The source and composition characteristics of dissolved organic matter (DOM) are crucial to identify and evaluate the sources of pollution in the watershed. The construction of reservoirs changes the ...hydrological condition and pollutant fate of the river. However, the effects of reservoirs' construction on DOM in the watershed and the underlying mechanisms are still unclear. This study aims to examine and compare the characteristics of DOM in reservoirs and streams in the Huangbai River, a typical reservoir-affected and P-contaminated river within the Yangtze River catchment. The results showed that DOM in reservoirs was characterized by more contribution from autochthonous source, under the influence of reservoirs’ construction; while, DOM in rivers was mainly originated from terrestrial input. Reservoirs had more lipid-like and protein-like compounds, while rivers contained more oxy-aromatic-like compounds. The percentage of CHOP molecules in reservoirs was significantly higher than that in rivers. The underlying mechanism is that more suitable conditions were created for plankton to grow after constructing reservoirs, which converted inorganic orthophosphate into organic phosphorus, and over time, organic phosphorus was gradually enriched in reservoirs, which exacerbated the risk of eutrophication in the reservoir water body. This study can provide theoretical support for monitoring and evaluation of water quality in reservoir-affected rivers.
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•Find differences on DOM characteristics in reservoirs and mainstream.•Elucidate the influence of reservoirs construction on DOM in a P-contaminated river.•DOM in reservoirs and rivers are more autochthonous and more allochthonous, respectively.•Reservoirs contained higher amounts of CHOP molecules than rivers.•Stable conditions convert more inorganic P into organic P in reservoirs.
Numerous studies have focused on the spectral characteristics and seasonal variations of dissolved organic matter (DOM) in rainwater. However, the relationship between the optical indices of DOM and ...nutrients in rainwater from different ecological areas of large reservoirs is poorly understood. A one-year monitoring study was conducted between March 2019 and February 2020 in the Danjiangkou Reservoir in Henan Province, China, to compare the composition, spectral characteristic parameters, and relationship between the optical indices of DOM and nutrients in rainwater under different ecological environments. The study showed that the average value of a300 in all samples was 5.29 ± 2.16 m-1 and showed a seasonal trend of higher in spring and winter and lower in summer and autumn as well as a regional difference of agricultural area > urban area > reservoir area. A three-dimensional fluorescence with parallel factor analysis (EEM-PARAFAC) revealed four components of the rainwater: C1 and C2 as UV humic-like substances, and C3 and C4 as protein-like substances. The protein-like components of rainwater from agricultural areas had a high fluorescence intensity, whereas the UV humic-like components of rainfall from urban and reservoir areas had a high fluorescence intensity. Analysis of the fluorescence indices showed that rainwater DOM humification was low and had a strong endogenous character in the Danjiangkou Reservoir. The redundancy analysis revealed that NO3−-N, DTN, and SO42− mainly influenced the DOM optical indices of rainwater in urban areas, EC, DTN, and DOC had the highest interpretation of the DOM optical indices of rainwater in agricultural areas, and SO42−, DOC, and DTN had the highest interpretation of the DOM optical indices of rainwater in the reservoir. Overall, understanding the characteristics of rainfall DOM fluorescence and the relationships with nutrients in different ecological regions provides important information for comprehending biogeochemical processes in reservoirs.
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•Concentration of dissolved organic matter (DOM) in rainwater exhibited seasonal variations and regional differences.•Rainwater DOM consists of humic-like and protein-like substances.•Low humification and aromaticity of DOM in rainwater, but high microbial contribution.•Atmospheric nutrients are closely coupled with rainwater DOM.
The photoactivity of dissolved organic matter (DOM) has a great impact on the photodegradation of organic pollutants in natural waters. In this study, the photodegradation of TBBPA was investigated ...under simulated sunlight irradiation in the presence of copper ion (Cu2+), dissolved organic matter (DOM) and Cu-DOM complexation (Cu-DOM) to illustrate the effect of Cu2+ on photoactivity of DOM. The rate of photodegradation of TBBPA in the presence of Cu-DOM complex was 3.2 times higher than that in pure water. The effects of Cu2+, DOM and Cu-DOM on the photodegradation of TBBPA were highly pH dependent and hydroxyl radical(·OH) responded for the acceleration effect. Spectral and radical experiments indicated that Cu2+ had high affinity to fluorescence components of DOM, and acted as both the cation bridge and electron shuttle, resulting the aggregation of DOM and increasing of steady-state concentration of ·OH (·OHss). Simultaneously, Cu2+ also inhibited intramolecular energy transfer leading to the decrease of steady-state concentration singlet oxygen (1O2ss) and triplet of DOM (3DOM⁎ss). The interaction between Cu2+ and DOM followed the order of conjugated carbonyl CO, COO− or CO stretching in phenolic groups and carbohydrate or alcoholic CO groups. With these results, a comprehensive investigation on the photodegradation of TBBPA in the presence of Cu-DOM was conducted, and the effect of Cu2+ on the photoactivity of DOM was illustrated. These findings helped to understanding the potential mechanism of interaction among metal cation, DOM and organic pollutants in sunlit surface water, especially for the DOM-induced photodegradation of organic pollutants.
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•The photodegradation of TBBPA is investigated in different solutions.•Cu-DOM accelerates the photodegradation of TBBPA due to the more hydroxyl radical formation.•Cu2+ plays as cation bridge and electron shuttle, resulting in the aggregation of DOM and electron transfer process.•Cu2+ inhibits the energy transfer process of DOM resulting in the less triplet state and singlet oxygen formation.•The interaction mechanism between Cu2+ and DOM is explored through multiple spectra combined with 2D-COS.
The Dominion Range 2010 howardite pairing group contains an evolved lithic clast of dacite composition. The dacite contains an assemblage of plagioclase, quartz, and augite, with minor pigeonite, ...troilite, ilmenite, FeNi metal, K‐feldspar, and phosphates. Primary augite occurs as >1 mm oikocrysts enclosing plagioclase. Quartz is abundant, comprising approximately 30% of the clast. Textural and geochemical characteristics support the hypothesis that the dacite is a primary igneous lithology, and represents a partial melt of the eucritic crust. Numerical modeling (MELTS) suggests 10–20% partial melting of a Juvinas source could have produced the dacite lithology; quantitative trace element modeling further supports crustal partial melting as the magma source for the dacite. The dacite likely formed as evolved‐melt pockets, and thus represents a volumetrically minor lithology in the Vestan crust, although its formation provides direct support for a genetic relationship between Stannern and residual trend eucrites, and is the first identification of residual eucrite complementary melts. We propose the dacite clast is the first characterized sample of tertiary crust on Vesta.
In this paper, the new concept Topologized domination on Neutrosophic Graphs is introduced. The idea of N-Top domination is discussed in cycle, path, complete graph, star graph. The basic properties ...of N-Top dom set, N-Top minimum dom set, N-Top minimal dom set are introduced and N-Top dom number is also established with some necessary examples.
There is growing concern about the rising levels of dissolved organic matter (DOM) in surface waters across the Northern hemisphere. However, only limited research has been conducted to unveil its ...precise origin. Compositional changes along terrestrial-aquatic pathways can help determine the terrestrial sources of DOM in streams. Stream water, soil water and soil horizons were sampled at four sites representing typical settings within a forested catchment in the Ore Mountains (Erzgebirge, Germany) from winter 2020 to spring 2022. The samples were analyzed using pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS). The resulting data were successfully subjected to semi-automatic processing of the molecular composition of DOM, reaching a percentage of identified peaks up to 98 %. Principal component analysis (PCA) and cluster analyses were carried out to identify distinct differences between DOM from the potential sources and in the streams. According to the PCA, organic soil horizons, soil water, and stream water samples could be clearly distinguished. Cluster analysis revealed that soil water DOM at all depths of Peats and deeper horizons of the Peaty Gleysols contributed the most to DOM in the stream section dominated by organic soils. In areas dominated by mineral soils, stream DOM resembled the DOM from the deeper mineral horizons of Cambisols and Podzols. Overall, our results suggested that most of the DOM exported from the catchment was derived from deeper mineral soil horizons, with little contribution of DOM derived from organic soils. Therefore, DOM fingerprint analysis of in-situ soil water proved to be a promising approach for tracing back the main sources of stream water DOM.
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•Chemical signature was used to identify sources of DOM in stream water.•Solid organic matter samples were of limited use for source identification.•Peats contributed hardly to downstream DOM.•Peaty Gleysol signals still detectable downstream the source location.•Mineral soil horizons exerted the strongest overall control on stream DOM.
As the first step of methylmercury (MeHg) entry into the aquatic food webs, MeHg uptake by phytoplankton is crucial in determining the final human MeHg exposure risks. MeHg availability to plankton ...is regulated by dissolved organic matter (DOM) in the water, while the extent of the impacts can vary largely based on the sources of DOM. Here, we investigated impacts of DOM sources on MeHg bioconcentration by three freshwater phytoplankton species (i.e. S. quadricauda, Chlorella sp., Microcystis elabens) in the laboratory system. We found that algae-derived DOM would prohibited the cellular MeHg bioconcentration by a percent up to 77–93%, while the soil-derived DOM didn't show similar inhibition effects. DOM characterization by the excitation‒emission matrices, Fourier transform infrared spectrum, ultra‒high performance liquid chromatography‒tandem quadrupole time of flight mass spectrometry shown that the molecular size of S-containing compound, rather than thiol concentration, has played a crucial role in regulating the MeHg uptake by phytoplankton. Climate change and increasing nutrient loadings from human activities may affect plankton growth in the freshwater, ultimately changing the DOM compositions. Impacts of these changes on cellular MeHg uptakes by phytoplankton should be emphasized when exploring the aquatic Hg cycling and evaluating their risks to human beings and wild life.
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•MeHg availability to algae is regulated by DOM yet impacts are rarely known.•Algae-derived DOM could prohibit cellular MeHg uptake by a range of 77–93%.•Molecular size of the S-containing compounds has played crucial roles.•Impacts of DOM change on MeHg uptake by phytoplankton should be integrated.
Dissolved organic matter (DOM), a ubiquitous and active ingredient, is extensively involved in the transformation and migration of environmental pollutants in aquatic ecosystems. However, its ...chemical composition in acid mine drainage (AMD)-impacted rivers remains poorly characterized, hindering our understanding of its role in the biogeochemistry of key elements in contaminated fluvial environments. Here, we investigated the concentration of dissolved organic carbon (DOC) and spectroscopic and molecular characteristics of DOM in a headwater river contaminated with polymetallic mine-derived AMD in southern China. Terrestrial humic-like (C1) and typically groundwater-supplied aromatic protein/tyrosine-like (C2) substances which were partially from AMD, were identified as the predominant fluorescent components in the river water. Notably, tryptophan-like (C3) substances originating from tailings pond spills were only occasionally detected in the river. Although DOM biogeochemical transformations and degradation occurred in the lateral soil-water riparian interface and longitudinal in-stream transport processes, the molecular compositions identified by FT-ICR MS showed a core set of molecular formulae in the lignin/saturated compound/tannin region of the van Krevelen diagram of the water samples across the rivers. The complexation of DOM with typical metals in AMD was investigated using fluorescence quenching experiments. The results showed that the highest binding ability of Fe(III) to C2 followed by C1, with both detected in the experimental water samples. Mg(II) and Ca(II) strengthened the binding of DOM-Fe(III) when the ferric/DOM ratio was low, while Cu(II) weakened the binding of DOM-Fe(III) due to competition. Ca(II) inhibited the binding of Fe(III) to C1 but promoted the binding of the complex to C2 when both Cu(II) and Mg(II) were present. Since DOM-Fe(III) complexation was associated with the cotransport of AMD-derived metals/metalloids in diverse aqueous environments with multiple co-existing ions (typically Ca(II) input for remediation), our study on the composition of DOM and its complexation with metals can contribute to managing and remediating AMD-impacted rivers.
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•Spectroscopic and molecular characteristics of DOM in rivers were investigated.•Terrestrial autochthonously produced substances dominated the DOM components.•A core set of lignin/saturated compounds/tannins was presented across rivers.•Ca(II) inhibited and promoted the Fe(III)-DOM complexation with the co-existing ions.
Recent studies have increasingly focused on the occurrence of plastic leachate and its impacts on aquatic ecosystems. Nonetheless, the environmental fate of this leachate in the presence of abundant ...natural organic matter (NOM)—a typical scenario in environments contaminated with plastics—remains underexplored. This study investigates the photo-induced leaching behaviors of dissolved organic matter (DOM) from terrestrial-sourced particles (forest soil and leaf litter) and microplastics (MPs), specifically polystyrene (PS) and polyvinyl chloride (PVC), over a two-week period. We also examined the biodegradability and spectroscopic characteristics of the leached DOM from both sources. Our results reveal that DOM from microplastics (MP-DOM) demonstrates more persistent leaching behavior compared to terrestrial-derived DOM, even with lesser quantities per unit of organic carbon. UV irradiation was found to enhance DOM leaching across all particle types. However, the photo-induced leaching behaviors of fluorescent components varied with the particle type. The MP group exhibited a broader range and higher biodegradability (ranging from 19.7% to 61.6%) compared to the terrestrial-sourced particles (ranging from 3.7% to 16.5%). DOM leached under UV irradiation consistently showed higher biodegradability than that under dark conditions. Furthermore, several fluorescence characteristics of DOM, such as the protein/phenol-like component (%C2), terrestrial humic-like component (%C3), and humification index (HIX)—traditionally used to indicate the biodegradability of natural organic matter—were also effective in assessing MP-DOM (with correlation coefficients R2 = 0.6055 (p = 0.003), R2 = 0.5389 (p = 0.007), and R2 = 0.4640 (p = 0.015), respectively). This study provides new insights into the potential differences in environmental fate between MP-DOM and NOM in aquatic environments heavily contaminated with MPs.
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•Comparison of DOM leaching behaviors from MPs versus terrestrial sourced particles.•Photo-induced leaching behaviors of fluorescent components were dependent on particle types.•DOM from MPs is more biodegradable than that leached from terrestrial sources.•Protein-like fluorescence can serve as a biodegradability index regardless of sources.
The characteristics of lake dissolved organic matter (DOM) pool and lake ecosystem interact, and studying the responses between sediment DOM characteristics and lake ecosystem changes may shed light ...on the inherent connection between ecosystem evolution and carbon biogeochemical cycles. Lakes in cold and arid regions are sensitive to changes and accumulate large amounts of carbon as DOM, which may provide a window into more explicit relationships between ecosystem evolution and changes in sediment DOM characteristics in time dimension. However, considerable blind spots exist in the responses between the sediment DOM and ecosystem evolution on time scale and the underlying mechanisms. In this study, multiple approaches were combined to investigate the relationship between the variation trend of sediment DOM characteristics and the evolution of fragile lake ecosystems across three different lake ecosystems in cold and arid regions of China. A strong positive relationship between sediment DOM stabilities, especially humification, and ecosystem degradation was found, consistent for the three lakes. Ultra-high-resolution mass spectrometry and structural equation modeling revealed that the changes of ecosystems affected sediment DOM stability through direct pathways (0.24), such as the contents of terrestrial DOM in lake DOM pool, and indirect pathways, including algae-mediated (0.43) and salinity-mediated pathways (0.22), which all increased the contents of refractory DOM in the lake DOM pool and sediments. Based on the fact that DOM stability changes could act on the ecosystem in turn, a possible positive feedback mechanism between ecosystem degradation and increased DOM stability was further inferred. These results suggested that the continuous increased stability of sediment DOM in may implies ecosystem degradation of lakes in the cold and arid regions. This study provides a new perspective for recognizing ecosystem evolution through sediment DOM and improves the understanding of the interaction of lake ecosystem evolution and the biogeochemical cycle of DOM.
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•Sediment DOM stability showed negative correlations with lake ecosystem health.•Terrestrial DOM, increased salinity and algae blooms increase lake stable DOM.•Positive feedback exists between ecosystem degradation and increased DOM stability.•The stability of sediment DOM is potentially indicative of ecosystem degradation.
