Saline Ecosystems Research Articles

Formation Mechanism and Biotransformation of Halogenated polycyclic aromatic hydrocarbons (HPAHs) from Ecological sources to Food chain sink

Halogenated polyaromatic hydrocarbons (HPAHs, H = F, Cl, Br) are a new class of PAHs derivatives that mainly originate from the incomplete combustion of halogen-laden materials and via metallurgical operations. These compounds circulate extensively in various environmental matrices. This survey provides a comprehensive review on governing synthesis routes of HPAHs, their environmental occurrence, and their health and ecological effects. The review comprehensively enlists and presents emission sources of these emerging organic pollutants into the air that serves as their main reservoir. The formation of HPAHs ensues through successive addition reactions of smally compounds accompanied by ring cyclization steps; in addition to direct unimolecular fragmentation of parents halogenated. Halogenation of parent PAHs rapidly occurs in saline ecosystems thus multiplying the availability of these notorious compounds in the environment. Certain HPAHs appear to be more carcinogenic than dioxins. Transmission routes of HPAHs from their emission sources to water bodies, soil, aquatic life, plants, terrestrial animals, and humans are well-documented. Later, the direct and indirect diffusion of HPAHs from air to the biotic (plants, animals, humans) and abiotic components (soil, water, sediments) are described in detail. The study concludes that HPAHs are permeable to the carbon matrices resulting in the alleviation of the source-to-to-sink interface. As a potential future perspective, understanding the transmission interfaces lays a foundation to intervene in the introduction of these toxicants into the food chain.

Hydrochemical gradients driving extremophile distribution in saline and brine groundwater of southern Poland.

Extreme environments, such as highly saline ecosystems, are characterised by a limited presence of microbial communities capable of tolerating and thriving under these conditions. To better understand the limits of life and its chemical and microbiological drivers, highly saline and brine groundwaters of Na-Cl and Na-Ca-Cl types with notably diverse SO4 contents were sampled in water intakes and springs from sedimentary aquifers located in the Outer Carpathians and the Carpathian Foredeep basin and its basement in Poland. Chemical and microbiological methods were used to identify the composition of groundwaters, determine microbial diversity, and indicate processes controlling their distribution using multivariate statistical analyses. DNA sequencing targeting V3-V4 and V4-V5 gene regions revealed a predominance of Proteobacteriota, Methanobacteria, Methanomicrobia, and Nanoarchaea in most of the water samples, irrespective of their geological context. Despite the sample-size constraint, redundancy analysis employing a compositional approach to hydrochemical predictors identified Cl/SO4 and Cl/HCO3 ratios, and specific electrical conductivity, as key gradients shaping microbial communities, depending on the analysed gene regions. Analysis of functional groups revealed that methanogenesis, sulphate oxidation and reduction, and the nitrogen cycle define and distinguish the halotolerant communities in the samples. These communities are characterised by an inverse relationship between methanogens and sulphur-cycling microorganisms.

Different halophytes orchestrate microbial diversity in the rhizosphere of salinity-impacted soils

Investigating rhizosphere communities in saline soils is crucial for identifying the taxonomic groups that play significant roles in halophyte adaptation. However, how the microbiome is structured under different saline conditions remains unclear. This study aimed to analyze bacterial communities in the rhizospheres of halophyte species in different saline environments. Five rhizospheres were analyzed using high-throughput sequencing of the 16S rRNA gene: S1, Salicornia fruticosa from a hypersaline tidal plain; S2, Sporobolus virginicus; S3, Cyperus ligularis from a hypersaline lagoon; S4, Salicornia fruticosa and S5, Blutaparon portulacoides from an abandoned salt pan. Bacterial communities in the S4 and S5 rhizospheres were influenced by P and K content, suggesting that specific nutrients can foster unique microbial structures, potentially assisting in adaptation to saline soils. The unique ASV (Amplicon Sequence Variant), richness, diversity, and microbial core of the S1 system, along with its similarities to S2 and S3, suggest common halophyte adaptation strategies across different saline environments, aiding targeted survival efforts. Identifying keystone species such as Thermoleophilia in S1, Alphaproteobacteria in S2 and S3, multiple species in S4, and the presence of Clostridia and Bacilli in S5 shed light on the roles these bacteria play in halophyte survival. Metagenomic prediction analysis demonstrated that chemoheterotrophy and aerobic chemoheterotrophy were the main prediction functions. In summary, this study revealed the intricate microbial structures in halophyte rhizospheres, enriching our understanding of saline ecosystems.

Options for Intensification of Cropping System in Coastal Saline Ecosystem: Inclusion of Grain Legumes in Rice-Based Cropping System

The coastal saline zone of West Bengal in India is the home to millions of the world’s poorest and most vulnerable people. Due to a gradual increase in salt accumulation on soils of the coastal saline zone of West Bengal in India from winter to summer days, cultivation of the second crop in the winter season becomes possible in a limited area. To address these issues, field experiments was conducted in rainy and winter seasons of 2016–17 and 2017–18 at the farmer’s field of the coastal saline zone (CSZ) of West Bengal, India. The experiment was carried out to study the system productivity, nutrient uptake, and profitability vis-à-vis salinity dynamics of the crops in rice-pulse-based cropping systems under different land elevations (medium upland and medium lowland). The experiment was conducted in a strip-split plot design having horizontal factors namely, Factor A: Six dates of sowing of rice at an interval of one week (2nd week of June to 3rd week of July), Factor B: Two land situations (medium upland and medium lowland) and Two Cropping Systems (Rice-Lathyrus and Rice-Lentil) as vertical factor, replicated four times. The results suggest that irrespective of land situation, early sown rice (15 June to 21 June) produces higher dry matter and grain yield compared to late sown crops. This early sowing of rice also facilitated the better performance of subsequent lathyrus and lentil, by avoiding the worst situation of the salinity build-up and drought stress later in the winter. Moreover, significantly higher productions were obtained from medium-lowland situations for both the cropping systems. Sowing date has also significantly influenced macro-nutrient uptake (NPK) by rice and pulse grains. It may be concluded that early sowing of rice may be a potential option for intensification of rice-pulse-based cropping systems under CSZ of West Bengal, India.

Salt-tolerant endophytic Bacillus altitudinis NKA32 with ACC deaminase activity modulates physiochemical mechanisms in rice for adaptation in saline ecosystem

Salt-tolerant endophytic Bacillus altitudinis NKA32 with ACC deaminase activity modulates physiochemical mechanisms in rice for adaptation in saline ecosystem

Comparative Analysis of Macronutrients in Wild Plants from the Saline Ecosystem of the Lluta Valley, Northern Chile

Comparative Analysis of Macronutrients in Wild Plants from the Saline Ecosystem of the Lluta Valley, Northern Chile

High-throughput 16S rRNA gene-based amplicon sequencing reveals the functional divergence of halophilic bacterial communities in the Suaeda salsa root compartments on the eastern coast of China

The rhizosphere environment of plants, which harbors halophilic bacterial communities, faces significant challenges in coping with environmental stressors, particularly saline soil properties. This study utilizes a high-throughput 16S rRNA gene-based amplicon sequencing to investigate the variations in bacterial community dynamics in rhizosphere soil (RH), root surface soil (RS), root endophytic bacteria (PE) compartments of Suaeda salsa roots, and adjoining soils (CK) across six locations along the eastern coast of China: Nantong (NT), Yancheng (YC), Dalian (DL), Tianjin (TJ), Dongying (DY), and Qingdao (QD), all characterized by chloride-type saline soil. Variations in the physicochemical properties of the RH compartment were also evaluated. The results revealed significant changes in pH, electrical conductivity, total salt content, and ion concentrations in RH samples from different locations. Notably, the NT location exhibited the highest alkalinity and nitrogen availability. The pH variations were linked to HCO3− accumulation in S. salsa roots, while salinity stress influenced soil pH through H+ discharge. Despite salinity stress, enzymatic activities such as catalase and urease were higher in soils from various locations. The diversity and richness of bacterial communities were higher in specific locations, with Proteobacteria dominating PE samples from the DL location. Additionally, Vibrio and Marinobacter were prevalent in RH samples. Significant correlations were found between soil pH, salinity, nutrient content, and the abundance and diversity of bacterial taxa in RH samples. Bioinformatics analysis revealed the prevalence of halophilic bacteria, such as Bacillus, Halomonas, and Streptomyces, with diverse metabolic functions, including amino acid and carbohydrate metabolisms. Essential genes, such as auxin response factor (ARF) and GTPase-encoding genes, were abundant in RH samples, suggesting adaptive strategies for harsh environments. Likewise, proline/betaine transport protein genes were enriched, indicating potential bioremediation mechanisms against high salt stress. These findings provide insight into the metabolic adaptations facilitating resilience in saline ecosystems and contribute to understanding the complex interplay between soil conditions, bacterial communities, and plant adaptation.

Differential response of bacteria and fungi to drought on the decomposition of Sarcocornia fruticosa woody stems in a saline stream

AbstractInland saline ecosystems suffer multiple stresses (e.g., high radiation, salinity, water scarcity) that may compromise essential ecosystem functions such as organic matter decomposition. Here, we investigated the effects of drought on microbial colonization and decomposition of Sarcocornia fruticosa woody stems across different habitats in a saline watershed: on the dry floodplain, submerged in the stream channel and at the shoreline (first submerged, then emerged). Unexpectedly, weight loss was not enhanced in the submerged stems, while decomposition process differed between habitats. On the floodplain, it was dominated by fungi and high cellulolytic activity; in submerged conditions, a diverse community of bacteria and high ligninolytic activity dominated; and, on the shoreline, enzyme activities were like submerged conditions, but with a fungal community similar to the dry conditions. Results indicate distinct degradation paths being driven by different stress factors: strong water scarcity and photodegradation in dry conditions, and high salinity and reduced oxygen in wet conditions. This suggests that fungi are more resistant to drought, and bacteria to salinity. Overall, in saline watersheds, variations in multiple stress factors exert distinct environmental filters on bacteria and fungi and their role in the decomposition of plant material, affecting carbon cycling and microbial interactions.

Effect of establishment methods in rainy season (kharif) and tillage practices in winter season (rabi) on yield and economics of rice (Oryza sativa)–maize (Zea mays) cropping system under coastal saline ecosystem

A field experiment was carried out during 3 consecutive rainy seasons (kharif) June–November and winter (rabi) December–May seasons of 2013–16 at Canning Town, West Bengal to evaluate 3 rice (Oryza sativa L.) es tablishment methods, viz. dry direct seeding (DSR), unpuddled transplanting (UNPT) and puddled transplanting (PT), followed by 3 tillage practices for sowing rabi maize (Zea mays L.), viz. zero tillage (ZT), conventional tillage (CT) and raised bed sowing (RBS). The DSR was done in the last week of May when the soil salinity was higher (12–15 dS/m); however, it reduced to 4–5 dS/m in the month of June due to leaching of salts by monsoon rain. The transplanting in the UNPT and PT plots was done during the first week of July using 40 days old seedlings. Submergence caused by the heavy rain, affected the transplanted rice (PT and UNPT) but not the DSR, as the plants with DSR were sufficiently above the standing water due to higher plant height. The mean grain yields in 3 establishment methods of rice (5,117; 4,477 and 4,740 kg/ha in PT, UNPT and DSR respectively) were statistically at par. However, net returns ( 36,000/ha) and benefit: cost ratio (2.2) were the highest in DSR owing to 24% re duction in cost of cultivation than PT rice. The positive effects of DSR also observed on the succeeding rabi maize crop in terms of 7.4 ha-cm less irrigation water requirement and 27% higher irrigation water productivity. Maize gave the highest yield (5,600 kg/ha), net returns ( 37,910/ha) and benefit: cost ratio (BCR) 1.86 with RBS tillage practices. The system rice-equivalent yield, net returns and BCR were 11,659 kg/ha, 77,470/ha and 2.05, re spectively, for dry direct-seeded rice-raised bed sown maize with higher mean irrigation water productivity (79 kg/ ha-cm) and energy productivity (461 kg/GJ) of rabi maize.

Quenching of quorum sensing in multi-drug resistant Pseudomonas aeruginosa: insights on halo-bacterial metabolites and gamma irradiation as channels inhibitors

BackgroundAnti-virulence therapy is a promising strategy to treat multi-drug resistant (MDR) pathogens. Pseudomonas aeruginosa is a potent opportunistic pathogen because of an array of virulence factors that are regulated by quorum sensing systems.MethodsThe virulence features of four multi-drug resistant P. aeruginosa strains were investigated upon exposure to the sub-lethal dose of gamma rays (1 kGy), and sub-inhibitory concentrations of bioactive metabolites recovered from local halophilic strains in comparison to control. Then, the gene expression of AHL-mediated quorum sensing systems (las/rhl) was quantitatively determined in treated and untreated groups by real-time PCR.ResultsThe bioactive metabolites recovered from halophilic strains previously isolated from saline ecosystems were identified as Halomonas cupida (Halo-Rt1), H. elongate (Halo-Rt2), Vigibacillus natechei (Halo-Rt3), Sediminibacillus terrae (Halo-Rt4) and H. almeriensis (Halo-Rt5). Results revealed that both gamma irradiation and bioactive metabolites significantly reduced the virulence factors of the tested MDR strains. The bioactive metabolites showed a maximum efficiency for inhibiting biofilm formation and rhamnolipids production whereas the gamma irradiation succeeded in decreasing other virulence factors to lower levels in comparison to control. Quantitative-PCR results showed that AHL-mediated quorum sensing systems (las/rhl) in P. aeruginosa strains were downregulated either by halo-bacterial metabolites or gamma irradiation in all treatments except the upregulation of both lasI internal gene and rhlR intact gene in P. aeruginosa NCR-RT3 and both rhlI internal gene and rhlR intact gene in P. aeruginosa U3 by nearly two folds or more upon exposure to gamma irradiation. The most potent result was observed in the expression of lasI internal gene that was downregulated by more than ninety folds in P. aeruginosa NCR-RT2 after treatment with metabolites of S. terrae (Halo-Rt4). Analyzing metabolites recovered from H. cupida (Halo-Rt1) and H. elongate (Halo-Rt2) using LC–ESI–MS/MS revealed many chemical compounds that have quorum quenching properties including glabrol, 5,8-dimethoxyquinoline-2-carbaldehyde, linoleoyl ethanolamide, agelasine, penigequinolones derivatives, berberine, tetracosanoic acid, and liquidambaric lactone in the former halophile and phloretin, lycoctonine, fucoxanthin, and crassicauline A in the latter one.ConclusionQS inhibitors can significantly reduce the pathogenicity of MDR P. aeruginosa strains; and thus can be an effective and successful strategy for treating antibiotic resistant traits.

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.

Fungal and Fungal-like Diseases of Halophytes in the Mediterranean Basin: A State-of-the-Art Review

Halophytes are salt-tolerant plants growing in saline ecosystems and are spread throughout the Mediterranean area. Recently, there has been a renewed interest in agricultural exploitation of halophytes, but poor attention has been given to pest and disease management of these species. The objective of this review is to assess the extent and distribution of pathogenic fungal and fungal-like (Oomycota) organisms on major Mediterranean halophytes. We retrieved 92 references spanning over 100 years, with more than half published since 2000. Ascomycota is the best-represented phylum, and the order Pleosporales has the highest species diversity. The order Pucciniales prevails in Basidiomycota, whereas Peronosporales is the richest order within Oomycota. Most of the pathogenic species have been isolated from aboveground organs, especially from leaves. Portulaca oleracea is the species with the most associated pathogens (16) and records (28). Leveillula powdery mildew, caused by Leveillula taurica, is the most common disease among the selected species. Cakile maritima was found to be vulnerable to different mycotoxigenic Alternaria species. Strengthening the research on diseases of halophytes is essential to successfully grow these species and to evaluate the risks related to the presence of mycotoxigenic species, which is crucial for the effective exploitation of halophytes as crops.

Arbuscular mycorrhizal fungi communities and promoting the growth of alfalfa in saline ecosystems of northern China.

Arbuscular mycorrhizal fungi (AMF) are universally distributed in soils, including saline soils, and can form mycorrhizal symbiosis with the vast majority of higher plants. This symbiosis can reduce soil salinity and influence plant growth and development by improving nutrient uptake, increasing plant antioxidant enzyme activity, and regulating hormone levels. In this study, rhizosphere soil from eight plants in the Songnen saline-alkaline grassland was used to isolate, characterize, and screen the indigenous advantageous AMF. The promoting effect of AMF on alfalfa (Medicago sativa L.) under salt treatment was also investigated. The findings showed that 40 species of AMF in six genera were identified by high-throughput sequencing. Glomus mosseae (G.m) and Glomus etunicatum (G.e) are the dominant species in saline ecosystems of northern China. Alfalfa inoculated with Glomus mosseae and Glomus etunicatum under different salt concentrations could be infested and form a symbiotic system. The mycorrhizal colonization rate and mycorrhizal dependence of G.m inoculation were significantly higher than those of G.e inoculation. With increasing salt concentration, inoculation increased alfalfa plant height, fresh weight, chlorophyll content, proline (Pro), soluble sugar (SS), soluble protein (SP), peroxidase (POD), superoxide dismutase (SOD), and catalase (CAT) activity while decreasing the malondialdehyde (MDA) content and superoxide anion production rate. The results highlight that inoculation with G.m and G.e effectively alleviated salinity stress, with G.m inoculation having a significant influence on salt resistance in alfalfa. AMF might play a key role in alfalfa growth and survival under harsh salt conditions.

Correction to: Halophyte functional groups influence seasonal variations in rhizosphere microbial necromass and enzyme activities in an inland saline ecosystem

Correction to: Halophyte functional groups influence seasonal variations in rhizosphere microbial necromass and enzyme activities in an inland saline ecosystem

Halophyte functional groups influence seasonal variations in rhizosphere microbial necromass and enzyme activities in an inland saline ecosystem

Halophyte functional groups influence seasonal variations in rhizosphere microbial necromass and enzyme activities in an inland saline ecosystem

Exploring the Bioprotective Potential of Halophilic Bacteria against Major Postharvest Fungal Pathogens of Citrus Fruit Penicillium digitatum and Penicillium italicum

Citrus fruits are vulnerable to green mold (caused by Penicillium digitatum) and blue mold (caused by Penicillium italicum) during storage, posing significant challenges to the industry. Therefore, biological control utilizing antagonistic bacteria has emerged as a dependable strategy for managing postharvest diseases. In this study, halophilic bacterial isolates were carefully selected from diverse saline ecosystems, including the Dead Sea, the Agadir Sea, the Rabat Sea, saline soil, and water of the Amassine Oued in Taounate, based on rigorous in vitro and in vivo antagonism bioassays. Out of 21 bacteria from different saline environments, 10 were chosen for further characterization based on the 16S rDNA gene. Notably, the EAM1 isolate demonstrated exceptional inhibitory effects, reaching a 90% inhibition rate against P. digitatum, while the ER2 isolate closely followed with an 89% inhibition rate against P. italicum. Furthermore, in bacterial supernatant experiments, six bacterial isolates effectively curbed the growth of P. digitatum, and three demonstrated efficacy against P. italicum development. In an in vivo trial spanning ten days of incubation, three highly effective isolates against P. digitatum displayed zero severity, and two of these isolates also demonstrated zero severity against P. italicum. Interestingly, a comparison of bacterial filtrates revealed that all isolates exhibited a severity level of over 50% against the pathogen causing green rot (P. digitatum), while the severity was lower than 50% for the supernatants of the two isolates used against P. italicum. In conclusion, this study highlights the promising role of halophilic bacteria, specifically Bacillus amyloliquefaciens EAM1 and B. amyloliquefaciens ER2, in controlling postharvest fruit pathogens. The findings shed light on the potential of utilizing these bioprotective agents to address the challenges posed by green and blue citrus molds, providing valuable insights for the citrus industry.

What Is Wrong with Frankenia nodiflora Lam. (Frankeniaceae)? New Insights into the South African Sea-Heaths.

The taxonomic identity and phylogenetic relationships of several southern African perennial taxa related to Frankenia repens are discussed. In particular, F. nodiflora Lam., a misunderstood species described from the Cape region and synonymised to F. pulverulenta, is restored for plants endemic to salt-pans and riverbeds in the coastal lowlands across the Cape Flats (Western Cape province, South Africa). Further, a revision of morphologically close plants, usually identified as F. pulverulenta or F. repens, also occurring in similar saline ecosystems of the inland western South Africa revealed the existence of two distinct new entities not matching any described taxa of the genus. Molecular analyses of nuclear ribosomal (ITS1-5.8S-ITS2 region) DNA sequence data together with morphological divergence allow recognition of those taxa at species rank, within an independent lineage close to F. repens. In consequence, two new sea-heath species are described in the so-called "F. repens group": F. nummularia from the Nama-Karoo Biome (Western Cape and Northern Cape provinces), and F. anneliseae from the Succulent Karoo Biome (Northern Cape province). Full morphological description and type designation are reported for each accepted species as well as data on ecology, habitat, distribution, and taxonomic relationships to other close relatives are given. Further, an identification key is presented to facilitate recognition of the southern African taxa of Frankenia.

Effect of planting salt-tolerant legumes on coastal saline soil nutrient availability and microbial communities

Soil salinization is a serious global environmental problem affecting sustainable development of agriculture. Legumes are excellent candidates for the phytoremediation of saline soils; however, how soil microbes mediate the amelioration of coastal saline ecosystems is unknown. In this study, two salt-tolerant legumes, Glycine soja and Sesbania cannabina were planted in coastal saline soil for three years. Soil nutrient availability and microbiota structure (including bacteria, fungi, and diazotrophs) were compared between the phytoremediated soils and control soil (barren land). Planting legumes reduced soil salinity, and increased total carbon, total nitrogen, and NO3−-N contents. Among the soil microbiota, some nitrogen-fixing bacteria (e.g., Azotobacter) were enriched in legumes, which were probably responsible for soil nitrogen accumulation. The complexity of the bacterial, fungal, and diazotrophic networks increased significantly from the control to the phytoremediated soils, suggesting that the soil microbial community formed closer ecological interactions during remediation. Furthermore, the dominant microbial functions were chemoheterotrophy (24.75%) and aerobic chemoheterotrophy (21.97%) involved in the carbon cycle, followed by nitrification (13.68%) and aerobic ammonia oxidation (13.34%) involved in the nitrogen cycle. Overall, our findings suggested that G. soja and S. cannabina legumes were suitable for ameliorating saline soils as they decreased soil salinity and increased soil nutrient content, with microorganisms especially nitrogen-fixing bacteria, playing an important role in this remediation process.

Potential of Halophytes-Associated Microbes for the Phytoremediation of Metal-Polluted Saline Soils

Saline ecosystems are often the target of spills and releases of pollutants such as metals, as many industrial companies settle in or around these areas. Metal pollution is a major threat for humans and ecosystems. In line with sustainable development, nature-based solutions and biological tools such as phytoremediation offer eco-friendly and low-cost solutions to remove metals or limit their spread in the environment. Many plant-growth-promoting (PGP) effects are frequently prospected in plant-associated microbes such as the production of auxins, siderophores, or extracellular polymeric substances to enhance phytoremediation. Halophytes are nowadays presented as good phytoremediators for metal-contaminated saline environments such as coastal regions, but little is known about the potential of their associated microbes in the bioaugmentation of this technique. Here, we review the studies that focused on halophytes-associated microbes and their plant-growth-promotion capacities. Moreover, we discuss the limitation and applicability of bioaugmented phytoremediation in saline ecosystems.

Ecological Responses of Meiofauna to a Saltier World—A Case Study in the Van Uc River Continuum (Vietnam) in the Dry Season

Increasing intensity of storms, typhoons, and sea level rise in conjunction with high water demand, especially for agriculture, in dry seasons in the Red River Delta may have led to seawater intruding deeper into the rivers’ estuaries. Given that losses of agricultural productivity and shortages of freshwater resources are projected, a reliable early warning of salinity invasion is, therefore, crucially needed. To evaluate the impact of salinity variations on riverine ecosystems, distribution patterns of meiofauna were examined at 20 stations along the Van Uc River continuum in the dry season. Meiofaunal richness indices were higher in the estuary and slightly decreased upriver. Nematoda was the most dominant taxon in salty stations, while Rotifera was more abundant in the less salty ones. A multiple variate analysis showed a strong interplay among salinity, nutrients, and pore water conductivity, which shaped the meiofaunal distribution. The inclusion of pore water salinity, nutrients, and meiofaunal community structure indicated a greater extent of the saline ecosystem in the estuary, posing a greater risk of freshwater salinization. Our results highlight the potential role of meiofauna as bioindicators but also call for a reformation of salinity assessment for better freshwater conservation and management.