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Anthropogenic landcover could rise nutrient concentrations and impact the characteristics and bioavailability of dissolved organic matter (DOM) in a river network. Exploring the interactions between DOM and microbials might be conducive to revealing biogeochemistry behaviors of organic matter. In this study, synchronous fluorescence spectra (SFS) with Gaussian band fitting and two-dimensional correlation spectroscopy (2D-COS) were employed to identify DOM fractions and reveal their interactions with bacterial communities. DOM was extracted from a river network under eco-agricultural rural (RUR), eco-residential urban (URB), eco-economical town (TOW), and eco-industrial park (IND) regions in Jiashan Plain of eastern China. The overlapping peaks observed in the SFS were successfully separated into four fractions using Gaussian band fitting, i.e., tyrosine-like fluorescence (TYLF), tryptophan-like fluorescence (TRLF), microbial humic-like fluorescence (MHLF), and fulvic-like fluorescence (FLF) materials. Across all four regions, TRLF (44.79% ± 7.74%) and TYLF (48.09% ± 8.85%) were the dominant components. Based on 2D-COS, variations of TYLF and TRLF were extremely larger than those of FLF in RUR-TOW. However, in URB-IND, the former exhibited lower variations compared to the latter. These suggested that FLF be likely derived continuously from lignin and other residue of terrestrial plant origin along the river network, and TYLF and TRLF be originated discontinuously from domestic wastewater in RUR-TOW. By high-throughput sequenced OTUs, the number of organisms in RUR-TOW could be higher than those in URB-IND, while genes associated with carbohydrate metabolism were lower in former than those in the latter. According to co-occurrence networks, microbes could promote the production of TYLF and TRLF in RUR-TOW. In contrast, microbial communities in URB-IND might contribute to decompose FLF. The obtained results could not only reveal interactions between DOM fractions and bacterial communities in the river network, but this methodology may be applied to other water bodies from different landscapes., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023 Elsevier Inc. All rights reserved.)

Water replenishment can be a key factor in driving lake eutrophication status. In arid and semi-arid regions of China, water replenishment for a lake has been widely carried out for not only improving water environmental quality, but also maintaining ecological system function. However, it is still unclear in terms of mechanism by which water replenishment drives lake eutrophication status. In this study, fluorescence excitation-emission matrix spectroscopy (EEMs) combined with multiple statistical analysis models (including parallel factor analysis, correlation analysis, redundancy analysis, and partial least squares structural equation modeling) was utilized to reveal potential driving mechanism and causality between water replenishment, dissolved organic matter (DOM) fractions and eutrophic status of Lake Shahu in China. Based on variations of DOM fractions, fulvic-like substances could be accumulated during the replenishment period, while nutrients carried along the replenishment might conduce to increase microbial activities during the non-replenishment period. This should be contributed to an alteration of prominent component from fulvic-like substances to tyrosine-like substances during the replenishment period to non-replenishment period. According to partial least squares structural equation modeling, two potential indirect paths were finally revealed, i.e., water replenishment derived the eutrophic status of Lake Shahu: water replenishment → microbial activity → algae → eutrophication, and water replenishment → microbial activity → eutrophication. This supposed that the water replenishment should indirectly drive the algae and eutrophication of the lake by promoting the transformation of DOM fractions. In addition, natural conditions could indirectly contribute to the eutrophication of the lake through impacting the algae growth. These findings should be conducive to trace the alteration of DOM fractions in lakes by water replenishment and in recognizing potential driving mechanisms of water replenishment on eutrophication of lakes by changing DOM fractions. This could provide basic theoretical support for policymakers to regulate and treat the eutrophication of lakes., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023. Published by Elsevier B.V.)

Rivers are well known as one of the most threatened aquatic environments, whose structure and water quality can be deeply impacted by intensive anthropogenic activities. Despite the fact that anthropogenic influences on river ecosystems could indeed be deduced from the composition and chemistry of fluvial dissolved organic matter (DOM), sources of anthropogenic loading to DOM are still poorly explored. Here, by uniting fluorescence excitation-emission matrices (EEM) and principal component absolute coefficient, four sources of DOM from seventeen rivers in major drainage basins of China could be identified, i.e., originating from municipal sewage, domestic wastewater, livestock wastewater, and natural origins, and thus being defined as MS-DOM, DW-DOM, LW-DOM, NO-DOM, respectively. Based on the random forest model, special nodes in EEM could be traced from four sources, respectively. According to parallel factor analysis, DOM mainly contained protein-like, microbial humic-like, and fulvic-like fluorescence substances, among which protein-like was dominant in MS-DOM and DW-DOM, microbial humic-like in LW-DOM, and fulvic-like in NO-DOM. Based on key peaks and essential nodes in EEM, the identifying source indices were first proposed, which could be introduced to simply distinguish the different anthropogenic-derived sources of fluvial DOM. It was associated with intensity ratios of the key peaks and the essential nodes of EEM spectra from four sources, i.e., municipal sewage (MS-SI: Ex/Em = 280/(335, 410) nm), domestic wastewater (DW-SI: Ex/Em = 280/(340, 410) nm), livestock wastewater (LW-SI: Ex/Em = 235/(345, 380) nm), and natural origins (NO-SI: Ex/Em = 260/(380, 430) nm). By statistical analysis, the high identifying source indices of municipal sewage (>0.5) and natural origins (>0.4) values could be related to MS-DOM and NO-DOM, respectively. The identifying source indices of domestic wastewater with 0.1–0.3 might be linked to DW-DOM and the identifying source indices of livestock wastewater with 0.3–0.4 to LW-DOM. Compared with conventional optical indices, the novel identifying source indices showed remarkable discrimination for the sources of fluvial DOM with different forms of anthropogenic disturbances. Hence the innovative approach could be relatively convenient and accurate to evaluate water quality or pollution risk in river ecosystems. [ABSTRACT FROM AUTHOR]

To identify the influences of anthropogenic activities on the composition, spatial distribution, sources, and transformation mechanism of sedimentary fulvic acid (FA) fractions from different reaches of an urban river were tracked via excitation-emission matrix (EEM) fluorescence spectroscopy with parallel factor (PARAFAC) analysis and two-dimensional correlation spectroscopy (2D-COS). Sediment samples were collected from Baitapu River (BR) along gradients with human activities (e.g., rural, town, and urban sections) in Shenyang, northeast China, from which FA fractions were extracted and then determined via EEM fluorescence spectroscopy. According to optical indices, the autochthonous sources of sedimentary FA fractions in BR were more significant than the terrestrial sources. Among the sections, the contribution from autochthonous sources decreased in the following order: Rural > Urban > Town. Six components of sedimentary FA fractions were identified via EEM–PARAFAC: C1 comprised tryptophan-like (TRL) compounds; C2 was associated with microbial humic-like (MHL) compounds; C3, C4, and C5 were associated with FA-like (FAL) compounds; and C6 comprised humic acid-like (HAL) compounds. The proportion of sedimentary FA fractions decreased in the following order: MHL + FAL + HAL (humus, 77.37–88.90%) > TRL (protein, 11.10–22.63%) for the three sections, showing that humus dominated. The town section exhibited the highest sedimentary FA fractions (5328.87 ± 1315.82 Raman unit [R.U.]), followed by the urban (4146.49 ± 535.75 R.U.) and rural (2510.56 ± 611.00 R.U.) sections. Three pollution sources were determined via principal component analysis (i.e., the dominant industrial source, domestic wastewater, and agricultural effluent). Additionally, the results from 2D-COS revealed that sedimentary FA fractions tended to stabilize as the protein-like component was transformed into the HAL component. Furthermore, we used the structural equation model to validate the critical environmental variables affecting the FA fraction transformation. The results can elucidate the influences of human activities on the dynamics of sedimentary FA fractions in urban rivers. [ABSTRACT FROM AUTHOR]

The compositional characteristics of dissolved organic matter (DOM) have important implications for lake water quality and aquatic ecology. Seasonal changes of dissolved organic matter (DOM) as well as phytoplankton abundance and composition in Shahu Lake from April to July were characterized by three-dimensional fluorescence spectroscopy (3DEEMs) combined with parallel factor (PARAFAC) analysis. The relationship between the response of components of the DOM and phytoplankton abundance were explored via Pearson correlation and redundancy analysis (RDA) in the overlying water. The results showed that the DOM was composed mainly of tryptophan-like (C2+C4), fulvic-acid-like (C3), humic-acid-like (C1), and tyrosine-like (C5) compounds that accounted for 44.47%, 20.18%, 20.04%, and 15.31%, respectively, of the DOM. The DOM was derived from both endogenous and terrestrial sources. With seasonal changes, endogenous DOM produced by phytoplankton growth and metabolism gradually increased. In spring and summer (April–July), Chl-a concentrations were significantly correlated with C3 (p < 0.01) and C5 (p < 0.05). The concentration of protein-like fractions (C2+C4, C5) were correlated with Cyanobacteria abundance, and the concentrations of humic-like component content (C1, C3) were correlated with the abundance of Xanthophyta, Chlorophyta, and Cryptophytes. Overall, phytoplankton density and Chl-a content increased by 125% and 197%, respectively, and the abundance of C3 and C5 in the DOM increased by 7.7% and 22.15% in parallel. Thus, seasonal phytoplankton growth had an important influence on the composition of the DOM. [ABSTRACT FROM AUTHOR]

Synchronous fluorescence spectroscopy (SFS) combined with principal component analysis (PCA) and two-dimensional (2D) correlation was applied to investigate removal efficiencies and variations of dissolved organic matter (DOM) fractions in the wastewater treatment plant (WWTP) with an A2O craft. A decreasing order of total removal efficiencies was tyrosine-like fluorescence component (89.58%) > humic-like fluorescence (HLF) component (39.83%) > tryptophan-like fluorescence component (36.89%) > microbial humic-like fluorescence (HLF) component (12.47%) > fulvic-like fluorescence component (6.37%). The tyrosine-like, tryptophan-like and HLF components were deeply decomposed by anaerobic bacteria in the anaerobic zone. The tyrosine-like component was the preponderant fraction of DOM in the raw water and primary sediment tank. The tyrosine-like component was the dominant component of DOM too in the anaerobic and anoxic zones, but its proportion was slightly more than the tryptophan-like component. The tryptophan-like component was the dominant component in the facultative zone, the oxic zone and the secondary sediment tank. Based on the changing band order of 279 → 304 → 490 → 330 → 380 → 430 nm, the decreasing variation order was tyrosine-like > tryptophan-like > humic-like > microbial humic-like > fulvic-like component. Therefore, the SFS combined with PCA and 2D correlation is an effective tool for not only monitoring the removal of DOM components but also characterizing variations of DOM fractions in the WWTP. [ABSTRACT FROM AUTHOR]

UV-visible absorption spectroscopy combined with principal component analysis (PCA) and two-dimensional correlation (2D correlation) is used to trace components of dissolved organic matter (DOM) extracted from soils in a larger estuarine delta and to investigate spatial variations of DOM fractions. Soil samples of different depths were collected from native halophyte soils along a saline gradient, i.e., Suaeda salsa Comm. (SSC), Chenopodium album Comm. (CAC), Phragmites australis Comm. (PAC), and Artemisia selengensis Comm. (ASC). Molecular weights of DOM within the SSC soil profile were the lowest, followed by the CAC, PAC, and ASC soil profiles. Humification degree of DOM within the ASC soil profile was the highest, followed by the PAC, SSC, and CAC soil profiles. DOM within the soil profiles mainly contained phenolic, carboxylic, microbial products, and aromatic and alkyl groups through the PCA, which presented the significant differentiation among the four native halophyte soil profiles. The 2D UV correlation spectra of DOM within the SSC soil profile indicated that the variations of the phenolic groups were the largest, followed by the carboxylic groups, microbial products, and humified organic materials according to the band changing order of 285 → 365 → 425 → 520 nm. The 2D UV correlation spectra of DOM within the CAC soil profiles determined that the decreasing order of the variations was phenolic groups > carboxylic groups > microbial products according the band changing order of 285 → 365 → 425 nm. The 2D UV correlation spectra of DOM within the PAC soil profile proved that the variations of the phenolic groups were larger than those of the carboxylic groups according to the band changing order of 285 → 365 nm. The 2D UV correlation spectra of DOM within the ASC soil profile demonstrated that the variations of the phenolic groups were larger than those of the other DOM fractions according to the broad cross-peak at 285/365-700 nm. [ABSTRACT FROM AUTHOR]

Accumulative fluorescence emission (AFE) spectroscopy combined with principal component analysis (PCA), second derivative and canonical correlation analysis (CCA) was firstly developed into an available tool to track variations in dissolved organic matter (DOM) fractions and contents during wastewater treatment. Samples were collected from a wastewater treatment plant with a traditional anaerobic/anoxic/oxic (A2O) process. The AFE spectroscopy deduced from the sum of intensities along the excitation wavelengths of fluorescence excitation emission matrix (EEM), could distinctly track tyrosine-like, tryptophan-like, fulvic-like substances. The AFE spectroscopy with the PCA not only disaggregated DOM fractions into the tyrosine-like, tryptophan-like, microbial humic-like, fulvic-like and humic-like substances, but discriminated DOM fractions from the physical sedimentation, anaerobic/anoxic and oxic processes. Absolute areas of fluorescence components obtained by the second derivative AFF spectra had positive liner correlations with Fmax of the relevant components modeling from EEM-PARAFAC, especially the tryptophan-like ( R 2 = 0.95, p < 0.01) and tyrosine-like ( R 2 = 0.83, p < 0.01) substances. The CCA of the sites presented that the potential factors contained the tryptophan-like and tyrosine-like substances. This indirectly proved that the tryptophan-like and tyrosine-like substances were the dominant components of fluorescent DOM, which were further removed in A2O than the other fluorescent components. The CCA of the fluorescent components exhibited that the potential factors included the sites #1 to #6, which were located in the original wastewater, sand setting, primary sedimentation, anaerobic, anoxic, facultative units. This elaborated that the fluorescent components were mainly degraded in the physical sedimentation, anaerobic and anoxic processes. [ABSTRACT FROM AUTHOR]

Dissolved organic matter (DOM) and heavy metals can form strong complexes, which might determine distribution, toxicity, bioavailability, and environmental trend of heavy metals in aquatic environment. Synchronous fluorescence spectroscopy combined with Gaussian band fitting and two-dimensional correlation (2DCOS) was applied to characterize Cu2+ interactions with DOM fractions from sediments in Xihe River. DOM from four layers was mainly associated with tyrosine-like (TYLF), tryptophan-like (TRLF), microbial humic-like (MHLF), fulvic-like (FLF), and humic-like fluorescence (HLF) substances based on Gaussian band fitting. At the first layer, the f value of FLF was the highest among five components, while TRLF at the second and third layers represented the highest f values. Besides, at the fourth layer, the f value of TYLF was the highest. According to 2DCOS and moving window 2DCOS, the decreasing binding sensitivities were HLF→MHLF→TYLF→TRLF→FLF in the first layer, which almost represented high efficiencies at 40 μM Cu2+. The binding order was MHLF→HLF→FLF→TRLF→TYLF in the second layer, where TYLF and TRLF shared the identical efficiencies at 120 μM Cu2+. For the third layer, the varying order was TYLF→FLF→TRLF→MHLF→HLF, whose high efficiencies occurred at 10 μM Cu2+. In the fourth layer, the order was TYLF→FLF→MHLF→TRLF→HLF, whose efficiencies almost covered whole titrate concentrations. At a given layer, structural equation model showed Cu2+ concentration negatively affected the fluorescence intensity of DOM components except FLF at the substrate layer. This study might provide an effective method to illustrate the interaction mechanism of the heavy metals and DOM fractions. [Display omitted] • DOM from sediment mainly included TYLF, TRLF, MHLF, FLF, and HLF. • HLF and MHLF had strong sensitivities in the pollution layer, whereas TYLF and FLF showed solid sensitivities in transition and substrate layers. • FLF showed a significant binding ability with copper (Ⅱ), followed by TRLF and TYLF. • Structural equation model showed Cu (II) concentration negatively affected the fluorescence intensity of TYLF, TRLF, and MHLF. [ABSTRACT FROM AUTHOR]

Combination of fluorescence excitation-emission matrix spectroscopy with parallel factor analysis (PARAFAC) and principal component analysis (PCA) was engaged to track fluorescent components of dissolved organic matter (DOM) extracted from soils, to seek potential factors, and to reveal their correlations with physico-chemical properties of soils. Soil samples at different depths were collected in Hetao irrigated area of Inner Mongolia, China. Five fluorescent components (C1 to C5) were identified by PARAFAC modeling of DOM extracted from the soil samples. C1 was referred as fulvic-like fluorescent component, by which DOM was dominated in the whole soil samples. C2 was associated with salinity and agriculture, which was similar to marine humic-like fluorescent component. C3 was assigned as traditional humic-like fluorescent component. The three components were of the terrestrial origin. C4 was involved in tryptophan-like fluorescent component, which was autochthonous productions of biological degradation. C5 might be a polycyclic aromatic hydrocarbon contaminant, which could be relative to anthropogenic sources of pesticides. The C1, C2, and C3 were the potential factors of characterizing DOM fractions using PCA on fluorescent components and physico-chemical parameters. Moreover, DOM might restrained by exchangeable sodium percentage, and its formation and decomposition might be influenced by soil moisture. [ABSTRACT FROM AUTHOR]

[Display omitted] • EEM-PARAFAC was applied to probe DOM fractions in four types of riparian zones. • 2DCOS was used to explore variations of DOM fractions with depth. • PLS-SEM was employed to reveal latent factors of DOM from four riparian soils. • The forest soils were distinguished from the grassland and cropland. Dissolved organic matter (DOM) plays key roles in species-distribution of contaminants and the biogeochemical cycle of carbon in ecosystems. Riparian zone is the representative of water-land ecotone and controls the DOM exchange between water and land. However, the variance of DOM in different landcover areas of an urban river riparian zone is unknown. In this study, fluorescence excitation-emission matrix (EEM) spectroscopy coupled with parallel factor analysis (PARAFAC) and partial least squares structural equation model (PLS-SEM) was applied to character dissolved organic matter (DOM) fractions in four types of landcover riparian areas (natural forest, artificial forest, semi-natural grassland, and cropland) of Puhe River and trace latent factors. Soil samples were collected at 0–20 cm, 20–40 cm, 40–60 cm, and 60–80 cm. The results showed that soil DOM components and humification varied between forests with grassland and cropland samples, and soil humification was obviously higher in the forest samples than that in the grassland and cropland samples. In the natural and artificial forest soils, the humic/fulvic-like were the dominant fractions of DOM, whose variations were smaller than the protein-like with soil depths. However, the tyrosine-like was the representative component in the grassland and cropland soils, whose variation was smaller than the humus substances. According to the PLS-SEM, the DOM components and humification were affected by soil physiochemical properties and DOM sources. The humification in the forest soils had a positive correlation with tryptophan-like, which derived from blended source of the autochthonous and terrigenous. Nevertheless, a positive correlation was observed between humification and humus substances, which could derive from microbial degradation of tyrosine-like, in the grassland and cropland soils. Moreover, the soil physiochemical properties were negatively related to DOM components in all soil samples, which could affect indirectly soil humification. Therefore, EEM combined with PARAFAC and PLS-SEM might be an effective method to investigate DOM fractions and trace the latent factors in different landcover areas of the riparian zone. [ABSTRACT FROM AUTHOR]

[Display omitted] • EEM combined with self-organizing map were used to analyze the DOM composition and structural characteristics of saline-alkali soil. • CART was used to trace the critical factors of DOM fluorescence components to distinguish soil samples. • SEM was occupied to reveal the latent factors of improving the DOM humification degree of DOM from saline soils in Hetao irrigation area. Soil salinization has been occurring all over the world, which severely affected crop production and threatened the life of mankind. It is necessary to take serious steps to improve soil fertility for the sustainability and productive capacity of agriculture. Soil samples of different depths were collected from native vegetation communities (Comm. Phragmites communis (CPC) and Comm. Populus alba (CPA)) and irrigated crops (corn fields (CFD) and seed melon fields (SMF)) in Hetao irrigation area of China. Three dimensional excitation-emission matrix (EEM) fluorescence technology combined with self-organizing map were used to analyze the dissolved organic matter (DOM) composition and structural characteristics in saline-alkali soils and its spatial distribution under different vegetation covers. Critical factors were recognized by classification and regression tree (CART) for distinguishing soil samples, and latent factors were revealed with structural equation modeling (SEM) for improving the humification degree of DOM from saline soils in Hetao irrigation area. Five components were obtained in the DOM substances, i.e., tyrosine-like (C1), tryptophan-like (C2), UV fulvic-like (C3), visible fulvic-like (C4) and humic-like (C5). The protein-like peaks were all obvious, and the fulvic-like peaks (600-735 a.u.) were conspicuous in the CPC soil than in others, except CFD1 and SMF1. C1 was the critical factor to distinguish native vegetation from irrigated crops, and C1 and C2 were the critical factors to distinguish CFD from SMF. Contrary to the HA/FA (0.20) and A/C (0.25), the path coefficient (-0.15) of sources with T/H was negative, indicating that the incremental contents of fluorenscense substances were in the sequences of protein-like > visible fulvic-like > UV fulvic-like > humic-like, affecting by the allochthonous. C1 (1.00) and C4 (1.00) were the primary components for improving the humification degree of DOM, which were principally originated from plant debris. EEM combined with self-organizing map, CART and SEM is an efficient way to distinguish different salinized soils and reveal the latent factors for improving the soil fertility. [ABSTRACT FROM AUTHOR]

Potential water pollution derived from melting snow is a growing concern to watershed management in northern climates. For most small watersheds in the Hun River Basin, substantial portions of the annual load of pollutants such as organic matter, ammonia, phosphorus and metals come from snowmelt and early spring runoff. Thus, the annual spring flood is a real threat to the trophic state and water quality of Hun River. By three-dimensional fluorescence technology, the composition and characteristics of dissolved organic matter (DOM) in early spring runoff of a small watershed (the Baitapu River) were analyzed, and the correlation with land use was investigated. The result showed that compared with NH-N and TP, DOM was not the major contributor to water quality deterioration in spring flooding, but its composition still presented significant differences. Compared with that in medium flow period, the abundance of a soluble microbial byproduct-like material in the spring-flood period decreased from 28.6 to 15.8 %, while those of tyrosine-like material and humic-like material increased from 36.0 and 1.8 % to 44.4 and 10.7 %, respectively. DOM in spring flooding had a relatively higher aromaticity degree, a greater humification level, and a larger molecular weight. Meanwhile, DOM from urban areas contained more tyrosine-like material. For the Baitapu River, urban areas were the major DOM source in both the medium flow period (from dispersed point sources) and the spring flood period (from a wastewater treatment plant). Therefore, DOM composition can be used as an effective indicator for tracking pollution sources. [ABSTRACT FROM AUTHOR]

This study was conducted to discuss fluorescence spectroscopic properties of water dissolved organic matter (DOM) in a large-scale constructed wetland and to reveal the composition and humification degree. Four humification indices (HIXs) deduced from emission spectra ( A/ A), excitation spectra ( I/ I), synchronous fluorescence spectra ( I/ I) and derivative ( I/ I) were used for the description of composition and humification degree of DOM. Three components (C1-C3) were derived from excitation-emission matrices with parallel factor analysis (PARAFAC). The results showed that dissolved organic carbon (DOC), total nitrogen (TN) and total phosphorus (TP) concentrations in tributaries water decreased when they flowed through the constructed wetland. The values of A/ A, I/ I, I/ I and I/ I suggested that the DOM consisted of organic components with low molecular weight and low aromatic contents in the tributary. I/ I could differentiate humification degree more clearly than the other three HIXs. The fluorescence index indicated a more microbially derived composition of DOM in the constructed wetland. The DOM fluorescence was dominated by the tryptophan-like fluorescence material (C3, more than 40 %), followed by humic-like substance (C1, about 30 %). Non-humic component (C2, about 20 %) was the least component. The percentage of C1 declined from upstream to downstream along the wetland, while C3 showed inverse tendency. The proportion of C2 remained relatively constant in all sampling points. Principal component analysis suggested that the humification degree of the DOM in the slowly flowing region was the highest among the wetlands, followed by those from the regions disturbed by tributaries, the sampling sites in mainstream and the outlet zone of wetland. The humification degree also showed a good correlation mainly with TN, TP and Chlorophyll a. Therefore, fluorescence spectroscopy technique coupled with derivative and PARAFAC might be a useful method to investigate composition and to evaluate the humification degree of DOM in aquatic environment. [ABSTRACT FROM AUTHOR]

Excitation-emission matrix fluorescence spectroscopy combined with multivariable analysis was employed to discriminate structural component of dissolved organic matter (DOM) in Xihe River, an urban river, located in western Shenyang City of China, and to reveal its correlation with water quality. Eight water samples were collected along the river across the centralized wastewater-discharge region and the dispersed wastewater-discharge region. Water quality had deeply deteriorated in the river. Based on DOM fluorescence spectroscopic properties, DOM was composed of tyrosine-like, tryptophan-like, soluble microbial by-product-like, fulvic-like and humic-like materials, among which protein-like material was dominant in the DOM fractions. The DOM in the centralized wastewater-discharge region had a lower level of aromaticity than that in the dispersed wastewater-discharge region, and its humification degree was lower than that in the latter too. Key factors for the trophic state contained NH-N, DO, DOC, TP, Φ and Φ by multivariable analysis. DOM was mainly derived from treated and untreated industrial wastewater with weak biodegradability. [ABSTRACT FROM AUTHOR]

The stabilization of latent tracers of dissolved organic matter (DOM) of wastewater was analyzed by three-dimensional excitation-emission matrix (EEM) fluorescence spectroscopy coupled with self-organizing map and classification and regression tree analysis (CART) in wastewater treatment performance. DOM of water samples collected from primary sedimentation, anaerobic, anoxic, oxic and secondary sedimentation tanks in a large-scale wastewater treatment plant contained four fluorescence components: tryptophan-like (C1), tyrosine-like (C2), microbial humic-like (C3) and fulvic-like (C4) materials extracted by self-organizing map. These components showed good positive linear correlations with dissolved organic carbon of DOM. C1 and C2 were representative components in the wastewater, and they were removed to a higher extent than those of C3 and C4 in the treatment process. C2 was a latent parameter determined by CART to differentiate water samples of oxic and secondary sedimentation tanks from the successive treatment units, indirectly proving that most of tyrosine-like material was degraded by anaerobic microorganisms. C1 was an accurate parameter to comprehensively separate the samples of the five treatment units from each other, indirectly indicating that tryptophan-like material was decomposed by anaerobic and aerobic bacteria. EEM fluorescence spectroscopy in combination with self-organizing map and CART analysis can be a nondestructive effective method for characterizing structural component of DOM fractions and monitoring organic matter removal in wastewater treatment process. [ABSTRACT FROM AUTHOR]

A novel coagulation combined with UV/O3 process was employed to remove the effluent organic matter (EfOM) from a biotreated pharmaceutical wastewater for harmlessness. The removal behavior of EfOM by UV/O3 process was characterized by synchronous fluorescence spectroscopy (SFS) integrating two-dimensional correlation (2D-COS) and principal component analysis (PCA) technology. The highest dissolved organic carbon (DOC) and ratio of UV254 and DOC (SUVA) removal efficiency reached 55.8% and 68.7% by coagulation-UV/O3 process after 60 min oxidation, respectively. Five main components of pharmaceutical tail wastewater (PTW) were identified by SFS. Spectral analysis revealed that UV/O3 was selective for the removal of different fluorescent components, especially fulvic acid-like fluorescent (FLF) component and humus-like fluorescent (HLF) component. Synchronous fluorescence/UV-visible two-dimensional correlation spectra analysis showed that the degradation of organic matter occurred sequentially in the order of HLF, FLF, microbial humus-like fluorescence component (MHLF), tryptophan-like fluorescent component (TRLF), tyrosine-like fluorescent component (TYLF). The UV/O3 process removed 95.6% of HLF, 80.0% of FLF, 56.0% of TRLF, 50.8% of MHLF and 44.4% of TYLF. Therefore, the coagulation-UV/O3 process was proven to be an attractive way to reduce the environmental risks of PTW. [ABSTRACT FROM AUTHOR]

• Ultraviolet tryptophan-like substances only occurred in RDOM, and tyrosine-like substances just in UDOM with Cu (II) addition. • Phenol-/fulvic-like substances from autochthonous sources exhibited high binding ratios with Cu (II). • Cu (II) had great binding capacity on protein-like substances from livestock, poultry and industrial wastewater. • Phenol-/protein-like substances in NDOM and fractions in RDOM were sensitive to 160 μM Cu (II) addition. Dissolved organic matter (DOM) in aquatic environment distinctly affects the behavior and fate of heavy metals via complexation, while the interfacial mechanisms and processes are still lacking in detail. Here, Cu (II) binding characteristics of DOM originated from hilly (NDOM), rural (RDOM) and urban (UDOM) regions in an urbanized river was explored by fluorescence excitation-emission matrix spectroscopy (EEM) combined with principal component coefficients, parallel factor analyses (PARAFAC), moving-window two-dimensional correlation spectroscopy (MW2DCOS) and structural equation modeling (SEM). Eight components were extracted from the titrants through EEM-PARAFAC, i.e., phenol-like substance (C1), tyrosine-like substance (C2), visible tryptophan-like substance (C3), ultraviolet tryptophan-like substance (C4), recent biological production (C5), wastewater-derived organic matter (C6), microbial humic-like substance (C7) and fulvic-like substance (C8). Interestingly, NDOM only contained C1, C3, C5 and C8, while nearly all components were found in RDOM (except for C2) and UDOM (except for C4). The f value of C1 (1.239) in NDOM was much higher than those in RDOM (0.134) and UDOM (0.115), so was of C8. It indicated that phenol-like and fulvic-like derived from autochthonous sources exhibited great binding ratios in the complexation with Cu (II). Moreover, C3 and C5 from UDOM exhibited higher f values (0.591 and 1.983) than those from NDOM and RDOM, suggesting that Cu (II) has a great binding capacity on protein-like from domestic and industrial wastewater. The MW2DCOS revealed that phenol-like and protein-like in NDOM and RDOM were essential for the binding of 160 μmol L−1 Cu (II), whereas fulvic-like in NDOM and UDOM could react significantly with 10 μmol L−1 Cu (II). Based on SEM, Cu (II) concentration had a negative direct effect on the fluorescence intensity of C7 or C8, whereas it showed an indirect positive effect on C7 or C8 through influencing C5, so was C6. It suggested that Cu (II) showed an indirect positive effect on the C8. This study might present a further comprehend of the environmental behaviors of Cu (II) in rivers. [Display omitted] [ABSTRACT FROM AUTHOR]

• Surface water recharge enhances bioavailability of DOM in groundwater. • Tyrosine-like peak only occurs in IGW, representing recent microbial activities. • Microbial indicators are more sensitive to surface water recharge. • Strong correlations of DOM with microbials drives organic matter conversion. Dissolved organic matter (DOM) plays a crucial role in driving biogeochemical processes and determining water quality in shallow groundwater systems, where DOM could be susceptible to dynamic influences of surface water influx. This study employed fluorescence excitation-emission matrix (EEM) spectroscopy combined with principal component coefficients, parallel factor analysis (PARAFAC), co-occurrence network analysis and structural equation modeling (SEM) to examine changes of DOM fractions from surface water to shallow groundwater in a mesoscale lowland river basin. Combining stable isotope and hydrochemical parameters, except for surface water (SW), two groups of groundwater samples were defined, namely, deeply influenced by surface water (IGW) and groundwater nearly non-influenced by surface water (UGW), which were 50.34 % and 19.39 % recharged by surface water, respectively. According to principal component coefficients, reassembled EEM data of these categories highlighted variations of the tyrosine-like peak in DOM. EEMs coupled with PARAFAC extracted five components (C1-C5), i.e. C1, protein-like substances, C2 and C4, humic-like substances, and C3 and C5, microbial-related substances. The abundance of the protein-like was SW > IGW > UGW, while the order of the humic-like was opposite. The bacterial communities exhibited an obvious cluster across three regions, which hinted their sensitivity to variations in environmental conditions. Based on co-occurrence, SW represented the highest connectivity between bacterial OTUs and DOM fractions, followed by IGW and UGW. SEM revealed that microbial activities increased bioavailability of the humic-like in the SW and IGW, whereas microbial compositions promoted the evolution of humic-like substances in the UGW. Generally, these results could be conducive to discern dissimilarity in DOM fractions across surface water and shallow groundwater, and further trace their interactions in the river watershed. [Display omitted] [ABSTRACT FROM AUTHOR]

[Display omitted] • The research applies fluorescence spectroscopy to analyze DOM in the Anyang River. • Urbanization's influence on DOM composition during heavy rainfall is investigated. • The study offers valuable insights for managing urban water quality in changing environments. This research delves into the dynamic interplay between urbanization and the characteristics of Dissolved Organic Matter (DOM) in the Anyang River, particularly under the stress of torrential rain. The motivation stems from a critical need to decipher how urban landscapes influence water quality, focusing on the intricate transformations and movements of DOM. Employing advanced fluorescence spectroscopy techniques like Excitation-Emission Matrices (EEM) and Parallel Factor Analysis (PARAFAC), the study meticulously differentiates DOM compositions in urban and agricultural settings. It unveils a pronounced distinction, with urban streams showing elevated proteinaceous DOM from wastewater, contrasting with the humic substances prevalent in agricultural runoff. The analysis also captures how intense rainfall events catalyze significant shifts in DOM profiles, thereby emphasizing the need for tailored water quality management strategies in urbanized catchments. This comprehensive approach not only bridges gaps in understanding the urban impact on riverine ecosystems but also sets a foundation for future research and policy development in the face of escalating environmental changes. [ABSTRACT FROM AUTHOR]

Abstract: Dissolved extracellular and intracellular polymeric substances (DEPS and DIPS) from floccular sludge and aerobic granules were extracted and fractionated based on compound hydrophobicity. Compared with floccular sludge, aerobic granules contained lower amounts of DEPS and DIPS. Fourier transforms infrared spectra suggested that large amounts of proteins and polysaccharides existed in colloidal form in the extracellular polymeric substances of aerobic granules. Fluorescence excitation-emission matrix spectra revealed that tightly bound DEPS (TB-DEPS) and DIPS were humified after sludge granulation. Meanwhile, the proportions of hydrophilic contents in the TB-DEPS and DIPS fractions decreased from 45.3% to 28.3% and from 40.1% to 18.9%, respectively. These data indicated that TB-DEPS and DIPS from aerobic granules were more hydrophobic than those from floccular sludge. The results of the hierarchical cluster analysis further confirmed that the characteristics of dissolved organic matters between floccular and granular sludge were distinctly different. [Copyright &y& Elsevier]

Heavy metal speciation and distribution is significantly influenced by dissolved organic matter (DOM) exhibited in ecosystems, particularly in urbanized rivers. Synchronous fluorescence spectroscopy (SFS) conjunct second derivative and two-dimensional correlation spectroscopy (2D-COS) was devoted to characterizing interactions of DOM-copper (II). Three typical water samples were collected from Baitapu River. Only protein-like fluorescence (PLF) and fulvic-like (FLF) were identified from the SFS. Stability constant (log K) values of PLF complexes with copper (II) varied from 4.277 to 5.833, and proportion of binding fluorescent materials (f) were 0.054–2.640. The log K values of FLF complexes with copper (II) varied from 3.996 to 4.243, while the f values were 0.001–0.036. Obviously, PLF had much stronger complexing capacity than FLF. There were four obvious peaks in the principal component analysis and second derivative fluorescence spectroscopy (SDFS), i.e., tyrosine-like (TYLF), tryptophan-like (TRLF), microbial humus-like (MHLF) and FLF. The log K values of TYLF and TRLF complexes were 4.899–5.907 and 4.598–5.831, respectively, which were similar to those from PLF. The log K values of MHLF complexes varied from 4.311 to 5.760, and the f values were 0.261–8.688. The log K values of FLF complexes were ranged from 4.598 to 5.831, which were higher than those deduced from the SFS. Interestingly, by the SDSF, PLF was divided into TYLF and TRLF, which increased the parameters values from DOM-copper (II) complexes. 2D-SFS-COS revealed that the TRLF was more susceptive response to copper (II) appended than TYLF, MHLF, and FLF. Moreover, TYLF and TRLF could priorly interact with copper (II). The SDSF conjunct 2D-COS could be effective approaches for insight into the complexing heterogeneity of DOM with copper (II). The study could present a support to preventing heavy metals and organic pollution in urbanized rivers. [Display omitted] • The modified Stern-Volmer model was applied to measure binding parameters of dissolved organic matter with copper (II). • PCA and SDFS were used to characterize more information on copper (II) binding properties to dissolved organic matter. • 2D-COS was occupied to reveal dynamic spectral properties of dissolved organic matter fractions with copper (II) addition. [ABSTRACT FROM AUTHOR]

[Display omitted] • MBR effluent, tap water and surface water mainly contain proteinoid and humic acid DOM. • The UF-RO process can effectively remove more than 80 % of all types of DOMs. • The effect of UF pretreatment on subsequent RO membrane fouling by different water bodies is different. Ultrafiltration (UF) is often used as a pretreatment for reverse osmosis (RO) units due to its high rejection of microorganisms and particulate matter. UF has different removal effects on different kinds of dissolved organic matter (DOM) in water and affects the pollution of RO membrane. This study aimed to investigate the changes of DOM during the ultrafiltration-reverse osmosis (UF-RO) process. The ultraviolet–visible absorption spectrum and three-dimensional excitation-emission matrix spectrum (3DEEMs) were used to examine the DOM components of the effluent from membrane bioreactor (MBR), tap water and surface water treated by the UF-RO process. The results revealed that UF removed 3.19 %–36.85 % of aromatic DOM components and 5.71 %–32.25 % of hydrophobic DOM components. Based on parallel factor analysis (PARAFAC), all the water samples predominantly contained protein-like substances (e.g., high-excitation and low-excitation of tryptophan and tyrosine), and fulvic acid-like substances. Due to the different quality of feed water, the removal rate of the same type of DOMs varied significantly. While the highest removal rates for both protein-like substances and fulvic acid-like substances in tap water were higher than 80 %, the highest removal rates for these substances in MBR effluent were only about 40 %. For surface water, the highest removal rates were 28.07 % for fulvic acid-like substances and 70 %–80 % for protein-like substances. Pretreatment by UF membranes of different pore sizes had no impact on the content of DOMs in RO effluent. However, after treatment with the UF-RO process, the removal rates of all types of DOMs exceeded 80 %. It was found that the membrane fouling was reduced by pretreatment of tap water and surface water, while the fouling deteriorated faster after pretreatment of the MBR effluent. This study suggested that based on types of water to be treated, UF membranes of the appropriate pore sizes can be selected for use in the UF-RO process to better achieve the desired effluent quality, water flux, and economy. [ABSTRACT FROM AUTHOR]

• SFS combined with Gaussian banding fitting acquired DOM for small-sample. • 2D-COS was used to reveal the variations of DOM in town, urban, and rural region. • PCMW2D were used to trace the variations of DOM along the whole river. Synchronous fluorescence spectroscopy (SFS) combined with Gaussian band fitting, two-dimensional correlation (2D-COS) and perturbation-correlation moving-window two-dimensional (PCMW2D) can provide an excellent mothed to extract fluorescent components of dissolved organic matter (DOM) and reveal its variations in an urban river. Fifteen water samples were collected from the Anyanghe River, which flew across the town, urban, and rural regions. Five peaks (peak1 tyrosine-like, peak2 tyrosine-like, peak3 tryptophan-like, peak4 microbial humic-like, peak5 fulvic-like) were extracted using the Gaussian Amp model from the SFS in the river, while the peak1 only occurred in the rural region. The microbial humic-like in the town region accounting for 50.02 % was the representative substance. The tyrosine-like dominated in the rural regions, for its percentage range was 62.26 %-75.78 %. The average percnetage of tyrosine-like (29.77 %) in the urban region was similar to that of the tryptophan-like (21.86 %), microbial humic-like (25.56 %), and fulvic-like (22.82 %). Based on the two-dimensional correlation, the variation order of DOM fractions in the town and urban regions was tryptophan → tyrosine → microbial humic → fulvic, and the variation order in the rural region was tyrosine → tryptophan → microbial humic → fulvic. This indicated that the changing trend of DOM fractions existed from the labile protein-like to the stable humus in the whole river. According to the perturbation-correlation moving-window two-dimensional correlation spectroscopy, the spectral intensity of tyrosine-like should be linear increase in the town and urban regions, and concave increase in the rural region. The spectral intensity trend of tryptophan-like mainly was linear increase in the whole river. And the intensity of microbial humic-like showed the rough convex increase in the whole river. The trend of the fulvic-like in the town and rural regions was similar to the microbial humic-like. However the fulvic-like intensity in the urban region exhibited a trend from the concave increase to the convex increase, which was obviously different from the tyrosine-like, tryptophan-like and microbial humic-like. This attribute that the untreated domestic sewage in the urban region could discharge into the river. Therefore, for small amounts of samples, the SFS combined with Gaussian band fitting, 2D-COS and PCMW2D can be used as a powerful tool to investigate fluorescent components of DOM, and reveal their variations along the river. [ABSTRACT FROM AUTHOR]