Properties Of Dissolved Organic Matter Research Articles

Coupled variations of dissolved organic matter distribution and iron (oxyhydr)oxides transformation: Effects on the kinetics of uranium adsorption and desorption

The interactions between dissolved organic matter (DOM) molecules and minerals play significant roles in affecting the fate of carbon and contaminants in soil environment. However, the mechanisms controlling the variations of DOM molecules distribution during the transformation of Fe (oxyhydr)oxides, and the effects of these variations on contaminant behaviors are still largely unknown. In this study, the dynamic variations of DOM properties and distributions, and the kinetics of uranium adsorption on and desorption from Fe (oxyhydr)oxides during the transformation were investigated, employing a combination of Orbitrap mass spectrometry (MS), high-resolution transmission electron microscopy (HR-TEM), and kinetic experiments. Orbitrap MS results indicated that aliphatic molecules and phenolic and polyphenolic molecules with lower O/C values were preferentially released to solution. HR-TEM results indicated that the coprecipitated DOM molecules by ferrihydrite were mainly released to solution rather than sorbed on the newly formed lepidocrocite or goethite during the transformation. Furthermore, the stirred-flow experiment results suggested that soil DOM significantly reduced the adsorption of uranium on, and accelerated the release of uranium from Fe (oxyhydr)oxides, which was ascribed to the changed distribution of DOM molecules and the structure and composition of Fe (oxyhydr)oxides. Our results contribute to predicting contaminant behaviors in soils.

The desorption mechanism of dissolved organic matter on pollutants and the change of biodiversity during sediment dredging

Sediment dredging is an effective means to control the endogenous pollution of lakes, which could significantly change the concentration and composition of organic matter, especially dissolved organic matter (DOM) in the lake. DOM is particularly important for the release of endogenous pollutants, which will inevitably bring an impact on aquatic biodiversity. Nevertheless, in recent research little attention has been paid to the desorption mechanism of DOM on pollutants and the change of biodiversity during dredging. This study investigated the physicochemical properties of DOM in the sediment by taking a sediment dredging project in Dianchi Lake in China for example. The correlations of DOM properties with the desorption behavior of nitrogen (N), phosphorus (P), cadmium (Cd), lead (Pb) and the biodiversity of aquatic organisms were analyzed. The results show that the aromaticity and humification of DOM were improved after dredging, and the high molecular weight DOM was degraded into low molecular weight substance. The desorption amount of N, P and heavy metals (Cd, Pb) were decreased as the pH values increased. Moreover, NH4+-N promoted the release of Pb2+ from DOM, while the release of PO43--P was inhibited. Correlation analysis shows that the physicochemical properties of DOM exactly affected the release of N, P, Cd and Pb. It was easier to desorb pollutants with low aromaticity and humification of DOM, leading to a decrease in the diversity of aquatic organisms. This study identified the desorption mechanism of endogenous pollutants in DOM and the ecological risk to aquatic organisms, providing a theoretical basis for the prevention and control of water pollution.

Release of dissolved organic carbon from biochar and formation of humic-like component during photoreaction: Effects of Ca2+ and pH

The photochemical reactivity of dissolved organic carbon from biochar (DBC) was higher than dissolved organic matter (DOM), but the photo-transformation of DBC in the presence of DOM under various conditions are poorly understood. Here, we studied the effects of Ca2+ and pH on the photo-induced changes in the optical and structural properties of DOM in source water with biochar. During DBC photobleaching, the DBC released from bulk DBC while the humic-like component formed. The release of DBC and the formation of humic-like component were inhibited by the presence of Ca2+ attributed to the inhibition of triplet excited state of DOM (3DOM*) and singlet oxygen (1O2) generation. Moreover, the 3DOM* yield increased while the 1O2 generation decreased as pH decreased from neutral, resulting in the increased formation of humic-like component and decreased release of DBC. The characterizations of ultrafiltration-isolated colloidal DOM after irradiation showed that hydrophilicity and the colloidal size of released DBC decreased in the presence of Ca2+. Additionally, the colloidal size of released DBC decreased while the hydrophilicity of DBC enhanced with increasing pH from neutral. This study not only gives insight into the DBC photo-transformation in the presence of DOM under various conditions but also reveals the influence of DBC on the variation of DOM properties during irradiation.

Characterizing Molecular Weight Distribution and Optical Properties of Dissolved Organic Matter and Unraveling the Origins of Anthropogenic Fluorophores in Yangtze River and Its Tributaries

In this study, size exclusion chromatography (SEC) coupled with multiple detectors was used to characterize the composition, molecular weight (MW), and optical properties of dissolved organic matter (DOM) in the Yangtze River main stream and its 88 tributaries. The SEC chromatograms revealed that DOM in the investigated water samples mainly comprised nonhumic proteinaceous biopolymers with apparent MW > 20 kDa and humic substances with apparent MW ranging from ∼0.5 to ∼7 kDa. The SEC fluorescence chromatograms further unraveled that there was a kind of characteristic fulvic-acid-like fluorophore in downstream tributaries, which showed triple-excitation peaks at ∼250, 310, and 365 nm with an emission peak at ∼460 nm (designated as HS-Em460-Ex3 hereinafter). Via field investigation and parallel factor analysis, this characteristic HS-Em460-Ex3 fluorophore was identified to originate from the discharge of residual naphthol and naphthylamine moieties in biologically treated textile wastewater. The SEC fluorescence fingerprints also demonstrated the occurrence of the characteristic HS-Em460-Ex3 fluorophore in the Yangtze River main stream from Changzhou to Nantong, suggesting that the discharge of textile wastewater might have altered the optical properties of riverine DOM and advanced treatment processes should be applied to eliminate residual aromatic fluorophores in textile wastewater.

Comparison of Organic Matter Properties and Disinfection By-Product Formation between the Typical Groundwater and Surface Water

The disinfection by-product (DBP) formation was affected by the dissolved organic matter (DOM). Therefore, the DOM properties and DBP formation potential of the two most widely used source waters: groundwater (GW) and surface water (SW), were comparatively studied in this work. The results suggested that the GW mainly consisted of protein-like organics with smaller molecular weight (Mw) less than 3000 Da, while the SW contained the humic- and fulvic-like substances with larger Mw. The tap water DBP concentration of GW as source water was lower than that of SW as well as the cytotoxic index (CI). The total DBP formation potential of the SW under chlorine and chloramine disinfection was higher than that of GW, especially the trihalomethanes (THMs) and haloacetic acid (HAAs). The higher THM and HAA formation potential of the SW was mainly attributed to the relatively hydrophobic and aromatic humic and fulvic substances. The halonitromethanes (HANs) formation was mainly due to the less hydrophobic protein-like components with smaller Mw. In addition, the total CI of the GW was lower than the SW under both chlorine and chloramine disinfection. Therefore, for the DBPs control, using the GW as source water was more beneficial to human health.

Biological and photochemical reactivity of dissolved organic matter in a large temperate river

AbstractLarge rivers are critical conduits from continents to oceans as they receive, produce and process huge amounts of dissolved organic matter (DOM). Yet, the relative influence of intrinsic DOM properties and extrinsic environmental properties on these processes at the ecosystem‐level is rarely studied. We assessed DOM optical properties as well as bioreactivity and photoreactivity at 40 sites along a >200 km transect of the freshwater portion of the St. Lawrence River through a series of standardized microbial incubations and exposure to simulated sunlight, and then estimated in situ areal rates of processing. We found that biological and photochemical processes preferentially targeted contrasting pools of DOM, but that DOM composition had an undiscernible effect on in situ degradation rates compared to other environmental factors. Total daily processing across the whole water column ranged from 36.7 to 892.1 mg C m−2. In situ photochemical degradation was largely driven by intrinsic DOM photoreactivity rather than environmental drivers in the water. In contrast, we found a relatively constant baseline pool of biolabile DOM that appeared to be independent from changes in concentration and environmental conditions. In situ DOM processing was mostly driven by biological degradation (on average 95%), and disproportionately high biodegradation rates (2.5–4x the average) were found in a few shallower sites near effluents or islands, potentially driven by local increases in nutrient concentration and in the proportion of protein‐like DOM. These results illustrate how DOM composition and degradability interact with ambient environmental and morphological properties to dictate an ecosystem‐level reactivity of DOM.

Characterization of DBP precursor removal by magnetic ion exchange resin using spectroscopy and high-resolution mass spectrometry

The characteristics of dissolved organic matter (DOM) play an important role in the formation and speciation of carcinogenic disinfection byproducts. This study investigated changes in the characteristics and reactivity of DOM caused by the magnetic ion exchange resins, MIEX® DOC and MIEX® GOLD, using fluorescence excitation-emission matrix (EEM) with parallel factor (PARAFAC) analysis and Orbitrap mass spectrometry (Orbitrap MS) with unknown screening analysis. A five-component PARAFAC model was developed and validated from 208 EEMs of raw and MIEX®-treated water samples. The two resins exhibited preferential removal of the humic-like components (67–87% removal) and successfully removed protein-like components to a lesser extent (5–61% removal). Unknown screening analysis indicated removal of most condensed aromatic structures and lignin-like features that had high O/C values and refractory characteristics of lipid-like features by MIEX® treatments. MIEX® preferentially removed DOM molecules with more oxidized and shorter CH2 chains. The two resins had similar performance in trihalomethanes formation potential removal, but MIEX® GOLD achieved greater haloacetonitriles formation potential removal owing to its larger pore opening. Over 100 CHOCl DBP features were commonly found in all the samples while tens of CHOCl DBPs were uniquely formed in the samples with and without pre-treatments by MIEX®. Treatments by MIEX® before chlorination resulted in more intermediate CHOCl DBPs formed after chlorination compared to chlorinated raw waters. By optical spectroscopic analysis together with Orbitrap MS molecular characterization, we were able to confirm both quantitative and qualitative changes in DOM properties by MIEX® treatment related to DBP formation.

Fluorescence Spectral Characteristics of Dissolved Organic Matter in Songhua Lake Sediment

Dissolved organic matter (DOM) has a significant impact on the main pollution indicators of the lake (e.g., COD), and sediment is the main source of pollution in the lake. Research on the fluorescence spectral characteristics of DOM in sediments is important to reveal the mechanism of lake pollution. In this study, sediments were collected from 20 sites in Songhua Lake. The DOM components in the sediment were analyzed using the excitation emission matrix-parallel factor analysis (EEM-PARAFAC) technique, and the properties of the sediment DOM were clarified via spectroscopy. Additionally, the relationship between DOM and eutrophication of the water column was explored. The results showed that four components were identified from the sediment DOM of Songhua Lake:humic-like C1 (330/415 nm), C2 (255/440 nm), C3 (365/470 nm), and protein-like C4 (280/355 nm). The high HIX and low BIX indicated that the source of sediment DOM was mainly terrestrial and included some biological sources. The spatial distribution of the fluorescence intensity of the four components was relatively similar, showing that the fluorescence intensity was higher in the upstream (S1-S7) than that in the downstream (S8-S20). The massive deposition of suspended particulate matter (SPM) carried by the three rivers (Huifa River, Songhua River, and Jiao River) was the main reason for this spatial distribution. Eutrophication status in the water column of Songhua Lake was similar to the fluorescence intensity distribution of sediment DOM. Meanwhile, there was a strong correlation between eutrophication level and sediment DOM fluorescence intensity in the downstream water column of Songhua Lake.

Environmental Risk and Management of Herbal-Extraction Residues Induced by the Composition and Metal Binding Properties of DOM

As the consumption of Chinese medicine resources increases, the waste of traditional Chinese medicine extraction cannot be disposed of reasonably, which has a serious impact on the environment. Dissolved organic matter (DOM), a crucial fraction in herbal extraction residue, can bond to heavy metals (HMs), creating a potential environmental risk. This study investigated the binding property of herbal extraction residue DOM with Cu(II) via two-dimensional Fourier transform infrared (FTIR) and synchronous fluorescence correlation spectroscopy (2D-COS) in conjunction with parallel factor (PARAFAC) modeling. Through PARAFAC analysis, three kinds of protein components and one kind of fulvic acid can be obtained, and protein-like substances are dominant in the residual DOM of Chinese medicine extracts, becoming the main factor of water quality deterioration. A fluorescence quenching experiment shows that protein-like materials provide the primary binding sites with Cu(II). During the detection, the long-wavelength low-intensity signal will be obscured. The 2D-COS obtained by the 1/9th power transformation can enhance the fluorescence signal so as to get even more information about the binding sites and heterogeneity of DOM and heavy metal ion ligands. The N−H of amine in the protein-like materials could prioritize combining with Cu(II). This study urges that continuous and effective attention be paid to the impact of the herbal extraction residue on the geochemical behavior of HMs.

Trapped Under Ice: Spatial and Seasonal Dynamics of Dissolved Organic Matter Composition in Tundra Lakes

AbstractArctic lakes store, modify, and transport large quantities of carbon from terrestrial environments to the atmosphere; however, the spatial and temporal relationships between quantity and composition of dissolved organic matter (DOM) have not been well characterized across broad arctic regions. Moreover, most arctic lake DOM compositions have been examined during the ice‐free summer, whereas DOM cycling between the ice‐covered winter months and summer have not been addressed. To resolve these spatial and seasonal uncertainties in DOM cycling, we sampled a series of arctic lakes from the North Slope of Alaska across a latitudinal gradient in the winter and summer over 3 years. Samples were analyzed for dissolved organic carbon concentration and DOM composition was characterized using optical and fluorescence properties combined with molecular‐level analysis using Fourier transform‐ion cyclotron resonance mass spectrometry. Tundra lake DOM properties including aromaticity and molecular stoichiometries were similar to other northern high‐latitude lakes, but optical parameters related to aromaticity and molecular weight were greater in major arctic rivers and in coastal lakes in the North Slope region. DOM composition was highly seasonal, with ice exclusion concentrating microbially processed DOM in the winter water columns, potentially influencing DOM cycling the following summer. However, the greatest variations in DOM composition were related to lake depth and likely other physical features including morphology and bathymetry. As the Arctic warms, we expect changes in hydrology and ice cover to enhance under‐ice microbial DOM processing, early summer photodegradation, and ultimately carbon fluxes to the atmosphere after ice‐out.

Characterization of the Colloidal Properties of Dissolved Organic Matter From Forest Soils

Components of dissolved organic matter (DOM) span from sub-nm molecules to colloidal aggregates of several hundred nm. The colloidal fraction is important for the transport of organic matter and associated elements in the environment, and for the stability of DOM constituents with respect to microbial decomposition. This study focuses on the colloidal properties of DOM extracted from spruce forest soils of a chronosequence. The DOM samples were obtained by common water extraction procedures at 21 and 100°C, respectively. We applied an experimental approach combining chemical analysis with light and X-ray scattering techniques that informed on the colloidal size, charge, and structure of DOM. Results showed that two main types of colloids were present: semi-flexible cylinders and fractal aggregates. The cylinders consisted of carbohydrates, presumably hemicelluloses, while the aggregates were a composite material containing a large fraction of carbohydrates together with aliphatics and clay particles. These fractal aggregates dominated the cold-water extracts whereas the strong increase in total organic carbon by hot-water extraction caused a concomitantly strong increase of semi-flexible cylinders, which became the predominant species. Comparison between the chronosequence soils showed that with increasing forest age, the amount of carbon extracted per gram of soil declined and the concentration of the semi-flexible cylinders decreased. Thus, the distribution between the fractal aggregates and cylinders in the forest soil DOM samples depends on the composition of the soil organic matter and the leaching temperature. Changes in this distribution may have important implications for the reactivity and stability of DOM colloids.

Characterization of coagulant-induced ultrafiltration membrane fouling by multi-spectral fusion: DOM properties and model prediction based on machine learning

This study used the ultraviolet-visible (UV–vis), synchronous fluorescence, and excitation-emission matrix (EEM) spectroscopy coupled with zeta potential and particle size to explore the dissolved organic matter (DOM) solutions properties with the addition of two kinds of coagulants, including aluminum chloride and ferric chloride, in humic solutions and surface water. The results of zeta potential and particle size showed the size of aggregates became larger with the addition of coagulant. The binding sequence of coagulant to DOM was followed from aromatic amino acids to fulvic-like and humic-likes fractions. The results of the unified membrane fouling index (UMFI) were showed negatively correlated with the concentrations of coagulant due to the cake layers formed by aggregates being looser and more permeable. Among all the 12 spectral parameters, slope radio (SR) and specific fluorescence intensities (SFI) had the most significant correlation to UMFI. The multi-spectral fusion for predicting UMFI was established via multiple linear regressions and the backpropagation neural network (BPNN) by using the parameters with both SR and SFI with good accuracy and robustness. Sensitivity analyses results showed that SFI was more sensitive than SR in solutions with high protein-like substances, while SR was more sensitive than SFI with high humic-like substances.

Spectroscopic properties and driving factors of dissolved organic matter in the Yellow River Delta

AbstractRiver deltas are hot spots of biogeochemical cycling. Understanding sources and driving factors of dissolved organic matter (DOM) in river deltas is important for evaluating the role of river deltas in regulating global carbon flux. In this study, spectroscopic properties of soil DOM were analyzed in both freshwater and tidal areas of the Yellow River Delta. Five fluorescent components of soil DOM (two humic-like DOM, two protein-like DOM and one possible contaminant) were identified by parallel factor analysis and further confirmed by comparison with an online database. Concentration, spectroscopic properties and sources of soil DOM and its components differed between freshwater and tidal areas. DOM concentration was much higher in freshwater areas than in tidal areas. In freshwater areas, soil DOM was mainly derived from phytoplankton and microorganisms, while it was mainly derived from microorganisms and human activities in tidal areas. These differences in DOM between both areas were strongly driven by environmental factors, especially soil carbon (C), nitrogen (N) and its stoichiometric ratio C/N. These explained 80.7% and 69.6% of variations in DOM and chromophoric DOM (CDOM), respectively. In addition, phytoplankton also contributed to soil DOM, CDOM and fluorescent components C1–C4 as identified by significant positive correlations between them. These results imply that both the concentration and composition of soil DOM are strongly driven by soil properties and phytoplankton density in the Yellow River Delta.

Properties of sediment dissolved organic matter respond to eutrophication and interact with bacterial communities in a plateau lake

Sediment dissolved organic matter (DOM) in inland waters is commonly affected by environmental changes. However, knowledge about how sediment DOM responds to eutrophication and the associations between sediment DOM and bacterial communities requires further investigation. We selected a sediment core from Dianchi Lake (China) that was dated from 1864 to 2019 by the activity of radionuclides (210Pb and 137Cs). δ13CDOC changes fit well with the historical record that heavy eutrophic status in Dianchi Lake were observed since 1980s. Large amounts of dissolved organic carbon (DOC), chromophoric (CDOM) and fluorescent (FDOM) DOM accumulated at the top of the sediments during the eutrophication period (1982-present). The additional algae sources with a higher degradation rate altered the composition, aromaticity and humification of DOM. After long-term mineralization, the remaining DOM became more and more recalcitrant and kept a relatively stable level at older sediments. A co-occurrence network analysis revealed that Proteobacteria, Chloroflexi, Acidobacteriota, Bacteroidota and Desulfobacterota were the most abundant species at the phylum level and clustered into three primary modules. Different microbes shared unique preferences for niches, causing a heterogeneous bacterial distribution at different depths. We conducted Spearman's correlation and redundancy analysis (RDA) to explore potential interactions between bacterial community and sediment DOM. The richness and diversity of bacterial communities were positively related to DOM content, suggesting abundant DOM can produce more available resources for bacteria. RDA results showed some specific species might modify DOM composition and structure. This study suggests that sediment DOM properties were regulated by source transformation during eutrophication, and emphasizes the importance of microbial role on sediment biogeochemical process.

Evaluation of the pollutant interactions between different overlying water and sediment in simulated urban sewer system by excitation-emission matrix fluorescence spectroscopy.

The water quality in the sewer systems can be significantly influenced by the interaction between sediment and overlying water, which are still many doubts about the impact of pollutants transformation, degradation sequence, and reaction time. In this study, the exchanging processes between sewer sediment and four different overlying waters were evaluated in simulated urban sewer systems (dark and anaerobic environments). Dissolved organic matter (DOM) was used as an indicator to reflect the mitigation and exchange processes of pollutants. Excitation-emission matrix (EEM) fluorescence spectroscopy coupled with parallel factor analysis (PARAFAC) as an effective method for deciphering DOM properties was applied. There are three findings: (1) Three main processes (biological degradation, desorption, and adsorption) happened in the simulated sewer systems, in which the predominant pathway in the interaction process is biological degradation though consuming amino acid components. (2) The characteristics of overlying water could induce significant changes in sediment signatures; the amino acid-like components are more susceptible to degradation, and the humic-like compositions are more readily absorbed by sediments. (3) The reaction time is another significant factor (14days was the turning point of the processes). This study unravels the transformation processes in sediment and different overlying waters, which provides the theoretical foundation for urban sewer efficient management and operation.

Effect of dissolved organic matter (DOM) on greenhouse gas emissions in rice varieties

Rice paddy fields are important sources of atmospheric methane (CH4) and nitrous oxide (N2O). Dissolved organic matter (DOM) is one of the most reactive organic matter fractions in the soil. However, the relationships between greenhouse gas emissions and DOM properties associated with different rice varieties in paddy fields are unclear. Here, a two-year field experiment was conducted to investigate the relationships between DOM characteristics and microbial gene abundance on CH4 and N2O emissions in seven rice varieties. The dissolved organic carbon, dissolved sugar, and NH4-N and NO3-N contents were positively correlated with CH4 and N2O emissions, and dissolved phenol was negatively correlated with CH4 and N2O emissions. Fourier transform infrared (FTIR) and three-dimensional fluorescence (EEM) spectroscopy analysis further indicated that DOM includes more O-H and CO phenol and protein content, of which tryptophan-like and tyrosine-like protein materials were positively correlated with CH4 and N2O emissions. In addition, CH4 and N2O emissions were significantly correlated with microbial functional genes (mcrA, pmoA, AOA, AOB, nirS, and nosZ). The redundancy analysis indicated that dissolved organic carbon, dissolved sugar, NH4-N, NO3-N, and tyrosine-like and tryptophan-like proteins in the DOM were significantly correlated with soil microbial functional gene abundance, suggesting that DOM could regulate CH4 and N2O emissions by influencing microbial abundance. The rice variety with lower greenhouse gas emissions (YY 1540) had the highest yield. These results demonstrated that the differences in greenhouse gas emissions among different rice varieties were dependent on DOM properties and microbial abundance, providing a theoretical basis for mitigating greenhouse gas emissions in rice paddy fields.

Ultraviolet-visible and fluorescence spectra indicate the binding and transformation properties of hexavalent chromium in DOM solution

Dissolved organic matter (DOM) with complex functional groups affects the trace of binding and transformation of hexavalent chromium (Cr(VI)) in the environment. However, the mechanisms and quantitative indicators are still ambiguous. In this study, the perspectives of spectroscopy with synchronous and excitation-emission matrix (EEM) fluorescence, and ultraviolet-visible (UV–vis) were employed to probe the interaction of DOM and Cr(VI). The spectroscopic parameters with Dslope240–280 (the slope of the log-transformed absorbance in the range of 240–280 nm), DSlope325–375 (the slope of the log-transformed absorbance in the range of 325–375 nm), SR (the ratio of the slope of the log-transformed absorption coefficient with 275–295 nm to 350–400 nm), SFI (specific fluorescence intensities), AvgFI/AvgUVA (the ratio of average fluorescence to average UV), and SS (Stokes shift) of UV–vis and fluorescence were extracted to characterize the DOM properties. The UV–vis results showed carboxylic-like and total phenolic/carboxylic-like groups were contributed to the complexation of Cr, which resulted in forming macromolecular aggregates, however, the degree of participation of different functional groups was uneven and the binding sequence depended on the types of fractions especially the ratio of protein. Meanwhile, the EEM results proved interaction between DOM and Cr also affected the hydrophobicity and quantum yield of solutions. In addition, according to the change orders of substances and functional groups by Two-dimensional correlation spectroscopy (2DCOS) analysis, aromatic amino acids substances were much more sensitive binding onto Cr than fulvic-like fractions and humic-like fractions, and the mechanisms for Cr(VI) retention were developed. Statistical analysis results showed that SR and SFI were significantly correlated with the concentration of Cr(VI), and multiple linear regression models were developed to predict concentrations of Cr(VI). Moreover, it was found the goodness of fit of SFI was better than that of SR at low Cr concentrations, but opposite at high concentrations.

Iron (hydr)oxides mediated immobilization and interaction of dissolved organic matter and inorganic phosphate: A review

铁(氢)氧化物介导的溶解性有机质(DOM)和无机磷(DIP)的固定在水生态系统中普遍存在，对碳、磷元素的生物地球化学循环有重要的影响. 铁(氢)氧化物主要通过吸附和共沉淀两种过程固定DOM和DIP，且铁(氢)氧化物、DOM和DIP三者存在复杂的相互作用. 本文主要从铁(氢)氧化物对DOM和DIP的固定，铁(氢)氧化物、DOM和DIP之间的相互影响等方面综述了相关研究进展，梳理了铁(氢)氧化物、DOM和DIP在吸附和共沉淀过程中的相互作用机制与影响因素. DOM的存在会通过占据铁(氢)氧化物表面吸附点位、络合、抑制铁水解沉淀等途径影响铁(氢)氧化物对DIP的固定; 且不同机制与DOM的不同性质如分子大小、芳香组分、羧基官能团含量等有关. 而DIP的存在会改变铁(氢)氧化物对DOM的固定分馏过程，改变溶液中DOM的组分和性质. 在明晰三者相互作用基础上，探讨了铁(氢)氧化物介导的DOM和DIP的固定过程对湖泊内源磷释放和碳埋藏的可能影响，并对未来的研究方向进行了展望.;Iron(hydr)oxides mediated immobilization of dissolved organic matter (DOM) and inorganic phosphate (DIP) is ubiquitous in aquatic ecosystems, which plays an important role in the biogeochemical cycle of carbon and phosphorus. The immobilization of DOM and DIP based on iron(hydr)oxides is mainly via adsorption and coprecipitation, and there is a complex interaction among iron(hydr)oxide, DOM and DIP. This paper reviewed the relevant studies on the immobilization of DOM and DIP by iron(hydr)oxides and their interactions. We discussed the interaction mechanism and influencing factors on the interaction among iron (hydr)oxides, DOM and DIP during the processes of adsorption and coprecipitation. The presence of DOM affects the fixation of DIP by occupying the adsorption sites on the surface of iron(hydr)oxides, complexing and inhibiting iron hydrolysis and precipitation. The properties of DOM, such as molecular size, aromatic components, carboxyl functional group content are the main decisive factors. The presence of DIP changes the immobilization and fractionation of DOM by iron(hydr)oxides, and thus the composition and properties of DOM in solution. After clarifying the interaction of iron(hydr)oxides, DOM and DIP, the potential effects of these interactions on internal phosphate release and carbon burial in lakes were discussed. The potential future research issues were proposed.

Characterization of the vertical size distribution, composition and chemical properties of dissolved organic matter in the (ultra)oligotrophic Pacific Ocean through a multi-detection approach

This work presents a multi-analytical approach for the characterization of marine dissolved organic matter (DOM). The determination of marine dissolved organic carbon (DOC) was performed by size exclusion chromatography (SEC) and validated using a certified reference material (CRM) as well as through an intercomparison exercise. Multi-detection SEC, fluorescence and electrochemical methods were used in order to describe the size distribution spectra, the composition and chemical properties of marine DOM, in the (ultra)oligotrophic West Tropical South Pacific Ocean (WTSP). In this work, we defined the state of degradation of DOC in the different size fractions, operationally defined by SEC. We estimated that on average 62% of DOC was of humic nature (0.5–10 kDa), of which ~9% was able to complex trace elements, such as iron (Fe). Our results tend to support that non-refractory DOC is of high molecular weight (HMW), nitrogen (N)-rich, aliphatic, and has a weak fluorescence quantum yield and an enhanced binding capacity for Fe. The ageing of marine DOM occurring within mesopelagic waters is mainly driven by microbial respiration and alters these chemical properties. Although our results are in agreement with a paradigm describing oceanic DOM biogeochemistry known as the size-reactivity continuum, 3 μmolC L−1 of very HMW (> 10 kDa) were still observed in a water mass mainly composed of Pacific Deep Waters. This persistence could be explained by a significant content (5%) of aromatic carbon that may protect HMW DOM from long term biodegradation.

Computational Calculation of Dissolved Organic Matter Absorption Spectra.

The absorption spectrum of dissolved organic matter (DOM) is a topic of interest to environmental scientists and engineers as it can be used to assess both the concentration and physicochemical properties of DOM. In this study, the UV-vis spectra for DOM model compounds were calculated using time-dependent density functional theory. Summing these individual spectra, it was possible to re-create the observed exponential shape of the DOM absorption spectra. Additionally, by predicting the effects of sodium borohydride reduction on the model compounds and then calculating the UV-vis absorbance spectra of the reduced compounds, it was also possible to correctly predict the effects of borohydride reduction on DOM absorbance spectra with a relatively larger decrease in absorbance at longer wavelengths. The contribution of charge-transfer (CT) interactions to DOM absorption was also evaluated, and the calculations showed that intra-molecular CT interactions could take place, while inter-molecular CT interactions were proposed to be less likely to contribute.