and sequestration potential in the planted mangrove stands of Avicennia marina of different age groups (16–27.2 years), as influenced by vegetation and soil characteristics in an estuarine system of southeast coast of India. The carbon storage was 22-folds higher in soil and 56-folds greater in both tree biomass and soil in the mangrove stands than that in non-planted site. The carbon sequestration was 90-folds higher in soil and 9890-folds greater in both tree biomass and soil than that in control site. Hence, mangrove planting had an extraordinary potential for carbon sequestration in barren areas. The carbon sequestration and storage increased with increasing levels of silt, clay, moisture and nutrients (N, S, Cu, K, P, Fe, Zn, Mn, and Mg) in the mangrove soil. In contrast, the carbon sequestration and storage reduced with increasing levels of temperature, pore-water salinity, pH, bulk density and sand in the mangrove soil. This work calls for an attention on the mangrove stands of low carbon holding for remedial measures through soil management to improve the carbon storage and sequestration potential towards mitigating the global warming.

A 100-km wide slump along the upper slope of the Canadian Arctic was likely preconditioned for failure by brackish pore water flushing

Exploration of the continental slope of the Canadian Beaufort Sea has revealed a remarkable coalescence of slide scars with headwalls between 130 and 1100 m water depth (mwd). With increased depth, the scars widen and merge into one gigantic regional slide scar that is more than 100 km wide below ~1100 mwd. To understand the development of these features, five sites were investigated with an Autonomous Underwater Vehicle, which provided 1-m bathymetric grids and Chirp profiles, and surveyed with a Remotely Operated Vehicle. The morphologies are consistent with retrograde failures that occurred on failure planes located between 30 and 75 m below the modern seafloor. At issue is whether the continental slope in this area is preconditioned for failure. While rapid sedimentation during glacial periods, and the presence of shallow gas cannot be ruled out, given the geological environment, it is unclear that they are primary preconditioning factors. Evidence of widespread flushing of the slope with brackish waters, and observed flows of brackish water within slide scars, suggest fluid venting and overpressure may play a role in the development of the extensive slope failures seen along this margin. The impact of pore water salinity changes at the depth of the failure plane on slope stability has not been considered in marine settings previously.

Effects of salinity and water content on apparent conductivity in an alluvial setting in the Canadian Prairies

Electromagnetic induction surveys are commonly used to assess soil salinity. In this study, a DualEM 1S instrument was used to survey an area in southern Manitoba to characterize sulphate-dominated salinity in clay-rich alluvial soils. The efficacy of predicting apparent conductivity (corrected for departure from low induction number responses) was determined by regression analysis of parameters including saturated-paste salinity, pore-water salinity, volumetric water content, porosity and combinations of these terms determined from 542 soil samples at 65 sampling sites. Predictors were depth-weighted using the V–H mode (exploration depth of 0.5 m) and the V–V mode (exploration depth of 1.5 m) of the electromagnetic instrument. The analysis yielded strong correlations of apparent conductivity (ECa) with saturated-paste or pore water conductivity, with Pearson r2 correlation coefficients exceeding 0.75 for the V–H mode and 0.86 for the V–V mode. The strong correlations of ECa with salinity are explained by moisture conditions being close to field capacity during the survey. These results are similar to those for chloride-dominated salinity. The study yielded less commonly observed results related to the clay-rich soils, including a threshold value of ~ 10% below which volumetric water content does not affect ECa, and an improved prediction of ECa by dividing the porosity data based on clay content. The study results demonstrate the efficacy of using ECa to parameterize sulphate-dominated salinity in clay-rich soils. They also show that salinity can be estimated relatively accurately from saturated paste conductivity at near-field capacity without considering moisture content.

Passive seismic recording of cryoseisms in Adventdalen, Svalbard

Abstract. A series of transient seismic events were discovered in passive seismic recordings from 2-D geophone arrays deployed at a frost polygon site in Adventdalen, Svalbard. These events contain a high proportion of surface wave energy and produce high-quality dispersion images using an apparent offset re-sorting and inter-trace delay minimisation technique to locate the seismic source, followed by cross-correlation beamforming dispersion imaging. The dispersion images are highly analogous to surface wave studies of pavements and display a complex multimodal dispersion pattern. Supported by theoretical modelling based on a highly simplified arrangement of horizontal layers, we infer that a ∼3.5–4.5 m thick, stiff, high-velocity layer overlies a ∼30 m thick layer that is significantly softer and slower at our study site. Based on previous studies we link the upper layer with syngenetic ground ice formed in aeolian sediments, while the underlying layer is linked to epigenetic permafrost in marine-deltaic sediments containing unfrozen saline pore water. Comparing events from spring and autumn indicates that temporal variation can be resolved via passive seismic monitoring. The transient seismic events that we record occur during periods of rapidly changing air temperature. This correlation, along with the spatial clustering along the elevated river terrace in a known frost polygon, ice-wedge area and the high proportion of surface wave energy, constitutes the primary evidence for us to interpret these events as frost quakes, a class of cryoseism. In this study we have proved the concept of passive seismic monitoring of permafrost in Adventdalen, Svalbard.

Hydroperiod and Salinity Interactions Control Mangrove Root Dynamics in a Karstic Oceanic Island in the Caribbean Sea (San Andres, Colombia)

Mangroves sustain high soil accretion and carbon sequestration rates, yet it is still unknown if they can keep pace with increasing sea level rise (SLR) across a wider range of coastal geomorphic settings. Because accretion rates are controlled by mineral sediment inputs and organic matter accumulation, it is paramount to assess the relative contribution of root productivity to soil formation. Here, we evaluated root biomass, production, and turnover in three mangrove ecotypes to evaluate the role of soil nutrient limitation, stressors, and hydroperiod in controlling root dynamics in San Andres Island (SAI), a karstic oceanic island in the Caribbean Sea. Root production was modulated by soil stress conditions and not by nutrient availability as it has been reported for other karstic environments. The lowest root biomass allocation, and both production and turnover of fine roots were measured under low flooding duration, and low salinity (&amp;lt;20 PSU) and sulfide concentrations (0.84 ± 0.4 mM). Yet, when soil stress conditions increased during high flooding duration (6207 h y–1) and low oxygen conditions (Eh), root tissues reached the highest biomass and production values, including a relative fast turnover of fine roots (&amp;lt;2 mm; 0.75 y–1). Our results follow the predictions of the plant root longevity cost-benefit hypothesis where plants maintain roots only until the efficiency of resource acquisition is maximized by water and nutrient acquisition. Because of the importance of groundwater in controlling porewater salinity and mangrove root productivity in karstic oceanic islands such as SAI, water use and coastal development should be regulated in the short term to avoid the loss of mangrove area and concomitant ecosystem services.

Geochemistry of Coastal Permafrost and Erosion-Driven Organic Matter Fluxes to the Beaufort Sea Near Drew Point, Alaska

Accelerating erosion of the Alaska Beaufort Sea coast is increasing inputs of organic matter from land to the Arctic Ocean, and improved estimates of organic matter stocks in eroding coastal permafrost are needed to assess their mobilization rates under contemporary conditions. We collected three permafrost cores (4.5–7.5 m long) along a geomorphic gradient near Drew Point, Alaska, where recent erosion rates average 17.2 m year−1. Down-core patterns indicate that organic-rich soils and lacustrine sediments (12–45% total organic carbon; TOC) in the active layer and upper permafrost accumulated during the Holocene. Deeper permafrost (below 3 m elevation) mainly consists of Late Pleistocene marine sediments with lower organic matter content (∼1% TOC), lower C:N ratios, and higher δ13C values. Radiocarbon-based estimates of organic carbon accumulation rates were 11.3 ± 3.6 g TOC m−2 year−1 during the Holocene and 0.5 ± 0.1 g TOC m−2 year−1 during the Late Pleistocene (12–38 kyr BP). Within relict marine sediments, porewater salinities increased with depth. Elevated salinity near sea level (∼20–37 in thawed samples) inhibited freezing despite year-round temperatures below 0°C. We used organic matter stock estimates from the cores in combination with remote sensing time-series data to estimate carbon fluxes for a 9 km stretch of coastline near Drew Point. Erosional fluxes of TOC averaged 1,369 kg C m−1 year−1 during the 21st century (2002–2018), nearly doubling the average flux of the previous half-century (1955–2002). Our estimate of the 21st century erosional TOC flux year−1 from this 9 km coastline (12,318 metric tons C year−1) is similar to the annual TOC flux from the Kuparuk River, which drains a 8,107 km2 area east of Drew Point and ranks as the third largest river on the North Slope of Alaska. Total nitrogen fluxes via coastal erosion at Drew Point were also quantified, and were similar to those from the Kuparuk River. This study emphasizes that coastal erosion represents a significant pathway for carbon and nitrogen trapped in permafrost to enter modern biogeochemical cycles, where it may fuel food webs and greenhouse gas emissions in the marine environment.

Pore distribution of compacted Ca-montmorillonite using NMR relaxometry and cryoporometry: Comparison with Na-montmorillonite

Abstract This study investigated the pore distributions in water-saturated Ca-montmorillonite using 1H nuclear magnetic resonance (NMR) measurements for various dry densities (0.8–1.6 g/cm 3 ) and porewater salinity conditions (deionized water, 0.1 and 1 M CaCl2) at a temperature range of 233–303 K. The volume fractions of the interlayer pore and the non-interlayer pore in the compacted Ca-montmorillonite were quantified by NMR relaxometry. At a lower Ca-montmorillonite density (0.8 g/cm 3 ), the volume fraction of the 3-HL-dominated interlayer pore was close to 20%, while that of the non-interlayer pore was higher ( > 80%) than that in Na-montmorillonite. For the higher density (1.4 g/cm 3 ), the volume fraction of the interlayer pore in both Ca- and Na-montmorillonite seemed to be more than 90% close to the total porosity. This comparison showed that the main factor affecting the pore distribution in the compacted Ca- and Na-montmorillonite is density. Meanwhile, the effect of the porewater salinity is relatively smaller. The effect of the interlayer cations is also relatively smaller at the higher density. The established method based on NMR relaxometry is expected to provide structural parameters for a realistic modeling of mass transport in water-saturated compacted clay.

Surface Resistivity Sounding and Borehole Data Analysis for the Evaluation of Aquifer Characteristics of Southern Districts Barguna and Patuakhali, Bangladesh

The study delineates the aquifer system of the study area and determines the extension of potential fresh water aquifer and suitable locations for groundwater development through geophysical electrical resistivity method. Vertical electrical sounding with Schlumberger electrode configuration, a method for surface resistivity measurement, has been used for data collection. Resistivity data along with borelog data analyses are used for this investigation. Lithological cross section analyses show that sand and clay dominated lithology with frequent facies changes occur throughout the area and also show an aquifer system similar to the three-tier aquifer system proposed by Aggarwal for coastal area of Bangladesh. This study reveals the presence of three aquifers. 1staquifer occurs at a very shallow depth at some places &lt;5 m and thickness of the aquifer varies 10-70 m all over the region, and shows very low resistivity value indicating saline pore water. Average depth to the 2nd aquifer ranges from 60-70 m and also contaminated by saline water. In few places of 2nd aquifer resistivity values more than 20 Ωm suggest some fresh water pockets. Depth to the 3rd aquifer that spreads all over the study area is more than 220 m at maximum part of the area. Only potential fresh water aquifer is the 3rd or deep aquifer, but low resistivity values of this aquifer at Patharghata and small portion of Kalapara and Rangabali Upazilas hint that there may have saline water intrusion. More precise information for this complex geological set up require greater number of sounding points.&#x0D; The Dhaka University Journal of Earth and Environmental Sciences, Vol. 8(1), 2019, P 11-18