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Priming effect (PE) is increasingly recognized as an important mechanism in the microbial degradation of dissolved organic matter (DOM) from freshwater to the ocean. However, potential PE during the mixing of DOM from different sources and the effects on different DOM constituents are still largely unknown. This study examined the PE after adding DOM from typical natural and anthropogenic sources (rainwater, fresh plant, leaf litter, and wastewater) into pre-aged river DOM, using dissolved organic carbon (DOC) measurement, absorption spectroscopy, and fluorescence excitation-emission matrices-parallel factor analysis (EEMs-PARAFAC). The plant-derived DOM had a low humic content and was dominated by benzoic acid-like and tyrosine-like fluorescent components (C4 and C5), which showed a high DOC bioavailability of 80%. DOC in rainwater and wastewater also had high bioavailabilities (45%–50%), while DOM in the leaf litter leachate showed high aromaticity, average molecular weight, and humic content but low DOC bioavailability (12%). There was generally limited PE (<5% of the initial values) on the degradation of DOC and chromophoric DOM (CDOM) for most samples. Two humic-like components (C2 and C3) showed little PE, while the humic-like C1 and C6, tyrosine-like C5, and tryptophan-like C7 showed variable PE after adding rainwater, wastewater, and plant leachate. Overall, the results revealed that the DOM from typical natural and anthropogenic sources had different composition and bioavailability, and their inputs to aquatic environments would result in variable PE on the bulk DOC and different DOM components. Image 1 • The composition and bioavailability of DOM changed notably with different sources. • Priming effect of DOM from typical natural and anthropogenic sources was tested. • Fluorescence EEMs-PARAFAC revealed variable priming effects on different DOM components. [ABSTRACT FROM AUTHOR]

Abstract Rainwater brings considerable amounts of dissolved organic matter (DOM) from atmosphere to freshwater and marine environments, but little is known about the chemical composition and bioavailability of rainwater DOM. The quantity, quality, and bioavailability of DOM were investigated for 21 rain events at a coastal site in southeast China, using dissolved organic carbon (DOC) measurements, absorption spectroscopy, and fluorescence excitation-emission matrices-parallel factor analysis (EEM-PARAFAC). The DOC concentration ranged from 35 to 457 μM, which was affected by the prevailing monsoon, rainfall amount and terrestrial/anthropogenic inputs. The volume-weighted average DOC was 118 μM, corresponding to a rainwater DOC flux of 1.98 g m−2 yr−1. Four fluorescent components were identified with EEM-PARAFAC, including three humic-like components (C1-C3) and one tyrosine-like component C4. Absorption coefficient (a CDOM (300)) and fluorescence intensities of C2-C4 strongly correlated with DOC, indicating they can be used for DOC estimation. Rainwater DOM was characterized by low DOC-specific UV absorbance (SUVA 254) and humification index (HIX), which indicated a low aromaticity and humification degree. Principal component analysis (PCA) based on DOM indices revealed two principal factors, which were related to the DOM concentration and humification degree respectively. PCA, together with air-mass trajectory analysis, successfully separated different rain events with variable inputs from living plants/local sources, soil organic matter/humified materials, and the marine source. Rainwater DOM generally showed a high bioavailability of 50% ± 19%, with higher degradability of non-chromophoric constituents and C1-C2 than other components. This study demonstrated the applicability of absorption and EEM-PARAFAC combined with PCA and air-mass trajectory analysis in differentiating rain events and tracking organic matter sources, and revealed different effects of microbial degradation on individual PARAFAC components in rainwater. Graphical abstract Image 1 Highlights • DOC was affected by monsoon, rainfall amount and terrestrial/anthropogenic inputs. • Absorption and fluorescent EEM-PARAFAC provide valuable indices for estimating DOC. • Rain events of different sources were discriminated with PCA and air-mass trajectory analysis. • Rainwater DOC was highly labile to microbial degradation. [ABSTRACT FROM AUTHOR]

Particulate organic matter (POM) in the coastal zone plays an important role in global carbon cycle, yet its spectral properties under human disturbance are not well understood. This study investigated the source and dynamics of POM in a typical coastal area (Minjiang Estuary, China) under the influences of estuarine mixing, urbanization and dam construction, based on spectral and isotopic analysis. The yield of particulate organic carbon from the watershed (0.38 g m−2 yr−1) was in part limited by the historical decrease in sediment discharge downstream hydropower station. The absorption and fluorescence indices of POM suggested an important contribution from biological production with a low humic content. The importance of river and estuarine production was supported by elemental and isotopic analysis, in particular for N-bound constituents of POM. Three humic-like and two protein-like fluorescent components were identified from POM using fluorescence excitation-emission matrices-parallel factor analysis (EEMs-PARAFAC). They showed weak correlations with salinity, suggesting non-conservative behaviors of fluorescent POM during the estuarine mixing. Principal component analysis (PCA) identified two principal factors, which were related to the level of chromophoric POM (PC1) and biological production (PC2), respectively. The PCA results indicated stronger influence of biological production in the estuarine zone and potential effect of sediment re-suspension and/or wastewater discharge in the urban zone. Overall, our results demonstrated significant influences of human disturbance on the flux, source and dynamics of POM in the coastal zone, which could be assessed by spectral and stable isotopic analysis. Unlabelled Image • The POM export in the middle stream reach was partly affected by the dam. • Isotopic analysis showed the contribution of biological production to N-bound POM. • PARAFAC components of POM were non-conservative in the estuary. • PCA revealed potential effects of biological production in the estuary. • POM in urban sites was probably affected by re-suspension and wastewater discharge. [ABSTRACT FROM AUTHOR]

Dam construction and fish culture can change the biogeochemical processes in river, yet their impact on the spectral properties of particulate organic matter (POM) remains to be studied. This was investigated in a reservoir-type river (Minjiang river, SE China) using absorption spectroscopy and fluorescence excitation-emission matrices-parallel factor analysis (EEMs-PARAFAC). Five fluorescent components were identified from POM with PARAFAC. Four components C1-C4 were affected by the seasonal variations of rainfall and runoff, indicating the influences of hydrological condition and terrestrial inputs. The Chlorophyll a concentration (Chl a) correlated significantly with the humic-like C3 (p < 0.05) and the protein-like C4 (p < 0.01), indicating phytoplankton was an important source of C3 and C4. The Chl a and fluorescence intensities of C3-C4 were higher in the fish culture zones than in other areas, and the absorption coefficient a 300 and C1-C4 were lower downstream the dam. These results indicated that fish farming in the reservoir probably promoted the production of POM. The a 300 and C1 per unit mass of suspended particulate matter (a 300 /TSM and C1/TSM) correlated significantly with the median particle size (p < 0.01), which might be related to the contribution of micro-phytoplankton. The absorption spectra of POM showed a shoulder peak at ∼280 nm, and its intensity correlated significantly and positively with Chl a (p < 0.01). These results indicated that the peak was probably derived from phytoplankton production. Our results have implications for better understanding the influences of human activities on the dynamics of river POM., (Copyright © 2019 Elsevier Ltd. All rights reserved.)

The restriction of sulfur content in fuels has become increasingly stringent as a result of the growing environmental concerns. Although several MOF-derived materials like POM@MOF composites have shown the ability to catalyze oxidative desulfurization (ODS), their catalytic activities inevitably obstructed by the encapsulated catalytic sites like POM due to the blockage of cavities. Therefore, MOFs with intrinsic and accessible catalytic sites are highly desirable for their applications in ultradeep ODS. Herein, four representative Zr-based MOFs (Zr-MOFs), namely, UiO-66, UiO-67, NU-1000, and MOF-808, were assessed for catalytic ODS. These MOFs were confirmed that they have peroxidase-like activity and can catalyze ODS with H 2 O 2 as oxidant. Among them, MOF-808 showed the highest catalytic activity and it can fully desulfurize dibenzothiophene (DBT) in a model gasoline with a S concentration of 1000 ppm under 40 °C within 5 min. An extremely low apparent Arrhenius activation energy (22.0 KJ·mol -1 ) and an extraordinarily high TOF value (42.7 h -1 ) were obtained, ranking MOF-808 among the best catalysts for the catalytic DBT oxidation. Further studies confirmed that the excellent catalytic activity is mainly responsible for the high concentration of the accessible Zr-OH(H 2 O) catalytic sites decorated in MOF-808. The superoxide radicals ( • O 2 - ) and hydroxyl radicals ( • OH) were identified and were proved to involve in the DBT oxidation. Besides, the effects of Brönsted and lewis acidity to the catalytic efficiency were also discussed. Based on the experimental results, a plausible mechanism concerning on Zr-OH(H 2 O) groups promoting the H 2 O 2 decomposion in to both • O 2 - and • OH was first proposed. Moreover, MOF-808 can be facilely reused for at least eight runs without significant loss of its catalytic activity. By the integration of facile synthesis, high catalytic efficiency, and good stability, MOF-808 thus represents a new benchmark catalyst for catalytic oxidative desulfurization.