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

Freshwater lakes play a critical role in the global carbon cycle by storing and transforming organic matter (OM) from both terrestrial and aquatic sources. Small lakes in northern temperate regions, despite their limited surface area, disproportionately influence regional carbon budgets. Buried sediments integrate OM inputs over time and archive ecosystem responses to natural and anthropogenic disturbances. However, the direction and magnitude of recent environmental changes on sediment carbon (C) dynamics remain poorly understood. A 23-centimeter core was collected from a small temperate lake in northeastern USA to evaluate sediment OM content and composition over timescales relevant to historical land-use change, damming, and recovery from acid deposition. Patterns in OM burial and source contributions were revealed via elemental and isotopic analyses of bulk OM and UV–Vis spectrophotometry of water-extractable organic matter (WEOM). The optical metrics expanded observations of likely OM sources beyond the information gained from bulk carbon metrics (total carbon, δ 13 C). The aromaticity of WEOM increased downcore, which is consistent with a shift from increased terrestrial inputs during early logging and damming activity (pre ∼1920) to more microbial-derived OM in recent surficial sediments. Future applications of WEOM optical properties as complements to traditional geochemical metrics can enhance interpretations of lake ecosystem responses recorded in lake sediments to environmental perturbations in temperate lakes. • Highlights (85 character max per point including spaces) • Water-extractable organic matter from lake sediments reveals environmental history • WEOM optical metrics vary more across sediment depth than bulk geochemical metrics • WEOM metrics show promise for broader geochemical applications in lake sediments

Rethinking membrane biofouling: A functional and mechanistic perspective

The dual role and mechanism of insoluble humic substances governing the fate of Cu in sediments: Rapid accumulation and long-term stabilization.

Long-term bioelectricity generation in microbial fuel cell exposed to perfluorooctanoic acid.

To elucidate the sources and spatial variations in organic matter in surface sediments from Lingdingyang of the Pearl River Estuary, 18 surface sediment samples were collected and analyzed for obtaining total organic carbon (TOC), total nitrogen (TN), atomic TOC/TN ratio (C/Natom), stable carbon and nitrogen isotopes (δ13C, δ15N), and glycerol dialkyl glycerol tetraethers (GDGTs). A three-endmember framework was constructed using the BIT and δ13C to constrain the sources of the organic matter. The results showed a significant positive correlation between TOC and TN, with relatively higher values in Jiaoyi Bay and western Lingdingyang, lower values in eastern Lingdingyang, and intermediate values in Shenzhen Bay. The C/Natom, δ13C, and δ15N results revealed that the sedimentary organic matter in the study area exhibits mixed-source characteristics, influenced by soil, C3 plants, and marine autochthonous organic matter. Among the subregions, Jiaoyi Bay is more strongly influenced by terrestrial inputs, while Shenzhen Bay receives relatively higher contributions from marine autochthonous organic matter. The GDGTs results showed that Jiaoyi Bay is characterized by elevated abundances of both brGDGTs and isoGDGTs, whereas isoGDGTs were also relatively enriched in Shenzhen Bay. brGDGTs exhibited a significant negative correlation with δ13C, whereas BIT showed no significant correlation with either brGDGTs or δ13C, indicating that BIT cannot be simply regarded as a unique proxy for soil input, but rather reflects the combined effects of in situ production, changes in archaeal lipids, and sedimentary preservation. The three-endmember model further revealed significant spatial variations in the sources of organic matter in surface sediments from Lingdingyang. Overall, the combined use of multiple proxies is more effective than any single proxy in revealing the sources and spatial differentiation of sedimentary organic matter in this subtropical, complex estuarine environment.

Abstract Deep‐water of the eastern Mediterranean basins mainly forms in the Adriatic Sea and episodically in the Aegean Sea. However, past and future variability under changing temperature and freshwater inputs remains unclear. We reconstruct seawater ε Nd from Northern Ionian Sea cores to trace intermediate‐ and deep‐water provenance during the Holocene. High organic matter deposition during S1a and S1b corresponds to radiogenic ε Nd values (up to −4.9), indicating reduced and shallower Adriatic Deep Water (AdDW) formation, with Ionian Sea increasingly dominated by Aegean deep water (AeDW). The re‐ventilation of deep‐water at ∼8.2 ka is marked by unradiogenic ε Nd (−6.5), implying active AdDW formation. In contrast, a second re‐ventilation within the S1b at intermediate depth is associated with radiogenic ε Nd values (−4.5) attributed to the formation of the radiogenic intermediate water from the eastern basin (LIW). These results demonstrate the high sensitivity of Mediterranean deep‐water formation to freshwater forcing and abrupt climate change.

Distribution, sources, and controlling factors in surface sedimentary organic matter of a typical degraded coral reef ecosystem in China.

Abstract Anaerobic oxidation of methane (AOM) is a potentially important sink for methane in freshwater sediments. Assessing the contribution of AOM to methane budgets requires an understanding of AOM process kinetics, yet such information remains scarce. In the present study, we experimentally quantified the kinetics of AOM in the sediments of the Danish Lake Ørn, where sulfate‐ and iron‐dependent AOM occur side by side. The process exhibited saturation kinetics for methane, sulfate, and Fe(III), and the derived half‐saturation constants ( K m ) implied that these substrates co‐limit in situ AOM rates across concentration ranges typical for the study site and many other freshwater systems. Nevertheless, values of K m for methane (414 ± 79 μ M) and sulfate (31 ± 29 μ M) were low relative to marine systems, indicating an adaptation of the microbial community to the limnic environment. Experiments involving a synthetic analog of humic substances, anthraquinone‐2,6‐disulfonate (AQDS), demonstrated that sedimentary organic matter could play a role in alleviating restrictive Fe‐AOM kinetics. Incorporation of the obtained kinetic parameters into predictions of AOM rate profiles based on methane, sulfate, and Fe(III) concentrations revealed similar contributions of sulfate‐ and Fe(III)‐AOM pathways in the sulfate–methane transition zone. Our study expands the limited knowledge on the kinetics of microbial methane oxidation in freshwater systems and highlights the potential importance of AOM in regulating methane emissions from inland waters.

Abstract Tidal flats are dynamic ecosystems where bivalves play a key role in nutrient cycling through selective feeding on suspended and benthic organic matter. However, conventional bulk stable isotope analysis can have limited resolving power for distinguishing among multiple food sources when their carbon isotope ratios (δ 13 C) overlap, particularly with respect to identifying the dominant organic matter sources. In this study, we evaluated the applicability of fatty acid compound-specific isotope analysis (FA-CSIA) to identify the food sources of benthic organisms inhabiting tidal flat ecosystems. We collected bivalves and polychaetes from the Gamou tidal flat and analyzed their δ 13 C values using bulk isotope analysis, fatty acid biomarkers, and FA-CSIA. Principal component analysis of fatty acid biomarkers revealed differences in the characteristics of benthic organisms and their food sources. FA-CSIA improved the accuracy of source identification for essential fatty acids such as linoleic acid and α-linolenic acid. Bivalves showed isotopic signatures similar to those of particulate organic matter (POM), while polychaetes aligned more closely with those of sediment organic matter (SOM). These findings suggest that FA-CSIA can effectively resolve trophic relationships in complex environments where conventional methods are limited.

Sediment and particle relocation through bioturbation significantly influences biogeochemical processes and community structure in marine benthic ecosystems. Rays displace large amounts of sediment while feeding, forming ray pits that affect prey diversity, patch dynamics and seabed morphology. However, the effect of ray pit formation and presence on benthic nutrient dynamics remains unclear. Our study focused on the biogeochemical effects of New Zealand eagle ray ( Myliobatis tenuicaudatus ) bioturbation on an intertidal flat in Whangateau Harbour (Auckland, New Zealand). We analysed the differences in benthic fluxes (O 2 , N 2 , PO 4 3 - and NH 4 + ) and sediment characteristics (grain size, porosity, sediment organic matter and chlorophyll a ) in manually excavated experimental ray feeding pits relative to undisturbed sediments over a period of 14 d that encompassed major changes in pit morphology. The study revealed significant differences in benthic fluxes between experimental pits and controls, as well as over time, with a 50.2% increase in oxygen consumption in the pits and more than a 95% increase in nutrient efflux. While the artificial ray pit had an impact on nutrient dynamics, thus playing a role in ecosystem functioning, its impact on sedimentary characteristics was not evident within the study site or experimental timeframe. This research underscores the importance of rays as bioturbators and highlights the need for a better understanding of megafaunal influence on nutrient cycles and sediment turnover to define their role in ecosystem multifunctionality and aid conservation efforts.

Abstract. This paper describes the ocean BiogeochemicAl Model for Hypoxic and Benthic Influenced areas (BAMHBI). BAMHBI is a moderate complexity marine biogeochemical model that describes the cycling of carbon, nitrogen, phosphorus, silicon and oxygen through the marine foodweb. It involves 22 state variables, extends from bacteria up to mesozooplankton and includes three phytoplankton functional types (PFTs), two zooplankton size-classes, a microbial loop with several classes of detritic materials. Five optional modules are available allowing to extend the model with the explicit modelling of Chlorophyll a (Chl a) in each PFT, benthic degradation, gelatinous dynamics, particles aggregation and the carbonate system. BAMHBI describes the degradation of organic matter according to oxygenation conditions using an approach similar to that used in the sediment to simulate early diagenesis. The model is particularly appropriate for modelling low oxygen environments and the generation of sulfidic waters. An optional benthic module solves the degradation of sedimentary organic matter and the benthic-pelagic fluxes of solutes using an efficient formulation based on meta-modelling. This paper describes in details model formulations, implementation and coupling with the physics. BAMHBI's code is written in Fortran and can be coupled with many hydrodynamical models. Two case studies of application of BAMHBI in the Black Sea are described. One describes the application of BAMHBI to simulate the biogeochemical dynamics of the northwestern shelf during the eutrophication period. In particular, the ability of BAMHBI to simulate the oxygen dynamics at seasonal and interannual scales is assessed with a focus on the simulation of bottom hypoxia. We highlight the results of the benthic modelling module and its ability to represent benthic-pelagic fluxes. The second case study compares the BAMHBI simulated Chl a, oxygen and nitrate dynamics in the deep sea with respect to biogeochemical Argo.

Extreme drought drives contrasting fates of labile and recalcitrant mangrove soil organic matter.

Coral mucus input promotes sedimentary organic matter degradation: Evidence from a typical coral reef area, northern South China Sea.

Ecological regime shifts weaken sedimentary carbon sequestration in shallow Lake liangzi.

TEMPORARY REMOVAL: Organic and isotopic indicators for sorting of sedimentary organic matter along a marginal submarine canyon

Abstract Identifying organic matter (OM) distribution and origins in sediments is vital for distinguishing archival records, depositional dynamics, and extent of terrigenous inputs to marine systems. However, degradation and modification of OM before deposition can camouflage and mask its source signals in sedimentary sinks. Also, limited number of samples, matrix complexity, and multiple available tracers for single‐proxy mixing models can all challenge source apportionment of sedimentary OM. To overcome these limitations and deconvolute the origins of deposited OM along a land‐ocean transect, this study integrates machine learning and multivariate analyses of elemental contents (C and N), biomarker abundances (C17‐C27 n ‐alkanes), and bulk and compound specific stable carbon isotope values (δ 13 C) of sediments across the St. Lawrence Estuary and Gulf (SLEG). With pronounced provenance and terrestrial‐marine regimes, the most proximal and distal sedimentary endmembers of the SLEG (60 and 780 km away from outlet) retain distinct geochemical information for training Principal Component Analysis and Partial Least Squares Regression model, predicting OM distribution across in‐between stations. Results reveal a gradual shift in sedimented OM composition along the continuum due to OM inputs and source‐to‐sink processes; with a gradient of 2% decrease in terrestrial character of sedimentary OM per each 10 km distance from river outlet, findings reflect that the inputs and signals of terrigenous OM are progressively diluted and transformed offshore. Also, isotopic and molecular signatures exert stronger predicting controls than conventional tracers such as C/N ratios, highlighting that the diagnostic strength of proxies is system‐specific, particularly under dynamic conditions. Integrative multivariate approaches can hence capture the complexity and covariances of multiple biogeochemical proxies to better decode camouflaged sedimentary archives and provide more holistic estimations of OM transportation and transformation across systems with strong geo‐spatial and input gradients.

Species invasions are one of the main anthropogenic forces reshaping ecological structure and function in lakes during the 21st century. Common carp (Cyprinus carpio) are among the most globally widespread and damaging aquatic invasive species, with the capacity to significantly alter lake ecosystems. While it is well documented that carp feeding activity can disturb sediments, decrease water quality, and reduce macrophyte and fish diversity, less is known about how carp influence sediment chemistry and nutrient cycling. Here, we examined the effect of carp invasion on sediment phosphorus (P) dynamics and organic matter quality in shallow lakes. We compared P fractions in sediments of lakes with established carp populations and those from carp-free reference lakes. We found that lakes with carp had depleted surficial sediments, with significantly lower organic P (0.16 vs. 0.41 mg g-1) and higher C/P ratios (972 vs. 639) than lakes without carp. Carp lakes had higher concentrations of water-column total P (370 vs. 160 μg L-1), though a mass balance between sediment labile P and water-column P was similar for lakes with and without carp, indicating sediment P loss due to carp is largely kept in the water column. Sediments are a crucial component of lake ecosystems, and a reduction in sediment organic matter quality by invasive carp can alter food web dynamics and geochemical processes in invaded lakes.

Abstract Coastal hypoxia is profoundly affected by sediment depletion of oxygen and recycling of nutrients—processes sustained by long‐term accumulation of sediment organic matter. While sediment‐water interactions are widely recognized, quantitative understanding of sediment legacy effects remains limited. To address this gap, we developed a two‐layer sediment model integrated with a physical‐biogeochemical framework for the Pearl River Estuary to elucidate how legacy organic matter perpetuates hypoxia via benthic‐pelagic coupling. Results show that sediment oxygen consumption accounts for 44% of total oxygen depletion in low‐oxygen zones, increasing to 81% in near‐bottom waters. This oxygen demand is significantly supported by legacy organic matter, without which would reduce primary production by 68% and the hypoxic area by 53%. Furthermore, we demonstrate that sediment legacy effects amplify hypoxia sensitivity to nutrient loading and may lead to hysteresis and regime shifts if unaddressed. Therefore, effective hypoxia mitigation requires management strategies tailored to system‐specific sediment‐water coupling dynamics.

Freshwater bivalves influence ecosystem functioning by transferring pelagic material to the benthos through filtration and biodeposition, yet quantitative multiscale evidence remains scarce for South American lakes. We assessed the role of the native mussel Diplodon chilensis in Laguna Chica de San Pedro (southern Chile) by integrating laboratory measurements, seasonal in situ mesocosm experiments, and lake-scale estimates. Individual filtration rates were quantified under contrasting temperature and phytoplankton biomass conditions, while field experiments evaluated mussel effects on sediment biogeochemistry and zoobenthic assemblages. Filtration increased strongly with temperature, whereas food availability exerted a detectable effect only at lower temperatures. Live mussels consistently enhanced sediment organic matter and total nitrogen, while total phosphorus responses were weak and variable. Macroinvertebrate richness and abundance increased in association with mussel presence, whereas meiofaunal responses were weaker and inconsistent. When scaled to the lake level using bathymetric population distribution and seasonal deposition rates, D. chilensis accounted for substantial annual fluxes of organic matter and nitrogen to surface sediments, largely driven by shallow and intermediate depths. These results demonstrate that native freshwater mussels mediate a persistent downward component of benthic–pelagic coupling in clear-water temperate lakes of southern South America.