Freshwater Sites Research Articles

Impact of salinity gradient, water pollution and land use types on greenhouse gas emissions from an urbanized estuary

Estuaries have been recognized as one of the major sources of greenhouse gases (GHGs) in aquatic systems; yet we still lack insights into the impact of both anthropogenic and natural factors on the dynamics of GHG emissions. Here, we assessed the spatiotemporal dynamics and underlying drivers of the GHG emissions from the Scheldt Estuary with a focus on the effects of salinity gradient, water pollution, and land use types, together with their interaction. Overall, we found a negative impact of salinity on carbon dioxide (CO2) and nitrous oxide (N2O) emissions which can be due to the decrease of both salinity and water quality when moving upstream. Stronger impact of water pollution on the GHG emissions was found at the freshwater sites upstream compared to saline sites downstream. In particular, when water quality of the sites reduced from good, mainly located in the mouth and surrounded by arable sites, to polluted, mainly located in the upstream and surrounded by urban sites, CO2 emissions from the sites doubled while N2O emissions tripled. Similarly, the effects of water pollution on methane (CH4) emissions became much stronger in the freshwater sites compared to the saline sites. These decreasing effects from upstream to the mouth were associated with the increase in urbanization as sites surrounded by urban areas released on average almost two times more CO2 and N2O than sites surrounded by nature and industry areas. Applied machine learning methods also revealed that, in addition to salinity effects, nutrient and organic enrichment stimulated the GHG emissions from the Scheldt Estuary. These findings highlight the importance of the interaction between salinity, water pollution, and land use in order to understand their influences on GHG emissions from dynamic estuarine systems.

Joint Biodiversity Management Committees: A Mechanism to Manage and Conserve Eco-Regions

Sasthamkotta Lake eco-region is a freshwater Ramsar site in Kerala, India. Eco-regions are ecologically and geographically defined larger land or water mass areas with a characteristic assemblage of the ecosystem and significant biodiversity. A decentralized and locally self-sustaining mechanism has been achieved in managing this eco-region by a participatory model through a joint Biodiversity Management Committee (jBMC) constitution. BMCs are custodians of the environment, and biodiversity, confined to a village/Panchayat, as per Convention on Biological Diversity (CBD) guidelines and the Indian Biodiversity Act. This jBMC constitutes a network of statutory biodiversity experts from the BMCs of three Local Self Governments (LSGs) or Panchayath administrations, where the Sasthamkotta Lake is located. It has been formed to develop strategies to manage and conserve the freshwater lake and its biodiversity. The management action plan proposed by the jBMC for the Sasthamkotta Ramsar site includes systematic and continuous assessment of the current biodiversity status, identifying and mitigating threats, appropriate use of its resources for eco-restoration and better administrative programs for biodiversity enhancement. Our case study shows that the conservation model of a Ramsar site Eco-region is successful and could be replicated in other damaged natural ecosystems which need attention, for a sustainable future.

Bioaccumulation of chemical elements at post-industrial freshwater sites varies predictably between habitats, elements and taxa: A power law approach

Elevated environmental levels of elements originating from anthropogenic activities threaten natural communities and public health, as these elements can persist and bioaccumulate in the environment. However, their environmental risks and bioaccumulation patterns are often habitat-, species- and element-specific. We studied the bioaccumulation patterns of 11 elements in seven freshwater taxa in post-mining habitats in the Czech Republic, ranging from less polluted mining ponds to highly polluted fly ash lagoons. We found nonlinear, power-law relationships between the environmental and tissue concentrations of the elements, which may explain differences in bioaccumulation factors (BAF) reported in the literature. Tissue concentrations were driven by the environmental concentrations in non-essential elements (Al, As, Co, Cr, Ni, Pb and V), but this dependence was limited in essential elements (Cu, Mn, Se and Zn). Tissue concentrations of most elements were also more closely related to substrate than to water concentrations. Bioaccumulation was habitat specific in eight elements: stronger in mining ponds for Al and Pb, and stronger in fly ash lagoons for As, Cu, Mn, Pb, Se, V and Zn, although the differences were often minor. Bioaccumulation of some elements further increased in mineral-rich localities. Proximity to substrate, rather than trophic level, drove increased bioaccumulation levels across taxa. This highlights the importance of substrate as a pollutant reservoir in standing freshwaters and suggests that benthic taxa, such as molluscs (e.g., Physella) and other macroinvertebrates (e.g., Nepa), constitute good bioindicators. Despite the higher environmental risks in fly ash lagoons than in mining ponds, the observed ability of freshwater biota to sustain pollution supports the conservation potential of post-industrial sites. The power law approach used here to quantify and disentangle the effects of various bioaccumulation drivers may be helpful in additional contexts, increasing our ability to predict the effects of other contaminants and environmental hazards on biota.

Macroparasite Communities with Special Attention to Invasive Helminths in European Eels Anguilla anguilla from Freshwaters and Brackish Lagoons of a Mediterranean Island

An extensive survey of macroparasites in 320 European eel Anguilla anguilla (Linnaeus, 1758) was conducted in two brackish lagoons and eleven freshwater localities in the Mediterranean island of Corsica (France) between spring 2021 and winter 2021–2022. It resulted in the identification of nineteen parasites: two Monogea, four Digenea, one Copepoda, four Acanthocephala, three Cestoda, and five Nematoda, including the first geographical records, as Corsican freshwater sites were studied for the first time. The silvering stage was determined, and the eels were aged through otolithometry to compare parasite communities. Classic parasitology indices, a multivariate analysis, and an analysis of indicator values (IndVal) showed clear preferences towards the host’s habitat and salinity. Seasonal variations were shown for several parasites. A dataset from the same two coastal lagoons was used to study the changes in the parasite communities over the last decade, and this showed an increase in the prevalence and abundance of three invasive helminth species: the Monogenea Pseudodactylogyrus bini (Kikuchi, 1929), Pseudodactylogyrus anguillae (Yin and Sproston, 1948) Gusev, 1965 and the Nematoda Anguillicola crassus Kuwahara, Niimi, and Itagaki, 1974. These pathogenic parasites were found in all sampled localities, except for the two Monogenea in the polyhaline-to-euhaline Urbino lagoon. It is thus advised that future management measures take into account the environmental preferences of the most concerning parasites.

Trematode Cercariae from Lymnaea gedrosiana in the Caspian Sea Littoral in Iran: a one health concern.

Lymnaea gedrosiana snails are hosts to a variety of trematode cercaria of public and veterinary health importance. In Guilan Province, Iran, a region with a high level of fish and bird farming and wetlands important for migratory birds, little is known about the trematode cercaria from L. gedrosiana. From April 2020 to October 2021, six freshwater sites in Guilan Province were sampled for Lymnaeidae snails three times per season (spring, summer, autumn and winter). Snails were exposed to light and heat to induce cercaria shedding and shredded cercaria were identified morphologically and molecularly. In total, 5,712 Lymnaeidae snails were collected of which 3,288 (57.6%) were identified to be L. gedrosiana with 54.3% containing trematode cercaria. Snail and cercaria recovery were highest in the spring and summer. Trematode cercaria identified included Telorchis assula, Hypoderaeum conoideum, Apharyngostrigea pipientis, Sanguinicola cf. inermis, Opisthioglyphe ranae, Diplostomum pseudospathaceum, and Australapatemon burti. The four trematodes D. pseudospathaceum, S. inermis, A. burti, and A. pipientis have not been previously reported in Iran; all four of these can infect migratory birds. The most common cercaria found, H. conoideum (18.3% of the snails) is of zoonotic importance. The third most common cercaria found, S. inermis (10.0% of the snails) is detrimental to fish production. Given the importance of the wetlands in the region for wildlife and migratory birds as well as the number of fish and bird farms in the area, efforts to control L. gedrosiana snails are needed to protect wildlife and human health. In addition, monitoring programs should be implemented to identify and prevent introductions of new trematode species.

Mixtures of sediment chemical contaminants at freshwater sampling sites across Europe with different contaminant burdens

Extended chemical analyses of fluvial sediments were undertaken to establish the key pollutant pressures and mixtures present across nine European Union inland waterways. A wide range of chemical components and physical parameters were investigated including substances from the EU Priority List and Watch List. The data set was examined for key indicator compounds, however it was found that a wide range of pollution pressures were present in the different sediments including organic hydrocarbons, metal(loid)s, nutrients, polycyclic aromatic hydrocarbon (PAH), polychlorinated biphenyl (PCB) compounds, perfluoroalkyl and polyfluoroalkyl substances and pesticides, some of which exceeded regulatory guidance at different sampling points. The presence of such a wide range of compounds underpins the complex chemical composition of sediments that have acted as sinks for many decades absorbing contaminants from urban, industrial and agricultural sources. This dataset has been used to describe average overall toxicity of the sediments sampled, a calculation which was based on key components identified by Principal Component Analysis (PCA) and for those that had existing freshwater sediment regulatory values. A total of 33 components were used including PCBs, PAHs, metal(iod)s and pesticides. This analysis reflected the contamination of each site, with most indicating some level of toxicity during the sampling period. Watch List chemicals triclosan (TCS) and diclofenac (DIC) were also investigated; levels were relatively low, typically 10–100's ng L−1, however they were present at all sampling sites. The dataset is available as a resource for future chemical, and toxicological, sediment analysis comparisons.

Seascape genomics reveals limited dispersal and suggests spatially varying selection among European populations of sea lamprey (Petromyzon marinus).

Sea lamprey Petromyzon marinus is an anadromous and semelparous fish without homing behaviors. Despite being a freshwater, free-living organism for a large part of their life cycle, its adulthood is spent as a parasite of marine vertebrates. In their native European range, while it is well-established that sea lampreys comprise a single nearly-panmictic population, few studies have further explored the evolutionary history of natural populations. Here, we performed the first genome-wide characterization of sea lamprey's genetic diversity in their European natural range. The objectives were to investigate the connectivity among river basins and explore evolutionary processes mediating dispersal during the marine phase, with the sequencing of 186 individuals from 8 locations spanning the North Eastern Atlantic coast and the North Sea with double-digest RAD-sequencing, obtaining a total of 30,910 bi-allelic SNPs. Population genetic analyses reinforced the existence of a single metapopulation encompassing freshwater spawning sites within the North Eastern Atlantic and the North Sea, though the prevalence of private alleles at northern latitudes suggested some limits to the species' dispersal. Seascape genomics suggested a scenario where oxygen concentration and river runoffs impose spatially varying selection across their distribution range. Exploring associations with the abundance of potential hosts further suggested that hake and cod could also impose selective pressures, although the nature of such putative biotic interactions was unresolved. Overall, the identification of adaptive seascapes in a panmictic anadromous species could contribute to conservation practices by providing information for restoration activities to mitigate local extinctions on freshwater sites.

Morphometric and Meristic Variations of Mystus albolineatus Roberts, 1994 in the Mekong Delta, Vietnam

This study contributed to investigating the changes in morphometric and meristic variations in Mystus albolineatus at two different sites in the Mekong Delta (VMD). This is a high economic-value fish species in the region. The study was conducted for 12 months (03/2022 - 02/2023) at two sites along the Hau River (a branch of the Mekong River) with different environmental characteristics, including a freshwater site year-round at Cai Rang (Can Tho City) and a site affected by saltwater intrusion during the dry season at Long Phu (Soc Trang province). Fish samples were collected using different fishing gear of various sizes. The results obtained 825 individuals (443 females and 382 males) at both sites (408 at Cai Rang and 417 at Long Phu). Through the analysis process, it was found that the total length (TL) and weight (W) of this fish species were significantly influenced by gender and season. Both parameters were significantly higher in females (TL:11.13±0.09 SE cm; W: 10.17±0.06 SE g) than in males (TL: 10.68±0.10 SE cm; W: 9.95±0.07 SE g). Meanwhile, during the dry season (TL: 10.15±0.10 SE cm; W: 9.58±0.08 SE g), the fish had lower length and weight compared to the wet season (TL: 11.42±0.08 SE cm; W: 10.39±0.05 SE g). The interaction between gender and season also significantly affected the TL of Mystus albolineatus. In addition, eye diameter (ED), eye distance (DE), body height (BH), head length (HL), ED/HL, DE/HL, BH/TL, and HL/TL all showed significant differences by gender and season. The results of this study on the morphological characteristics of this fish species indicate that it adapts well to the environment at both research sites. The findings of this study provide basic data on the variation in morphological characteristics of Mystus albolineatus in the VMD region.

Synthesizing historic and current evidence for anadromy in a northern pike (Esox lucius L.) meta-population inhabiting brackish lagoons of the southern Baltic Sea, with implications for management

Pike (Esox lucius) populations across the central and southern Baltic Sea have undergone declines in recent decades. The underlying reasons are not fully understood but the loss of access to freshwater habitats in tributaries to brackish lagoons may be one important factor in some localities. Our objective was to synthesize evidence for the presence of historic and contemporary anadromy in pike from the brackish lagoon systems around the Fischland-Darß-Zingst peninsula and the islands of Hiddensee, Rügen and Usedom (Germany) by combining a review of grey literature, interviews with local citizens with knowledge tracing back to the mid-20th century, and field studies based on a range of methods, including telemetry, fyke netting and electrofishing of tributaries during the spawning seasons in the years 2020–2022. Genetic analyses were used to validate the existence of reproductively isolated subpopulations among pike migrating into different streams. The collective findings confirm the existence of freshwater spawning activity and genetic subpopulations across the entire study system in a multitude of tributaries, streams and ditches, but many populations appear to be small. The prevalence of anadromy across tributaries has likely suffered from water management activities in the 1970s and 1980s that blocked access to many rivers, ditches, streams and wetlands. Reduced access to freshwater streams through migration barriers associated with wetland management and agriculture could have fostered selection pressures to fully recruit in brackish environments, at the cost of declines and perhaps even local extinctions of once abundant anadromous subpopulations, most likely reducing stock resilience through the loss of genetic diversity and biocomplexity. Restoration of wetlands and access to freshwater spawning sites to recover subpopulations and anadromy can be recommended.

Freshwater Lichens, Including New Species in the Genera Verrucaria, Placopyrenium and Circinaria, Associated with Lobothallia hydrocharis (Poelt & Nimis) Sohrabi & Nimis from Watercourses of Sardinia

This work summarizes the results of the exploration of freshwater lichen biota on the island of Sardinia associated with the regional flagship species Lobothallia hydrocharis, a large-sized crustose lichen from the splash zone along mountain streams, so far known from Sardinia only. Molecular data were used to confirm its distinctiveness from other taxa and its systematic placement and to identify critical taxa among its associated lichen biota. We found 25 species of lichenized fungi, including three species new to science in the genera Verrucaria, Placopyrenium, and Circinaria, and seven species new to Sardinia (Hydropunctaria rheithrophila, Ionaspis chrysophana, I. odora, Verrucaria aquatilis, V. collematodes, V. pseudovirescens), or new to Southern Europe (V. devensis). Specific traits for the freshwater lichen biota of Sardinia were identified and compared to those reported from freshwater sites in the Alps and Carpathian mountains, e.g., a relative scarcity of subgelatinous lichens. Parasitic or epilichenic interactions were found frequently but only in the splash zone and not in the permanently submerged zone, i.e., two parasitic Placopyrenium species, and clearly lichenicolous thalli of Kuettlingeria atroflava and Lobothallia hydrocharis. Due to its specific trait profile and the great potential for the discovery of new species, we recommend the inclusion of Sardinian and further Mediterranean sites in continental-scale monitoring programs for freshwater lichens.

Isolation and characterization of algicidal bacteria from freshwater aquatic environments in China.

Algicidal bacteria can inhibit the growth of algae or lyse algal cells, thus playing roles in shaping aquatic microbial communities and maintaining the functions of aquatic ecosystems. Nevertheless, our understanding of their diversities and distributions remains limited. In this study, we collected water samples from 17 freshwater sites in 14 cities in China and screened a total of 77 algicidal bacterial strains using several prokaryotic cyanobacteria and eukaryotic algae as target strains. According to their target-specificities, these strains were classified into three subgroups, cyanobacterial algicidal bacteria, algal algicidal bacteria, and broad-target algicidal bacteria, each displaying distinctive compositions and geographical distribution patterns. They are assigned to Proteobacteria, Firmicutes, Actinobacteria, and Bacteroidetes bacterial phyla, of which Pseudomonas and Bacillus are the most abundant gram-negative and gram-positive genus, respectively. A number of bacterial strains, such as Inhella inkyongensis and Massilia eburnean, are suggested as new algicidal bacteria. The diverse taxonomies, algal-inhibiting abilities and distributions of these isolates have suggested that there are rich algicidal bacterial resources in these aquatic environments. Our results provide new microbial resources for algal-bacterial interaction studies, and shed new insights into how algicidal bacteria can be used in the control of harmful algal blooms, as well as in algal biotechnology.

Molecular characterization of carbapenem resistant E. coli of fish origin reveals the dissemination of NDM-5 in freshwater aquaculture environment by the high risk clone ST167 and ST361.

Aquatic environment can act as reservoir and disseminator of antimicrobial resistance and resistant pathogens. Novel high-risk carbapenem resistant E. coli (CREC) are continuously emerging worldwide; however, the occurrence of CREC in freshwater aquaculture environment is largely unexplored. To fill this gap, large scale sampling of freshwater pond sites and retail fish markets was done between Oct 2020 and Oct 2021 to investigate the CREC contamination in fish. The frequency of CREC contamination in the freshwater fish was 6.99% (95% CI: 3.78-10.20%). All the isolates were MDR and harbored carbapenemase encoding gene, blaNDM-5 along with other antimicrobial resistance genes (ARGs), blaTEM (64.7%), blaCTX-M-15 (35.3%), blaOXA-1 (5.9%), tet(A) (100%), sul1 (94.1%), qnrS (82.3%), cat1 (35.3%), and cat2 (23.5%). The isolates belonged to phylogroup C and showed low virulence gene profile. ERIC-PCR grouped the isolates into five clusters (I-V). The isolates of clusters I, II, and III were identified as ST167 (76.4%) and of cluster IV as ST361 (17.6%). This is the first report documenting the contamination of NDM-5 producing E. coli ST167 and ST361 of clinical/livestock lineage in freshwater fish from India. The blaNDM-5 was significantly associated with ARGs, tet(A), and sul1; and plasmid replicons, IncF, IncI1, and IncP, signifying the presence of blaNDM-5 and associated ARGs on these transferable plasmids. These findings were validated by the successful conjugal transfer of blaNDM-5 and associated ARGs into non-CREC strain (J53). Our study highlights the ability of CREC to disseminate antimicrobial resistance which has health implications and environmental concerns.

Paired Synoptic and Long-Term Monitoring Datasets Reveal Decadal Shifts in Suspended Sediment Supply and Particulate Organic Matter Sources in a River-Estuarine System

The San Francisco Estuary, in central California, has several long-running monitoring programs that have been used to reveal human-induced changes throughout the estuary in the last century. Here, we pair synoptic records of particulate organic matter (POM) composition from 1990–1996 and 2007–2016 with more robust long-term monitoring program records of total suspended sediment (TSS) concentrations generally starting in the mid-1970s to better understand how POM and TSS sources and transport have shifted. Specifically, POM C:N ratios and stable isotope values were used as indicators of POM source and to separate the bulk POC pool into detrital and phytoplankton components. We found that TSS and POC sources have shifted significantly across the estuary in time and space from declines in terrestrial inputs. Landward freshwater and brackish water sites, in the Delta and near Suisun Bay, witnessed long-term declines in TSS (32 to 52%), while seaward sites, near San Pablo Bay, recorded recent increases in TSS (16 to 121%) that began to trend downwards at the end of the record considered. Bulk POM C:N ratios shifted coeval with the TSS concentration changes at nearly all sites, with mean declines of 12 to 27% between 1990–1996 and 2007–2016. The widespread declines in bulk POM C:N ratios and inferred changes in POC concentrations from TSS trends, along with the substantial declines in upstream TSS supply through time (56%), suggest measurable reductions in terrestrial inputs to the system. Changes in terrestrial TSS and POM inputs have implications for biotic (e.g., food web dynamics) and abiotic organic matter cycling (e.g., burial, export) along the estuarine continuum. This work demonstrates how human-generated environmental changes can propagate spatially and temporally through a large river-estuary system. More broadly, we show how underutilized monitoring program datasets can be paired with existing (and often imperfect) synoptic records to generate new system insight in lieu of new data collection.

Ecosystem Variability along the Estuarine Salinity Gradient: A Case Study of Hooghly River Estuary, West Bengal, India

Hooghly River, a ~460 km long distributary of the Ganga River, passes through a highly industrialized Metropolis-Kolkata in West Bengal, India, and eventually empties into the Bay of Bengal at Gangasagar. To determine the patterns and drivers of planktonic community, spatiotemporal variations in water quality and micronutrient content and planktic prokaryotic and microeukaryotic abundance and diversity across the salinity gradient (0.1 to 24.6 PSU) in the Hooghly River estuary (HRE) were studied. Plankton and water samples were collected at six sites during October 2017, February 2018, and June 2018. The biotic parameters—phytoplankton (Chlorophyll a), total bacterial abundance (cfu), and copepods—were significantly higher in the downstream estuarine sites than in the upstream riparian sites; conversely, rotifer and cladoceran abundances were significantly higher at upstream stations. The most culturable bacterial strains were isolated from the two freshwater sites and one at the confluence (estuarine) and are characterized as Bacillus subtilis, Pseudomonas songnenesis, and Exiguobacterium aurantiacum. Among zooplankton, rotifers (0.09 ± 0.14 ind L−1) and cladocerans (5.4 ± 8.87 ind L−1) were recorded in higher abundance and negatively correlated with bacterial concentrations at upstream stations. On the temporal scale, February samples recorded lower proportions of bacterivorous zooplankton at the three upstream stations. Cluster analysis separated samples on the basis of seasons and water mass movement. The February samples showed distinct spatial characteristics, as three freshwater (FW) stations grouped together and segregated at second 2nd hierarchical level, whereas the three estuarine stations formed a separate cluster at the 50% similarity level. Samples collected in October 2017 and June 2018 exhibited mixed attributes. June samples recorded higher influence of freshwater discharge. The zooplankton abundance showed significant negative correlation with Chl a. Our results demonstrate the relative role of river continuum, land-driven lateral discharge, and seawater intrusion in shaping community structure, which needs to be considered in management and conservation planning of aquatic ecosystems, especially in highly productive and overexploited HRE.

The return of the kinga (saltwater crocodile): Population ‘bust then boom’ shapes shifting baselines in Indigenous biocultural knowledge in northern Australia

The saltwater crocodile (Crocodylus porosus) can be regarded as a cultural keystone species for many Indigenous societies around the world, including for many Aboriginal clans in northern Australia. Here the regional population of Crocodylus porosus suffered a decline, almost to extinction, with unregulated commercial hunting between the 1940s to the early 1970s. Following protected status, saltwater crocodile populations made a rapid recovery. This research documents the perceptions and experiences of this rapid (within living memory) ‘bust then boom’ saltwater crocodile population change, among a regional group of Indigenous Australians (comprising several clans) from the Alligator Rivers Region of western Arnhem Land and Kakadu National Park in the Northern Territory. Using semi-structured interviews, archival work and on-Country (place-based) learning, significant influences on the continuity of Aboriginal people's contemporary engagement with freshwater Country were identified. In particular, the loss of access to freshwater customary harvesting sites and to key harvested species, and as a driver of adaptive changes in harvesting methods and consumption preferences for saltwater crocodile meat and eggs. Importantly, the experiential losses from restricted access to waterbodies were found to have significant impact on opportunities for inter-generational knowledge transmission, according with more recent applications of the Shifting Baseline Syndrome to Indigenous Ecological Knowledge. Findings demonstrate the need for monitoring and management programs of cultural keystone species, like the saltwater crocodile, to include Indigenous-led biocultural knowledge programs as a means of supporting local and Indigenous Knowledge systems. This is particularly critical in cross-cultural, First Nations, and joint-management contexts.

Whole genome sequence analysis of ESBL-producing Escherichia coli recovered from New Zealand freshwater sites.

Extended-spectrum beta lactamase (ESBL)-producing Escherichia coli are often isolated from humans with urinary tract infections and may display a multidrug-resistant phenotype. These pathogens represent a target for a One Health surveillance approach to investigate transmission between humans, animals and the environment. This study examines the multidrug-resistant phenotype and whole genome sequence data of four ESBL-producing E. coli isolated from freshwater in New Zealand. All four isolates were obtained from a catchment with a mixed urban and pastoral farming land-use. Three isolates were sequence type (ST) 131 (CTX-M-27-positive) and the other ST69 (CTX-M-15-positive); a phylogenetic comparison with other locally isolated strains demonstrated a close relationship with New Zealand clinical isolates. Genes associated with resistance to antifolates, tetracyclines, aminoglycosides and macrolides were identified in all four isolates, together with fluoroquinolone resistance in two isolates. The ST69 isolate harboured the bla CTX-M-15 gene on a IncHI2A plasmid, and two of the three ST131 isolates harboured the bla CTX-M-27 genes on IncF plasmids. The last ST131 isolate harboured bla CTX-M-27 on the chromosome in a unique site between gspC and gspD. These data highlight a probable human origin of the isolates with subsequent transmission from urban centres through wastewater to the wider environment.

Year-around survey and manipulation experiments reveal differential sensitivities of soil prokaryotic and fungal communities to saltwater intrusion in Florida Everglades wetlands

Global sea-level rise is transforming coastal ecosystems, especially freshwater wetlands, in part due to increased episodic or chronic saltwater exposure, leading to shifts in biogeochemistry, plant- and microbial communities, as well as ecological services. Yet, it is still difficult to predict how soil microbial communities respond to the saltwater exposure because of poorly understood microbial sensitivity within complex wetland soil microbial communities, as well as the high spatial and temporal heterogeneity of wetland soils and saltwater exposure. To address this, we first conducted a two-year survey of microbial community structure and bottom water chemistry in submerged surface soils from 14 wetland sites across the Florida Everglades. We identified ecosystem-specific microbial biomarker taxa primarily associated with variation in salinity. Bacterial, archaeal and fungal community composition differed between freshwater, mangrove, and marine seagrass meadow sites, irrespective of soil type or season. Especially, methanogens, putative denitrifying methanotrophs and sulfate reducers shifted in relative abundance and/or composition between wetland types. Methanogens and putative denitrifying methanotrophs declined in relative abundance from freshwater to marine wetlands, whereas sulfate reducers showed the opposite trend. A four-year experimental simulation of saltwater intrusion in a pristine freshwater site and a previously saltwater-impacted site corroborated the highest sensitivity and relative increase of sulfate reducers, as well as taxon-specific sensitivity of methanogens, in response to continuously pulsing of saltwater treatment. Collectively, these results suggest that besides increased salinity, saltwater-mediated increased sulfate availability leads to displacement of methanogens by sulfate reducers even at low or temporal salt exposure. These changes of microbial composition could affect organic matter degradation pathways in coastal freshwater wetlands exposed to sea-level rise, with potential consequences, such as loss of stored soil organic carbon.

Gross nitrogen transformations in intertidal sediments of the Yangtze Estuary: Distribution patterns and environmental controls

Nitrogen (N) transformations in estuarine and coastal ecosystems play a crucial role in the global biogeochemical cycles. However, simultaneous estimation of gross N transformations and the underlying drivers across estuarine and intertidal wetlands remain poorly understood. Here, the spatial changes in gross N transformation rates and related functional gene abundances were explored in varying habitats of the intertidal zone in the Yangtze Estuary via an optimized 15N tracing model and quantitative PCR. The results indicate that the gross N transformation rates changed remarkably in estuarine and intertidal wetlands, with comparatively higher gross N transformation rates at the upper freshwater and low-salinity sites relative to high-salinity sites. Meanwhile, the functional gene abundances (amoB, UreC, hzo, nirS and nrfA) exhibited a similar spatial distribution pattern to corresponding N transformation processes. Sedimentary total organic carbon (TOC), nitrite (NO2–), ferrous iron (Fe(II)), and microbial functional gene abundances jointly mediated the gross N transformations. This study carried out the first simultaneous estimation of the gross N transformation pattern and driving factors in estuarine and intertidal ecosystems based on the optimized 15N tracing model, providing a better understanding of internal mechanisms on the N cycling and strategy for estuarine and coastal N management.

In situ calibration of passive sampling methods for urban micropollutants using targeted multiresidue GC and LC screening systems

In this study, ChemcatcherTM (CC) and Polar Organic Chemical Integrative Samplers (POCIS) passive samplers were chosen to investigate trace organic chemical residues in urban streams of the megacity of Sydney, Australia. In situ calibration with these passive samplers investigated 1392 organic chemicals. Six sets of CC passive samplers fitted with SDB-XC or SDB-RPS disks and six POCIS containing Oasis HLB sorbent were deployed at three sites. Every week for six weeks across three deployments, composite water samples were retrieved from autosamplers, along with one set of CC/POCIS passive samplers. Samples were analysed by Automated Identification and Quantification System (AIQS) GC/MS or LC/QTOF-MS database methods with 254 chemicals detected. The most frequently detected compounds under GC/MS analysis were aliphatic, pesticides, phenols, PAHs, sterols and fatty acid methyl esters while from LC/QTOF-MS analysis these were pesticides, pharmaceuticals, and personal care products. Sampling rates (Rs) ranged between <0.001 - 0.132 L day−1 (CC SDB-XC, 18 chemicals), <0.001 - 0.291 L day−1 (CC SDB-RPS, 28 chemicals), and <0.001 - 0.576 L day−1 (POCIS Oasis HLB, 30 chemicals). Assessment of deployment duration indicated that about half of the chemicals that were continuously detected across all deployment weeks had maximal simple linear regression R2 values at four weeks for CC SDB-RPS (seven of 13 chemicals) and at three weeks for POCIS Oasis HLB (seven of 14 chemicals). Where ranges of Rs recorded from the estuarine site were able to be compared to ranges of Rs from one or both freshwater sites, only tributyl phosphate had a higher range of Rs out of 21 possible chemical comparisons, and suggested salinity was an unlikely influence on Rs. Whereas relatively higher rainfall of the third round of deployment aligned with higher Rs across the estuarine and freshwater sites for CC SDB-RPS and POCIS for nearly all possible comparisons.

Distribution and Diversity of Diaptomid Copepods in Freshwater Habitats of Cambodia (Crustacea: Copepoda: Calanoida: Diaptomidae)

Freshwater diaptomid copepods in Cambodia are poorly studied, and only seven taxa were known previously. From February to October 2007, 255 samples were collected from 237 freshwater sites in nine provinces representing four regions (northwest, Cardamom and Elephant Mountains, Mekong Lowlands, and east) of Cambodia. Diversity, seasonal occurrence, geographical distribution of each species, and a checklist of diaptomid copepods are documented. In this case, 24 species were recorded, including two undescribed species belonging to the genera Phyllodiaptomus and Tropodiaptomus. In this case, 14 species are recorded for the first time in Cambodia, and Mongolodiaptomus formosanus has been recorded for the first time in Southeast Asia. One species appears to be endemic to Cambodia and nine to the lower Mekong River Basin. Mongolodiaptomus malaindosinensis was the most common, frequently recorded throughout the four regions (40.5% of the sampled sites), followed by Vietodiaptomus blachei (39.2%), Eodiaptomus phuvongi (38.8%), Mongolodiaptomus formosanus (31.2%), and Eodiaptomus draconisignivomi (27.4%). Very rare species such as Eodiaptomus sanoamuangae, Tropodiaptomus vicinus, Mongolodiaptomus calcarus, and Tropodiaptomus sp. were only recorded at 0.4% to 0.8% of the sampled sites. The species diversity of Cambodia is most similar to that of Thailand, where 22 species (91.6%) occur both in Cambodia and Thailand, and 12 (50%) of the species have been recorded in both Cambodia and Vietnam.