Molecular Weight Dissolved Organic Matter Research Articles

Ceramic membrane with double catalytic layer for efficient peroxymonosulfate activation and dissolved organic matter (DOM) membrane fouling control

Membrane fouling and low removal of dissolved organic matter (DOM) are the main obstacles for the wide application of ultrafiltration membrane technology in water treatment. Herein, we reported the preparation and application of a novel ceramic membrane, which embedded the cobalt oxide in the membrane support layer, and simultaneously loaded the CoAl composite bimetallic oxide on membrane surface layer. The double catalytic layer membrane (CoAl@AM-Co) enabled more efficient DOM removal and membrane fouling mitigation via in situ peroxymonosulfate (PMS) activation during filtration of actual raw water. Compared to the ceramic membrane with only single catalytic layer, the CoAl@AM-Co/PMS system could achieve much higher normalized membrane flux (0.79 vs. 0.63 and 0.49) and TOC removal (87.47 % vs. 58.35 % and 47.16 %); meanwhile, the molecular weight of DOM in the permeate water would also be significantly decreased. The FT-ICR MS results indicated that the total amount of DOM molecules of the permeate was reduced; the DOM with high H/Cwa and low O/Cwa value could be more easily removed, accompanied with the production of DOM with higher oxidation and unsaturation degree. Singlet oxygen and surface-bound radicals were proved to play a critical role in mitigating the membrane fouling by DOM. The design of ceramic membrane equipped with double catalytic layer and its application in advanced water purification were systematically elucidated for the first time in this work, which provided a new pathway for efficient treatment of surface water containing DOM.

Solid phase extraction of ocean dissolved organic matter with PPL cartridges: efficiency and selectivity

Our current knowledge of the chemical composition of ocean dissolved organic matter (DOM) is limited, mainly because of its extreme molecular diversity, low concentration of individual compounds and the elevated ionic strength of ocean waters. As a result, many analytical methods require a previous extraction step. The efficiency and selectivity of the extraction method defines the representativeness of the extracted DOM fraction. Nowadays, the most widespread procedure for concentrating DOM is solid phase extraction (SPE) using styrene divinyl benzene polymer cartridges (PPL). Here, we investigate the effect of SPE-PPL on DOM elemental and optical properties to assess the efficiency and selectivity of this extraction method on water samples from the main intermediate and deep water masses of Arctic, Mediterranean and Antarctic origin present in the Cape Vert Frontal Zone (CVFZ, NW Africa). Furthermore, North and South Atlantic Central waters converge in this area and coastal DOM is injected by the giant upwelling filament of Cape Blanc. On one side, the colored fraction of DOM (CDOM) presented extraction efficiencies comparable to that of the bulk dissolved organic carbon (DOC), but decreased significantly with increasing wavelength, suggesting an affinity of PPL cartridges for low molecular weight organic compounds. While the protein-like fluorescent fraction of DOM (FDOM) was also extracted with the same efficiency than DOC, the extraction efficiency of the humic-like fraction was comparatively much higher. On the other side, dissolved organic nitrogen (DON) extraction efficiencies were about half that of DOC. These contrasting extraction efficiencies of the different DOM pools indicated that the extracts were enriched in N-poor, low molecular weight and recalcitrant DOM, therefore showing less variability than the corresponding bulk DOM. Furthermore, DOC, DON, CDOM and FDOM extracted were not homogeneous through the water column but displayed certain significant differences among water masses in both efficiency and selectivity.

Seasonal Trends of DOM Character in Soils and Stream Change With Snowmelt Timing

AbstractIn many watersheds, runoff occurring with snowmelt brings the largest pulse of dissolved organic matter (DOM) from soils to streams. Yet, exactly how soil and stream DOM fractions are altered as snowmelt timing changes is not well understood. We studied the optical character of DOM as it moved through a first‐order northern hardwood watershed through the snowmelt period. While stream dissolved organic carbon (DOC; mean = 4.6 mg C L−1) concentrations were not correlated with snowmelt flushing, stream DOM appeared humic‐like throughout the study period (humification index, HIX; mean = 10.9). Within the stream, we measured seasonal increases in an inverse index of DOM molecular weight and processing (spectral slope, S275–295; range = 0.0102–0.0214) and in an index of recently derived DOM (Biological Index, BIX; range = 0.2–1.1). We measured a decrease in an inverse index of DOM oxidation (ratio of Peak C to Peak A, or C/A; range = 0.59–2.01) through the snowmelt period. Stream BIX and C/A tracked those measured in the north aspect soils throughout the study. C/A was unique as it decreased from source to stream, likely reflecting the diagenesis of DOM through soils. These data suggest that changes in the timing of snowmelt and hydrologic connectedness within a watershed affect seasonal changes in stream DOM character. We suggest that watersheds with deep glacial till parent materials have stream connectivity limited by subsurface flow paths, with stream DOM character being determined largely by slow melt and a longer period of infiltration.

DOM influences Hg methylation in paddy soils across a Hg contamination gradient

Rice paddies provide optimum conditions for Hg methylation, and paddy soil is a hot spot for Hg methylation and the predominant source of methylmercury (MeHg) accumulated in rice grains. The role of dissolved organic matter (DOM) in controlling Hg bioavailability and methylation in rice paddy systems remains unclear. Paddy soils from eight various cultivation sites in China were chosen to investigate the variations in soil DOM and the influence of DOM concentration and optical characteristics on Hg methylation in rice paddy systems. In the present study, 151 rhizosphere soil samples were collected, and UV–Vis absorption and fluorescent spectroscopy were used to identify the optical properties of DOM. The relationship between MeHg and DOM's optical property indices revealed the production of MeHg consumes lower molecular weight DOM. Moreover, the correlation between DOM concentration and its optical characteristics highlighted the significant role of humic components on MeHg variability in paddy soil. Variation and correlation results demonstrated the allochthonous origin of DOM in the Hg-contaminated soil, with a higher molecular weight and humic character of DOM, as well as the dominant role of autochthonous DOM in promoting Hg methylation in uncontaminated soil. The current study indicated that soil organic matter and its dissolved fractions tend to limit Hg bioavailability and subsequently diminish MeHg production in contaminated paddy soils. Furthermore, the leading roles of allochthonous DOM in protecting MeHg from degradation and autochthonous DOM signatures in enhancing MeHg production in paddy soils. Overall, these findings provide insight into the correlative distributions of DOM and Hg along a Hg concentration gradient in paddy soil, thereby highlighting their potential role in controlling Hg bioavailability and regulating Hg methylation in the soil ecosystems.

Role of lake dissolved organic matter in cyanobacteria removal by cationic polyacrylamide flocculation and screen filtration

Prompt removal of densely accumulated cyanobacteria is a straightforward method to alleviate the harm of cyanobacterial blooms to lakes. In this study, a cyanobacteria harvesting ship based on flocculation and filtration was used for the removal of cyanobacteria in a bay of Dianchi Lake (Yunnan Province, China), in which the fate and influence of lake dissolved organic matter (DOM) were investigated. After flocculation with 1–3 mg/L cationic polyacrylamide (CPAM) and filtration with the 100-µm-pore-sized screens of a rotary drum filter (RDF), >90 % of cyanobacteria was removed and the DOM was slightly reduced from 7.83 mg/L to 4.61 ∼ 6.49 mg/L. Tryptophan protein-like and high molecular weight (MW) DOM was selectively removed, increasing the humification index and decreasing the biological index in the treated water. Lake DOM, especially the high MW fractions of lake DOM, played an important role in CPAM flocculation. Cyanobacteria could not be effectively flocculated in Milli-Q water while the removal efficiency increased to over 90 % when 1–3 mg/L high MW DOM of Dianchi Lake was added. Three lakes in Yunnan Province were also plagued by cyanobacterial blooms, including Erhai Lake, Qilu Lake, and Xingyun Lake. The high MW DOM (1.7–2.7 mg/L) in the lakes could also deduce the effective flocculation of cyanobacteria with CPAM. The flocculation mechanism could function by the interactions of quaternary ammonium groups of CPAM and carboxylate groups of high MW DOM that form net-like polyelectrolyte complexes (PECs), and coexisting cyanobacteria cells were encapsulated into the PECs, leading to the formation of large flocs under stirring conditions. In the lakes with high densities of cyanobacteria, there might be enough high-MW DOM to promote the flocculation of CPAM, and after flocculation-filtration treatment, both cyanobacteria and cyanobacteria-deprived DOM were effectively removed.

Interactions between dissolved organic matter and the microbial community are modified by microplastics and heat waves

Dissolved organic matter (DOM) exists widely in natural waters and plays an important role in river carbon cycles and greenhouse gas emissions through microbial interactions. However, information on DOM–microbe associations in response to environmental stress is limited. River environments are the main carriers of microplastic (MP) pollution, and global heat waves (HWs) are threatening river ecology. Here, through MP exposure and HW simulation experiments, we found that DOM molecular weight and aromaticity were closely related to initial microbial communities. Moreover, MP-derived DOM regulated microbial community abundance and diversity, influenced microorganism succession trajectories as deterministic factors, and competed with riverine DOM for microbial utilization. SimulatedHWs enhanced the MP-derived DOM competitive advantage and drove the microbial community to adopt a K-strategy for effective recalcitrant carbon utilization. Relative to single environmental stressor exposure, combined MP pollution and HWs led to a more unstable microbial network. This study addresses how MPs and HWs drive DOM–microbe interactions in rivers, contributes to an in-depth understanding of the fate of river DOM and microbial community succession processes, and narrows the knowledge gap in understanding carbon sinks in aquatic ecosystems influenced by human activities and climate change.

Dissolved organic metabolite extraction from high-salt media.

We describe considerations and strategies for developing a nuclear magnetic resonance (NMR) sample preparation method to extract low molecular weight metabolites from high-salt spent media in a model coculture system of phytoplankton and marine bacteria. Phytoplankton perform half the carbon fixation and oxygen generation on Earth. A substantial fraction of fixed carbon becomes part of a metabolite pool of small molecules known as dissolved organic matter (DOM), which are taken up by marine bacteria proximate to phytoplankton. There is an urgent need to elucidate these metabolic exchanges due to widespread anthropogenic transformations on the chemical, phenotypic, and species composition of seawater. These changes are increasing water temperature and the amount of CO2 absorbed by the ocean at energetic costs to marine microorganisms. Little is known about the metabolite-mediated, structured interactions occurring between phytoplankton and associated marine bacteria, in part because of challenges in studying high-salt solutions on various analytical platforms. NMR analysis is problematic due to the high-salt content of both natural seawater and culture media for marine microbes. High-salt concentration degrades the performance of the radio frequency coil, reduces the efficiency of some pulse sequences, limits signal-to-noise, and prolongs experimental time. The method described herein can reproducibly extract low molecular weight DOM from small-volume, high-salt cultures. It is a promising tool for elucidating metabolic flux between marine microorganisms and facilitates genetic screens of mutant microorganisms.

Dissolved Organic Matter Component and Source Characteristics of the Metropolitan Lakes and Reservoirs in a Typical Karst Region

In order to explore dissolved organic matter (DOM) components and their origins in metropolitan lakes and reservoirs in the karst region, the typical Hongfeng Lake, Baihua Lake, Songbaishan Reservoir, and Aha Reservoir were investigated in Guiyang City. Surface water parameters, including dissolved organic carbon (DOC), chlorophyll a (Chla), and optical parameters (a254, a280, a350, E2:E3, S275-295, FI, β:α, BIX, and HIX) were analyzed. Fluorescence peaks (B, T, A, M, C, D, and N) and three-dimensional matrix fluorescence with parallel factor analysis (EEM-PARAFAC) were employed to explain distinct DOM abundances and proportions. Meanwhile, Spearman's correlation coefficients and principal component analysis (PCA) were used to decipher parameter types and primary environmental processes. The results showed that aquatic ρ(DOC) and ρ(Chla) ranged between 4.24-11.9 mg·L-1 and 0.32-19.7 μg·L-1, respectively. High humic-like (a254) and protein DOM (a280) were observed in the Songbaishan Reservoir, resulting in higher DOM molecular weight when compared to that in other lakes and reservoirs. Surface water DOM mainly contained visible-light humic-like (23.8%-46.9%) and terrestrial fulvic-like components (17.6%-28.4%). High FI, β:α, and BIX but low HIX values in this study suggested that endogenous inputs largely contributed to aquatic DOM. Aquatic DOM component and source characteristics were significantly correlated with each other. Furthermore, inputs of humic-like DOM and microbial metabolism, as well as coupled carbonate dissolution and photosynthesis, drove dynamic DOM behaviors in the karst lakes and reservoirs.

Spectral Characteristics Change in Dissolved Organic Matter in Urban River Under the Influences of Different Intensities of Non-point Source Pollution

With the method of ultraviolet-visible absorption spectroscopy (UV-vis) and excitation-emission matrix spectroscopy combined with parallel factor analysis (EEMs-PARAFAC), this study analyzed the change in dissolved organic matter (DOM) content and composition in spring and summer of two non-point source urban rivers which had different input intensities. The results indicated that the level of humification and molecular weight of DOM in summer was significantly higher than that in spring in these two rivers (P<0.01). The PARAFAC model was used to analyze four chemical compositions, including C1 (UVC fulvic-like), C2 (tryptophan-like), C3 (humic-like), and C4 (UVA fulvic-like); furthermore, C1[(31±6)%] and C2[(31±4)%] were the main fluorescent contents of the water. The high non-point source input river had a higher fluorescence intensity of all four PARAFAC components in spring than in summer, contrary to the low non-point source input river. The random forest regression model showed that C3% had the highest sensitivity to the changes in water parameters (R2=0.75, P<0.001) and could be an effective indicator. Additionally, the coverage level of the water surface (Cover) had an essential effect on the prediction of C4% (P<0.001), and C4% was susceptible to photochemical oxidation. According to the principal component analysis (PCA) and Adonis test, nitrogen and phosphorus were the essential impetuses for the biological process of the river; non-point source inputs and seasonal changes had a significant impact on the urban river (R2=0.775, P<0.001). The contents and compositions of urban river DOM were affected by many essential factors. Non-point source inputs improved the input level of terrestrial humus in the water and promoted the biological process at the same time, dynamically contributing to the changes in the DOM of the water body.

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.

High molecular weight fractions of dissolved organic matter (DOM) determined the adsorption and electron transfer capacity of DOM on iron minerals

Dissolved organic matter (DOM) in the natural environment has a significant effect on the biogeochemical cycles of iron (Fe), such as adsorption and reduction reaction. However, the roles of the molecular weight (MW) fractions of DOM extracted from plants in adsorption onto Fe minerals coupled with the Fe reduction process are incompletely characterized. In this study, the effects of DOM (extracted from Carex cinerascens) with different MW fractions, labeled as low molecular DOM (L-DOM), medium molecular DOM (M-DOM), and high molecular DOM (H-DOM), respectively, on the adsorption onto Fe minerals and the electrons transfer capacity (ETC) during the Fe reduction process is investigated. The oxygen-rich and highly aromatic H-DOM exhibited stronger adsorption affinity onto Fe minerals, such as ferrihydrite, a poorly crystalline mineral, than other DOM fractions. The X-ray photoelectron spectra and the Fourier transform infrared spectra revealed that the functional groups of the oxygen-rich DOM, such as CO bonds and OCO bonds, preferentially adsorbed onto the Fe minerals. In addition, the cyclic voltammograms (CV) and the chronoamperometry (CA) measurements showed that H-DOM significantly enhanced the Fe reduction to its maximum extent, indicating that the efficiency of DOM on Fe reduction was strongly related to the ETC. Therefore, our findings confirm that H-DOM plays a key arole in the adsorption onto Fe minerals and Fe redox reaction. The results of this study may help evaluate the performance of the different MW of DOM from plants on the biogeochemical cycles of Fe in the soil environment.

Tracing carbon and nitrogen microbial assimilation in suspended particles in freshwaters

The dynamic interactions between dissolved organic matter (DOM) and particulate organic matter (POM) are central in nutrient cycling in freshwater ecosystems. However, the molecular-level mechanisms of such interactions are still poorly defined. Here, we study spatial differences in the chemical (i.e., individual proteinaceous amino acids) and microbial (i.e., 16S rRNA) composition of suspended sediments in the River Chew, UK. We then applied a compound-specific stable isotope probing (SIP) approach to test the potential assimilation of 13C,15N-glutamate (Glu) and 15N-NO3− into proteinaceous biomass by particle-associated microbial communities over a 72-h period. Our results demonstrate that the composition of suspended particles is strongly influenced by the effluent of sewage treatment works. Fluxes and percentages of assimilation of both isotopically labelled substrates into individual proteinaceous amino acids showed contrasting dynamics in processing at each site linked to primary biosynthetic metabolic pathways. Preferential assimilation of the organic molecule glutamate and evidence of its direct assimilation into newly synthesised biomass was obtained. Our approach provides quantitative molecular information on the mechanisms by which low molecular weight DOM is mineralised in the water column compared to an inorganic substrate. This is paramount for better understanding the processing and fate of organic matter in aquatic ecosystems.

Chemodiversity of dissolved organic matter in cadmium-contaminated paddy soil amended with different materials

Dissolved organic matter (DOM) in soil is a key factor affecting the bioavailability of heavy metals, but very few studies have focused on the role of DOM in the use of soil amendments to mitigate heavy metal accumulation in crops. Here, eleven materials were added to cadmium (Cd)-contaminated paddy soil in greenhouse pot trials; rice was grown and harvested, the chemodiversity of post-harvest soil DOM was characterized using Fourier-Transform Ion Cyclotron Resonance Mass Spectrometry, and the specific associations between soil DOM traits and water-extractable soil Cd concentration were identified at the molecular level. The results showed that the endogenous release caused by altering soil pH had a greater effect on soil DOM concentration than did the exogenous chemical input due to the application of organic amendments, which in turn contributed to the chemodiversity of DOM. After one season of rice cultivation, soil DOM molecules were mainly dominated by relatively low molecular weight heteroatom-free lignins. C/N, C/H ratios of organic materials influenced DOM molecular fingerprint patterns, and soil pH and redox potential were the main driving forces affecting the chemodiversity of DOM. Furthermore, the low molecular weight, high saturation, low aromaticity, and heteroatom-free DOM molecules are more likely to dissolve Cd from the soil solid phase, thus increasing the potential risk of Cd to the environment. The results provide critical information about amendments-induced changes in DOM chemodiversity and will inform the selection of appropriate soil amendments.

Biochar affects methylmercury production and bioaccumulation in paddy soils: Insights from soil-derived dissolved organic matter

Biochar has been used increasingly as a soil additive to control mercury (Hg) pollution in paddy rice fields. As the most active component of soil organic matter, soil dissolved organic matter (DOM) plays a vital role in the environmental fate of contaminants. However, there are very few studies to determine the impact of biochar on the Hg cycle in rice paddies using insights from DOM. This study used original and modified biochar to investigate their effect on DOM dynamics and their potential impact on methylmercury (MeHg) production and bioaccumulation in rice plants. Porewater DOM was collected to analyze the variations in soil-derived DOM in paddy soils. The results showed that the addition of biochar, whether in original or modified form, significantly reduced the bioaccumulation of MeHg in rice plants, especially in hulls and grains (p<0.05). However, MeHg production in soils was only inhibited by the modified biochar. Biochar addition induced a significant increase in DOM's aromaticity and molecular weight (p<0.05), which decreased Hg bioavailability. Furthermore, enhanced microbial activity was also observed in DOM (p<0.05), further increasing MeHg production in the soil. Thus, the effect of biochar on the fate of Hg cycle involves competition between the two different roles of DOM. This study identified a specific mechanism by which biochar affects Hg behavior in rice paddy soil and contributes to understanding the more general influence of biochar in agriculture and contaminant remediation.

Influence of DOM characteristics on the flocculation removal of trace pharmaceuticals in surface water by the successive dosing of alum and moderately hydrophobic chitosan

Hydrophobically-modified chitosan (HC) has emerged as a promising flocculant for trace pharmaceutical removal from surface water. However, the variation in the characteristics of dissolved organic matter (DOM) in different water sources influences the efficacy of HC in removing pharmaceutical compounds. In this work, the flocculation performance of sequentially dosing alum and HC (alum+HC) for the treatment of five water types (three synthetic waters, and samples of two real waters collected from the Yangtze River and the Thames River), having different DOM and five representative pharmaceuticals (initial concentration: 100 ng/L), was assessed by bench-scale jar tests. The DOM characteristics were correlated quantitatively with the removal efficiencies (REs) of the pharmaceuticals. Density functional theory computations were performed to illuminate the interfacial interactions in the flocculation. Alum+HC exhibited a remarkably higher RE of all five pharmaceuticals (maximum RE: 73%-95%) from all waters compared to a conventional coagulant or flocculant (alum or polyacrylamide, respectively). In contrast to using HC alone, alum+HC also achieved a higher RE of pharmaceuticals with nearly half the HC dosage, thereby enhancing the cost-effectiveness of the alum+HC dosing system. Among the different key DOM characteristics, the surface charge and molecular weight of DOM had no evident correlation with RE(pharmaceutical), but the hydrophobic/hydrophilic nature and functional group composition of organic carbon of DOM were strongly correlated: Strongly hydrophobic fractions, with C-C & C=C functional groups (binding pharmaceuticals via hydrophobic association), were beneficial, while hydrophilic fractions with C-OH groups were less effective, for pharmaceutical removal. This work showed the enhanced performance of the alum+HC dosing combination in the removal of different pharmaceutical compounds from different waters, and filled the knowledge gap regarding the performance of hydrophobically-modified flocculants in the treatment of different surface water sources.

Spatial Distribution Characteristics of the Spectrum, Source Analysis, and Nitrogen Response of Dissolved Organic Matter in Summer Rainfall in the Hebei Province

Dissolved organic matter(DOM) is an important component of the organic matter in the environment. This study explored the characteristics of DOM. The components and spectral characteristics of rainwater DOM were measured using Ultraviolet-visible absorption spectrum(UV-vis) and three-dimensional fluorescence spectrum in the Hebei province. The results showed significant differences for DOM molecular weight in the northern, central, and southern region; the DOM of the northern region exhibited the lowest molecular weight. Two humic-like(C1 and C4), one protein-like(C2) and one fulvic-like(C3) components were identified by parallel factor(PARAFAC) analysis. Component C2 had a significant positive correlation with components C3 and C4(P<0.001), which may have similar sources. The C2(protein-like substances) accounted for the major proportion of DOM with the average abundance 40.59%. The DOM components based on PARAFAC exhibited significantly difference between city and country regions without spatial difference, which was consistent with the result of fluorescence regional integration(FRI). The protein-like substances based on FRI were the main components, which accounted for 61.59%-89.01%. Redundancy analysis(RDA) showed that total nitrogen, nitrate, and ammonia were the main environmental factors determining the distribution of DOM. Spectral indices presented a significant difference between city and country regions. High fluorescence(FI) and biological(BIX) and low humification(HIX) values showed that summer rain exhibited the strong autochthonous and low humification characteristics, and country region have stronger autochthonous characteristics than city region. The regression analysis demonstrates that the prediction accuracy of rainwater quality parameters in city region is high. From all the results, rainwater DOM, showing strong autogenous characteristics, exhibited significant differences between city and country regions without spatial difference in Hebei. Meanwhile, it can also provide technical support for rainwater nitrogen concentration prediction based on DOM components.

Heterogeneous viral contribution to dissolved organic matter processing in a long-term macrocosm experiment

Viruses saturate environments throughout the world and play key roles in microbial food webs, yet how viral activities affect dissolved organic matter (DOM) processing in natural environments remains elusive. We established a large-scale long-term macrocosm experiment to explore viral dynamics and their potential impacts on microbial mortality and DOM quantity and quality in starved and stratified ecosystems. High viral infection dynamics and the virus-induced cell lysis (6.23–64.68% d−1) was found in the starved seawater macrocosm, which contributed to a significant transformation of microbial biomass into DOM (0.72–5.32 μg L−1 d−1). In the stratified macrocosm, a substantial amount of viral lysate DOM (2.43–17.87 μg L−1 d−1) was released into the upper riverine water, and viral lysis and DOM release (0.35–5.75 μg L−1 d−1) were reduced in the mixed water layer between riverine water and seawater. Viral lysis was stimulated at the bottom of stratified macrocosm, potentially fueled by the sinking of particulate organic carbon. Significant positive and negative associations between lytic viral production and different fluorescent DOM components were found in the starved and stratified macrocosm, indicating the potentially complex viral impacts on the production and utilization of DOM. Results also revealed the significant viral contribution to pools of both relatively higher molecular weight labile DOM and lower molecular weight recalcitrant DOM. Our study suggests that viruses have heterogeneous impact on the cycling and fate of DOM in aquatic environments.

Interaction between polychlorinated biphenyls and dissolved organic matter of different molecular weights from natural and anthropic sources

Polychlorinated biphenyls (PCBs) are compounds of significant interest due to high toxicity, persistence, long-range atmospheric transport, and bioaccumulation. These compounds can interact with components present in the environment, including dissolved organic matter (DOM) in soils and waters, thereby modifying its availability and movement. In this study, DOM was fractionated by ultrafiltration and characterized according to its hydrophobicity and hydrophilicity, then the interaction of a series of PCBs and different DOM fractions was evaluated. The DOM was collected from the surface waters of three sectors located along a river in the southern part of America. These sectors are subject to different anthropic activities, thus the DOM of sector 1, with the least anthropic influence, was mainly hydrophobic and with a high content of aromatic structures. In contrast, the DOM collected from sectors 2 and 3, where anthropic activity is highest, was slightly hydrophobic and hydrophilic, respectively. The DOM of these two sectors was mainly composed of low molecular weight macromolecules. These results revealed that more hydrophobic PCBs (i.e., 101, 118, 138, and 180) have a greater affinity to DOM with a higher molecular weight (i.e., >1 kDa). In turn, PCBs with lesser chlorination and hydrophobicity presented a greater affinity to DOM with a lower molecular weight. In conclusion, our study shows that the high molecular weight DOM is responsible for mobilizing PCBs with a high degree of chlorination.

Dynamic variations in DOM and DBPs formation potential during surface water treatment by ozonation-nanofiltration: Using spectroscopic indices approach

The combination of ozone and nanofiltration (NF) in drinking water treatment represents a potentially effective method of separating dissolved organic matter (DOM), and thereby reducing the potential formation of disinfection by-products (DBPs). This study has evaluated UV-absorbance and fluorescence-based optical descriptors, such as absorbance slope index (ASI), humification index (HIX), and the sum of fulvic-like and humic-like components (C1 + C2), etc., to track the variation of DOM constituents and DBP formation potential during the treatment of surface water samples by ozonation and nanofiltration (NF90 and NF270). Pre-ozonation markedly reduced the DOM molecular weight (MW) in the range of 5000–9000 Da by transforming the DOM into carboxylate-rich hydrophilic fractions, thereby mitigating the fouling of NF membranes. Among all the PARAFAC components, the humic-like component (C2) showed a predominant behavior against pre-ozonation and nanofiltration experiments. However, amino acid or microbial protein-like component (C3) was particularly associated with irreversible fouling of both membranes, compared to reversible fouling. C1 + C2 was found to be strongly correlated with both ASI and HIX, suggesting that C1 + C2 can be a useful surrogate for the humic-like content of the DOM. Principal DBPs detected after the chlorination were chloroform, bromodichloromethane and dichloroacetic acid, and DBP formation potential reduced with increased ozonation. A strong correlation between these DBPs and spectroscopic indices indicated that the humic content was an important factor in the formation of DBPs. In contrast, increasing ozonation not only shifted the DBP formation potential towards brominated precursors, but also resulted in increased brominated species of haloacetic acids. However, both NF membranes achieved approximately 90% removal of DBP precursors, for all of the detected DBPs, which was attributed to size exclusion and electrostatic interaction effects.

Temporal and Spatial Evolution Characteristics of DOM Spectra in Sediment Interstitial Water in Typical Zones of Baiyangdian Lake

The sources and distribution of dissolved organic matter (DOM) in the interstitial water of Baiyangdian Lake sediments were analyzed using the ultraviolet-visible absorption spectrum (UV-vis) method and three-dimensional excitation emission matrix fluorescence spectroscopy-parallel factor analysis (EEM-PARAFAC). Results showed that the DOM concentrations and molecular weight were significantly higher in summer than in spring and autumn, based on a254 and E2/E3 values. Three protein-like substance (C1, C2, and C3) and two humic-like substances (C4, C5) were identified with the PARAFAC model. Moreover, protein-like substances accounted for the majority of DOM, reaching (63.56±16.07)%. Total DOM fluorescence intensity, the fluorescence intensity of each component, and the relative abundance exhibited significant spatial variation among the different functional zones in Baiyangdian Lake. Protein-like substances were mainly found in the breeding area, whereas humic-like substances mainly occurred in the natural area. The high BIX, FI, β:α, and low HIX indicated that DOM in sediment interstitial water exhibited low humification and highly autochthonous characteristics. Moreover, the perfect regression equations between water quality and the fluorescent components could provide a useful reference for managers aiming to protect the ecosystem of Baiyangdian Lake.