Mixing Of Freshwater Research Articles

Enhanced Clean Energy Generation through Capacitive Electrode Utilization in Reverse Electrodialysis

Abstract In this study, we explore the potential of a novel energy generation method, Capacitive Reverse Electrodialysis (CRED), which combines seawater and river water to produce electricity. CRED integrates a membrane stack, similar to Reverse Electrodialysis (RED), with capacitive electrodes. The salinity gradient between the two water sources generates a potential difference across ion-selective membranes, enabling sustainable energy production. Unlike traditional RED systems that rely on redox reactions, CRED utilizes capacitive electrodes, preventing saturation and enhancing system longevity by periodically switching the water flows and reversing the direction of the electric current. The larger membrane stack in CRED allows for greater charge accumulation than previous capacitive mixing methods, leading to higher voltage and more efficient energy capture. As a result, CRED achieves a power density approximately ten times higher than previous capacitive power extraction trials, reaching performance levels comparable to or exceeding those of conventional RED systems with redox-based electrodes. Overall, CRED demonstrates a promising alternative to traditional energy generation methods, offering a stable, secure, environmentally friendly, and high-performance solution for harnessing energy from the mixing of saltwater and freshwater.

Microstructures along the Indian west-coast continental shelf: layering and vertical mixing

During the month of October, the West Indian Coastal Current (WICC) is in a stage of transition from equatorward to poleward flow. The sea surface salinity near the Indian Coast is lower in the south compared to the north. Whereas the sea surface temperature is higher in the north than in the south. A salinity maximum (SM, Salinity ≥ 35.7 psu) exists in the sub-surface between depth ranges of 50–80 m. In situ vertical microstructure profiles collected along the continental shelf off the West Coast of India (WCI) for the first time, are used in this study to characterize vertical mixing under these complex thermodynamic regimes. Estimated sectional mean (median) values of the dissipation rates of turbulent kinetic energy (ɛ) and thermal variance (χ) are in the range 10−9−10−8 (10−9−10−8) W kg−1 and 10−8−10−7 (10−9−10−8) °C2 s−1 respectively. Sectional mean (median) values of the diapycnal diffusivity (Kρ) and eddy thermal diffusivity (KT) are in the range 10−6−10−5 (10−6−10−5) m2 s−1 and 10−4−10−2 (10−6−10−4) m2 s−1, respectively. The barrier layer (BL) was observed at most of the measurement locations. The layering structures in the salinity profiles observed within BL indicate the phase of transition of halocline reformation. Experiments using a one-dimensional model suggest that this layering is caused by the mixing of surface freshwater (surface freshening caused by heavy rains) with mixed-layer water. Double diffusion with weak staircase structures in temperature and salinity is observed predominantly in the interior layer of the ocean in this region. The presence of SM at most stations, with its thickness decreasing from north to south, created conditions favorable for double-diffusive mixing. Signatures of salt fingering (SF) and diffusive convection (DC) were observed in 40% and 8% of the water column, respectively. Turbulent mixing in the column below the mixed layer (ML) is weak (KT≤10−6 m2 s−1) to moderate (KT∼10−4 m2 s−1), with some highly turbulent intermittent regions (KT∼10−2 m2 s−1) conducive to DC. The data presented here show the prevalence of two mixing regimes in the vertical: (1) vertical mixing of freshwater (due to rain) with the ambient mixed layer water, and (2) small-scale double-diffusive mixing due to contrasting temperature–salinity gradients predominantly in the ocean’s interior layer (below the isothermal layer).

Predicting chlorophyll-a dynamics in the Ashtamudi estuary using ANN and ANFIS techniques

Excessive nutrients and associated high chlorophyll-a concentration are of growing concern to the public health due to the occurrence of eutrophication in aquatic bodies. Continuous monitoring of chlorophyll-a has limitations, thereby necessitating the development of prediction models. Even though chlorophyll-a prediction models are numerous, they rarely fit into estuarine conditions, which is encountered with dynamic mixing of freshwater and sea water. Thus, the present study identifies the most appropriate driving factors that are relevant for estuarine conditions through chlorophyll-a prediction models developed using Artificial Neural Network and Adaptive Neuro Fuzzy Inference System (ANFIS) approaches in the Ashtamudi estuary, India. Salinity, which is an indirect measure of the estuarine mixing intensity, has been used to replicate the dynamic mixing in the estuary. The results indicate that the model incorporating salinity along with total nitrogen, total phosphorous and turbidity well-predicted chlorophyll-a concentration with a coefficient of determination ranging from 0.73 to 0.99. General Regression Neural Network (GRNN) and ANFIS models outperformed Back Propagation Neural Network (BPNN) and Recurrent Neural Network (RNN) models. Of the various ANFIS models, the ones that used Gaussian and Generalized Bell membership functions were most appropriate for the prediction of chlorophyll-a than the models with triangular and trapezoidal membership functions. The study identified that the models that considered salinity were less sensitive and can be used for modelling chlorophyll-a. The chlorophyll-a was observed to have a direct influence of salinity at salinity values greater than 5‰. The study highlighted that estuarine mixing further enhances the primary productivity through increased penetration of light leading to higher chlorophyll-a concentration. Further the study emplasized that the predictive models are important tools fitting well within estuarine environments due to its replicability.

Rare earth elements as indicators of post-Marinoan (∼635 Ma) paleoceanographic changes from the Amazon Craton

The extensive deglaciation linked to the Snowball Earth climate that elapsed in the terminal Neoproterozoic caused dramatic changes in ocean chemistry, exceptionally recorded in globally distributed cap carbonate successions. One of the most spectacular examples is the Puga cap carbonate (∼635 Ma), which is exposed in the Amazon Craton and associated with extensive sea level changes related to glacial-isostatic adjustment and local ice gravity, resulting in continuously mixed waters. This study meticulously evaluates complex post-Marinoan dynamics using a comprehensive multiproxy approach. The rare earth element + yttrium (REE+Y) patterns in the Puga cap carbonate do not accurately reflect the global ocean water composition; instead, they primarily fractionate in response to local expression of the post-Snowball Earth event, including alkalinity levels and freshwater mixing in the aftermath of the Marinoan glaciation. The flattened REE+Y pattern, accompanied by a positive Eu anomaly, may suggest the influence of continental weathering. Specifically, low Y/Ho ratios in the cap dolostone are consistent with seawater dilution due to meltwater influx (Y/Ho ∼ 29–32). Conversely, superchondritic Y/Ho ratios up to 71 in the basal cap dolostones suggest upwelling of hypersaline seawater in coastal areas. The shallow-water recurrence influenced by ice gravity resulted in continuous coastal uplift, forming isolated shelves and the deformation in diamicton, resulting in irregular substrate relief morphologies. This post-glaciation scenario was succeeded by significant landward shoreline migration concomitant with rapid recovery of primary productivity, with large microbial communities flourishing, inducing dolomite precipitation under restricted paleoenvironmental conditions on dolomitic platforms. The rapid rise in sea level led to the dilution of evaporative fluids, ultimately halting dolomicrite precipitation. Following the pos-tglacial transgression, the stratified waters gradually became more mixed, resulting in the termination of dolomitic platform deposition and coinciding with an increase in detrital components, as indicated by the increase of insoluble elements (e.g., REE, Zr, and Th), followed by abrupt replacement by CaCO3-oversaturated seas during the post-glacial transgression. These observations elucidate the interplay between post-glaciation and paleoceanographic dynamics during the Cryogenian-Ediacaran boundary.

Picophytoplankton prevail year-round in the Elbe estuary.

Picophytoplankton are important primary producers, but not always adequately recognized, for example, due to methodological limitations. In this study, we combined flow cytometry and metabarcoding to investigate seasonal and spatial patterns of picophytoplankton abundance and community composition in the Elbe estuary. Due to the mixing of freshwater and seawater and the tidal currents this ecosystem is characterized by typical estuarine features such as salinity gradients and high turbidity. Picophytoplankton (mostly picoeukaryotes such as Mychonastes and Minidiscus) contributed on average 70% (SD = 14%) to the total phytoplankton counts. In summer picocyanobacteria (e.g., Synechococcus) played a more significant role. The contributions of picophytoplankton to the total phytoplankton were particularly high from summer to winter as well as in the mid estuary. However, at salinities of around 10 PSU in the mixing area of freshwater and seawater, the proportion of picophytoplankton was comparably low (average 49%, SD = 13%). Our results indicate that picophytoplankton prevail in the Elbe estuary year-round with respect to cell counts. Picophytoplankton could occupy important niche positions to maintain primary production under extreme conditions where larger phytoplankton might struggle (e.g., at high or low temperature, high turbidity, and in areas with high grazing pressure) and also benefit from high nutrient availability here. However, we did not find evidence that they played a particularly significant role at the salinity interface. Our study highlights the importance of including picophytoplankton when assessing estuarine phytoplankton as has been suggested for other ecosystems such as oceans.

Research on the Compressive Strength of Saltwater Mixing and Curing Cement Mortar Incorporating Blast Furnace Slag

In this study, the blast furnace slag (BFS) was used to replace 30% cement (weight replacement), freshwater, and saltwater (half, same, and twice the concentration of seawater) used to produce the cement mortar. Then, these four types of mixing water were used to cure the mortar till the test ages (7 days and 28 days). The test results show that, at 7 days, the compressive strength of saltwater (half concentration) mixing and curing mortar incorporating BFS is the highest (78 MPa). The freshwater mixing and curing control mortar has the lowest compressive strength (36.2 MPa). At 28 days, the compressive strength of saltwater (twice concentration) mixing and saltwater (half concentration) curing mortar incorporating BFS is the highest (90.2MPa). The strength of the control mortar is 53.0MPa under the same curing water, which is still relatively low. It can be seen from this that the mixing and curing of saltwater are beneficial to improving the compressive strength of cement mortar. The freshwater mixing and saltwater (twice concentration) curing cement mortar incorporating 30% BFS can have a higher strength at 28 days.

Multi-technique analysis of seawater impact on the performance of calcium sulphoaluminate cement mortar

The construction of offshore islands and reefs requires the development of new seawater sea-sand concrete materials. This study investigated the impact of seawater on the performance of calcium sulphoaluminate (CSA) cement mortar, with mechanism analyses by the acoustic emission (AE) and digital image correlation (DIC). For all uniaxial compression tests, cumulated AE, average AE frequency, rise angle, b-value, and βt coefficient were considered to perform the failure analysis. In addition, other techniques such as X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy dispersive spectroscopy (EDS) were also employed to highlight the effects of seawater on the hydration products and microstructure of the CSA cement. The results show that seawater not only promotes the formation and growth of ettringite (AFt) but also interacts with cement hydration products to produce Friedel’s salt and various gel formations. Compared to freshwater mixing (0 %), using seawater mixing at normal concentrations (3.3 %) enhances the compactness of the CSA cement, thereby improving the strength and ductility of the CSA mortar. Specifically, the peak load increases from 77 kN to about 86 kN when mixed with seawater at normal concentration, whereas higher seawater concentrations (6.6 %, 9.9 %) resulted in a slight decrease in strength of the CSA mortar, with the peak load reaching approximately 80 kN, yet the ductility is enhanced, as evidenced by the softening post-peak branch of the loading curve. Additionally, AE bursts have a strong correlation with the fracture of the CSA mortar, which can also be forecast by the AE time-scaling coefficient βt. Therefore, when constructing oceanic island and reef foundations, this type of seawater sea-sand concrete is preferred due to its improved ductility and strength, which enhances the structural integrity of marine constructions and provides early warning for effective marine disaster prediction.

Biomimetic MOFs/GO membranes with enhanced charge density for osmotic power generation

Osmotic power generation is a renewable energy technology that harnesses energy from the natural mixing of freshwater and saltwater, offering a promising solution for sustainable energy. However, it is still a challenge to achieve high energy output without compromising scalability and stability. Herein, inspired by the nano-constrained dynamics of neuronal cell transmembrane transport, an anodic oxidation electrodeposition method is employed to fabricate metal organic frameworks (MOFs) within 2D graphene oxide (GO) layers. The in-situ integration of high-density charges within nanometer pore with 0.34 nm entrance of MOFs facilitates rapid and selective cation transport, which significantly increases the diffusion voltage (363.8 mV, 106 fold concentration gradient). Our device demonstrates a maximum output power of 6.82 μW under a 10 fold concentration gradient at a load resistance of 5000 Ω, possessing an energy conversion efficiency of 48.8% at an effective area of 12.56 mm2, which substantially surpasses the performance reported before. More importantly, the device performs exceptionally well, showing robust and stable performance. This is proven by its ability to power various electronic devices. These findings underscore the potential of biomimetic ion channel membranes in sustainable energy applications, offering a promising avenue for the broader field of energy harvesting technologies.

Geochemical fingerprints of Dongpu Depression crude oils in Bohai Bay Basin, northern China: Insights from biomarkers and isotopic compositions of selected alkylnaphthalenes and alkylphenanthrenes

The Dongpu Depression is a rift lake in the Bohai Bay Basin of eastern China, where abundant oil and gas resources were discovered. Previous geochemical investigations of Dongpu Depression oils have revealed a notable lack of data regarding the isotopic compositions of individual polycyclic aromatic hydrocarbons (PAHs) from the discovered Cenozoic crude oils. Using gas chromatography-mass spectrometry (GC–MS) and gas chromatography-isotope ratio mass spectrometry (GC-IRMS), a novel approach combining molecular parameters and stable carbon isotope compositions of individual PAH was applied to study the depositional environment conditions, the different source inputs, the maturation stage and to identify the potential family of five crude oils selected from Dongpu Depression.A decrease of Ga/C30H together with low Pr/Ph ratios and changes in isotopic compositions indicate that the five Dongpu Depression oils were derived from OM deposited in an anoxic saline environment with a stratified water column where mixing of saline water and freshwater occurred. The low isoprenoid, tricyclic and tetracyclic terpane ratios in combination with the δ13C values of 1,6-DMN, 1,2,5-TMN, 1,3,6,7-TeMN, 9-MP and 1-MP attest that their sources have a mixed origin with high aquatic organism (planktonic) input and a lower land plant (C3 plant) contribution. The δ13C values of phenanthrene between −30.0 ‰ and −20.0 ‰ indicate that the studied Dongpu Depression oils belong to a single family generated from the peak to the late oil generation stage (Rc-TNR-2 between 0.85 and 1.15 %). A correlation with various basins indicates that oil samples featured by δ13C values of Phen between −30.0 ‰ and −20.0 ‰ correspond to crude oils derived from mixing of aquatic and high plant contributions with different degrees of mixtures, which have not yet reached their cracking stage (Rc < 2.0 %). Crude oils from the Carboniferous and Mesozoic-Cenozoic Tarim rocks, Australian petroleum systems, Termit Basin, Bongor Basin, Fushan Depression and the studied Dongpu Depression oils belong to that group of oils. Crude oils characterized by lighter phenanthrene isotopic compositions (δ13C values of Phen < −30.0 ‰) are mainly derived from marine/aquatic input and have already entered the cracking window (Rc > 2.0 %). This group of oils is represented in this study by the Cambrian-Ordovician Tarim Basin oil samples. The research shows the importance of the aromatic isotopic compositions in petroleum system characterization and could be used as a reference for a practical exploration campaign of petroleum.

Dynamics and source characterization of chromophoric dissolved organic matter (CDOM) in a tropical monsoon driven lagoon

While there is a significant body of research on the dynamics of chromophoric dissolved organic matter (CDOM) in coastal and offshore waters, our understanding of CDOM dynamics in tropical inland water bodies remains limited. To bridge this knowledge gap, a monthly in-situ investigation was carried out at 33 stations along a monsoon driven lagoon, Chilika, on the southeast coast of India for one year i.e., from July 2018 to June 2019. CDOM absorption at 440 nm [aCDOM(440)] data were analyzed as a proxy for CDOM concentration which varied between a range of 0.04–65.14 m−1 with an average value of 2.77 ± 5.23 m−1. A gradient in aCDOM(440) was observed from the river discharge dominated shallower northern sector (4.91 ± 8.32) m−1 to the more isolated and less fresh water influenced deeper southern sector (1.21 ± 1.55) m−1. Spectral slope (S), spectral slope ratio (SR), and molecular weight proxy (M) were computed to understand the possible source and fate of CDOM in the lagoon. The average spectral slope of S280–500 and S350–500 vary between 0.002 and 0.096 nm−1 and 0.001–0.095 nm−1, respectively. The (SR) and (M) values ranged between of 0.01–6.81 and 0.31–52.28. It was observed that large-sized, high molecular weight CDOM from terrestrial origin was prevalent during monsoon with lower (S280–500), (SR), and (M)values. In contrast, lower molecular weight CDOM fractions were prevalent during pre- and post-monsoon which were mainly of autochthonous origin with higher (S350–500), (SR), and (M) values. Our findings indicate significant spatio-temporal variations of CDOM in Chilika Lagoon, influenced by the monsoon-driven influx of freshwater and the mixing of fresh and marine water. In-situ changes in CDOM are likely shaped by microbial breakdown and photodegradation.

Numerical Study on the Formation Mechanism of Plume Bulge in the Pearl River Estuary under the Influence of River Discharge

Previous studies have investigated the characteristics and influencing factors of plume bulge in the Pearl River Estuary (PRE) using observations and numerical simulations. However, the understanding of how river discharge affects plume bulge is not consistent, and the response mechanism of plume bulge to changes in river discharge has not been revealed in detail. In this study, a three-dimensional hydrodynamic Finite-Volume Coastal Ocean Model (FVCOM) is constructed, and five experiments were set to characterize the horizontal and vertical distribution of the plume bulge outside the PRE under different river discharge conditions during spring tide. The physical mechanisms of plume bulge generation and its response mechanisms to river discharge were discussed through standardized analysis and momentum diagnostic analysis. The results indicate that the plume bulge is sensitive to changes in river discharge. When the river discharge is relatively low (e.g., less than 11,720 m3/s observed in the dry season), the bulge cannot be formed. Conversely, when the river discharge is relatively high (e.g., exceeding 23,440 m3/s observed in flood season), the bulge is more significant. The plume bulge is formed by the anticyclonic flow resulting from the action of the Coriolis force on the strongly mixed river plume. The bulge remains stable under the combined effects of barotropic force, baroclinic gradient force, and Coriolis force. The reduction of river discharge weakens the mixing of freshwater and seawater, resulting in the reduction of both the volume and momentum of the river plume, and the balance between advective diffusion and Coriolis forces are altered, resulting in the plume, which is originally flushed out from the Lantau Channel, not being able to maintain the anticyclonic structure and instead floating out along the coast of the western side of the PRE, with the disappearance of the plume bulge. Due to the significant influence of plume bulges on the physical and biogeochemical interactions between estuaries and terrestrial environments, studying the physical mechanisms behind the formation of plume bulges is crucial.

Transitions between different estuarine states in a low-inflow estuary of arid coasts (Mond Estuary, Persian Gulf) with a focus on freshwater lenses

This study shows that the Mond Estuary, Persian Gulf experiences notable time-dependent longitudinal salinity variations. Monthly-seasonal variability in salinity changes from a positive estuarine system in wintertime to inverse and salt-plug estuaries during summertime. A highly unsteady state (time scale of hours-days) occurs in the wintertime named the freshwater lens estuary (FLE), in which a low-salinity water mass (lens) is confined by both marine and riverine saltwater sources. Here, FLE dynamics is investigated using realistic and idealized numerical models and two 25-hour data sets collected immediately before a hypersaline runoff (weak FLE condition) and during another one (strong FLE condition). The Péclet Number (Pe) reveals a much stronger advective transports than diffusive one (Pe>5.7) throughout the estuary. An exception from this behavior (stronger mixing with Pe=0.8) is observed at the estuary downstream, where a significant amount of freshwater mixes with seawater during the weak FLE conditions. Also, the minimum hypersaline runoff of ∼400 m3/s estimated by the numerical model can dampen tidal waves at the head of the estuary. In an idealized basin, the model shows that FLE longitudinal flows form two cells of positive estuarine circulation separated by a maximum mixing zone (the potential energy anomaly <0.75 J/m3). In the Mond Estuary, a sea-level rise of 20 cm increases salinity in the FLE state and the positive estuary during winter. Conversely, it decreases salinity in the inverse and salt-plug estuaries in summer.

Recent shallow-water benthic foraminifera from a tropical estuary, SW Nigeria

This paper presents a comprehensive survey of benthic foraminifera from shallow waters of the Apapa-Badagry Creek estuary in southwestern Nigeria. Sediments of the Apapa-Badagry Creek, an important estuary surrounded by sprawling estates and industrial parks, yielded diverse assemblages of benthic foraminifera with a total of eighty-eight species. They include hyaline-perforate taxa which dominated the inner western sites around the Lagos Harbor in the Apapa Creek with Ammonia aoteana, A. tepida, A. convexa, Ammonia sp. 1, Ammonia sp. 2. Agglutinated taxa are well established in the westernmost areas in the Badagry Creek, where there is seamless fresh-water mixing, with high populations of Ammotium salsum and few occurrences of Milliamina fusca and Ammobaculites species. The miliolids, represented mainly by species of Quinqueloculina, occupy sample stations in the Commodore Channel which flourish under conditions of marine and tidal influences. Cribroelphidium mirum, Pararotalia sarmientoi, Bolivina striatula and Rosalina species are also found within the Commodore Channel sediments. Our study widely extends and completes previous studies from the tropical eastern Atlantic, especially within the Gulf of Guinea and provides new information on the distribution, diversity, and species richness of shallow-water benthic foraminifera fringing the Atlantic coast of Africa.

Assessing Recharge Sources and Seawater Intrusion in Coastal Groundwater: A Hydrogeological and Multi-Isotopic Approach

One of the crucial challenges of our time is climate change. The consequences of rising sea levels and drought greatly impact water resources, potentially worsening seawater intrusion. Characterizing coastal aquifers is an essential step in devising strategies to address these phenomena. Seawater intrusion poses a critical socio-economic and environmental issue in the coastal plain of Muravera, southeastern Sardinia (Italy). This coastal plain is an important agricultural area in Sardinia, and the health of the crops is compromised by the increasing salinization of shallow groundwater. To enhance our understanding of the hydrogeological conceptual model, which is essential for a sustainable resource management system, hydrogeological investigations were conducted and complemented by the chemical and multi-isotopic analyses of groundwater. The main objectives of this study were to identify groundwater recharge areas, understand salinization mechanisms and trace the evolution of water chemistry. Within this framework, a monthly survey monitoring piezometric level and electrical conductivity was carried out for one year. This survey was integrated with chemical and isotope analyses, including δ18OH2O and δ2HH2O, δ11B, δ18OSO4, δ34SSO4, and 87Sr/86Sr. Hydrochemistry analysis results revealed the occurrence of seawater–freshwater mixing, extending up to 4 km inland. H2O isotope analysis confirmed the mixing processes and indicated the meteoric origin of recharge waters for both shallow and semi-confined aquifers. The strontium isotopes ratio facilitated the identification of four main groundwater flow paths, confirmed by the SIAR model. The results of this combined hydrogeological–geochemical–isotopic survey provide essential elements for the future implementation of an integrated and sustainable management system. These findings enable interventions to slow the process of seawater intrusion and meet the economic needs for the development of local communities.

Emission of CO2 and its related carbonate system dynamics in a hotspot area during winter and summer: The Changjiang River estuary

The carbonate chemistry in river-dominated marginal seas is highly heterogeneous, and there is ongoing debate regarding the definition of atmospheric CO2 source or sink. On this basis, we investigated the carbonate chemistry and air-sea CO2 fluxes in a hotspot estuarine area: the Changjiang Estuary during winter and summer. The spatial characteristics of the carbonate system were influenced by water mixing of three end-members in winter, including the Changjiang freshwater with low total alkalinity (TA) concentration, the less saline Yellow Sea Surface Water with high TA, and the saline East China Sea (ECS) offshore water with moderate TA. While in summer with increased river discharge, the carbonate system was regulated by simplified two end-member mixing between the Changjiang freshwater and the ECS offshore water. By performing the end-member mixing model on DIC variations in the river plume region, significant biological addition of DIC was found in winter with an estimation of −120 ± 113 μmol kg−1 caused by wintertime organic matter remineralization from terrestrial source. While this biological addition of DIC shifted to DIC removal due to biological production in summer supported by the increased nutrient loading from Changjiang River. The pCO2 dynamics in the river plume and the ECS offshore were both subjected to physical mixing of freshwater and seawater, whether in winter and summer. In the inner estuary without horizontal mixing, the pCO2 dynamics were mainly influenced by biological uptake in winter and temperature in summer. The inner estuary, the river plume, and the ECS offshore were sources of atmospheric CO2, with their contributions varying seasonally. The Changjiang runoff enhanced the inner estuary's role as a CO2 source in summer, while intensive biological uptake reduced the river plume's contribution.

Feasibility and challenges of high-pressure pressure retarded osmosis applications utilizing seawater and hypersaline water sources

Pressure retarded osmosis (PRO) harnesses salinity gradient energy through the mixing of freshwater and saltwater, addressing the demand for sustainable energy sources. PRO typically utilizes river water or secondary wastewater as the feed solution, paired with seawater reverse osmosis (SWRO) brine as the draw solution. However, the limited availability of low-saline water presents a significant obstacle to energy generation. Therefore, the feasibility of a high-pressure PRO process utilizing seawater as the feed solution and hypersaline water as the draw solution was assessed to generate sustainable blue energy. Seawater has the potential to achieve the maximum extractable Gibbs-free energy through high-pressure PRO by maximizing the feed/draw ratio. The performance of the high-pressure PRO was theoretically evaluated, resulting in a tenfold increase in specific energy production compared to conventional SWRO-PRO due to the higher feed/draw ratio. However, high hydraulic pressure increased the membrane structural parameter and further reduced water flux and power density due to significant internal concentration polarization. Nevertheless, the high-pressure PRO process can achieve a power density exceeding 84 W/m2 when the structural parameter remains below 100 μm. The implications of the high-pressure PRO were further discussed to advance the concept of a blue circular economy, enhance environmental resilience, and promote sustainability.

Hydrogeochemical characteristics of Thrissur Kole Wetland, Southwest India

ABSTRACT Surface water samples collected from Thrissur Kole wetland (UNSECO-protected Ramsar Site) were analysed for hydrogeochemical characteristics. The objectives of this work were to: (i) study the spatial and seasonal variability in water quality and (ii) analyse the hydrogeochemical characteristics of different water types and suitability status for irrigation. Remarkable season-wise and station-wise variation in salinity was attributed to the mixing of freshwater and seawater. Relatively lower values of pH during post-monsoon were due to the freshwater discharge and mineralisation of organic matter. Besides natural sources, agriculture activities, and droppings from birds also serve as sources of nutrients in the wetland. The average relative abundance of major cations and anions was Cl- > Na+ > Mg2+ > K+ > SO4 2- > HCO3 - > Ca2+. In addition, the contribution of dissolved ions from tidal ingression was established by the dominance of magnesium and sulphate. Based on Piper plot, three major hydro-chemical facies (Ca–Mg-HCO3 type, Ca–Mg-Cl-SO4 type, and Na-K-Cl-SO4 type) were identified. Irrigational suitability of water throughout the wetland was excellent during monsoon as per irrigational water quality indices. Piper plot indicated that the surface water chemistry was controlled by silicate weathering with contribution from seawater ingression and anthropogenic sources.

The stable isotope hydrology of Sable Island, Nova Scotia, Canada with implications for evaluating the water budget of wild horses

ABSTRACT We investigated the stable isotope hydrology of Sable Island, Nova Scotia, Canada over a five year period from September, 2017 to August, 2022. The δ 2H and δ 18O values of integrated monthly precipitation were weakly seasonal and ranged from –66 to –15 ‰ and from –9.7 to –1.9 ‰, respectively. Fitting these monthly precipitation data resulted in a local meteoric water line (LMWL) defined by: δ 2H = 7.22 ± 0.21 · δ 18O + 7.50 ± 1.22 ‰. Amount-weighted annual precipitation had δ 2H and δ 18O values of –36 ± 11 ‰ and –6.1 ± 1.4 ‰, respectively. Deep groundwater had more negative δ 2H and δ 18O values than mean annual precipitation, suggesting recharge occurs mainly in the winter, while shallow groundwater had δ 2H and δ 18O values more consistent with mean annual precipitation or mixing of freshwater with local seawater. Surface waters had more positive values and showed evidence of isolation from the groundwater system. The stable isotopic compositions of plant (leaf) water, on the other hand, indicate plants use groundwater as their source. Fog had δ 2H and δ 18O values that were significantly more positive than those of local precipitation, yet had similar 17O-excess values. δ 2H values of horsehair from 4 individuals lacked seasonality, but had variations typical to those of precipitation on the island. Differences in mean δ 2H values of horsehair were statistically significant and suggest variations in water use may exist between spatially disparate horse communities. Our results establish an important initial framework for ongoing isotope studies of feral horses and other wildlife on Sable Island.

Evolution of dissolved organic nitrogen chemistry during transportation to the marginal sea: Insights from nitrogen isotope and molecular composition analyses

Estuaries are hotspots where terrestrially originated dissolved organic matter (DOM) is modified in molecular composition before entering marine environments. However, very few research has considered nitrogen (N) modifications of DOM molecules in estuaries, limiting our understanding of dissolved organic nitrogen (DON) cycling and the associated carbon cycling in estuaries. This study integrated optical, stable isotopes (δ15N and δ13C) and molecular composition (FT-ICR MS) to characterize the transformation of DOM in the Yangtze River Estuary. Both concentration of dissolved organic carbon (DOC) and DON decreased with increasing salinity, while their δ13C and δ15N increased with the increasing salinity. A significant positive correlation was found between δ15N and δ13C during the transportation of DOM to marginal seas, indicating that the behavior of both DOC and DON are primarily controlled by the mixing of freshwater and the seawater in the YRE. During the mixing process, the DON addition was observed using the conservative mixing curves. In the view of molecular composition, DOM molecules became more aromatic as the number of N atoms increased. Spearman correlations reveal that DOM molecules with fewer N atoms exhibited a higher enrichment in protein-like components, while those with more N atoms were more enriched in humic-like components. In addition, the δ15N and δ13C tended to increase as the N content of DOM decreased. Therefore, DON molecules with fewer N atoms were likely to be transformed into those with more N atoms based on the isotopic fractionation theory. This study establishes a linkage between the molecular composition and the δ15N of DOM, and discovers the N transformation pattern within DOM molecules during the transportation to marginal seas.

Comparing Darcy’s Law and the Brinkman Equation for Numerical Simulations of Saltwater Intrusion

Saltwater intrusion into coastal aquifers presents a significant global challenge to fresh groundwater resources. Numerical modelling represents a valuable tool to study this phenomenon. Darcy’s Law is widely applied to groundwater studies and is extended into the Brinkman Equation to account for kinetic dissipations due to viscous shear. However, their comparative performance and accuracy in density-driven flows remain unclear. To determine the circumstances where the Brinkman Equation is required, numerical simulations with both models were implemented in hypothetical coastal aquifer scenarios. The results revealed that the largest discrepancies between the two models occur inside the dispersion zone during the break-through period, with concentration differences of up to 2.5%. The mixing of freshwater and saltwater induces rapid density and velocity variations. Brinkman’s viscous term moderates the rate of change and decreases the intrusion length by up to 6.1 m in a 180 m intrusion case. Furthermore, higher permeability and a lower recharge rate both strengthen the viscous effects in most sandy coastal aquifers. The Brinkman Equation excels at capturing intricate flow patterns with large variations. Therefore, it is necessary to be employed for studies on freshwater–saltwater interfaces and other similar conditions including groundwater–surface water interfaces, non-isothermal flows, and complex geological conditions.