Lead sources in seagrass sediments deciphered by isotopic signatures: Implications for organic matter-regulated accumulation.

Tracking organic mercury bioaccumulation by the brown mussel Perna perna (Linnaeus, 1758) in subtropical bays: Environmental exposure and seasonal effects.

Although lakes are major reservoirs for organic matter (OM), global warming may accelerate the decomposition of sedimentary OM. Enhanced OM decomposition under warming intensifies carbon cycling in the biosphere and can lead to ecosystem degradation through deoxygenation. However, it remains unclear whether this temperature-driven increase in decomposition primarily involves modern OM or aged OM. In this study, we applied a novel approach that integrates radiocarbon (Δ14C) analysis with aerobic incubation experiments using undisturbed sediment cores collected from the largest lake in Japan. This approach enabled us to examine directly whether warming accelerates the decomposition of aged OM in aquatic sediments. The age of decomposed OM was estimated by measuring the Δ14C in the dissolved inorganic carbon (DIC) of the overlying water before and after incubation. At the current hypolimnetic temperature of 8 °C, the Δ14C value of decomposed OM was -43.6 ± 50.8‰, which is comparable to the surface lake water DIC value. However, the Δ14C values decreased with increasing temperature, reaching -182.3 ± 31.1‰ at 18 °C. Monte Carlo simulations estimating the temperature sensitivity of modern OM and aged allochthonous OM indicated that aged allochthonous OM exhibits higher temperature sensitivity. This finding supports the carbon quality to temperature hypothesis. These results suggest that reducing anthropogenic erosion and implementing other land-based management measures could help slow the progression of lake deoxygenation under climate warming.

Multi-site investigation of microbial community profiles in mariculture waters and sediments.

Cross-media partitioning, ecological-health risks, and source apportionment of heavy metals in a river-sediment system.

Contemporary contamination and risk of persistent organic pollutants in sediments of an urbanised estuarine and coastal ecosystem.

Sorption in shales is a key process controlling their gas storage capacity. It is, however, a complex phenomenon due to the broad and variable petrophysical characteristics of shales. This complexity is further compounded by the simultaneous occurrence of gas adsorption on mineral and organic surfaces and absorption processes within sedimentary organic matter. In this study, gravimetric sorption experiments were conducted on three geologically distinct shales at 40 °C and pressures ranging from 2 to 15 MPa. We examined both pristine powdered shale samples and their solvent-extracted counterparts to investigate the dominant controls and sorption mechanisms of hydrogen (H 2 ) and carbon dioxide (CO 2 ) - two gases central to energy transition. The sorption capacity of H 2 is shown to be independent of the total organic carbon (TOC) content and is rather governed by the available pore volume in the shale, with thermal maturity exerting a positive influence on porosity development, particularly in samples exhibiting contrasting maturities. Conversely, the CO 2 sorption capacity is controlled by both TOC content and available pore volume. An increase in either parameter enhances the sorption capacity. Comparisons of H 2 and CO 2 sorption capacities among samples possessing relatively similar textural properties and contrasting TOC content indicate that the contribution of H 2 absorption in organic matter becomes increasingly significant at elevated pressures, while CO 2 absorption is shown to increase the total sorption capacity at all investigated pressures. This study provides the first experimental evidence on the role of H 2 and CO 2 absorption in increasing the sorption capacity of immature organic-rich shales. • H 2 retention occurs via adsorption, governed mainly by textural properties. • At high pressure and in TOC-rich shales, absorption enhances H 2 sorption. • CO 2 sorption is enhanced by larger textural properties and/or higher TOC content.

Successional dynamics of deep-sea nematode communities are shaped by environmental conditions, resource availability, and ecological processes such as species interactions, dispersal, and disturbance. This study investigates the in-situ response of free-living nematodes to artificial organic matter enrichment at the deep-sea floor in the Arctic Ocean. The experiment was conducted at 1265 m depth at the LTER HAUSGARTEN observatory in Fram Strait. We created azoic sediments with a grain size composition similar to natural deep-sea sediments and applied three treatments: (1) azoic sediment (control), (2) azoic sediment treated with fresh Phaeocystis , and (3) azoic sediment treated with decaying Phaeocystis . The organic content of the artificial sediments was adjusted to match that of natural sediments. The experimental setup was deployed for three months with a bottom lander and compared to natural sediment samples for reference. Despite similar organic carbon content, artificial sediments exhibited lower nematode abundance and diversity compared to natural sediments, indicating an early successional state dominated by opportunistic taxa. Organic enrichment influenced community composition, with fresh Phaeocystis favouring epistrate feeders and decaying Phaeocystis supporting later-stage colonisers. Natural sediments, characterized by long-term stability and organic accumulation, supported higher nematode abundance, functional diversity, and a balanced trophic structure. These findings indicate that a mature community requires more time to develop than the three-month duration of the experiment. Our findings emphasize the role of organic matter retention and long-term sediment accumulation in shaping deep-sea nematode communities and highlight the potential ecological consequences of anthropogenic-driven changes in organic matter deposition, which could affect deep-sea biodiversity and ecosystem resilience. • Artificial sediments had lower nematode abundance and were dominated by opportunistic genera, indicating early successional stages • Natural sediments supported a mature, diverse nematode community • Sediments enriched with fresh Phaeocystis favoured epistrate-feeding nematodes • Sediments enriched with decayed Phaeocystis favoured later-stage nematode colonisers

Reconstructing anthropocene carbon dynamics: Tracking sedimentary organic matter sources with multiple proxies in a temperate semi-arid lake (Hulun, northern China)

Coastal carbon cycle and budgets are significant drivers of regional climate change, generating widespread global attention. This study explored the spatial and seasonal variability of alkalinity biogeochemistry within a coastal aquifer-aquitard system in the Pearl River Delta, China. We measured physicochemical parameters including salinity, temperature, and pH, total alkalinity (TA), stable isotopes, cations, and anions of groundwater samples, which were collected every season using permanent multilevel groundwater sampling systems installed at three field sites of PRD. Results revealed that the elevated production of total alkalinity and dissolved inorganic carbon in the deltaic aquifer-aquitard system stemmed from sedimentary organic matter due to the presence of the aquitard formed during the Holocene marine transgressive event. Cluster analysis, incorporating various components of inorganic carbon and physical-chemical features, classified sources of TA in groundwater samples into four categories: modern weathering dominated, Holocene transgression dominated, late Pleistocene weathering dominated, and early Pleistocene weathering dominated. The study suggests that Holocene marine sediments act as dynamic biogeochemical reactors, supplying organic matters and influencing carbon cycles amidst complex hydrogeological and biogeochemical conditions.

Macrophyte restoration alters sedimentary organic matter-microbes-environment interactions and enhances carbon sequestration in lake sediment.

Spatial distribution and environmental controls of n-alkanes in gulf of oman sediments: Implications for organic matter sources and cycling in subtropical active marginal seas.

A century-scale sedimentary organic matter record of the South Yellow Sea: Response to climatic and anthropogenic changes in the Yellow River Basin

Abstract Methylphenanthrenes are widely used as molecular indicators of the thermal maturity of sedimentary organic matter; however, the reaction pathways controlling their isomer distributions at immature stages remain poorly constrained. In this study, we investigate the formation pathways of methylphenanthrenes from diterpenoid-derived precursors using heating experiments of abietic acid as a model compound, together with heating experiments and compositional analyses of immature coals. The results demonstrate that 1-methylphenanthrene is preferentially formed during the early stages of thermal alteration via degradation of abietane-type precursors, likely involving dealkylation and aromatization processes. In contrast, progressive thermal maturation promotes isomerization toward thermodynamically more stable β-substituted methylphenanthrenes, resulting in a shift toward equilibrium-controlled distributions. Analyses of immature coals show a strong positive correlation between retene, a key intermediate derived from abietic acid and related diterpenoids, and the relative abundance of 1-methylphenanthrene, supporting a precursor-driven reaction pathway. These findings indicate that methylphenanthrene compositions at low maturity primarily reflect kinetically controlled transformation processes rather than thermodynamic equilibration. The predominance of 1-methylphenanthrene thus provides insight into the reaction mechanisms governing the early-stage formation of alkylated aromatic hydrocarbons.

Land-use impacts on Amazon and Atlantic rainforest coastal ecosystems revealed by multiple biogeochemical markers.

Source-specific organic matter modulates Anammox via humic-like DOM in mangrove sediments: Implications for eutrophication mitigation.

The degradation of organic matter (OM) by microorganisms in thawing permafrost produces greenhouse gases. Terrestrial OM is transported into fjords through hydrological runoff, but it is unclear whether the microbial mechanisms of OM degradation on land persist after soils enter marine environments, which differ greatly in conditions and microbial communities. This question is particularly relevant for low-OM soils, which dominate Arctic landscapes and are more exposed to oxidants. Here, we compared OM-degrading capacity in permafrost-affected active layer soils and adjacent fjord sediments from Kongsfjorden, Svalbard, focusing on carbohydrate-active enzymes (CAZymes), which target some of the most abundant types of organic matter in soils. Using multi-omics approaches-metagenomics, metagenome-assembled genomes (MAGs), metabolomics, metatranscriptomics, and metaproteomics-we examined CAZyme presence, distribution, and activity. Despite environmental differences, both soils and sediments harbored diverse glycoside hydrolases and polysaccharide lyases, most of which showed evidence of activity. Verrucomicrobia expressed the highest number of CAZyme transcripts, indicating that they dominated active carbohydrate degradation in fjord sediments, while Acidobacteria and Actinobacteria were more active in soils. Notably, CAZymes in fjord sediments targeted primarily soil-derived OM, and the proportions of enzymes degrading terrestrial OM, marine OM, and microbial necromass-remnants of dead microbial cells were similar across both environments. These results suggest that microbial communities in both soils and fjord sediments are equipped to degrade carbohydrates, and that burial of terrestrial-derived OM in fjord sediments may not protect it from microbial breakdown under Arctic warming.IMPORTANCEPermafrost thaw may be a critical climate feedback because microbial degradation of organic matter (OM) can release greenhouse gases. While fjords serve as major carbon burial sites, our results show that burial of terrestrial-derived OM in these sediments does not ensure protection from microbial degradation. Microbial communities in both active layer soils and fjord sediments harbor a broad arsenal of carbohydrate-active enzymes, with evidence of activity across diverse taxa. This functional continuity indicates that once terrestrial material is washed into fjords, it remains vulnerable to microbial breakdown despite different environmental conditions. Understanding these cross-system continuities in microbial function is essential for predicting the fate of OM in a rapidly warming Arctic and highlights the importance of including fjord sediments in global carbon cycle models.

Elevated ammonium concentrations in deltaic groundwater pose a widespread environmental challenge, yet the microbial mechanisms linking depositional history to ammonium dynamics remain poorly understood. The Pearl River Delta, with the highest naturally occurring groundwater ammonium concentrations documented globally, provides a unique natural system to investigate these processes. Here, by integrating geochemical and metagenomic data, we show that fermentation-related genes are the most prevalent across all depositional zones, suggesting fermentation as the potential primary pathway for ammonium production, with the functional potential declining as sedimentary organic matter becomes increasingly recalcitrant with sediment age. Secondary mechanisms shift from nitrate reduction to nitrite ammonification across terrestrial-to-marine-dominated zones, reflecting salinity-driven metabolic partitioning. Notably, the marine-derived genus Brevirhabdus emerges as a key taxon linking depositional history to present-day biogeochemistry, demonstrating remarkable metabolic versatility. These findings demonstrate that paleo-depositional and hydrogeological evolution fundamentally shape microbial landscapes and dictate groundwater quality in deltaic systems worldwide.

Late Holocene monsoon-driven variability in sedimentary organic matter and lacustrine processes from Hulas Khera Lake, Central Ganga Plain, India

Constrained sediment carbon sequestration driven by agricultural diffuse pollution: Evidence from core-derived DOM.