Structure Of Dissolved Organic Matter Research Articles

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.

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.

Self-motivated photoaging of microplastics by biochar-dissolved organic matter under different pyrolysis temperatures

Dissolved organic matter (DOM) released from biochar (BDOM) can interact with microplastics (MPs) in the environment, inevitably affecting their environmental behaviour. Information regarding the influence of BDOM on MPs during photoaging and associated variations in the MP aging mechanism remains unclear. This study evaluated the effect of BDOM on the aging of polystyrene (PS) MPs. The results showed that among three pyrolysis temperatures, low-temperature BDOM significantly enhanced the photoaging process of PS MPs, with the smallest average particle size and highest carbonyl index value after 15 days of aging under light conditions. The DOM level decreased after 5 days, increased after 5–10 days, and stabilised after 15 d. BDOM accelerates PS MPs aging, leading to more DOM released from PS, which can be transformed into 1O2 via triplet-excited state (3DOM⁎ and 3PS⁎) to further enhance PS MPs aging, resulting in the realisation of the self-accelerated aging process of PS MPs. 1O2 plays a crucial role in the self-motivated accelerated aging process of PS MPs. These findings provide new insights into the effects of the DOM structure and composition on reactive oxygen species generation during MPs aging.

Exploring the diversity of dissolved organic matter (DOM) properties and sources in different functional areas of a typical macrophyte - derived lake combined with optical spectroscopy and FT-ICR MS analysis

Lake Baiyangdian is one of China's largest macrophyte - derived lakes, facing severe challenges related to water quality maintenance and eutrophication prevention. Dissolved organic matter (DOM) was a huge carbon pool and its abundance, property, and transformation played important roles in the biogeochemical cycle and energy flow in lake ecosystems. In this study, Lake Baiyangdian was divided into four distinct areas: Unartificial Area (UA), Village Area (VA), Tourism Area (TA), and Breeding Area (BA). We examined the diversity of DOM properties and sources across these functional areas. Our findings reveal that DOM in this lake is predominantly composed of protein - like substances, as determined by excitation - emission matrix and parallel factor analysis (EEM - PARAFAC). Notably, the exogenous tyrosine-like component C1 showed a stronger presence in VA and BA compared to UA and TA. Ultrahigh - resolution mass spectrometry (FT - ICR MS) unveiled a similar DOM molecular composition pattern across different functional areas due to the high relative abundances of lignan compounds, suggesting that macrophytes significantly influence the material structure of DOM. DOM properties exhibited specific associations with water quality indicators in various functional areas, as indicated by the Mantel test. The connections between DOM properties and NO3N and NH3N were more pronounced in VA and BA than in UA and TA. Our results underscore the viability of using DOM as an indicator for more precise and scientific water quality management.

Compositional and structural identification of organic matter contributing to high residual soluble aluminum after coagulation

Understanding the complexation of aluminum (Al) with dissolved organic matter (DOM) is of great significance for the control of residual Al in drinking water after treatment. Here, we used high-resolution and accurate mass measurements to identify the composition and structure of DOM contributing to the formation of soluble organically-bound Al during coagulation at near neutral pH (pH 7.50). The results showed that the organic compounds contributing to soluble organically-bound Al were primarily phenolic compounds and aliphatic compounds. Among them, phenolic compounds with a sulfonic acid group could greatly enhance the hydrolysis of polymeric Al and the formation of high concentrations of monomeric/oligomeric Al-DOM complexes. These organic molecules had a mass-to-charge ratio concentrated below 350. Based on the assumption that oxygen-containing functional groups providing unsaturation in the molecular structure were carboxyl groups, it was inferred that the maximum number of carboxyl groups in phenolic compounds and aliphatic compounds was concentrated between 1–2 and 2–4, respectively. The presence of these molecules was responsible for soluble organically-bound Al accounting for over 80 % of the total soluble Al in the supernatant after coagulation in this study. These findings deepen the understanding of the complexation of Al with DOM. In drinking water treatment plants, the combination of coagulation with processes that can remove such characteristic organics is beneficial for controlling residual Al.

Iron-Nitrogen Amendment Reduced Perfluoroalkyl Acids' Phyto-Uptake in the Wheat-Soil Ecosystem: Contributions of Dissolved Organic Matters in Soil Solution and Root Extracellular Polymeric Substances.

Understanding the mechanisms underlying perfluoroalkyl acids (PFAAs) translocation, distribution, and accumulation in wheat-soil ecosystems is essential for agricultural soil pollution control and crop ecological risk assessment. This study systematically investigated the translocation of 13 PFAAs under different iron and nitrogen fertilization conditions in a wheat-soil ecosystem. Short-chain PFAAs including PFBA, PFPeA, PFHxA, and PFBS mostly accumulated in soil solution (10.43-55.33%) and soluble extracellular polymeric substances (S-EPS) (11.39-14.77%) by the adsorption to amino- (-NH2) and hydroxyl (-OH) groups in dissolved organic matter (DOM). Other PFAAs with longer carbon chain lengths were mostly distributed on the soil particle surface by hydrophobic actions (74.63-94.24%). Iron-nitrogen amendments triggered (p < 0.05) soil iron-nitrogen cycling, rhizospheric reactive oxygen species fluctuations, and the concentration increases of -NH2 and -OH in the DOM structure. Thus, the accumulation capacity of PFAAs in soil solution and root EPS was increased. In sum, PFAAs' translocation from soil particles to wheat root was synergistically reduced by iron and nitrogen fertilization through increased adsorption of soil particles (p < 0.05) and the retention of soil solution and root EPSs. This study highlights the potential of iron-nitrogen amendments in decreasing the crop ecological risks to PFAAs' pollution.

Insight into the pathways of biochar/smectite-induced humification during chicken manure composting

As representative organic and inorganic additives, both biochar and smectite exhibit an excellent capacity to improve humification efficiency during composting. Nevertheless, the mechanisms underlying biochar/smectite-induced compost humification have still not been fully explored from the perspective of overall organic substances. In this study, three composting treatments were performed as follows: 10 % biochar-amended composting, 10 % smectite-amended composting and natural composting without any additive. UV–visible parameters and synchronous hetero two-dimensional correlation spectra showed that biochar accelerated dissolved organic matter (DOM) complications, unsaturation and aromatization. For example, biochar promoted the C2 and simple C3 peaks to convert into a sophisticated C3/360 peak. However, the effect of smectite was negligible in complicating the DOM structure. Both biochar and smectite displayed an invigorating role in promoting humic substance (HS) formation. The strengthened relations between bacterial richness and physicochemical indicators and HS fractions might contribute to the positive action of biochar/smectite on HS synthesis. Network analysis showed that both bacterial functional omnipotence and specialization in response to the addition of catalysts may contribute to compost humification. The chemical pathway involved in DOM humification was intensified by enhancing the role of pH in biochar composting and weakening the degradation of unsaturated aromatic compounds of DOM with smectite addition. These findings benefit the practical application of biochar/smectite in promoting composting efficiency.

Mechanisms shaping dissolved organic matter and microbial community in lake ecosystems

Lakes are active components of the global carbon cycle and host a range of processes that degrade and modify dissolved organic matter (DOM). Through the degradation of DOM molecules and the synthesis of new compounds, microbes in aquatic environments strongly and continuously influence chemodiversity, which can feedback to influence microbial diversity. Developing a better understanding of the biodiversity patterns that emerge along spatial and environmental gradients is one of the key objectives of community ecology. A changing climate may affect ecological feedback, including those that affect microbial communities. To maintain the function of a lake ecosystem and predict carbon cycling in the environment, it is increasingly important to understand the coupling between microbial and DOM diversity. To unravel the biotic and abiotic mechanisms that control the structure and patterns of DOM and microbial communities in lakes, we combined high-throughput sequencing and ultra-high resolution mass spectrometry together with a null modeling approach. The advantage of null models is their ability to evaluate the relative influences of stochastic and deterministic assembly processes in both DOM and microbial community assemblages. The present study includes spatiotemporal signatures of DOM and the microbial community in six temperate lakes contrasting continental and Mediterranean climates during the productive season. Different environmental conditions and nutrient sources characterized the studied lakes. Our results have shown high covariance between molecular-level DOM diversity and the diversity of individual microbial communities especially with diversity of microeukaryotes and free-living bacteria indicating their dynamic feedback. We found that the differences between lakes and climatic regions were mainly reflected in the diversity of DOM at the molecular formula-level and the microeukaryota community. Furthermore, using null models the DOM assembly was governed by deterministic variable selection operating consistently and strongly within and among lakes. In contrast, microbial community assembly processes were highly variable across lakes with different trophic status and climatic regions. Difference in the processes governing DOM and microbial composition does not indicate weak coupling between these components, rather it suggests that distinct factors may be influencing microbial communities and DOM assemblages separately. Further understanding of the DOM-microbe coupling (or lack thereof) is key to formulating predictive models of future lake ecology and function.

Understanding the Nanoscale Affinity between Dissolved Organic Matter and Noncrystalline Mineral with the Implication for Water Treatment.

In recent decades, the concentration of dissolved organic matter (DOM) in aquatic ecosystems has gradually increased, leading to water pollution problems. Understanding the interfacial chemical processes of DOM on natural minerals is important to the exploration of high-efficiency absorbents. However, studying DOM chemical processes and adsorption mechanisms are still challenging due to the complex DOM structure and environmental system. Hence, we characterized the microstructure changes after the formation of amorphous calcium phosphate (ACP) at the interface of montmorillonite (Mt) minerals in a simulated environment system. Combined with atomic force microscopy and density functional theory (DFT) simulation, the mechanism of interfacial interaction between Mt-ACP and DOM was characterized at the molecular level. Moreover, we further evaluated the adsorption behavior of Mt-ACP as a potential adsorbent for organic matter. The comprehensive investigation of humic acid adsorption, intermolecular force, and DFT simulation is conducive to our understanding of the interfacial interaction mechanism between organic matter and noncrystalline minerals in aquatic environments and provides new perspectives on the application of clay-based mineral materials in pollutant removal under exposure from DOM.

Natural sources and controlling factors of urea-nitrogen concentrations in agricultural drainage ditches.

Agricultural drainage ditches accumulate high urea-nitrogen (N) concentrations even in the absence of urea fertilizer applications to adjacent crop fields. The accumulated urea, and other bioavailable forms of dissolved organic nitrogen (DON), can be flushed downstream during substantial rainfall events altering downstream water quality and phytoplankton communities. Sources of urea-N supporting its accumulation in agricultural drainage ditches are poorly understood. A ditch flooding event was simulated using mesocosms with N treatment solutions and monitored for changes in N concentrations, physicochemical properties, dissolved organic matter (DOM) composition, and N cycling enzymes. N concentrations were also monitored in field ditches after two rainfall events. Urea-N concentrations were higher with DON enrichment, but the treatment effects were temporary. The DOM released from the mesocosm sediments was dominated by terrestrial-derived, high molecular weight material. The lack of microbial-derived DOM and evidence from the bacterial gene abundances in the mesocosms suggests that urea-N accumulation after rainfall may not be associated with fresh biological inputs. The urea-N concentrations after spring rainfall and flooding with DON substrates indicated the urea from fertilizers may only temporarily affect urea-N concentrations in drainage ditches. Because urea-N concentrations increased with a high degree of DOM humification, sources of urea may derive from the slow decomposition of complex DOM structures. This study provides further insights of sources contributing to high urea-N concentrations and the types of DOM released from drainage ditches to nearby surface waters after hydrological events.

Effects of dissolved organic matter on mercury speciation in rice rhizosphere amended with sulfur-rich biochar

Natural sulfur (S)-rich biochar (NRB) can be employed as an alternative for traditional S-modified biochar. However, the effect of dissolved organic matter (DOM) on mercury (Hg) speciation in rice rhizosphere soils under natural S-rich biochar application remains unclear. We conducted a pot experiment to study the effects of NRB application on the chemical composition and structure of DOM and the related speciation and availability of Hg in rice rhizosphere. Applying NRB significantly increased the concentration of methylmercury (MeHg) in the rhizosphere soils, which was enhanced with application frequency. This observation can be explained by MeHg immobilization in response to increasing S content in rice rhizosphere soils. We also observed increased molecular weight and functional group complexity of DOM, likely contributing to the decrease in MeHg mobility. Furthermore, the increase in pH and humification of DOM caused by S-rich biochar application generally reduced the concentrations of water-soluble and mercuric-sulfide fraction (easily-available Hg species) and organo-chelated fraction (potentially-available Hg species). Our findings highlight that the application of NRB can reduce the availability of MeHg in rice rhizosphere, thus providing a practical basis for reducing the potential risk of MeHg toxicity.

Seasonal and Spatial Variations in the Optical Characteristics of Dissolved Organic Matter in the Huma River Basin, China

Dissolved organic matter (DOM) plays a central role in the global carbon cycle. The Huma River Basin (HRB) in China is affected by humic substances in its forests with high background values. DOM in the HRB was studied using spectroscopic techniques combined with statistical analysis in order to better understand its characteristics in natural waters affected by humic substances in forests. UV-visible parameters showed that the DOM predominantly consisted of aromatic and high-molecular-weight natural organic matter. Fluorescence excitation-emission matrix (EEM) spectroscopy-parallel factor analysis (PARAFAC) recognized four characteristic components, representing humic-like substances (C1, C2, and C3) and protein-like substances (C4). Fluorescence parameters showed that the allochthonous terrestrially-derived DOM had a humic character. Fourier transform infrared (FT-IR) spectra characterized the structure of DOM, containing aromatic, aliphatic, carbohydrate, and protein compounds. Principal component analysis (PCA) revealed that humic-like components explained approximately 86.7% of the total variance, suggesting that terrestrial humic-like substances were dominant in the HRB. Correlation coefficient matrix analysis indicated that CODMn and DOC were mainly derived from humic-like substances. The results demonstrated that the background value in the HRB was mainly attributed to terrestrial humic-like substances. Such knowledge could assist in monitoring and managing rivers with high background values.

Dissolved Organic Matter as Affected by Forms and Doses of Nitrogen Applied to Soils of Temperate Deciduous Forests in China

Dissolved organic matter (DOM) is an important component in the biogeochemical cycles of elements like nitrogen (N) and carbon. The aim of this study was to elucidate the effect of long-term inorganic N addition on the quantity and quality of DOM in forest soils. A field study was conducted on three forms of inorganic N, namely (NH4)2SO4, NH4NO3, and NaNO3, applied at low (50 kg N ha−1) or high (150 kg N ha−1) annual doses from 2011 to 2019. The total dose was split into eight equal monthly doses applied during the growing season (from March to October). Both the form and the dose increased the content of dissolved organic carbon (DOC) in soil, the strongest effect being that of NaNO3. However, the higher dose had a weaker effect because of N enrichment. UV-visible (UV-vis) and excitation-emission matrix (EEM) spectroscopy showed that the addition of N made DOM more aromatic and increased the degree of humification. EEM-parallel factor analysis (PARAFAC) modelling suggested that DOM in the forest soils mainly contained a fulvic-like constituent (C1), humic-like substances (C2), and aromatic protein-like components (C3). The addition did not change the position of the DOM fluorophore in the soil but affected the proportions of the three PARAFAC-derived components (increasing those of C1 and C2 but decreasing that of C3), indicating that long-term addition of N may amplify the decrease in protein-like constituents of surface soil. Hence, N addition increased the complexity of the DOM structure.

Effects of warming on quantity and structure of litter-derived dissolved organic matter in subtropical natural Castanopsis kawakamii forests.

Litter-derived dissolved organic matter (DOM) is an important source of soil DOM, and the response of which to climate warming may change forest soil carbon and nitrogen dynamics, such as soil carbon and nitrogen mineralization. In this study, we conducted a field manipulative warming experiment in natural Castanopsis kawakamii forests. Combined with litter leaching solution collected in the field and ultraviolet-visible and three-dimensional fluorescence spectroscopy analyses, we explored the effects of warming on the content and structure of litter-derived DOM in subtropical evergreen broad-leaved forests. The results showed that litter-derived dissolved organic carbon and nitrogen content exhibited monthly dynamics, with the peak (in April) and the mean monthly content being 1.02 and 0.15 g·m-2, respectively. Litter-derived DOM had higher fluorescence index and lower biological index, indicating the microbial-origin of DOM from litter. The litter DOM mainly included humic-like fractions and tryptophan-like substances. Warming did not affect the content, aromaticity, hydrophobicity, molecular weight, fluorescence index, biological index and humification index of DOM, suggesting neutral effect of warming on the quantity and structure of litter DOM. Warming also did not affect the relative contribution of main components in DOM, indicating that the temperature variation exerted no effects on microbial degradation. In summary, warming did not change the quantity and quality of litter-derived DOM in subtropical evergreen broadleaved forests, indicating warming had little effect on litter-derived DOM input to soil.

Indirect photodegradation of ofloxacin in simulated seawater: Important roles of DOM and environmental factors

Dissolved organic matter (DOM) plays a non-negligible role in the indirect photodegradation of organic contaminants. This research investigated the roles of DOM and the environmental factors (salinity, pH, NO3−, and HCO3−) in the indirect photodegradation of ofloxacin (OFX) in simulated seawater. Results showed that DOM can significantly accelerate the indirect photodegradation of OFX, and 1O2 and 3DOM* were the main reactive intermediates (RIs) that could promote the indirect photodegradation of OFX. Fluorescence excitation–emission matrix spectroscopy–parallel factor analysis (EEMs-PARAFAC) was used to divide DOM into four fluorescence components. The indirect photodegradation rate of OFX was affected by DOM structure, and terrigenous DOM usually produced more RIs to promote the indirect photodegradation of OFX. Increased salinity significantly promotes the indirect photodegradation of OFX, while increased NO3− concentration had no effect on the OFX indirect photodegradation. pH affected the formation of RIs and the structure of OFX, thereby affecting the indirect photodegradation of OFX. The indirect photodegradation rate of OFX increased in the HCO3− solution, which is due to the formation of carbonate radical (CO3−). This study is essential in understanding the role of DOM in OFX indirect photodegradation and providing a novel insight into the fate, removal, and transformation of OFX.

Molecular transformation of dissolved organic matter in reverse osmosis concentrated leachate during a tight-ultrafiltration membrane combined with an O3/GAC system

The dissolved organic matter (DOM) composition in reverse osmosis concentrated landfill leachate (ROCL) is very complex and difficult to treat. In this study, tight ultrafiltration (TU) combined with the O3/granular activated carbon (GAC) catalytic oxidation system was used to treat DOM in ROCL. The treatment effect and mechanism of TU combined with the O3/GAC catalytic oxidation system were carefully studied using ESI FT-ICR MS. The results show that DOM in ROCL mainly has Ali and UnPh-like structures, showing the characteristics of reduction and unsaturation. In the membrane treatment link (i.e., TU and deamination system), the DOM with LO-UnPh-like structures can be effectively intercepted and removed, and the DOM in the effluent mainly has Ali and LO-UnPh-like structures, showing the characteristics of reduction and unsaturation. In the process of the O3/GAC system, DOM with HO-UnPh-like structures was further removed through catalytic oxidation, which not only destroys the aromatic structure of DOM but also forms daughter products with a higher degree of saturation, fewer aromatic properties, fewer carbon atoms, and more oxygen-containing functional groups. The action intensity of •OH in the O3/GAC catalytic oxidation system was verified, and the reaction mechanism of GAC catalytic O3 was analyzed according to the surface properties of GAC. Finally, the GAC after use was treated with several regeneration methods; the results showed that the morphology and structure of the deactivated GAC could be restored by the method of washing–microwave irradiation. This study provides a promising method for the proper treatment of ROCL.

Insights into the role of the microbial community lifestyle strategies in variations of the dissolved organic matter molecular composition along an effluent-dominated river

Urbanization has dramatically changed the quality and quantity of dissolved organic matter (DOM) fluxes in rivers, thereby affecting the diversity and lifestyle strategies of microbial communities. However, relationships between DOM molecular composition and microbial lifestyle strategies in effluent-dominated rivers are poorly understood. Herein, we investigated the variations in DOM structure and composition of an effluent-dominated river and further revealed how these changes alter the abundance and lifestyle strategies of microbial communities. Results demonstrated that macromolecular (MW > 35 kDa) humic-like substances constituted the major components of effluent-dominated riverine DOM. Also, due to the degradation of humic-like substances, the accumulation of protein-like substances was observed from upstream to downstream areas, corresponding to an apparent decrease in overall aromaticity. The abundance of bacterial, Actinobacteria, and eukaryotic was higher in the upstream and midstream areas but relatively lower in the downstream area. The response of bacterial and Actinobacteria communities to the changes in DOM composition was more prominent as compared to that of eukaryotic. Based on multivariate statistical analysis, the decrease in aromatic components (MW > 35 kDa) was mainly attributed to the degradation of Proteobacteria and Actinobacteria (K-strategists), resulting in a decrease in their relative abundance along the river course. Proteins and polysaccharides (15 kDa < MW < 35 kDa, MW < 6 kDa) were more easily utilized by Firmicutes and Bacteroidetes (r-strategists), leading to an increase in their relative abundance. With the decrease of macromolecular humic-like substances and the increase of protein-like substances, river microbial communities shifted from K-strategists to r-strategists. This work unveils the evolution of DOM in an effluent-dominated river and the influence of the degradation of macromolecular humic-like substances on r/K-strategists.

Effects of water quality and bacterial community composition on dissolved organic matter structure in Daihai lake and the mechanisms

The migration of organic matter in salinized lakes was critical in maintaining ecological balance and material circulation process of inland shallow lakes. To clarify the ecological and microbial mechanism of material transport and transformation, the microbial community structure and the characteristics of dissolved organic matter (DOM) in the sediment of Daihai Lake, a typical saline lake at the Yellow River Basin, were explored with three-dimensional excitation and emission matrix fluorescence (3DEEM), parallel factor analysis (PARAFAC) and 16 S rRNA techniques. The correlation between environmental factors, DOM composition and the bacterial community structure were also studied for identifying the key factors of community formation. DOM in the lake demonstrated both terrigenous and endogenous characteristics. Protein-like materials accounted for 74% of the total fluorescence intensity in the sediment, where 1127 species, 671 genera, 468 families, 157 classes, 317 orders, 59 phyla of microorganisms were detected. Among the top 10 abundant taxa of each level, Firmicutes, Actinobacterota, Acidimicrobiia and Alphaproteobacteria had the greatest influence on the composition and structure of DOM (|R| > 0.7, p < 0.01). Microbial metabolism was a key process of transforming sediment organic matter from terrestrial humic-like to protein-like matter, accounting for 81% of total fluorescence signal in saline lake samples, while salinity, temperature, dissolved oxygen and electrical conductivity also had significant impacts during the process (|R|>0.7, p < 0.05). The research provides fundamental data and enlightenment for the improvement of the saline inland lake environment.

Electric field applications enhance the electron transfer capacity of dissolved organic matter in sludge compost

ABSTRACT Dissolved organic matter (DOM) plays an important role in heavy metal passivation and organic pollutant degradation owing to its redox ability. The structure and composition of DOM are determinants of redox ability changes during composting. Electric field-assisted aerobic composting (EAAC) has been shown to promote the degradation and humification of organic matter in compost. However, how EAAC affects the redox ability of DOM remains unclear. Hence, electron transfer capacity (ETC) of DOM extracted from EAAC was studied using the electrochemical method. Various spectral methods, such as excitation–emission matrix and ultraviolet and visible spectrophotometry were used to study the relationship of ETC with the compositional and structural changes of DOM. Results indicated that EAAC enhanced ETC of DOM at the later stage of composting, and ETC of DOM extracted from the final EAAC product was 10.4% higher than that of the control group. Spectral and correlation analyses showed that EAAC resulted in structural and compositional changes of DOM, and humification degree, aromatic compounds, molecular weight, and fulvic- and humic-like substance contents were improved in EAAC. This conversion increased ETC of DOM. Results of this study will contribute to the understanding of the redox of DOM and in expanding the application of EAAC products.