Sediment-water Interface Research Articles

Biofilms in modern CaCO3-supersaturated freshwater environments reveal viral proxies

Biofilms are mucilaginous-organic layers produced by microbial activity including viruses. Growing biofilms form microbial mats which enhance sediment stability by binding particles with extracellular polymeric substances and promoting growth through nutrient cycling and organic matter accumulation. They preferentially develop at the sediment-water interface of both marine and non-marine environments, and upon the growing surfaces of modern tufa and travertine. In this context, however, little is known about the factors, environmental or anthropogenic, which affect viral communities in freshwater spring settings. To explore this issue, geochemical and metagenomic data were subjected to multidimensional analyses (Principal Component Analysis, Classical Multidimensional Scaling, Partial Least Squares analysis and cluster analysis based on beta-diversity), and these show that viral composition is specific and dependent on environment. Indeed, waters precipitating tufa and travertine do vary in their geochemistry with their viruses showing distinct variability between sites. These differences between virus groups allow the formulation of a viral proxy, based on the Caudoviricetes/Megaviricetes ratio established on the most abundant groups of viruses. This ratio may be potentially used in analysing ancient DNA preserved in carbonate formations as an additional source of information on the microbiological community during sedimentation.

Sequential oxidation procedures with KMnO4: Component characteristics of labile reducing capacity fractions in anaerobic sediments

Reducing substances are a mixture of different forms and types and play extremely important roles in manipulating the redox status of sediments, benthic habitats, and substance exchanges at the sediment-water interface in aquatic ecosystems. However, little is known about their abundance, forms, and reducibility in sediments. In this study, the procedures were developed to sequentially fractionate sediment reducing capacity (RC) fractions with the pH dependence of KMnO4 oxidability. The procedures were then applied to 60 sediments from 2 lakes and 3 reservoirs, generating an RCpH7.0 fraction (oxidized at ~0.48 V [reference: SHE]) and an RCpH2.0 fraction (oxidized at ~0.95 V [reference: SHE]), and the component of each fraction was characterized. The RCpH7.0 fraction amounted to 45.4 ± 25.9 cmol e−·kg−1 DW, and the RCpH2.0 fraction amounted to 42.8 ± 22.9 cmol e−·kg−1 DW; fraction sizes depended greatly on sediment origin. Reducing organic substances (ROS) were the main contributors to the RC fractions, with mean value of 30.0 ± 24.1 and 38.5 ± 22.2 cmol e−·kg−1 DW in RCpH7.0 (% contribution: 68.0 ± 5.3 % of RCpH7.0) and RCpH2.0 (90.0 ± 1.5 % of RCpH2.0), respectively. The next contributor was Fe(II), with mean value of 13.5 ± 8.2 and 3.8 ± 3.7 cmol e−·kg−1 DW in RCpH7.0 (28.3 ± 5.2 %) and in RCpH2.0 (9.9 ± 8.6 %), respectively. The smallest component was sulfide (Sn), which had a mean of 2.0 ± 3.1 cmol e−·kg−1 DW in RCpH7.0 and was essentially negligible in RCpH2.0. The number of electrons lost per mole of reducing substances (Ni) differed between the two RC fractions and among sediments of different origins. NROS was lower in the RCpH7.0 fraction (0.22 ± 0.09) compared to the RCpH2.0 fraction (0.31 ± 0.12) and significantly related to levels of active Fe(III) and sulfides (Sn) (p < 0.05). The opposite pattern was seen for NFe(II) and NSn. Based on the compositive reducing capacity (CRC) for the RCpH7.0 fraction, sediment redox status could be classified as ROS-Fe(II) (3.8 ± 1.7 cmol e−·kg−1 DW) or ROS-Sn (10.1 ± 4.8 cmol e−·kg−1 DW) (weaker vs. stronger, respectively; p < 0.01). The RC-based index provides a more comprehensive perspective on characterizing sediment redox status compared to the Eh.

Geochemical characterization of trace fossil assemblages in spotted marls and limestones of the Lower Jurassic of the Western Carpathians: environmental implications

AbstractThe trace fossils of the spotted limestones and marls from upper Pliensbachian of the Skladaná Skala section, Western Carpathians (Slovakia), are characteristic of Zoophycos ichnofacies preserved in outer shelf deposits. The ichnoassociation is dominated by Lamellaeichnus and Chondrites, while Palaeophycus, Planolites, Teichichnus, Thalassinoides, Trichichnus, and Zoophycos, are less abundant. The presence of relatively large sized traces (reaching a decimetre in horizontal dimension for Thalassinoides and Zoophycos) and continuously well bioturbated deposits point to well oxygenated shallow zone (mixed layer) and deeper part of stiffed substrate of the transitional layer of bottom substrate up to the first tens of centimetres to depth. A first tier (tier I) corresponds to the shallowest sediment occupied by Bathysiphon tests and other epifaunal body fossils. The tier II is characterized by shallow infaunal burrows of deposit feeders (Planolites) and permanent dwelling, open burrows (Palaeophycus, Thalassinoides) located in a Ca-rich sediment (corresponding to CaCO3). The tier III is dominated by deposit feeders (Lamellaeichnus, Teichichnus) that burrowed stiff Ca-rich sediment below the redox boundary. Trace fossils of tier III are rich in fine siliciclastics (high content in Si, Al, K mainly associated to clays) and pyrite framboids (enrichment in Fe, S and Co). The deposit-feeders of tier III maintain connection to the sediment-water interface. Tier IV (Zoophycos, Teichichnus and large Chondrites), and deepest infaunal forms of the tier V. (Trichichnus, Pilichnus and tiny forms of Chondrites) comprises trace fossils commonly rich in pyrite framboids with relatively high content of Fe, S, and Co, congruent with chemosymbiotic behaviour commonly inferred for Chondrites, Trichichnus, and the organic-matter storage of Zoophycos.

Implications of suspended sediment in the migration of nutrients at the water-sediment interface in retention reservoirs

The significance of suspended sediment in the context of nutrient cycling and distribution in reservoirs is rarely reported in the scientific literature. What’s more, suspended sediment (SS) have so far not been taken into account as a potential factor amplifying the degrading effects of nutrients on the functioning of reservoirs. In the experiment described here, the variability of SS concentrations and the content of total nitrogen (TN), total phosphorus (TP), total organic carbon (TOC) and organic matter (OM) were investigated to determine the potential and determinants of SS in the process of migration of these substances at the water-sediment interface in retention reservoirs. The results showed that SS significantly manipulate the distribution of values of total phosphorus and total organic carbon contained in bottom sediment. It was confirmed that the circulation and distribution of selected nutrients in reservoirs is closely related to suspended sediment. Thus, it was proven that SS significantly affect the quality of deposited sediment. Finally, it was concluded that suspended sediment in the water of reservoirs forms a kind of micro-ecosystem, in which it plays a hitherto undiscovered role of a catenary (hub) consolidating a number of phenomena and processes occurring between individual components in the water-bottom sediment system.

Delving into nitrogen and phosphorus dynamics in shallow eutrophic lakes: Multi-interface response to freeze-thaw cycles

Assessing the impact of freeze-thaw cycles on nutrient transfer in lakes is crucial for addressing the global eutrophication of freshwater ecosystems in cold and arid regions. However, available information about the dynamics of nitrogen (N) and phosphorus (P) release during intact freeze-thaw cycles, especially in the sediment–porewater–water column continuum of lakes, is limited. This study collected the samples during ice-covered (January) and non-ice-covered (April, July, and October) periods. The changes in total nitrogen (TN) and total phosphorus (TP) were analyzed to estimate their release fluxes from the sediment-water interface. Both redundancy analysis (RDA) and variance partitioning analysis (VPA) were used to explore the effects of environmental variables on N and P. The results indicated that during the ice-covered period (ICP), the surface water content of different forms of N and P was lower than that of the overlying water, whereas the opposite was true during the non-ice-covered period (NICP). The overall trend for the different forms of N was TN > DIN > NH4-N > NO3-N > NO2-N, and for P, it was TP > PP > DTP > DOP>DIP. The vertical profiles of the porewater TN and TP generally demonstrated an increase followed by a decrease from the surface to the bottom, with an inflection point at 15 cm. Sediment TN and TP trends over time matched porewater trends, with both being spatially highest at the lake inlet. ICP sediments acted as sinks for TN and TP, and NICP sediments acted as sources. N and P in the water column were significantly correlated mainly with physicochemical indicators, whereas sediment contributed positively to TN and TP in the porewater. VPA indicated that environmental factors explained 46.45 % of the variation in TN and TP in the porewater. These findings emphasize the importance of freeze-thaw cycling processes in driving N and P nutrient enrichment, source-sink effects, and multi-media coupling in shallow lakes in arid plateau regions.

Assessing the influence of thermal structure variation on Fe and P mobility in sediments cores using Yellow Spring Instrument, diffusive gradient technology, and HR Peeper for sustainable water quality management.

The freshwater ecological characteristics in terms of the daily inventory of thermal stratification, spatial variation of O2 distribution, and the mobility of potentially toxic elements (PTEs) at the water sediment interface (WSI) are prudent freshwater assessment indices for water quality management protocol. The study conducted daily observations within a monsoon-influenced region, utilizing high-resolution techniques such as HR Peeper, Yellow Spring Instrument (YSI), and ZrO-Chelex diffusive gradient technology (DGT) to analyze PTEs, specifically phosphorus (P) and iron (Fe),within the water-sediment interface (WSI) under different temperatures and oxygen conditions. The 66-day field study showed that high thermal structure contributed significantly to production Fe ions and P from sediment under reductive dissolution of FeOOH. The study also revealed that P and Fe exhibited comparable spatial distribution patterns at the WSI, indicating a linked relationship between these PTEs. This correlation was reinforced by high Pearson correlation coefficients ranging from 0.7 to 0.9 (bilateral, p < 0.05) indicating that the concentrations of labile P were predominantly influenced by the release of phosphorus bound to iron. The fluxes of the PTEs were positive with a range of Fe, 3.3-81.5 mg/m2 day and P, 0.03-0.5 mg/m2 day showing the sediments liberated the PTEs into the benthic water. Again, high positive fluxes (Fe≈60 mg/m2 day, P≈0.5 mg/m2 day) for PTEs were obtained when stratification was high (anoxic conditions) and low (Fe≈5 mg/m2 day, P≈0.08 mg/m2 day) when stratification did not exist. This depicts that Fe/P dynamics were hinged mainly on hypoxic conditions in the benthic water under the reductive dissolution of FeOOH. The findings showed that organic materials (both solid and dissolved) correlated (> 0.7) significantly with (positive high values) Fe. This indicates that their interaction contributed to the reservoir water deterioration. However, Ca2⁺ and Mg2⁺ had little impact on the liberation of Fe-DOC-P from sediments due to their inability to compete with Fe for binding to DOC and P, as shown by their low correlation values. The research provides in-depth insights into the dynamics of PTEs on a daily timescale and offers valuable information for water management practices in inland reservoirs, particularly concerning the cycling of phosphorus (P) and its effects on ecosystem health.

Origin and preservation mechanisms of organic matter in carbonate concretions from Lower Cambrian black shales in South China

Carbonate concretions are widely used in paleoclimate, paleoenvironmental, and paleontological studies, and even in the study of potential life on Mars. These petrological, elemental, isotopic, and lipid biomarker signals in Meso-Cenozoic carbonate concretions (relatively low thermal maturity) can effectively preserve details of seawater conditions and benthic ecosystems during the deposition of their host sediments/rocks. However, such research on Precambrian-Cambrian carbonate concretions under highly mature conditions remains scarce, and the ability of these ancient carbonate concretions to retain their original biogenic information remains uncertain. To achieve that, this study examines two Cambrian carbonate concretions, using samples from the center, transition, and rim of each, and their adjacent host black shales from the Lower Cambrian Qiongzhusi Formation in the Yangtze Block, South China. Organic and inorganic geochemical analyses were combined to elucidate the origin and preservation process of organic matter (OM) in these ancient Cambrian carbonate concretions. The results show that the thermal maturity of OM within these concretions (1.8 % EqVRo) is relatively low compared to their adjacent host shales (2.9 % EqVRo). Hopanes and steranes are detectable in both free and calcite-occluded hydrocarbons within these concretions, with concentrations of individual compounds ranging from 0.001 to 0.800 μg/g TOC, whereas kerogen-bound hydrocarbons lack detectable biomarkers. The results indicate that the two Cambrian carbonate concretions were formed mainly within the iron reduction and bacterial sulfate reduction zones, extending to depths of 10 to 38 m below the sediment-water interface. The OM within these concretions mainly inherited the initial unaltered signature of OM from the Qiongzhusi host shale. The carbonate concretions protected the internal OM from further thermal and secondary (e.g., biodegradation) alteration processes and might also prevent the formation of the conventional macromolecular skeletal kerogen manifested by the absence of bound biomarkers. The biomarkers, in both free and occluded forms, in the Cambrian carbonate concretions still retained their original source information, providing valuable insights into ancient biogeochemical processes during sediment burial and ancient seawater chemistry during the early Cambrian.

Evaluation and mitigation of potentially toxic elements contamination in mangrove ecosystem: Insights into phytoremediation and microbial perspective

Mangroves, essential coastal ecosystems, are threatened by human-induced Potentially-toxic-elements (PTEs) pollution. This study analyzed PTEs distribution, phytoremediation potential, and rhizosphere microbial communities in Taiwan's Xinfeng mangrove forest. Significant variations in physicochemical and PTEs concentrations were observed across adjacent water bodies, with moderate contamination in the river, estuary, and overlying water of mangroves sediment. The partition-coefficient showed the mobility of Bi, Pb, Co, and Sr at the water-sediment interface. The geochemical-indices revealed high Bi and Pb contamination and moderate Zn, Sr, Cu, and Cd contamination in sediment. The overall pollution indices indicated the significant contamination, while moderate ecological risk was found for Cd (40 ≤ Eri < 80). Mangroves Kandelia obovata and Avicennia marina exhibited promising PTEs phytoremediation potential (Bi, Cd, Mn, Sr, and Co). Metagenomics indicated a diverse microbial community with N-fixation, P-solubilization, IAA synthesis, and PTEs-resistance genes. These findings underscore the need for targeted conservation to protect these critical habitats.

Taxonomic and functional partitioning of Chloroflexota populations under ferruginous conditions at and below the sediment-water interface.

The adaption of the phylum Chloroflexota to various geochemical conditions is thought to have originated in primitive microbial ecosystems, involving hydrogenotrophic energy conservation under ferruginous anoxia. Oligotrophic deep waters displaying anoxic ferruginous conditions, such as those of Lake Towuti, and their sediments may thus constitute a preferential ecological niche for investigating metabolic versatility in modern Chloroflexota. Combining pore water geochemistry, cell counts, sulfate reduction rates, 16S rRNA genes with in-depth analysis of metagenome-assembled genomes, we show that Chloroflexota benefit from cross-feeding on metabolites derived from canonical respiration chains and fermentation. Detailing their genetic contents, we provide molecular evidence that Anaerolineae have metabolic potential to use unconventional electron acceptors, different cytochromes and multiple redox metalloproteins to cope with oxygen fluctuations, and thereby effectively colonizing the ferruginous sediment-water interface. In sediments, Dehalococcoidia evolved to be acetogens, scavenging fatty acids, haloacids and aromatic acids, apparently bypassing specific steps in carbon assimilation pathways to perform energy-conserving secondary fermentations combined with CO2 fixation via the Wood-Ljungdahl pathway. Our study highlights the partitioning of Chloroflexota populations according to alternative electron acceptors and donors available at the sediment-water interface and below. Chloroflexota would have developed analogous primeval features due to oxygen fluctuations in ancient ferruginous ecosystems.

Fast On-Site Speciation and High Spatial Resolution Imaging of Labile Arsenic in Freshwater and Sediment Using the DGT-SERS Sensor.

Diffusive gradients in thin films (DGT) technique is renowned for in situ passive sampling but not for rapid on-site analysis, whereas surface-enhanced Raman spectroscopy (SERS) excels in ultrasensitive on-site detection but is limited by substrate contamination from complex matrices. Here, a hierarchical nanostructure of silver (Ag) mirror-supported large Ag nanoparticles (∼120 nm) was grown in situ in polyacrylamide hydrogel with a restricted pore size (PAM/Ag mirror/AgNPs) to serve as both the DGT binding phase and the SERS substrate. The substrate exhibited a maximum electric field enhancement factor of 9.9 × 108 and a signal relative standard error of 4.8%. Using the DGT-SERS sensor, As(III) and As(V) in freshwater were simultaneously detected at limits of 0.9 and 0.8 μg L-1, respectively, applicable across a wide range of environmental conditions. The DGT-SERS effectively mitigated the interfacial reduction of As(V) caused by humic acid by excluding it from plasmonic hotspots through size exclusion of the diffusive layer. The Raman analysis of a DGT sample in the field requires only 2 s using a portable spectrometer without DGT device disassembly. More importantly, the DGT-SERS captured the first two-dimensional image of As(III) and As(V) in one DGT at the micron scale resolution, revealing their spatially supplementary distribution patterns at the sediment-water interface. This study paves the way for next-generation speciation imaging DGT and the application of SERS in complex environments.

Declining bivalve species and functional diversity along a coastal eutrophication-deoxygenation gradient in the northern Gulf of Mexico

Coastal eutrophication and hypoxia are growing challenges globally, yet their impacts can be difficult to evaluate because of limited biomonitoring that typically postdates the onset of these stressors. We address this limitation by investigating how the taxonomic and functional diversity of marine bivalve communities vary with primary productivity, dissolved oxygen, temperature, and seafloor sediment properties across the northern Gulf of Mexico, a region that includes one of the world's largest dead zones. We hypothesized that taxonomic and functional richness would decline in eutrophic and hypoxic coastal environments. Live bivalve mollusks were sampled at 15 stations, spanning more than 600 km of continental shelf habitat. Individuals were identified to species and characterized based on feeding, mobility, fixation, life position relative to the sediment-water interface, and body size. Alpha and beta taxonomic and functional diversity were computed using Hill numbers and linear models used to assess their covariation with regional environmental conditions. Taxonomic and functional diversity were highest in less eutrophic environments characterized by normoxic conditions, and lowest in more eutrophic environments where oxygen was more limited. Community-level differences were underlain by functional shifts, with abundant shallow-infaunal, deposit and mixed feeders in more eutrophic settings, in contrast with less eutrophic settings where suspension feeders were more abundant. Median body size increased with eutrophication, possibly as a result of hypoxia-induced declines in predator and competitor populations. These results suggest that intensifying nutrient loading and deoxygenation in the coastal zone will cause declines in multiple dimensions of benthic biodiversity with implications for ecosystem function.

Reconstructing the redox environment of the Cambrian Harkless Formation, Nevada, USA: Navigating the effects of iron-rich clay minerals on the iron speciation redox proxy

Understanding the oxygenation of ancient oceans is critical for contextualizing evolutionary events throughout Earth's history. While there are many geochemical proxies available for evaluating paleoredox state, iron speciation is one of the most robust and widely applied recorders of local bottom water redox. The proxy uses a series of sequential extractions which are operationally designed to target redox active iron in different mineral groups, including carbonates, oxides, magnetite, and sulfides. However, clay minerals that contain iron are not specifically targeted but can be important reservoirs of redox active iron. These clay minerals are abundant during many times in Earth's history, so it is critical to understand how they are extracted during iron speciation and their impact on paleoenvironmental interpretations.Here we apply the iron speciation proxy in combination with other geochemical proxies (FeT/Al, Mn enrichments) and mineralogical analyses to determine local bottom water redox conditions during deposition of the early Cambrian Harkless Formation exposed near Gold Point, Nevada, USA. The Harkless Formation contains one of the last occurrences of archaeocyathan reefs before their extinction, thus studying the underlying strata can provide information about the environmental conditions which led to reef development. Iron speciation results indicate oxic to potentially anoxic conditions in the water column. The presence of FeT/Al enrichments, Mn depletion, and the Fe-rich redox sensitive clay minerals chamosite and glauconite suggest intermittent anoxia in the water column and porewaters during some intervals of Harkless deposition. Further, by combining iron speciation extractions with petrographic and x-ray diffraction analyses, we demonstrate that glauconite and chamosite were likely formed at or below the sediment water interface and are also not consistently or fully removed by the standard sequential iron reagents, as noted by previous work.The presence of these authigenic Fe-bearing clay minerals overall results in an underestimation of the proportion of redox active iron during deposition and early sediment diagenesis that may lead to incorrect environmental characterization. We therefore advocate for caution and careful examination of the mineralogy of samples when applying the iron speciation proxy, particularly when authigenic and/or early diagenetic iron-bearing clay minerals are suspected to be present. Based upon these findings, we suggest that the Harkless Formation experienced variable local bottom water redox conditions ranging from oxic to anoxic during deposition. Changes in the relative abundances of chamosite and glauconite may also indicate an increase in oxygenation up section, suggesting that local water column oxygenation played a role in archaeocyathan reef development.

Seasonal euxinia in a coastal basin: Impact on sedimentary molybdenum enrichments and isotope signatures

Eutrophication and global warming are leading to increased deoxygenation of coastal waters worldwide. To predict future trajectories of oxygen loss, insight into the intensity and temporal dynamics of past coastal deoxygenation is essential. Here, we assess the use of sedimentary molybdenum (Mo) enrichments and isotopic signatures (δ98Mo) as redox proxies in sediments of a seasonally euxinic coastal basin (Scharendijke, Lake Grevelingen, the Netherlands). Strong drawdown of dissolved Mo (from ∼100 to ∼60 nmol L−1) was observed in the euxinic bottom waters from July to September in 2021, coinciding with sedimentary enrichment of Mo (with peak values up to 19 ppm). A mass balance for Mo indicates that both deposition of Mo in the form of particles and diffusion of dissolved Mo into the sediment account for this Mo enrichment. The δ98Mo composition of suspended matter in the euxinic waters (0.30 to −1.95 ‰) is in line with isotopic fractionation during formation of thiomolybdates, and removal of Mo by sulfur- and/or iron-rich particles. The δ98Mo composition of the bottom water increases from 2.42 to 3.16 ‰ throughout the euxinic period, thereby further supporting preferential uptake of light Mo isotopes during sulfidation in the water column and near the sediment-water interface. The exceptionally high sedimentation rate at this site (>13 cm yr−1) allows seasonal variations in sedimentary enrichments to be preserved in the sedimentary record. Notably, sediment δ98Mo values peak during the summer euxinic period, reaching 1.28 ‰ in 2021 and as high as 2.15 ‰ in 2020. The 2020 value is close to the mean ocean value of 2.3 ‰, implying that sediments overlain by seasonally and permanently euxinic bottom waters can record the same isotopic signatures for Mo. Further work is needed to determine the potential role of diagenesis in altering δ98Mo records on time scales of months to several years.

Metagenomics-resolved genomics provide novel ecological insights into resistome community coalescence of wastewater in river environment

The discharge of wastewater into rivers can lead to resistome coalescence, thereby enhancing the spread risk of antibiotic resistance genes (ARGs) through mixing of exogenous wastewater resistome communities with indigenous riverine communities. At present, the understanding on the role of resistome community coalescence in the dissemination of ARGs is still very limited, and little is known about the process and its ecological implications. To bridge the gap, this study has conducted field-based surveys and microcosm experiments to deeply dissect the coalescence of resistome community in wastewater within river environment, utilizing genome-centric metagenomic analysis approach. The field investigation suggests resistome coalescence enhances the abundance and diversity of ARGs in the receiving river. Furthermore, the microcosm experiments reveal the effect of mixing ratio on resistome coalescence in the water-sediment system and decipher the temporal attenuation dynamics of the coalesced resistome in the environment. The results show the higher proportion of wastewater has a greater impact on ARGs in the water, whereas the effect of mixing ratio is lesser in the sediments. Temporally, the source-specific ARGs originating from wastewater exhibit decreasing trends over the experimental duration, and relatively, the attenuation in the water is more pronounced than that in the sediments. Interestingly, natural light not only facilitates the attenuation of ARGs in the water but may also induce their deposition at the water-sediment interface. Variance partitioning analyses suggest the microbiome, mobilome, and abiotic factors collectively shape the coalescence of the resistome communities in the environment. The study provides empirical evidence on resistome coalescence in river systems, which is instrumental in gaining a better understanding of the spread mechanism of ARGs in the environment.

Elucidating the Composition and Transformation of Dissolved Organic Matter at the Sediment-Water Interface Using High-Resolution Mass Spectrometry.

The exchange and transformation of dissolved organic matter (DOM) at the sediment-water interface are crucial factors in regulating watershed biogeochemistry, with the molecular composition of DOM serving as a pivotal determinant in elucidating this process. High-resolution mass spectrometry (HRMS) is an effective tool for resolving the composition of DOM. By analyzing the compositional characteristics of DOM at the sediment-water interface under three different salinities at the same latitude region in northern China, the findings indicate certain variations in component characteristics of DOM between low-salinity inland waters and high-salinity seawaters, with the former exhibiting greater molecular diversity and higher molecular weights, whereas the latter displayed a higher saturation and bioavailability. Notably, the presence of more CHOS substances in the low-salinity inland waters underscores the transformation of the DOM influenced by terrestrial inputs and anthropogenic activities. Conversely, the presence of more CHO and CHNO substances in high-salinity seawater underscores the microbial effects. The chemical transformation process from overlying water to pore water to sediments was characterized by methylation, hydrogenation, decarboxylation, and reduction, as determined by calculating the relations between the H/C and O/C ratios of different compound types. These findings indicate that HRMS can yield more refined results in revealing the process of DOM at the sediment-water interface under different environments, which provides a more reliable basis for a deeper understanding of the source-sink mechanism of sediment organic matter.

Microbial nitrogen cycling in Microcystis colonies and its contribution to nitrogen removal in eutrophic Lake Taihu, China

Cyanobacterial blooms induced by excessive loadings of nitrogen (N) and other nutrients are a severe ecological problem in aquatic ecosystems. Previous studies of N removal have primarily focused on sediment-water interface, yet the role of cyanobacterial colonies has recently been attracting more research attention. In this study, N cycling processes were quantified for cyanobacterial colonies (primarily Microcystis colonies) and their contribution to N removal was estimated for a large, shallow eutrophic lake in China, Lake Taihu. Various N cycling processes were determined via stable 15N isotope, together with 16S rRNA gene sequencing and quantitative microbial element cycling (QMEC) chip. Denitrification was found to be the most prominent process, estimated to be 36.63, 9.85, 3.35, and 3.15 times higher than dissimilatory nitrate reduction to ammonium (DNRA), nitrification, ammonium (NH4+) uptake and nitrate (NO3−) uptake rates, respectively. Denitrifiers accounted for a large part of the bacterial taxa (35.50 ± 24.65%), and the nirS gene was the most abundant among N cycling-related genes, with (2.54 ± 0.51) × 109 copies g−1Microcystis colonies. A field investigation revealed a positive correlation between the potential denitrification rate and the Chl-a concentration (mostly derived from Microcystis colonies). Based on a multiple stepwise regression model and historical data from 2007 to 2015 for Lake Taihu, the total amount of N removed via denitrification by Microcystis colonies was estimated at 171.72 ± 49.74 t yr−1; this suggests that Microcystis colonies have played an important role in N removal in Lake Taihu since the drinking water crisis in 2007. Overall, this study revealed the importance of denitrification within Microcystis colonies for N removal in eutrophic lakes, like Lake Taihu.

Diving into the Depths: Uncovering Microplastics in Norwegian Coastal Sediment Cores.

High concentrations of microplastics (MPs) have been documented in the deep-sea surface sediments of the Arctic Ocean. However, studies investigating their high-resolution vertical distribution in sediments from the European waters to the Arctic remain limited. This study examines MPs in five sediment cores from the Norwegian Coastal Current (NCC), encompassing the water-sediment interface and sediment layers up to 19 cm depth. Advanced analytical methods for MP identification down to 11 μm in size were combined with radiometric dating and lithology observations. MPs were present across all sediment cores, including layers predating the introduction of plastics, with concentrations exhibiting significant variation (54-12,491 MP kg-1). The smallest size class (11 μm) predominated in most sediment layers (34-100%). A total of 18 different polymer types were identified across all sediment layers, with polymer diversity and depth correlations varying widely between stations. Our findings suggest that differences in seafloor topography and the impact of anthropogenic activities (e.g., fishing) lead to varying environmental conditions at the sampling sites, influencing the vertical distribution of MPs. This challenges the reliability of using environmental parameters to predict MP accumulation zones and questions the use of MPs in sediment cores as indicators of the Anthropocene.

Carbon–sulfur–calcium isotopic variability of lower Cambrian shale-hosted carbonate concretions: Insights into growth mechanisms and calcium cycling

Marine calcium cycling is closely linked with carbon cycling in the ocean, in which authigenic carbonates precipitated in sediments play a non-negligible role. However, calcium cycling during authigenic carbonate precipitation in organic-rich, shaly sediments in geological history remains underexplored. This study focuses on carbonate concretions (aggregates of authigenic carbonates) in the lower Cambrian Niutitang Formation, South China, to provide insights into calcium cycling during their growth. Sedimentological and mineralogical observations suggest that these concretions were formed through concentric growth by authigenic calcite and pyrite precipitation during the early diagenetic stage. Geochemical analyses reveal internal variations in “M-shaped” δ13Ccarb trends (from −11.9 ‰ to −4.4 ‰) and diverse δ34Spyr trends (from 4.7 ‰ to 14.0 ‰) along core-to-rim transects. These findings suggest formation through microbial sulfate reduction by organic matter in a shallow depth beneath the sediment–water interface. In contrast to the dynamic δ13Ccarb and δ34Spyr variations and multi-stage concentric growth, these carbonate concretions display nearly uniform δ44/40Cacarb values (from 0.80 ‰ to 1.03 ‰, average 0.96 ± 0.06 ‰, 1SD) and consistent internal trends, which are further attributed to strongly seawater-buffered porewater calcium geochemistry and small calcium isotope fractionation due to calcite precipitation at slow rates. This study confirms that early diagenetic carbonate concretions in the lower Cambrian Niutitang Formation are characterized by much heavier δ44/40Ca values compared to coeval shallow platform carbonates. In light of abundant authigenic carbonates observed in the lower Cambrian successions, their roles in calcium isotope mass balance in the early Cambrian ocean warrant further investigation in the future. Therefore, early diagenetic carbonate concretions in black shales could provide valuable insights into porewater and seawater calcium isotope signals, as well as early diagenetic and marine calcium cycling in geological history.

Dolomite formation in the Miocene Kardiva platform, Maldives archipelago: a tale of closed-system and open-system dolomitization by current pumping of seawater

Dolomites from two IODP Expedition 359 sites on the northeastern margin of the Miocene Kardiva platform, Maldives archipelago, were examined to explore the question of open versus closed system dolomitization in a drowned carbonate platform. The uppermost approx. 130 m of platform margin carbonate at site U1465 contains less than or equal to 12% dolomite except for five, meters-thick intervals with up to 65% dolomite. All U1465 dolomites consists of decimicron-sized euhedral cement crystals and mimetically replaced peloids and coralline red algal clasts. The abundance and the petrographic features of these dolomites are similar to periplatform and slope dolomite in many other settings that have been interpreted as the product of hydrologically closed-system diagenesis. In contrast, the recovered platform margin deposits at site U1469 are greater than 99% dolomite. Those dolomites are partially fabric retentive with fine-to-medium crystalline, planar subhedral to euhedral crystal mosaics of replacive dolomite and dolomite cement, all with Sr contents that average 256 ppm. Their characteristics are comparable to Neogene platform carbonates universally interpreted to signify hydrologically open-system dolomitization. Sr-isotope ages indicate Miocene dolomitization at both sites after platform drowning, and 18Odolomite values are compatible with dolomitization by cold (10⁰ to 15⁰ C) seawater when the platform margin was, on average, approx..400 m below sea level (mbsl). A current pumping mechanism for the advection of seawater into the top of the platform at site U1469 is proposed and tested with a computational fluid-flow simulation. Current pumping occurs when strong ocean bottom currents flow over sedimentary bedforms and generate lateral pressure differences along the sediment-water interface. The pressure differentials drive seawater through the underlying sediments. The flow simulation shows that the ocean currents that swept large sediment sand waves over and off the drowned Kardiva platform for many millions of years could have vigorously pumped Miocene seawater to sub-seafloor depths of many tens of meters . Mass balance considerations suggest complete dolomitization of the upper 20 m of the platform within 500 Ky or less. The current pumping mechanism could drive dolomitization and mineralogical stabilization below hiatal surfaces, or very slowly accumulating sediments, in any marine setting characterized by strong bottom currents. The greater acidity of Mioc ene seawater relative to younger seawater possibly made the pumping, by any means, of Miocene seawater of normal salinity an effective dolomitizing agent at site U1469 and in undrowned Miocene platforms globally.

Uptake time and enrichment mechanism of rare earth elements in deep-sea bioapatite

Bioapatite is widely recognized as the primary carrier for rare earth elements and yttrium (REY) in deep-sea REY-rich muds. The incorporation of REY into bioapatite occurs at the water-sediment interface, which has the potential to serve as a proxy for reconstructing paleoenvironmental conditions. The timing of REY uptake and the fractionation of rare earth elements (REEs) within bioapatite are crucial factors to understanding the application of these proxies. In this study, we present in-situ geochemical data for bioapatite obtained from surface sediments in the high sedimentation rate Somali Basin of the northwestern Indian Ocean (NWIO), as well as fish teeth within nodules from the low sedimentation rate in the northwestern Pacific Ocean (NWPO). Our findings indicate that the uptake time of REY occurred rapidly, with the ΣREY content reaching 7265 μg/g in bioapatite from the surface sediments in the NWIO within several thousand years. The bone fragments exhibited a high ΣREY content, which was primarily attributed to substitution processes. This led to a notably elevated proportion of middle rare earth elements (MREE) compared to fish teeth. In contrast, the adsorption and substitution mechanisms responsible for REY incorporation decreased from the root to the tip in fish teeth, resulting in a pronounced decline in ΣREY content. The adsorption mechanism was identified as the primary process responsible for REY uptake in the fish teeth within the studied nodules from the NWPO. The fractionation pattern of REEs in these teeth exhibited similarities to that of fish teeth from the NWIO. Therefore, we inferred that the fish teeth within the studied nodules may preserve the original information during late diagenesis. The variation of REY contents in the nodules was influenced by the redox environment, and there is no evidence to support the migration of REY from the nodules into the fish teeth.