Further Increase In Salinity Research Articles

Effect of Dielectric Constant on the Zeta Potential of Spherical Electric Double Layers.

Zeta potential refers to the electrokinetic potential present in colloidal systems, exerting significant influence on the diverse properties of nano-drug delivery systems. The impact of the dielectric constant on the zeta potential and charge inversion of highly charged colloidal particles immersed in a variety of solvents spanning from polar, such as water, to nonpolar solvents and in the presence of multivalent salts was investigated through primitive Monte Carlo (MC) model simulations. Zeta potential, ξ, is decreased with the decreasing dielectric constant of the solvent and upon further increase in the salinity and the valency of the salt. At elevated levels of salt, the colloidal particles become overcharged in all solvents. As a result, their apparent charge becomes opposite in sign to the stoichiometric charge. This reversal of charge intensifies until reaching a saturation point with further increase in salinity.

Harnessing waste glycerol to mitigate salinity constraints in freshwater microalgae cultivation for enhanced biodiesel recovery

The current study investigated the synergistic effect of waste glycerol and salinity on Scenedesmus obliquus cultivation for enhanced biomass and biodiesel production. Optimal glycerol concentration was identified at 0.08 M supplementation, resulting in 23.1 % significant increase in biomass productivity. However, higher glycerol concentrations resulted in growth retardation. Salinity of +200 % NaCl showed positive impact on the growth, with the highest recorded dry weight of 1.76 g/L and biomass productivity of 0.206 g/L.day. However, further increases in salinity resulted in 53.4 % reduction in biomass yield at +800 % NaCl compared to +200 % NaCl. The combined treatment of the optimum glycerol concentration at different salinities (Glyc + Salin) showed superior growth performance up to +600 % NaCl, which confirmed mitigation of salinity inhibitory effects. Glyc + Salin exhibited the highest recorded nitrogen and phosphorus removal efficiencies (98.1 % and 96.6 %, respectively at day 8), dry weight (2.02 g/L), and biomass productivity (0.231 g/L.day). Notably, lipid content increased to 240.4 mg/g dw, and lipid productivity reached 56.0 mg/L.day, representing 76.1 % improvement over the control. Biodiesel characteristics, including cetane numbers and iodine values, showed also improvement, confirming the potential of Glyc + Salin for sustainable microalgal cultivation and biodiesel production.

Effect of Different Salinity Levels on Growth Performance, Hematological Parameters and Proximate Composition of Cyprinus Carpio

The current study was conducted to evaluate the effect of different salinity levels on the growth performance, proximate composition, and hematological parameters of Common carp (Cyprinus carpio). The experiment was designed under Laboratory conditions with twice replica as five treatments: T0: 0-ppt, (control); T1: 2-ppt, T2: 4-ppt, T3: 6-ppt and T4: 8-ppt and fish were randomly stocked (5 fish /aquarium). The C. carpio were fed 5% (commercial diet CP-30%) of their body weight and water was replaced regularly after every alternate day. The present study describes the significant changes (p<0.05) in growth parameters (viz; final weight, weight gain, feed intake and feed conversion ratio) with poor feeding behavior and stress were observed with further increase in salinity. Furthermore, body composition (Protein, fat, moisture, and ash contents) also showed significant changes (p<0.05). The crude protein and moisture contents were significantly decreased while crude fat and ash contents were increased with the increase of salinity respectively. The results of hematological parameters also decrease with the increase of salinity and found significant changes (p<0.05). The results of this study indicate that C. carpio exhibits a great degree of adaptability and resistance to salinity stress. This study serves as a basis for developing strategies to optimize the rearing conditions and welfare of common carp in different salinity regimes. Further research is warranted to elucidate the molecular and cellular mechanisms involved in the observed responses, enabling more precise management practices for the sustainable cultivation of C. carpio.

Comparison of salinity tolerance between Avicenna marina and Rhizophora mucronata Karachi coast, Pakistan

Mangrove propagule size variation is an important factor in their survival. The main aim of this study was to determine the productivity and identify the comparison between Avicenna marina and Rhizophora mucronata. However, it is less studied about the comparison of mangrove species and their salt tolerance in terms of seedling establishment of propagules. We investigated the propagules size variation of Avicennia marina and Rhizophora mucronata from the Indus delta and were grown in the polythene bags of 5x10″ filled with silty soil from field nursery. We used salinity and nutrients treatments to propagules to identify the growth rate of mangrove species. The surveying technique was also used to collect the information of mangrove forest from local communities. We detected that Rhizophora mucronata had a higher productivity rate due to the given concentration of 50% sea water. While the Avicennia marina showed a lower decline ratios growth at 25% salinity level with further increases in salinity. Using diffusion porometers and infrared gas analyzers (IRGAs), we revealed that stomatal conductance was higher in Rhizophora mucronata, followed by Avicennia marina. Moreover, our outcomes showed a higher Sodium and chloride ions with the increase in salinity and also demonstrated a higher accumulation in Avicennia marina. Overall, its was found that Avicennia marina is the most salt resistant species and it’s a dominated species in littoral forest. Our outcomes can help us to better understand the green infrastructure design of mangroves, suggesting that selecting multiple techniques ensure many post-tsunami restoration initiatives are encountering problems.

The effect of salinity on the pressure susceptibility of the NF270 membrane

To avoid structural changes within nanofiltration membranes during operation, pre-compaction of filtration membranes is usually performed. However, even after pre-compaction, the NF270 membrane has previously been shown to display a level of pressure susceptibility in pure water systems, particularly evident at low pressures. For the first time, this study provides experimental evidence for the effect of salinity on the pressure susceptibility of the NF270 membrane. Permeability was shown to decrease with increasing salinity up to 189 mM MgSO4, with the largest reduction (22 %) observed at the lowest MgSO4 concentration (31.49 mM MgSO4). A significant reduction (35 %) in the membrane susceptibility was also observed following the introduction of MgSO4 to a concentration of 31.49 mM. A mathematical expression, developed for pure water systems, was modified to account for salinity effects and fitted the experimental data well for concentrations up to 0.2 M. These results are explained by compaction of the membrane polymer, due to either charge neutralisation at the membrane surface, or electric double layer compression, or both. However, further increases in salinity had no significant effect on membrane susceptibility, suggesting that salt induced membrane compaction occurs at very low concentrations.

Combined acute effect of salinity and substrate concentration on simultaneous sulfide and nitrite removal process

Nitrite or sulfide accumulation has always been a challenge for the treatment of saline or hypersaline wastewater. Simultaneous sulfide and nitrite removal process (SSNIR) targeting sulfide and nitrite as substrates, is a robust and potentially practical autotrophic denitrification biotechnology. Its feasibility to operate under hypersaline wastewater is not fully understood so far. Therefore, the current work explored the practicability of SSNIR to treat saline or hypersaline wastewater, evaluation of the toxicological effects of substrate and salinity on the denitrification and sulfide removal performance and product types. Additionally, the type of combined toxicity of substrate and salinity to SSNIR was determined. The results showed that the respective IC50 values for substrate shock on Specific sulfide oxidation activity (SSOA) and Specific denitrification activity (SDA) were 289.29 mg S/L and 300.92 mg S/L. The IC50 values of salinity shock on SSOA and SDA were 6.19 % wt (98.07 ms/cm) and 3.78 % wt (61.74 ms/cm), even the salinity level as high as 13.2 % wt (204 ms/cm) resulted in the reduction of 40 % nitrite removal efficiency. At salinity value>2.4 % wt (41 ms/cm), increase in salinity casted significantly positive effect on the nitrous oxide emission (P < 0.01). In addition, the combined salinity, substrate toxicity and salinity exposure value of<2.67 % wt (45 ms/cm) on SSNIR showed synergistic inhibition. A further increase in salinity (>45 ms/cm) alleviated the strength of synergistic inhibition and the effect on SSOA was identified as antagonistic inhibition.

Comparison of mechanical behaviour of geopolymer and OPC-based well cement cured in saline water

Well cement plays a vital role in maintaining wellbore integrity in a carbon capture and storage project. To date, ordinary Portland cement (OPC)-based well cement has been used and there are contrasting research findings on its suitability as well cement. This research aims to use geopolymer as well cement, and major aim of this work is to analyse the mechanical behaviour of both geopolymer and OPC subjected to various down-hole conditions including different salinity (0–30% NaCl) and confinements (0–15 MPa). This research comprises experimental and numerical works. Under the experimental work, series of unconfined compressive strength (UCS) test were conducted for geopolymer and OPC samples cured in saline water with 0–30% NaCl salinity for a period of 45 days. COMSOL multiphysics software was used for the numerical study, and first, laboratory scale uniaxial stress–strain behaviour of both geopolymer and OPC was validated numerically. The model was then extended to study the triaxial mechanical behaviour under different salinity (0–30% NaCl) and confining pressures (0–15 MPa) conditions. Based on the results, it was noticed that UCS of geopolymer increases with salinity due to the high resistance against alkali leaching in saline water compared to fresh water. The UCS of OPC increases with salinity up to 10% NaCl, and then it reduces with any further increase in salinity. The UCS of geopolymer is 6% to 66% higher than that of OPC depending on the salinity conditions and geopolymer possesses higher UCS than OPC for any given salinity condition. COMSOL multiphysics numerical software predicted the stress–strain behaviour of geopolymer and OPC accurately up to yield point. Failure strength of geopolymer in saline water is 3% to 61% higher than that of OPC for a given confining pressure. Findings of this research indicate that geopolymer can be a good alternative for OPC based well cement under deep down-hole conditions.

Phytoplankton of Tiligulsky Liman in conditions of change of salt regime

The article represents the research on influence of a number of hydrochemical parameters on the phytoplankton formation in the Tiligulsky Liman in 2015 and the forecast of possible changes in terms of increasing salinity. In the northern, central, southern and coastal part of the Liman, 65 species of microalgae were found, which were mainly diatoms (44) and dinoflagellates (12 species). The coastal waters were characterized by the highest number of phytoplankton (4.3 million cells·l-1) due to the massive development of green algae. The biomass was almost the same at all regions (1618.2 – 1955.8 mg·m-3), except the southern (358.7 mg·m-3). The salinity varied in the following range: 13‰ – in the coastal part, 24‰ – in the south and north, 25‰ – in the central. In the lower part it was revealed the dominance of dinoflagellates of the genera Prorocentrum, Protoperidinium, Gymnodinium (contribution to biomass up to 82%), on the sea coast – green algae Monoraphidium contortum (Thur.) Komark.-Legn., M. minutum (Nageli) Komark.-Legn. (up to 11% by biomass and 67% by abundance). Flagellates reached a fairly high abundance at different sites (up to 10% by biomass and 15% by abundance). Among the diatoms Skeletonema costatum (Grev.) Cl. developed massively in the southern part of the Liman; Ceratoneis closterium (Ehr.) Reimann et JCLewin and Tabularia fasciculata (Ag.C) DMWilliams et Round – in the coastal part; Chaetoceros socialis – in the central, Navicula sp. – in the northern. Correlation and ordination analysis revealed that salinity is the main factor determining the development of plankton microphytes at the studied sites. Oxygen content, depth and temperature are also important factors in the bottom horizon. The content of nutrients is more significant on the surface horizon. Regarding the salinity, 35 species-indicators of salinity were identified, of which 11% were indifferent (freshwater-brackish-water), 37 – mesogalobes (brackish-water) and 51 polyhalobes (marine). In comparison with the studies of the 1980s and 2000s, it was found that the share of freshwater-brackish-water species has decreased significantly, and freshwater algae were absent. Further increase in salinity will lead to raising of the proportion of eurygaline species, such as diatoms Achnanthes brevipes, Halamphora coffeaeformis, Navicula salinarum, N. pontica, N. cancellata, Nitzschia hybrida, Tabularia fasciculata, Ceratoneis closterium, Cocconeis scutellum. These species can withstand fairly large salinity ranges and are the first who massively develop in salinized water bodies.

Influence of Seawater Salinity on Corrosion of Austenitic Steel

Abstract Due to the paramagnetic properties and the ability to passivation, for the production of hulls of some vessels (mainly warships), corrosion-resistant (stainless) steels with austenitic structure are used. This article describes the influence of seawater salinity on selected corrosion properties of high-alloy steel X5CrNi 18-10 (304). The average salinity of the seas is taken as 3.5% content of sodium chloride. Corrosion rate of the tested material was evaluated in an aqueous solution of sodium chloride was evaluated. The NaCl concentration in corrosive solutions was 0.7%, 1.4%, 2.1%, 2.8%, 3.5%, 4.2%. Corrosion tests were performed using the potentiodynamic method. The range of electrochemical potential changes was Ecorr ±150 mV. Corrosion rate was assessed on the basis of corrosion current density measurements. Corrosion potential values against the saturated calomel electrode were also determined. Based on the obtained measurement results and non-parametric significance tests carried out, a significant influence of seawater salinity on the value of corrosion current density and corrosion potential was found. The highest value of corrosion current density (jcorr), and thus the highest corrosion rate, was recorded for 3.5% NaCl solution. In the concentration range from 0.7 to 3.5% NaCl in solution, the corrosion rate of austenitic steel increases. A further increase in salinity of electrolyte results in the inhibition of corrosion rate of steel. There is almost a full negative, linear correlation between the proportion of sodium chloride in the corrosive solution and the value of corrosion potential. Along with the rise in the salinity of seawater, increase the electrochemical activity, and thus the corrosion susceptibility, thus the corrosion susceptibility, of the austenitic steel X5CrNi 18-10 was observed.

Impacts of physical alterations on salt transport during the dry season in the Modaomen Estuary, Pearl River Delta, China

Physical alterations (e.g., land reclamation and riverbed down-cutting) caused by human activity may significantly affect the process of salt transport in estuarine systems. Between the 1970s and 2010s, the Modaomen Estuary, an outlet of the Pearl River Delta (PRD), was subject to large-scale land reclamation and riverbed down-cutting, which exerted dramatic changes in the transport of salt. In this study, a three-dimensional hydrodynamic model (EFDC) is used to quantitatively evaluate the impacts of different physical alterations in the estuary during the dry season. The modeled results indicate that large-scale land reclamation has decreased landward salt transport, which has weakened the tidal mixing and diffusion in the estuary and has resulted in decreased salinity and a shortened salt intrusion length. In addition, the significant degree of riverbed down-cutting has caused the import of more salt into the estuary, which has enhanced the estuarine circulation to cause further increases in salinity and an extended salt intrusion length. Further, the enhancement of landward salt transport owing to the riverbed down-cutting is much stronger than the weakening effect of land reclamation. All of these local physical alterations have significantly augmented the salt intrusion extent and has intensified the salinity stratification. Consequently, the Modaomen Estuary has changed from partial stratification to high stratification during the past four decades. Although both upstream riverbed down-cutting and sea-level rise facilitate salt intrusion, the impacts from these processes are one order of magnitude smaller than those from the physical alterations made in the estuary. The results obtained in this study have significant implications for the sustainable development of estuarine systems and provide scientific guidelines for general water management, particularly for the prevention of brine tides in the PRD.

Simultaneous removal of carbon, nitrogen and phosphorus from hypersaline wastewater by bioaugmented intermittently aerated biological filter (IABF)

AbstractSimultaneous removal of carbon, nitrogen and phosphorus from hypersaline wastewater by halophiles bioaugmented intermittently aerated biological filter (IABF) was systematically investigated in this research. The bioaugmented IABF showed significantly improved simultaneous nutrient removal efficiency in salinity range of 6–11% compared to the uninoculated IABF although the benefit of inoculation was no more evident with further increase in salinity. As high as 12% difference in COD removal efficiency, 18% difference in TN removal efficiency and 14.6% difference in TP removal efficiency were observed between the inoculated and uninoculated IABF. Reactor performance was negatively affected by backwashing at hypersaline conditions. However, inoculation of halophiles reduced the biofilm recovery time after backwashing. Growth curve of halophiles, as well as biomass loading and dehydrogenase activity, at different salinities were studied to explore the bioaugmentation mechanism. Excellent correlation was observed between the halophile growth curve, biomass loading and DHA and the removal efficiency of the organic pollutant, which can be used to predict the biofilter performance in removing the organic matters through the analysis of halophiles growth curve, biomass loading and DHA in the reactor.

Stimulation of Native Microorganisms for Improving Loose Salty Sand

Prolonged droughts and excessive water harvesting in western Asia has accelerated desertification and caused longer dry seasons of salt lakes. The Aral Sea experience has proven that dust from saline soil is a serious health issue. Various stabilization techniques to reduce wind erosion have been used in the past. However, in recent years, a potentially viable method has been developed; microbial induced calcite precipitation (MICP) has been introduced as a method of soil stabilization, though its effectiveness in saline soils remains to be examined. The effect of salt content in loose sandy soil on calcite precipitation of calcite through stimulation of native bacteria is investigated in this article. Samples with salinity up to 30% salt content were prepared and treated with different culture medium compounds. A number of tests were used to evaluate the effect of the mentioned parameters. The results show that improvement increases with increasing salinity up to 5% salt, and further increase in salinity reduces the effectiveness of improvement. It is also shown that the addition of urea in the culture medium has a significant effect on the urea hydrolysis which resulted in a five-fold increase in compressive strength. Four native strains of halotolerant urease-positive bacteria were also identified.

SPOROBOLUS SPICATUS, A POTENTIAL TURF GRASS UNDER THE CLIMATIC CONDITIONS OF UAE

Different accessions of Sporobolus spicatus were tested for the possible use in the landscaping sector of United Arab Emirates. In this regards, fifty accessions of S. spicatus were screened against five salinity levels of 15, 30, 45, 60 and 75dSm-1 at 3cm mowing height. Significant variations were found among the treatment for various characters of leaf colour, fresh and dry weight. Most of the accessions of the grass tolerated up to 45 dSm-1, without compromising on quality. Further increase in salinity, most of the accessions ceased to grow, except a few accessions which survived even at salinity levels of 75dSm-1. Many of the grasses exhibit better performance than Paspalam vaginatum, the prevailing commercial turf grass in UAE (used as control in this instance). As a whole accessions 45S, 18S, 35S and 37S showed salinity tolerance at 3cm mowing height and maintaining quality up to the acceptable level. Based on their tolerance to salinity and better performance, these accessions are recommended for turf use in public landscaping.

Salinity induced changes in light harvesting and carbon assimilating complexes of Desmostachya bipinnata (L.) Staph.

The present study was carried out to determine stomatal, photochemical and biochemical limitations of photosynthesis in Desmostachya bipinnata under saline conditions. We hypothesized that processes determining plant growth and photosynthetic rates will be differentially regulated under various salinity treatments. Plants were grown with 0mM, 100mM (moderate) and 400mM (high) NaCl concentrations in a semi-hydroponic quick check system. Production of biomass was not affected by moderate salinity but a significant reduction was observed at high salinity. High salinity decreased stomatal conductance without affecting Ci. Dark respiration increased at moderate salinity compared to control and high salinity. Salinity treatments had no effect on the WUE. Photosynthetic efficiency was improved at moderate salinity compared to the control but was inhibited at high salinity. Net photosynthesis was similar to the control at moderate salinity but was inhibited with a further increase in salinity. Photosynthetic pigments, electron transport rate, and photochemical quenching were not affected at moderate salinity but declined significantly at high salinity. MDA content significantly increased at high salinity suggesting ROS accumulation. A linear decrease in Vc,max, Jmax, TPU and Rubisco content was observed with increasing salinity treatments. Relative expression of photosynthetic complex proteins was either enhanced (D1, PetD, AtpA) or unaffected (PsbO) with moderate salinity but decreased at high salinity with the exception of AtpA. Our data indicates that photosynthesis rates were maintained at moderate salinity. Damages to photochemical reactions and down-regulated expression of chloroplast proteins in combination with biochemical limitations, rather than stomatal limitations, restrained photosynthetic performance of D. bipinnata under high salinity.

Saltwater intrusion as potential driver of phosphorus release from limestone bedrock in a coastal aquifer

An important but often overlooked consequence of saltwater intrusion is the potential increase of groundwater soluble reactive phosphorus concentrations. The phosphorus sorption dynamics of two limestone rocks of different composition were investigated by simulating seawater intrusion over a wide range of mixing ratios between freshwater and saltwater. Both rocks exhibited a logarithmic loss of sorption efficiency in mixtures containing more than approximately 3 mM Cl− concentration (100 mg Cl−/L; about <1% saltwater). We infer that aquifer solids immersed in freshwater would undergo phosphorus desorption in response to the introduction of this minor amount of seawater. This Cl− concentration is within the range designated as fresh water. Thus we conclude that increased soluble reactive phosphorus availability from saltwater-induced desorption may occur at the ion exchange front, which is actually landward of the saltwater intrusion front as it is commonly defined. Sorption efficiency in our experiments continued to decline as salinity increased, until Cl− concentration reached a second threshold of 50 or 200 mM (1700 or 7700 mg Cl−/L), depending on the rock composition, particularly iron content. Further increase in salinity would produce little increase in groundwater soluble reactive phosphorus concentration. Our results have implications for soluble reactive phosphorus availability in estuaries that receive mixing zone groundwater discharge.

Desmostachya bipinnata manages photosynthesis and oxidative stress at moderate salinity

Desmostachya bipinnata is a C4 grass distributed in arid-saline lands of the subtropical region. There are many economic usages of this perennial grass ranging from folk-medicine to cattle-fodder. However, information regarding the mechanism of salinity tolerance of this species is rare. This study examines the effects of salinity (0, 200 and 400mM NaCl) on growth, osmotic relations, photosynthesis and antioxidant defense. Salinity caused progressive decrease in fresh weight; however, dry weight decreased only at 400mM NaCl. Leaf sap osmotic potential and xylem pressure potential decreased while quantities of ash, proline and sugars increased in response to salinity increments. Stomatal conductance, photosynthetic CO2 gain and transpiration decreased with increasing salinity, while intercellular CO2 levels remained unaffected. Maximum and actual quantum yield of PS II and electron transport rate were inhibited with enhanced non-photochemical quenching under high salinity. Levels of superoxide dismutase and total phenols increased, those of guaiacol peroxidase and ascorbate peroxidase remained unaltered and catalase increased transiently at 200mM NaCl. Leaf hydrogen peroxide and malondialdehyde content increased with salinity. Our data suggest that D. bipinnata could maintain photosynthesis and manage oxidative stress at moderate salinity but a further increase in salinity compromised both photosynthesis and the antioxidant system.

Germination and Dormancy in Annual Halophyte &lt;i&gt;Juncus ranarius&lt;/i&gt; Song &amp;amp; Perr.

The effects of cold stratification and gibberellic acid (GA3) on dormancy breaking for seeds of the annual halophyte species Juncus ranarius were tested. Germination percentage and recovery responses of salt stressed seeds were also tested. Freshly collected seeds germinated slowly under all incubation conditions. Thus, the seeds of J. ranarius have physiological dormancy, e.g. they are water permeable, have a fully developed embryo and require cold stratification to come out of dormancy. Furthermore, promotion of germination by GA3 after-ripening in dry storage also indicated that these seeds have non-deep physiological dormancy. In general, the higher the GA3 concentration, the more germination occurred within the studied range. Juncus ranarius demonstrated a germination preference for light. The highest germination percentage and rate of germination were recorded under constant light conditions at 22 °C after 24 weeks of cold stratification. In saline solutions, the highest percentage of germination was obtained at 25 mM L-1 NaCl, and further increase in salinity resulted in a gradual decrease in germination. However, ungerminated seeds were not damaged by salt, showing a high level of recovery. The greater the reduction in salinity, the better the germination rate became. It was concluded that dormancy could be completely broken by cold stratification, indicating spring germination. Juncus ranarius can grow well at lower NaCl concentrations under constant light conditions at 22 °C.

Review of Archie's equation through theoretical derivation and experimental study on uncoated and hematite coated soils

Abstract This theoretical and experimental study investigated the applicability of Archie's equation to iron oxide coated soils as a function of pore water chemistry, with the ultimate goal of developing a relationship to estimate electrical conductivity based on the physical properties of soils. The study performed an experimental investigation to quantify the electrical properties of uncoated and lab-prepared iron oxide coated sands and clay, in order to evaluate the role of sorbed hematite on the measured electrical conductivity/resistivity of the soils. It was demonstrated that the observed conductivity/resistivity of hematite coated and uncoated clean sands showed good agreement under the tested salinities and iron contents, and both coated and uncoated sands could be represented by Archie's equation. In contrast, the electrical conductivity of iron oxide coated clay indicated a slightly higher value than that of clean kaolinite at low salinity due to the higher relevance of surface conduction; however, with further increase in salinity, the electrical properties of both coated and uncoated kaolinites were comparable and governed by pore water conduction, which agreed with the prediction from Archie's equation.

A laboratory study of ikaite (CaCO3·6H2O) precipitation as a function of pH, salinity, temperature and phosphate concentration

Ikaite (CaCO3·6H2O) has only recently been discovered in sea ice, in a study that also provided first direct evidence of CaCO3 precipitation in sea ice. However, little is as yet known about the impact of physico-chemical processes on ikaite precipitation in sea ice. Our study focused on how the changes in pH, salinity, temperature and phosphate (PO4) concentration affect the precipitation of ikaite. Experiments were set up at pH from 8.5 to 10.0, salinities from 0 to 105 (in both artificial seawater (ASW) and NaCl medium), temperatures from 0 to −4°C and PO4 concentrations from 0 to 50μmolkg−1. The results show that in ASW, calcium carbonate was precipitated as ikaite under all conditions. In the NaCl medium, the precipitates were ikaite in the presence of PO4 and vaterite in the absence of PO4. The onset time (τ) at which ikaite precipitation started, decreased nonlinearly with increasing pH. In ASW, τ increased with salinity. In the NaCl medium, τ first increased with salinity up to salinity 70 and subsequently decreased with a further increase in salinity; it was longer in ASW than in the NaCl medium under the same salinity. τ did not vary with temperature or PO4 concentration. These results indicate that ikaite is very probably the only phase of calcium carbonate formed in sea ice. PO4 is not, as previously postulated, crucial for ikaite formation in sea ice. The change in pH and salinity is the controlling factor for ikaite precipitation in sea ice. Within the ranges investigated in this study, temperature and PO4 concentration do not have a significant impact on ikaite precipitation.

Effect of saline water on relative water content, rate of photosynthesis, chlorophyll content and yield of indian mustard (Brassica junceal.)

Effect of salinity on relative water content, rate of photosynthesis, total chlorophyll content and seed yield plant−1 of Indian mustard (viz., urvashi, Basanti, Varuna, Rohini and Ashirwad) of five genotypes showed increasing trend with 3 dS m−1 salinity over normal salinity in all characters, but further increase in salinity beyond 3 dS m−1 recorded significant reductions in all above mentioned crop characters up to highest salinity of 12 dS m−1. among genotypes, Urvashi registered significantly highest values of all crop parameters, while Ashirwad performed poorest in all cases. Thus, urvashi proved to be more salt tolerant than other genotypes, while Ashirwad proved to be most susceptible towards irrigation water salinity.