Sedimentary Organic Matter Research Articles

Wetland Ecosystem Service Preservation? Geochemical Changes in Systems with Mangroves and Shrimp Farms in the Northern Ecuadorean Coast

Mangrove sediments serve as paleoenvironmental records of organic matter and nutrient accumulation. Ecuador, the world’s largest producer of whiteleg shrimp Penaeus vannamei in brackish waters, lost 43% of its continental mangroves between 1969 and 1999. Currently, more than 70,000 hectares of shrimp farms operate in estuaries with mangroves and within mangrove reserves. Variations in mangrove coverage and the extent of shrimp farms are described for the period 1996–2020 for two mangrove reserves, REMACAM and RVSMERM, with an observed increase in the extent of shrimp farms in both reserves. Four sediment cores obtained from mangrove drains and drains transformed into shrimp farm infrastructures were analyzed to observe the impact of this activity on the cumulative changes in total organic carbon (TOC) content and total nitrogen (TN) content, the fractionation of stable isotopes δ13C and δ15N, as well as the TOC/TN ratio. The mangrove drains in REMACAM had 3.8 times more TOC and 2.3 times more TN than drains transformed into shrimp farms in RVSMERM, with lower TOC/TN ratios. The organic matter in sediments from sectors with a higher proportion of shrimp farms mainly came from particulate organic matter of freshwater and freshwater algae compared to mangrove drains. Increases in TOC and TN content were recorded in all analyzed sectors, which could be attributed to the cumulative impact of population growth, the development of other agricultural crops, and continental deforestation, despite the fact that proportionally, the highest increases occurred in the sector with a greater influence of shrimp farms.

Different dissolved organic matter sources sustain microbial life in a sandy beach subterranean estuary – an incubation study

In subterranean estuaries (STE), fresh and saline groundwater introduce dissolved organic matter (DOM) of different origin. This DOM serves as substrate for microorganisms that thrive in the STE. In high-energy beaches with dynamic porewater advection, microbial communities face frequent changes in groundwater composition, even at several meters depth. It is unknown how DOM from deep STE groundwater (> 5 m depth) is transformed by prevailing microbial communities. To address this question, we performed sediment incubations in flow-through reactors (FTRs) with deep (6 m depth) STE groundwater of low (1.6) and high salinity (29.1). FTR setups were sampled daily for quantification of dissolved organic carbon (DOC), and at start and end (day 13) of the incubation for analysis of DOM composition, microbial cell numbers and community composition. Solid-phase extracted DOM was molecularly characterized via ultrahigh-resolution Fourier-transform ion cyclotron resonance mass spectrometry. Both groundwater types contained mainly reworked DOM. Corroborating its presumed origin, the fresh groundwater had a more terrestrial DOM signature with a higher proportion of aromatic compounds compared to the saline groundwater. Over the course of the incubation, DOC concentrations increased primarily due to leaching of sedimentary organic matter, providing an additional source of DOM. In all setups, the DOM composition changed significantly from start to end, and similarly for fresh and saline groundwater. From the ~2700 molecular formulae (MF) detected on day 0, 34-35% were removed during the incubations, demonstrating the potential of deep STE microbial communities to degrade recalcitrant DOM that is supplied with the advective porewater flow. However, a substantial portion of MF (63-64%) was retained in both groundwater types, indicating that a fraction of deep STE-DOM is resistant to removal. Properties of MF that were newly detected on day 13 (26-28%) were indicative of labile DOM. Some of these newly detected MF were also identified in sediment-leachates, suggesting that beach sediments are a source of fresh DOM for the STE microbial communities. It is likely that due to longer groundwater residence time in the STE, continuous leaching and microbial processing shift the molecular composition of released DOM from more labile to more recalcitrant DOM.

Changes in accumulation of land-based organic matter under recent climate change and anthropogenic impact: A tropical coastal perspective

Tropical continental shelves play an important role in the global carbon cycle especially in the context of increased anthropogenic interference and climate change. However, the long-term fate and response of sedimentary organic carbon (OC) in these regions remain poorly understood. In this study, we analyzed bulk OC and molecular biomarkers in a sediment core collected from the lower Gulf of Thailand, and compiled with several published records of sedimentary organic matter (OM) from other tropical Asian margins. Our results reveal a dramatic ∼ 40 % increase in terrestrial OC inputs since the 1980s, likely driven by the effects of accelerated coastal erosion from rising sea levels and the degradation of mangrove ecosystems. In addition, shifts in regional human activities, including changes in energy consumption patterns, have altered the sources of pyrogenic OM, contributing to the observed spatial and temporal variability of anthropogenic OM across tropical coastal margins. Molecular fingerprints highlight recent changes in the accumulation of land-based OM, showing an increased presence of erosion-derived and degraded OC, along with pyrogenic OM. This shift is linked to the combined effects of coastal retreat and basin-wide emissions, influenced by both natural climate forces and anthropogenic activities.

Transport and deposition of terrestrial organic matter in marine littoral deltas: New evidence from flume experiments and 3D laser scanning

Terrestrial organic matter (TOM) serves as the primary parent material for source rocks in marine-terrestrial transitional environments. The transport and deposition process of TOM affects the development of high-quality source rocks in shallow marine areas. Based on the sequence stratigraphy of the Enping Formation (upper Eocene to lower Oligocene) in the Baiyun Sag and the petrological characteristics of the source rocks, simulation experiments of terrestrial dispersed organic matter deposition constrained by topography, provenance composition, sedimentation period and other conditions were conducted. Comparative experiments of individual constraints such as topographic slope, hydrodynamic conditions, water salinity and particle size of organic matter were also conducted. The results indicate that TOM enrichment in the littoral delta system initially increases with transport distance but subsequently decreases. Four TOM distribution patterns were identified: interrupted, interbedded, lenticular, and banded types. The interrupted, interbedded, and lenticular types predominantly occur in delta plains, whereas the banded type primarily develops in delta fronts and prodeltas. In the early stages of delta formation, gentle slope conditions are more conducive to the forward transport of TOM. As the delta develops, the sediment thickness increases, which reduces the slope gradient and thus weakens the effect on the transport distance of TOM. Higher flow intensity promotes TOM transport, however, wave action can impede forward transport, creating localized TOM enrichment areas on the delta plain. In shallow water, the increase in water salinity enhances the flocculation of TOM, thus reducing the transport distance of TOM. Meanwhile, Smaller TOM particle sizes correspond to greater transport distances and increased heterogeneity in its planar distribution within the delta-shallow sea sedimentary system.

Late-Holocene paleoreconstruction of the Southwestern Atlantic Ocean: A multiproxy understanding of the paleoclimatic, paleoproductivity and paleotemperature variability

A multiproxy evaluation focusing on sedimentological, molecular, and isotopic proxies was used to reconstruct the environmental changes on the SW Atlantic Ocean margin enabling an integrated assessment of this basin’s Late-Holocene oceanographic and climatic dynamics. Variations in paleoproductivity, climate, and sea surface temperature (SST) indicate three phases throughout the core. The first phase (2800–1600 cal yr BP) showed a generally low marine and terrigenous organic matter input, marked by terrigenous material input pulses transported by the Brazil Current (BC) from small rivers of the South Brazil Bight (SBB) and/or Paraiba do Sul River. The second interval (1600–1300 cal yr BP) registered the lowest levels of fine sediments, total organic carbon content, and concentrations of all analyzed lipid biomarkers, indicating the occurrence of a semi-stationary meander of the BC that hindered the sedimentation of fine sediments. This phase may indicate a varied timing and duration due to the sparsed radiocarbon data. The third interval (1300 cal yr BP to modern years) presented the highest levels of marine and terrigenous proxies and were influenced by the strengthening of the South America Monson System (SAMS), the El Niño Southern Oscillation (ENSO) events, and the NE winds, which caused higher precipitation in the La Plata River drainage basin. A northward displacement of the Brazil Coastal Current (BCC) and the transport of the Plata Plume Water (PPW) to the central regions of the SBB, as well as the occurrence of more regular upwelling events may also influence the sedimentary organic matter composition. SST showed a variation up to ~3.2°C through the core and was related to the influence of the BC current associated with the Tropical Water (TW) and the South Atlantic Central Water (SACW), and the PPW influence on the shelf.

Characteristics of Stable Carbon and Nitrogen Isotopes in Different Ecological Plant Groups and Sediments Collected from 14 Softwater Lakes in Poland

Softwater lakes with specific, rare, and protected aquatic plant vegetation are very sensitive to increased trophic and water chemical changes, especially alkalization. These changes might be reflected in the stable carbon and nitrogen isotopes of the organic matter (OM) of those plants (δ13CORG and δ15NORG) and sediments (δ13CORG and δ15NTN) which they cocreated. To recognize the relationship between OM in the aquatic plants of softwater lakes and the cocreated sediments, we analyzed the plants δ13CORG and δ15NORG in light of four ecological groups (as well as the sediments δ13CORG and δ15NTN in which these plants thrived). Studies were performed in July 2020 on 14 softwater lakes in northern Poland with varying pH gradients from 4.86 to 9.20. For each lake, a single stand was examined for each species detected. The goal was to investigate each species at 10 sites, but this target was not reached for several species. Among the investigated ecological groups, isoetids and mosses showed the least variation in obtained values. In contrast, elodeids exhibited the highest variation in δ13C results due to their diverse carbon uptake strategies, involving both CO2 and HCO3− forms. Moreover, the δ13C values of charophytes and elodeids were highly related to the increasing pH of water. The slight differences between the δ13C results of plants and sediments in isoetid stands further support this finding. Furthermore, we noticed an increase in sediment δ13CORG values along the alkalization gradient, suggesting that macrophytes were the primary source of OM for the sediments. The positive correlation between the δ13C values of plants and sediments (r = 0.69, p < 0.05) might also confirm that the macrophytes were a significant source of OM in sediments. Regarding δ15N values, we did not find significant differentiation between plants and sediments across ecological groups. However, sediment consistently exhibited 15N-enrichment compared to plant material. This enrichment is likely attributed to the accumulation of 15N during the decomposition of the deposited material. This study confirms the possibility of tracking changes in the aquatic vegetation of softwater lakes based primarily on the sediment δ13CORG values along the alkalization gradient.

Role of Metalloproteinases in Adhesion to Radicular Dentin: A Literature Review.

Root dentin is a porous and complex dental surface that may have irregularities and deposits of organic material. To achieve an effective bond between restorative materials and root dentin, it is necessary that the restorative materials adhere intimately to the dentin surface. Metalloproteinases (MMPs) are a group of proteolytic enzymes that perform an important role in degrading the extracellular matrix and remodeling connective tissue. The aim of this research was to determine the scientific evidence available on the role played by MMPs in adhesion to root dentin and their putative inhibitors. Several techniques have been used to evaluate the presence of MMPs in the root dentin of human and bovine teeth, such as Western blot, immunohistochemistry, immunofluorescence, and zymography, the latter also being used together with the EnzCheck assay to evaluate the inhibitory effect of adhesion protocols on the activity of root MMPs in vitro. When analyzing the databases, 236 articles were found, 12 of which met the selection criteria. The variables analyzed were articles that evaluated different MMP inhibitors in root dentin. In the adhesion to radicular dentin, MMPs have a crucial role in the degradation of the extracellular matrix of dentin and the remodeling of the dentin surface because excessive MMP activity can be harmful to dental health, since excessive degradation of the extracellular matrix of dentin can weaken the tooth structure and decrease fracture resistance. Therefore, it is important to monitor MMP activity during root dentin bonding procedures.

A Stable Isotope Analysis to Quantify the Contribution of Basal Dietary Sources to Food Webs of Drinking Water Reservoirs

This study investigates the food web structure of the Xinlicheng Reservoir, a drinking water source of critical importance in Changchun, China, by employing stable isotope analysis (SIA) to quantify the contribution ratios of four basal dietary sources—phytoplankton, zooplankton, sediment organic matter, and particulate organic matter (POM)—to the diets of two key filter-feeding fish species, Hypophthalm ichthys molitrix and Aristichthys nobilis. The analysis reveals that phytoplankton is the dominant dietary source for both species, contributing 32.08% and 34.06%, respectively, whereas the POM contribution is discernably lower (13.25%). The average trophic level of the fish assemblage in Xinlicheng Reservoir is 3.03, while the trophic levels of the two filter-feeding species lie between 3.00 and 3.50. Furthermore, a random forest model was used to identify key environmental drivers of isotopic variations in these basal dietary sources, highlighting the significant role of pH, total nitrogen (TN), chloride (Cl−), calcium (Ca2+), phosphorus (TP), and silicate (SiO44−) in influencing carbon and nitrogen isotopic ratios. These findings provide critical insights to optimize biomanipulation strategies aimed at improving water quality in drinking water reservoirs by enhancing our understanding of the environmental factors that govern trophic interactions and broader food web dynamics.

Microplastics alter the migration and transformation of vanadium in the riverine sediment environment

Microplastics (MPs, size <5 mm) have emerged as environmental hazards and are widespread in the environment. They can significantly alter the reactivity and mobility of co-occurring elements. Vanadium, a strategic resource, was witnessed rising in the environment because of extensive anthropogenic activities. Nevertheless, the impact of MPs on the migration and transformation of vanadium has yet been investigated. This study therefore investigated the vanadium behavior in riverine sediment and overlying river water in the presence of MPs. 1.5 g representative non-degradable MPs (polyamide, polyethylene terephthalate) and biodegradable MPs (polybutylene succinate, polyhydroxyalkanoates) were separately amended into the reactors, which contained 50 mg vanadium-rich sediment. After incubation for 60 days, vanadium in the sediments decreased substantially, while vanadium increased in the overlying water, especially in reactors amended with biodegradable MPs. The biodegradable and non-degradable MPs were found to influence vanadium behavior through distinct mechanisms. The amendment of non-degradable MPs did not substantially impact humification process, during which the mobile and reducible vanadium passively leached out from the riverine sediment and migrated into overlying water. Conversely, amendment of biodegradable MPs significantly enriched several microbial genera (e.g., Massilia) in the MPs biofilm. These genera confer heavy metal resistance and synthetic polymer degradability, and were significantly correlated with specific sediment organic matter components (C3, Ex/Em = 270/352; C4, Ex/Em = 280(370)/504). The microbial community was found to alter sediment DOM when biodegradable MPs were introduced. These changes in microbial dynamics and sediment chemistry subsequently influenced the bioavailability and mobility of vanadium within the riverine sediment.

Ebullition mediated transport dominates methane emission from open water area of the floating national park in Indo Burma hotspot.

Ebullition is an important route of methane emission from aquatic ecosystems. Ebullitive CH4 emissions from the wetlands, particularly the mountain wetlands of Eastern Himalayan, are poorly understood. To gain insights into the role of ebullition in CH4 emissions and understand the factors influencing CH4 ebullition, we conducted field measurements of the spatial and temporal variation of ebullition in a freshwater wetland area in floating national park (40 sq. km, 780m amsl, maximum depth < 4.5) in Northeast India. The average ebullitive CH4 flux ranged from 220.24 to 1889.35mgm-2 d-1, while the overall CH4 fluxes varied widely ranging from 345.81 to 2240.56mgm-2 d-1. Methane constituted 90.18% of the gas bubbles produced from the sediment, with CO2 comprising 8.82% of the total sediment gas in the wetland. This suggests that CH4 emission through ebullition plays an important role in transporting biogenic CH4 to the atmosphere. The ebullition rate was markedly higher during summer and lower during winter and exhibited a significant seasonal variation. At a spatial scale, the sites with dense aquatic vegetation growth increase CH4 emission where plants derived autochthonous sediment organic matter, substantiating the supply of carbon substrate for CH4 production. Linear mixed-effect models revealed that water temperature, organic matter, organic carbon and dissolved organic matter are the important factors affecting the ebullitive methane flux. Our results indicate that mountainous wetlands with organic-rich sediments may be potential hotspots for CH4 ebullition. However, the lack of information on these wetlands in the scientific literature emphasizes the need for further research.

Spatial distribution studies on sedimentary organic matter along the shoreline of Arabian Sea: insights from Kollam, Southwest Coast, India.

The present study was aimed at investigating the source, quality, and quantity of organic matter and labile fraction of biochemical constituents in the surficial sediments of Arabian Sea Shoreline at Kollam, India, which gives an input into the processes associated with the subsurface geochemistry pattern. About 15 surface sediment samples were collected from the five beaches for this study during January 2021. The samples were analyzed for CHN, total organic carbon (TOC), and labile fraction such as carbohydrates (CHO), proteins (PRO), and lipids (LIP). The TOC/TN ratio revealed that the source organic matter (OM) in the samples was primarily of marine origin and autochthonous, except TM3 at Thirumullavaram. Thirumullavaram is a sheltered beach, and it has low hydrodynamic process. The high organic matter content in TM3 (13.9) may be the originated from the terrestrial input. The hierarchical cluster analysis revealed that TM3 indicate that unique character to other stations. Principal component analysis revealed that three components accounted for 78% of the total variance. PC1 variance was associated with carbon-based organic compounds. PC2 was predominantly influenced by CHO and LOM, suggesting that PC2 may encompass variability associated with these nutritional profiles. PC3 was influenced by LIP and LIP/CHO, showing it may be a lipid-related component. The PRO to CHO ratio is < 1, exhibiting old aged organic matter deposited in sediments and the meso-oligotrophic status. The LIP to CHO ratio, recorded as < 1, exhibits the poor quality of energetic (food) OM in sediments. The sediment samples exhibit the following trend CHO > PRO > LIP.

The Role of Benthic TA and DIC Fluxes on Carbon Sequestration in Seagrass Meadows of Dongsha Island

Coastal blue carbon ecosystems sequester carbon, storing it as plant biomass and particulate organic matter in sediments. Recent studies emphasize the importance of incorporating dissolved inorganic and organic forms into carbon assessments. As sediment-stored organic matter decomposes, it releases dissolved inorganic carbon (DIC) and total alkalinity (TA), both of which are critical for regulating the partial pressure of CO2 (pCO2) and thus carbon sequestration. This study investigated the role of benthic DIC and TA fluxes in carbon sequestration within seagrass meadows in Dongsha Island’s inner lagoon (IL) during the winter and summer seasons. Chamber incubation experiments revealed elevated benthic DIC and TA fluxes compared to global averages (107 ± 75.9 to 119 ± 144 vs. 1.3 ± 1.06 mmol m−2 d−1 for DIC, and 69.7 ± 40.7 to 75.8 ± 81.5 vs. 0.52 ± 0.43 mmol m−2 d−1 for TA). Despite DIC fluxes being approximately 1.5 times higher than TA fluxes, water pCO2 levels remained low (149 ± 26 to 156 ± 18 µatm). Mass balance calculations further indicated that benthic DIC was predominantly reabsorbed into plant biomass through photosynthesis (−135 to −128 mmol m−2 d−1). Conversely, TA accumulated in the water and was largely exported (−60.3 to −53.7 mmol m−2 d−1), demonstrating natural ocean alkalinity enhancement (OAE). This study highlights the crucial role of IL seagrass meadows in coastal carbon sequestration through net autotrophy and carbonate dissolution. Future research should explore the global implications of these processes and assess the potential of natural OAE in other coastal blue carbon ecosystems.

Linking Biodiversity and Functional Patterns of Estuarine Free-Living Nematodes with Sedimentary Organic Matter Lability in an Atlantic Coastal Lagoon (Uruguay, South America)

We examined the taxonomical and functional traits of free-living nematodes, focusing on their density by genus, maturity index (MI), and trophic diversity index (ITD) to determine whether these indices are sensitive to changes in the organic content of the sediment. Samples were collected in autumn and spring from 12 subtidal sampling stations in Rocha Lagoon, distributed between the outer (near the mouth) and the inner sector. We identified 26 genera, with higher abundance in the inner sector, likely due to increased organic matter and biopolymers. In spring, both sectors had sediments rich in fresh organic matter, dominated by deposit-feeding nematodes and showing low trophic diversity (high ITD values). In autumn, the inner sector maintained similar characteristics to spring sampling, while the outer one was dominated by older organic matter, predatory nematodes and higher trophic diversity. The MI showed low variation between sectors, suggesting a disturbed environment. Our findings support the use of ITD to assess other aspects of communities such as the response of trophic groups to the freshness of organic matter, while the MI seems less effective for assessing the ecological status of Rocha Lagoon. Understanding nematode biodiversity and functional traits is crucial for effective ecological quality assessments.

Hydrogen isotope fractionation during aromatization to form alkylnaphthalene: Insights from pyrolysis experiments of 1-n-butyldecalin

Alkylnaphthalene homologues are important components of aromatic fraction in sedimentary organic matter and contain significantly geochemical information relative to formation and evolution of the host organic matter. They mainly originate from hydrocarbon aromatization reaction which involves the dehydrogenation of aliphatic rings resulting in the fractionation of stable hydrogen isotopes between aromatic hydrocarbons and their precursors. To examine these processes, this study thermally pyrolysed 1-n-butyldecalin (BD) at different time intervals under 360 °C/50 MPa to study the aromatization and hydrogen isotope fractionation during alkylnaphthalene formation and evolution. The relative content of aromatic products, such as naphthalene (N) and 1-methylnaphthalene (1-MN), increases with increasing aromatization. Sulfur enhanced the degree of aromatization during BD thermal evolution, resulting in greater N and 1-MN formation. For the compounds with the same carbon skeleton, i.e. tran-1-methyldecalin (1-MD), 5-methyltetraline (5-MT) and 1-MN, the 2H enrichment follows the order δ2H1-MD < δ2H5-MT < δ2H1-MN during the low thermal conversion of BD. However, the order was subsequently destroyed with increasing aromatization. The results indicate that hydrocarbon aromatization can enrich aromatic hydrocarbon in 2H, resulting in a higher δ2H value of higher aromatic-ring-number hydrocarbon than that of a lower aromatic-ring-number at low aromatization. However, 2H enrichment will decrease and even result in a reverse order with enhanced aromatization. Our findings are beneficial for understanding genetic mechanism and hydrogen isotope fractionation effect during the formation and evolution of aromatic hydrocarbons.

Discriminative characteristics of hydrochemical components and sedimentary organic matter in Korean coastal aquaculture systems during summer

Understanding the spatial distribution and sources of sedimentary organic matter (OM) in coastal environments is crucial for effective water quality management and the preservation of ecosystem health. Although extensive research has been conducted on OM dynamics, there remains a gap in understanding the ongoing biogeochemical processes in Korean coastal aquaculture zones, particularly during the summer season. To address this gap, we investigated the spatial variation of water chemical properties and isotopic composition of sedimentary OM to trace the composition, source, and reactivity of mixed OM in aquaculture systems along the Korean coast during the summer season. The isotopic approach was applied to surface sediments from five sections: western (W)-1, W-2, southern (S)-1, S-2, and eastern (E)-1. With respect to increased nutrients (mainly nitrate; 1.2 ± 0.6 mg/L) by dam-water discharge near W sections, our isotopic signatures revealed that a substantial fraction of sedimentary OM might dominantly originated from autochthonous OM source (algae; 36.5%) related to the increase of terrestrial nutrients. Simultaneously, the deposition of allochthonous OM (aquacultural feces; 44%) was predominant in the S-2 sections. The 34S-depleted patterns (approximately -7.2‰) in the S-2 section was indicative of active sulfate reduction occurring at the sedimentary boundary. Therefore, together with the precise determination of ongoing OM, our isotopic results provide valuable insights for effectively managing water-sedimentary qualities under the increase of anthropogenic contamination.

Method development and comprehensive study of matrix effects for the determination of trace organic contaminants in lake sediments

The presence of trace organic contaminants (TrOCs), such as pharmaceuticals, personal care products, additives, and polar pesticides in sediments of rivers and lakes highly impacted by anthropogenic activities makes sediments a secondary source of contamination for aquatic ecosystems. Considering this, a method for analyzing 44 TrOCs of diverse nature (including five transformation products, 13 pharmaceuticals, five personal care products, 14 pesticides, and seven additives) was developed and validated. It is based on extraction by pressurized liquid extraction (PLE), followed by purification and pre-concentration by solid phase extraction (SPE) and quantification by liquid chromatography coupled to a triple quadrupole mass spectrometer (LC-QqQMS). The method was optimized according to dispersant type, temperature, and extraction solvent. The influence of organic matter in sediments on quantitative analysis was also investigated in detail. Matrix effects were highly and significantly correlated (r=-0.9146, p < 0.0001) with retention time. Using internal standards showed the best results for effectively correcting matrix effects without affecting method sensitivity. The method was then validated according to key figures of merit: linearity (R2 > 0.990), extraction recoveries (> 60 % for 34 compounds), trueness (bias % < 15 %), precision (relative standard deviation < 20 %) and matrix effects (between -13.3 % and 17.8 %). This method can be applied for routine analysis of TrOCs in different sediment matrices. The method was applied to ten lake sediment samples collected in Québec, Canada. Results demonstrated the presence of 17 compounds in at least one lake at concentrations between 0.07 to 1531 ng g-1. The reported concentrations provide a first picture of the occurrence of chemical stressors in sediments of small lake highly anthropized ecosystems in Eastern Canada.

Apportioning sources of natural and anthropogenic organic matter in sediment from Lake Shihwa: An integrated approach using molecular ratios and compound-specific stable-isotope analysis

We tested an integrated multi-isotopic analysis framework to quantitatively estimate anthropogenic organic matter (OM) loads in different land-use types of a watershed (Lake Shihwa, South Korea). The isotopic signatures of increased bulk-element abundances in urban areas and industrial complexes may reflect the mixed contributions of natural and anthropogenic sources. Together with the predominant abundance of n-alkanes and polycyclic aromatic hydrocarbons at both boundaries, specific indices derived from their abundance may be indicative of mixed contributions from terrestrial plants, petroleum, and combustion deposited through various pathways (e.g., atmospheric deposition, outfall pipes, and surface runoff). Based on these properties, compound isotopic signatures (δ13CC27+C29+C31, δ13CFl, δ13CPyr, δ13CBaA+Chry, δ13CIcdP, δ13CBghiP,) for both land-use types may provide significant evidence of an increase in anthropogenic derived-OM loads (> 90 %) in Lake Shihwa. This approach suggests that total organic carbon–weighted source apportionments can provide useful quantitative estimates of OM loads within complex river systems.

Utilizing fluorescence indicators to apportion organic sources in estuarine/coastal sediments: A comparison with a stable isotopic model

Coastal sediments accumulate organic matter (OM) from diverse sources, including local anthropogenic pollution. Effective source tracking of sediment OM is crucial for pollution source management. This study compares fluorescence proxies and stable isotopic ratios as tracers for sediment OM in Gangu Port, Korea. An optimized extraction method using distilled water for 0.5 h yielded distinct fluorescence signatures. The humification index (HIX) and protein-like component (C3%) showed ideal mixing behavior with two end-members (fishery market sediment and algae). A Bayesian end-member mixing analysis model revealed that agricultural soil is the prevalent contributor to sediments, aligning with land use patterns. The fluorescence-based model showed higher sensitivity to anthropogenic influences compared to traditional stable isotope ratios. The results strongly agreed with isotope ratio-based predictions, exhibiting a positive correlation (p < 0.05) at 8 out of 14 sites. This study highlights the potential of fluorescence-based tracking to complement or replace conventional stable isotope methods.

Discovery of calcium sulfate at different hydration states on Mars - based on perseverance SHERLOC analysis

Organic matter on planets is often co-deposited with evaporites, and evaporation of lakes in the Jezero region of Mars may have led to the deposition of abundant organic matter and minerals such as sulfates, making sulfates important minerals for preserving the remains of potential life on Mars, especially in different hydration states, will help to invert the variability of the Martian environment and provide guidance for the exploration of life on Mars. Raman spectroscopy can detect the molecular composition of organic matter and acid anion information of the target of interest, thus enabling in situ analysis of life information and its living environment. In order to realize the detection of life remains on Mars, The Perseverance rover is equipped with SHERLOC in situ material detection payload, which adopts a 248.6 nm deep ultraviolet (DUV) laser to simultaneously excite Raman and fluorescence signals of the target. In this paper, five scans in three modes (survey scan, HDR scan and detail scan) from two sites on Mars (Quartier and Bellegarde) were selected for preliminary analysis, and the presence of sulfate minerals at these two sites was confirmed. The detail scans at Quartier were analyzed in depth, and the presence of four calcium sulfate minerals, gypsum (CaSO4∙2 H2O), bassanite (CaSO4∙0.5 H2O), anhydrite (β-CaSO4) and gamma-calcium sulfate (γ-CaSO4)was inferred from the states of ν1 (SO4), ν3 (SO4) and hydrated peaks. The differences in the degree of hydration of calcium sulfate minerals suggest that there may have been active water activity on Mars. By comparing data collected by SHERLOC with spectra from spectral libraries, the composition of small-scale structures on Mars may be assessable. However, due to the complexity of the Martian geology, more accurate water activity will need to be combined with more detailed ions, temperatures, humidity, and other conditions for a more precise analysis.

Sedimentary organic matter signature hints at the phytoplankton-driven biological carbon pump in the central Arabian Sea

Abstract. The central Arabian Sea, a unique tropical basin, is profoundly impacted by monsoon wind reversal affecting its surface circulation and biogeochemistry. Phytoplankton blooms associated with high biological productivity and particle flux occur in the northern part of the central Arabian Sea due to summer-monsoon-induced open-ocean upwelling and winter convection. The core oxygen minimum zone (OMZ) at intermediate water depths is another important feature of the northern central Arabian Sea and fades southward. In this study, we attempt to interlink how these factors collectively impact phytodetrital export to the sediment. Short sediment core-top (1 cm) samples representing the recent particle flux signatures were analysed from five locations (21 to 11° N; 64° E) in the central Arabian Sea. Previously, we used core-top (0–0.5 cm) samples and observed a trend between diatom frustule abundance and diversity with bulk sedimentary parameters indicating a spatial variability in phytodetrital export to the sediment. To verify this observation further, lipid biomarkers of key phytoplankton groups and a sea surface temperature (SST) proxy have been analysed in addition to diatom frustules. The C37 alkenone-based SST proxy indicated cooler SST (27.6 ± 0.25 °C) in the north (21–15° N) mostly due to upwelling (summer) and convective mixing (winter). Warmer SSTs (+0.4 °C) are measured in the south, which usually remains nutrient-poor. This trend was consistent with satellite-derived average SST values (2017–2020). Lipid biomarker analysis suggests that dinoflagellates were likely to be the highest contributor, as indicated by dinosterol and its degradative product dinostanol, followed by brassicasterol and C37 alkenone, likely representing diatoms and coccolithophores, respectively. The north, which largely experiences periodic phytoplankton blooms and is influenced by the thick OMZ, revealed the highest contents of organic matter, diatom frustules (diversity and abundance), dominated by large, thickly silicified cells (e.g. Coscinodiscus and Rhizosolenia) and phytoplankton lipid biomarkers, as well as lower contents of zooplankton biomarkers (cholesterol and cholestanol). In contrast, relatively smaller chain-forming centric (e.g. Thalassiosira) and pennate (e.g. Pseudo-nitzschia, Nitzschia, Thalassionema) diatom frustules along with lower phytoplankton lipid biomarker contents were found in the south, where zooplankton biomarkers and silicious radiolarians were more abundant. The possible impacts of the OMZ on particle flux related to the phytoplankton community, including zooplankton grazing and other factors, have been discussed.