Mixture Of Seawater Research Articles

An Effective Method for Quantitative Interpretation of Seawater Intrusion in Shallow Aquifers from Electrical Resistivity Data

Groundwater in coastal areas is vulnerable to saltwater intrusion. Electrical resistivity is commonly used in order to detect saltwater intrusion due to its ability to distinguish the occurrence of saltwater in the pore water. In this research, a correlational approach was used to estimate percentage seawater content that was mixed with fresh water in a shallow aquifer. The study area was located in Dumai City, which was covered mainly by peat soil, but some areas were covered by sand and silt. A ground surface resistivity survey and direct soil resistivity measurements were used in the study. For both experiments, the Wenner configuration of electrical resistivity was employed. In order to determine the direct soil resistivity values, measurements of the soil's fluid content and character were made. The findings indicate that the resistivity value in the aquifer increased to 5–10 Wm at a 25% seawater content, from roughly 2–5 Wm at a 50% seawater content. The pore soil's rising salt content was the primary source of the sharp decline in resistivity values. By measuring the electrical resistivity on the surface, it is possible to accurately forecast the percentage of seawater mixture in the pore soil fluid.

Source and age of the Ngaye banded iron formations, Adamawa Yadé Domain, Central Cameroon: Constraints from whole-rock geochemistry and U-Pb zircon geochronology

The Ngaye inlier of the Adamawa Yadé Domain is located in the Central African Fold Belt, adjacent to the Nyong Complex at the northern margin of the Congo craton, in central Cameroon. This area consists of metamorphosed granite-greenstone associations comprising amphibole- and pyroxene-rich banded iron formations (BIFs), amphibolites, and migmatitic gneisses. This study reports detailed petrographic, whole-rock geochemical, and LA-ICP-MS U-Pb zircon data for the Ngaye BIFs and associated amphibolites to better constrain their source, tectonic setting, and age. Amphibole-rich BIFs exhibit high REE-Y content and uncommon LREE-enriched patterns. In contrast, pyroxene-rich BIFs display combined low REE-Y content, seawater-like patterns, and positive Eu anomalies, suggesting a mixture of seawater and hydrothermal fluids during their deposition. The geochemical data of associated amphibolites suggest a back-arc setting for the Ngaye metavolcanosedimentary sequence, similar to that of the Nyong Complex. LA-ICP-MS U-Pb zircon dating of amphibole-rich BIFs indicate a maximum depositional age of ca. 2186 Ma and subsequent metamorphism at ca. 2038 Ma, overlapping with that of metavolcanosedimentary sequences from the Nyong Complex. Neoproterozoic age of ca. 598 Ma obtained for these BIFs is interpreted as the Pan-African metamorphic/hydrothermal imprint. This finding suggests that the post-depositional fluid overprint was probably related to the regional Pan-African tectono-thermal event.

Role of malic acid in enhancing the efficiency of barley (Hordeum vulgare L.) and alfalfa (Medicago sativa L.) plants for phytoremediation of salt affected soil

Soil salinization is a growing global problem that influences plant growth and crop productivity. Most of the reclamation efforts in the past have focused on the installation of surface drainage systems. Other management approaches, such as excessive leaching and chemical amendments, have also been used on a limited scale to enhance the productivity of these soils. Phytoremediation can be cost-effective and environmentally sound technology.A laboratory experiment was carried out to study the role of malic acid which is low molecular weight organic acid (LMWOA) in enhancing the efficiency of barley and alfalfa plants for the phytoremediation of salt-affected soil. Seeds of barley and alfalfa were cultured in pots and irrigated with full strength Hoagland nutrient solution with three concentrations of seawater (SW) (10%, 20% and 30%) and a mixture of seawater with malic acid (MA) at 2, 4 and 6 mM l-1 (MA+SW), Hoagland solution was used as control. After twelve weeks, plants were harvested, and three types of soils (barley soil, alfalfa soil, and plant-free soil) were subjected to physical and chemical analysis for EC (electrical conductivity), TOC (total organic carbon), pH, potassium, sodium, and chloride ions. Results indicated a significant decrease was recorded in soil EC, pH, potassium, sodium, and chloride ions and a significant increase in soil TOC in barley and alfalfa soil compared with plant-free soil. Treatments with (MA+SW), especially at (2+10%) resulted in a significant increase in ions availability and phytoremediation activity in barley and alfalfa soils comparing with plant-free soil.

Hypoxia exerts greater impacts on shallow groundwater nitrogen cycling than seawater mixture in coastal zone.

There is no doubt that hypoxia and seawater mixture are profoundly affecting the global nitrogen (N) cycle. However, their mechanisms for altering N cycling patterns in shallow coastal groundwater are largely unknown. Here, we examined shallow groundwater N transformation characteristics (dissolved inorganic N and related chemical properties) in the coastal area of east and west Shenzhen City. Results showed that common hypoxic conditions exist in this study area. Ions/Cl- ratios indicated varying levels of saltwater mixture and sulfide formation across this study area. Dissolved oxygen (DO) affects the N cycle process by controlling the conditions of nitrification and the formation of sulfides. Salinity affects nitrification and denitrification processes by physiological effects, while sulfide impacts nitrification, denitrification, and dissimilatory nitrate reduction to ammonium (DNRA) processes through its own toxicity mechanism and the provision of electron donors for DNRA organisms. Redundancy analysis (RDA) results indicate that the influence magnitude is in the following order: DO > sulfide > salinity. Seawater mixture weakened the nitrification and denitrification of groundwater by changing salinity, while hypoxia and its controlled sulfide formation not only weaken nitrification and denitrification but also stimulated the DNRA process and promotes N regeneration. In this study area, hypoxia is considered to exert greater impacts on N cycling in the coastal shallow groundwater than seawater mixture. These findings greatly improve our understanding of the consequences of hypoxia and seawater mixture on coastal groundwater N cycling.

Sulphate removal by membrane filtration minimizes the risk of hydrogen sulphide formation in fixed bed biofilters

Hydrogen sulphide (H2S) is one of the suspected reasons behind sudden mass fish mortalities in recirculating aquaculture systems (RAS) in recent years. H2S production in aquaculture systems depends on sulphate and organic matter availability, presence of specific microbial groups, and local anoxic conditions. Specific potential H2S production hotspots in RAS have been identified within biofilters and in accumulated sludge. Current H2S control methods have been identified, such as improved hydrodynamics, increasing degassing efficiency, chemical addition of hydrogen peroxide or ozone, but have not been efficient or widespread applied. In this study, a nanomembrane filtration system was installed at a brackish water (mixture of seawater and freshwater to 15 ppt) smolt production site in Norway to remove sulphate ions from the seawater intake line (15 times reduction). The hydrogen sulphide production potential of the nanofiltered seawater mixed with freshwater (n = 3) was compared to an unfiltered seawater and freshwater mixture (15 ppt, n = 3) for 42 days in experimental scale biofilters using industrial fixed bed media. In both treatments, the linear production of H2S started around the time that bulk water measurements of oxidation-reduction potential (ORP) and dissolved oxygen (DO) dropped below 0 mV and 1 mg/L, respectively. As expected, the highest H2S concentration was observed in unfiltered water reactors, which also reached the highest concentration faster than filtered-water reactors. A 15 times reduction in initial sulphate levels by the nanofiltration membrane led to overall three times lower H2S production and delayed the onset of production by two days. Hence, membrane-filtering intake water decreased the risk of H2S production. A limitation in this study, however, was that sulphate was not completely removed from the intake water, and the next steps should evaluate how increasing the effort of membrane operation to completely remove sulphate affect the dynamics of H2S production in RAS.

On the origin of chevron marks and striated grooves, and their use in predicting mud bed rheology

AbstractUnderstanding of the formative conditions of many sole structures is limited, with chevron marks and striated groove marks being particularly enigmatic. These sedimentary structures are examined here through laboratory modelling. An idealized tool, resembling an armoured mud clast, was dragged through substrates of kaolinite–seawater mixtures of different yield strengths while submerged in seawater. The experiments suggest that armoured mud clasts are the likely tools producing fine striae in striated grooves and, given the common occurrence of striated groove marks in outcrops, that these clasts are more prevalent in deep‐marine settings than previously thought. Chevron marks were observed to form over a narrow range of substrate yield stresses, likely explaining their relative rarity. Furthermore, their form is shown to be a function of substrate rheology, with chevron angle relative to the movement direction of the tool being less in weaker substrates. Moreover, the size of cut chevron marks, characterized by a narrow central cut, bears no relationship to the size of the incising tool, but rather reflects a substrate with a low yield stress that is sufficiently mobile to close behind the tool. In contrast, interrupted chevron marks, characterized by a distinct central groove, reflect greater substrate strength. Striated grooves without chevrons formed at the highest yield stresses simulated in the experiments. The relationship between tool mark type and yield stress, in combination with changes in chevron angle, enables these sole structures to be utilized as indicators of palaeosubstrate rheology. The conditions required to preserve such features include a prolonged period of bed consolidation, flow bypass and lack of bioturbation. Given changes in seafloor communities and bioturbation over time and their impact on substrate rheology, particularly during the early Palaeozoic, the present work supports the idea that the frequency of these sole structures likely changed over geological time.

Two metasomatic events recorded by noble gas characteristics in the Finero mantle wedge: Extreme fractionation (He, Ar) and seawater penetration into the mantle deformation zone

Here, we report that the Finero phlogopite peridotite massif, southern Italy, a sliver of the former subcontinental lithospheric mantle (SCLM), experienced two stages of fluid/melt percolation, which had different origins and scales in the mantle wedge based on noble gas analysis and the deformation structure. In the field investigation, we found a mylonite zone several tens of meters wide in the massif, inferred to have been caused by deformation in the mantle. Systematic differences in noble gas compositions between samples from inside and outside the mylonite zone reflect two stages of fluid/melt infiltration. In the first event, the fluid/melt with a noble gas mixture of seawater, radiogenic, and mantle components penetrated the Finero SCLM. It likely occurred simultaneously with the famous metasomatism that crystallized phlogopite and amphibole throughout the massif. This first event produced a 4He/40Ar ratio much higher than those of the convecting mantle and crustal components, probably during metasomatism by hydrous melt derived from the slab in the mantle wedge. The second event was probably synchronous with the development of mylonitization and locally supplied seawater-rich components. The 40Ar/36Ar ratios tend to be atmospheric as mylonitization progresses. Our results provide two insights: (i) the first demonstration of the formation of extremely high He/Ar ratios during mantle metasomatism of natural samples and (ii) differences in the deformation structure affecting the noble gas composition and distribution in the SCLM. Regarding (i), the elemental fractionation can be attributed to two factors: one is the difference in the solubility between noble gas elements in particular minerals in the slab, and the other is the difference in the diffusion coefficients of He and Ar. Our results imply that the recycling of volatiles within subduction zones is significantly influenced by the thermal structures of slabs. This is because these thermal structures control the stability of hydrous minerals on the slabs, temperature conditions, and potentially the efficiency of diffusion in mantle wedges.

Enhancement of flocculation processes of metals during estuarine mixing by electrodes

Millions of tons of heavy metals enter the ocean through estuaries each year. Estuaries can serve as the interconnection between the sea and the river, preventing the transfer of tons of heavy metals from the river to the sea. These heavy metals are flocculated during the estuarine process, but flocculation process enhancement in estuaries has received limited attention. This study examined the flocculation of dissolved heavy metals in mixtures of freshwater and seawater with varying salinities (0.7 ‰ to 2.49 ‰). The research objectives were first to examine the natural flocculation rate in one of the heavy metals contaminated sites, Namak-abrud River, in the world's largest lake, and then to compare electro-flocculation with self-purification of estuaries using aluminum and graphite electrodes. This multilateral strategy elucidates the practical enhancement of the natural flocculation process in greater detail. The mean removal efficiency of mixtures subjected to natural flocculation at various salinities is as follows: Fe (54.67 %) > Mn (47.82 %). The results indicated that salinity and the mean removal of metals were positively correlated. The most efficient removal of these metals, excluding Cd and Co, generally occurred between 1 and 2 %. Using aluminum electrodes has a negative impact on metal removal rates in comparison to natural flocculation. In contrast, the efficiency of a graphite electrode used for the first time is distinct. Graphite electrodes increased the Co, Cr, and V elimination rates compared to natural flocculation. By eliminating 36 % of metals, nature once again demonstrates its ecological role in estuaries' self-purification.

Application of the symmetric Poisson-Boltzmann theory to equilibrium thermodynamic properties of primitive model electrolyte mixtures

A symmetric Poisson-Boltzmann theory is applied to a primitive model electrolyte solution containing 7 different ion species. Only 7 coupled equations need to be solved for the mean electrostatic potential around the ions once the uncharged hard sphere radial distribution function is specified. Comparison is made with the individual activity and osmotic coefficients of a simulation study of a sea water mixture. Good overall agreement is found with the simulation results.

Aluminum foil immersed in alkalized seawater removes Escherichia coli from household drinking water

Abstract The contamination of drinking water by pathogens poses a serious health hazard in developing countries. Herein, a simple sanitization tool for drinking water is proposed using layered double hydroxide (LDH), which adsorbs most pathogens with its positive charges. By immersing aluminum foil in a mixture of seawater and NaOH without heating, a Mg–Al type LDH was directly formed and adhered to the surface (LDH foil). An LDH foil of 20 cm2 was shaken in 100 mL of test water containing Escherichia coli (DH5α) for up to 24 h and manually removed from the water. The initial viable count of approximately 103 CFU mL−1 decreased to 14 CFU mL−1 in 1 h, reaching 0.25 CFU mL−1 in 24 h; without the LDH foil, the variation 980–1,270 CFU mL−1. The simplicity in its development and use makes LDH foil a promising tool for sanitizing household water among rural residents.

Salinity Tolerance of Dormitator lebretonis (Pisces: Eleotridae: Steindachner, 1870) Reared in Water Tanks: Implications for Coastal Wetlands and Swamp Valorizations

Dormitator lebretonis (Eleotridae: Steindachner, 1870) is a fish species that inhabits West African coastal environments from Senegal to Angola where this squeaker appears to be an important component of the artisanal fisheries. In particular, this eleotrid is widespread in Benin coastal waters including wetlands, and is intensively exploited for food. The current rearing experiment aimed to determine the salinity levels that favor the survival and growth factors of this squeaker. Six (6) treatments corresponding to six (6) salinity levels (0‰, 5‰, 10‰, 15‰, 20‰, 25‰) and three replicates with 15 individuals of D. lebretonis per replicate were considered for the experiment. Appropriate salinity levels were obtained from a mixture of sea water and fresh water. Overall, within each six (6) treatments, physicochemical features showed insignificant (P>0.05) variations. Regardless of rearing water salinity (0‰ - 25‰), D. lebretonis displayed high survivals ranging between 86.66% (salinity: 0‰) and 100% (salinity: 5‰ - 20‰). Percent weight gained (PWG: 7.94±0.01% - 14.39±0.02%) were moderate and significantly (P<0.05) varied with treatments. Also, significant (P<0.05) variations in the condition factors (K) were recorded, with means ranging between 1.68±0.04 and 1.92±0.01. Nevertheless, specific growth rates (SGR) did not show any significant (F5,18=0.328; P=0.890) variations across treatments. These findings could serve as reference data for an extensive aquacultural valorization of D. lebretonis in numerous Benin coastal wetlands and swamps.

A differential titration method for determining the dissociation characteristics of natural organic acids in the coastal zone

Characterizing the concentrations and equilibrium characteristics of organic acid/base pairs is essential for quantifying CO2-system components and their behaviors and interactions in organic-rich coastal environments. Relatively few studies have been devoted to characterization of titratable organics, and their contributions to total alkalinity are frequently implicitly or explicitly considered negligible. In this work, novel potentiometric titration procedures were developed to quantify the concentrations and dissociation constants of river-derived titratable organics and thereby their alkalinity (Org-Alk) contributions to the total alkalinity (TA) of coastal seawater. The overall approach was to compare the titration properties of two paired solutions of identical salinity (S ≈ 5): (a) a sample of “estuarine” water formulated as a mixture of organic-rich river water plus open-ocean seawater and (b) an organics-free “baseline” approximation of that estuarine water, formulated as a mixture of dilute aqueous sodium chloride plus open-ocean seawater. Acid was incrementally added to both solutions, and the resulting two titration curves were then compared to provide direct visualization and quantification of the contributions of organics to TA. In other words, at any given pH, the difference in acid added to the two solutions (with a small correction for silicate alkalinity) indicates acid uptake by titratable organics in the estuarine sample. This procedure was performed for four replicate samples at 15, 25, and 35 °C. Our titrations indicated the presence of three types of titratable organics. The dominant type had a concentration of approximately 200 μmol∙kg−1 and a well-defined dissociation constant (pK) that did not vary with temperature: pKOrg2(average) = 6.33 ± 0.01. The second type had a concentration of approximately 110 μmol∙kg−1 and a moderately well-defined and high pK: 8.56 ≤ pKOrg3 ≤ 9.32. The third type had a concentration of approximately 40 μmol∙kg−1 and a low, poorly defined pK: 4.1 ≤ pKOrg1 ≤ 6.1. Inference of this third type was required to eliminate systematic residuals that were otherwise present in our fitted titration data (residuals = direct observations – model predictions). These data allow for a summation of TA contributions from organic constituents that may contribute (especially in coastal waters) but are typically uncharacterized. Such data are required for rigorous CO2-system models that rely on inputs of the commonly used data pair of TA and dissolved inorganic carbon (DIC). Studies of CO2 system behavior in the coastal zone clearly require two types of alkalinity titrations – one that includes a summation of inorganic and organic components (i.e., conventional titrations), and a second CO2-free titration in which the concentrations and pK characteristics of organic acids are quantified.

The transition from hydrothermal oxic conditions to restricted euxinia in the lower cambrian yurtus formation black shale, Tarim Basin

The Yurtus Formation is generally believed as one of the most potential hydrocarbon source rocks under the Cambrian gypsum-salt bed in the Tarim Basin of China. This formation exhibits unique geochemical characteristics during the Ediacaran-Cambrian transition period. In this study, we investigated the lower and upper black shales from the Yurtus Formation for the high-resolution geochemical analysis in order to further characterize the prevailing redox conditions and sedimentary mechanisms involved in the organic matter accumulation process. During the deposition of the lower black shale with high TOC in Unit2, the high concentrations of phosphorite and barite, and the REE geochemistry manifested a mixture of hydrothermal fluid and seawater. Through in-situ laser ablation–inductively coupled plasma–mass spectrometry (LA-ICP-MS), we explored the element distribution of the drill-core-preserved phosphate nodule, indicating that the phosphogenesis may be related to the involvement of bacteria activities under intermittently oxic bottom waters or consistently free oxygen conditions. Biomarker evidence by the identification of green sulfur bacteria demonstrated the occurrence of photic zone euxinia (PZE), and the trace metal patterns revealed intermittently bottom water oxygenation and stratified ocean which was consistent with the scenario of phosphate nodule formation. In contrast, the upper black shale with relatively low TOC was characterized by a detrital input, with significantly decreasing redox-sensitive trace mental enrichment (UEF, MoEF, VEF) and positive excursion of carbon isotopes, as well as a positive relationship between ∑REE and Al. The present study provides more explicit insights into not only the sedimentary mechanism of the black shale, but also the evolution of the Earth system at the key interval of the early Cambrian.

The B isotopic signature of serpentine from obducted ophiolites: Mixing of fluids and tectonic implications

Obducted ophiolites expose oceanic lithosphere slivers in suture zones. The few previous studies focusing specifically on the serpentinization of the ultramafic part of ophiolites mostly concluded that serpentinization was driven by seawater. Recent developments in B isotope geochemistry have enabled the tracking of fluid source(s) in serpentinites, suggesting δ11B values above +10‰ mostly reflect seawater hydration and δ11B values below +10‰ mostly reflect hydration by subducted crust-derived metamorphic fluids. In this study, we further investigate the fluid sources recorded by ophiolitic serpentinites by presenting B isotopic geochemistry for seventeen samples from well-characterized ophiolites in Guatemala, Iran, and Brazil. The samples from Guatemala and Iran are from fossil Supra Subduction Zones (SSZ), while samples from Brazil represent a fossil Ocean-Continent Transition (OCT). Most of the samples display the pseudomorphic mesh matrix and bastite microtexture typical of serpentinites. Nine of the samples are either totally (both microtextures) or partially (one microtexture only) out of isotopic equilibrium, with δ11B variations of up to 18‰ within individual samples/textures. Among the samples with a narrow δ11B range (i.e., at isotopic equilibrium), those from a fossil OCT ophiolite have δ11B ranging from +3.8 to +23.2‰, which is broadly consistent with serpentinization by seawater. In contrast, serpentinites from fossil SSZ ophiolite have δ11B straddling 0‰, ranging from −7.7 to +13.5‰. These data indicate that seawater alone cannot be responsible for serpentinization of these ultramafic rocks, but rather either subducted crust-derived metamorphic fluids, or a mixture of seawater and subducted crust-derived metamorphic fluids. This interpretation agrees with the recent suggestions that SSZ ophiolites possibly represent fossil forearc lithosphere.

Phaeodactylum tricornutum as Fucoxanthin Biofactory Model and Hepatoprotective Effect of Encapsulated Spirulina and Fucoxanthin

In recent decades, the worldwide production of microalgae has been carried out on an industrial scale. In recent years, the market for natural products has grown because of changes in consumer preferences for more natural products. The objective of this study was to demonstrate the hepatoprotective capacity of fucoxanthin extract obtained from an industrial culture of the microalgae Phaeodactylum tricornutum (Culture Collection of Alga and Protists in Scotland). The microalga was grown in an artificial and natural seawater mixture (1:9), using Walne’s culture medium in columns and raceway photobioreactors (RWP) inside a greenhouse. The carotenoid content in the tested systems continued to increase from day 5 of the culture, when the stationary phase was reached. The final biomass powder contained 4.9 mg (2.59%) of pure fucoxanthin. The possible hepatoprotective activity of fucoxanthin was then studied in the HepG2 cell line for 24 h in culture, and compared with the cytotoxicity of methotrexate (MTX). In conclusion, the active ingredient showed hepatoprotective activity against MTX in the human hepatocyte cell line HEPG-2 at a concentration of 0.25 mg/mL. The current results also suggest that it has beneficial properties for liver health and is a suitable ingredient for all types of nutraceutical products.

The Transformer Bridge Principle Circuit Using RF Admittance Technology

To investigate the problem of the lag stability of the capacitance value during the level drop of the dirty U-shaped liquid level sensor, the equivalent circuit of the dirty U-shaped liquid level sensor was analyzed, and the transformer bridge’s principle circuit that uses RF admittance technology was designed accordingly. Using the method of controlling a single variable, the measurement accuracy of the circuit was simulated when the dividing capacitance and the regulating capacitance had different values. Then, the right parameter values for the dividing capacitance and the regulating capacitance were found. On this basis, the change of the sensor output capacitance and the change of the length of the attached seawater mixture were controlled separately under the condition of removing the seawater mixture. The simulation outcomes showed that the measurement accuracy was excellent under various situations, validating the transformer principle bridge circuit’s efficacy in minimizing the influence of the output capacitance value’s lag stability.

Geochemistry of syntaxial calcite veins in ultra-deep sandstone reservoirs from the Kuqa depression, western China

Extensional fractures filled with calcite are widespread in the ultra-deep reservoir sandstones of the Cretaceous Bashijiqike Formation (>6000 m) in the Kuqa Depression, western China. Microstructures of calcite veins provide an excellent opportunity for investigating fracture opening processes in a tectonically active, ultra-deep foreland basin setting. The syntaxial calcite vein is the dominant type and is formed through a single crack-seal event. Calcite crystals in fractures show blocky and elongated blocky shapes. The textural and geochemical characteristics of syntaxial calcite veins were investigated in detail using optical cathodoluminescence, trace element distributions and stable carbon and oxygen isotopes. Calcite veins were inferred to have precipitated from a mixture of seawater and meteoric water. ∑REE + Y and elemental concentrations of Mg2+, Mn2+, Fe2+ and Sr2+ both increase from fracture walls to the center. This process was controlled by temperature, crystal growth rate and variations in elemental concentration in a relatively closed environment. Medium REE-bulge patterns after Post Archean Average Shale (PAAS) normalization, negative δCe and positive δEu anomalies all indicate that calcite wall-rock cements and veins may inherit constituents from seawater and from meteoric water containing feldspar-weathering components, respectively. Both 13δCPDB and 18δOSMOW of the parent fluids imply that calcite veins were primarily precipitated from seawater under a relatively closed diagenetic environment. Considering the scope and timing of the transgression of the Tethyan Ocean in the study area, meteoric water may have been retained prior to the seawater invasion (65 Ma). The mixing of meteoric water and seawater within the reservoir could be the primary origin of the fluids forming the calcite veins.

A valuable approach in a quantitative seawater intrusion interpretation from the geoelectrical resistivity data for groundwater investigation in Dumai area, Indonesia

An improvement of geoelectrical resistivity interpretation has been done through this research. Up to now, the geoelectrical resistivity data was interpreted qualitatively especially in the case of the aquifer intruded by seawater, and the percentage of seawater mixture content in the aquifer cannot be predicted. In this research, a valuable approach was used in the prediction of percentage seawater mixture in the shallow aquifer that is intruded by seawater. The study was conducted in the coastal area which is mainly covered by peat soil. The research employed the direct soil resistivity measurement and the ground surface resistivity survey. Geoelectrical resistivity with the Wenner configuration was used for both measurements. The soil character and the fluid content in the soil were measured to obtain their correlation to the direct soil resistivity value. The results show that resistivity value is about 2-5 ohm.m for 50% seawater content mixture in aquifer and it increase to be 5-10 ohm.m for 25% seawater mix to freshwater in the aquifer. The increasing seawater content in the pore soil caused the decreases in resistivity value drastically. The percentage of seawater mixture in the fluid pore soil has been successfully predicted through the geoelectrical resistivity measurement on the surface.

Application of the practical salinity scale to the waters of San Francisco estuary

The Practical Salinity Scale 1978 (PSS-78)—developed using samples of standard seawater—is widely used as a conductivity-based measure of salinity in oceans and estuaries. Here we evaluate the application of the scale across San Francisco Estuary where salinity reflects a mixture of seawater, riverine inflows, and agricultural return flows from islands within the estuary. We employ an extensive salinity data set that includes measurements of specific electrical conductance (EC) and major ion concentrations to demonstrate the scale's applicability in this estuary. We find the scale to be valid in waters dominated by seawater intrusion as well as in waters dominated by the largest riverine input to the estuary, i.e. the Sacramento River. In these waters, we further find that the scale to be valid well below its recommended lower-bound value of 2.0. However, the scale under-estimates salinity in waters dominated by the San Joaquin River, the second largest riverine input to the estuary. Similarly, the scale under-estimates salinity in agricultural return flows to the estuary. This work shows that a singular PSS-78 relationship cannot be used to accurately compute salinity across the entire estuary from EC measurements—a finding of considerable importance for salinity monitoring and modeling applications. Using data from the estuary, we propose appropriate corrections to the scale for these drainage-influenced waters. We recommend further research into how these modified PSS-78 formulations can be used to more accurately estimate salinity and ionic constituent concentrations in this and other estuaries.

Fe-Si-C isotope constraints on the genesis of iron ores in Gongchangling iron deposit in northeastern China

The Gongchangling iron deposit is an oxide-facies Algoma-type banded iron formation (BIF) and one of the most representative iron deposits in northeastern China. We present new data from petrological, whole-rock geochemical, and Fe-Si-O isotope compositional data from the Gongchangling BIFs to constrain the origin of ore-forming materials and mineralization processes. The low Al2O3 and TiO2 contents in iron ores indicate that the sources of the BIFs were not contaminated by terrigenous clastic sediments. The Gongchangling BIFs are characterized by depletions in LREEs and 30Si and enrichments in HREEs, with positive Eu and Y anomalies. Given these and the Fe isotope results, we conclude that both high-temperature hydrothermal fluid and seawater contributed to the formation of the BIFs and that a mixture of seawater and ~ 0.1 % hydrothermal fluid, which percolated and dissolved the submarine volcanic rocks, provided the ore-forming materials. Combining the Ce anomalies, enrichments in heavy Fe isotopes and low δ13C compositions, we conclude that the fO2 of Archean seawater was limited. Integrated petrographic and geochemical evidence indicates that the high-grade iron ores from the Gongchangling BIFs experienced incomplete oxidation and low amounts of Fe precipitation in a marine environment and that dissimilatory iron reduction and metamorphic hydrothermal fluid played important roles.