Low Salinity Research Articles

Significance and Applications of the Thermo-Acidophilic Microalga Galdieria sulphuraria (Cyanidiophytina, Rhodophyta).

Galdieria sulphuraria is a thermo-acidophilic microalga belonging to the Cyanidiophyceae (Rhodophyta) class. It thrives in extreme environments, such as geothermal sulphuric springs, with low pH, high temperatures, and high salinity. This microalga utilises various growth modes, including autotrophic, heterotrophic, and mixotrophic, enabling it to exploit diverse organic carbon sources. Remarkably, G. sulphuraria survives and produces a range of bioactive compounds in these harsh conditions. Moreover, it plays a significant role in environmental remediation by removing nutrients, pathogens, and heavy metals from various wastewater sources. It can also recover rare earth elements from mining wastewater and electronic waste. This review article explores the diverse applications and significant contributions of G. sulphuraria.

Tracing Sediment‐Affected Water Masses From Coastal Areas to Offshore Oceans Using In Situ Sensing of Fluorescent Organic Matter

AbstractThe lateral transport of nutrient‐rich water masses from coastal areas to offshore areas is an important factor controlling the primary production of phytoplankton in offshore regions. If the coastal low‐salinity waters have high nutrient levels, lateral transport can be traced via salinity observations. However, if high level of nutrients in the waters are not coupled with low salinity, for example, input from coastal sediments, water transport cannot be traced via salinity observations. In this study, visible fluorescent organic matter (FOMvis) was monitored by an in situ sensor as a tracer for sediment‐affected water masses from coastal areas. The FOMvis distribution in the upper 500 m water layer in offshore Japan along the 143°E transect was generally controlled by the distributions of subtropical water (i.e., Kuroshio water and Tsugaru warm current water) and subarctic water (i.e., Oyashio water). However, anomalously high levels of FOMvis were observed at depths of 20–60 m at an observational station, which could not be explained by physical mixing. This likely originated from the lateral transport of water masses from coastal areas. In and around Sendai Bay, where observations were carried out as an example of the Japanese coast, high levels of FOMvis were observed, accompanied by negative N*, an indicator of denitrification, and phosphate and silicic acid inputs from anoxic sediments. These observational results imply that FOMvis observation via in situ sensors can be useful for tracing the input of nutrient‐rich sediment‐affected water masses from coastal areas to offshore oceans.

Soil salinity regulates spatial-temporal heterogeneity of seed germination and seedbank persistence of an annual diaspore-trimorphic halophyte in northern China

Background and aimsSeed heteromorphism is a plant strategy that an individual plant produces two or more distinct types of diaspores, which have diverse morphology, dispersal ability, ecological functions and different effects on plant life history traits. The aim of this study was to test the effects of seasonal soil salinity and burial depth on the dynamics of dormancy/germination and persistence/depletion of buried trimorphic diaspores of a desert annual halophyte Atriplex centralasiatica.MethodsWe investigated the effects of salinity and seasonal fluctuations of temperature on germination, recovery of germination and mortality of types A, B, C diaspores of A. centralasiatica in the laboratory and buried diaspores in situ at four soil salinities and three depths. Diaspores were collected monthly from the seedbank from December 2016 to November 2018, and the number of viable diaspores remaining (not depleted) and their germinability were determined.ResultsNon-dormant type A diaspores were depleted in the low salinity “window” in the first year. Dormant diaspore types B and C germinated to high percentages at 0.3 and 0.1 mol L-1 soil salinity, respectively. High salinity and shallow burial delayed depletion of diaspore types B and C. High salinity delayed depletion time of the three diaspore types and delayed dormancy release of types B and C diaspores from autumn to spring. Soil salinity modified the response of diaspores in the seedbank by delaying seed dormancy release in autum and winter and by providing a low-salt concentration window for germination of non-dormant diaspores in spring and early summer.ConclusionsBuried trimorphic diaspores of annual desert halophyte A. centralasiatica exhibited diverse dormancy/germination behavior in respond to seasonal soil salinity fluctuation. Prolonging persistence of the seedbank and delaying depletion of diaspores under salt stress in situ primarily is due to inhibition of dormancy-break. The differences in dormancy/germination and seed persistence in the soil seedbank may be a bet-hadging strategy adapted to stressful temporal and spatial heterogeneity, and allows A. centralasiatica to persist in the unpredictable cold desert enevironment.

Effect of salinity on arsenic uptake, biotransformation, and time-dependent speciation pattern by Sargassum species

The arsenic (As) content of seaweed has been extensively studied due to its toxicological concerns. As a primary producer, seaweed plays a vital role in the biochemical cycling of As in marine environments. Several studies have focused on the growth and behavior of seaweed under a salinity gradient; however, information related to the impact of salinity on As uptake, biotransformation mechanism, and time-dependent speciation patterns of these plants is limited. This study aimed to investigate the temporal effects of salinity on these factors in seaweed. Three seaweed species, Sargassum fusiforme, Sargassum thunbergii, and Sargassum horneri, were maintained in a 1% Provasoli-enriched seawater medium for 14 d under 5‰, 15‰, 25‰, and 34‰ salinities. The results revealed that the high salinity media promoted a rapid uptake of As by all three species. Arsenic accumulation inside the cell approached 100% within seven days of culture for S. thunbergii, irrespective of the salinity content of the media. In addition, As(V) biotransformation and release by S. fusiforme and S. thunbergii were time-dependent, while S. horneri released dimethylarsinic acid (DMAA) from day 3 of the culture. All seaweed species showed methylation of As(V) to DMAA during the culture period. Furthermore, S. thunbergii released DMAA when As(V) was completely depleted from the culture media, whereas the release by S. fusiforme and S. horneri was relatively earlier than that of S. thunbergii. S. horneri showed minimal tolerance to low salinity, as the cells revealed significant damage. Based on the results of this study, a conceptual model was developed that demonstrated the effects of salinity on As uptake and the biotransformation mechanism of seaweed.

Unraveling the mechanisms and responses of aniline-degrading biosystem to salinity stress in high temperature condition: Pollutants removal performance and microbial community

To explore the intrinsic influence of different salinity content on aniline biodegradation system in high temperature condition of 35 ± 1 °C, six groups at various salinity concentration (0.0%–5.0%) were applied. The results showed that the salinity exerted insignificant impact on aniline removal performance. The low-level salinity (0.5%–1.5%) stimulated the nitrogen metabolism performance. The G5-2.5% had excellent adaptability to salinity while the nitrogen removal capacity of G6-5.0% was almost lost. Moreover, high throughput sequencing analysis revealed that the g__norank_f__NS9_marine_group, g__Thauera and g__unclassified_f__Rhodobacteraceae proliferated wildly and established positive correlation each other in low salinity systems. The g__SM1A02 occupying the dominant position in G5 ensured the nitrification performance. In contrast, the Rhodococcus possessing great survival advantage in tremendous osmotic pressure competed with most functional genus, triggering the collapse of nitrogen metabolism capacity in G6. This work provided valuable guidance for the aniline wastewater treatment under salinity stress in high temperature condition.

Effect of Salinity and Substrate on the Emergence and Growth of Propagules of the Mangrove Species Rhizophora racemosa in the Sassandra-Dagbego Ramsar Complex, Côte d’Ivoire

This study aimed to evaluate the behaviour of seeded propagules of Rhirophora racemosa (R. racemosa) on different substrates and under different salinity levels. Three substrates including sand, mud and a mixture of the two were tested together with tree salinity levels (low 5%, moderate 10% and high 25%). R. racemosa seedlings were more likely to emerge and grow under moderate and low salinity conditions. The propagules had significant early growth in mud compared to sand and mud-sand mixture. The combined effect of salt and substrate influenced significantly propagules performance in nursery (p<0.001). High propagules emergence and growth were observed in the combination mud and salt treatments as compared to sand and san-mud mixture substrates. These results provide valuable information for the management and restoration of mangroves, highlighting the optimal environmental conditions for the successful regeneration of this species.

Freshwater input significantly reduces specific and functional diversity of small subarctic estuaries

Estuaries face mounting anthropic pressures. Climate change is projected to increase heavy precipitations, while agricultural and logging activities reduce land permeability, leading to more frequent flooding events that lower estuarine salinity. These hyposaline conditions pose physiological challenges for marine species, potentially reducing taxonomic diversity and biomass, and ultimately, ecosystem functions and services. Polar and subpolar estuaries, historically understudied, will undergo significant changes in freshwater discharge timing and variability due to predicted shifts from snow to rainfall regimes in these high latitudes. The investigation of biotic communities structure through functional traits is crucial for understanding biodiversity changes, evaluating ecosystem tolerance, and addressing the loss of function under stressful conditions. Therefore, our study aims to characterize the taxonomic and functional diversity of hard-substrate benthic communities along a salinity gradient in small subarctic estuaries. We hypothesize that communities closer to the riverine input will be less taxonomically diverse and abundant and with smaller individuals, leading to a loss of functions due to environmental filtering. To test our hypotheses, we measured traditional (biomass, taxonomic richness and diversity) and functional (functional richness and Rao's quadratic entropy) indices, as well as observed traits, of epibenthic hard-substrate macroalgae and macroinvertebrates along a four-level salinity gradient found in five small subarctic estuaries in Quebec (Canada). As predicted, freshwater inputs induced a decrease in biomass, taxonomic richness, functional richness, and Rao's quadratic entropy, with a fivefold reduction in total biomass of the epibenthic community from marine to low salinity zones. Freshwater inputs significantly shaped both taxonomic and functional trait structures, as the proportion of suspension feeders and long-distance dispersers decreased with rising freshwater inputs. While there was no clear trend for the size-class structure of invertebrate taxa, macroalgae were smaller at low salinities. Estuarine communities in subarctic regions may be vulnerable to future alterations in flooding patterns caused by global change, potentially affecting key ecosystem services such as suspended matter filtration. Functional trait indices were found to be efficient and serve as a valuable complement to taxonomic measures in detecting community shifts along salinity gradients, highlighting their usefulness in developing effective conservation and management strategies.

On the selection of humidification dehumidification desalination system cycle for high productivity, low energy consumption and low capital cost

Humidification Dehumidification (HDH) desalination is a convenient process to produce drinking water from low temperature saline water in waterfront areas. High energy consumption of the system remains as a limiting factor, besides many enhancements done in improving the system performance. Though HDH system cycles are classified on the basis of air and water cycles, detailed performance analysis of different HDH cycles is absent till date. The present study aims at carrying out parametric analysis of possible HDH layouts and finally proposing a layout with high Gain Output Ratio (GOR) and Recovery Ratio (RR) at the low equipment volumes. Simulations are carried out using the Scilab® software. Simulation results are validated using the experimental data obtained from a pilot plant of open-air open-water single stage system. Variation of system parameters like humidifier volume, dehumidifier volume, GOR and RR were analysed in detail for each individual layouts. Out of the eight different layouts investigated, Layout 8 is found to be the best based on GOR, RR, equipment volume and specific energy consumption. Hence it is recommended to use Layout 8 with an inlet temperature of 74 °C and MFR of 2.4 for productivity of 90 LPH.

Combining biotelemetry and genetics provides complementary insights relevant to the management and conservation of a freshwater predator (Esox lucius) living in brackish lagoons

To inform the management of wild fish populations, it is equally important to understand both the ecological connectivity of habitat patches, apparent at annual and seasonal scales, and the genetic connectivity, emerging at evolutionary scales across generations. Ecological connectivity indicates the potential for rapid recolonization upon local depletion, while genetic connectivity informs about the conservation needs related to the evolution of subpopulations and ecotypes in metapopulations. We combined acoustic biotelemetry and pooled-genome sequencing to study a northern pike (Esox lucius) population as a model of a freshwater piscivore that inhabits a network of shallow brackish lagoons in the southern Baltic Sea. We found limited ecological connectivity among genetically similar subpopulations of pike, suggesting a metapopulation structure characterized by discrete local subpopulations with infrequent migrations between them. Connectivity of different lagoons increased during spawning, suggesting directed spawning migrations to either freshwater rivers or low salinity patches in connected lake-like bays. Spawning site fidelity to either brackish or freshwater spawning sites was observed, further contributing to the reproductive isolation of certain subpopulations. The genetic population structure aligned with salinity gradients and geographical distance and was significant between pairs of rivers draining into the lagoon network, but it was unrelated to ecological connectivity. The results collectively suggest that local subpopulations may not rapidly replenish upon local depletion and that even weak connectivity among subpopulations was sufficient to maintain genetic homogeneity across lagoons with similar salinity levels. Effective management and conservation of species forming metapopulations, such as the coastal northern pike studied here, necessitate localized approaches that adapt fishing mortality to local abundance and promote access to specific habitats, especiallyrivers, during spawning to conserve the entire genetic biodiversity and foster resilience of the metapopulation.

Exploring factors that affect Microcystis abundance in the sacramento san joaquin delta

Cyanobacteria harmful algal blooms (cHABs) are increasing in frequency, intensity and duration in estuaries worldwide. In the upper San Francisco Estuary, also known as the Sacramento San Joaquin Delta (Delta), cHABs have been a topic of concern over the past two decades. In response, managers are urgently working to understand the factors that drive cHABs and identify feasible management options to avert ecological and human health consequences. We used a six year data set to explore relationships between flow parameters, temperature, and Microcystis biovolume to determine the potential for managing large scale hydrodynamic conditions to address Delta cHABs. We also looked at the relationship between Microcystis biovolume and the low salinity zone to see if it could be used as a proxy for residence time, because residence time is positively related to cyanobacteria abundance. We found the low salinity zone is not a useful proxy for residence time in the area of the Delta that experiences the most severe cHABs. Our finding suggest that climatic conditions (i.e., temperature and water year type) have the greatest influence on Microcystis biovolume in the Delta, with higher biovolume during years with lower flow and higher temperatures. Further, there are interannual differences in Microcystis biovolume that cannot be fully explained by flow parameters or temperature, meaning other factors not included in our model may be involved. We conclude that management actions to increase flow may be ineffective at reducing Microcystis to desired levels if water temperatures remain high.

Freezing-induced acidification of sea ice brine

The acidity of sea ice and snow plays a key role in the chemistry of the cryosphere; an important example lies in the photochemical catalytic release of reactive bromine in polar regions, facilitated at pHs below 6.5. We apply in-situ acid-base indicators to probe the microscopic acidity of the brine within the ice matrix in artificial sea water at a range of concentrations (0.35–70 PPT) and initial pHs (6–9). The results are supported by analogous measurements of the most abundant salts in seawater: NaCl, Na2SO4, and CaCO3. In the research herein, the acidity is expressed in terms of the Hammett acidity function, H2−. The obtained results show a pronounced acidity increase in sea water after freezing at −15 °C and during the subsequent cooling down to −50 °C. Importantly, we did not observe any significant hysteresis; the values of acidity upon warming markedly resembled those at the corresponding temperatures at cooling. The acidity increase is attributed to the minerals' crystallization, which is accompanied by a loss of the buffering capacity. Our observations show that lower salinity sea water samples (≤ 3.5 PPT) reach pH values below 6.5 at the temperature of −15 °C, whereas higher salinity ices attain such values only at −30 °C. The ensuing implications for polar chemistry and the relevance to the field measurements are discussed.

Heavy sulfur isotopes recorded in contrasted redox conditions in Holocene sediments from the Yangtze River Delta

Sulfur isotopic signatures of pyrite (δ34Spy) sensitively react to local environmental change. Here we elucidate mechanism of δ34Spy variation in the Holocene sedimentary strata of the Yangtze River Delta, through the analyses of multiple geochemical and physical indicators including total organic carbon, total nitrogen, stable isotopes of organic carbon, different iron solid phases, Sr/Ba ratios, and changes in sedimentation rates. Two heavy δ34Spy (∼30‰) layers that formed under contrasting redox conditions are preserved in the early Holocene transgressive tidal flat and late Holocene regressive mouth bar facies, respectively. Two hypotheses are proposed to explain these heavy δ34Spy layers: 1) in the transgression process, the heavy δ34Spy layers formed under stronger reducing conditions due to methane leakage; 2) in the regression process, the heavy δ34Spy layers formed under relatively weaker reducing conditions due to rapid deposition and low salinity. This study emphasizes the importance of physicochemical condition characterization in sediments, including redox conditions, in distinguishing the mechanisms that act to produce heavy δ34Spy signals.

Impact of Salinity on Growth and Physiological Responses of Striped Catfish Pangasionodon hypophthalmus Fingerling

Background: A 90-day experiment was conducted to study the impact of salinity on growth and physiological response of Pangasionodon hypophthalmus fingerling at the Brackish water fish farm of Central Institute of Fisheries Education (CIFE), Kakinada Centre, Kakinada, East Godavari District, Andhra Pradesh, India. Method: The study used different salinities condition such as 0 (control), 5 (T1), 10 (T2) and 15 (T3) ppt. Fingerlings (8.47±0.46 g) were gradually acclimatized to different salinities in 1000 l fibre reinforced plastic (FRP) tanks, in triplicates and fed with a commercial feed (crude protein 30%). Result: Growth indicators such as specific growth rate (SGR), feed conversion ratio (FCR), feed efficiency ratio (FRR) and protein efficiency ratio (PER) revealed that growth and survival were negatively affected above 10 ppt salinity. Significantly higher amylase and protease activities were observed up to 10 ppt group. In contrast, significantly higher cortisol (97.71±1.94 ng/ml) and glucose (113.32±2.66 mg/dl) levels in the blood were recorded in 15 ppt group. Overall, the study proved that P. hypophthalmus can be cultured in low saline water (up to 10 ppt) without affecting its growth and physiological homeostasis.

Regulation and Response Mechanism of Acute Low-Salinity Stress during Larval Stages in Macrobrachium rosenbergii Based on Multi-Omics Analysis

Macrobrachium rosenbergii is an essential species for freshwater economic aquaculture in China, but in the larval process, their salinity requirement is high, which leads to salinity stress in the water. In order to elucidate the mechanisms regulating the response of M. rosenbergii to acute low-salinity exposure, we conducted a comprehensive study of the response of M. rosenbergii exposed to different salinities’ (0‰, 6‰, and 12‰) data for 120 h. The activities of catalase, superoxide dismutase, and glutathione peroxidase were found to be significantly inhibited in the hepatopancreas and muscle following low-salinity exposure, resulting in oxidative damage and immune deficits in M. rosenbergii. Differential gene enrichment in transcriptomics indicated that low-salinity stress induced metabolic differences and immune and inflammatory dysfunction in M. rosenbergii. The differential expressions of MIH, JHEH, and EcR genes indicated the inhibition of growth, development, and molting ability of M. rosenbergii. At the proteomic level, low salinity induced metabolic differences and affected biological and cellular regulation, as well as the immune response. Tyramine, trans-1,2-Cyclohexanediol, sorbitol, acetylcholine chloride, and chloroquine were screened by metabolomics as differential metabolic markers. In addition, combined multi-omics analysis revealed that metabolite chloroquine was highly correlated with low-salt stress.

Microscopic characteristics of CO2 residual trapping in saline aquifers: Experimental study based on X-ray microtomography

The occurrence form and migration characteristics of CO2 in pores have a direct impact on CO2 residual trapping and the safety of CO2 sequestration. In this work, we conduct core flooding and CT scanning experiments at different permeabilities, brine salinities, and sodium dodecyl sulfate (SDS) concentrations. We measure the CO2-brine-rock contact angles in situ and quantitatively analyze the microscopic characteristics of CO2 residual trapping in the pores. The experimental results indicate that CO2 primarily occurs in the form of network, cluster, and droplet. The efficiency of CO2 residual trapping is closely linked to the pore structure, with a higher permeability resulting in less effective trapping. Furthermore, an increase in salinity weakens the hydrophilicity of the sandstone, while the addition of SDS enhances it. The higher the SDS concentration, the greater the sandstone hydrophilicity. When the sandstone hydrophilicity is enhanced, the efficiency of CO2 residual trapping also increases. Additionally, a low permeability, low salinity, and high SDS concentration all result in 20%–35% increase in the frequency of CO2 network formed in the pores, which is advantageous for CO2 residual trapping. These findings clarify the possible occurrence forms of gaseous CO2 in the pores and their variations under different conditions and are also expected to help establish methods for improving CO2 residual trapping efficiency to enhance the long-term safety of CO2 sequestration in shallow saline aquifers.

Species-specific metabolome changes during salinity downshift in sub-Arctic populations of Mytilus edulis and M. trossulus

The blue mussels Mytilus edulis and Mytilus trossulus are ecologically and economically important species distributed widely across the Northern Hemisphere. Understanding their behavioral and physiological disparities is crucial for assessing their ecological success and aquacultural value. The recent finding of non-native M. trossulus in the White Sea raises concerns regarding its potential competition with native M. edulis and its prospective spread in light of climate change and surface water freshening. We investigated the responses of M. edulis and M. trossulus to salinity variations by examining shell closure thresholds and tissue levels of 35 metabolic intermediates in mussels acclimated to different salinities (25, 16, and 10). The salinity threshold for valve closure was similar in both studied species, but M. trossulus consistently opened at lower salinities (by 0.2–0.7 practical salinity units) compared to M. edulis. Salinity-induced changes in metabolite levels were similar between the two species. Taurine emerged as the dominant osmolyte, comprising over 50% of the total free amino acid pool, with aspartate and glycine contributing 15–30%. Concentrations of taurine, glycine, and total free amino acids declined with decreasing salinity. Taurine to glycine ratios were higher in M. edulis and increased in both species with declining salinity. Acclimation salinity significantly influenced urea cycle intermediates and methionine sulfoxide content, a cellular biomarker of amino acid oxidation. Species-specific differences were observed in purine metabolism, with higher levels of GMP and AMP found in M. edulis. Likewise, aromatic amino acids and histidine levels were higher in M. edulis compared to M. trossulus. However, no evidence suggests superior adaptation of M. trossulus metabolism to hypoosmotic stress compared to M. edulis. Further research is necessary to elucidate the functional implications of subtle metabolic differences between these Mytilus congeners and their ecological consequences in changing marine environments.

Genome-Wide Identification of the Cation/Proton Antiporter (CPA) Gene Family and Functional Analysis of AtrNHX8 under Salt Stress.

Amaranthus tricolor is an important vegetable, and its quality is affected by salt stress. Cation/proton antiporters (CPA) contribute to plant development and tolerance to salt stress. In this study, 35 CPA genes were identified from a genome database for A. tricolor, including 9 NHX, 5 KEA, and 21 CPA2 genes. Furthermore, in A. tricolor, the expression levels of most AtrNHX genes were higher at a low salinity level (50 or 100 mM NaCl) than in the control or 200 mM NaCl treatment. Levels of most AtrNHX genes were elevated in the stem. Moreover, AtrNHX8 was homologous to AtNHX4, which is involved in the regulation of sodium homeostasis and salt stress response. After AtrNHX8 overexpression in Arabidopsis thaliana, seed germination was better, and the flowering time was earlier than that of wild-type plants. Additionally, the overexpression of AtrNHX8 in A. thaliana improved salt tolerance. These results reveal the roles of AtrNHX genes under salt stress and provide valuable information on this gene family in amaranth.

Roles of eyestalk in salinity acclimatization of mud crab (Scylla paramamosain) by transcriptomic analysis

Salinity acclimatization refers to the physiological and behavioral adjustments made by crustaceans to adapt to varying salinity environments. The eyestalk, a neuroendocrine organ in crustaceans, plays a crucial role in salinity acclimatization. To elucidate the molecular mechanisms underlying eyestalk involvement in mud crab (Scylla paramamosain) acclimatization, we employed RNA-seq technology to analyze transcriptomic changes in the eyestalk under low (5 ppt) and standard (23 ppt) salinity conditions. This analysis revealed 5431 differentially expressed genes (DEGs), with 2372 upregulated and 3059 downregulated. Notably, these DEGs were enriched in crucial biological pathways like metabolism, osmoregulation, and signal transduction. To validate the RNA-seq data, we further analyzed 15 DEGs of interest using qRT-PCR. Our results suggest a multifaceted role for the eyestalk: maintaining energy homeostasis, regulating hormone synthesis and release, PKA activity, and downstream signaling, and ensuring proper ion and osmotic balance. Furthermore, our findings indicate that the crustacean hyperglycemic hormone (CHH) may function as a key regulator, modulating carbonic anhydrase expression through the activation of the PKA signaling pathway, thereby influencing cellular osmoregulation, and associated metabolic processes. Overall, our study provides valuable insights into unraveling the molecular mechanisms of mud crab acclimatization to low salinity environments.

Unravelling the signatures of submarine groundwater discharge and seawater intrusion along the coastal plains of Odisha, India: a multi-proxy approach.

Submarine Groundwater Discharge (SGD) and Seawater Intrusion (SWI) are two contrary hydrological processes that occur across the land-sea continuum and understanding their nature is essential for management and development of coastal groundwater resource. Present study has attempted to demarcate probable zones of SGD and SWI along highly populated Odisha coastal plains which is water stressed due to indiscriminate-exploitation of groundwater leading to salinization and fresh groundwater loss from the alluvial aquifers. A multi-proxy investigation approach including decadal groundwater leveldynamics, LANDSAT derived sea surface temperature (SST) anomalies and in-situ physicochemical analysis (pH, EC, TDS, salinity and temperature) of porewater, groundwater and seawater were used to locate the SGD and SWI sites. A total of 340 samples for four seasons (85 samples i.e., 30 porewater, 30 seawater and 25 groundwater in each season) were collected and their in-situ parameters were measured at every 1-2km gap along ~ 145km coastline of central Odisha (excluding the estuarine region). Considering high groundwater EC values (> 3000 μS/cm), three probable SWI and low porewater salinities (< 32 ppt in pre- and < 25 ppt in post-monsoons), four probable SGD zones were identified. The identified zones were validated with observed high positive hydraulic gradient (> 10m) at SGD and negative hydraulic gradient (< 0m) at SWI sites along with anomalous SST (colder in pre- and warmer in post-monsoon) near probable SGD locations. This study is first of its kind along the Odisha coast and may act as initial basis for subsequent investigations on fresh-saline interaction along the coastal plains where environmental integrity supports the livelihood of coastal communities and the ecosystem.

Seasonal Phytoplankton Characteristics Related with Region-Specific Coastal Environments in the Korean Peninsula

The seasonal dynamics of phytoplankton communities in Korean coastal waters (KCWs) are influenced by complex interactions between ocean currents and nearshore human activities. Despite these influences, the understanding of seasonal phytoplankton changes and their environmental relationships in KCWs remains limited. We investigate the influence of the distinct characteristics of the three seas surrounding the KCWs (the Yellow Sea, the South Sea, and the East Sea) on seasonal phytoplankton communities based on field surveys conducted at 23 stations between 2020 and 2021. The East Sea exhibited higher winter temperatures due to the Jeju and Tsushima warm currents, while summer temperatures were lower compared to the other regions, highlighting the role of currents and deeper oceanic waters. The Yellow Sea showed significant freshwater influence with low salinity levels from major rivers, contrasting with the higher salinity in the East Sea. These differences led to a disparity in the productivity of the two regions: the highest value of Chl. a was observed to be 6.05 µg L–1 in the Yellow Sea in summer. Diatoms dominated in nutrient-rich conditions, particularly in the Yellow Sea, where they comprised up to 80–100% of the phytoplankton community in summer, winter, and spring. PCA analysis revealed positive correlations between diatoms and Chl. a, while cryptophytes, which thrive in the absence of diatom proliferation, showed no such correlation, indicating their opportunistic growth in nutrient-limited conditions. This study highlights the significant impact of region-specific hydrographic factors on phytoplankton communities in KCWs, with diatoms dominating in summer and cryptophytes and dinoflagellates showing seasonal and regional variations. Understanding these dynamics is crucial for predicting phytoplankton bloom dynamics and their ecological implications in coastal ecosystems.