Salinity Enrichment Research Articles

Hydrochemical characteristics and salinity formation mechanism of different water bodies in the southern Tibet, China.

Understanding the hydrochemical evolution of surface water and groundwater is crucial for protecting regional ecological environments. Currently, there are few quantitative studies on the relative contributions of different processes to salinity enrichment of water bodies. In this study, sixty-seven water samples were collected for chemical, and isotopic analysis, along with simulation calculations. The results reveal distinct hydrochemical types of river water, phreatic water, lake water and hot spring water in the investigated area are Ca-Mg-HCO3, Na-Ca-HCO3, Na-SO4-HCO3 and Na-HCO3, respectively. Average temperature and depth of geothermal water storage are 196℃ and 1338m, respectively. Average arsenic (As) content in hot spring water (298μg/L) higher than that in lake water (39.2μg/L), river water (9.59μg/L) and phreatic water (4.02μg/L). The ∑REEs content of river water in the study area is much higher than that of phreatic water and lake water. Result of δD and δ18O indicate that atmospheric precipitation is the source of recharge for all water bodies in the study area. Quantitative calculations indicate that evapo-concentration significantly enriches lake water salinity, contributing on average 90% of its salt content. In contrast, mineral dissolution contributes predominantly to the salinity of hot spring water (90.7%), phreatic water (65.8%), and river water (45.2%). Evapo-concentration emerges as the dominant mechanism for lake water salinity, while carbonate mineral dissolution primarily affects river water. Phreatic water and hot spring water are mainly controlled by the weathering and dissolution of silicate. The results can provide a theoretical basis for the study of the formation mechanism of water salinity in other regions with similar geological environment in the world.

Effect of salinity stress and nitrogen depletion on growth, morphology and toxin production of freshwater cyanobacterium Microcoleus anatoxicus Stancheva & Conklin

AbstractCyanobacterium Microcoleus anatoxicus, isolated from a coastal stream in northern California, produces both anatoxin-a (ATX) and dihydroanatoxin-a (dhATX), responsible for dog deaths, but its environmental preferences are unknown. We tested the effect of environmentally relevant stressors, e.g., salinity enrichment and nitrogen (N) depletion, on mat formation and toxicity of M. anatoxicus during the stationary growth phase in culture. Microcoleus anatoxicus showed broad salinity tolerance and the potential to enter estuaries and produce toxins in mesohaline conditions. Maximum growth was observed in oligohaline waters with salinity of 4.6 ppt. Moderate salinity stress (up to 7.8 ppt) did not affect dhATX production significantly. In contrast, higher salinity above 9.3 ppt had a detrimental effect on cell growth and significantly suppressed dhATX production. Formation of a common polysaccharide sheath covering multiple filaments was characteristic with increased salinity and may provide protection against osmotic stress. Microcoleus anatoxicus grown for 40 days in N-depleted medium formed mats with significantly elevated dhATX and increased ATX concentrations. Phycobilisome degradation was a possible acclimation response to N-limitation, as indicated by distinctly keritomized and pale cells in these cultures. In both experiments, most of the anatoxins were extracellular, probably due to toxin leaking during the stationary growth phase.

Large submarine groundwater discharges to the Arabian Sea from tropical southwestern Indian Coast: Measurements from seepage meters deployed during the low tide

Submarine Groundwater Discharge (SGD) is the flow of fresh groundwater and recirculated seawater to the sea. SGD plays a crucial role in the transport of solute-rich terrestrial groundwater as well as recirculated seawater. We conducted seasonal investigations for two years on a tropical, high-rainfall occurring coastline in southwestern India to quantify the SGD from the nearshore. A combination of subsurface seepage meters and porewater samplers was used for an entire tidal cycle to estimate the seepage rates and to understand the processes controlling the discharge. The estimated seepage rates from this region are one of the highest reported in the world. This could be due to the large span of the highly porous coastal aquifer and the high annual rainfall (over 450 cm) in this region. The seepage rates are 754 cm/day, 572 cm/day and 296 cm/day for the pre-monsoon (February 2020), post-monsoon (December 2020) and pre-monsoon (February 2021) seasons, respectively and showed high spatial and temporal variability. The end-member concentrations of groundwater and seawater were used to delineate the fresh and recirculated SGD from the total seepage. The recirculated SGD (rSGD) dominates during all the seasons taking up to 99 % of the total SGD during the pre-monsoon seasons (February) and 70 % during the post-monsoon (December) season. The fresh SGD (fSGD) is low (∼1 %) during the pre-monsoon season and increases up to 30 % during the post-monsoon. A considerable amount (0.1–10 % of the total SGD) of salinity enrichment was observed at the upper saline plume. We suspect this could be due to the evaporation of recirculated seawater due to ambient weather conditions. The fSGD in the study area is mainly controlled by the high inland hydraulic head, and the rSGD is regulated by the tides. The subsurface seepage meters used in this study eliminate the instabilities in seepage measurements and can be replicated in less-studied tropical coastal zones to quantify the volume of SGD entering the world oceans. The inferences reported can benefit the public and decision-makers in managing coastal groundwater resources and are interesting to the researchers working on delineating the hydrological and geochemical processes in the nearshore.

Distinctive differences in the granulation of saline and non-saline enriched anaerobic ammonia oxidizing (AMX) bacteria

The growing interest in the anaerobic ammonium oxidizing (AMX) process in treating high nitrogen containing wastewaters and a comprehensive study into the granulation mechanism of these bacteria under diverse environmental conditions over the years have been unequal. To this effect, the distinctive differences in saline adapted AMX (S_AMX) and non-saline adapted AMX (NS_AMX) granules are presented in this study. It was observed that substrate utilisation profiles, granule formation mechanism, and pace towards granulation differed marginally for the two adaptation conditions. The different microbial dominant aggregation types aided in splitting the 471 days operated lab-scale SBRs into three distinct phases. In both reactors, phase III (granules dominant phase) showed the highest average nitrogen removal efficiency of 87.9% ± 4.8% and 85.6% ± 3.6% for the S_AMX and NS_AMX processes, respectively. The extracellular polymeric substances (EPS) quantity and major composition determined its role either as a binding agent in granulation or a survival mechanism in saline adaptation. It was also observed that granules of the S_AMX reactor were mostly loosely and less condensed aggregates of smaller sub-units and flocs while those of the NS_AMX reactor were compact agglomerates. The ionic gradient in saline enrichment led to an increased activity of the Na+/K+ – ATPase, hence enriched granules produced higher cellular adenosine triphosphate molecules which finally improved the granules active biomass ratio by 32.96%. Microbial community showed that about three to four major known AMX species made up the granules consortia in both reactors. Proteins and expression of functional genes differed for these different species.

The impact of the abnormal salinity enrichment in pore water on the thermodynamic stability of marine natural gas hydrates in the Arctic region

In this study, the thermodynamic and structural characteristics of natural gas hydrates (NGHs) retrieved from gas hydrate mounds (ARAON Mound 03 (AM03) and ARAON Mound 06 (AM06)) in the Chukchi Sea in the Arctic region were investigated. The gas compositions, crystalline structure, and cage occupancy of the NGHs at AM03 and AM06 were experimentally measured using gas chromatography (GC), 13C nuclear magnetic resonance (NMR), Raman spectroscopy, and powder X-ray diffraction (PXRD). In the NGHs from AM03 and AM06, a significantly large fraction of CH4 (> 99%) and a very small amount of H2S were enclathrated in small (512) and large (51262) cages of sI hydrate. The NGHs from AM03 and AM06 were almost identical in composition, guest distributions, and existing environment to each other. The salinity of the residual pore water in the hydrate-bearing sediment (AM06) was measured to be 50.32‰, which was much higher than that of seawater (34.88‰). This abnormal salinity enrichment in the pore water of the low-permeability sediment might induce the dissociation of NGHs at a lower temperature than expected. The saturation changes in the NGHs that corresponded with an increase in the seawater temperature were also predicted on the basis of the salinity changes in the pore water. The experimental and predicted results of this study would be helpful for understanding the thermodynamic stability of NGHs and potential CH4-releasing phenomena in the Arctic region.

Thermokarst Lagoons: A Core-Based Assessment of Depositional Characteristics and an Estimate of Carbon Pools on the Bykovsky Peninsula

Permafrost region subsurface organic carbon (OC) pools are a major component of the terrestrial carbon cycle and vulnerable to a warming climate. Thermokarst lagoons are an important transition stage with complex depositional histories during which permafrost and lacustrine carbon pools are transformed along eroding Arctic coasts. The effects of temperature and salinity changes during thermokarst lake to lagoon transitions on thaw history and lagoon deposits are understudied. We analyzed two 30-m-long sediment cores from two thermokarst lagoons on the Bykovsky Peninsula, Northeast Siberia, using sedimentological, geochronological, hydrochemical, and biogeochemical techniques. Using remote sensing we distinguished between a semi-closed and a nearly closed lagoon. We (1) characterized the depositional history, (2) studied the impact of marine inundation on ice-bearing permafrost and taliks, and (3) quantified the OC pools for different stages of thermokarst lagoons. Fluvial and former Yedoma deposits were found at depth between 30 and 8.5 m, while lake and lagoon deposits formed the upper layers. The electrical conductivity of the pore water indicated hypersaline conditions for the semi-closed lagoon (max: 108 mS/cm), while fresh to brackish conditions were observed beneath a 5 m-thick surface saline layer at the nearly closed lagoon. The deposits had a mean OC content of 15 ± 2 kg/m3, with higher values in the semi-closed lagoon. Based on the cores we estimated a total OC pool of 5.7 Mt-C for the first 30 m of sediment below five mapped lagoons on the Bykovsky Peninsula. Our results suggest that paleo river branches shaped the middle Pleistocene landscape followed by late Pleistocene Yedoma permafrost accumulation and early Holocene lake development. Afterward, lake drainage, marine flooding, and bedfast ice formation caused the saline enrichment of pore water, which led to cryotic talik development. We find that the OC-pool of Arctic lagoons may comprise a substantial inventory of partially thawed and partially refrozen OC, which is available for microbial degradation processes at the Arctic terrestrial-marine interface. Climate change in the Arctic leading to sea level rise, permafrost thaw, coastal erosion, and sea ice loss may increase the rate of thermokarst lagoon formation and thus increase the importance of lagoons as biogeochemical processors of former permafrost OC.

Metagenomic Insights into Salinity Build-up in Microbial Communities and Metabolism of Hydrolytic Bioreactor Treating High-color PDWW

In this study, to solve the problem of salinity enrichment in industrial wastewater recycling, a hydrolytic bioreactor was continuously operated to treat high-color printing and dyeing wastewater (PDWW) with salinity build-up. Nearly complete color removal was achieved even with salinity build-ups from 0.5 to 4 g·L-1 in the influent. Pyrosequencing of 16S rRNA genes showed that the salinity build-up results in the decrease of microbial species from 882 to 631; however, the biodiversity of the bacterial community remains stable. Metagenomic analysis indicated that salinity build-up caused no obvious effect on the overall function of the bacterial community, but altered the abundance of specific decoloring genes. Proteobacteria dominated in the bioreactor, and Methanothrix and Geobacter were the dominant genera under low salinity conditions. Proteobacteria increased in abundance with salinity build-up. Desulfovibrio and Desulfococcus were the two predominant genera in the bioreactor fed with sodium sulphate salinity build-up, demonstrating opposite responses to the sodium stress. PICRUSt functional analysis showed that the relative abundance of the decolorizing enzymes SOD1 and SOD2 decreased significantly, but the relative abundance of CAT and TYR increased, ensuring the stability of the decolorizing function of the hydrolysis biological system. From the perspective of the functional genes of hydrolysis decolorization, this study explored the effect of salinity build-up on the microbial community and function of hydrolysis, providing a theoretical basis for the study of decolorization and organic matter removal mechanism of PDWW under the condition of salinity build-up.

Salinity enrichment, sources and its contribution to elevated groundwater arsenic and fluoride levels in Rachna Doab, Punjab Pakistan: Stable isotope (δ2H and δ18O) approach as an evidence.

The present study aimed at exploring the sources of salinity and the link it shares with the enrichment of As (arsenic) and F- (fluoride) in the groundwater of Rachna Doab. Total Dissolved Solids (TDS) were used as the measure of salinity to classify samples into three groups: TDS <1000mg/L (freshwater), 1000-3000mg/L (slightly saline) and 3000-10,000mg/L (moderately saline). The stable isotope analysis (δ2H and δ18O relative to VSMOW) were used to explore the sources of salinity and a conceptual model, based on secondary data was used for comparing the current and past scenarios of groundwater salinization sources. Groundwater ion chemistry and geochemical modeling (PHREEQC) were used to develop a link between the occurrence of salinity and enrichment patterns of As and F- in the groundwater of study area. TDS, As and F- concentrations in groundwater ranged from 234 to 4557mg/L, below detection limit to 240μg/L and below detection limit to 3.9mg/L, respectively. Mineral dissolution, ion exchange processes, and partial input of evaporation were identified as the factors affecting groundwater salinity in the region in accordance with the conceptual model developed based on secondary data. Groundwater salinity accounts as one of the factors that positively influence the enrichment of F- in groundwater, whereas As shows no clear relationship with saline groundwaters.

Development of an improved hydrogeological and hydro-geochemical conceptualization of a complex aquifer system in Ethiopia

Comprehensive aquifer characterization requires the development of a three-dimensional (3D) geological model and estimation of hydraulic and hydro-geochemical properties. This can be used to discern the governing processes of groundwater flow and chemistry, and plan pertinent groundwater management approaches. This study evaluated the influence of geological settings and groundwater flow on the groundwater development potential and chemistry in a Quaternary aquifer system in the Raya Valley, Ethiopia. Surface geology, digital elevations, groundwater-level measurements, and data from drill logs, pumping tests and vertical electrical soundings were combined to characterize the physical properties of the aquifer system. 3D geological and hydrogeological models were developed and used to delineate subsurface formations and to quantify groundwater flow. The aquifer was characterized as a heterogeneous and anisotropic unconfined system. The available groundwater volume was estimated to be 80 ± 1 km3 with a maximum sustainable yield of 530,409 ± 16,800 m3/day. The use of geochemical models and principal component analysis revealed that the origin and geochemical composition of the groundwater were spatially variable. Rock weathering, mineral dissolution, ion-exchange and anthropogenic activities were the major processes governing the hydro-geochemical characteristics of the aquifer, while evaporation processes caused groundwater salinity enrichment. However, even though mineral saturation of the groundwater at specific locations was highly influenced by the geologic matrix, advective groundwater transport led to areas with mixed groundwater chemistry. The observed and modelled complexity of this aquifer system suggests that such evaluations are important to design appropriate groundwater management strategies in heterogeneous and structurally complex aquifer systems.

Shallow water phytoplankton responses to nitrate and salinity enrichment may be modified by benthic processes

ABSTRACTThe effects of salinity (as chloride [Cl] at 600, 1000, 1600, and 2500 mg L−1) and nitrate (as nitrogen [N] loading rates using concentrations of 1, 2, 5, and 10 mg L−1) additions on phytoplankton communities (as chlorophyll and carotenoid pigments) were determined using a fully factorial 3 m3 mesocosm pond experiment. Redundancy analysis followed by variance partitioning analysis (VPA) statistically compared phytoplankton with water chemistry, zooplankton, phytobenthos (aquatic plants and periphyton), and zoobenthos to understand relationships among benthic and pelagic components. Repeated measures analysis of variance (RM-ANOVA) indicated no interactive effects of the 2 treatments. In VPA, physicochemical variables explained the most variance (33.6%) in the phytoplankton pigment dataset relative to benthic primary producers (0.4%) and invertebrates (2.3%). Salinisation led to an increase in biomass of planktonic siliceous algae (Cl ≥1600 mg L−1) and chlorophytes and cyanobacteria (Cl ≥2500 mg L−1), which we infer was caused by increased phosphorus release from sediments while aquatic plants and periphyton declined. Nitrate additions increased the biomass of cryptophytes and chlorophytes at intermediate N loading rates using concentrations of 5 mg L−1 (associated with greater ammonium [NH4-N] availability and shifts in aquatic plant composition). These findings support the hypothesis that the relative availability of reduced versus oxidised N forms is an important driver of phytoplankton composition. Together, these results suggest that pelagic biota are highly sensitive to salinity and nitrate increases, and that the phytoplankton compositional shifts are driven by indirect effects on water chemistry (bioavailable P mobilisation, changes in N forms), which are mediated by benthic processes.

Joint interpretation of the hydrochemistry of two neighbouring basins by N-way multivariate methods

The objective of this work is to compare the chemical composition and the spatial and temporal variabilities of groundwater in two basins, the Langueyu and Del Azul creeks basins, located in the Pampean plain, Buenos Aires province (Argentina). The Pampean plain is the most productive region in Argentina, agriculture and livestock being the main economic activities. Groundwater is the principal water resource in the region, with a strong and growing demand for human supply and for agriculture and industrial activities. Several sampling campaigns were carried out on shallow wells of the two studied basins along a period of 3 years (2010–2013) to identify seasonal variations. Electrical conductivity, pH, bicarbonate, chloride, sulphate, nitrate, calcium, magnesium, sodium and potassium were determined following standard methods. For hydrochemical interpretation, descriptive statistical analyses, matrix augmentation principal component analysis, MA-PCA, and multidimensional principal component analysis, N-PCA (Parafac and Tucker3 models), were applied to the hydrochemical datasets from both basins. Three main hydrochemical processes have been identified in both basins: saline enrichment in the groundwater flow direction caused by dissolution of carbonates; exchange of calcium and magnesium by sodium in the same direction, and located areas of nitrate pollution. The paper shows that N-PCA is a good tool to deepen in the understanding of the hydrochemical features of groundwater from two neighbour basins, simplifying the analysis of large amounts of data, as well as establishing relations between the compared basins. Therefore the work is considered an interesting contribution to the study of groundwater resources with a regional scope. This knowledge is essential in basins with high socio-economic interests it causes a direct impact on resources management.

Groundwater management options in North district of Delhi, India: A groundwater surplus region in over-exploited aquifers

Abstract Study region North district of Delhi, India. Study focus The North district of Delhi has mostly shallow water levels and is a groundwater surplus region in contrast to the over-exploited aquifers of the region. The surface runoff and flood waters during monsoon season in the district either causes water logging in lower elevation areas or they join drains and rivers as rejected recharge. This study aims to understand groundwater dynamics of the region in perspective of the aquifer architecture and proposes groundwater management options to meet local water requirements. New hydrological insights in the region Three distinct hydrogeological domains are identified with subtle differences in groundwater occurrence. Insights are obtained in stream–aquifer interaction and baseflow to the Yamuna River is quantified. The salinity enrichment in groundwater has been attributed to water logging in clay rich formations under semi arid condition. The viability of limited dewatering of shallow aquifers and its replenishment by enhanced recharge from surface runoff and flood waters during the monsoon period have been established.

The role of evapotranspiration in the groundwater hydrochemistry of an arid coastal wetland (Península Valdés, Argentina)

Coastal wetlands are complex hydrogeological systems, in which saline groundwater usually occurs. Salinity can be attributed to many origins, such as dissolution of minerals in the sediments, marine contribution and evapotranspiration, among others. The aim of this paper is to evaluate the processes that condition the hydrochemistry of an arid marsh, Playa Fracasso, located in Patagonia, Argentina. A study of the dynamics and geochemistry of the groundwater was carried out in each hydrogeomorphological unit, using major ion and isotope (18O and 2H) data, soil profiles descriptions and measurements, and recording of water tables in relation to the tidal flow. Water balances and analytical models based on isotope data were used to quantify the evaporation processes and to define the role of evaporation in the chemical composition of water. The results obtained show that the groundwater salinity of the marsh comes mainly from the tidal inflow, to which the halite and gypsum dissolution is added. These mineral facies are the result of the total evaporation of the marine water flooding that occurs mostly at the spring high tides. The isotope relationships in the fan and bajada samples show the occurrence of evaporation processes. Such processes, however, are not mainly responsible for the saline content of groundwater, which is actually generated by the dissolution of the typical evaporite facies of the arid environment sediments. It is concluded that the evapotranspiration processes condition groundwater quality. This is not only due to the saline enrichment caused by the evapotranspiration of shallow water, but also because such processes are the main drivers of the formation of soluble salts, which are then incorporated into the water by groundwater or tidal flow.

Modeling the winter‐spring transition of first‐year ice in the western Weddell Sea

AbstractA new halodynamic scheme is coupled with the Los Alamos sea ice model to simulate western Weddell Sea ice during the winter‐spring transition. One‐dimensional temperature and salinity profiles are consistent with the warming and melt stages exhibited in first‐year ice cores from the 2004 Ice Station POLarstern (ISPOL) expedition. Results are highly sensitive to snowfall. Simulations which use reanalysis precipitation data do not retain a snow cover beyond mid‐December, and the warming transition occurs too rapidly. Model performance is greatly improved by prescribing a snowfall rate based on reported snow thicknesses. During ice growth prior to ISPOL, simulations indicate a period of thick snow and upper ice salinity enrichment. Gravity drainage model parameters impact the simulation immediately, while effects from the flushing parameter (snow porosity at the ice top) appear as the freeboard becomes negative. Simulations using a snow porosity of 0.3, consistent with that of wet snow, agree with salinity observations. The model does not include lateral sources of sea‐water flooding, but vertical transport processes account for the high upper‐ice salinities observed in ice cores at the start of the expedition. As the ice warms, a fresh upper‐ice layer forms, and the high salinity layer migrates downward. This pattern is consistent with the early spring development stages of high‐porosity layers observed in Antarctic sea ice that are associated with rich biological production. Future extensions of the model may be valuable in Antarctic ice‐biogeochemical applications.

The chemical development of a hypersaline coastal basin in the High Arctic

We investigated a hypersaline, seasonally isolated marine basin (SIMB) in the Canadian High Arctic to elucidate the role of brine rejection, tidal forcing, and groundwater input over the formation of hypersalinity. Analyses of physical parameters and seasonal sampling of ionic and isotopic composition were carried out on a coastal basin near Shellabear Point, Melville Island, Northwest Territories (75°N, 113°W). Observations reveal daily and seasonal variability in the water column due to a seasonal tidal connection during the ice‐free season, which lasts substantially longer than the period of freshwater inflow from the catchment. An ice formation model of the volume of brine rejected from surface ice formed from marine water indicates that rapid saline enrichment of the basin due to ice formation is possible from tidally replenished marine water, and that the current hypersalinity may have formed in less than a decade. Modeled isotopic composition of brines are consistent with observations and provide an alternative to freshwater isotopic dilution suggested by other workers. A tidal connection is a critical consideration in lake evolution, and many hypersaline polar lakes could have developed their current chemical composition before full marine isolation. By contrast, in some coastal lakes, marine stratification caused by ice shelves before isolation provides a setting for minimal brine formation and subsequent meromictic conditions to develop. Hence, the marine setting at the time of isolation represents a key factor in explaining divergent lake chemical evolution in the High Arctic.