Dissolved Organic Matter Composition Research Articles

Post column infusion of an internal standard into LC-FT-ICR MS enables semi-quantitative comparison of dissolved organic matter in original samples.

Ultrahigh resolution mass spectrometry hyphenated with liquid chromatography (LC) is an emerging tool to explore the isomeric composition of dissolved organic matter (DOM). However, matrix effects limit the potential for semi-quantitative comparison of DOM molecule abundances across samples. We introduce a post-column infused internal standard (PCI-IS) for reversed-phase LC-FT-ICR MS measurements of DOM and systematically evaluate matrix effects, detector linearity and the precision of mass peak intensities. Matrix effects for model compounds spiked into freshwater DOM samples ranging from a headwater stream to a major river were reduced by 5-10% for PCI-IS corrected mass peak intensities as compared to raw (i.e., untransformed) intensities. A linear regression of PCI-IS corrected DOM mass peak intensities across a typical DOM concentration range (2-15 mg dissolved organic carbon L-1) in original, non-extracted freshwater samples demonstrates excellent linearity of the detector response (r2 > 0.9 for 98% of detected molecular formulas across retention times). Importantly, PCI-IS could compensate for 80% of matrix effects across an environmental gradient of DOM composition from groundwater to surface water. This enabled studying the ionization efficiency of DOM isomers and linking the observed differences to the biogeochemical sources. With PCI-IS original, non-extracted DOM samples can be analysed by LC-FT-ICR MS without carbon load adjustment, and mass peak intensities can be reliably used to semi-quantitatively compare isomer abundances between compositionally similar DOM samples.

Linking Dissolved Organic Matter Composition to Landscape Properties in Wetlands Across the United States of America

AbstractWetlands are integral to the global carbon cycle, serving as both a source and a sink for organic carbon. Their potential for carbon storage will likely change in the coming decades in response to higher temperatures and variable precipitation patterns. We characterized the dissolved organic carbon (DOC) and dissolved organic matter (DOM) composition from 12 different wetland sites across the USA spanning gradients in climate, landcover, sampling depth, and hydroperiod for comparison to DOM in other inland waters. Using absorption spectroscopy, parallel factor analysis modeling, and ultra‐high resolution mass spectroscopy, we identified differences in DOM sourcing and processing by geographic site. Wetland DOM composition was driven primarily by differences in landcover where forested sites contained greater aromatic and oxygenated DOM content compared to grassland/herbaceous sites which were more aliphatic and enriched in N and S molecular formulae. Furthermore, surface and porewater DOM was also influenced by properties such as soil type, organic matter content, and precipitation. Surface water DOM was relatively enriched in oxygenated higher molecular weight formulae representing HUPHigh O/C compounds than porewaters, whose DOM composition suggests abiotic sulfurization from dissolved inorganic sulfide. Finally, we identified a group of persistent molecular formulae (3,489) present across all sites and sampling depths (i.e., the signature of wetland DOM) that are likely important for riverine‐to‐coastal DOM transport. As anthropogenic disturbances continue to impact temperate wetlands, this study highlights drivers of DOM composition fundamental for understanding how wetland organic carbon will change, and thus its role in biogeochemical cycling.

Eutrophication in cold-arid lakes: molecular characteristics and transformation mechanism of DOM under microbial action at the ice-water interface

During freezing periods, nutrients (carbon and organic matter, etc.) are enriched in the water and sediment of lakes in cold-arid regions, leading to potential algal bloom outbreaks and other health risks to the ecosystem. Particularly, dissolved organic matter (DOM) is a critical component of the nutrients and plays an important role in the global carbon cycle. However, the mechanisms of DOM transfer between ice and water remain unclear. This study analyzed the influence of microbial community on DOM composition using 16 s RNA, 3DEEM, and FT-ICR MS in Daihai Lake and Wuliangsuhai Lake in the Yellow River Basin, China. According to the spectral analysis, the content of endogenous organic matter, such as humus, accounted for 40% of the total DOM in water, while the content of tryptophan and tyrosine accounted for 80% of the total DOM in ice. The results of mass spectrometry showed that lignin was the main component, and the content of organic matter in the ice was less than that in the water. Molecular structures of seven DOM coexisting in the lake ice and water were elucidated with adapted Kendrick-analogous network visualization, which clearly illustrates that long-chain DOM molecules are derived from small molecules, while other heteroatoms are complexed with the side groups. The positive correlations between CHO, CHNO, CHOS, CHOS and Actinomyces indicate that DOM actively interacted with the microbial community. 44% of CHO compounds have the same molecular formula in water, the content of CHOS in the water of the two lakes was closed to 7% higher than that in the ice. Meanwhile, DOM dynamically migrate between ice and water via interstitial water because of the solubility changes under microbial transformation, which has been proved by the decrease in the contents of the humus and tryptophan-like substances in the ice from the bottom to the surface and lower contents of carbohydrate and unsaturated aromatic hydrocarbon in the water than the ice. This study helps to predict the composition and structure of DOM during the migration in lakes and provides a scientific basis for environmental remediation with high concentration of carbon.

Combination Mechanism of Soil Dissolved Organic Matter and Cu2+ in Vegetable Fields, Forests and Dry Farmland in Lujiang County

Dissolved organic matter (DOM) serves as a critical link in the migration and transformation of heavy metals at the soil–solid interface, influencing the migration behaviour and transformation processes of Cu2+ in soil. There have been studies on the combination mechanisms between DOM and Cu2+ in paddy soils. However, the adsorption/complexation and redox processes between DOM and Cu2+ in other agricultural soil types (such as dry farmland and vegetable fields) are unclear. In order to reveal the combination process of DOM with Cu in different agricultural soil types and the dynamic changes in chemical behaviour that occur, this study analysed the variability of DOM components and structure in three soils using three-dimensional fluorescence spectroscopy and X-ray photoelectron spectroscopy. In addition, the priority order of different DOM compounds in combination with Cu and the change process in relation to the Cu valence state in the soil of Lujiang County, Anhui Province, was revealed based on laboratory experiments. The results showed that the composition of soil DOM was mainly composed of humic-like and fulvic-like substances with a clear terrestrial origin and that the organic matter showed a high degree of decomposition characteristics. The results indicated that the composition of soil DOM is mainly composed of humic and fulvic acid-like substances, and they have obvious characteristics of terrestrial origin. In addition, the soil organic matter showed high decomposition characteristics. The complex stability constants (lgKM) of humic acid-like substances with Cu2+ follow the order of forest land (lgKM = 5.21), vegetable land (lgKM = 4.90), and dry farmland (lgKM = 4.88). The lgKM of fulvic acid-like substances with Cu2+ is in the order of dry farmland (lgKM = 4.51) and vegetable land (lgKM = 4.39). Humic acid-like substances in soil DOM combine preferentially with Cu2+, showing a stronger chelating affinity than fulvic acid-like substances. Cu2+ complexes mainly include hydroxyl, phenolic hydroxyl and amino functional groups are included in soil DOM, accompanied by redox reactions. In comparison to dry farmland, the soil DOM in forest and vegetable fields undergoes more intense redox reactions simultaneously with the chelation of Cu2+. Therefore, the application of organic fertilisers to vegetable and forest soils may lead to uncertainties concerning the fate of heavy metals with variable chemical valence. These results contribute to a deeper understanding of the interaction mechanisms between DOM and Cu2+ in agricultural soils.

Characterization and differentiation of dissolved organic matter in leachate derived from an old Japanese landfill site through Orbitrap mass spectrometry

AbstractElucidating the characteristics of dissolved organic matter (DOM) is crucial to assessing its impact on the bioavailability and mobility of pollutants in landfill leachate. This study reports a comprehensive 5–month investigation into the characteristics of DOM in leachate from an old Japanese landfill, collected at six different sampling points. The molecular composition, chemical properties, and structural characteristics of DOM were assessed using Orbitrap mass spectrometry and spectral analysis. The leachate DOM mainly consisted of CHO-containing molecules (58.5–88.9%), low-oxygen unsaturated phenolic compounds (40.5–54.0%), and aliphatic compounds (19.4–47.3%), with slight variation among sampling points. A significant portion of the nominal oxidation state of carbon was in the reduced zone (76.2–95.4%). The results underscore the distinct molecular composition of DOM in mature Japanese landfill leachate compared to young and mature leachates from other countries. Two of six sampling points, with notable differences in molecular characteristics, were compared and elucidated. The composition of landfill waste, rather than landfill age, was the main factor affecting the characteristics and differentiation of leachate DOM.

Novel insights into antimony mobilization in different high- antimony aquifers from the molecular signatures of dissolved organic matter

The crucial role of the fluorescent components of dissolved organic matter (DOM) in controlling antimony (Sb) mobilization in groundwater has been confirmed. However, the molecular signatures contributing to Sb enrichment in DOM remain unknown. This study aims to investigate the origins and molecular compositions of DOM in different high-Sb aquifers (Sb-mining and no-Sb-mining aquifer), as well as compare different molecular signatures of DOM and mechanisms for Sb migration. The findings showed that Sb concentrations in Sb-mining aquifer exhibited a positive correlation with lignin- and tannin-like molecules characterized by high O/C and low H/C ratios, indicating an increased abundance of aromatic components with higher Humification Index and SUV-absorbance at 254 nm, compared to no-Sb-mining aquifer. Correspondingly, the complexation and competitive adsorption were considered as the predominate formation mechanisms on Sb enrichment in Sb-mining aquifer. In addition, high abundances of bioreactivity DOM may facilitated the migration of Sb via electron transfer and competitive adsorption in native no-Sb-mining aquifer. The outcomes of this investigation offer novel insights into the mechanism on Sb enrichment influenced by DOM at the molecule level.

Optical properties and molecular compositions of dissolved organic matter in multiple runoff components during rainfalls on the karst hillslope

Understanding the chemical composition, origin, and molecular structure of dissolved organic matter (DOM) in multi-interface runoff is essential for comprehending the fate of laterally transported DOM in complex soil-epikarst systems of karst hillslopes. Limited information, however, is available for the optical properties and molecular compositions of the transported OM in multiple runoff components on the karst hillslope in relation to land-uses and soil thicknesses. In this study, we conducted a study to observe the changes in the quantity and quality of DOM in multiple interface flow (surface, subsurface, and epikarst) during natural rainfall events in 2022 in karst hillslopes that are covered by different land uses (cropland and shrubland) and soil thicknesses (with mean depths of 66.0 cm for deeper soil and 35.4 cm for shallower soil) in the karst region of southwest China. chemcial compositions of runoff DOM were determined by optical analysis and microbial compositions in runoff were inferred with high-throughput sequencing. The results showed that the soil-epikarst structure was controlling the runoff DOM quantity and quality during rainfall events. A decrease in the aromaticity, humification, unsaturation, and oxidation degree and an increase in carbohydrate, aminosugars, protein, and lipid compounds were found from surface to epikarst flow, indicating that plant-and soil-derived carbon decreased, while the microbially-derived carbon increased. The results were further comfirmed by the higher bacterial richness and diversity, along with fungal diversity in the epikarst flow compared to other runoff components. The bio-labile protein materials (C2) were the most important component of runoff DOM output in karst hillslopes. In surface and subsurface flow, rainfall amount, runoff rate, and discharge significantly affected the DOM concentration and quality during rainfalls, indicating that the dynamics of DOM in runoff from karst hillslopes were predominantly influenced by hydrological processes. Furthermore, the runoff DOM quality in cropland was dominated by lower unsaturation and oxidation degrees and higher protein component, compared to those in shrubland. The compositions of DOM in runoff from hillslope plots with thicker soils were primarily characterized by microbially-derived materials. Our findings were conducive to understanding the mechanism governing the migration of DOM quality and quantity in discharge during multi-interface hydrological processes on karst hillslopes.

Spatiotemporal dynamics of dissolved organic matter in subtropical karst cave waters identified by optical properties

Natural dissolved organic matter (DOM) is ubiquitous in aquatic environments and is an essential component in the carbon cycle in karst areas. To improve understanding of the carbon cycle in karst caves with heterogeneous hydrological processes, we examined the spatiotemporal variability of DOM composition and further uncovered its source and fate. Results may also provide insights into the feedbacks of organic carbon to carbon sinks in karst regions. In this study, concentrations and compositions of DOM, partial pressure of aqueous carbon dioxide (pCO2), dissolved inorganic carbon, and other physicochemical parameters were investigated in a karst cave at Mahuang, Southwest China. Ultraviolet-visible absorption spectroscopy was coupled with multiple statistical analyses to identify the compositional variations and potential fates of DOM in cave waters. The results showed that DOM dynamics were regulated by both terrigenous and biogenic drivers under the control of meteorological conditions. With higher air temperature, precipitation, and microbial activity, fulvic fractions were consumed to generate CO2, leading to the accumulation of refractory DOM in cave waters and changing the hydrochemical features. When temperature and precipitation decreased, DOM was dominated by lignin fractions, which served as an indicator of terrestrial inputs and vascular plants, suggesting variation in the preferential fraction of biological consumption. In addition, different hydrological path patterns influenced DOM properties in cave waters due to differences in recharging, the leaching process, and subsurface reworking. Thus, hydrology could serve as an important constraint on the coupling between dissolved organic and inorganic carbon.

Optical characteristics of dissolved organic matter in relation to phytoplankton in Lake Erhai, China

Dissolved organic matter (DOM), as the primary form of organic carbon in lakes, is crucial for the lake carbon cycling. As an important component of lake ecosystems, phytoplankton plays a crucial role in carbon fixation. However, we are not yet clear about the contribution of phytoplankton composition to DOM. To clarify this issue, we conducted we conducted continuous monitoring for 6 months in Lake Erhai, a plateau lake in China. Through quantitative detection of phytoplankton and spectral characteristic analysis, four fluorescence components were identified: tryptophan-like (C1), tyrosine-like (C2), fulvic-like (C3), and humic-like (C4). The Fluorescence Index (FI) ranged from 1.70 to 2.54, and the Biogenic Index (BIX) was above 0.8, indicating the DOM in Lake Erhai’s overlying water was predominantly autochthonous. Cyanophyta prevailed in September and November, while Chlorophyta dominated in other months. Phytoplankton diversity was significantly related to DOM concentration that may be related to the difference in the DOM contribution of different phytoplankton. The effect of phytoplankton biomass on C3 and C4 was prominent. Whereas, phytoplankton did not stimulate C1 and C2 significantly, indicating that protein-like may originate from terrestrial input and microbial activity. The composition of phytoplankton significantly affects the DOM composition in Lake Erhai. Therefore, the autochthonous DOM production by phytoplankton warrants further consideration in plateau lake systems.

Characteristics of DOM and Their Relationships with Potentially Toxic Elements in the Inner Mongolia Section of the Yellow River, China.

The characterization of dissolved organic matter (DOM) is important for better understanding of the migration and transformation mechanisms of DOM in water bodies and its interaction with other contaminants. In this work, fluorescence characteristics and molecular compositions of the DOM samples collected from the mainstream, tributary, and sewage outfall of the Inner Mongolia section of the Yellow River (IMYR) were determined by using fluorescence spectroscopy and Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS). In addition, concentrations of potentially toxic elements (PTEs) in the relevant surface water and their potential relationships with DOM were investigated. The results showed that the abundance of tyrosine-like components increased significantly in downstream waters impacted by outfall effluents and was negatively correlated with the humification index (HIX). Compared to the mainstream, outfall and tributaries have a high number of molecular formulas and a higher proportion of CHOS molecular formulas. In particular, the O5S class has a relative intensity of 41.6% and the O5-7S class has more than 70%. Thirty-eight PTEs were measured in the surface water samples, and 12 found above their detective levels at all sampling sites. Protein-like components are positively correlated with Cu, which is likely indicating the source of Cu in the aquatic environment of the IMYR. Our results demonstrated that urban wastewater discharges significantly alter characteristics and compositions of DOM in the mainstream of IMYR with strongly anthropogenic features. These results and conclusions are important for understanding the role and sources of DOM in the Yellow River aquatic environment.

Characterizing the regional distribution, interaction with microorganisms, and sources of dissolved organic matter for summer rainfall: Insights from spectroscopy, community structure, and back-trajectory analyses

Dissolved organic matter (DOM) in rainfall participates in many biogeochemical cycles in aquatic environments and affects biological activities in water bodies. Revealing the characteristics of rainfall DOM could broaden our understanding of the carbon cycle. Therefore, the distribution characteristics and response mechanisms of DOM to microorganisms were investigated in different regions of Hebei. The results indicated that the water quality of the northern region was worse than that of the middle and southern regions. The two protein like components (C1, C2) and one humic like component (C3) were obtained; at high molecular weight (MW), the fluorescence intensity is high in the northern region (0.03 ± 0.02 R.U.), while at low MW, the fluorescence intensity is highest in the southern region (0.50 ± 0.18 R.U.). Furthermore, C2 is significantly positively correlated with C1 (P < 0.01), while C2 is significantly negatively correlated with C3 (P < 0.05) was observed. The spectral index results indicated that rainfall DOM exhibited low humification and highly autochthonous characteristics. The southern region obtained higher richness and diversity of microbial species than northern region (P < 0.05). The community exhibits significant spatiotemporal differences, and the Acinetobacter, Enterobacter, and Massilia, were dominant genus. Redundancy and network analyses showed that the effects of C1, C2, and nitrate on microorganisms increased with decreasing MW, while low MW exhibited a more complex network between DOM and microorganisms than high MW. Meanwhile, C1, C2 had a large total effect on β-diversity and function through structural equation modeling. The backward trajectory model indicates that the sources of air masses are from the northwest, local area, and sea in the northern, middle, and southern regions, respectively. This study broadened the understanding of the composition of summer rainfall DOM and its interactions with microorganisms during rainfall.

Impact of climate change on formation of nitrogenous disinfection by-products. Part II: water blooming and enrichment by humic substances.

Climate change affects the concentration and characteristics of dissolved organic matter (DOM) in surface water. The changes in composition of DOM have many implications to drinking water quality, especially in the case of formation of disinfection by-products (DBPs). The aim of this study was to investigate the formation of nitrogenous DBPs (N-DBPs) during chlorination and chloramination, caused by the alternation of surface water's DOM driven by climate change. For this reason, two different cases were examined: (a) rise of algal organic matter (AOM) due to water blooming and (b) water enrichment by humic substances. The target compounds were haloacetonitriles (HANs), haloacetamides (HAcAms), and halonitromethane (TCNM). The results showed that Anabaena appears to be a major precursor for HAcAms and TCNM, while humic acids are precursors for HANs. The results of the mixtures presented the same pattern. During the water blooming case, HAcAms and TCNM formation are in favor, while during water enrichment by humic substances case, HANs is the N-DBP group with higher formation yield. Cloraminated samples presented higher values of cytotoxicity and genotoxicity compared to the chlorinated.

Appling fluorescence spectroscopy with absolute principal component coefficient to explore dynamic migration of DOM fractions from an urbanized river during torrential rainfall

This research delves into the dynamic interplay between urbanization and the characteristics of Dissolved Organic Matter (DOM) in the Anyang River, particularly under the stress of torrential rain. The motivation stems from a critical need to decipher how urban landscapes influence water quality, focusing on the intricate transformations and movements of DOM. Employing advanced fluorescence spectroscopy techniques like Excitation-Emission Matrices (EEM) and Parallel Factor Analysis (PARAFAC), the study meticulously differentiates DOM compositions in urban and agricultural settings. It unveils a pronounced distinction, with urban streams showing elevated proteinaceous DOM from wastewater, contrasting with the humic substances prevalent in agricultural runoff. The analysis also captures how intense rainfall events catalyze significant shifts in DOM profiles, thereby emphasizing the need for tailored water quality management strategies in urbanized catchments. This comprehensive approach not only bridges gaps in understanding the urban impact on riverine ecosystems but also sets a foundation for future research and policy development in the face of escalating environmental changes.

Continuous planting of Chinese fir monocultures significantly influences dissolved organic matter content and microbial assembly processes

Monoculture plantations in China, characterized by the continuous cultivation of a single species, pose challenges to timber accumulation and understory biodiversity, raising concerns about sustainability. This study investigated the impact of continuous monoculture plantings of Chinese fir (Cunninghamia lanceolata [Lamb.] Hook.) on soil properties, dissolved organic matter (DOM), and microorganisms over multiple generations. Soil samples from first to fourth-generation plantations were analyzed for basic chemical properties, DOM composition using Fourier transform ion cyclotron resonance mass spectrometry, and microorganisms via high-throughput sequencing. Results revealed a significant decline in nitrate nitrogen content with successive rotations, accompanied by an increase in easily degradable compounds like carbohydrates, aliphatic/proteins, tannins, Carbon, Hydrogen, Oxygen and Nitrogen- (CHON) and Carbon, Hydrogen, Oxygen and Sulfur- (CHOS) containing compounds. However, the recalcitrant compounds, such as lignin and carboxyl-rich alicyclic molecules (CRAMs), condensed aromatics and Carbon, Hydrogen and Oxygen- (CHO) containing compounds decreased. Microorganism diversity, abundance, and structure decreased with successive plantations, affecting the ecological niche breadth of fungal communities. Bacterial communities were strongly influenced by DOM composition, particularly lignin/CRAMs and tannins. Continuous monoculture led to reduced soil nitrate, lignin/CRAMs, and compromised soil quality, altering chemical properties and DOM composition, influencing microbial community assembly. This shift increased easily degraded DOM, accelerating soil carbon and nitrogen cycling, ultimately reducing soil carbon sequestration. From environmental point of view, the study emphasizes the importance of sustainable soil management practices in continuous monoculture systems. Particularly the findings offer valuable insights for addressing challenges associated with monoculture plantations and promoting long-term ecological sustainability.

Characterization of dissolved organic matter in rivers impacted by acid mine drainage: Components and complexation with metals

Dissolved organic matter (DOM), a ubiquitous and active ingredient, is extensively involved in the transformation and migration of environmental pollutants in aquatic ecosystems. However, its chemical composition in acid mine drainage (AMD)-impacted rivers remains poorly characterized, hindering our understanding of its role in the biogeochemistry of key elements in contaminated fluvial environments. Here, we investigated the concentration of dissolved organic carbon (DOC) and spectroscopic and molecular characteristics of DOM in a headwater river contaminated with polymetallic mine-derived AMD in southern China. Terrestrial humic-like (C1) and typically groundwater-supplied aromatic protein/tyrosine-like (C2) substances which were partially from AMD, were identified as the predominant fluorescent components in the river water. Notably, tryptophan-like (C3) substances originating from tailings pond spills were only occasionally detected in the river. Although DOM biogeochemical transformations and degradation occurred in the lateral soil-water riparian interface and longitudinal in-stream transport processes, the molecular compositions identified by FT-ICR MS showed a core set of molecular formulae in the lignin/saturated compound/tannin region of the van Krevelen diagram of the water samples across the rivers. The complexation of DOM with typical metals in AMD was investigated using fluorescence quenching experiments. The results showed that the highest binding ability of Fe(III) to C2 followed by C1, with both detected in the experimental water samples. Mg(II) and Ca(II) strengthened the binding of DOM-Fe(III) when the ferric/DOM ratio was low, while Cu(II) weakened the binding of DOM-Fe(III) due to competition. Ca(II) inhibited the binding of Fe(III) to C1 but promoted the binding of the complex to C2 when both Cu(II) and Mg(II) were present. Since DOM-Fe(III) complexation was associated with the cotransport of AMD-derived metals/metalloids in diverse aqueous environments with multiple co-existing ions (typically Ca(II) input for remediation), our study on the composition of DOM and its complexation with metals can contribute to managing and remediating AMD-impacted rivers.

Urban and agricultural influences on the coastal dissolved organic matter pool in the Algoa Bay estuaries

While anthropogenic pollution is a major threat to aquatic ecosystem health, our knowledge of the presence of xenobiotics in coastal Dissolved Organic Matter (DOM) is still relatively poor. This is especially true for water bodies in the Global South with limited information gained mostly from targeted studies that rely on comparison with authentic standards. In recent years, non-targeted tandem mass spectrometry has emerged as a powerful tool to collectively detect and identify pollutants and biogenic DOM components in the environment, but this approach has yet to be widely utilized for monitoring ecologically important aquatic systems. In this study we compared the DOM composition of Algoa Bay, Eastern Cape, South Africa, and its two estuaries. The Swartkops Estuary is highly urbanized and severely impacted by anthropogenic pollution, while the Sundays Estuary is impacted by commercial agriculture in its catchment. We employed solid-phase extraction followed by liquid chromatography tandem mass spectrometry to annotate more than 200 pharmaceuticals, pesticides, urban xenobiotics, and natural products based on spectral matching. The identification with authentic standards confirmed the presence of methamphetamine, carbamazepine, sulfamethoxazole, N-acetylsulfamethoxazole, imazapyr, caffeine and hexa(methoxymethyl)melamine, and allowed semi-quantitative estimations for annotated xenobiotics. The Swartkops Estuary DOM composition was strongly impacted by features annotated as urban pollutants including pharmaceuticals such as melamines and antiretrovirals. By contrast, the Sundays Estuary exhibited significant enrichment of molecules annotated as agrochemicals widely used in the citrus farming industry, with predicted concentrations for some of them exceeding predicted no-effect concentrations. This study provides new insight into anthropogenic impact on the Algoa Bay system and demonstrates the utility of non-targeted tandem mass spectrometry as a sensitive tool for assessing the health of ecologically important coastal ecosystems and will serve as a valuable foundation for strategizing long-term monitoring efforts.

Structure and composition of dissolved organic matters in sludge by ultrasonic treatment

The leaching of dissolved organic matter (DOM) from the sludge into the liquid phase is induced by ultrasound. However, there is limited investigation into the structure and molecular composition of sludge DOM in this process. The molecular structure and composition of sludge DOM in ultrasonic treatment were comprehensively elucidated in this study. The sludge dissolved organic carbon (DOC) and three-dimensional fluorescence spectroscopy (3D-EEM) image had most significant change at 15-min ultrasonic time and 1.2 W/mL ultrasonic density, respectively. Gas Chromatography-Mass Spectrometry (GC-MS) analysis indicated that ultrasonic treatment of sludge reduced the macromolecules to small molecules in DOM. Then, electrospray ionization Fourier-transform ion cyclotron resonance mass spectrometry (ESI FT-ICR-MS) analysis revealed that lignin, tannins, and carbohydrates were the main components of sludge DOMs after ultrasound treatment. analysis revealed that lignin, tannins, and carbohydrates were the main components of sludge DOMs after ultrasound treatment. Furthermore, through the Van Krevelen analysis, the major components were CHO (48.50%) and CHOS (23.20%) in the DOM of ultrasonicated sludge. This research provides the basis for the practical application of ultrasonic treatment of sludge and provides basic information for DOM components.

Biogeochemistry of dissolved organic matter and inorganic solutes in soil profiles of tropical pasturelands

Tropical soils play a critical role in the global biogeochemical cycles and are essential for maintaining the Earth's carbon balance. Understanding the dynamics of dissolved organic matter (DOM) is paramount due to its implications for ecosystem functioning and nutrient cycling. This study comprehensively evaluated the origin, distribution, and composition of DOM and inorganic solutes in Brazilian tropical agricultural soils. Multiple analytical techniques were utilized to assess DOM from soil profiles (0–100 cm depth) across a spectrum of land uses, including a native Atlantic Forest, a degraded pasture, as well as intensive grazing, extensive grazing, and silvopastoral systems. Inorganic elements were quantified to assess the coupling between the organic and inorganic biogeochemical cycles. The dominance of C4 carbon in topsoil layers suggested substantial contributions of organic matter from grasses to the soil organic matter pool. However, with increased depth, C3 carbon inputs became more prominent, indicating the influence of forest vegetation that existed prior to the implementation of agricultural managements. DOM concentrations decreased with soil depth due to reduced carbon inputs, sorption to minerals, or oxidation. DOM composition did not show significant changes among different land use and managements. Lignin was identified as the primary contributor to oxidized DOM with increasing soil depth. The composition of DOM exhibited a shift from more aromatic and higher molecular weight compounds in topsoil layers to smaller, more aliphatic compounds in subsoil layers. Our key findings revealed that aliphatic compounds, particularly fatty acids, tend to accumulate in deeper soil layers. This phenomenon was consistent in pastures dominated by grasses but not in soils near treed vegetation. Overseeding (from C3 plants) did not significantly impact DOM compositions, emphasizing the persistence of C4 plants in these systems. The presence of inorganic elements in soil water extracts showed minimal impact on DOM dynamics, suggesting decoupled organic and inorganic biogeochemical cycles in tropical pasturelands.

Strong associations between dissolved organic matter and microbial communities in the sediments of Qinghai-Tibetan Plateau lakes depend on salinity

In aquatic ecosystems, dissolved organic matter (DOM) plays a vital role in microbial communities and the biogeochemical cycling of elements. However, little is known about the associations between DOM and microbial communities in lake sediments. This study investigated the composition of water-extractable organic matter and microbial communities in surface sediments of lakes with different salinities on the Qinghai-Tibet Plateau. Ultrahigh-resolution mass spectrometry and high-throughput microbial sequencing techniques were employed to assess the associations between molecular diversity and microbial diversity and the effects of salinity in 19 lakes spanning a salinity range from 0.22 ‰ to 341.87 ‰. Our results show that increasing salinity of lake water led to higher molecular diversity of DOM in surface sediments. High-salinity lakes exhibited distinct DOM characteristics, such as lower aromaticity, smaller molecular weight, and higher oxidation degree, compared to freshwater lakes. The complexity of the microbial network composition of sediments first increased and then decreased with the increase of salinity. Moreover, as salinity increases, the dominant species transitioned from Gammaproteobacteria to Bacteroidia, and this transition was accompanied by a decrease in microbial diversity and an increase in molecular diversity. Microbial factors accounted for 34.68 % of the variation in the molecular composition of DOM. Overall, this study emphasizes the significant effects of salinity on both molecular and microbial diversity in lake sediments. Furthermore, our findings underscore the importance of microbes in controlling the range of organic compounds present in lakes and deepen our knowledge of the biogeochemical cycling of DOM.

Aging behavior and leaching characteristics of microfibers in landfill leachate: Important role of surface mesh structure

Mesh-structured films formed by the post-processing of microfibers improves their permeability and dexterity, such as disposable masks. However, the aging behavior and potential risks of mesh-structured microfibers (MS-MFs) in landfill leachate remain poorly understood. Herein, the aging behavior and mechanisms of MS-MFs and ordinary polypropylene-films (PP-films) microplastics, as well as their leaching concerning dissolved organic matter (DOM) in landfill leachate were investigated. Results revealed that MS-MFs underwent more significant physicochemical changes than PP-films during the aging process in landfill leachate, due to their rich porous habitats. An important factor in the photoaging of MS-MFs was related to reactive oxygen species produced by DOM, and this process was promoted by photoelectrons under UV irradiation. Compared with PP-films, MS-MFs released more DOM and nano-plastics fragments into landfill leachate, altering the composition and molecular weight of DOM. Aged MS-MFs-DOM generated new components, and humus-like substances produced by photochemistry showed the largest increase. Correlation analysis revealed that leached DOM was positively correlated with oxygen-containing groups accumulated in aged MS-MFs. Overall, MS-MFs will bring higher environmental risks and become a new long-term source of DOM contaminants in landfill leachate. This study provides new insights into the impact of novel microfibers on landfill leachate carbon dynamics.