Salinity Variations Research Articles

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.

Effect of salinity on geotechnical properties of soft marine clay

ABSTRACT Marine clays are soft clays with low shear strength and high compressibility. These soils are prone to seawater intrusion, due to which their engineering properties may be altered. Therefore, the effect of salinity on engineering properties of marine clay has to be investigated prior to any engineering activity in those areas. In this paper, an attempt has been made to study the effect of salinity on various geotechnical properties of Cochin marine clay. As sodium chloride is the most abundant mineral salt in seawater, the effect of 0%, 0.5%, 1%, 2%, 3% and 4% sodium chloride on marine clay for different curing periods were studied. The results of the study show that liquid limit decreases whereas the strength and compressibility characteristics improve as the concentration of salinity increases. Leaching, however, reverses these improvements, amplifying compressibility by 30% and decreasing pre-consolidation pressure by almost 50%. ITherefore, prior to design of any foundation structures on coastal areas prone to salt water intrusion, the behaviour of clay with variation in salinity should be investigated.

Statistical Assessment of Water-quality Parameters for Different Flow Regimes

Groundwater and drainage-water sustainability is crucial to water management. Controlling the interaction between the groundwater and drain-water salinity at the watershed level has only been the topic of a limited number of studies. This study statistically compares salt concentration rate across time and four different flow regimes. We sampled water from 2014 to 2018. The study used R software to analyze water-quality parameters utilizing PCA and indices. Multiple water-quality indices were used to test irrigation water. A linear model with TDS as the response was fitted to the data. Another two-factor repeated-measurement covariate model was built. Water-quality indices suggest that measured water from varied flow regimes in the study area is suitable for irrigation. Based on the statistical models, Tukey's adjustment pairwise demonstrates considerable salinity variations between drain water and surface water. However, the main effect of the flow regime on TDS is significant. This indicates that the TDS value varies depending on the flow regime, not on time plus the interactions between these regimes. Keywords: Total dissolved solids (TDSs), Groundwater, ANCOVA, Flow condition, Tile drain, PCA

Calibration complexities: full-scale error impact and simultaneous variation of salinity, temperature, and moisture content on sensor performance in soil

Calibration complexities: full-scale error impact and simultaneous variation of salinity, temperature, and moisture content on sensor performance in soil

Formation of Ediacaran stromatolitic cherts through a combination of biogenic and abiotic processes: New insights from the Bohemian Massif

Stromatolites are remarkable organosedimentary laminated structures that grow gradually through time due to the activity of microorganisms, mostly algae and cyanobacteria. The appearance of stromatolites in formations as old as ∼ 3.7 Ga represents the earliest macroscopic traces of life on Earth. Yet, the biogenic origin of some presumed stromatolites has been questioned as abiotic processes (e.g., fluid precipitation, diagenesis and metamorphism) can also be responsible for the formation of stromatolite-like textures. This is especially true in case of pervasively silicified stromatolites (stromatolitic cherts) that have rarely been reported from Neoproterozoic successions. Here, we present a detailed study of the Ediacaran stromatolitic cherts from the Blovice accretionary complex (Bohemian Massif) that combines petrography, trace element and Si–O isotopic compositions and Raman spectroscopy of organic matter to decipher the complex processes leading to their formation and evaluate the biogenicity of their precursor. Textural evidence (i.e. the presence of pseudomorphs after carbonate/evaporate and micro-ooids, variable thickness and spacing of organic-rich laminae) as well as trace element/isotopic compositions argue for a multi-stage formation of stromatolitic cherts. The primary carbonaceous stromatolitic precursors first formed in shallow-water lagoons with variable salinity at seamount slopes, were then fragmented by surface processes (erosion, mass wasting), and finally silicified by low-temperature hydrothermal fluids. The primary biogenic character of stromatolitic textures is evidenced by the non-equidistant alternation of dark (organic matter-rich) and light laminae with markedly different oxygen isotopic compositions reflecting probably seasonal cycles during stromatolite deposition, enrichment of bio-essential elements (e.g., Cu, Zn, Co and Mn) in dark laminae, and Raman spectra of organic matter indicative for variably matured kerogens. The presence of late-stage diagenetic modifications might be related to subsequent burial and low-grade metamorphism of stromatolitic cherts within the accretionary wedge.

Spatiotemporal Variations in Upper‐Ocean Salinity Over the North Pacific in 2004–2021

AbstractInterannual variations in upper ocean salinity in the North Pacific Ocean (NP) were examined comprehensively over a period of 18 years (2004–2021) with gridded data sets considering vertical profiles of salinity. The salinity in nearly half of the basin varied in phase with a slight lag, and the rest of the basin exhibited the opposite phase on a decadal scale. The average salinity above 400 dbar prominently increased in the eastern and western mid‐latitude regions from approximately 2010 to the latter half of the 2010s, and decreased in the central subarctic and subtropics during the same period. This spatial pattern was similar to that of temperature change. While the freshening in the subtropics was remarkably above 100 dbar, salinity changes in the subarctic were large even in the subsurface. The first mode of the complex empirical orthogonal function analysis indicated the eastward (westward) propagation of salinity anomalies in the subarctic (subtropics), that is, a clockwise shift. Salinity budget analysis revealed that the changes in the 2010s were mainly caused by geostrophic advection in zonal regions around 40°N and 20°N, and the eastern NP. Precipitation also contributed to freshening in the subtropics, but not in the central subarctic. The meridional migration of salinity fronts in the subarctic and subtropics induced by wind stress, which is meridional contraction of the subtropical gyre, contributed to freshening in the central NP. It is unclear whether salinification in the eastern and western regions inevitably synchronizes and should be further examined.

Disentangling responses of aquatic and terrestrial invertebrates to drying in saline streams and shallow lakes

In inland aquatic ecosystems, drying and salinity can co-occur as natural stressors, affecting aquatic invertebrate communities. Despite recent appreciation of the importance of temporary waterbodies for terrestrial invertebrates, knowledge about the effects of drying on dynamics of aquatic and terrestrial invertebrate communities is scarce, especially in saline ecosystems. This study analyzed structural and compositional responses of both communities to the coupled effects of drying and salinity in two streams and two shallow lakes in Spain, during three hydrological phases: wet, contraction, and dry. In the two studied saline streams, the contraction phase presented the highest aquatic and terrestrial abundance and richness, and the main compositional changes were mainly due, to an increase in aquatic lentic taxa (e.g., Coleoptera), and Araneae and Formicidae as terrestrial taxa. In shallow lakes, which presented highly variable salinity conditions, the highest abundance and diversity values were found at the wet phase for aquatic invertebrates and at the dry phase for terrestrial invertebrates. Compositional invertebrate community changes were due to a decrease in Rotifera and Anostraca (aquatic taxa) in the contraction phase for aquatic communities, and to an increase of Araneae, Coleoptera, and Formicidae (terrestrial taxa) at the dry phase for the terrestrial. Our study evidences the significant effect of drying on both aquatic and terrestrial invertebrates communities in natural inland saline waters and the need to integrate aquatic and terrestrial perspectives to study temporary inland waters.

First Insights into Body Localization of an Osmoregulation-Related Cotransporter in Estuarine Annelids.

The expression of the Na+-K+-2Cl- cotransporter (NKCC), widely associated with cell volume regulation, has never been directly demonstrated in annelids. Its putative presence was firstly recovered in silico, and then using immunofluorescence, its signal was retrieved for the first time in different tissues of four species of estuarine annelids from southern Brazil that are regularly subjected to salinity fluctuations. We tested two euryhaline species (wide salinity tolerance), the nereidids Alitta yarae and Laeonereis acuta (habitat salinity: ~10-28 psu), and two stenohaline species (restricted salinity tolerance), the nephtyid Nephtys fluviatilis (habitat salinity: ~6-10 psu), and the melinnid Isolda pulchella (habitat salinity: ~28-35 psu). All four species showed specific immunofluorescent labelling for NKCC-like expression. However, the expression of an NKCC-like protein was not homogeneous among them. The free-living/burrowers (both euryhaline nereidids and the stenohaline nephtyid) displayed a widespread signal for an NKCC-like protein along their bodies, in contrast to the stenohaline sedentary melinnid, in which the signal was restricted to the branchiae and the internal tissues of the body. The results are compatible with NKCC involvement in cell volume, especially in annelids that face wide variations in salinity in their habitats.

The behavior of surfactant microemulsion in clay-hosted nanopores

The utilization of microemulsions to boost well productivity is gaining traction, particularly in unconventional shale wells during fracturing. However, the subsequent behavior and stability of microemulsions remain less clear, especially in clay-hosted nanopores where clay minerals exhibit unbalanced surface charges. This study employs the molecular dynamics (MD) approach to characterize the behavior and stability of microemulsion droplets through clay-hosted nanopores with different surface chemistries and salinities in shales, under typical reservoir pressures and temperatures. Our findings reveal that in the bulk, microemulsion droplets remain stable across all salinities. Yet, depending on the surface chemistry (charge distribution) in clays, the stability of microemulsion droplets becomes contingent on salinity. When clay surfaces are charge-balanced or have a moderate imbalance, microemulsion droplets remain stable. However, with a strong charge imbalance, induced local electric fields in the slit pore affect the fluids, leading to the essential role of both the electric field and clay surface in breaking the microemulsion droplet. Increasing salinity results in the formation of an electrical double layer, diminishing the strength of the electric field, and preserving the stability of microemulsion droplets. This modeling-based work enhances our comprehension of salinity variations' impact on microemulsions in charged clay hosted nanopores. Notably, this is the inaugural study combining and assessing microemulsion sensitivity to salinity and pore surface chemistry, thereby broadening possibilities for the effective delivery of EOR agents to shales.

Changes in hydrodynamics and nutrient load of the coastal bay induced by Typhoon Talim (2023)

Typhoons can greatly alter the hydrodynamic and nutrient supply in coastal oceans. However, due to the complex conditions of typhoons, such as their intensity, even slight changes may cause substantial changes in hydrodynamics and nutrient supply, which needs to be better understood. In this study, we conducted two cruises before and after Typhoon Talim (2023) to quantitatively investigate changes in hydrodynamics and nutrient supply in Zhanjiang Bay using dual water isotopes. Before the typhoon, strong stratification occurred in the bay. However, the strong external force of the typhoon destroyed the stratification and substantially changed the water mixing in the bay after the typhoon. In the upper bay, massive freshwater input remarkably decreased the salinity during the post-typhoon period (freshwater increased by 18%). In contrast, the salinity variation in the lower bay was minimal, mainly due to massive seawater intrusion from the outer bay induced by the typhoon; the seawater mixed with freshwater columns from the upper bay, forming a strong ocean front. The intensity of ocean fronts induced by typhoons directly depended on the typhoon intensity landing in Zhanjiang Bay, as stronger typhoons will cause more intrusion of high-salinity seawater from the outer bay. Due to the formation of the ocean front, freshwater and terrestrial nutrients from the upper bay are prevented from being transported downwards, resulting in a large amount of accumulated pollutants within the bay. By contrast, due to the impact of high-salinity seawater intrusion, the contribution of seawater from the outer bay has increased, thereby diluting the nutrients in the lower bay. This study provides a new insight into the responses of coastal marine eco-environment systems to typhoons.

Spatio-Temporal Variation Analysis of Soil Salinization in the Ougan-Kuqa River Oasis of China

In order to investigate the mechanism of environmental factors in soil salinization, this study focused on analyzing the temporal-spatial variation of soil salinity in the Ogan-Kuqa River Oasis in Xinjiang, China. The research aimed to predict soil salinity using a combination of satellite data, environmental covariates, and advanced modeling techniques. Firstly, Boruta and ReliefF algorithms were employed to select variables that significantly affect soil salinity from the Sentinel-2 satellite data and environmental covariates. Subsequently, a soil salinity inversion model was established using three advanced strategies: comprehensive variable analysis, a Boruta-based variable selection algorithm, and a ReliefF-based variable selection algorithm. Each strategy was modeled using a Light Gradient Boosting Machine (LightGBM), an Extreme Learning Machine (ELM), and a Support Vector Machine (SVM). Finally, the Boruta-LightGBM strategy was proven to be the most effective in predicting soil electrical conductivity (EC), with a coefficient of determination (R2) of 0.72 and a Root Mean Square Error (RMSE) of 12.49 ds/m. The experimental results show that the red-edge band index is the foremost variable in predicting soil salinity, succeeded by the salinity index and soil attribute data, while the topographic index has the least influence, which further demonstrates that proper variable selection could significantly improve model functionality and predictive precision. Furthermore, the Multiscale Geographically Weighted Regression (MGWR) model was utilized to reveal the influence and temporal-temporal-spatial heterogeneity of environmental factors such as soil organic carbon (SOC), precipitation (PRE), pH value, and temperature (TEM) on soil EC. This research offers not just a viable methodological framework for monitoring soil salinization but also new perspectives on the environmental drivers of soil salinity changes, which have implications for sustainable land management and provide valuable information for decision-making in soil salinity control and mitigation efforts.

Diagnosing the causes of AMOC slowdown in a coupled model: a cautionary tale

Abstract. It is now established that the increase in atmospheric CO2 is likely to cause a weakening, or perhaps a collapse, of the Atlantic Meridional Overturning Circulation (AMOC). To investigate the mechanisms of this response in CMIP5 models, Levang and Schmitt (2020) have estimated the geostrophic streamfunction in these models offline and have decomposed the simulated changes into a contribution caused by the variations in temperature and salinity. They concluded that under a warming scenario, and for most models, the weakening of the AMOC is fundamentally driven by temperature anomalies, while freshwater forcing actually acts to stabilise it. However, given that both 3-D fields of ocean temperature and salinity are expected to respond to a forcing at the ocean surface, it is unclear to what extent the diagnostic is informative about the nature of the forcing. To clarify this question, we used the Earth system Model of Intermediate Complexity (EMIC), cGENIE, which is equipped with the C-GOLDSTEIN friction-geostrophic model. First, we reproduced the experiments simulating the Representative Concentration Pathway 8.5 (RCP8.5) warming scenario and observed that cGENIE behaves similarly to the majority of the CMIP5 models considered by Levang and Schmitt (2020), with the response dominated by the changes in the thermal structure of the ocean. Next, we considered hysteresis experiments associated with (1) water hosing and (2) CO2 increase and decrease. In all experiments, initial changes in the ocean streamfunction appear to be primarily caused by the changes in the temperature distribution, with variations in the 3-D distribution of salinity only partly compensating for the temperature contribution. These experiments also reveal limited sensitivity to changes in the ocean's salinity inventory. That the diagnostics behave similarly in CO2 and freshwater forcing scenarios suggests that the output of the diagnostic proposed in Levang and Schmitt (2020) is mainly determined by the internal structure of the ocean circulation rather than by the forcing applied to it. Our results illustrate the difficulty of inferring any information about the applied forcing from the thermal wind diagnostic and raise questions about the feasibility of designing a diagnostic or experiment that could identify which aspect of the forcing (thermal or haline) is driving the weakening of the AMOC.

Salinity mixing in a tidal multi-branched estuary with huge and variable runoff

The study of estuarine hydrodynamics within an isohaline framework has been well established in recent years. However, most studies of estuarine mixing and exchange flow using salinity coordinates have been conducted for idealized estuaries or realistic estuaries with simple bathymetry and constant runoff. In this study, a realistic numerical model is applied to the Changjiang River estuary, a complex multi-branched estuary with huge and variable runoff. The destruction of salinity variance is used to quantify salinity mixing, in which numerical mixing accounts for about one third of the total mixing. The results of total mixing per salinity class mS indicate that the universal law of estuarine mixing applies to realistic simulations under huge and variable runoff when averaged over two spring-neap cycles (28 days). During the flood season, volume integrated salinity mixing is approximately twice that of the dry season due to the double runoff. Salinity mixing at different channels displays distinct characteristics in both horizontal and vertical distributions. The patchy distribution of effective vertical diahaline velocity implies that the volume flux across an isohaline surface can exhibit significant spatial variability. The most vigorous salinity mixing occurs in the North Passage, where about 58 % of the freshwater enters the sea. We found that the estuarine mixing within different branches is linearly correlated with the corresponding water transport. Dikes fringing the navigational channel on both sides downstream of the North Passage significantly increase the length of saltwater intrusion in the North Passage, alter the distribution of horizontal and vertical flow velocities, and further cause significant changes in local mixing, especially near the mouth of the dikes.

The Carbonate System of Penzhina Bay and the Shelikhov Gulf in the Sea of Okhotsk during Extreme Tides in Summer

Understanding the factors that control carbonate systems is an important goal due to the complex interactions between the hydrophysical and chemical–biological conditions in coastal basins. The results of this paper present the state of the carbonate system in Penzhina Bay and its adjacent waters—the Shelikhov Gulf—in July 2023, during spring tides with 13 m height. The area we studied included the length of the largest river in the region, the Penzhina River, from the peak of its summer flood to its boundary with the Shelikhov Gulf (the Sea of Okhotsk). This unique dynamic basin, with a length of about 800 km, was studied over 17 days. During this period, the entire water column of Penzhina Bay, down to a depth of about 60 m, and the surface water layer of the Shelikhov Gulf were undersaturated in terms of CO2, with low levels relative to those of the atmosphere. To explain this observation, the dissolved oxygen, nutrients in mineral and organic forms, humic substances, chlorophyll a, and photic zone thickness are presented for the entire basin under study, together with its hydrological data. The results of daily observations of the carbonate system at fixed anchorage stations characterize two contrasting regions of Penzhina Bay: one that was more exposed to continental runoff, which had salinity levels in the range of 8.0–21.3 psu during one tidal cycle; the second had smaller variations in salinity in the range of 31.6–32.9 psu during one tidal cycle. This study emphasizes the importance of biological processes and continental runoff on the variability of the carbonate system parameters and CO2 fluxes at a water/atmosphere boundary with extreme tidal conditions in this ecosystem that is barely affected by human activities.

Qualitative Model of the Causal Interactions between Phytoplankton, Zooplankton, and Environmental Factors in the Romanian Black Sea

In order to analyze how environmental factors affect planktonic organisms along the Romanian Black Sea coast, this study created semi-quantitative models of the causal relationships between phytoplankton, zooplankton, and physicochemical parameters by utilizing user-friendly modeling tools. Eleven years of time-series data (March–September 2008–2018) were used to investigate the relationships between phytoplankton, zooplankton, and environmental factors (such as temperature, salinity, and nutrients). Variables such as marine reporting units and phytoplankton species and classes were used to identify developmental patterns, utilizing the Mental Modeler platform to consider interactions between the physicochemical parameters and phytoplankton, phytoplankton and zooplankton, and zooplankton and physicochemical parameters. Although the increase in the overall number of elements and linkages was uncertain in waters with variable salinity compared to marine ones, the semi-quantitative models created for the three marine reporting units along the Romanian Black Sea coast were comparable in terms of complexity. Across the typical and examined types of phytoplankton proliferation (normal, abundant, and blooms), the number of components and connections in the case of phytoplankton blooms substantially decreased as species- and growth-promoting variables increased.

Drivers of Laptev Sea interannual variability in salinity and temperature

Abstract. Eurasian rivers provide a quarter of total fresh water to the Arctic, maintaining a persistent fresh layer that covers the surface Arctic Ocean. This freshwater export controls Arctic Ocean stratification, circulation, and basin-wide sea ice concentration. The Lena River supplies the largest volume of runoff and plays a key role in this system, as runoff outflows into the Laptev Sea as a particularly shallow plume. Previous in situ and modelling studies suggest that local wind forcing is a driver of variability in Laptev sea surface salinity (SSS) but there is no consensus on the roles of Lena River discharge and sea ice cover in contributing to this variability or on the dominant driver of variability. Until recently, satellite SSS retrievals were insufficiently accurate for use in the Arctic. However, retreating sea ice cover and continuous progress in satellite product development have significantly improved SSS retrievals, giving satellite SSS data true potential in the Arctic. In this region, satellite-based SSS is found to agree well with in situ data (r&gt;0.8) and provides notable improvements compared to the reanalysis product used in this study (r&gt;0.7) in capturing patterns and variability observed in in situ data. This study demonstrates a novel method of identifying the dominant drivers of interannual variability in Laptev Sea dynamics within reanalysis products and testing if these relationships appear to hold in satellite-based SSS, sea surface temperature (SST) data, and in situ observations. The satellite SSS data firmly establish what is suggested by reanalysis products and what has previously been subject to debate due to the limited years and locations analysed with in situ data; the zonal wind is the dominant driver of offshore or onshore Lena River plume transport. The eastward wind confines the plume to the southern Laptev Sea and drives alongshore transport into the East Siberian Sea, and westward wind drives offshore plume transport into the northern Laptev Sea. This finding is affirmed by the strong agreement in SSS pattern under eastward and westward wind regimes in all reanalyses and satellite products used in this study, as well as with in situ data. The pattern of SST also varies with the zonal wind component and drives spatial variability in sea ice concentration.

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.

Potential of solar-induced chlorophyll fluorescence (SIF) to access long-term dynamics of soil salinity using OCO-2 satellite data and machine learning method

The accumulation of soil salt becomes a worldwide widespread phenomenon, being a major threat to global production. As an environmental stress, soil salinity can reduce the vegetation photosynthetic activity. Solar-induced chlorophyll fluorescence (SIF) is an electromagnetic signal actively released by vegetation during photosynthesis. SIF not only can capture lower vegetation photosynthetic activity due to environmental stress promptly, but also is less affected by atmosphere and soil background. However, the ability of SIF observation to detect soil salinity remains unclear. Here, we use standardizedsolar-induced chlorophyll iluorescence index (SIFI) from SIF observation time series (2000 ∼ 2020) of global OCO-2 based SIF product (GOSIF) to develop soil salinity model. The results show that: SIF observation can identify salt affected soil (EC ≥ 2 ∼ 4 dS m−1) and salinity class a global scale. The SIFI calculated from SIF observation at May ∼ August (hereafter SIFI5-8) is the optimal sensitivity indices for rainfed cropland, herbaceous cover, irrigated cropland, shrubland, grassland. SIFI10-11 is the optimal sensitivity indices for forest and sparse vegetation; (2) By comparison, the ovrerall classification accuracy of predicted salinity class is above 70 %. The order of classification accuracy is rainfed cropland > irrigated cropland > bare area > forest > grassland > shrubland > herbaceous cover > sparse vegetation; (3) During at least three-quarters of the period from 2000 to 2020, the area of salt affected soil (EC ≥ 2 ∼ 4 dS m−1) was 4.9 Mkm2; (4) The annual change rate of global soil salt content is generally between −0.05 and 0.05 dS m−1 yr−1. Soil salinity in South Africa and West Asia increased greatly with an annual change rate of 0.02 ∼ 0.03 dS m−1 yr−1. These results demonstrate the ability of SIF observation to estimate soil salinity, providing a new perspective for explaining and evaluating soil salinity variation.

Analysis of spatiotemporal variations of drought and soil salinity via integrated multiscale and remote sensing-based techniques (Case study: Urmia Lake basin)

In this study, the spatiotemporal variations of drought and salinity were assessed for the Urmia Lake basin, which is a very critical and challenging ecosystem problem. The lowering of water level in the Urmia Lake and the associated risk of becoming a completely saline land has become an important issue in Iran. In the first step of the study, using the ground- and satellite-based datasets, a new multiscale technique based on Empirical Wavelet Transform (EWT) and Differential Symbolic Entropy (DSE) was proposed to monitor the variations of drought in the selected region. In the next step, variations in the water level and salinity of Urmia Lake and its impacts on the environment were investigated using satellite datasets. Results showed that the Southern parts of the basin were more prone to severe droughts, and there was a direct relationship between entropy and drought intensity. Based on the results, it was concluded that climate change had an impact on the shrinkage of the lake; however, these changes were not solely responsible of causing the dramatic water loss of the Lake. Variations of the Salinity Index (SI) showed that saline lands were mostly seen in the Eastern and Southern parts of the lake, causing negative impacts on air quality and agricultural activities in these parts. It was found that the proper management of water resources would play an effective role in the restoration of the lake.

Effects of medium- and long-term high-salinity environments on free amino acid content and related genes of Sinonovacula constricta

IntroductionThe razor clam, Sinonvacula constricta, one of the important mariculture bivalves in China, has unique flavor and wide salinity adaptability. The unique flavor mainly depends on the content of free amino acids and other umami substances in vivo. However, the flavor divergence of razor clam caused by the variable salinity breeding environment, while the mechanisms remain unclear.MethodsHere, the razor clams were cultured in high salinity (30 ppt) and normal salinity (20 ppt) for eight weeks, and the effects of salinity on free amino acids and related genes expression in S. constricta were investigated by transcriptomics and metabolomics method.ResultsThe results showed the free amino acid content under high salinity environment was significantly higher than normal salinity environment through the duration of the experiment (P &amp;lt; 0.05). The combination of transcriptomic and metabolomic data also indicated that high salinity environment resulted in enhanced metabolism of free amino acids. Furthermore, eight genes such as RALDH2, ACOX1, ALDH-E2 were potentially important for enhancing free amino acids metabolism under high salinity environment.DiscussionThis study preliminarily explained the regulation processes of high salinity environment on the metabolism of free amino acids in razor clams, providing a reference for the flavor regulation mechanism.