Typical Freshwater Research Articles

Organophosphate diesters (DAPs) and hydroxylated organophosphate flame retardants (HO-OPFRs) as biomarkers of OPFR contamination in a typical freshwater food chain

Organophosphate flame retardants (OPFRs) can rapidly biotransform into two types of metabolites in biota: (1) organophosphate diesters (DAPs) and (2) hydroxylated OPFRs (HO-OPFRs). Therefore, the levels of parent OPFRs alone are not sufficient to indicate OPFR pollution in biological organisms. This study analyzed 12 OPFR metabolites, including 6 DAPs and 6 HO-OPFRs, in a typical freshwater food chain consisted of crucian carp, catfish, mud carp, snakehead, and oriental river prawn. The total concentrations of OPFR metabolites were comparable to those of parent OPFRs, and ranged from 0.65 to 17 ng/g ww. Bis(2-butoxyethyl) 3′-hydroxy-2-butoxyethyl phosphate (14%–77%), di-n-butyl phosphate (DNBP) (6.7%–24%), bis(1-chloro-2-propyl) phosphate (BCIPP) (0.7%–35%), and 1-hydroxy-2-propyl bis(1-chloro-2-propyl) phosphate (BCIPHIPP) (6.0%–24%) were the major OPFR metabolites. Various aquatic species exhibited significant differences in their OPFR metabolite/parent ratios (MPR) (p < 0.05), indicating varying biotransformation potentials of different organisms for various OPFRs. The growth-independent accumulation of tri-n-butyl phosphate (TNBP), tris(chloro-2-propyl) phosphate (TCIPP), triphenyl phosphate, and 2-ethylhexyl diphenyl phosphate in mud carps could be explained by their biotransformation potential. A significant negative correlation was found between the concentration of bis(2-butoxyethyl) phosphate and δ15N values (p < 0.05), with a calculated trophic magnification factor (TMF) of 0.66. Significant positive correlations were observed between BCIPP and TCIPP (R2 = 0.25, p < 0.05), as well as between DNBP and TNBP (R2 = 0.30, p < 0.01), implying that these two DAPs could be used as biomarkers to quantitatively assess TCIPP and TNBP contamination in wild aquatic organisms.

PENINGKATAN ANGKA KONSUMSI IKAN PROVINSI JAWA TIMUR MELALUI PENGENALAN IKAN-IKAN KONSUMSI DAN PRODUK OLAHAN PERIKANAN PADA BALITA

Fisheries have an important role in society, one of which is as a food source rich in nutritional content and animal protein. Even though the fishery potential in Indonesia is very high, in fact, in several areas, the level of fish consumption is still below the national fish consumption level, one of which is in East Java. This is very ironic when compared with the fact that in 2022 East Java was the province with the highest capture fisheries production in Indonesia. Efforts that can be made to increase fish consumption in East Java are by introducing the types of fish consumed, both freshwater fish and sea fish, and introducing processed fishery products to toddlers. The method of implementing this community service activity consists of 3 (three) stages, i.e. the preparation, implementation, and reporting stages. During the implementation, the participants showed quite high enthusiasm because the event was packaged by leading illustrations accompanied by children's songs about fish. The results of the community service activities can be seen from an increase in the preferences to eat fish and an increase in toddlers' knowledge of the types of freshwater and marine fish that can be consumed.

Ingestion and egestion of microplastic by aquatic insects in Egypt wastewater

AbstractMicroplastics (MPs) are frequently regarded as environmental and biota contaminants. Yet, research on the accumulation of MPs in living entities, particularly aquatic insects that serve as food resources in the aquatic food chain, is limited. This study to investigate the accumulation of MPs in aquatic insects from water and sediment in an Egyptian wastewater basin. Four typical freshwater insect groups were used. The highest MP load per gram wet weight was reported by collector‐gatherers (Chironomus sp. and Hydrophilus sp.), followed by collector‐filterers (Culex sp.) with the second highest MP load. However, Predators (Aeshna sp.) had the lowest values. Also, the present results showed a reduction in the number of MPs in all insect taxa tested after a 24 h depuration time, with differences in the observed egestion ability. The mean number of MPs per individual significantly reduced after 24 h in both Chironomus sp. and Culex sp. larvae, where 53% and 40% of MPs particles were ejected from them, respectively. However, the ability of MP egestion decreases in Aeshna sp. nymph (25%), and the lowest proportion of ejection was observed in Hydrophilus sp. adults (9%). Polyethylene terephthalate fibers were the most abundant type of MP in both sediment and water, followed by fragments (polyethylene and polypropylene). Yet, only polyester fibers were detected in the various insect species. The average length of fibers in the various insects was somewhat shorter than in the surrounding environment. The current study reveals that MP ingestion by aquatic insects is not always related to levels of pollution in the environment, since other factors such as feeding strategies may play a role in MP ingestion. Based on these observations, further studies should be carried out on studies on toxicological impacts of MPs on freshwater/aquatic biota.

Spatial Rhythm and Periodic Pattern of Fish Species in Eniong River, South Eastern Nigeria

The spatial rhythm and periodic pattern of fish species was studied in lower and upper streams in Eniong River, Southeastern Nigeria for 12 consecutive months (April, 2019- March, 2020) using standard methods and procedures. A total of 178 individuals of fish species belonging to 14 families and 25 species were recorded in the study. The results revealed species abundance in favour of the lower stream with only two species: Clarias macromystax (Clariidae) and Malapterurus electricus (Malapteruridae) not found in the lower stream. Populations were generally bigger in lower stream 122 (69.32%) than their counterparts in upper stream with 56 (30.68%) samples. The family Cichilidae dominates the lower stream while Clariidae dominates the upper stream. The result of Jaccard Index Similarity of the number of species found between the upper stream and lower stream revealed the value of 0.461˂50%. The overall range of fish sampled falls within (9.7-25.5cmTL) with size structure generally bigger in the wet season than in the dry season. Species had seasonal abundance in the wet season than the dry season. In the wet season, Oreochromis niloticus and Clarias macromystax were the most abundant species in June and September (wet season) while Malapterurus electricus and Citharinus citharus were not found in the wet season. In the dry season, twelve (12) species were completely absent-Hepsetus akawo, Ctenopoma nebulosum, pollimyrus asperses, Marcusens senegaleusis, Ccoptodon zelli, Cclarias gariepinus, Cclarias macromystax, Synodontis obesus, Schilbe mystus, Schilbe uranoscopus and Protopterus annectens and Hemichromis fasciatus. The most abundant species found in both dry and wet seasons were Oreochromis niloticus, Chrysichthys nigrodigitatus and Hemichromis fasciatus. The fish diversity ranges from typical freshwater fishes to brackish species. The greatest dissimilarity between the wet and dry seasons’ samples was generated by Oreochromis niloticus. The study recorded the highest species richness (Margaleaf) and diversity (Shanno-Wiener) in the wet season with 23 species while the lowest with the smallest abundance was observed in the dry season with 13 species. The study recommends low exploitation in the upper stream and in the dry season to enhance species productivity and sustainability in Eniong River, Southeastern Nigeria.

Diversity, distribution, and expression of opsin genes in freshwater lakes.

Microbial rhodopsins are widely distributed in aquatic environments and may significantly contribute to phototrophy and energy budgets in global oceans. However, the study of freshwater rhodopsins has been largely limited. Here, we explored the diversity, ecological distribution, and expression of opsin genes that encode the apoproteins of type I rhodopsins in humic and clearwater lakes with contrasting physicochemical and optical characteristics. Using metagenomes and metagenome-assembled genomes, we recovered opsin genes from a wide range of taxa, mostly predicted to encode green light-absorbing proton pumps. Viral opsin and novel bacterial opsin clades were recovered. Opsin genes occurred more frequently in taxa from clearwater than from humic water, and opsins in some taxa have nontypical ion-pumping motifs that might be associated with physicochemical conditions of these two freshwater types. Analyses of the surface layer of 33 freshwater systems revealed an inverse correlation between opsin gene abundance and lake dissolved organic carbon (DOC). In humic water with high terrestrial DOC and light-absorbing humic substances, opsin gene abundance was low and dramatically declined within the first few meters, whereas the abundance remained relatively high along the bulk water column in clearwater lakes with low DOC, suggesting opsin gene distribution is influenced by lake optical properties and DOC. Gene expression analysis confirmed the significance of rhodopsin-based phototrophy in clearwater lakes and revealed different diel expressional patterns among major phyla. Overall, our analyses revealed freshwater opsin diversity, distribution and expression patterns, and suggested the significance of rhodopsin-based phototrophy in freshwater energy budgets, especially in clearwater lakes.

Unique Populations of Sulfur-Oxidizing Bacteria in Natural Cold Sulfur Springs in Slovakia

Currently, there are over 200 officially registered sulfur springs in Slovakia, most of which are cold hydrogen sulfide springs with a characteristic strong odor of rotten eggs. Their typical inhabitants are filamentous sulfur-oxidizing bacteria. The aim of this study was to identify the major bacterial populations inhabiting sulfur springs in Slovakia using a combination of non-cultivation and cultivation approaches. Non-cultivation analyses revealed high variability of sulfur-oxidizing bacteria in Slovak springs. Sulfur mats were usually dominated by chemolithotrophic sulfur-oxidizers from the phylum Proteobacteria (more than 87%), followed by photoautotrophic sulfur-oxidizers of the phylum Chlorobi. The group of nonsulfur-oxidizers was composed of typical freshwater species and bacteria with genetic potential for sulfur oxidation. The low similarity in the 16S rRNA gene sequence of the sequenced DGGE bands indicates that about half of the sulfur-oxidizing bacteria identified represent new species/genera of sulfur-oxidizing bacteria. In attempts to cultivate potential new species of sulfur-oxidizing bacteria, a very low overlap was observed between non-cultivation and cultivation analyses, and a new species of the Thiofaba genus was cultivated. Our results expand knowledge on the diversity of sulfur bacteria in cold sulfur springs in Slovakia and indicate that the diversity of sulfur-oxidizing bacteria is significantly underestimated and that sulfur springs could be inhabited by unique bacterial populations.

A national isotope survey to define the sources of nitrate contamination in New Zealand freshwaters

A national survey identifies the extent and origin of nitrates in New Zealand’s freshwater resources using nitrogen (δ15N) and oxygen (δ18O) isotopes. A comprehensive database with 1042 samples investigates freshwater type, land-use, geology, soil type and geographic effects on nitrate isotopes across New Zealand. Nitrate contamination is the biggest threat to New Zealand’s drinking water resources with almost 60 % of samples in the study having above-baseline nitrate (NO3-N) concentrations >0.9 mg/L, a threshold noted for higher colorectal cancer risk. Groundwater (2.89 mg/L) had higher median NO3-N concentration than surface water (0.65 mg/L). Traditional nitrate isotope biplots based on the Haber-Bosch cycle (which integrates synthetic fertilizers into the food chain), are reinterpreted to place New Zealand’s unique farming nitrogen contributions from urea and ammonia into context. The majority of New Zealand’s freshwater nitrate isotopes lie in a Normal-Nitrogen-Retention (NNR) zone which also acts as a Mixed Urea-Urine-Fertilizer (Mixed UUF) zone, transitioning nitrified fertilizers and animal waste via redox reactions, microbial action and/or dissipation towards a denitrification zone. Nitrogen ‘hot spots’ with strong urea/urine input can be differentiated from natural N cycling in the NNR/Mixed UUF transition zone by a combined NO3-N concentration and dual isotope approach to identify high-risk sites.

FACIES ANALYSIS AND PALAEODEPOSITIONAL ENVIRONMENT OF THE TANJONG FORMATION IN THE KALABAKAN AREA, SOUTHEAST SABAH

An integrated approach is adopted to study the sedimentary deposits of the well-exposed Early to Middle Miocene Tanjong Formation in the Southeastern part of Sabah. The integrated sedimentological and palynological data will provide a better insight into the depositional architecture of the area. This work presents the first detailed sedimentological facies analysis of the Tanjong Formation within the Kalabakan area. The integration of facies analysis, ichnological and palynological data provide a better evaluation of the organic matter (OM) origin and the reconstruction of the palaeodepositional model. An extensive outcrop-based sedimentological facies analysis was performed on eight (8) well-exposed outcrops with studied stratigraphic sections. Seven facies associations are classified in the Tanjong Formation from twelve lithofacies elements which have been interpreted from the fluvialdeltaic to shallow marine environment: FA1 - Floodplain facies association; FA2 – Fluvial channel facies association; FA3 - Coastal swamps facies association; FA4 – Tidal flat facies association; FA5 – Delta front facies association; FA6 – Mouth bar facies association; FA7 - Upper shoreface facies association. The palynomorphs of the studied coal samples yielded abundant mangrove and freshwater types of pollen assemblage, while the analysed mudstone samples suggest deposition within a lower coastal plain setting with proximity to the marine environment. The presence of Florschuetzia levipoli (Sonneratia caseolaris) and Florschuetzia trilobata suggest an age not older than the Early Miocene and/or younger. The reconstructed palaeodepositional environment model is essential in improving the predictability of the petroleum system mechanisms and the hydrocarbon potential for conventional petroleum exploration.Keywords: Sedimentology, facies association, fluvial-deltaic, shallow marine, geochemical, palynology

Exploring the Impacts of Full-Scale Distribution System Orthophosphate Corrosion Control Implementation on the Microbial Ecology of Hydrologically Connected Urban Streams.

Many cities across the nation are plagued by lead contamination in drinking water. As such, many drinking water utilities have undertaken lead service line (LSL) replacement to prevent further lead contamination. However, given the urgency of lead mitigation, and the socioeconomic challenges associated with LSL replacement, cities have used phosphate-based corrosion inhibitors (i.e., orthophosphate) alongside LSL replacement. While necessary to ensure public health protection from lead contamination, the addition of orthophosphate into an aging and leaking drinking water system may increase the concentration of phosphate leaching into urban streams characterized by century-old failing water infrastructure. Such increases in phosphate availability may cascade into nutrient and microbial community composition shifts. The purpose of this study was to determine how this occurs and to understand whether full-scale distribution system orthophosphate addition impacts the microbial ecology of urban streams. Through monthly collection of water samples from five urban streams before and after orthophosphate addition, significant changes in microbial community composition (16S rRNA amplicon sequencing) and in the relative abundance of typical freshwater taxa were observed. In addition, key microbial phosphorus and nitrogen metabolism genes (e.g., two component regulatory systems) were predicted to change via BugBase. No significant differences in the absolute abundances of total bacteria, Cyanobacteria, and "Candidatus Accumulibacter" were observed. Overall, the findings from this study provide further evidence that urban streams are compromised by unintentional hydrologic connections with drinking water infrastructure. Moreover, our results suggest that infiltration of phosphate-based corrosion inhibitors can impact urban streams and have important, as-yet-overlooked impacts on urban stream microbial communities. IMPORTANCE Elevated lead levels in drinking water supplies are a public health risk. As such, it is imperative for cities to urgently address lead contamination from aging drinking water supplies by way of lead service line replacements and corrosion control methods. However, when applying corrosion control methods, it is also important to consider the chemical and microbiological effects that can occur in natural settings, given that our water infrastructure is aging and more prone to leaks and breaks. Here, we examine the impacts on the microbial ecology of five urban stream systems before and after full-scale distribution system orthophosphate addition. Overall, the results suggest that infiltration of corrosion inhibitors may impact microbial communities; however, future work should be done to ascertain the true impact to protect both public and environmental health.

Ecotoxicological effects of the antidepressant fluoxetine and its removal by the typical freshwater microalgae Chlorella pyrenoidosa

The antidepressant fluoxetine (FLX) has gained increasing attention due to its frequent detection in aquatic environments and negative effects on non-target organisms. However, knowledge on the ecotoxicological effects of FLX and its removal by microalgae is still limited. In this study, the ecotoxicological effects of FLX (10-1000μg/L) were assessed using batch cultures of the freshwater microalgae Chlorella pyrenoidosa for 10 days based on changes in growth, antioxidant response, and photosynthetic process. The removal efficiency, removal mechanism, and degradation pathway of FLX by C. pyrenoidosa were also investigated. The results showed that the growth of C. pyrenoidosa was inhibited by FLX with a 4 d EC50 of 0.464mg/L. Additionally, FLX significantly inhibited photosynthesis and caused oxidative stress on day 4. However, C. pyrenoidosa can produce resistance and acclimatize to FLX, as reflected by the declining growth inhibition rate, recovered photosynthetic efficiency, and disappearance of oxidative stress on day 10. Despite the toxicity of FLX, C. pyrenoidosa showed 41.2%-100% removal of FLX after 10 days of exposure. Biodegradation was the primary removal mechanism, accounting for 88.2%-92.8% of the total removal of FLX. A total of five metabolites were found in the degradation processes of FLX, which showed less toxicity than FLX. The main degradation pathways were proposed as demethylation, O-dealkylation, hydroxylation, and N-acylation. Our results not only highlight the potential application of microalgae in FLX purification, but also provide insight into the fate and ecological risk of FLX in aquatic environments.

Spatiotemporal variations of dissolved CH4 concentrations and fluxes from typical freshwater types in an agricultural irrigation watershed in Eastern China

Inland freshwater ecosystems are of increasing concerns in global methane (CH4) budget in the atmosphere. Agricultural irrigation watersheds are a potential CH4 emission hotspot owing to the anthropogenic carbon and nutrients loading. However, large-scale spatial variations of CH4 concentrations and fluxes in agricultural catchments remain poorly understood, constraining an accurate regional estimate of CH4 budgets. Here, we examined the spatiotemporal variations of dissolved CH4 concentrations and fluxes from typical freshwater types (ditch, reservoir and river) within an agricultural irrigation watershed from Hongze catchment, which is subjected to intensive agricultural and rural activities in Eastern China. The dissolved CH4 concentrations and fluxes showed similar temporal variations among the three freshwater types, with the highest rates in summer and the lowest rates in winter. The total CH4 emission from this agricultural irrigation watershed was estimated to be 0.002 Gg CH4 yr−1, with annual mean CH4 concentration and flux of 0.12 μmol L−1 and 0.58 mg m−2 d−1, respectively. Diffusive CH4 fluxes varied in samples taken from different freshwater types, the annual mean CH4 fluxes for ditch, reservoir and river were 0.31 ± 0.06, 0.71 ± 0.13 and 0.72 ± 0.25 mg m−2 d−1, respectively. Among three freshwater types, the CH4 fluxes were the lowest in ditch, which was associated with the lowest responses of CH4 fluxes to water dissolved oxygen (DO), nitrate nitrogen (NO3−-N) and sediment dissolved organic carbon (DOC) concentrations in ditch. In addition, water velocity and wind speed were significantly lower in ditch than in reservoir and river, suggesting that they also played important roles in explaining the spatial variability of dissolved CH4 concentrations and fluxes. These results highlighted a need for more field measurements with wider spatial coverage and finer frequency, which would further improve the reliability of flux estimates for assessing the contribution of agricultural watersheds to the regional and global CH4 budgets.

Historical Global Review of Acid-Volatile Sulfide Sediment Monitoring Data

Acid-volatile sulfides (AVS) are strongly associated with the bioavailability of some divalent metals such as cadmium, copper, lead, nickel and zinc. However, the global spatial variability of AVS for aquatic systems is unknown. The specific goals of this study were to: (1) summarize all available AVS monitoring data from all types of freshwater and saltwater waterbodies (streams/creeks, rivers, lakes/ponds/reservoirs and estuarine/marine areas) and (2) compare AVS concentrations from these various types of waterbodies considering both soil type classification and biomes. AVS measurements were reported from 21 different countries. A total of 17 different soil types were reported for all waterbody types and both podzols and luvisols were found in all waterbody types. Nine different biomes were sampled for all waterbody types. The temperate broadleaf and mixed forest biome was sampled for AVS in all waterbody types. Mean AVS concentrations ranged from 0.01 to 503 µmoles/g for 140 different waterbody types and the 90th centile for all these waterbodies was 49.4 µmoles/g. A ranking of waterbody type means from low to high AVS measurements showed the lowest mean value was reported for streams/creeks (5.12 µmoles/g; range from 0.1 to 39.8 µmoles/g) followed by lakes/ponds/reservoirs (11.3 µmoles/g; range from 0.79 to 127 µmoles/g); estuarine/marine areas (27.2 µmoles/g; range from 0.06 to 503 µmoles/g) and rivers (27.7 µmoles/g; range from 1.13 to 197 µmoles/g). The data provided in this study are compelling as it showed that the high variability of AVS measurements within each waterbody type as well as the variability of AVS within specific locations were often multiple orders of magnitude differences for concentration ranges. Therefore, a comprehensive spatial and temporal scale sampling of AVS in concert with divalent metals analysis is critical to avoid possible errors when evaluating the potential ecological risk of divalent metals in sediment.

Triple immunochromatographic test system for detection of priority aquatic toxins in water and fish.

Aquatic toxins are a group of toxic compounds produced by several types of freshwater and marine algae and cyanobacteria and transported through the food chains of water bodies. Potential contamination of aquaculture products (raw and processed fish and seafood) with aquatic toxins requires the use of efficient screening methods for their control. In this study, a multiplex immunochromatographic test system for the simultaneous detection of three aquatic toxins-phycotoxins domoic acid (DA) and okadaic acid (OA), and cyanotoxin microcystin-LR (MC-LR)-is for the first time developed. For this, a competitive indirect immunochromatographic analysis (ICA) based on gold-labeled secondary antibodies was carried out. The LODs/cutoffs/working ranges of the ICA were 0.05/0.3/0.07-0.29, 1.3/100/3.2-58.2, and 0.1/2.0/0.2-1.1ng/mL for MC-LR, DA, and OA, respectively. The assay duration was 18min. The developed test system was used to analyze water samples from natural sources (salt and fresh water) and fish samples. For sample preparation of water, simple dilution with a buffer was proposed; for fish samples, methanol-water extraction was utilized. It was demonstrated that the triple LFIA specifically detected target aquatic toxins with recoveries of 85.0-121.5%. The developed multiplex LFIA can be considered a promising analytical solution for the rapid, easy, and sensitive control of water and food safety.

Distribution of SOCD along different offshore distances in China's fresh-water lake-Chaohu under different habitats

Carbon storage in wetland ecosystems is an important part of the carbon cycle of terrestrial ecosystems and provides important ecosystem services. Chaohu Wetland is a typical freshwater lake wetland in China. In this study, soil and plant samples were collected every 500 m through three sample lines of different vegetation habitats (estuarine banks, woodlands and shrub beaches) and different offshore distances, revealing the spatial distribution characteristics of soil organic carbon density (SOCD) in Chaohu wetland. The overall SOCD of Chaohu wetland was low, with different habitats ranking as Woodland > Estuary and riverside > Shrub and beach. SOCD of different offshore distances had no obvious law, and the SOCD decreased significantly with soil depth. The plant biomass was significantly higher at the woodland habitat than at other habitats. Most of soil nutrient indicators were the highest at the woodland habitat, while the estuary-riverside habitat had the highest N and P contents. Soil and plant nutrients at different offshore distances had no obvious change patterns. The contents of soil K, Ca, Mg, and N were significantly positively correlated with SOCD, but soil bulk density and pH were significantly negatively correlated with SOCD, and vegetation P content was significantly negatively correlated with SOCD. The spatial pattern of SOCD changes in this lake coastal wetland was determined by the combined effects of plant nutrients, biomass, and soil physical and chemical properties. Our results indicate Chaohu wetlands may have been experiencing serious degradation. The SOCD of Chaohu wetland is lower than that of other wetlands in China, which is mainly affected by human activities. Different offshore distances and habitat heterogeneity are the main factors affecting the soil carbon cycle of the wetland.

Biodegradation of microplastic in freshwaters: A long-lasting process affected by the lake microbiome.

Plastics have been produced for over a century, but definitive evidence of complete plastic biodegradation in different habitats, particularly freshwater ecosystems, is still missing. Using 13 C-labelled polyethylene microplastics (PE-MP) and stable isotope analysis of produced gas and microbial membrane lipids, we determined the biodegradation rate and fate of carbon in PE-MP in different freshwater types. The biodegradation rate in the humic-lake waters was much higher (0.45% ± 0.21% per year) than in the clear-lake waters (0.07% ± 0.06% per year) or the artificial freshwater medium (0.02% ± 0.02% per year). Complete biodegradation of PE-MP was calculated to last 100-200 years in humic-lake waters, 300-4000 years in clear-lake waters, and 2000-20,000 years in the artificial freshwater medium. The concentration of 18:1ω7, characteristic phospholipid fatty acid in Alpha- and Gammaproteobacteria, was a predictor of faster biodegradation of PE. Uncultured Acetobacteraceae and Comamonadaceae among Alpha- and Gammaproteobacteria, respectively, were major bacteria related to the biodegradation of PE-MP. Overall, it appears that microorganisms in humic lakes with naturally occurring refractory polymers are more adept at decomposing PE than those in other waters.

Plastisphere in lake waters: Microbial diversity, biofilm structure, and potential implications for freshwater ecosystems

Once dispersed in water, microplastic (MP) particles are rapidly colonised by aquatic microbes, which can adhere and grow onto solid surfaces in the form of biofilms. This study provides new insights on microbial diversity and biofilm structure of plastisphere in lake waters. By combining Fourier Confocal Laser Scanning Microscopy (CLSM), Transform Infrared Spectroscopy (FT-IR) and high-throughput DNA sequencing, we investigated the microbial colonization patterns on floating MPs and, for the first time, the occurrence of eukaryotic core members and their possible relations with biofilm-forming bacterial taxa within the plastisphere of four different lakes. Through PCR-based methods (qPCR, LAMP-PCR), we also evaluated the role of lake plastisphere as long-term dispersal vectors of potentially harmful organisms (including pathogens) and antibiotic resistance genes (ARGs) in freshwater ecosystems. Consistent variation patterns of the microbial community composition occurred between water and among the plastisphere samples of the different lakes. The eukaryotic core microbiome was mainly composed by typical freshwater biofilm colonizers, such as diatoms (Pennales, Bacillariophyceaea) and green algae (Chlorophyceae), which interact with eukaryotic and prokaryotic microbes of different trophic levels. Results also showed that MPs are suitable vectors of biofilm-forming opportunistic pathogens and a hotspot for horizontal gene transfer, likely facilitating antibiotic resistance spread in the environments.

Groundwater characterization and non-carcinogenic and carcinogenic health risk assessment of nitrate exposure in the Mahanadi River Basin of India

Agriculture is the mainstay of India's economy and chemical fertilizers have been extensively used to meet increasing demands. Anthropogenic interventions at the soil surface, especially the application of nitrogenous fertilizers in agricultural fields, provide essential nutrients but become major pollutant sources in terrestrial ecosystems and aquatic environments. Groundwater samples from phreatic aquifers of the Mahanadi River Basin, Chhattisgarh, India, showed that the Ca2+-Mg2+-HCO3ˉ freshwater type dominates, followed by the Ca2+-Mg2+-Clˉ and Na+-HCO3ˉ types. Increasing trends in the ionic ratios of (NO3ˉ+Clˉ)/HCO3ˉ over TDS and of NO3ˉ/Clˉ over Clˉ indicated the significant impact of anthropogenic pollution on groundwater contamination. Deterministic and probabilistic approaches were used to assess the non-carcinogenic and carcinogenic health risks of nitrate to children and adults. Both approaches produced the same results and indicated children were more prone to non-carcinogenic health risk than adults. An excess gastric cancer risk (ER) exposure model showed that approximately 42% of the groundwater samples had a non-negligible ER (1.00 × 10−4 to 1.00 × 10−5). Sensitivity analysis indicated groundwater nitrate concentration, ingestion rate, and the percentage of nitrite from nitrate were the most significant variables in determining HI and ER. It is suggested to adopt proper management of control policies for reducing the elevated groundwater nitrate concentration in the present study area.

Chemodynamic features of nickel(II) and its complexes: Implications for bioavailability in freshwaters

A robust description of the bioavailability of Ni(II) in freshwaters is fundamental for the setting of environmental quality standards. Current approaches assume that bioavailability is governed by the equilibrium concentration of the free metal ion in the bulk aqueous medium. Such strategies generally have limited predictive value: a suite of empirical fitting parameters is required to deal with variations in water chemistry. Herein we compile data on Ni(II) speciation under typical freshwater conditions and compute the lability of Ni(II) complexes with typical molecular and nanoparticulate components of dissolved organic carbon. In combination with an analysis of the kinetic setting of Ni(II) biouptake by freshwater organisms, we assess the potential contribution from dissociation of Ni(II) complexes to the diffusive supply flux of free Ni2+. The strategy takes into account the absolute and relative magnitudes of the Michaelis-Menten bioaffinity and bioconversion parameters for a range of freshwater organisms, together with dynamic chemical speciation descriptors under environmentally relevant conditions. The results show that the dissociation kinetics of Ni(II) complexes play a crucial role in buffering the free metal ion concentration at the biointerface. Our results highlight the need to couple the timescales of chemical reactivity with those of biouptake to properly identify the bioavailable fraction of Ni(II) in freshwaters.

Salinity and seasonality shaping free-living and particle-associated bacterioplankton community assembly in lakeshores of the northeastern Qinghai-Tibet Plateau

Microorganisms in lakeshore zones are essential for pollution interception and biodiversity maintenance. However, the biogeographic patterns of bacterioplankton communities in lakeshore zones and the mechanisms that driving them are poorly understood. We analyzed the 16 S rRNA gene sequences of particle-associated (PA) and free-living (FL) bacterioplankton communities in the lakeshore zones of 14 alpine lakes in two seasons on Qinghai-Tibet Plateau to investigate the bacterial diversity, composition and assembly processes. Our results revealed that PA and FL bacterioplankton communities were driven by both seasonality and salinity in the lakeshores on Qinghai-Tibet Plateau. Compared to FL bacterioplankton, PA bacterioplankton communities were more susceptible to seasonality than spatial salinity. FL bacterioplankton communities were more salinity constrained than the PA counterpart. Besides, the Stegen null model analyses have validated a quantitative bias on stochastic processes at different spatial scales. At a regional scale, stochasticity was the predominant assembly process in both PA and FL bacterioplankton. While at a subregional scale, dispersal limitation was the main contributor of stochastic processes for PA bacterioplankton in summer and heterogeneous selection was the dominant deterministic processes in winter, whereas the community assembly of FL bacterioplankton was more stochastic processes (i.e., dispersal limitation) dominated in the freshwater type but deterministic process (i.e., heterogeneous selection) increased with increasing salinity. Our study provides new insights into both significant spatiotemporal patterns and distinct assembly processes of PA and FL bacterioplankton in alpine lakeshores on the northeastern Qinghai-Tibet Plateau.

Chromosome-level genome of Pedinomonas minor (Chlorophyta) unveils adaptations to abiotic stress in a rapidly fluctuating environment.

The Pedinophyceae (Viridiplantae) comprise a class of small uniflagellate algae with a pivotal position in the phylogeny of the Chlorophyta as the sister group of the 'core chlorophytes'. We present a chromosome-level genome assembly of the freshwater type species of the class, Pedinomonas minor. We sequenced the genome using Pacbio, Illumina and Hi-C technologies, performed comparative analyses of genome and gene family evolution, and analyzed the transcriptome under various abiotic stresses. Although the genome is relatively small (55 Mb), it shares many traits with core chlorophytes including number of introns and protein-coding genes, messenger RNA (mRNA) lengths, and abundance of transposable elements. Pedinomonas minor is only bounded by the plasma membrane, thriving in temporary habitats that frequently dry out. Gene family innovations and expansions and transcriptomic responses to abiotic stresses have shed light on adaptations of P. minor to its fluctuating environment. Horizontal gene transfers from bacteria and fungi have possibly contributed to the evolution of some of these traits. We identified a putative endogenization site of a nucleocytoplasmic large DNA virus and hypothesized that endogenous viral elements donated foreign genes to the host genome, their spread enhanced by transposable elements, located at gene boundaries in several of the expanded gene families.