Brackish Research Articles

Influence of salinity on rainbow trout (Oncorhynchus mykiss) smolt development and postsmolt performance

Rainbow trout aquaculture has large potential for growth, but requires better understanding of aspects like smoltification and its effect on trout performance after seawater transfer. The present study examined the effect of three different salinities (fresh water, 3–5 ‰ and 15–16 ‰) on smoltification and growth of rainbow trout (70 ± 10 g) reared under constant light between March–June 2018; it also documented hypoosmoregulatory performance and growth of trout from all salinity treatments transferred to full seawater at three different times (Transfer 1: 26 April; Transfer 2: 24 May; Transfer 3: 21 June). Smolt development was assessed with markers commonly used for Atlantic salmon like gill Na+, K+-ATPase activity, gill mRNA transcription of key genes (nkaα1a, nkaα1b and nkcc1a) and plasma concentration of Cl− and Na+. Results evidenced that trout in brackish water experienced an earlier onset of smoltification, displayed by rapid changes in mRNA transcription of the ATPase α-isoforms nkaα1a (freshwater isoform) and nkaα1b (seawater isoform), which, in turn, induced an earlier peak of the Na+, K+-ATPase (NKA) activity. However, smoltification also commenced and progressed in fresh water most likely as a result of reaching a certain size. The salinity treatment did not influence growth during the smoltification period. After seawater transfer, all treatments in Transfer 1 (26 April) displayed the best capacity to acclimatize to full seawater (with clear upregulations of nkaα1b and nkcc1a after seawater entry) and the highest growth, compared to all treatments in Transfers 2 and 3. In contrast, few differences in growth and smoltification markers occurred between salinity treatments within each of the seawater transfers. This suggests that trout in the first transfer had the best smolt condition (were at the peak of smolt window), which allowed them to adapt and grow better in seawater. Overall, such results indicate that timing of seawater transfer can be more important for trout performance in the grow-out phase in the sea than the water salinity during the early rearing period. As such, although brackish water can be used to induce rainbow trout smoltification, transferring the fish at the peak of the smolt window can increase chances for best seawater performance.

Effect of Benthic Flux on the Nutrient Dynamics of Bottom Water during Stratification in an Artificial Brackish Lake

In semi-closed coastal brackish systems, the stratification of the water column due to the interaction between freshwater and seawater can lead to a reduction in the dissolved oxygen (DO) levels in the bottom layers, consequently affecting the benthic nutrient flux and causing the degradation in water quality. We performed in situ investigations using a benthic lander to examine changes in the sediment oxygen demand (SOD) and benthic nutrient flux during the development of stratification in the downstream area of an artificially constructed brackish lake. During each measurement period, the temperature and salinity of the water column showed vertically stable stratification. The potential energy anomaly was 88.1–125.7 J/m3, with the stratification intensity strengthening gradually over the measurement period. The concentration of DO in bottom waters gradually decreased as the stratification of the water intensified and the temperature increased, establishing hypoxic conditions. As the stratification intensified, the SOD decreased with the DO concentration in bottom waters, while the benthic fluxes of NH4-N and PO4-P exhibited an opposite effect. When the effect of offshore water (introduced through a sluice gate) was insignificant, the SOD contributed 33% of the net loss of DO below the pycnocline. During this period, the benthic NH4-N and PO4-P fluxes were estimated to contribute 55% and 87% to the net fluxes in NH4-N and PO4-P, respectively, in the water column below the pycnocline. The benthic NH4-N and PO4-P fluxes resulted in excess phosphorus in the bottom water. When the inflow of seawater through the sluice gate was sufficient, the flow in the upstream direction of the bottom layer moved phosphorus-rich bottom water downstream, which is important for algal growth in the middle-upstream region.

Flexible batch electrodialysis for low-cost solar-powered brackish water desalination

Globally, 1.6 billion people in rural regions face water scarcity. Expanding freshwater access via brackish groundwater desalination can provide additional resources to address this challenge. In this study, we have developed a time-variant electrodialysis reversal (EDR) technology that flexibly uses available solar energy for desalination. Our proposed photovoltaic-powered desalination system can vary pumping and EDR power to match the availability of intermittent solar power, maximizing the desalination rate. Our results show improved system performance with the direct use of 77% of available solar energy—91% more than in conventional systems—and a 92% reduction in battery reliance. In a village-scale desalination case study in India, these system improvements lead to a 22% reduction in water cost, making the technology competitive with the currently used on-grid, village-scale reverse osmosis systems that are mainly powered by fossil fuels. Future advances could further reduce costs, providing an improved, sustainable solution to water scarcity in remote areas.

Enhancing pakchoi (Brassica chinensis L.) agriculture with magnetized-ionized brackish water and organic fertilizers: A sustainable approach to soil quality and crop yield optimization

The scarcity of freshwater, the increasing use of brackish water (B) for irrigation, and the judicious application of organic fertilizers have significant research and practical value for environmental science, water resource management, and clean production. This study investigated the combined impact of B, magnetized-ionized brackish water (MIB), and organic fertilizer on pakchoi (Brassica chinensis L.) growth, yield, and soil quality. Over a two-year period (2022–2023), this study explored the impacts of two types of irrigation water (B and magnetized-ionized brackish water, MIB) in combination with varying rates of water-soluble bio-organic fertilizer (0, 20, 40, 60, and 80 kg/ha, corresponding to treatments 0 through 4, respectively). The findings indicated that the application of 60 kg/ha of organic fertilizer greatly improved the growth rate of pakchoi in terms of plant height, leaf area index, and fresh weight. Moreover, under MIB irrigation, the fresh weight growth rate of pakchoi was superior to that observed under B irrigation. Notably, B irrigation necessitated additional fertilizer to maintain elevated levels of alkali-hydrolyzed nitrogen (AN) and soil quality. Furthermore, the use of organic fertilizer substantially enhanced soil quality, with AN, available phosphorus (AP), organic matter (OM), and soil quality index (SQI) demonstrating a strong positive correlation (P < 0.05). Mantel test analysis showed significant correlations (P < 0.05) between soil OM, SWC, AP, and pakchoi growth and yield. According to the partial least squares path modeling analysis, the use of organic fertilizer had a relatively minor effect on the yield and quality of pakchoi under B irrigation, with path coefficients of 0.088 and 0.298, respectively. However, under MIB irrigation, organic fertilizer enhances yield and quality by improving soil quality (path coefficients of 0.914). In conclusion, the application of MIB irrigation coupled with organic fertilizer contributed to sustainable soil fertility, enhanced crop productivity, and mitigated the environmental impacts associated with conventional irrigation and fertilization methods. Our research underscores the importance of supporting agricultural research and development focused on sustainable irrigation and fertilization methods for farmers and policymakers. This integrated approach offers a harmonious solution for optimizing crop yields and enhancing water use efficiency, and the reduction of in chemical pollutants within agricultural production systems.

Assessing combined effects of long-term exposure to copper and marine heatwaves on the reef-forming serpulid Ficopomatus enigmaticus through a biomarker approach

Sessile benthic organisms can be affected by global changes and local pressures, such as metal pollution, that can lead to damages at different levels of biological organization. Effects of exposure to marine heatwaves (MHWs) alone and in combination with environmentally relevant concentration of copper (Cu) were evaluated in the reef-forming tubeworm Ficopomatus enigmaticus using a multi-biomarker approach. Biomarkers of cell membrane damage, enzymatic antioxidant defences, metabolic activity, neurotoxicity, and DNA integrity were analyzed. The exposure to Cu alone did not produce any significant effect. Exposure to MHWs alone produced effects only on metabolic activity (increase of glutathione S-transferase) and energy reserves (decrease in protein content). MHWs in combination with copper was the condition that most influenced the status of cell homeostasis of exposed F. enigmaticus. The combination of MHWs plus Cu exposure induced increase of protein carbonylation and glutathione S-transferase activity, decrease in protein/carbohydrate content and carboxylesterase activity. This study on a reef-forming organism highlighted the additive effect of a climate change-related stressor to metals pollution of marine and brackish waters.

Hydrogeochemical conditions of submarine and terrestrial karst sulfur springs in the Northern Adriatic

Submarine springs near Izola, in the Northern Adriatic Sea, appear in funnel-shaped depressions and smell strongly of sulfur. Along the Mediterranean coast there are many submarine karst springs containing brackish or fresh water, but submarine sulfur springs are not particularly common. Three submarine sulfur springs and one terrestrial sulfur spring were investigated to better understand the water properties, water–rock interaction within the aquifer, and to explore the origin of the spring water. Groundwater and seawater samples were also collected for comparison. Based on the geological setting, physicochemical parameters, hydrogeochemical data, and stable isotope data (δ18O, δ2H, δ13CDIC, δ34SSO4, δ18OSO4), we can affirm that (1) the large concentration of seawater in the submarine springs samples is due to sampling challenges; (2) springs recharge from precipitation where confined karst aquifers outcrop; (3) deep water circulation is indicated; (4) redox conditions can provide a suitable environment for bacterial reduction of the marine or organic sulfate to the odorous H2S; (5) geological data suggests that the coals beneath the alveolinic-nummulitic limestones are the source of sulfur. A multi-parameter and interdisciplinary approach has proven important in assessing submarine sulfur springs affected by seawater input.

Cell voltage control on ion selectivity of carbon nanotube-copper hexacyanoferrate with enhanced electrochemical deionization performance

This study utilizes a simple co-precipitation method to synthesize copper hexacyanoferrate (CuHCF) composites reinforced with carbon nanotubes (CNTs) (denoted as CuHCF@CNTs) serving as superior electrode materials for the electrochemical deionization (ECDI) application, a versatile method for brackish water deionization, water softening, and heavy metal removal. The enhanced performance of CuHCF, one of the Prussian blue analogues (PBAs) with typical Faradaic cation-capturing capability, is attributed to the increased charge transfer and a large surface area provided by multi-wall carbon nanotubes (MWCNTs) for the promoting the utilization of CuHCF units within the composites. The ion selectivity of electrode materials is investigated using both batch and microfluidic reactors, revealing a selectivity sequence of K+ > Ca2+ > Na+ > Mg2+. Additionally, this study introduces a novel approach for controlling the ion selectivity of CuHCF@CNT from the operating voltage. By varying the cell voltage, the selectivity factor, βK/Mg, can be increased from 1.7 at 1.2 V to 4.5 at 0.6 V. Our research offers a new perspective on the ion-capturing selectivity of ECDI systems using Faradaic materials in deionization and ion-concentrating applications.

Polyethylene glycol-polyvinylidene fluoride/TiO2 nanocomposite polymer coatings with efficient antifouling strategies: Hydrophilized defensive surface and stable capacitive deionization

Capacitive deionization (CDI) is flourishing as an energy-efficient and cost-effective water desalination method. However, challenges such as electrode degradation and fouling have hindered the practical deployment of CDI technology. To address these challenges, the key point of our strategy is applying a hydrophilic coating composed of polyethylene glycol (PEG)-functionalized nano-TiO2/polyvinylidene fluoride (PVDF) to the electrode interface (labeled as APPT electrode). The PEG/PVDF/TiO2 layer not only mitigates the co-ion depletion, but also imparts the activated carbon (AC) electrode hydrophilicity. As anticipated, the APPT electrode possessed an enhanced desalination capacity of 83.54 μmol g−1 and a low energy consumption of 17.99 Wh m−3 in 10 mM sodium chloride solution compared with the bare AC electrode. Notably, the APPT maintained about 93.19 % of its desalination capacity after 50 consecutive adsorption–desorption cycles in the presence of bovine serum albumin (BSA). During the trial, moreover, no obvious overall performance decline was noted in concentration reduction (Δc), water recovery (WR) and productivity (P) over 50 cycles. This strategy realizes energy-efficient, antifouling and stable brackish water desalination and has great promise for practical applications.

Plant-Derived Products Selectively Suppress Growth of the Harmful Alga Prymnesium parvum

Prymnesium parvum is a harmful alga found in brackish waters worldwide whose toxins can be lethal to aquatic organisms. Established field methods to control blooms of this species, however, are unavailable. Earlier studies showed that various extracts of giant reed (Arundo donax) can suppress P. parvum growth and that ellipticine, an allelochemical present in giant reed, is a potent algicide against this species. The unintended effects of giant reed products on nontarget organisms, however, are not fully understood. This study determined the effects of giant reed leachate (aqueous extract of dried chips) and ellipticine on growth of P. parvum and the green microalga Chlorella sorokiniana; survival and reproduction of the planktonic crustacean Daphnia pulex; and hatching success, larval survival, and larval swimming behavior of the teleost fish Danio rerio. Leachate made with 3 g chips L−1 was lethally toxic to P. parvum and D. pulex, stimulated C. sorokiniana growth, and impaired D. rerio behavior. Leachate at 1 g L−1 fully suppressed P. parvum growth, had moderate effects on D. pulex reproductive output, and had no effects on D. rerio. Ellipticine at 0.01 mg L−1 irreversibly inhibited P. parvum growth, acutely but reversibly inhibited C. sorokiniana growth, slightly delayed D. pulex reproduction, and had no effects on D. rerio. These observations suggest that when applied at appropriate concentrations, natural products derived from giant reed can be used as tools to specifically control P. parvum growth with minimal effects on nontarget species.

Migratory history of the threespine stickleback Gasterosteus aculeatus in western Ireland

Microchemical analysis of trace elements in otoliths and bio-mineralised earstones of teleost fishes is an emerging approach to analysing the environmental migratoryand life histories of fish species. The migration history of the three-spine stickleback (Gasterosteus aculeatus) collected in western Ireland was examined using calcium (Ca) and strontium (Sr) concentrations in otoliths. The otolith Sr:Ca values fluctuated with the habitat. The habitat use and migration history of G. aculeatus can be categorised into two types, as determined by the mean value and life history transect of the otolith Sr:Ca; that is, freshwater and estuarine residents, whereas there were no anadromous sticklebacks which is believed to be a typical migration pattern in the species. The otolith Sr:Ca profiles of the freshwater resident fishes exhibited constantly low Sr:Ca values, averaging 0.41–0.58 × 10−3 from the core towards the edge. However, the otolith Sr:Ca profiles of the estuarine resident fishes exhibited constantly high Sr:Ca values from the core towards the edge without a clear transition point from low to high Sr:Ca values, as found in the anadromous fish, averaging 1.82–4.26 × 10−3. The present study is the first published confirmation that 100 % of sticklebacks living in coastal habitats in Ireland > have an estuarine resident migratory pattern, constantly residing in marine environments or brackish water throughout their lifespan and not in freshwater environments in Ireland.

Hydrogeochemical characterization and assessment of factors controlling groundwater salinity in the Chamwino granitic complex, central Tanzania

Chamwino district, central Tanzania is a semi-arid granitic complex province, where groundwater is the major source of water for domestic and other uses. However, groundwater in the area is affected by salinity, thus, lowering the availability of potable water for various uses, decrease in crop production, taste less, wastage of soap, and abnormal pain. Due to this, this study sought to characterize groundwater using hydrogeochemical facies and signatures in order to identify the factors influencing the distribution of salt water in the Chamwino Granitic Complex. A total of 141 groundwater samples were collected from wells spatially distributed within the study area from January 2023 to April 2023, (a season of relatively low rainfall). All samples were subjected to in situ analyses of physicochemical parameters pH, temperature (T), total dissolved solids (TDS), electrical conductivity (EC), and salinity using a multi-parameter water analyzer and analyses of major ions (Ca2+, Mg2+, K+, Na+, Cl−, SO42−, HCO3−, and NO3−). The study revealed that the dominant cations in the groundwater are Na+ > Ca2+ > Mg2+, and the anions are Cl− > HCO3− > SO42. Five geological formations (granodiorite, tonalitic orthogenesis, migmatite, tonalite, and alluvium) were identified, and each is characterized by its unique groundwater facie. In the areas that are dominated with granodiorite, the major hydrogeochemical facies were Ca–HCO3, Na–Cl, Ca–Na–HCO3, Ca–Mg–Cl, and Ca–Cl water types; tonalitic orthogenesis was dominated by Ca–HCO3, Na–Cl, Ca–Mg–Cl, and Ca–Cl water types; migmatite was dominated by Ca–HCO3, Na–Cl, Ca–Mg–Cl, and Ca–Cl water types; tonalite was dominated by Na–Cl, Ca–Mg–Cl, and Ca–Cl water types; and alluvium was dominated by Na–Cl and Ca–Mg–Cl and Ca–Cl water types. The common hydrogeochemical facies in all five geological units are Na–Cl, Ca–Mg–Cl, and Ca–Cl water types. It is revealed that the groundwater in the study area is alkaline in nature and slightly saline with salinity level between 0.2 mg/L (fresh water) and 2.8 mg/L (brackish water) with mean 1.07 mg/L (of 141 samples). The factors controlling groundwater salinity distribution are mainly rock-water interaction and ion exchange reactions. Groundwater salinity in the study area is largely attributed to the abundance of Na+, Ca2+, Cl− and SO42−. Abundance of Na+ and Ca2+ is the results of both, weathering of feldspar minerals particularly plagioclase (Na–Ca feldspars) which are the major mineral in granites, and evaporation crystallization cycles of evaporates in semi-arid areas such as Chamwino. Also, such evaporation crystallization cycles account for the abundance of Cl− and SO42− especially in areas dominated by alluvium. However, anthropogenic activities as evidenced by elevated nitrate up to 212.6 mg/L in congested areas are also likely to contribute in area) to the elevated Cl− and SO42−. In other geological units such as tonalitic orthogneiss, migmatite and granodiorite, there was an ostensible mixing of saline water with fresh water from local recharge as indicated by the abundance of HCO3− ions. Nonetheless, the hydrogeochemical characterization of groundwater in the Chamwino granitic complex suggests that there is little possibility for groundwater to evolve to a carbonate water type (fresh water) because the groundwater salinity is mainly geogenic, unless artificial recharge through rainwater harvesting is applied.

Novel Variable Configuration Design for Ultrahigh Recovery Reverse Osmosis Desalination of Brackish Water

Novel Variable Configuration Design for Ultrahigh Recovery Reverse Osmosis Desalination of Brackish Water

Chlorella vulgaris in biodesalination: a sustainable future from seawater to freshwater

Demand for freshwater is increasing rapid due to population growth and climate change. A potential solution to this problem is the use of biodesalination, which involves the removal of salt from seawater and brackish water using biological agents. In this study, we investigated the feasibility of using Chlorella vulgaris, a green microalga, to remove salt from seawater to produce fresh water. The effects of salinity, light intensity, and nutrient concentration on the growth and salt removal efficiency of C.vulgaris were examined. Our results showed that C. vulgaris was able to grow and remove salt from seawater under salinities of approximately 24ppt and nutrient concentrations of 50%. The highest salt removal efficiency was achieved at a desalination setup involving C. vulgaris and seawater concentration of 1:5 ratio. We also evaluated the economic feasibility of biodesalination using C. vulgaris by estimating the production costs and comparing them with those of conventional desalination technologies. Our results showed that biodesalination using C.vulgaris is potentially a cost-effective and sustainable alternative to conventional desalination technologies. In conclusion, our study demonstrated the potential of C. vulgaris for the biodesalination of seawater, which could contribute to meeting the growing demand for fresh water.

Increasing the Non-Specific Immunity of Vannamei Shrimp (Litopenaeus vannamei) Maintained in Traditional Ponds with the Addition of Fitoimun®

Vannamei shrimp (Litopenaeus vannamei) is a commodity that is in great demand by the community. The purpose of this study were to examine the use of Fitoimun® mixed in feed to increase non-specific immunity, survival the morphology of vannamei shrimp. This study used a completely randomized design, with 3 treatments and 3 replications. The Fitoimun® product used made from extracts of fingerroot (Boesenbergia pandurata) and tamarind eggplant (Solanum ferox) was mixed with pellet feed. The doses used in the treatment were 0 mL/kg, 20 mL/kg, 24 mL/kg. The feed was given twice a day, in the morning and evening as much as 500 grams per repetition. The research was conducted for 3 months and observations were carried out for one month. The shrimp was purchased from the Brackish and Sea Water Central Seed Center (BBU) manggar Balikpapan with an average weight of 27 g. Sampling was carried out once a week. Haemolymph was taken for the observation of immunity. The results showed that the administration of Fitoimun® increased non-specific immunity such as total haemocytes with the highest value of 125.7 cells/mL and differential haemocytes with the highest value in granulocyte cells 43.90%, semi granulocyte cells 42.57% and hyaline 32.63 %. The Survival were 52% and there was no significant difference between treatments. Fitoimun® did not affect the morphology of Pasific whiteleg shrimp.

Exergy analysis for enhanced performance of integrated batch reverse osmosis – Forward osmosis system for brackish water treatment

Concept of integrated brackish water batch reverse osmosis – forward osmosis (BRO – FO) is relatively new in the field of desalination. Recovery of the reverse osmosis (RO) system can be elevated using the free piston BRO concept, and the specific energy consumption (SEC) can be reduced. This study focuses on exergy, advanced exergy, and parametric analysis of the integrated BRO - FO system. The conventional exergy analysis suggests that the largest rate of exergy destruction is associated with the system's RO membrane module and pump, with values of 6.51 and 87.06 %, respectively. However, advanced exergy analysis shows that this rate can be reduced by 3.53 % and 62.89 %, respectively. Endogenous exergy destruction of pumps and membranes is higher compared to exogenous exergy destruction. These results are utilised to determine the system's optimal performance using parametric analysis. Sensitivity analysis was utilised to obtain an optimum recovery for system design, fresh water cost (FWC), and specific solution cost (SSC). The BRO can achieve >80 % recovery with 0.43 kWh/m3 SEC, and FO technology helps to attain minimal/zero waste discharge. Thus, a FWC of 0.50 $/m3 and a SWC of 0.44 $/m3 can be achieved.

Effects of culture salinity on growth and reproduction of the polychaete Dendronereis chipolini

Dendronereis chipolini is an important brackish water polychaete and has been wildly used as fattening feed for marine shrimp broodstocks. Investigation into the effects of salinity on performance of this worm species is fundamental for the development of mass culture procedure to produce feed for fattening shrimp broodstock and reduce pressure on wild catch. The study was conducted in a tank system with an area of 0.25 m2 in which the young worms (0.9±0.2 cm in length and 0.007±0.003 g in body weight) were stocked at 100 inds/tank. Four salinity treatments, including 15, 20, 25, 30 ppt, were designed with three replicates each. The worms were fed once a day at 9 am with commercial shrimp feed at a rate of 3% body weight. After 150 days of rearing, the fastest growth of worms was recorded in 20 ppt. The survival rate was also higher in 20 ppt but no significant difference was found (p&gt;0.05) between treatments. Higher absolute fecundity (103,890±17,389 and 112,740±22,328 eggs/female) was recorded at 20 and 25 ppt, respectively. The males in 20 ppt also produced a higher number of sperms. Overall, the polychaete D. chipolini reared at 20 ppt performed higher growth, survival and reproduction rates.

Taxonomy, paleoecology, and paleobiogeographical significance of the middle-late Eocene molluscs from the Garet Gehannem section in the Fayoum depression, Egypt

The studied middle-upper Eocene Garet Gehannam section exhibits moderate macrofossil diversity and notably high macrofossil abundance. Eleven molluscan species were identified and described, including five bivalves and six gastropods. Three macrobenthic assemblages were recognized: The turritelline-dominated assemblage, Carolia placunoides assemblage and Turkostrea multicostata assemblage. The Turritelline-dominated assemblage indicates high-nutrient environments, which typically exhibit normal to slightly below normal marine salinities, low sedimentation rates, and high-energy environments. Carolia placunoides assemblage indicates brackish water environment during times of sea level regression. Turkostrea multicostata assemblage provides compelling evidence of a prevailing hot climate and an environment rich in calcium, characterized by nutrient-rich water and low to moderate energy levels and high light availability. The investigation of the articulation of Carolia placunoides Cantraine1838 and Turkostrea multicostata (Deshayes, 1818) shells strongly suggests a parautochthonous assemblage. In terms of paleobiogeography, Turkostrea multicostata (Deshayes, 1818) first appeared during the Paleocene in the southern Tethys, specifically in Tunisia and Algeria, as well as in the Trans-Saharan Seaway in Mali. Consequently, its paleobiogeographic distribution can be allied to current circulation along the Tethys Ocean, firstly from its original area in the southern Tethys regions and Trans-Saharan Seaway to neighboring regions of the southern and northern Tethys, as well as the West Africa provinces. The paleobiogeographic map of the identified species shows that the identified species were prevailing in two bioprovinces during the middle – late Eocene epochs: i) the North-West, North, and South Tethyan Margins Province, ii) and the West Africa Province.

Influence of early/mid-Holocene climate change and sea level rise on a coast with barrier islands, Rio de Janeiro State, SE Brazil

AbstractThis work aims to identify the influence of climate change on sedimentary processes associated with the usual regression process during the rise of sea level in the early/middle Holocene in southeastern Brazil. The studied area is on the eastern side of Marambaia Barrier Island, which borders the eastern side of Sepetiba Bay (Rio de Janeiro State, SE Brazil). Nowadays, the Marambaia Barrier Island, a ≈ 40 km long and ≈ 5 km wide sandy ridge, shields Sepetiba Bay from the direct influence of the Atlantic Ocean. To achieve this goal, grain size, geochemical data (including elemental and stable isotopes), and radiocarbon dating data from sediment core SP10 (spanning depths from 8.2 to 45.5 m), collected in the eastern sector of the Marambaia Barrier Island were analyzed. Core SP10 predominantly consists of sandy sediments with some textural variations. However, Sr/Ba ratios suggest that brackish waters primarily influenced the depositional environment, which was also subject to cyclical marine incursions. The essentially felsic sediments of the interval between 45 and 41 m (≈ 10.0–8.5 ka BP) were probably deposited in a protected tidal plain estuary with mangroves. They were possibly mainly sourced from the nearby Pedra Branca Complex. Subsequently, between ≈ 41 and 11 m, the marine influence and hydrodynamics increased, and the sediments exhibited a more mafic mineralogical composition resulting probably from the erosion of the Rio Negro Complex, which is mainly found in the northern region of Sepetiba Bay. The mafic component likely reached the study area through coastal drift connected with Sepetiba Bay. During the drought period, recorded between ~ 7.5 and 7.0 ka cal BP (section 25–21 m), the contribution of the mafic component from the Rio Negro Complex decreased and less weathered sediments were accumulated. On the other hand, marine incursions into the study area became more prominent. During the drier climate phase recorded in the interval ≈ 11–9 m (after ≈ 4.0 ka BP), the La/Sc values indicate that the sediment included a higher proportion of felsic particles, probably due to more significant restrictions on the connection of the study area with Sepetiba Bay due to the development of the Marambaia Barrier Island. These findings are significant as they demonstrate the influence of geomorphology, climate change, sea level, and the development of Holocene barrier islands on the sedimentation in coastal regions.

Fish assemblages across a salinity gradient in the Zeeschelde estuary (Belgium)

Between 1991 and 2008 a total of 71 fish species was recorded in the brackish and fresh water zone of the Schelde estuary (Zeeschelde). The results were obtained from fish surveys from the cooling water filter screens of the power plant at Doel (between 1991 and 2008) and fyke net surveys along the length of the estuary between 1995 and 2008. Species abundance in the different salinity zones was analysed using the fyke net data only. The ten most abundant species represent 90.8% of the total number of individuals caught. In decreasing order of abundance: flounder (Platichthys flesus), roach (Rutilus rutilus), herring (Clupea harengus), eel (Anguilla anguilla), pike-perch (Sander lucioperca), sole (Solea solea), common goby (Pomatoschistus microps), seabass (Dicentrarchus labrax), three-spined stickleback (Gasterosteus aculeatus) and white bream (Blicca bjoerkna). With fyke nets 33 species were caught in the tidal freshwater zone, 43 species in the oligohaline zone and 59 species in the mesohaline zone. Each salinity zone is characterised by a typical fish assemblage, although some species are shared between all three salinity zones: e.g. three-spined stickleback (Gasterosteus aculeatus), Prussian carp (Carrasius gibelio), roach (Rutilus rutilus) and eel (Anguilla anguilla). Diadromous species occur in all zones and make up, on average up 22% of the species richness. Freshwater species comprise about 70% of the species in the tidal freshwater zone. In the oligohaline zone the contribution of the freshwater species to the species richness is less while marine migrants become more abundant. As expected, the contribution of marine migrants and estuarine species is higher in the mesohaline zone. The recent increase in species richness in the freshwater and oligohaline zone coincides with a remarkable increase in dissolved oxygen since 2007.

Cyanobacterial Genomes from a Brackish Coastal Lagoon Reveal Potential for Novel Biogeochemical Functions and Their Evolution.

Cyanobacteria are recognised for their pivotal roles in aquatic ecosystems, serving as primary producers and major agents in diazotrophic processes. Currently, the primary focus of cyanobacterial research lies in gaining a more detailed understanding of these well-established ecosystem functions. However, their involvement and impact on other crucial biogeochemical cycles remain understudied. This knowledge gap is partially attributed to the challenges associated with culturing cyanobacteria in controlled laboratory conditions and the limited understanding of their specific growth requirements. This can be circumvented partially by the culture-independent methods which can shed light on the genomic potential of cyanobacterial species and answer more profound questions about the evolution of other key biogeochemical functions. In this study, we assembled 83 cyanobacterial genomes from metagenomic data generated from environmental DNA extracted from a brackish water lagoon (Chilika Lake, India). We taxonomically classified these metagenome-assembled genomes (MAGs) and found that about 92.77% of them are novel genomes at the species level. We then annotated these cyanobacterial MAGs for all the encoded functions using KEGG Orthology. Interestingly, we found two previously unreported functions in Cyanobacteria, namely, DNRA (Dissimilatory Nitrate Reduction to Ammonium) and DMSP (Dimethylsulfoniopropionate) synthesis in multiple MAGs using nirBD and dsyB genes as markers. We validated their presence in several publicly available cyanobacterial isolate genomes. Further, we identified incongruities between the evolutionary patterns of species and the marker genes and elucidated the underlying reasons for these discrepancies. This study expands our overall comprehension of the contribution of cyanobacteria to the biogeochemical cycling in coastal brackish ecosystems.