DOC export is exceeded by C fixation in May Creek: A late-successional watershed of the Copper River Basin, Alaska

Photochemical behavior of dissolved organic matter derived from Alternanthera philoxeroides hydrochar: Insights from molecular transformation and photochemically reactive intermediates

Hydrochar-derived dissolved organic matter (HDOM) enters aquatic ecosystems through soil leaching and surface runoff following the application of hydrochar. However, the photochemical behavior of HDOM remains unclear. The photo-transformation of HDOM was analyzed by Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS), multiple spectroscopy methods, high-performance liquid chromatography, and combining synchronous fluorescence and Fourier-transform infrared spectroscopy with two-dimensional correlation spectroscopy. The results showed that with the increase of carbonization temperature, amide II in protein-like substances were observed to be preferentially photolyzed, and the protein-like substances were more sensitive to low irradiation time, while the duration time of the photochemical behavior of amide II and aliphatic C-H were more persistent. FT-ICR MS results showed that N and S-containing molecules, including lignins and lipids were more sensitive to ultraviolet irradiation. Furthermore, the photo-transformation of HDOMs was accompanied by the generation of triple excited state dissolved organic matter and singlet oxygen. Our findings will be beneficial for understanding the mechanisms of photo-transformation of HDOM and for predicting the possible behaviors of hydrochar produced at different temperatures before large-scale application.

Removal and toxic forecast of microplastics treated by electrocoagulation: Influence of dissolved organic matter

In recent years, the break of COVID-19 makes the large use of disposable products, which causes the removal of microplastics become an imperative problem. Electrocoagulation is one of the effective removal technologies, but there is hardly research concentrating on the effect of substrate in the actual water on the microplastics removal with electrocoagulation. As an important role of water bodies, dissolved organic matter (DOM) has a vital and inevitable effect on the efficiency of electrocoagulation. In this study, the effect of DOM in tailwater on microplastics during electrocoagulation is elucidated by comparing the electrocoagulation treatment results between simulated wastewater and tailwater, using parallel factor analysis (PARAFAC), Scanning Electron Microscopy (SEM), Fourier Transform Infrared Spectrometer (FTIR) and zeta potential analyzer. Three kinds of microplastic particles (i.e. polypropylene, polyethylene, and polymethyl methacrylate) were added into each of the two kinds of wastewaters to form six electrocoagulation systems. Results show that DOM in tailwater promotes the production of flocs and free radicals during electrocoagulation process. Fe²⁺ and Fe³⁺ are adsorbed on the surface of DOM molecules and combined with •OH form flocs. Although DOM accelerates the production of free radicals and thus promotes the aging of microplastics, flocs with DOM as crystal nucleus can prevent toxic substances and small-sized microplastics from leaching into water again. Therefore, electrocoagulation is preferred to removal microplastics in water with high concentration of DOM. This study provides a significant reference for microplastics removal by electrocoagulation in actual water, and promote the practical application of electrocoagulation for microplastics removal in water treatment.

Dissolved organic matter production from herder application and in-situ burning of crude oil at high latitudes: Bioavailable molecular composition patterns and microbial community diversity effects

Chemical herders and in-situ burning (ISB) are designed to mitigate the effects that oil spills may have on the high latitude marine environment. Little information exists on the water solubilization of petroleum residues stemming from chemically herded ISB and whether these bioavailable compounds have measurable impacts on marine biota. In this experiment, we investigated the effects of Siltech OP40 and crude oil ISB on a) petroleum-derived dissolved organic matter (DOM_HC) composition and b) seawater microbial community diversity over 28 days at 4 °C in aquarium-scale mesocosms. Ultra-high resolution mass spectrometry and fluorescence spectroscopy revealed increases in aromaticity over time, with ISB and ISB+OP40 samples having higher % aromatic classes in the initial incubation periods. ISB+OP40 contained a nearly 12-fold increase in the number of DOM_HC formulae relative to those before ISB. 16S rRNA gene sequencing identified differences in microbial alpha diversity between seawater, ISB, OP40, and ISB+OP40. Microbial betadiversity shifts were observed that correlated strongly with aromatic/condensed relative abundance and incubation time. Proteobacteria, specifically from the genera Marinomonas and Perlucidibaca experienced -22 and +24 log₂-fold changes in ISB+OP40 vs. seawater, respectively. These findings provide an important opportunity to advance our understanding of chemical herders and ISB in the high latitude marine environment.

Fluorescence Characteristics of Coalbed Methane Produced Water and Its Influence on Freshwater Bacteria in the South Qinshui Basin, China

Production of coalbed methane (CBM) resources commonly requires using hydraulic fracturing and chemical production well additives. Concern exists for the existence of chemical compounds in CBM produced water, due to the risk of environmental receptor contamination. In this study, parallel factor method analysis (PARAFAC), fluorescence index, and the fluorescence area integral methods were used to analyse the properties of CBM produced water sampled from Shizhuang Block (one of the most active CBM-producing regions in the Qinshui Basin). A culture experiment was designed to determine the effect of discharged CBM produced water on microorganisms in freshwater. Water quality analysis shows the hydrochemistry of most water samples as Na-HCO₃ type produced water of CBM appears as a generally weak alkaline (pH 8.69 ± 0.185) with high salinity, high alkalinity, and a high chemical oxygen demand (COD) value. Three individual components were identified by using parallel factor method analysis as humic-like components (C1), fulvic-like components (C2), and amino acid-like substances (C3). The fluorescence characteristic index comprehensively explains that the fluorescent substances in CBM produced water has the characteristics of a low degree of humification and a high recent self-generating source. The region integration results of characteristic peaks show that tyrosine-like and tryptophan-like materials account for more than 67% of fluorescent substances in CBM produced water. The addition of produced water from coalbed methane promotes the growth of freshwater bacteria, and this process is accompanied by the decrease of the proportion of fulvic acid, humic acid, and the increase of the proportion of soluble microbial metabolites. This paper proposes a convenient method for organic matter identification of CBM produced water and provides some theoretical support and reference for the improvement of CBM water treatment and utilization.

Hydrocarbons to carboxyl-rich alicyclic molecules: A continuum model to describe biodegradation of petroleum-derived dissolved organic matter in contaminated groundwater plumes

Relationships between dissolved organic matter (DOM) reactivity and chemical composition in a groundwater plume containing petroleum-derived DOM (DOM_HC) were examined by quantitative and qualitative measurements to determine the source and chemical composition of the compounds that persist downgradient. Samples were collected from a transect down the core of the plume in the direction of groundwater flow. An exponential decrease in dissolved organic carbon concentration resulting from biodegradation along the transect correlated with a continuous shift in fluorescent DOM_HC from shorter to longer wavelengths. Moreover, ultrahigh resolution mass spectrometry showed a shift from low molecular weight (MW) aliphatic, reduced compounds to high MW, unsaturated (alicyclic/aromatic), high oxygen compounds that are consistent with carboxyl-rich alicyclic molecules. The degree of condensed aromaticity increased downgradient, indicating that compounds with larger, conjugated aromatic core structures were less susceptible to biodegradation. Nuclear magnetic resonance spectroscopy showed a decrease in alkyl (particularly methyl) and an increase in aromatic/olefinic structural motifs. Collectively, data obtained from the combination of these complementary analytical techniques indicated that changes in the DOM_HC composition of a groundwater plume are gradual, as relatively low molecular weight (MW), reduced, aliphatic compounds from the oil source were selectively degraded and high MW, alicyclic/aromatic, oxidized compounds persisted.