Salinity Variations Research Articles

Effects of the Interaction of Salinity and Rare Earth Elements on the Health of Mytilus galloprovincialis: The Case of Praseodymium and Europium

The growing use of products containing rare earth elements (REEs) may lead to higher environmental emissions of these elements, which can potentially enter aquatic systems. Praseodymium (Pr) and europium (Eu) are widely used REEs with various applications. However, their ecotoxicological impacts remain largely unexplored, with poorly understood risks to wildlife. Moreover, organisms also face environmental stressors like salinity fluctuations, and the nature of the interaction between salinity variations and contaminants is not yet clear. Therefore, this study aimed to evaluate the influence of salinity shifts on the impacts of Pr and Eu on adult mussels and the sperm of the species Mytilus galloprovincialis after 28 days and 30 min of exposure, respectively. To do so, biochemical and histopathological alterations were evaluated in adults, while biochemical and physiological changes were analysed in sperm. Additionally, the Integrated Biological Index (IBR) was calculated to understand the overall impact of each treatment. The results showed that adult mussels were most affected when exposed to the combination of high salinity and each element, which altered the behaviour of defence mechanisms causing redox imbalance and cellular damage. On the other hand, sperm demonstrated sensitivity to specific REE-salinity combinations, particularly Pr at lower salinity and Eu at higher salinity. These specific treatments elicited changes in sperm motility and velocity: Pr 20 led to a higher production of O2− and a decrease in velocity, while Eu 40 resulted in reduced motility and an increase in irregular movement. At both lower and higher salinity levels, exposure to Eu caused similar sensitivities in adults and sperm, reflected by comparable IBR scores. In contrast, Pr exposure induced greater alterations in sperm than in adult mussels at lower salinity, whereas the reverse was observed at higher salinity. These findings suggest that reproductive success and population dynamics could be modulated by interactions between salinity levels and REE pollution, highlighting the need for further investigation into how REEs and environmental factors interact. This study offers valuable insights to inform policymakers about the potential risks of REE contamination, emphasising the importance of implementing environmental regulations and developing strategies to mitigate the impact of these pollutants.

Long-Term Stable Reference Electrodes with High-Pressure Tolerance and Salinity-Independence.

The reference electrode's performance is essential for ensuring the accuracy of electrochemical sensors in marine environments. Yet, the many existing reference electrodes can exhibit sensitivity to salinity variations, potentially leading to inaccuracies in the measurement process. Herein, we have designed a reliable solid-state reference electrode by introducing SiOx-stabilized 1-methyl-3-octylimidazolium bis(trifluoromethyl sulfonyl)imide ([C8mim+] [Ntf2-]) into a P(VdF-co-HFP) matrix with a SPEEK/[C8mim+] [Ntf2-] coated Ag/AgCl as substrate. The SPEEK/[C8mim+] [Ntf2-] coating protects the AgCl substrate, and the incorporation of SiOx improves the compatibility of the IL with the polymer matrix, thereby increasing the electrode's resistance to interference and extending its long-term stability and lifespan. The developed reference electrode showed a stable and rapid response, with potential variations of less than 0.7 mV across various salinity solutions, including practical seawater, lake water, and their mixture samples. During extended periods of 18 days in deionized water and artificial seawater, the electrode demonstrated negligible potential drifts of 0.36 and 0.14 mV/d, respectively. Notably, the electrode could maintain a stable potential even after being stored in a preservative solution for 67 days. Furthermore, the electrode showed a stable response to withstand pressures of up to 100 MPa, covering the vast majority of the seafloor. This innovative reference electrode is capable of maintaining a stable reference potential across various salinities, ionic strength, and full ocean depth, making it versatile for use in diverse aquatic environments, underscoring its significant potential for advancing oceanographic research and enabling new insights into the unexplored depths of oceans.

The role of spirulina in food security: Nutritional and ecological implications in the context of climate change

Abstract In the context of a changing climate and the goal of achieving carbon neutrality by 2050, microalgae, particularly spirulina, are emerging as a versatile and sustainable solution to ensure food security, serving as an alternative protein source for human consumption. Spirulina can absorb carbon dioxide during photosynthesis, grows rapidly, does not require arable land, is cultivated year-round, and is rich in protein as well as other macro- and micronutrients. Spirulina stands out not only for its resilience and adaptability to a range of environmental conditions – including variations in light, temperature, pH, and salinity – but also for its low water requirements, making it a promising option for regions with limited water resources. It can address food security challenges by providing nutritional benefits as a dietary supplement and enhancing animal feed quality. Additionally, it supports sustainable agriculture as a biostimulant, improving crop productivity and soil health while reducing reliance on chemical inputs. Its potential as a raw material across various industries and the exploration of new applications make spirulina an attractive candidate for future research, which should focus on enhanced profitability and large-scale accessibility.

Exchange flow in a highly stratified fjord in drought conditions

Fjords are known for their biodiversity and abundant aquaculture resources. However, climate and anthropogenic pressures are altering fjord biological, physical, and chemical processes that will undoubtedly change the ecosystem as a whole. To investigate the impact of climate change on fjord functioning, this study examines the impacts of drought conditions on the physical dynamics and salinity variations in a fjord known for its bolstering aquaculture industry in Northern Chilean Patagonia, the Reloncaví Fjord (41.5° S). Using a high-resolution hydrodynamic model and the Total Exchange Flow (TEF) framework, we analyzed the impacts of river discharge, tides, and wind during a dry year (2016) and a typical year (2018). In 2016, reduced freshwater input decreased exchange flow and increased salinity compared to 2018. In 2018, river discharge dominated TEF variability (74%), while tides and wind contributed 17% and 9%, respectively. In summer 2016, tidal and wind influences rose to 21% and 16%, highlighting their role under low freshwater conditions. Increased wind facilitated destratification, mixing high-salinity subsurface waters with fresh surface layers, affecting ecosystem dynamics. From these results we developed a method to predict long-term stratification variability (1980–2021), identifying critical ecological shifts. Logistic regression models showed significant links between stratification levels and harmful algal blooms (HABs) of Pseudchatonella spp. and Alexandrium catenella. Lower stratification was linked to higher Pseudchatonella spp. HABs in summer, while higher stratification correlated with Alexandrium catenella blooms in spring, tied to increased river discharge. These results suggest that severe HAB events in Northern Patagonia may become more frequent with climate change, underscoring the need to consider local environmental dynamics and stratification in HAB studies.

Limited Microbial Contribution in Salt Lake Sediment and Water to Each Other’s Microbial Communities

Climate change and human activities have led to frequent exchanges of sedimentary and aquatic microorganisms in lakes. However, the ability of these microorganisms to survive in their respective habitats between saline lake sediment and water remains unclear. In this study, we investigated microbial sources and community composition and metabolic functions in sediments and water in Yuncheng Salt Lake using a combination of source tracking and Illumina MiSeq sequencing. The results showed that 0.10–8.47% of the microbial communities in the sediment came from the corresponding water bodies, while 0.12–10.78% of the sedimentary microorganisms contributed to the aquatic microbial populations, and the microbial contributions depended on the salinity difference between sediment and water. Habitat heterogeneity and salinity variations led to the differences in microbial diversity, community composition, and assembly between sediment and water communities. The assembly of sedimentary communities was mainly controlled by stochastic processes (>59%), whereas the assembly of aquatic communities was mainly controlled by deterministic processes (>88%). Furthermore, sediments had a higher potential for metabolic pathways related to specific biogeochemical functions than lake water. These results provide insights into the survival ability of microorganisms and the mechanisms of microbial community assembly under frequent exchange conditions in saline lakes.

Statistical approach to the monitoring of groundwater quality for drinking in Northern Algeria

The scarcity of surface water during prolonged droughts makes the Mitidja quaternary aquifer in north-central Algeria essential for drinking water supply. This study aims to improve understanding of the hydrochemical behavior of this aquifer using multivariate statistical analysis. The main objective is to identify the factors influencing the chemical composition of the water and determine its suitability for domestic use. To this end, water samples were taken from 20 boreholes and analyzed for electrical conductivity, pH, and significant ions during the dry and wet seasons. The results showed significant spatial variations in salinity, particularly in the plain's extreme eastern and western regions, where several parameters exceeded WHO standards. Chemical quality was higher in the western and central boreholes than in those to the east, which were deemed unsuitable for human consumption. Various chemical facies result from the dissolution of dolomitic and evaporitic formations, leading to increased mineralization. In addition, human activity has affected water quality, notably through the excessive use of chemical fertilizers and the discharge of untreated wastewater. This study underlines the need for sustainable environmental management to preserve water quality in the Mitidja quaternary aquifer, which is essential for guaranteeing local communities' drinking water access.

Salinity Effects on Soil Structure and Hydraulic Properties: Implications for Pedotransfer Functions in Coastal Areas

Understanding the effects of salinity on soil structure and hydraulic properties is critical for addressing environmental challenges in coastal saline and sodic areas. In this study, soil samples were collected from a coastal region in eastern China to investigate how salinity affected the soil structure and hydraulic properties based on lab experiments. A comprehensive soil dataset was also compiled from the experimental results to develop a salinity-based pedotransfer function (PTF-S) tailored to the coastal environment. The results showed that salinity significantly altered the soil aggregate size distribution and hydraulic properties. Higher salinity promoted the formation of larger aggregates (0.25–2 mm), particularly in silty clay soil. Salinity positively correlated with the saturated hydraulic conductivity (Ks) in sandy loam soil, regardless of the cation type (Na⁺ or Ca2⁺). By comparison, Na+ increased the Ks of silty clay soil up to a certain threshold, while Ca2+ enhanced the Ks regardless of the soil texture. Increased salinity also reduced the soil water retention of sandy loam soil; however, Na+ increased the soil water retention of silty clay soil and Ca2+ had different effects depending on the suction levels. The newly developed PTF-S model, which included the electrical conductivity (EC) and cation exchange capacity (CEC), showed better predictions for the volumetric water content (R = 0.886 and RMSE = 0.057 cm3/cm3) and log Ks (R = 0.991 and RMSE = 0.073 mm/h) than the traditional model that excludes the salinity variables EC and CEC (PTF-N) (R = 0.839 and RMSE = 0.066 cm3/cm3 for the volumetric water content, and R = 0.966 and RMSE = 0.140 mm/h for the log Ks). This study highlights the importance of developing salinity-based PTFs for addressing soil salinization challenges.

Influence of river runoff and precipitation on the seasonal and interannual variability of sea surface salinity in the eastern North Tropical Atlantic

Abstract. In tropical regions, the freshwater flux entering the ocean originates primarily from precipitation and, to a lesser extent when considering basin-scale averages, from continental rivers. Nevertheless, at the regional scale, river flows can have a significant impact on the surface ocean dynamics. Riverine freshwater modifies salinity and, therefore, density, stratification, and circulation. With its particular coastline and high cumulative river discharge, as well as its being in the vicinity of the intertropical convergence zone (ITCZ), the eastern part of the North Tropical Atlantic (e-NTA) region off northwestern Africa is a particularly interesting location to study the linkage between precipitation, river outflow, and sea surface salinity (SSS). Here, we focus on the regional e-NTA SSS seasonal cycle and interannual variability and on the impact of using various river runoff and precipitation forcing data sets to simulate SSS with a regional model. The simulated SSS values are compared with the Climate Change Initiative (CCI) satellite SSS values; in situ SSS values from Argo floats, ships, and a coastal mooring; and the GLORYS reanalysis SSS values. An analysis of the mixed-layer salinity budget is then conducted. Overall, the simulations reproduce the seasonal cycle and interannual variability well despite a positive mean model bias north of 15° N. The seasonal cycle is impacted by the phasing of the different runoff products. The mixed-layer SSS decrease during the rainy season is mainly driven by precipitation followed by runoff by means of horizontal advection and is partly compensated for by vertical mixing. In terms of interannual anomalies, river runoff has a more direct impact on SSS than precipitation. This study highlights the importance of properly constraining river runoff and precipitation to simulate realistic SSS values and the importance of observing SSS in coastal regions to validate such constraints.

Continental freshwater discharge influences sea surface salinity variability near world’s megadeltas

Sea surface salinity ([Formula: see text]) is a key parameter in the thermohaline circulation of global oceans. Near the megadeltas, inland streamflow through large catchments plays a crucial role in mediating salinity. While some regional studies have investigated how [Formula: see text] is impacted through water cycle and climate components, a global scale quantification of inland streamflow contribution on [Formula: see text] variability is lacking. Here, we utilized remote sensing and observation-driven datasets to quantify the statistical associations between [Formula: see text] and streamflow ([Formula: see text]) at 48 megadeltas worldwide. This study uncovers a robust negative association between [Formula: see text] and [Formula: see text], with correlation coefficients [Formula: see text] less than [Formula: see text] for seasonal data found in 26 of the 48 megadeltas, and less than [Formula: see text] for deseasoned data in 21 megadeltas. The anticorrelation relationship is more pronounced in large deltas, particularly near tropical climates and in river-influenced deltas. The study also underscores the significant roles of climate, morphological, and anthropogenic stratification in impacting the natural influence of freshwater discharge on SSS. By highlighting the interconnected impacts of alterations in terrestrial water cycle upstream and [Formula: see text], this work contributes to enhancing our understanding of global ocean and climate circulation patterns and in tackling environmental issues pertaining to marine ecosystems.

Global cooling controls Eocene environmental change in the Lunpola Basin, central Tibetan Plateau: Evidence from salinity and weathering reconstructions

Detailed investigations of sedimentary rocks from the Tibetan Plateau interior, which has been shaped by plateau development and climate change, will provide new insights into its uplift history. However, few continuous environmental records with clear climatic significance and precise age controls from the Tibetan Plateau hinterland exist, particularly in the early Cenozoic. This shortage hinders a full understanding of the impact of uplift on regional climate change. In this study, we present detailed mineralogical, micromorphological and geochemical investigations of the middle–upper Eocene (~39.6–35.3 Ma) lacustrine sediments from the well-dated Dayu section in the Lunpola Basin, central Tibetan Plateau, to explore the paleoenvironmental evolutionary history of the middle–late Eocene from paleoweathering and paleohydrological perspectives. The results reveal that the regional weathering process continuously weakened, as indicated by a long-term decrease in the (smectite + mixed-layer illite–smectite)/(illite + chlorite) ratio. The quantitative reconstruction of salinity variations via clay boron-based paleosalimeters reveals long-term salinization of paleolakes from freshwater–mesosaline conditions (averaging 9.0 psu) at ~39.6–37.8 Ma to freshwater–polysaline conditions (averaging 13.4 psu) at ~37.8–35.3 Ma. The long-term continuous weakening of the weathering intensity and lake salinization collectively suggests a secular drying trend in the central Tibetan Plateau. This drying was consistent with the climatic evolution of the southeastern and northern Tibetan Plateau, which is attributed primarily to global cooling, with secondary contributions from the increasing distance from moisture sources in the Paratethys and regional tectonics.

Isolation, identification, and characterization of Bacillus subtilis SMP-2 from panitenga and exploring its potential for biosurfactant production

A traditional Assamese fermented food, Panitenga, was explored for potential probiotic isolation. A potent bacterial strain exhibiting biosurfactant production ability was isolated, characterized, and identified as Bacillus subtilis SMP-2. Environmental parameters were optimized for maximum cell growth and biosurfactant production that was found to be pH 6, 30°C, 130 rpm, with glycerol as the carbon (C) source, yeast extract as the nitrogen (N) source, and a C/N ratio of 3:1. At these optimized conditions, the strain yielded 8.13 ± 0.9 g/L of lipopeptide biosurfactant. This biosurfactant remarkably reduced the surface tension of water from 72 mN/m to 37 ± 0.36 mN/m, possessed a low critical micelle concentration (CMC) of 125 mg/L, and exhibited antimicrobial properties. It persisted to be stable across a wide range of physical conditions, including variations in pH, temperature, and salinity. The significantly high production yield and noteworthy properties of the biosurfactant from Bacillus subtilis SMP-2 make it a promising candidate for applications in microbial-enhanced oil recovery (MEOR), bioremediation of oil spills, production of cosmetics and pharmaceuticals, contributing to economic growth and sustainable development.

Microbial Life in Playa-Lake Sediments: Adapted Structure, Plastic Function to Extreme Water Activity Variations

Saline shallow lakes in arid and semi-arid regions frequently undergo drying episodes, leading to significant variations in salinity and water availability. Research on the impacts of salinity and drought on the structure and function of biofilms in hypersaline shallow lakes is limited. This study aimed to understand the potential changes of biofilms in playa-lake sediments during the drying process. Sediments were sampled at different depths (surface, subsurface) and hydrological periods (wet, retraction, and dry), which included a decrease in water activity (aw, the availability of water for microbial use) from 0.99 to 0.72. aw reduction caused a greater effect on functional variables compared to structural variables, indicating the high resistance of the studied biofilms to changes in salinity and water availability. Respiration and hydrolytic extracellular enzyme activities exhibited higher values under high aw, while phenol oxidase activity and prokaryote biomass increased at lower aw. This shift occurred at both depths but was more pronounced at the surface, possibly due to the more extreme conditions (up to 0.7 aw). The increased levels of extracellular polymeric substances and carotenoids developed at low aw may help protect microorganisms in high salinity and drought environments. However, these harsh conditions may interfere with the activity of hydrolytic enzymes and their producers, while promoting the growth of resistant prokaryotes and their capacity to obtain C and N sources from recalcitrant compounds. The resilience of biofilms in hypersaline lakes under extreme conditions is given by their resistant biochemichal structure and the adaptability of their microbial functioning.

Physicochemical perturbation increases nitrous oxide production from denitrification in soils and sediments

Abstract. Atmospheric concentrations of nitrous oxide (N2O), a potent greenhouse gas that is also responsible for significant stratospheric ozone depletion, have increased in response to the intensified use of agricultural fertilizers and other human activities that have accelerated nitrogen cycling processes. Microbial denitrification in soils and sediments is a major source of N2O, produced as an intermediate during the reduction of oxidized forms of nitrogen to dinitrogen gas (N2). Substrate availability (nitrate and organic matter) and environmental factors such as oxygen levels, temperature, moisture, and pH influence rates of denitrification and N2O production. Here we describe the role of physicochemical perturbation (defined here as a change from the ambient environmental conditions) in influencing rates of denitrification and N2O production. Changes in salinity, temperature, moisture, pH, and zinc in agricultural soils induced a short-term perturbation response characterized by lower rates of total denitrification and higher rates of net N2O production. The ratio of N2O to total denitrification (N2O : DNF) increased strongly with physicochemical perturbation. A salinity press experiment on tidal freshwater marsh soils revealed that increased N2O production was likely driven by transcriptional inhibition of the nitrous oxide reductase (nos) gene and that the microbial community adapted to altered salinity over a relatively short time frame (within 1 month). Perturbation appeared to confer resilience to subsequent disturbance, and denitrifiers from an environment without salinity fluctuations (tidal freshwater estuarine sediments) demonstrated a stronger N2O perturbation response than denitrifiers from environments with more variable salinity (oligohaline and mesohaline estuarine sediments), suggesting that the denitrifying community from physicochemically stable environments may have a stronger perturbation response. These findings provide a framework for improving our understanding of the dynamic nature of N2O production in soils and sediments, in which changes in physical and/or chemical conditions initiate a short-term perturbation response that promotes N2O production that moderates over time and with subsequent physicochemical perturbation.

Taking Application Rates With a Grain of Salt: Uncovering the Impact of Road De‐Icing Salt on Freshwaters of a Mountain Catchment in the Italian Alps

ABSTRACTWhile application of salt for de‐icing purposes has been extensively studied in urban areas of North America, little attention has been paid to it in Europe, particularly in mountain areas. Here, after assessment of baseline salinity, and through applying different approaches (i.e., univariate statistical techniques, Multivariate Regression Trees, multivariate regressions), we investigated the potential changes in water chemistry and benthic macroinvertebrate community structure caused by the application of de‐icing salt over an entire winter season, in a mountain catchment located in the Italian Alps (N 46°, E 11°). Concurrently, we tested and compared the application of three different benthic macroinvertebrate indices used to assess salinisation impacts. Overall, we identified a constant level of baseline salinity across a 13‐year period, accompanied by a strong seasonality factor. Despite an application rate comparable to those of large North American cities, macroinvertebrate communities showed little evidence of change. However, chemical ions whose concentrations are known to be influenced by de‐icing salt (e.g., Na+, Cl−) were identified as the structuring drivers of the macroinvertebrate communities, thus suggesting that the studied riverine environment show a high potential for change in relation to salinity. In conclusion, we caution against the simple evaluation of application rates to assess the risk/level of salinisation within a catchment, and encourage further specific analysis and study of salinisation in mountain areas: they appear as sensitive habitats to potential variations in salinity, and stressors such as increased urbanisation and climate change will further exacerbate the risk of increasing salinisation in mountain freshwaters.

Seasonal and Interannual Salinity Variability on the Northeast U.S. Continental Shelf: Insights From Satellite Sea Surface Salinity and Implications for Stratification

AbstractThe Northeast U.S. continental shelf (NEUS) is a highly productive and economically important region that has undergone substantial changes in recent years. Warming exceeds the global average and several episodes of anomalously warm, sustained temperatures have had profound impacts on regional fisheries. A majority of recent research studies focused on the analysis of temperature; however, salinity can serve as a valuable tracer as well. With now more than a decade of remote‐sensing sea surface salinity data, we shed new light onto salinity variability in the region with focus on the Mid‐Atlantic Bight and assess its role for modulating stratification on the shelf using historical hydrographic data. Local river discharge drives decreasing salinities not only in spring and summer on the shelf but also in the Slope Sea. In spring, fresher water aids the build‐up of stratification and a low salinity surface layer extends to the shelf break above the pycnocline by the beginning of summer. An observed salinification in the fall is linked to offshore forcing over the slope associated with the presence of Warm Core Rings. Coherent low‐frequency salinity variability is found over the slope and shelf, highlighting that shelf conditions are significantly impacted by offshore variability. Conditions on the NEUS in 2015 were characterized by anomalously high salinities, associated with a northerly position of the Gulf Stream. A freshening between 2015 and 2021, is in agreement with increased river cumulative discharge as well as lower offshore salinities. Overall, salinity serves as a valuable additional tracer of these multi‐variate processes.

Unveiling the paleosalinity constraints on southern peri-Pannonian Lower Miocene lacustrine systems in Serbia and Bosnia and Herzegovina: Lopare (Dinaride Lake System) versus Toplica basin (Serbian Lake System)

Early Neogene saline lakes were widely developed across Central Paratethys, particularly across its „Dinaride-Anatolide“ landbridge (area of Dinarides, Balkans). The constraints on Lopare (western part of Jadar block; eastern Bosnia and Herzegovina) and Toplica (Jastrebac Mt., central Serbia) Neogene paleolakes provide a better understanding of deep-time climate evolution. The study focused on early Neogene paleolacustrine configuration, paleogeography, and the factors affecting a considerable paleosalinity increase. The study integrated available records on the predominantly Lower Miocene sedimentary sequence by analyzing and interpreting several paleosalinity markers (inorganic geochemical proxies, mineralogical data). The constraints on paleosalinity markers are afterward coupled with rather complex tectonic inferences. The two wellbores drilled in the Lopare and Toplica basins expose Neogene sections from which the critical paleosalinity markers are extracted (drillhole depths up to 350 and 1000 m, respectively). The mineral searlesite (NaBSi2O5(OH)2), and high B/Ga, markers of alkaline and arid paleoenvironmental lacustrine conditions, suggested intense evaporation (frequent drought periods). The evaporation was associated with paleoclimatic conditions during the Miocene Climatic Optimum. The Early Neogene arid climate and frequent evaporation episodes resulted in significant salinization of the Lower Miocene Lopare lacustrine sequence. The salinity in the Lopare sequence changed its character between brackish and saline, as evidenced by S/TOC and Ca/(Ca + Fe) ratios (TOC—Total Organic Carbon). At the same time, the salinity in the early Toplica basin was significantly lower and characterized by freshwater and brackish environments. The salinity variations between Toplica and Lopare were further exposed by Fe/(Ca + Mg), (Al + Fe)/(Ca + Mg), and C-value, yielding the change in the (paleo)water column. These markers further indicated the influence of warm climate conditions, consistent with the Miocene paleoclimatic record. Regarding paleogeography and Early Neogene tectonics, the results showed that before the Middle Miocene Badenian transgression, the Paratethyan Sea had no interference with the investigated intramontane lacustrine basins.

Local freshwater fluxes determine salinity variations of the Bohai Sea: Based on 60 years of observations

Salinity, a fundamental characteristic of seawater, significantly influences the ocean's physicochemical properties and directly affects marine biodiversity and its spatial distribution. The semi-enclosed Bohai Sea is home to diverse marine organisms and serves as a critical area for human mariculture. Salinity variations in this region are crucial for the stability of the ecosystem and the sustainability of the marine economy. However, significant discrepancies have been observed between the practical salinity measurements of the Bohai Sea in winter 2007 and that recorded in widely used national and international marine atlases prior to 2000. To identify these discrepancies, this study systematically investigates the salinity variations and the regulatory mechanisms in the Bohai Sea. First, we constructed a climatological salinity dataset with a broader temporal scope based on in-situ salinity data from 1960 to 2020, confirming that the climatological salinity field of the Bohai Sea did not undergo a significant shift, but exhibited phase changes. Subsequently, using the principles of conservation of mass and salinity, we developed a box model to analyze annual salinity changes in the Bohai Sea. This model was optimized using in-situ hydrological measurements and reanalysis data spanning over 60 years, successfully revealing the central regulatory role of local freshwater fluxes in annual salinity changes in the Bohai Sea. Furthermore, we elucidated that the anomalously high salinity in the Bohai Sea in the winter of 2007 resulted from the cumulative effect of several consecutive years of negative freshwater fluxes. The results of this study not only enhance our understanding and prediction of salinity changes in semi-enclosed seas, providing a scientific basis for ecosystem protection and management, but also offer valuable insights for studying long-term salinity changes in other semi-enclosed seas.

Effects of physicochemical stressors on marine copepod populations: A review

Copepods are the key organisms in aquatic ecosystems; they are exposed to a variety of stressors that can significantly influence their behavior, distribution, and life cycle. Understanding how stressors influence such communities becomes a priority in marine ecology. This paper reviews the most important effects of stressors such as temperature, salinity, light, oxygen, and nutrients, and their effects on marine copepods that have been analyzed in laboratory experiments highlighting the impact of stressors on organisms. Most stressors influence the distribution and behavior of the organisms. Temperature also influences the metabolic activity, development, and reproduction of copepods; variations in salinity can affect osmotic regulation and physiological functioning, while oxygen influences the processes of respiration and metabolism. Light and nutrients also significantly impact the growth and reproduction of copepods and are essential for sustaining their populations in aquatic ecosystems. Complex interactions between multiple stressors and their effects on marine copepods are less studied. By studying the bibliography related to the experiments carried out on marine copepods and how they are influenced by the environmental factors mentioned above, I can provide a better understanding of the fact that copepods are vulnerable to environmental changes, and this information can contribute to the development of strategies effective for the conservation and management of marine ecosystems.

Large Mixed Layer Salinity Variation in the Southern Tropical Indian Ocean Due To the Blending of Water Masses

AbstractThe southern tropical Indian Ocean (TIO) displays large mixed layer salinity (MLS) variation. Circulation in this region is governed by the Indian Ocean tropical gyre (IOTG), where the source water proportion and associated mixing remain unclear. Particles integrating into the IOTG and entering the central southern TIO originate from the Bay of Bengal, Malacca Strait, western Indian Ocean, and Indonesian Throughflow. Surprisingly, cross‐equatorial advection is particularly important, implying a significant connection between both the Bay of Bengal and the South China Sea via Malacca Strait into the southern TIO. The anomalous anticlockwise circulation weakens the IOTG during positive Indian Ocean Dipole (IOD). An opposite pattern is observed in the negative IOD. A particle experiment reveals that water masses are modulated by the anomalous circulation that drives the redistribution of MLS by changing the proportion of the different source waters. This represents a potential predictability for the southern TIO MLS variability.

Sustainable environmental management impact on tourist areas Anza and Cap Ghir in Agadir (Center of Morocco) between 2010 and 2022: Integrated Biomarker response

This research investigates the effects of environmental interventions on pollution levels along the Anza coast of Morocco from 2010 to 2022 through the analysis of biomarkers in Perna perna. Historically, the Anza area has been highly polluted compared to the nearby Cap Ghir coast. Following the relocation of a cement factory and the establishment of wastewater treatment facilities, notable environmental improvements were noted in Anza. Pollution biomarkers such as acetylcholinesterase (AChE), catalase, glutathione S-transferases (GSTs), and malondialdehyde (MDA) were analyzed to assess these changes. The findings indicated an increase in catalase and AChE levels at Anza, suggesting reduced contamination, while GST activity declined, indicating lower exposure to pollutants. In contrast, Cap Ghir showed an increase in oxidative stress biomarkers, suggesting worsening environmental conditions. The Integrated Biomarker Response (IBR) index demonstrated a significant reduction in pollution levels in Anza, with a corresponding increase at Cap Ghir. Principal Component Analysis (PCA) supported these outcomes, revealing a positive correlation between catalase activity and reduced oxidative stress at Anza, whereas Cap Ghir showed elevated oxidative stress markers linked to variations in temperature and salinity. These results underscore the effectiveness of the interventions in enhancing marine health at Anza and highlight the necessity for protective actions at Cap Ghir. This study emphasizes the importance of biomonitoring in shaping environmental policies for coastal areas of Agadir city.