Sediment Profile Research Articles

Carbon sequestration potential of transplanted mangroves and exotic saltmarsh plants in the sediments of subtropical wetlands

Coastal blue carbon ecosystems offer promising benefits for both climate change mitigation and adaptation. While there have been widespread efforts to transplant mangroves from the tropics to the subtropics and to introduce exotic saltmarsh plants like Spartina alterniflora in China, few studies have thoroughly quantified the chronological records of carbon sequestration with different organic carbon (OC) sources. To understand how variations in OC sources can affect the carbon sequestration potential of coastal wetland environment over time, we conducted a study on typical islands with two scenarios: S. alterniflora invasion and mangrove transplantation. Our study determined chronological records of carbon sequestration and storage from five sediment profiles and traced changes in the OC sources using carbon stable isotope (δ13C) and C:N ratios in response to these scenarios. The S. alterniflora invasion resulted in an 84 ± 19 % increase in the OC burial rate compared to unvegetated mudflats, while mangrove transplantation resulted in a 167 ± 74 % increase in the OC burial rate compared to unvegetated mudflats. S. alterniflora and mangroves showed greater carbon sequestration potential in areas with high supplies of suspended particulate matter, while mangroves needed to grow to a certain scale to display obvious carbon sequestration benefits. In the mangrove saltmarsh ecotone, mature mangrove habitats exhibited resistance to the S. alterniflora invasion, while mangrove transplantation in the environment invaded by S. alterniflora had a significant effect on OC contribution. Besides, plant-derived OC can be exported to the surrounding environment due to the rapid turnover of sediments. The blue carbon chronosequence-based estimation of OC sources and burial rates provides a useful reference for establishing carbon accounting policies.

Horizontal and vertical distribution of nitrate-driven anaerobic methane oxidation process in coastal wetlands under different plant species cover across southeast China

Coastal wetlands are an important methane emission source. Nitrate-driven anaerobic oxidation of methane (AOM), catalyzing via a novel clade of anaerobic methanotrophic archaea (ANME-2d), is a potentially important process for methane emission mitigation in coastal wetlands. However, the influence of regional and local environmental conditions, as well as plant species cover on this AOM process, remains unclear. Here, we investigated the horizontal and vertical distribution of nitrate-driven AOM activity and ANME-2d archaeal community in four coastal wetlands under both native and invasive plant species across southeast China. It was estimated that this AOM process could potentially reduce 5.7–9.5% methane emissions from the studied wetlands. Generalized linear mixed-effects model showed that sampling locations and sediment layers had greater impact on nitrate-driven AOM activity than plant species cover, and all these factors significantly affected the abundance of ANME-2d archaea. Nitrate-driven AOM activity was higher in low-latitude coastal wetlands than in high-latitude areas, and the activity positively correlated with mean annual temperature. Furthermore, both nitrate-driven AOM activity and ANME-2d archaeal abundance showed significant vertical variations along sediment profiles, with higher values in the slightly alkaline surface sediment. The plant species cover was found to impact the ANME-2d archaeal abundance and diversity by regulating the availability of substrates for the archaea. Overall, our study provides valuable insights into effects of regional and local environmental parameters and plant species cover on the horizontal and vertical distribution of nitrate-driven AOM activity and ANME-2d archaeal community in coastal wetlands.

“Mn(II) Curtain” in the riparian sediment at the lower reaches of the Hanjiang River, China

Manganese (Mn) is an abundant valent-variable element whose transformation plays an essential role in pollutant fates. This study investigated the distributions of total Mn (T-Mn) and its existing forms, such as exchangeable Mn (EX-Mn), those bound to carbonate (Carb-Mn), iron (manganese) oxides (Ox-Mn), organic matter or sulfide (Om-Mn), and residual lattice combined state Mn (Res-Mn) in three two-dimension sediment profiles of the riparian zone at the lower reaches of Hanjiang River, China, with different water flow directions caused by the dam. The mechanism for the distribution of the Mn forms was discussed through correlation analysis with other sediment indices and modelling studies using the hydrogeochemical simulation software PHREEQC. Results showed that Res-Mn dominated the whole profiles, and the Carb-Mn and Ex-Mn were accumulated and formed an “Mn(II) curtain” at the interface of groundwater and river water, most likely derived from reducing Ox-Mn and Om-Mn at low Eh of this area. The correlation analysis results demonstrated that T-Mn positively correlated with Fe, Ca, Mg, and P in the sediments, inferring the deposition of the primary geological environment or coprecipitation in the riparian zone. Both EX-Mn and Carb-Mn were positively correlated with the average depth of the sampling site and the moisture content of sediments, indicating that the reductive environment below the water level was more favourable for the accumulation of EX-Mn and Carb-Mn. Ox-Mn tended to accumulate above the groundwater level, and Om-Mn were mainly enriched in the subsurface of farmland. The modelling results suggested that the formation of “Mn(II) curtain” was related to the release of CO2 pressure, high HCO3– concentration from the regional groundwater or the aerobic decomposition of TOC from river water, and the low Eh caused by the depth or exhaustion of the DO from river water. This study helps us understand the hydrogeochemical process and environmental fate of Mn and related pollutants in the riparian zone.

Spatiotemporal records of major historical events and human activities in river sediments: A coupled study of heavy metals distribution and lead isotopic dating

Thirty sediment samples (11 on the surface and 19 from a 55 cm core) collected in the Dadu River, upstream of the Yangtze River, China, were analyzed by ICP-MS and Laser diffraction particle size techniques to determine heavy metal spatial-temporal distribution and particle size characteristics, respectively. The intent was to clarify the impact of human activities such as Pb-Zn mining and exploration on the distribution of potentially toxic elements (As, Cd, Cr, Cu, Pb and Zn) in adjacent fluvial deposits. Moreover, 210Pb isotope dating was applied to study the historical variation and distribution of heavy metal pollution in a sedimentary profile in the middle section of the Dadu River. Results suggest that Cd concentration is notably high, exceeding by 16.3 times the soil background value in Sichuan Province, China, which can be intensified by Pb-Zn ore smelting. Surface sediments are mainly composed of silt, accounting for 79% on average, and relatively minor amounts of clay and sand. The fraction of clay in the downstream segments of the Dadu River is significantly higher than that upstream, indicating that the hydrodynamic force in the downstream region is relatively low compared with the upstream flow. Samples in the sedimentary profile, collected at 3 cm intervals, are mainly composed of silty sand, accounting for 75.6%, which comprehensively reflects the strong hydrodynamic force in this area. The results of 210Pb dating of these samples indicate three intervals of historical fluctuation in heavy metal concentrations: 1950–1966, 1988–1991 and 1996–2006, respectively, which coincide to significant historical events (the Cultural Revolution, the construction of Pubugou reservoir and local smelting activities, and the implementation of environmental protection policies). Enrichment factor (EF) values of all heavy metals in the profile began to increase after 1994, and relatively high EF values of Cr and Cd indicated a significant enrichment due to increasing anthropogenic activities during this period. Our study demonstrates that anthropogenic activities can be well recorded in sedimentary profiles and provide new insights to retrieving the history of human developments.

Geochemical characterization of rare earth elements in sediment profiles from the Oualida lagoon (Morocco)

Geochemical characterization of rare earth elements in sediment profiles from the Oualida lagoon (Morocco)

Monitoring hydroecology and climatic variability since ~4.6 ka from palynological, sedimentological and environmental perspectives in an Ox-bow lake, Central Ganga Plain, India

The Ganga-Sai River Interfluve contains several ox-bow lakes in the fertile Central Ganga plains (CGP). A ~2.20-meter deep sedimentary profile obtained near the Chandra Shekhar Azad bird sanctuary (Nawabganj lake-NL) of the CGP was studied to understand the evolution of the ecosystem and climate using pollen/spores, diatoms, testate amoebae, environmental magnetic data,and carbon and nitrogen isotopes. This sedimentary profile is chronologically well-constrained by five radiocarbon (14C) dates. Between 4.6 and 4.4 ka, the sandy sediment and pollen evidence for riparian forest, the absence of aquatic pollen and sponge spicules suggest scant water in the vicinity through the river channel. A semi-closed fluvial ecosystem between 4.4 and 4.2 ka is indicated by testate amoebae, sponge spicules and arboreal pollen. At least two intermittent warm conditions prevailed between 4.6 and 4.2 ka. Between 4.2 and 2.8 ka, high aquatic pollen, diatoms and testate amoebae indicate a lake ecosystem. By ~2.8–0.9 ka the gammoscleres from sponges formed during dry seasons indicate recharging during monsoon as the river shifted. Thereafter, agricultural pollen ( Brassica and Apiaceae) indicates a further shift in the lake boundary exposing land. The highly sandy texture, fluctuating δ13C, δ15N and magnetic mineral values indicate an unstable fluvio-lacustrine deposition inducing hydroecological changes influenced by intermittent about 5–6 humid and dry climatic conditions since ~4.6 ka to present. The calcrete layer in the bottom sediments shows high aridity in CGP between ~5 and 4.6 ka reaching the climax cold-dry event of ~4.2 ka recorded worldwide. The spectral analysis of palynological data from NL and the contemporary Barela Lake, reveals de Vries and Gleissberg cycles of low and high solar irradiance at centennial to multi-centennial scale during the Holocene. The impact on vegetation, sediment depositional dynamics, and shift in river channel was more rapid showing the dominance of ~200 years. periodicity post ~5 ka as compared to ~300 years of dominance prior to this. This centennial timescale is of great speculation for future climate predictions in CGP coupled with the anthropogenic forcings.

Inverted Sedimentation of Active Particles in Unbiased ac Fields.

Gaining control over the motion of active particles is crucial for applications ranging from targeted cargo delivery to nanomedicine. While much progress has been made recently to control active motion based on external forces, flows, or gradients in concentration or light intensity, which all have a well-defined direction or bias, little is known about how to steer active particles in situations where no permanent bias can be realized. Here, we show that ac fields with a vanishing time average provide an alternative route to steering active particles. We exemplify this route for inertial active particles in a gravitational field, observing that a substantial fraction of them persistently travels in the upward direction upon switching on the ac field, resulting in an inverted sedimentation profile at the top wall of a confining container. Our results offer a generic control principle that could be used in the future to steer active motion, direct collective behaviors, and purify mixtures.

Tidal dynamics regulates potential coupling of carbon‑nitrogen‑sulfur cycling microbes in intertidal flats

Tide-driven hydrodynamic process causes significant geochemical gradients that influence biogeochemical cycling and ecological functioning of estuarine and coastal ecosystems. However, the effects of tidal dynamics on microbial communities, particularly at the functional gene level, remain unclear even though microorganisms play critical roles in biogeochemical carbon (C), nitrogen (N) and sulfur (S) cycling. Here, we used 16S rRNA gene amplicon sequencing and microarray-based approach to reveal the stratification of microorganisms related to C, N and S cycles along vertical redox gradients in intertidal wetlands. Alpha-diversity of bacteria and archaea was generally higher at the deep groundwater-sediment interface. Microbial compositions were markedly altered along the sediment profile, and these shifts were largely due to changes in nutrient availability and redox potential. Furthermore, functional genes exhibited redox partitioning between interfaces and transition layer, with abundant genes involved in C decomposition, methanogenesis, heterotrophic denitrification, sulfite reduction and sulfide oxidation existed in the middle anoxic zone. The influence of tidal dynamics on sediment function was highly associated with redox state, sediment texture, and substrates availability, leading to distinct distribution pattern of metabolic coupling of microbes involved in energy flux and elemental cycling in intertidal wetlands. These results indicate that tidal cycles are critical in determining microbial community and functional structure, and they provide new insights into sediment microbe-mediated biogeochemical cycling in intertidal habitats.

Holocene geomorphodynamics of a rural catchment in the Pergamon micro-region (eastern Mediterranean)

The Pergamon micro-region (western Türkiye) has experienced several phases of increased geomorphodynamics during the Holocene. However, the role of local–regional human activities during a transformation between Hellenism and the Roman Imperial period and supra-regional climate fluctuations is still under discussion. Five sediment profiles from the alluvial fan of the rural Deliktaş catchment are analyzed and radiocarbon-dated to provide a sedimentological record covering the Holocene. Our results indicate seven phases of changing sediment dynamics. Five Holocene cycles of coarse- and fine-textured fan sediment deposition covered the paleochannel deposits of the Çaylak creek, and the floodplain sediments of the receiving Geyikli river which aggraded toward the piedmont during the Mid-Holocene. The landscape became stable on the Deliktaş fan and Geyikli floodplain at least ca. 4–3.4 cal ka BP as indicated by paleosols. These paleosols were again buried by fan sediments marking the first phase of accelerated geomorphodynamics during the Late Holocene. Both the local onset of human activities and the regional Mid-Holocene aridization with rapid climate changes play a role. The increased number of archeological sites and high human pressure on the environment during the Hellenistic–Roman transformation in the Deliktaş area and Pergamon micro-region were hypothesized to contribute to a phase of increased geomorphodynamic activity during the last 2.5 ka. This, however, is less apparent in our record. Our study emphasizes the importance of both, the climatic system and rural-urban cultural history, on landscape development, suggesting potential responses of locally diverse geomorphodynamics on regional-scale transformation in the eastern Mediterranean.

A 1500-year record of mercury isotopes in seal feces documents sea ice changes in the Antarctic

Temporal and spatial variations in sea ice coverage at high Northern Hemisphere latitudes have been shown to affect the photodegradation of methylmercury in seawater and the mercury isotope signatures in biological samples, suggesting the potential of mercury isotopes to reconstruct sea ice variability. Here we study the mercury isotopic composition of a 1500-year sediment profile strongly affected by seal activities on the Fildes Peninsula, King George Island, Antarctic Peninsula. The mass independent isotope fractionation of mercury (represented by Δ199Hg) in sediments dominated by seal feces input reflects the Δ199Hg of marine methylmercury before entering the food web, documenting the changes in the degree of photodemethylation. We found much higher Δ199Hg in sediments deposited during a warm period (~700-1000 years ago), suggesting that reduced sea ice promoted greater photodemethylation. Thus, this study demonstrates the modulation of methylmercury photodegradation by sea ice in the Antarctic, and that mercury isotopes can record historical sea ice changes.

Looking at Phytoliths in Archaeological Soil and Sediment Thin Sections

ABSTRACT Traditionally, phytolith research focusses on the study of bulk samples collected during archaeological field campaigns. However, phytoliths are frequently reported by soil micromorphologists studying their archaeological soil and sediment thin sections. Within these thin sections all components, including the phytoliths, are captured in the position they had in the original soil and sediment profiles. This opens perspectives towards a better understanding of phytolith depositional and post-depositional histories, but also towards the identification of invisible archaeological remains, such as previous vegetal floor covers. Furthermore, the study of phytoliths in thin sections opens up prospects for morphometrical analysis. Despite a series of limitations – the phytolith record is not concentrated, issues of visibility, the fact that phytoliths cannot be rotated and are cut at random angles – the study of phytoliths in thin sections is a rewarding effort. Beyond being a feasible task, it is also a promising asset, given a full integrative approach involving both phytolith specialists and micromorphologists.

Silicon fractionations at the margin of a coastal wetland and its response to sea level rise

Silicon (Si) and its biogeochemical cycling play an important role in maintaining the functions of terrestrial and marine ecosystems. However, the effects of sea level rise on the biogeochemical cycling of Si in coastal wetlands remain poorly understood. To explore this impact on biogeochemical Si cycling, we sampled a gradient from sediment to soil without the impact of tidal inundation in the Beidagang Wetland Nature Reserve, and then assayed non-crystalline Si (labile Si), including mobile Si (CaCl2-Si), adsorbed Si (Acetic-Si), Si bound to soil organic matter (H2O2-Si), Si occluded in pedogenic oxides/hydroxide (Oxalate-Si), and amorphous Si (Na2CO3-Si) fractions. Analytical results showed that the content of CaCl2-Si ranged from 13.0 to 53.3 mg kg−1 and the content of Acetic-Si ranged from 32.3 to 80.9 mg kg−1, both of which were lower in sediments compared to soils. The content of H2O2-Si (84.1–160.1 mg kg−1) and Oxalate-Si (306.6–655.1 mg kg−1) in the soil profiles showed non-significant variations along the sampling slope. The Na2CO3-Si fraction accounted for 82%–90% of labile Si in soil and sediment, mainly being contributed from phytoliths or diatoms. Diatoms were only detected in sediment profiles. The storage of labile Si in sediment was significantly (p = 0.0009) lower than the storage in soil, suggesting that the coastal wetland ecosystems are an important source of Si to the estuary. With future sea level rise and increased margin erosion, the inter-transformation processes among different Si fractions would likely be weakened to increase dissolved Si for marine diatoms.

Greenhouse gases concentrations influence on vertical distribution of nematode communities in the Ba Lai river, Vietnam

Vertical distribution of free–living nematodes from the tropical region are still poorly documented, especially in Vietnam. Field sampling was conducted at the Ba Lai river, a tributary of the Mekong river, to insight into the regularity of the vertical pattern of nematode assemblages. Furthermore, some sediment environmental characteristics such as greenhouse gases were also detected in order to understand how to influence nematode distribution. The study found that nematode composition differed significantly between the upper and deeper layers of sediment but not among the deeper layers. Nematode density showed spatial variability across layers, with higher values in the upper layer. Nematode diversity decreased with increasing depth. Non–selective deposit feeders (1B) were dominated in the surface layers, while the predator–omnivores feeders (2B) was numerous in the deeper layers. In the dry season, both methane and hydrogen sulfur were found negatively affecting nematode diversity in sediment profile, particularly, methane effects negatively also to species richness, densities, and evenness. However, only methane has a significant correlation to the diversity, species richness, densities, and evenness of the nematode communities.

The Role of Sediment Records in Environmental Forensic Studies: Two Examples from Italy of Research Approaches Developed to Address Responsibilities and Management Options

The coupling of scientific evidence from sediment cores with historical information represents an effective way to reconstruct and quantify recent anthropogenic impacts in transitional and marine-coastal areas. These are both key points pertaining to studies that aim at establishing the responsibility for envi ronmental pollution. Good practices for the selection of sampling sites and specific survey techniques are fundamental to understand pollution histories and dynamics, together with reliable dating methods and analytical procedures. In addition, a certain degree of flexibility and willingness to explore different research pathways is necessary, particularly when unexpected questions arise from scientific data or from requests posed by authorities in charge of preliminary investigations or court debates. In this paper, two different study cases are reviewed, and the approaches developed to tackle with specific issues are presented. Its main purpose is both to explain study paths undertaken to answer challenging scientific-legal questions and to provide examples for developing countries that present similar risks of uncontrolled industrialization. Results were used in preliminary investigations or court debates for the attribution of responsibility for environmental pollution to past or present industrial managements. In addition, they were fundamental for other studies aiming at implementing models that simulate the fate and distribution of contaminants and human exposure. In the Augusta Harbor, an integrated approach merged archive information, bathymetry, and high-resolution seismic profiles with the results of an independent tracer (hexachlorobenzene, HCB). This approach helped attribute the presence of high surficial Hg concentrations to resuspension and redistribution of deep sediments caused by dredging and maritime traffic and not to active outfalls. In the Venice Lagoon, an extensive literature search supported analytical results for the correct identification of industrial processes responsible for the contamination by polychlorinated dibenzo-p-dioxins and furans (PCDD/Fs) in the canals of the Porto Marghera Industrial Area. In addition, sedimentary profiles of PCDD/Fs in local salt marshes (“barene”) recorded well the events relative to the industrial development and management of the area reported by historical documents, confirming their potential for this kind of investigation.

Research on flood sediments and rainstorm events in Huangtuwa, Northern Shaanxi

The research purpose of this paper is to reveal the relationship between flood deposits, rainfall and flooding in the Loess Plateau over the last 50 years. The research in this paper is of great significance as it reveals the torrential flood events and soil erosion in the central region of the Loess Plateau. Through grading analysis and 137Cs content determination of a closed lake sedimentary profile formed by landslide-blocked rivers in middle part of Loess Plateau, Zizhou County, Shaanxi Province, the age of the sedimentary formation in the section, as well as the rainstorm events and changes of soil erosion since 1954 are studied. The results show that the sediment particle size composition in the study section is fine, mainly comprising of coarse silt, while the content of sand particles (>100 μm) is very low. The changes in137Cs content show that the sedimentary layer at a depth of 280–210 cm in the research profile was formed between 1954 and 1964, while the deep sedimentary layer at 210–70 cm was formed between 1965 and 1986 and the sedimentary layer above 70 cm depth was formed between 1987 and 2011. In total, 20 coarse particle layers (particle size >50 μm) were deposited in the lake between 1954 and 2011. The sedimentation timing of the 20 coarse particle layers was basically consistent with the timing of rainstorm events (daily rainfall ≥60 mm) in the study area, indicating that the coarse particle sediments in the lake represent rainstorm events. Soil erosion was stronger between 1954 and 1985 and was weaker after 1986.

Vertical Distribution of Suspended Sediment Concentration in the Unsaturated Jingjiang Reach, Yangtze River, China

The Rouse formula and its variants have been widely used to describe the vertical distribution of the sediment concentration in sediment-laden flows in equilibrium. Han’s formula extends the Rouse formula to non-equilibrium regimes, where the diffusive flux is still assumed to be Fickian. The turbulent flow and suspension regimes downstream of a mega-reservoir, e.g., the Three Gorges Reservoir, usually exhibit fractal and unsaturated properties, respectively. To characterize the non-Fickian dynamics of suspended sediment and the non-equilibrium regime in natural dammed rivers, this study proposes a new formula for the concentration profile of unsaturated sediment based on the Hausdorff fractal derivative advection–dispersion equation. In addition, we find that the order of the Hausdorff fractal derivative is related to the sizes of the sediment and the degrees of non-equilibrium. Compared to Rouse and Han’s formulae, the new formula performs better in describing the sediment concentration profiles in the Jingjiang Reach, approximately 100 km below the Three Gorges Dam.

Using geochemical elements to discriminate sediment sources in a typical karst watershed

Knowledge of temporal variations in sediment sources is necessary to identify the principal sources of sediment for effective implementation of soil conservation measures and to improve the calibration and validation of process-based soil erosion models. Quantitative information on sediment provenance is often limited in karst regions because of their complex surfaces and underground three-dimensional erosion systems. Peak-cluster depressions are typical landforms in karst areas and can well intercept most sediment from hillsides such as dams or reservoirs. Thus, peak-cluster depressions are suitable areas for sediment source identification. The objective of this study was to quantify the contribution of sediment sources in a typical karst watershed and to identify temporal variations in sediment sources in the watershed in the past 60 years. We collected 194 soil samples from three sediment profiles in a karst depression and 58 source samples from cropland, fissure soil, and forestland. We used a composite fingerprinting method based on 45 geochemical properties and an IsoSource multivariate mixed model in a typical karst watershed. The results indicate that cropland was the principal sediment source (89.2 %) in the last 60 years, followed by fissure soil (9.6 %) and forestland (1.2 %). Importantly, compared with the period from 1949 to 1999, the contribution of sediment from fissure soil reached a maximum value of approximately 20 % from 1999 to 2015. This result implies that the “Grain for Green” program, which was implemented in 1999, clearly reduced the amount of soil erosion from cropland. Therefore, the program may greatly affect sediment deposition in karst depressions. Using metal ratios as fingerprint factors, the IsoSource mixed model can be effectively used to study the source of sediments in karst watersheds quantitatively. This study can aid the existing understanding of soil erosion processes and contributes to the sustainable development of agro-ecology in karst watersheds.

Molecular Characterization of the Convergent Carbapenem-Resistant and Hypervirulent Klebsiella pneumoniae Strain K1-ST23, Collected in Chile during the COVID-19 Pandemic.

The aim of this study was to investigate the genomic features of a carbapenem-resistant hypervirulent Klebsiella pneumoniae (CR-hvKp) isolate (K-2157) collected in Chile. Antibiotic susceptibility was determined using the disk diffusion and broth microdilution methods. Whole-genome sequencing (WGS) and hybrid assembly were performed, using data generated on the Illumina and Nanopore platforms. The mucoid phenotype was analyzed using both the string test and sedimentation profile. The genomic features of K-2157 (e.g., sequence type, K locus, and mobile genetic elements) were retrieved using different bioinformatic tools. Strain K-2157 exhibited resistance to carbapenems and was identified as a high-risk virulent clone belonging to capsular serotype K1 and sequence type 23 (ST23). Strikingly, K-2157 displayed a resistome composed of β-lactam resistance genes (blaSHV-190, blaTEM-1, blaOXA-9, and blaKPC-2), the fosfomycin resistance gene fosA, and the fluoroquinolones resistance genes oqxA and oqxB. Moreover, several genes involved in siderophore biosynthesis (ybt, iro, and iuc), bacteriocins (clb), and capsule hyperproduction (plasmid-borne rmpA [prmpA] and prmpA2) were found, which is congruent with the positive string test displayed by K-2157. In addition, K-2157 harbored two plasmids: one of 113,644 bp (KPC+) and another of 230,602 bp, containing virulence genes, in addition to an integrative and conjugative element (ICE) embedded on its chromosome, revealing that the presence of these mobile genetic elements mediates the convergence between virulence and antibiotic resistance. Our report is the first genomic characterization of a hypervirulent and highly resistant K. pneumoniae isolate in Chile, which was collected during the coronavirus disease 2019 (COVID-19) pandemic. Due to their global dissemination and public health impact, genomic surveillance of the spread of convergent high-risk K1-ST23 K. pneumoniae clones should be highly prioritized. IMPORTANCE Klebsiella pneumoniae is a resistant pathogen involved primarily in hospital-acquired infections. This pathogen is characterized by its notorious resistance to last-line antibiotics, such as carbapenems. Moreover, hypervirulent K. pneumoniae (hvKp) isolates, first identified in Southeast Asia, have emerged globally and are able to cause infections in healthy people. Alarmingly, isolates displaying a convergence phenotype of carbapenem resistance and hypervirulence have been detected in several countries, representing a serious threat to public health. In this work, we analyzed the genomic characteristics of a carbapenem-resistant hvKp isolate recovered in 2022 from a patient with COVID-19 in Chile, representing the first analysis of this type in the country. Our results will provide a baseline for the study of these isolates in Chile, which will support the adoption of local measures aimed at controlling their dissemination.

Trace metals distribution along sediment profiles from the Doce River Continental Shelf (DRCS) 3 years after the biggest environmental disaster in Brazil, the collapse of the Fundão Dam

The Doce river adjacent continental Shelf (DRCS) was evaluated regarding sediment quality three years after the biggest environmental disaster in Brazil, the rupture of the Fundão Dam, that released 39 million cubic meters in the Doce river basin. Five sediment cores were sampled in the shelf, two at the south of the river mouth (T3, T4), two at the north (T6, T7) and one in front of it (T13). Analyses of sedimentary variables (grain size, organic matter and carbonates), trace and major metals occurred in the first 30 cm of each core. The presence of the tailings along the cores was investigated through an Iron Mineralogical Set (IMS). Results of the geoccumulation index (Igeo) revealed sediment enrichment with Fe, Mn, Zn, Cu, Pb, Ni, Cr reaching class 6 of contamination in every core. The contamination index (mCd) revealed high contamination levels by trace and major metals, for T3, T4, T6 and T13. Sediment Quality Guideline Quotient (SQG-Q), revealed moderate impact for all the cores, regarding the potential observation of adverse biological effects. The presence of the tailings along the cores T4, T6, T7 and T13 was confirmed through the IMS. Core T13 showed the presence of the tailings all along its extension, characterizing a depocenter of this material in front of the river mouth. IMS has proved to be a good proxy to identify presence of the tailings and revealed the trend of transport of this material towards north in DRCS. Despite the prevailing accumulation of the tailings in the north and in front of the river mouth, higher levels of metal contamination were registered in the south suggesting contamination originated from anthropogenic activities previous to the rupture of the dam.

Vertical Profiles of Microplastics in the Hyporheic Zone Sediment: A Case Study in the Yangtze River, Nanjing Section

Microplastics are ubiquitous in the river environment, although their abundance in sediment profiles has received little attention. The river hyporheic zone (HZ) sediment is the area influenced by surface and groundwater flow dynamics, and pollutants are more likely to be transported vertically in this area, thus entering the groundwater. Understanding the microplastic abundance and composition in the HZ sediment is crucial for microplastic pollution management. Hence, this study investigated the vertical distribution and characteristics of microplastic in the HZ sediment of the Yangtze River (Nanjing section). The results show that the abundance of microplastics in the HZ sediment ranged from 207 ± 95 to 1817 ± 467 items/kg dry wet in a vertical profile. With the increase of sediment depth, the abundance of microplastics decreased obviously in most sites, whereas the proportions of pellet shapes and smaller sizes of microplastics increased only at S1. No significant variation was found in the microplastic colors between different depth layers. Polypropylene and polyethylene were the dominant polymer types in all sediment samples. These results provided insights into the understanding of the microplastic fates in a river HZ region.