Typical Freshwater Research Articles

Microbiome and network analysis reveal potential mechanisms underlying Carassius auratus diseases: The interactions between critical environmental and microbial factors

Despite the rapid development of research on aquatic environment microbiota, limited attention has been paid to exploring the complex interactions between microbial communities and aquatic environments. Particularly, the mechanisms underlying fish diseases based on such dynamic interactions remain unknown. This study aimed to address the gap by conducting microbiome and co-occurrence network analyses on the typical freshwater aquaculture systems. High-throughput 16S rRNA gene sequencing results revealed significant differences in the microbiota between the disease and healthy groups. Notably, disease mortality varied consistently with the gradient of relative abundance of Proteobacteria (intestine, R2 = 0.46, p < 0.05) and Cyanobacteria (gill, R2 = 0.67, p < 0.01), indicating their potential use as diagnostic criteria. Furthermore, the elevated hepatosomatic index, NO3-N, COD and TC (sediment) were directly correlated with diseases (r > 0.54, p < 0.01). Mean concentrations of NO3-N, COD and TC were elevated by 78.87%, 25.63% and 44.2%, respectively, in ponds where diseases occurred. Quantitative analysis (qPCR) revealed that Aeromonas sobria infected hosts through a potential pathway of “sediment (4.4 × 105 copy number/g)-water (1.1 × 103 copy number/mL)-intestine (1.2 × 106 copy number/g)”. Similarly, the potential route for Aeromonas veronii was sediment (4.9 × 106 copy number/g) to gill (5.1 × 105 copy number/g). Additionally, the complexity of microbial networks in the intestine, water, and sediment was significantly lower in the disease group, although no similar phenomenon was observed in the gill microbial network. In summary, these findings reveal that elevated concentrations of crucial environmental factors disrupt the linkages within microbiota, fostering the growth of opportunistic bacteria capable of colonizing fish gut or gills. This offers new insights into potential mechanisms by which environmental factors cause disease in fish.

The Invertebrates of The Romualdo Formation, Araripe Basin: Analysis of Paleoecological and Paleogeographical Data

Fossil invertebrates are good paleoenvironmental indicators due to their sensitivity to abiotic conditions, which contributes to the understanding of the Aptian-Albian of the Araripe Basin. However, much of the paleoecological and paleobiogeographical information on these organisms is scarce in the literature. The aim of this paper is to compile relevant data on the macroinvertebrates of the Romualdo Formation and to analyze and point out gaps in knowledge. To achieve this, extensive bibliographical research was carried out, using scientific publications based on the families of Spinicaudata, echinoids, gastropods, bivalves, shrimps and crabs of the Romualdo Formation and their distribution in Brazil and globally throughout the Aptian-Albian, using specialized online databases. Paleoecological and paleogeographical data were compiled for 46 invertebrate taxa, highlighting those with better studied routes of origin. Thus, it was possible to highlight the lack of data regarding the way of life of certain mollusc families and systematic problems regarding the identification of the families of several species of shrimp. Finally, the predominance of taxa from marine (34), brackish (7) and lacustrine (5) waters was shown. Of these, 18 taxa have a typical tethyan distribution and another 12 also present occurrences in the Austral, Boreal or both domains. The only typical freshwater group was Spinicaudata, marking environments with little or no marine influence and with rare occurrences during the Aptian-Albian.

Transcriptome analysis reveals the importance of phototransduction during the first-feeding in mandarin fish (Siniperca chuatsi).

The mandarin fish (Siniperca chuatsi), as a typical freshwater carnivorous fish, has high economic value. Mandarin fish have a peculiar feeding habit of feeding on other live fry during the first-feeding period, while rejecting zooplankton or particulate feed, which may be attributed to the low expression of zooplankton-associated gene sws1 in mandarin fish. The domesticated strain of mandarin fish could feed on Artemia at 3 days post hatching (dph). However, the mechanism of mandarin fish larvae recognize and forage Artemia as food is still unclear. In this study, we employed transcriptional analysis to identify the representative differential pathways between mandarin fish larvae unfed and fed with Artemia at 3 dph. The comparative transcriptome analysis has unveiled a tapestry of genetic expression, highlighting 403 genes that have been up-regulated and 259 that have been down-regulated, all of which constitute the differentially expressed genes (DEGs). KEGG pathway analysis revealed that the number of differentially expressed genes in the photoconductive signaling pathway was the largest. Next, the Vorinostat (suberoylanilide hydroxamic acid, SAHA) was used to assess whether sws1 induced ingestion of Artemia in mandarin fish larvae. We discovered that SAHA-treated larvae had more food intake of Artemia and up-regulated the transcription level of npy, which might have been associated with the up-regulated of sws1 opsin. Additionally, exposure to 0.5 µM SAHA increased the expression of genes involved in phototransduction pathway. These findings would provide insights on the molecular processes involved in mandarin fish larvae feeding on Artemia at the first-feeding stage.

Entomoneis parikhani sp.nov., Aras Nehri (İran)’nden yeni bir diatom (Entomoneidaceae, Bacillariophyta)

The diatom Entomoneis has a series of unique features such as connecting lines with different shapes, sigmoid raphe on the bilobate keel, different curtains, and multiple girdle bands. Most species belonging to this genus are found in marine and saline habitats. In fact, the genus Entomoneis is an epipelic diatom that is found in streams with high salinity and high electrolyte concentration. To date, no specific type of freshwater has been identified for this species. In this study, a new species of freshwater diatom, Entomoneis parikhani, is described based on detailed morphological observations using a scanning electron microscope. The samples were collected the Aras River near Oltan village of Parsabad city in the northwest Iran. A special feature of Entomoneis parikhani is its triple valve. The genus Entomoneis comprises of diatoms with sigmoidal raphe canals and girdle bands. This taxon is similar to Entomoneis annagodhei and Entomoneis tenera, as shown by LM and SEM observations, and there are sufficient morphological differences to separate Entomoneis parikhani. This new species had very small cells, delicate frustules without valve lines, and wide lanceolate valves. In this study, the wide distribution of this taxon in the Aras River has been evaluated.

Exploring potentials to enhance fish sauce industry in Sri Lanka: A review

Fish sauce, an amber-colored liquid derived from the fermentation of fish with sea salt, is a vital condiment in Southeast Asian and East Asian cuisines. Despite its culinary importance, fish sauce remains underutilized in Sri Lanka, where it is predominantly imported, resulting in high costs and substantial foreign exchange outflows. The technology for fish sauce production is relatively simple, presenting an opportunity for local production using abundant fish resources. Various types of fish, including marine, freshwater, and shellfish, are used globally in fish sauce production, and it could harness the nutritional benefits of fish, transforming underutilized species into a valuable condiment. The production process of fish sauce involves salting, fermenting, maturing, filtering, and blending, resulting in a product rich in hydrolyzed proteins and essential minerals. Quality standards are regulated to ensure safety and purity, with a focus on maintaining the distinctive fishy odor and taste characteristic of pure fish sauce. Establishing a local fish sauce industry in Sri Lanka promises economic growth and culinary enrichment. By leveraging local fish resources and employing cost-effective production methods, Sri Lanka can reduce imports of fish sauce, and can utilize fish in a sustainable manner.

Quantitative Assessment of Factors Contributing to Variations in Sea Surface pCO2 in the Pacific Sector of the Arctic Ocean

AbstractTo quantitatively assess seasonal variations in the partial pressure of carbon dioxide (pCO2) in the Pacific sector of the Arctic Ocean (Canada Basin and Chukchi Sea) in 2021, water temperature, salinity, chlorophyll‐a, pCO2, dissolved inorganic carbon (DIC), total alkalinity (TA), and nutrients were measured. During summer 2021, surface water pCO2 in our study area (315 ± 41 μatm) was undersaturated with respect to the atmosphere (404 ± 4 μatm), and the ocean was a sink for atmospheric CO2 (−10.5 ± 11.0 mmol C m−2 day−1). Using DIC, TA, and nutrients in the temperature minimum layer, we estimated the under‐ice pCO2 in the water during the previous winter and calculated changes in pCO2 (δpCO2) due to temperature changes, freshwater inflow, biological activity, and other factors (gas exchange and advection) from winter to summer. In the Chukchi Sea, biological activity and temperature changes had significant impacts on pCO2, whereas in the Canada Basin, the influx of freshwater caused a significant decrease in pCO2. Our results suggested that different types of freshwaters had different effects on pCO2, with sea ice meltwater having a greater effect on reducing pCO2 than river water or snowmelt water. We therefore emphasize the importance of freshwater type and proportion, as well as freshwater supply, for prediction of future pCO2 changes.

Description of a 'plankton filtration bias' in sequencing-based bacterial community analysis and of an Arduino microcontroller-based flowmeter device that can help to resolve it.

Diversity studies of aquatic picoplankton (bacterioplankton) communities using size-class filtration, DNA extraction, PCR and sequencing of phylogenetic markers, require a robust methodological pipeline, since biases have been demonstrated essentially at all levels, including DNA extraction, primer choice and PCR. Even different filtration volumes of the same plankton sample and, thus, different biomass loading of the filters, can distort the sequencing results. In this study, we designed an Arduino microcontroller-based flowmeter that records the decrease of initial (maximal) flowrate as proxy for increasing biomass loading and clogging of filters during plankton filtration. The device was tested using freshwater plankton of Lake Constance, and total DNA was extracted and an 16S rDNA amplicon was sequenced. We confirmed that different filtration volumes used for the same water sample affect the sequencing results. Differences were visible in alpha and beta diversities and across all taxonomic ranks. Taxa most affected were typical freshwater Actinobacteria and Bacteroidetes, increasing up to 38% and decreasing up to 29% in relative abundance, respectively. In another experiment, a lake water sample was filtered undiluted and three-fold diluted, and each filtration was stopped once the flowrate had reduced to 50% of initial flowrate, hence, at the same degree of filter clogging. The three-fold diluted sample required three-fold filtration volumes, while equivalent amounts of total DNA were extracted and differences across all taxonomic ranks were not statistically significant compared to the undiluted controls. In conclusion, this work confirms a volume/biomass-dependent bacterioplankton filtration bias for sequencing-based community analyses and provides an improved procedure for controlling biomass loading during filtrations and recovery of equivalent amounts of DNA from samples independent of the plankton density. The application of the device can also avoid the distorting of sequencing results as caused by the plankton filtration bias.

Ecological implications and drivers of emerging contaminants in Dongting Lake of Yangtze River Basin, China: A multi-substance risk analysis

Emerging contaminants (ECs) are increasingly recognized as a global threat to biodiversity and ecosystem health. However, the cumulative risks posed by ECs to aquatic organisms and ecosystems, as well as the influence of anthropogenic activities and natural factors on these risks, remain poorly understood. This study assessed the mixed risks of ECs in Dongting Lake, a Ramsar Convention-classified Typically Changing Wetland, to elucidate the major EC classes, key risk drivers, and magnitude of anthropogenic and natural impacts. Results revealed that ECs pose non-negligible acute (30% probability) and chronic (70% probability) mixed risks to aquatic organisms in the freshwater lake ecosystem, with imidacloprid identified as the primary pollutant stressor. Redundancy analysis (RDA) and structural equation modeling (SEM) indicated that cropland and precipitation were major drivers of EC contamination levels and ecological risk. Cropland was positively associated with EC concentrations, while precipitation exhibited a dilution effect. These findings provide critical insights into the ecological risk status and key risk drivers in a typical freshwater lake ecosystem, offering data-driven support for the control and management of ECs in China.

Bioconcentration of Inorganic and Methyl Mercury by Algae Revealed Using Dual-Mass Single-Cell ICP-MS with Double Isotope Tracers.

Algae are an entry point for mercury (Hg) into the food web. Bioconcentration of Hg by algae is crucial for its biogeochemical cycling and environmental risk. Herein, considering the cell heterogeneity, we investigated the bioconcentration of coexisting isotope-labeled inorganic (199IHg) and methyl Hg (201MeHg) by six typical freshwater and marine algae using dual-mass single-cell inductively coupled plasma mass spectrometry (scICP-MS). First, a universal pretreatment procedure for the scICP-MS analysis of algae was developed. Using the proposed method, the intra- and interspecies heterogeneities and the kinetics of Hg bioconcentration by algae were revealed at the single-cell level. The heterogeneity in the cellular Hg contents is largely related to cell size. The bioconcentration process reached a dynamic equilibrium involving influx/adsorption and efflux/desorption within hours. Algal density is a key factor affecting the distribution of Hg between algae and ambient water. Cellular Hg contents were negatively correlated with algal density, whereas the volume concentration factors almost remained constant. Accordingly, we developed a model based on single-cell analysis that well describes the density-driven effects of Hg bioconcentration by algae. From a novel single-cell perspective, the findings improve our understanding of algal bioconcentration governed by various biological and environmental factors.

Identifying intrusion of seawater in coastal aquifers by modified GALDIT (M-GALDIT) index

Contamination of coastal aquifers by seawater intrusion (SWI) is a major environmental problem. A modified GALDIT method (M-GALDIT), and multi-criteria decision model AHP has been used to identify regions vulnerable to seawater intrusion. We have used the groundwater suitability index for seawater intrusion (GQISWI) in estimating the M-GALDIT index. While the GALDIT analysis indicates that ∼28% of the area is moderately vulnerable, and 8% of the area is relatively highly vulnerable, our estimates using AHP and M-GALDIT method indicate ∼19% of the area as moderately vulnerable, ∼22% of the area as relatively highly vulnerable zones. The GQISWI values in the region vary between 0 and 96.96, indicating that most of the groundwater samples belong to mixed water types. Faults and fractures, population distribution, water-rock interaction, ionic exchange reactions, and evaporation appear to be the dominant mechanisms, besides seawater intrusion that control the overall groundwater geochemistry in the region. Ca2+-HCO3-, Ca2+-Na+-HCO3−, and Ca2+-Mg2+-Cl− are the most dominant water types in the study area. The seawater mixing index (SMI) reveals that ∼34.5% of samples are of relatively freshwater types, whereas ∼61% of samples appear contaminated to some extent, presumably due to the mixing of seawater, or anthropogenic activities such as mining, agricultural activities, etc. Furthermore, analysis of the HFE-D diagram indicates that ∼23% of samples are directly affected by seawater intrusion.

Species Composition of the Volgograd Reservoir Basin Rivers (the Yeruslan River)

The river network of the vast territory of the Lower Volga basin in the semidesert area of the Russian Plain belongs to the least studied tributaries of the River. Among the rivers of the left bank in this natural and climatic zone, the Yeruslan River is the most important one, which largely determines the ecological characteristics of the area. The article presents the data of long-term (2015–2017) studies of macrozoobenthos of the Yeruslan River (a tributary of the Volgograd Reservoir) are presented. For the first time the detailed composition of fauna including 148 species and taxa of higher systematic rank is given. The basis of the taxonomic composition of the river is formed by a complex of eurybiont species. The limnophilic taxa Limnodrilus hoffmeisteri, Polypedilum nubeculosum, Cladotanytarsus mancus and Paratanytarsus sp. have the highest frequency. These taxa are widely distributed in plain rivers of the Upper, Middle and Lower Volga basin. The vast majority of species recorded in the Yeruslan River are typically freshwater forms. In the observed water salinity gradient (0,235–1,42 g/l), the highest species richness of macrozoobenthos was observed in the range of 0,5–0,8 g/l. Under highly saline conditions (&gt;1,2 g/l) there are mayflies Caenis robusta and Cloeon gr. dipterum, caddisflies Oecetis furva, dragonflies Ischnura elegans, mollusks Viviparus viviparus, ceratopogonids Sphaeromias pictus, oligochaetes Limnodrilus hoffmeisteri, Stylaria lacustris, Tubifex tubifex, chironomids Cladotanytarsus mancus, Cryptochironomus gr. defectus, Dicrotendipes nervosus, Glyptotendipes barbipes, Glyptotendipes glaucus, Polypedilum nubeculosum, Parachironomus varus, Paratanytarsus sp, Psectrocladius sordidellus, Tanytarsus pallidicornis, Tanytarsus sp. etc. These species should be classified as euryhaline taxa. The flat character of the Yeruslan River, characterized by low gradients of the river bed and low flow velocity, determines the development of limnophilic, lake-pond fauna of macrozoobenthos. Along with typical freshwater taxa, euryhaline groups of hydrobionts inhabiting areas where saline soils are drained by river waters are widespread. The contribution of rheophilic species to macrozoobenthos composition is negligible, which distinguishes bottom communities of the Yeruslan River from plain rivers of forest and forest-steppe natural-climatic zones of the Volga River basin.

Breeding of whitefish Coregonus Lavaretus L. at the Knyazhegubsky fish hatchery

The article describes whitefish Coregonus lavaretus L., 1758 (Baltic environmental type) breeding results at the Knyazhegubsky fish hatchery (Murmansk region, Russia). Since 2017, the major goal of this fish hatchery has been the breeding of freshwater type of whitefish. Technology for whitefish breeding was tested in 2018-2019. A number of problems encountered by fish breeders were identified. Live fertilized Baltic whitefish eggs at the “eye pigmentation” phase are purchased every year from OOO “Forvat” fish farm (Sosnovo settlement, Priozersky district, Leningrad region, Russia) and transported to the Knyazhegubsky fish hatchery. Major fish-farming activities subsequently performed at the fish hatchery include: eggs incubation in Weiss machines, summer and winter rearing of juveniles in rearing facilities, in trout ditches, and at equipped summer site as well as release of young whitefish aged under one year into the Kovdozerskoe water reservoir. The average mass of a single young fish in the first batch released in 2019 was 0.5 grams. Juvenile fish is available for release on a partial basis into water bodies of the Murmansk region for fish-stocking purposes under contracts with business entities. Currently, technology is being worked on for rearing and formation of the breeding stock. In general, the results of the work performed indicate that Baltic whitefish (freshwater type) rearing conditions at the Knyazhegubsky fish hatchery are favorable.

Haff disease: overview and clinical features.

Haff disease was first described at the beginning of the twentieth century in Europe. Almost a century later, thousands of cases have now been reported in different countries. In Brazil, most cases are observed in the Amazon region, and its associated factors remain to be fully understood. This disease is an uncommon syndrome characterized by intense myalgia and rhabdomyolysis, which manifests within 24 h after consuming some types of freshwater or saltwater fish and crustaceans. A possible heat-stable toxin contained in seafood may be the cause of Haff disease, but this hypothesis is not yet completely proven. This review will describe the clinical and epidemiological aspects of Haff disease with updated literature.

Development and validation of diffusive gradients in thin-films for in situ monitoring of ionic liquids in waters.

Due to their wide applications, occurrence and "PFAS-like" environmental behaviors, ionic liquids (ILs) represent a new challenge for the environmental monitoring community, who require robust analytical methods that can determine accurately and efficiently their environmentally relevant concentrations. A new passive sampling method based on the diffusive gradients in thin films (DGT) technique was developed for the measurement of imidazole-based ILs in waters using a mixed-mode cation exchange (MCX) resin as the adsorbent. The selected binding gel had a high binding capacity (>170 μg per disc) for ILs. Diffusion coefficients measured using a diffusion cell correlated well with alkyl chain lengths (r2 = 0.95) and retention times (r2 = 0.88), providing a simple and rapid prediction approach for other ILs. The assembled MCX-DGT sampler exhibited a linear accumulation for at least 120 h. MCX-DGT also showed good performance under typical freshwater conditions (pH 5-8, ionic strength 0.001-0.01 M, and humic acid 0-5 mg L-1), while still being problematic for aquatic conditions with higher ionic strength (>0.1 M) or DOM (>10 mg L-1). Laboratory deployment (for up to 3 days) in spiked natural freshwater (SNW) resulted in linear mass uptakes for the short-chain ILs (C2-C8), and their DGT-measured concentrations agreed well with solution concentrations. However, MCX-DGT significantly overestimated the concentrations of the long-chain ILs (C10-C12) when deployed in SNW for one day or more, which is attributed to the strong competitive adsorption of the long-chain ILs by natural organic matter. In situ field evaluation along with grab sampling found no target ILs in a wastewater treatment plant and its receiving river, implying that these new chemicals might not be widely used in South China now. This is the first report on the DGT technique for ILs and might provide an effective tool for monitoring short chain length ILs in the aquatic environment in the near future.

Features of microbial communities in fresh lakes of Buryatia

The taxonomic composition of microbial communities of eight large fresh lakes of Buryatia was studied. These lakes are Baikal, Kotokel, Gusinoye, Shchuchye and lakes of the Eravno-Kharginskaya group (Isinga, Gunda, Sosnovoe, Bolshoe Eravnoe). They have water management, fishery and recreational significance. At the phylum level, the microbial communities of the studied lakes were similar but the phyla abundance was varied. They consisted of typical freshwater taxa Pseudomonadota, Actinobacteriota, Bacteroidota, Cyanobacteriota, Firmicutes, Planctomycetes and Verrucomicrobia. At the genus level, Acinetobacter and Pseudomonas were numerous in all lakes. Other dominant taxa were Flavobacterium, hgcI clade in the fresh lakes of the Baikal region and Exiguobacterium, Klebsiella in the Eravno-Kharginskaya lakes. The feature of Eravno-Kharginskie lakes was the abundance of the genera Exiguobacterium and Klebsiella, as well as the detection of sanitary-significant bacteria. These facts may indicate pollution as a result of pressing various factors, including anthropogenic ones.

Hydrochemical characterization and water quality perspectives for groundwater management for urban development

The present study was conducted to assess groundwater quality for drinking and industrial water purposes, evaluate the driving mechanisms of groundwater chemistry, and suggest appropriate management measures to protect groundwater resources for sustainable urban development in a part of Odisha, India. Overall Water Quality Index (OWQI) and Industrial Water Quality Index (IWQI), geochemical ratios and chemometric analyses were used to identify the causes of ionic sources of natural and anthropogenic inputs. Groundwater samples were collected and analysed for chemical parameters. The OWQI indicated that 95.93% of the study region is unfit for drinking water purposes due to high concentrations of Mg2+, Na+, Cl−, SO42−, NO3−, and F− ions supported by the ANOVA test. The IWQI found corrosion and incrustation activities in 80.05% and 94.33% of the study region, respectively, which hinders urban development. The trilinear diagram illustrated that the freshwater type changes completely to mixed water type, and then to reverse ion exchange water and saline water types due to the influence of anthropogenic sources. Gibbs diagrams explaining the mechanisms responsible for groundwater chemistry that groundwater quality moves from the rock domain to the evaporation domain due to human-induced activities. Saturation indices showed that fluoride, gypsum, and halite are in a dissolved state, and calcite is in a precipitated state. Different ionic ratios clearly illustrated that groundwater quality is mainly modified by anthropogenic sources from lithological origin. Principal component analysis (PCA) classified the chemical parameters into salinity, alkalinity, and soil-controlled factors of groundwater chemistry based on their high-positive loadings. High positive scores of PCA, and Clusters 1 and 2 of the hierarchical cluster analysis clearly differentiated polluted and unpolluted affected groundwater samples. Therefore, it is suggested to take appropriate preventive measures to improve the groundwater resources. Otherwise, there will be adverse conditions for urban activities.

Higher contribution by comammox bacteria than AOA and AOB to nitrification in the sediments of lake Taihu

Nitrification is the initial reaction and maintains the nitrogen balance in natural ecosystem. The discovery of complete ammonia oxidation (comammox) has revolutionized the traditional theory of ‘two-step nitrification’. However, the comammox bacteria and contribution in lake sediment are little known, therefore Lake Taihu was selected for the study, which is a typical freshwater lake with heterogeneity in China. The sediments from five areas with different nutrient levels were selected to investigate the phylogeny and distribution of comammox bacteria by amoA gene at different spatial scales, as well as their correlation with environmental factors and the contribution in lake sediment. The result showed that comammox bacteria amoA gene abundance ranged from 5.29 × 105 to 5.49 × 1011 copies·g−1 dry sediment, which was generally higher than that of AOA and AOB. The abundance of comammox bacteria was significantly correlated with the N concentration (p < 0.05). Moreover, through high-throughput sequencing of amoA gene, comammox Nitrospira were widely distributed in the phylogeny of clade A and clade B, approximately 50.88%–76.19% and 18.32%–36.68% of clade A.1 and A.2, respectively. The potential rate of comammox bacteria was ranged from 0.131 to 3.793 mg N·kg−1 d−1 in the sediment by microcosm incubation, followed by AOB and AOA. According to the calculation, the contribution of comammox bacteria to the overall nitrification was ranged from 45.06% to 91.43%. In this study, comammox possessed a high rate in the lake sediments, which should be paid more attention on in the future.

Influence of the Hydrological Variability on Water Quality and Benthic Macroinvertebrates in a Chilean Estuary During a Megadrought

The climate crisis has accelerated the frequency and intensity of droughts in the Mediterranean areas, impacting the hydrology and the ecology of their basins. Maule River is the largest watershed in the Chilean Mediterranean Zone. The growing anthropic and environmental pressure has led to changes in the structure and function of its terrestrial ecosystem. However, little is known about its influence on aquatic ecosystems. The effect of the recent extreme drought on the streamflow and its influence on water quality and the benthic macroinvertebrate community structure were evaluated in the Maule River’s lower section. Beyond temporal and spatial fluctuations, healthy and permanently well-oxygenated waters prevailed in the study area. However, during the megadrought period, evidenced by a significant decrease in both precipitation and river streamflow, a greater salt wedge influence was observed, at least, in the last 7 km of the river. Although with certain asynchrony, a change in the structure of the benthic macroinvertebrate community was observed in the upstream stations. This marinization reveals an increase in the domain of marine taxa associated with the Polychaeta group and a clear decrease in typical freshwater Oligochaeta individuals. This modification in the structure of the benthic community is expected to affect the function of this estuarine system. The results presented here highlight the importance of considering the variability associated with biological components for the management of water resources and related ecosystem services, considering that one of the main problems associated with changes in land use and the pressures caused by the climate crisis is the decrease in the quality and availability of water in this and other Mediterranean basins globally.

A carbonate palustrine system with marshes and shallow ephemeral lakes (Campanian, northeastern Iberian Basin)

The sedimentary and stratigraphic features of the low-gradient slope carbonate palustrine system of the Fortanete Formation (northeast Spain) during the early Campanian have been studied. The succession of the Fortanete Fm provides depositional record of a progressive transition to continental settings in an area that was predominantly marine for most of the Late Cretaceous. Palustrine systems can be developed in a wide variety of environments, however, modern analogues are scarce. The Fortanete Fm thus presents a great opportunity to study the stratigraphy, the sedimentary features and isotopic composition of a palustrine–marine influenced system. A total of 10 stratigraphic sections distributed along a 40 km wide and 80 km long area have been carried out in order to decipher the facies distribution in the system. This study led to the differentiation of three palaeoenvironments based on predominant lithofacies and sedimentary structures: (1) marshes and shallow low-gradient slope lakes; (2) ephemeral lakes, lake margins and prairies with variable water level and marine influence; and (3) mudflats with evaporites and fine siliciclastic input. The Fortanete Fm serves as an excellent case study for palustrine environments with the presence of typical palustrine features such as pseudomicrokarst, brecciation, black pebbles, desiccation cracks, nodules, Microcodium, and fenestral fabric. Most palustrine systems are associated with continental freshwater settings, whereas the Fortanete Fm displays evidence of intermittent marine influence in the distal studied sections. Carbon and oxygen isotope composition is within the range of typical freshwater lake carbonates and also corresponds to isotope composition of palustrine carbonates with marine influence. The Fortanete Fm shares a number of characteristics with freshwater continental and freshwater modern analogues. Comparison with these systems provides new insights on how modern analogues can be used to decipher the complexity of the processes developing these systems in the past.

Strontium isotope analysis of otoliths reveals differences in the habitat salinity among three sympatric stickleback species of the genus Pungitius.

The analysis of otolith Sr isotope ratios (87Sr/86Sr) is a powerful method to study fish migration in freshwater areas. However, few studies have applied this method to study fish movement in brackish-water environments. Furthermore, despite the fact that habitat differentiation has been shown to drive genetic differentiation and reproductive isolation among stickleback fish, no studies have used the otolith 87Sr/86Sr ratios to analyze habitat differentiation between stickleback ecotypes and species. In this study, we analyzed the otolith 87Sr/86Sr ratios of three sympatric stickleback species of the genus Pungitius in the Shiomi River on Hokkaido Island, Japan: P. tymensis, the brackish-water type of the P. pungitius-P. sinensis complex, and the freshwater type of the P. pungitius-P. sinensis complex. First, we created a mixing equation to depict the relationship between habitat salinity and the 87Sr/86Sr ratios of river water. We found that the otolith 87Sr/86Sr ratios differed significantly among the three species, indicating that the three species utilize habitats with different salinities: P. tymensis and the brackish-water type inhabit freshwater and brackish-water environments, respectively, with the freshwater type using intermediate habitats. In addition, we found that some freshwater individuals moved to habitats with higher salinities as they grew. Our study demonstrates that the analysis of otolith 87Sr/86Sr ratios is a useful method for studying the habitat use of fish in brackish-water environments and habitat differentiation among closely related sympatric and parapatric species.