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Potential rainfall-intensity and pH-driven shifts in the apparent fluorescent composition of dissolved organic matter in rainwater
Abstract
Perturbations of rainwater chromophoric dissolved organic matter (CDOM) fluorescence induced by changes in rainfall intensity and pH were investigated by field observations and laboratory pH titrations. Microbial humic-like fluorophores dominated the rainwater CDOM pool, followed by tryptophan-like and tyrosine-like substances. Increased rainfall intensity had notable dilution effects on all six fluorescent components (C1-C6) identified using parallel factor (PARAFAC) analysis, the effect being especially pronounced for the microbial humic-like C1, tryptophan-like C3, and tyrosine-like C5. The results also indicated that increasing pH from 7 to 9 led to decreased fluorescence intensity (Fmax) of all the six components, while a pH increase from 5 to 7, resulted in increasing Fmax of terrestrial humic-like C2, tyrosine-like C5, and tryptophan-like C6 and decreasing microbial humic-like C1, tryptophan-like C3, and fulvic-like C4. Two-dimensional correlation spectroscopy (2D-COS) demonstrated that synchronous fluorescence responded first to pH modifications at fulvic-like wavelength (λEx/λEm = ∼316/416 nm), followed by tyrosine-like wavelength (λEx/λEm = ∼204/304 nm), tryptophan-like wavelength (λEx/λEm = ∼226/326 nm), microbial humic-like wavelength (∼295/395 nm), and finally terrestrial humic-like wavelength (∼360/460 nm). Our results suggest that a decrease in areas affected by acid rain in South China occurring at present may possibly result in apparent compositional changes of CDOM fluorescence. The decreased rainfall in South-West China and increased rainfall in North-West China during the past five decades may possibly accordingly result in increased and decreased Fmax of all the six components identified in South-West and North-West China, respectively.
... PARAFAC modeling was applied to identify the fluorescent components of the biochar DOM, conducted in MATLAB R2014a (Math-Works) with the DOMFluor toolbox (www.models.life.ku.dk) (Zhou et al., 2017). The PARAFAC was computed using 2-7 components models for the biochar DOM dataset, which contained a total of 72 EEMs from the titration experiment. ...
... The changes in the selected region of fluorescence spectra for the Cu titration DOM samples are presented in SI Fig. S4. The 2D-COS analysis was performed according to the method of Noda and Ozaki (2004), using the MIDAS 2010 toolbox released by the University of Saskatchewan, Canada (Zhou et al., 2017). Besides, the modified Ryan-Weber model was used to determine the Cu(II) binding capacity and affinity of different components of the biochar DOM. ...
... As shown in Fig. 2, C1 showed two Ex peaks: one below 230 nm and the other at 370 nm, corresponding to a single Em peak at 440 nm. These features are similar to those of typical terrestrial humic-like fluorophores (Wei et al., 2015;Zhou et al., 2017). C2 displayed a major Ex peak at 325 nm with a single Em peak at 380 nm. ...
Multiple spectroscopic technologies and chemometric analyses were combined to explore the compositional characteristics and Cu binding performance of biochar-derived dissolved organic matter (DOM). The DOM samples were extracted from biochars produced from lignocellulose-rich rapeseed cake (RSC) by pyrolysis at 300, 500, and 700 °C (i.e., RSC300, RSC500, RSC700). Fourier transform infrared spectroscopy (FTIR) and carbon K-edge near-edge X-ray absorption fine structure spectroscopy (NEXAFS) analyses were combined to elucidate the molecular-level C species in the DOM. With the increasing pyrolysis temperature, DOM aromaticity increased, whereas the proportion of metal complexing sites (e.g., carboxyl and phenolic groups) decreased. Fluorescence excitation-emission matrix (EEM) spectroscopy with parallel factor analysis (PARAFAC) indicated that biochar DOM, irrespective of pyrolysis temperature, was mostly composed of three types of humic-like components (C1-C3), and a small amount of a protein-like component (C4). As charring temperature increased, DOM concentrations decreased substantially, but the humic-like C3 with abundant aromatic structures became predominant. Fluorescence quenching experiment and two-dimensional correlation spectroscopy (2D-COS) analysis suggested that the preferential Cu(II) binding fractions of the DOM were the humic-like substances. Moreover, the quenching curve fitting results for individual components indicated that despite the Cu(II) binding affinity was slightly enhanced as the pyrolysis temperature increased, the binding capacities of the four components decreased. In general, the DOM components from RSC biochar exhibited limited Cu(II) binding capacities (2.18-17.7 μmol L-1). Results from this study improved understanding of the mechanisms by which biochar DOM interacts with Cu, and provided tools for fast screening of biochars to reduce their environmental risks.
... The emission (E m ) and excitation (E x ) of different components determine the basic properties of individual fluorophores (Zhou et al. 2017). Different fluorescent components can be identified through PARAFAC analysis using EEM data. ...
Dissolved organic matter (DOM) plays an important role in the cycling and toxicity of heavy metals in aquatic systems. However, most studies have focused only on DOM in either water or sediments. This study aimed to analyze the source, composition, and structural characteristics of DOM in both surface water and bottom sediments of the Le’an River and its major tributaries. In addition, the potential ecological risks of three typical heavy metals (Cu, Pb, and Zn) were quantitatively evaluated based on the characteristics of DOM and in situ data. The results showed that sediment DOM is more aromatic and hydrophobic than surface water DOM. Although humic-like components dominated the DOM pool in both surface water and sediments, their sources were different. Surface water DOM is mainly autochthonous, while sediment DOM is controlled by both autochthonous and allochthonous sources. Risk prediction results based on DOM characteristics show that surface water has a higher potential risk of heavy metal release than sediments. Comprehensively considering the ecological risk of water and sediments, high-risk areas were found to be mainly distributed in the upper and middle reaches of the Le’an River. This distribution is attributable to the developed mining and smelting industries in these areas and consistent with the risk assessment results of measured concentrations of heavy metals. This study established a new technique for predicting the ecological risk of aquatic systems based on the characteristics of DOM in surface water and sediments.
... Moreover, parallel factor (PARAFAC) analysis is a mathematical method for decomposing overlapped fluorescence components, which allowed a much more accurate quantitative analysis of EEMs data than peakpicking or regional integration (FRI) method (Yu et al., 2015). EEMs coupled with PARAFAC have been widely used to characterize DOM in environmental samples (Qian et al., 2017;Yang et al., 2019;Zhou et al., 2017). ...
The structural compositions of dissolved organic matter (DOM) could profoundly affect formation and evolution of black-odor waterbodies (BOWs). In this study, 81 samples of BOWs were collected from three different latitudinal rural regions in eastern China, including low, middle and high latitude regions. Based on fluorescence index (FI) and biological index (BIX) deduced from excitation-emission matrices (EEMs) of rural BOWs, biological source of DOM was dominant in low latitude, while DOM derived from both biological and terrestrial in mid-latitude and high-latitude. Furthermore, humification degree of DOM in the former was lower than those in the latter based on humification index (HIX) deduced from EEMs. Seven fluorescence components of DOM were extracted by EEMs combined with parallel factor analysis: components 1 and 2 (C1 and C2) known as tryptophan-like substances, C3 and C4 associated with tyrosine-like, C5 related with biological byproducts, C6 relative to fulvic-like, and C7 referred as humic-like. The roughly decreasing order of percentages in DOM fractions from the rural BOWs was tyrosine-like > tryptophan-like > fulvic-like > microbial byproduct > humic-like in three regions. According to hierarchical cluster analysis and redundancy analysis, the autochthonous fresh DOM was dominant in low latitudinal rural BOWs, which was relative to actions of phytoplankton and microorganisms. However, humification degree of DOM increased with a rise in latitude, which could attribute to variations of climate and agriculture industrial structure. Based on structure equation model, the C5 and FI were the potential factors of the rural BOWs, which suggested that microbial activity and pollution sources should affect formation and evolution of rural BOWs. These findings are conductive to reveal composition and fluorescence properties of DOM and in recognizing the potential factors of forming mechanism in rural BOWs, which could provide basic theoretical support for policymakers to regulate and treat it.
... Current research suggests that CDOM in water comes from multiple sources, including (a) allochthonous sources, which mainly include degraded organic matter from the surrounding terrestrial environment as input from terrestrial runoff, precipitation and groundwater recharge, and resuspension of sediments [7], and (b) autochthonous sources, which include the chemical degradation products of organisms from phytoplankton, mac-rophyte and bacteria [8]. The degradation process of CDOM mainly includes photochemical degradation and microbial degradation, which can degrade large molecules into small molecules that can be used by phytoplankton and microorganisms [9,10]. ...
Chromophoric dissolved organic matter (CDOM) is crucial in the biogeochemical cycle and carbon cycle of aquatic environments. However, in inland waters, remotely sensed estimates of CDOM remain challenging due to the low optical signal of CDOM and complex optical conditions. Therefore, developing efficient, practical and robust models to estimate CDOM absorption coefficient in inland waters is essential for successful water environment monitoring and management. We examined and improved different machine learning algorithms using extensive CDOM measurements and Landsat 8 images covering different trophic states to develop the robust CDOM estimation model. The algorithms were evaluated via 111 Landsat 8 images and 1708 field measurements covering CDOM light absorption coefficient a(254) from 2.64 to 34.04 m−1. Overall, the four machine learning algorithms achieved more than 70% accuracy for CDOM absorption coefficient estimation. Based on model training, validation and the application on Landsat 8 OLI images, we found that the Gaussian process regression (GPR) had higher stability and estimation accuracy (R2 = 0.74, mean relative error (MRE) = 22.2%) than the other models. The estimation accuracy and MRE were R2 = 0.75 and MRE = 22.5% for backpropagation (BP) neural network, R2 = 0.71 and MRE = 24.4% for random forest regression (RFR) and R2 = 0.71 and MRE = 24.4% for support vector regression (SVR). In contrast, the best three empirical models had estimation accuracies of R2 less than 0.56. The model accuracies applied to Landsat images of Lake Qiandaohu (oligo-mesotrophic state) were better than those of Lake Taihu (eutrophic state) because of the more complex optical conditions in eutrophic lakes. Therefore, machine learning algorithms have great potential for CDOM monitoring in inland waters based on large datasets. Our study demonstrates that machine learning algorithms are available to map CDOM spatial-temporal patterns in inland waters.
... CDOM absorption in the blue region of visible light overlaps with the absorption band of phytoplankton chlorophyll a (Chla) and total suspended matter (TSM), which will lead to the inhibition of phytoplankton photosynthesis, a reduction of primary productivity, and interference in the estimation of phytoplankton biomass and TSM concentration by remote sensing (Rochelle-Newall and Fisher 2002;Doxaran et al. 2002;Zhang et al. 2009). CDOM is complex in composition, mainly including humic acid and fulvic acid, which originate from aquatic biological secretions, algae and aquatic vegetation degradation, river inputs from land and marshes, atmospheric wet deposition through rainfall and release from sediment, especially in inland waters (Rochelle-Newall and Fisher 2002;Zhang et al. 2007a;Zhou et al. 2017;Burdige et al. 2004). In addition to the absorption of light, CDOM also fluoresces when excited by light in the UV and blue regions of the spectrum . ...
The source regions of the Yangtze and Yellow Rivers on the Qinghai-Tibet Plateau are extremely important water resources and ecological functional areas in China, and the ecological environment is fragile and sensitive to climate change. Chromophoric dissolved organic matter (CDOM) is an important component that plays a crucial role in the biogeochemical cycle in aquatic ecosystems. However, knowledge of the distribution characteristics of CDOM in this area is limited. In this study, the optical properties, possible sources of CDOM, and their relationships with environmental variables were investigated in the two regions. The results indicated that the CDOM absorption spectra of these two source regions had a high degree of consistency, and the absorption coefficient aCDOM(355) was small, with a mean of 2.07 ± 1.10 m−1. Two fluorescence components (C1 and C2) were identified and grouped into the humic-like component with parallel factor analysis (PARAFAC) of fluorescence excitation-emission matrices (EEMs), which exhibited highly similar (excitations/emission)max positions between each pair of components in the two regions. Comprehensive CDOM spectral absorption and fluorescence parameters suggested that CDOM was mainly derived from externally input humus, and the source region of the Yellow River showed stronger allochthonous sources. The dissolved organic carbon (DOC) gradients in the water affected the fluorescence intensity and indicated that the humic-like component was an important component of DOC. Water temperature (WT) and turbidity (Turb) positively affected the concentration of CDOM and the ability to absorb light in the aquatic ecosystems. Due to global warming, the rising temperature may lead to an increase in meltwater inflow in the source area and will also bring more external inputs through the runoff.
... The fluorescence excitation-emission matrix (EEM) offers multiple advantages, such as high sensitivity, easy sample preparation and non-destructivity to samples (Birdwell 10 and Valsaraj, 2010), and has been widely used to identify the source and composition (humic-like or protein-like) of CDOM in natural waterbodies (Birdwell and Engel, 2010;Coble, 1996;Zhao et al., 2016), rainwater (Zhou et al., 2017b), fog water (Birdwell and Valsaraj, 2010) and aerosols (Chen et al., 2016a(Chen et al., , 2016bFu et al., 2015). ...
Chromophoric dissolved organic matter (CDOM) plays an important role in the global carbon cycle and energy budget. A field campaign was conducted across northwestern China from January to February 2012, and surface seasonal snow samples were collected at 39 sites in Xinjiang and Qinghai provinces. Light-absorption measurements, fluorescence measurements and chemical analysis were conducted to investigate the optical properties and potential sources of CDOM in seasonal snow. The abundance of CDOM (the absorption coefficient at 280nm, a280) and the spectral slope from 275 to 295nm (S275–295) ranged from 0.15–10.57m−1 and 0.0129–0.0389nm−1, respectively. The highest average a280 (2.30±0.52m−1) and lowest average S275–295 (0.0188±0.0015nm−1) in Qinghai indicated that the snow CDOM in this region had strongly terrestrial characteristic. Relatively low regional average a280 values were found in sites located to the north of the Tianshan Mountains and northwestern Xinjiang along the border of China (0.93±0.68m−1 and 0.80±0.62m−1, respectively). Parallel factor analysis (PARAFAC) identified three types of chromophores that were attributed to two humic-like substances (HULIS, C1 and C2) and one protein-like material (C3). C1 was mainly from soil HULIS, while the potential sources of C2 were complex and included soil, microbial activities, anthropogenic pollution and biomass burning. The good relationship between a280 and the intensity of C1 (R² = 0.938, p<0.001) indicated that the CDOM abundance in the surface snow across northwestern China was mainly controlled by terrestrial sources. In addition, the regional variations of sources for CDOM in snow were further assessed by the analysis of chemical species (e.g., soluble ions) and air mass backward trajectories combined with satellite fire locations.
Both concentrations and compositions of dissolved organic matter (DOM) and the availability of oxygen affect transformation processes in close-to-nature drinking water treatments such as bank filtration and artificial groundwater infiltration. This study focused on quantitative and qualitative analyses of DOM in different saturated sand column systems of different dimensions, histories and operating conditions using fluorescence spectroscopy. The study revealed the presence of two fluorescent DOM (fDOM) fractions (humic-like compounds) through parallel factor analysis (PARAFAC). DOM, fDOM and specific UV absorbance (SUVA) at 254 nm were reduced and correlated in indoor systems. In outdoor columns, the removals of DOM and fDOM were comparably high, but the increased SUVA indicated an increase in aromaticity. Dissolved oxygen consumption corresponded to organic content in sand, independent of residence times. Overall, bank filtration is an effective option to remove biodegradable DOM under outdoor natural conditions.
Understanding the environmental correlation of microbial community under external stimulation is significant for ecological restoration. However, few studies focused on the response of soil biodiversity induced by black carbon (BC) derived from pyrolysis of straw and microplastics (MPs) due to their widespread existence in natural environment. In this study, polystyrene MPs (PS) and maize straw with different mass ratios were used as raw materials to prepare BC by pyrolysis. The surface morphology, chemical composition and sequential variations of different functional groups of BC were systematically analyzed. The leachate from BC was identified by three-dimensional excitation emission matrice (3D-EEM). The corresponding results showed that yield, value of O/C and N element content of BC decreased with more PS. The changed C content and oxygen-containing functional groups occurred. The order of functional groups of BC formed by co-pyrolysis was: C=C > C-O > C-H > Si-O-Si. The main component of leaching from BC was humic-like and fulvic-like acid. Simultaneously, the input of exogenous BC into soil affected abundance, composition and metabolic pathways of microorganisms. The study helps to understand environmental implication of BC which was pyrolyzed from maize straw and MPs, providing an idea for improving biogeochemical cycle process in soil.
Chromophoric Dissolved Organic Matter (CDOM) plays a critical role in the carbon and biogeo-chemical cycles within aquatic ecosystems. Satellite imagery can be employed to determine aquatic CDOM concentrations, highlighting the need for effective and precise algorithms for this task. In this study, a cruise survey dataset containing CDOM absorption coefficients and water-leaving radiances in the Pearl River estuary (PRE) was utilized to develop machine learning algorithms for CDOM retrieval from Landsat-8 Operational Land Imager (OLI) observations. Based on OLI wavelength bands, five bands and six band-ratios were chosen as input parameters for the machine learning models. Six machine learning models were trained to develop CDOM algorithms, including Support Vector Regression (SVR), Random Forest (RF), Extreme Gradient Boosting (XGBoost), Multi-Layer Perceptron (MLP), and Convolutional Neural Network (CNN). The results indicated that, among the six machine learning models, the XGBoost algorithm performed best, with the highest R2 value of 0.9 and the lowest CDOM root mean square error (RMSE) of 0.37 m-1, outper-forming empirical algorithms. The XGBoost algorithm identified B4/B1 as the most critical input parameter, contributing 71%, followed by B3/B2 with a 16% contribution, where B1, B2, B3, and B4 are the wavelength bands of the OLI. These two band-ratios accounted for most of the contributions, suggesting their significant role in CDOM retrieval from Landsat OLI images. By employing the developed XGBoost algorithm, CDOM spatial patterns at six instances were derived from Landsat-8 OLI image reflectance, illustrating CDOM variations in the PRE influenced by various factors. Further analysis revealed that, in the PRE, tides and winds are the primary driving forces behind the spatial and temporal variability of CDOM. At present, the exploration of employing machine learning algorithms to infer CDOM concentrations in this region remains relatively limited; there-fore, with a higher R2 value, the machine learning model we established unveils fresh and novel results.
Coal mine drainage (CMD) discharged into surface waters results in serious environmental pollution risk to rivers, lakes, and reservoirs. Coal mine drainage generally contains a variety of organic matter and heavy metals due to coal mining activities. Dissolved organic matter (DOM) plays an important role in the physicochemical and biological processes of many aquatic ecosystems. In this study, the investigations were carried out in the dry and wet seasons in 2021 to assess the characteristics of DOM compounds in coal mine drainage and the CMD-affected river. The results indicated that the pH of CMD-affected river pressed close to coal mine drainage. Besides, coal mine drainage lowered DO by 36% and increased total dissolved solids by 19% in the CMD-affected river. Coal mine drainage decreased absorption coefficient a(350) and absorption spectral slope S275-295 of DOM in the CMD-affected river; hence, DOM molecular size increased with decreasing S275-295. Three-dimensional fluorescence excitation-emission matrix spectroscopy and parallel factor analysis identified humic-like C1, tryptophan-like C2, and tyrosine-like C3 in the CMD-affected river and coal mine drainage. DOM in the CMD-affected river mainly originated from microbial and terrestrial sources, with strong endogenous characteristics. The ultra-high-resolution Fourier transform ion cyclotron resonance mass spectrometry analysis revealed that coal mine drainage had a higher relative abundance of CHO (44.79%), with a higher unsaturation degree of DOM. Coal mine drainage decreased the AImod,wa, DBEwa (double bond equivalents), Owa, Nwa, and Swa values and increased the relative abundance of the O3S1 species with DBE of 3 and carbons number range of 15–17 at the CMD inlet to the river channel. Moreover, coal mine drainage with the higher protein content increased the protein content of water at the CMD inlet to the river channel and the downstream river. DOM compositions and proprieties in coal mine drainage were investigated to further understand the influence of organic matter on heavy metals in future study.
The environmental behavior of heavy metals in soil is significantly regulated by their binding with dissolved organic matter (DOM), which is affected by soil moisture contents. However, the mechanism of this interaction in soils with varying moisture is still not well understood. Using a combination of ultrafiltration, Cu(II) titration, and multispectral (ultraviolet-visible absorption, 3D fluorescence, Fourier transform infrared) analysis techniques, we studied the differences in the spectral characteristics and Cu(II) binding properties of soil dissolved organic matter (DOM) and its different molecular weight (MW) fractions with moisture gradients. We found that the abundance and spectral characters of soil DOM changed with increasing soil moisture, i.e., the increase in abundance while the decrease in aromaticity and humification index. The components of DOM, shown by Fluorescence region-integration (FRI) analysis, also changed, with an increase in the proportion of protein-like substances and a decrease of humic-like and fulvic-like substances. The overall Cu(II) binding potential of soil DOM diminished with increasing soil moisture, as indicated by the fluorescence parallel factor (PARAFAC) analysis. This is aligns with the changes in DOM composition, as the humic-like and fulvic-like fractions exhibited higher Cu(II) binding potential compared to the protein-like fractions. The low MW fraction of the MW-fractionated samples showed a stronger binding potential for Cu(II) compared to the high MW fraction. Finally, the active binding site of Cu(II) in DOM, as revealed by UV-difference spectroscopy and 2D-FTIR-COS analysis, decreased with increasing soil moisture, with the order of preferentially functional groups shifting from OH, NH, and CO to CN and CO. This study emphasizes the impact of moisture variations on the characteristics of DOM and its interaction with Cu(II), providing insight into the environmental fate of heavy metal contaminants in soil in areas with alternating land and water conditions.
Three-dimensional excitation–emission matrix (EEM) fluorescence spectroscopy is an important method for the identification of the occurrence, chemical composition, and source of atmospheric chromophores. However, current knowledge on the identification and interpretation of fluorescent components is mainly based on aquatic dissolved organic matter and might not be applicable to atmospheric samples. Therefore, this study comprehensively investigated EEM data of different types of strong light-absorbing organic compounds, water-soluble organic matter (WSOM) in different aerosol samples (combustion source samples and ambient aerosols), soil dust, and purified fulvic and humic acids supplemented by parallel factor (PARAFAC) modeling. The results demonstrated that organic compounds with high aromaticity and strong electron-donating groups generally present strong fluorescence spectra at longer emission wavelengths, whereas organic compounds substituted with electron-withdrawing groups have relatively weaker fluorescence intensity. In particular, aromatic compounds containing nitro groups (i.e., nitrophenols), which show strong absorption and are the major component of atmospheric brown carbon, exhibited no significant fluorescence. The EEM–PARAFAC method identified three fluorescent components (i.e., C1, C2, and C3) in ambient WSOM. Although EEM–PARAFAC-derived C1 (Ex/Em = 235, 270/330 nm) in ambient WSOM is generally considered to be protein-like groups, our findings suggested that it is mainly composed of aromatic acids, phenolic compounds, and their derivatives, with only traces of amino acids. C2 is associated with the atmospheric chemical reaction of biomass burning and/or biogenic organic molecules, with a relatively lower degree of oxidation, which are more abundant in Guangzhou WSOM (56 %–69 %). C3, in contrast, is mainly attributed to highly oxygenated organic molecules derived from soil and atmospheric aging processes and has a relatively higher contribution in Chuzhou WSOM (23 %). These findings provide new insights into the analysis of chemical properties and sources of atmospheric fluorophores using the EEM method.
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.
Lakes are hotspots for global carbon cycling, yet few studies have explored how rainstorms alter the flux, composition, and bio-lability of dissolved organic matter (DOM) in inflowing rivers using high-frequency monitoring. We conducted extensive campaigns in the watershed of Lake Taihu and made daily observations for three years in its two largest inflowing tributaries, River Dapu and River Yincun. We found higher DOC, bio-labile DOC (BDOC), and specific UV absorbance (SUVA254) levels in the northwestern inflowing regions compared with the remaining lake regions. DOC and BDOC increased during rainstorms in River Dapu, and DOC declined due to local dilution and BDOC increased during rainstorms in River Yincun. We found that rainstorms resulted in increased DOM absorbance a350, SUVA254, and humification index (HIX) and enhanced percentages of humic-like fluorescent components, %polycyclic condensed aromatic and %polyphenolic compounds as revealed from ultrahigh-resolution mass spectrometry (FT-ICR MS), while spectral slope (S275-295) and the percentages of protein-like C1 and C3 declined during rainstorms compared with other seasons. This can be explained by a combined flushing of catchment soil organic matter and household effluents. The annual inflows of DOC and BDOC to Lake Taihu were 1.15 ± 0.18 × 10⁴ t C yr⁻¹ and 0.23 ± 0.06 × 10⁴ t C yr⁻¹ from River Dapu and 2.92 ± 0.42 × 10³ t C yr⁻¹ and 0.53 ± 0.07 × 10³ t C yr⁻¹from River Yincun, respectively, and the fluxes of DOC and BDOC from both rivers increased during rainstorms. We found an elevated frequency of heavy rainfall and rainstorms in the lake watershed during the past six decades. We conclude that an elevated input of terrestrial organic-rich DOM with concurrent high aromaticity and high bio-lability from inflowing rivers is likely to occur in a future wetter climate.
Three-dimensional excitation-emission matrix (EEM) fluorescence spectroscopy is an important method for identification of occurrences, chemical composition, and sources of atmospheric chromophores. However, current knowledge on identification and interpretation of fluorescent components is mainly based on aquatic dissolved organic matter and might not be applicable to atmospheric samples. Therefore, this study comprehensively investigated EEM data of different types of strong light-absorbing organic compounds, water-soluble organic matter (WSOM) in different aerosol samples (combustion source samples and ambient aerosols), soil dust, and purified fulvic and humic acids by an EEM-parallel factor method. The results demonstrated that organic compounds with high aromaticity and strong electron-donating groups generally present strong fluorescence spectra at longer emission wavelength, whereas organic compounds substituted with electron-withdrawing groups have relatively weaker fluorescence intensity. In particular, aromatic compounds containing nitro groups (i.e., nitrophenols), which show strong absorption and are the major component of atmospheric brown carbon, exhibited no significant fluorescence. Although fluorescent component 1 (235, 270/330 nm) in ambient WSOM is generally considered as protein-like groups, our findings suggested that it is mainly composed of aromatic acids, phenolic compounds, and their derivatives, with only traces of amino acids. Principal component analysis and Pearson correlation coefficients between mass absorption efficiency at 365 nm (MAE365) and humification index (HIX), C1, C2, and C3 indicated that the highly aromatic and oxidized fluorescent component 3 may be an important contributor to the light-absorption capacity of ambient WSOM. These findings provide new insights for the analysis of chemical properties and sources of atmospheric fluorophores using the EEM method.
Dissolved organic matter (DOM) can strongly influence the behavior and risk of metal pollutants in aquatic ecosystems. However, a comprehensive study on the effects of DOM level and environmental factors on the binding of DOM with Pb(II) is lacking. This study examined the DOM-Pb(II) interaction in the river water under variable DOM level, pH, and major ions, using fluorescence excitation-emission matrices-parallel factor analysis (EEMs-PARAFAC). Four humic-like and one protein-like component were identified, and the abundant humic-like components showed higher Pb(II)-binding fractions (f) than the protein-like component. The f of PARAFAC components decreased while the conditional stability constants (logKM) increased for the diluted DOM, indicating the influence of DOM level on its metal binding. The DOM-Pb(II) interaction was sensitive to changes in pH, with generally higher f and lower logKM at the alkaline condition due to changes in the DOM conformation. The addition of major ions significantly decreased the fluorescence quenching by Pb(II), due to competitive effects and potential DOM conformation changes at elevated ions. Overall, our results show that the DOM-Pb(II) complexation is highly dependent on both the DOM properties and environmental factors, which have implications for optimizing the experimental conditions and for comparing the results in different environments.
Dissolved organic matter (DOM) is a central component in the biogeochemical cycles of marine and terrestrial carbon pools, and its structural features greatly impact the function and behavior of ecosystems. In this study, the Wanggang River, which is a seagoing river that passes through Yancheng City, was selected as the research object. Three-dimensional (3D) fluorescence spectral data and UV–visible spectral data were used for component identification and source analysis of DOM based on the PARAFAC model. The results showed that the DOM content of the Wanggang River during the dry season was significantly higher than during the wet season; the DOM content increased gradually from the upper to lower reaches; the proportion of terrigenous components was higher during the wet season than during the dry. UV–Vis spectral data a280 and a355 indicated that the relative concentrations of protein-like components in the DOM of the Wanggang River were higher than those of humic-like components, and the ratio of aromatic substances in the DOM of the Wanggang River water was higher during the wet season. The DOM in the Wanggang River was dominated by protein-like components (>60%), and the protein-like components were dominated by tryptophan proteins (>40%). This study showed that the temporal and spatial distributions of DOM in rivers can be accurately determined using 3D fluorescence spectroscopy combined with the PARAFAC model. This provides useful insight into the biogeochemical process of DOM in rivers of coastal areas.
To address the potential roles of atmospheric wet deposition in carbon cycling in coastal waters, a comprehensive study of the biogeochemical properties of dissolved organic matter (DOM) in precipitation and the resulting implication in a mariculture area in North Yellow Sea was conducted. The annual mean concentrations of dissolved organic carbon (DOC), chromophoric and fluorescent dissolved organic matter (CDOM and FDOM) were 1.52 ± 1.52 mg C L⁻¹, 0.36 ± 0.66 m⁻¹ and 0.38 ± 0.35 QSU, respectively. The concentrations of most DOM proxies exhibited significant negative correlations with the corresponding precipitation amount (R² = 0.15–0.40, P < 0.01), but the dilution effects became less significant when the precipitation amount exceeded 10.2, 10.7, 10.2 and 2.4 mm for DOC, CDOM, highly‑oxygenated and hypoxic structured humic-like substances, respectively. Seasonally, the dominant precipitation type in winter was snowfall, in which the DOM contained more high-molecular-weight compounds with higher aromaticity and humification degree, while the characteristics of DOM in intensive rainfall in summer were contrary to those in winter. The wet deposition flux of DOC to this region was estimated to be 6.31 × 10⁸ g C a⁻¹, which was 3.3 and 1.4 times that of the dry deposition and local riverine input, thereby contributing to 4.0 % of the DOC storage in the study area. In summer, the intensive input of DOC through wet deposition (0.43 g C m⁻²) to surface seawater could enrich its bioavailable DOC by 10.7 μmol L⁻¹, the complete aerobic decomposition of which would cause an obvious dissolved oxygen depletion in the surface seawater by 21.4 μmol L⁻¹, demonstrating the influence of wet deposition on summer deoxygenation in coastal waters.
Dissolved organic matter (DOM) is a ubiquitous group of organic compounds in rainwater that contributes to DOM pools and plays a vital role in the marine biogeochemical cycle. Here, we presented the rainwater DOM components and sources attribution (in δ¹³C-DOMSPE and δ¹⁵N-DOMSPE perspective) to an intensified anthropogenic influenced embayment, and discussed the biogeological effects of atmospheric DOM deposition. The results showed an apparent seasonal variation in the DOM concentration dominated by precipitation. Moreover, the excitation-emission matrix spectroscopy coupled a parallel factor analysis (PARAFAC) results revealed that five fluorescent components (C1-C5) of the rainwater DOM. C1 and C5 are protein-like DOM components and derived from biogenic emissions. The fluorescence intensity of C1 and C5 were significantly higher in the wet season, whereas C2 and C3, which are humic-like substances with higher molecular weights and aromatization, were mainly derived from fossil fuel combustion. The δ¹³C-DOMSPE and δ¹⁵N-DOMSPE results indicated that fossil fuel contributed approximately 80% of the DOM in the precipitation in the dry seasons, whereas the marine emission contribution of DOM was higher in the wet seasons due to the influence of air masses originating from the South China Sea. However, the maritime emissions only contributed 4% to the rainwater DOM. The deposition fluxes of dissolved organic carbon (DOC) and dissolved organic nitrogen (DON) were 799 mmol·C·m˗2·yr˗1 and 46 mmol·N·m˗2·yr˗1, respectively, and they played a substantial role for the DOM input flux of Daya Bay (28% of DOC and 12% of DON, respectively). Overall, our results suggest that atmospheric wet deposition represents a potentially critical source of organic carbon and nitrogen for coastal waters, particularly in intensified anthropogenically influenced embayments characterized by substantial monsoon shifts between seasons.
The formation of humic-like acids (HLAs) is an essential process for converting liquid digestate into organic soil amendments to enhance agricultural sustainability. The aim of this study was to investigate the impact of oxygen and/or MnO2 on the production of HLAs. Herein, abiotic humification performance of the digestate dissolved organic matter (DOM) is investigated with fluxes of air and N2 in the absence and presence of MnO2. Our results demonstrated that the fate of digestate DOM greatly depends on the oxidizing environment, the MnO2 enhanced nitrogen involved in the formation of HLAs. The synergistic effects of MnO2 and oxygen effectively improved the production of HLAs, and the corresponding component evolution was analyzed using spectroscopic evidence. The two-dimensional correlation spectroscopy results demonstrated that the reaction sequence of digestate DOM followed the order of protein-like substances, substances with an absorbance at 325 nm, substances with UV absorbance at 254 nm and HLAs. Additionally, excitation emission matrix fluorescence combined with parallel factor analysis (EEM-PARAFAC) showed that tryptophan-like C3 was more prone to transformation than tyrosine-like C2 and was responsible for the humification process. The substance with an absorbance at 325 nm was a reaction intermediate in the transformation process of protein-like substances to HLAs. The above findings can be used to promote the production of liquid fertilizer associated with carbon sequestration as well as the sustainable development of biogas production.
Fluorescence is widely used to detect functional groups and ions, and peptides are used in various fields due to their excellent biological activity. In recent years, research on fluorescent amino acids has intensified, especially with the natural fluorescent amino acids such as tryptophan (Trp), tyrosine (Tyr) and phenylalanine (Phe). They use their respective fluorophores to undergo π-π transition under excitation with light of a particular wavelength, and then release a large number of photons, which produce fluorescence. Thus, they are widely used as building units to enhance the fluorescence properties of other molecules. Peptide-based fluorescence technology has expanded the research in the field of biochemistry. Peptide-based fluorescence involving fluorescent amino acids not only retains the biocompatibility of peptides, but also relies on their fluorescent groups to enhance the fluorescent properties of the peptide itself, breaking the original limitations and connecting different fields to complement each other. This review summarizes the luminescence mechanism and fluorescent properties of the natural fluorescent amino acids and focuses on the fluorescence emission of peptides embedded with these fluorescent amino acids or fluorophores. Finally, we summarize the applications of peptide-based fluorescence in sensing drug release, metal ions and biomolecules, and present new challenges and expectations for the future development in this field. © The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2021.
Dissolved organic matter (DOM) in rivers is a critical regulator of the cycling and toxicity of pollutants and the behavior of DOM is a key indicator for the health of the environment. We investigated the sources and characteristics of DOM in surface water and sediment samples of the Wei River, China. Dissolved organic carbon (DOC) concentration and ultraviolet absorbance at 254 nm (UV254) increased in the surface water and were decreased in the sediment downstream, indicating that the source of DOM in the water differed from the sediment. Parallel factor (PARAFAC) analysis of the excitation-emission matrices (EEM) revealed the presence of terrestrial humus-like, microbial humus-like and tryptophan-like proteins in the surface water, whereas the sediment contained UVA humic-like, UVC humic-like and fulvic-like in the sediment. The DOM in the surface water and sediment were mainly derived from microbial metabolic activity and the surrounding soil. Surface water DOM displayed greater photodegradation potential than sediment DOM. PARAFAC analysis indicated that the terrestrial humic-like substance in the water and the fulvic-like component in the sediment decomposed more rapidly. These data describe the characteristics of DOM in the Wei River and are crucial to understanding the fluctuations in environmental patterns.
Palladium (Pd) is widely used in vehicle exhaust catalysts (VECs) to reduce toxic emissions from motor vehicles. The study aimed to quantitatively determine Pd content and water quality parameters, to analyze the variation differences and to explore the effect of water quality parameters on Pd content in the urban water environment system (wet deposition – rainfall runoff – receiving water body – estuary) of the city of Haikou, Hainan Island, China. The method used in this study included microwave digestion under high pressure and temperature, analysis by inductively coupled plasma mass spectrometry (ICP MS), quality control of the experimental procedure and guaranteed recovery(85% −125%). The results showed that the dissolved Pd average content in the urban water environment system was the highest in rainfall runoff (4.93 ng/L), followed by that in the receiving water body (4.56 ng/L), and it was the lowest in wet deposition (0.1 ng/L). The suspended Pd average content was the highest in the estuary (2.83 ng/L), followed by that in rainfall runoff (1.26 ng/L), and it was the lowest in wet deposition (6 × 10−4 ng/L). The particle-water partition ratio of the estuary Pd was the highest (1.26), followed by that of Pd in rainfall runoff (0.26). The particle-water partition ratio of the wet deposition Pd was the lowest (6 × 10−3). The dissolved Pd was correlated with the pH, Cl−, and total suspended solids (TSS) (correlation coefficient = 0.52, −0.68, 0.39, p < 0.05; regression coefficien = 1.27, −1.39, 0.01). The suspended Pd was only correlated with Cl− and TSS (correlation coefficient = −0.36, 0.76, p < 0.05; regression coefficien = −1.45, 0.01). Cl− and TSS were the most closely related to Pd in the water environment system. Although individual factors such as pH, Cl−, and TSS had certain migration and transformation effects on Pd in the wet deposition – rainfall runoff – receiving water body – estuary system, the probability of strong correlations was not high. In particular, Eh was not related to the dissolved nor suspended Pd content (correlation coefficient = 0.14, 0.13), which may be due to the synergistic effect of the multiple physical factors on Pd. This study was helpful to better understand the environmental behavior of Pd and provided important theoretical support for the prevention and protection against urban water environmental pollution.
In this chapter, we report the fundamental criteria and applications of two-dimensional correlation spectroscopy (2DCOS) in the environmental studies of the natural organic matter (NOM) and all its fractions like dissolved organic matter (DOM) and humic substances. The applications of the 2DCOS techniques to spectroscopic and chromatographic signals offer many peculiar advantages. 2DCOS allows to describe the dynamic evolutions, chemical reactions, and structural changes in the complex molecular systems of NOM exploiting the changes in correlations among the functional groups. The transition from the conventional mono-dimensional examination of spectra to the examination of 2DCOS spectra allows to improve the analytical resolution of data supporting a better interpretation of the chemical information present. In addition, 2DCOS plots also allow to describe the sequential order of the structural changes occurring during the processes of aggregation and degradation of NOM and during the evolution of other processes like interaction with pollutants and xenobiotics.
Dissolved organic matter (DOM) is widely present in aqueous environments and plays a significant role in pollutant mitigation and transformation. So far, excitation-emission matrix (EEM) fluorescence spectroscopy coupled with parallel factor analysis (PARAFAC) has been widely applied to quantify fluorescent DOM. However, this approach fails to provide accurate concentration of DOM when fluorescent contaminants exist. In this work, a new method, prior linear decomposition (PLD), is developed to solve this problem by introducing prior information, i.e., EEMs of DOM, into data decomposition. First, EEM of humic acid (HA) with different numbers of random Gaussian peaks are tested to confirm the robustness of PLD. The percentages for the relative errors within 5% are found to be 97.7% and 69% using PLD and PARAFAC, respectively. Then, the determination of mixture of HA with several contaminants is performed, validating the feasibility of DOM quantification and capability of contaminant diagnosis using PLD for synthetic water samples. Finally, DOM-containing natural water samples collected from a polluted lake, river and wastewater treatment plant (WWTP) are measured. The testing results confirm that PLD provides an accurate result with less evaluated error than PARAFAC and the EEMs of the contaminants can be inferred precisely. This work clearly demonstrates that PLD offers a robust approach for quantifying fluorescent DOM, which is of great significance in both natural and engineered aqueous environments.
Dissolved organic matter (DOM) exists ubiquitously in environments and plays critical roles in pollutant mitigation, transformation and organic geochemical cycling. Understanding its properties and environmental behaviors is critically important to develop water treatment processes and environmental remediation strategies. Generalized two-dimensional correlation spectroscopy (2DCOS), which has numerous advantages including enhancing spectral resolution and discerning specific order of structural change under an external perturbation, could be used as a powerful tool to interpret a wide range of spectroscopic signatures relating to DOM. A suite of spectroscopic signatures, such as UV-Vis, fluorescence, infrared, and Raman spectra that can be analyzed by 2DCOS, is able to provide additional structural information hiding behind the conventional one-dimensional spectra. In this paper, the most recent advances in 2DCOS applications for analyzing DOM-related environmental processes are reviewed, and the state-of-the-art novel spectroscopic techniques in 2DCOS are highlighted. Furthermore, the main limitations and requirements of current approaches for exploring DOM-related environmental processes and how these limitations and drawbacks can be addressed are explored. Finally, suggestions and new approaches are proposed to significantly advance the development of 2DCOS in analyzing the properties and behaviors of DOM in natural and engineered environments.
Chromophoric dissolved organic matter (CDOM) plays an important
role in the global carbon cycle and energy budget but is rarely studied in
seasonal snow. A field campaign was conducted across northwestern China from
January to February 2012, and surface snow samples were collected at 39 sites
in Xinjiang and Qinghai provinces. Absorption and fluorescence
spectroscopies,
along with chemical analysis, were used to investigate the optical
characteristics and potential sources of CDOM in seasonal snow. The abundance of CDOM, shown as the absorption coefficient at 280 nm,
aCDOM(280), and the spectral slope from 275 to 295 nm
(S275−295) ranged from 0.15 to 10.57 m−1 and
0.0129 to 0.0389 nm−1. The highest average
aCDOM(280) (2.30±0.52 m−1) was found in
Qinghai, and the lowest average S275−295 (0.0188±0.0015 nm−1) indicated that the snow CDOM in this region had a strongly
terrestrial characteristic. The lower values of aCDOM(280) were found at sites located to the north of the Tianshan Mountains and
northwestern Xinjiang along the border of China (0.93±0.68 m−1 and
0.80±0.62 m−1). Parallel factor (PARAFAC) analysis
identified three types of fluorophores that were attributed to two humic-like
substances (HULIS, C1 and C2) and one protein-like material (C3). C1 was
mainly from soil HULIS, C3 was a type of autochthonously labile organic
matter, while the potential sources of C2 were complex, including soil,
microbial activity, anthropogenic pollution, and biomass burning.
Furthermore, the regional variations of sources for snow CDOM were assessed
by analyses of chemical species (e.g., soluble ions), fluorescent components,
and air mass backward trajectories combined with satellite-derived active-fire
locations.
In view of the adverse effects of CDOM (chromophoric or colored dissolved organic matter) on in vivo algal pigment concentration measurements in natural water bodies, a CDOM influence correction method for algal concentration measurements based on three-dimensional fluorescence spectra is investigated. The three-dimensional fluorescence spectra of five common species of algae belonging to five categories, HA (humic acid), and natural water sampled from the Dongpu reservoir, Hefei were analyzed, and the spectral similarity of endogenous/exogenous CDOM in the algal fluorescence spectra region was compared. HA was selected to represent the CDOM spectrum group. The CDOM modified algal pigment concentration measurement method was developed using three-dimensional fluorescence spectra coupled with non-negative weighted least squares linear regression analysis. The results show that under the presence of CDOM interference factors, the recognition accuracy rate of Pyrrophyta, Bacillariophyta, Cyanophyta, and Chlorophyta increased 100%, 100%, 40%, and 40%, respectively. The average recovery rate of Cryptomonas, Pyrrophyta, Bacillariophyta, and Chlorophyta increased 162.7%, 50.3%, 106.4%, and 19.1%, respectively. In addition, the classification accuracy of Pyrrophyta, Bacillariophyta, Cyanophyta, Chlorophyta increased 83.9%, 100%, 38.2%, and 48%, respectively. This was concluded by comparing these results with the results of the algal pigment concentration measurement method without the CDOM modification. This study provides an experimental basis for the development of accurate phytoplankton fluorescence classification monitoring technology.
Parallel Factor Analysis (PARAFAC) was applied to assess the composition of chromophoric dissolved organic matter (CDOM) from the excitation-emission matrix (EEM) fluorescence spectra of the water samples collected from Meiliang Bay and the open area in Lake Taihu during a cyanobacterial bloom event, and three fluorescent components were identified: a tyrosine-like component, a tryptophan-like component and a humic-like component. Correlation analysis showed that the concentrations of chlorophyll-a(Chl.a) were significantly correlated with the fluorescence intensities of the three components, respectively, as well as the proportion of humic-like to total fluorescence intensities, suggesting that cyanobacteria might be an important source of CDOM and can greatly change the composition of CDOM in Lake Taihu. For further investigation, a simulation experiment was performed on the shore of Meiliang Bay. PARAFAC model showed that the number of components and the spectral characteristics of CDOM EEM data from the simulation experiment are similar in terms of the number of fluorescence peaks and their position to previously identified components in the water samples from Lake Taihu, except that the fluorescence peaks of humic acids showed a certain degree of blue shift, which suggested that endogenous humic substances were produced during the simulation experiment. It was found that the higher initial concentrations of Chl.a, the greater contribution of humic acids to total CDOM fluorescence intensity derived by the PARAFAC model. Moreover, at the end of the experiment, the ratios of humic substances to total fluorescent substances increased significantly in the two treatments with relatively high concentrations of cyanobacteria. Thus, the long-term outbreak of cyanobacterial blooms can significantly alter the composition of the CDOM in lakes, resulting in an increase of the proportion of humic-like substances.
Roxarsone (ROX) is an organoarsenic feed additive of increasing interest used in the poultry industry. Soybean responses to ROX stress were investigated in root exudates (REs) using two-dimensional correlation spectroscopy (2D-COS) with fluorescence and Fourier transform infrared spectra. Environmentally-relevant ROX concentrations caused negligible toxicity to crop growth and photosynthesis activity, but blackened soybean roots at high concentrations. 2D-COS analysis revealed that the protein-like fluorophore and C=C and C=O, aliphatic-OH, and polysaccharide C-O-H moieties in soybean REs were most sensitive to ROX stress. Hetero-spectral 2D-COS results suggested that aromatic, amide I, quinone, ketone, and aliphatic functional groups were the foundational components of protein-like and short wavelength excited humic-like fluorophores in soybean REs. Carboxyl and phenolic moieties were related to the long wavelength excited humic-like fluorophore. Overall, 2D-COS combined with molecular-based spectral analysis of REs provided an innovative approach to characterize the physiological responses of crops to contaminants at sub-lethal levels.
Mediterranean reservoirs receive frequent Saharan dust inputs with soil-derived organic compounds mostly during stratification periods, when run-off inputs are particularly limited. Here, we quantified and optically characterized the water-soluble organic carbon (WSOC) of the (dry and wet) atmospheric deposition in collectors located near three reservoirs from the Western Mediterranean Basin. In addition, we determined, during the stratification period, the WSOC contribution to the pool of dissolved organic carbon (DOC) and the influence of the chromophoric organic compounds from the dust on water transparency.
We found synchrony both in the WSOC atmospheric inputs among collectors and in the DOC dynamics among the three reservoirs. DOC concentrations and WSOC atmospheric inputs were positive and significantly correlated in the two reservoirs more sensitive to atmospheric inputs: the most oligotrophic reservoir (Quentar) and the reservoir with the highest ratio of surface area to mixing water depth (Cubillas). Nevertheless, WSOC atmospheric inputs, during the stratification period, represented less than 10 % of the total DOC pool, suggesting that indirect effects of dust inputs such as primary productivity stimulation may also induce these synchronic patterns. Chromophoric compounds from dust inputs can significantly reduce water transparency to ultraviolet radiation (UVR). The depths where UVR at λ = 320 nm is reduced to ten percent of surface intensity (Z10 %) decreased 15 cm (about 24 %) in Beznar, 17 cm (about 27 %) in Cubillas, and 43 cm (about 39 %) in Quéntar due to dust inputs.
Despite the rapidly increasing volume of research on the biological and
photochemical degradation of DOC (dissolved organic carbon) in aquatic environments, little is known
of the large-scale patterns in biologically and photochemically degradable DOC
(BDOC and PDOC, respectively) in continental watersheds, and on the links
that exist between these two key properties that greatly influence the flow
of carbon from continents to oceans. Here we explored the patterns in the
concentrations and proportions of BDOC and PDOC across hundreds of boreal
lakes, rivers and wetlands spanning a large range of system trophic status and
terrestrial influence, and compared the drivers of these two reactive pools
of DOC at the landscape level. Using standardized incubations of natural
waters, we found that the concentrations of BDOC and PDOC covaried across
all systems studied but were nevertheless related to different pools of
dissolved organic matter (DOM; identified by fluorescence analyses) in
ambient waters. Concentrations of nutrients and protein-like fluorescent DOM
(FDOM) explained nearly half of the variation in BDOC, whereas PDOC was
exclusively predicted by DOM optical properties, consistent with the
photochemical degradability of specific FDOM pools that we experimentally
determined. The concentrations of colored DOM (CDOM), which we use here as a
proxy of terrestrial influence, almost entirely accounted for the observed
relationship between FDOM and the concentrations of both BDOC and PDOC. The
concentrations of CDOM and of the putative biolabile fluorescence component
shifted from complete decoupling in clear-water environments to strong
coupling in darker streams and wetlands. This suggests a baseline
autochthonous BDOC pool fueled by internal production that is gradually
overwhelmed by land-derived BDOC as terrestrial influence increases across
landscape gradients. The importance of land as a major source of both
biologically and photochemically degradable DOC for continental watersheds
resulted in a partial coupling of those carbon pools in natural freshwaters,
despite fundamental contrasts in terms of their composition and regulation.
It is known that when crude Pinelliae rhizome and Pinelliae rhizoma preparatum are combined with Aconiti Radix Cocta respectively, the toxicity of the combination varies. However, the component's transformation between different compatibility have remained unclear.
In this paper, a novel approach using rapid resolution liquid chromatography-quadrupole time-of-flight mass spectrometry (RRLC-Q-TOF-MS) coupled with multivariate statistical analysis was established for exploring the influence of processing adjuvants (PAs) on the compatibility of Aconiti Radix Cocta and Pinelliae rhizome.
In order to obtain information about the representative markers between different groups, an exhaustive study of different protocols based on adding or removing different PAs step by step was carried out and the influence of PAs on compatibility was investigated.
It was found that lime can facilitate diester diterpenoid alkaloids with high toxicity in Aconiti Radix Cocta to be converted into low-toxic or non-toxic derivatives. Glycyrrhizae Radix et Rhizoma had no remarkable effect on the process.
The established method in this study will be of great significance to process research mechanism and study on traditional Chinese Medicine compatibility and clinical application.
Rapid industrialization and urbanization in developing countries has led to an increase in air pollution, along a similar trajectory to that previously experienced by the developed nations. In China, particulate pollution is a serious environmental problem that is influencing air quality, regional and global climates, and human health. In response to the extremely severe and persistent haze pollution experienced by about 800 million people during the first quarter of 2013 (refs 4, 5), the Chinese State Council announced its aim to reduce concentrations of PM2.5 (particulate matter with an aerodynamic diameter less than 2.5 micrometres) by up to 25 per cent relative to 2012 levels by 2017 (ref. 6). Such efforts however require elucidation of the factors governing the abundance and composition of PM2.5, which remain poorly constrained in China. Here we combine a comprehensive set of novel and state-of-the-art offline analytical approaches and statistical techniques to investigate the chemical nature and sources of particulate matter at urban locations in Beijing, Shanghai, Guangzhou and Xi'an during January 2013. We find that the severe haze pollution event was driven to a large extent by secondary aerosol formation, which contributed 30-77 per cent and 44-71 per cent (average for all four cities) of PM2.5 and of organic aerosol, respectively. On average, the contribution of secondary organic aerosol (SOA) and secondary inorganic aerosol (SIA) are found to be of similar importance (SOA/SIA ratios range from 0.6 to 1.4). Our results suggest that, in addition to mitigating primary particulate emissions, reducing the emissions of secondary aerosol precursors from, for example, fossil fuel combustion and biomass burning is likely to be important for controlling China's PM2.5 levels and for reducing the environmental, economic and health impacts resulting from particulate pollution.
Dissolved organic matter is a ubiquitous constituent of natural waters that plays key roles in several important processes. The fluorescence properties of DOM have been linked to its functionality, but these properties may vary with pH. In this study the Kohonen's self-organizing maps (SOM)were applied to EEMs of fresh dissolved organic matter (DOM) from three sources: senescent sugar-maple leaves and white spruce needles, and humified white spruce needles, over a pHrangeof ~4.5 – 12.5.SOM were applied to: raw EEMs, EEMs reduced in dimensionality by pre-processing using parallel factor analysis (PARAFAC), and PARAFAC loading proportions normalized to values at initial pH. Some separation of EEMs into source-based clusters was achieved in the SOM of raw EEMs, but commingling was apparent and evidence of changes over pH gradients was overshadowed. SOMs of PARAFAC component proportions demonstrated clear source-based clustering, and pH-based gradients were visible for DOM from senescent and humified spruce needles. Changes in optical properties were obvious over pH gradientsin the SOM of components normalized to starting condition.Component proportions decreased to values as low as 5 % of initial values for microbial humic-like peak M, and increased to as high as 278 % for a humic-like component. Tyrosine-like fluorescence increased to 112 % of initial over increasing pH in humified spruce leachates, but decreased to as low as 45 % in the other leachates.The combination of PARAFAC and SOMdrastically enhanced visualization and interpretability of pH-induced changesin DOM compared to either method alone.
Dissolved organic matter (DOM) of 27 prairie saline lake ecosystems was investigated in the Northern and Central Great Plains of the United States using absorbance, fluorescence, lignin concentration, and stable C isotope values. The majority of variation in DOM fluorescence among lakes was due to humic (peak C) and microbially formed (peak M) fluorescent components, which appear to be derived from autochthonous primary production. Strong correlations between peak M and nutrients allow us to model total phosphorus (TP) concentration using peak M fluorescence and chromophoric dissolved organic matter (CDOM) absorption. The rate of primary production (PP) was positively correlated with peak M fluorescence and negatively with lignin concentration. Lignin phenol yields in the DOM were generally smaller than those of most freshwater systems. δ13C values of dissolved organic carbon (DOC) ranged from −25.0‰ to −20.1‰ and were generally enriched relative to typical freshwaters (ca. −27‰). Terrestrial DOM is degraded in prairie lakes, spanning a gradient from mixotrophic to eutrophic, as determined by a color-nutrient model. The photodegradation of autochthonous DOM was significant: CO2 fluxes from these prairie lakes, modeled from peak M fluorescence, ranged from 5 to 228 mmol C m−2 d−1 (median, 37 mmol C m−2 d−1) and was similar to community respiration estimated from protein fluorescence (median, 50 mmol C m−2 d−1). The combined estimates were about 50% of the global mean total C release previously reported for saline lake ecosystems. The implication of these new results is that the global C release from saline lake ecosystems is likely underestimated.
Major fraction of marine dissolved organic matter (DOM) is biologically recalcitrant, however, the accumulation mechanism of recalcitrant DOM has not been fully understood. Here, we examine the distributions of humic-like fluorescent DOM, factions of recalcitrant DOM, and the level of apparent oxygen utilization in the Japan Sea. We find linear relationships between these parameters for the deep water (>200 m) of the Japan Sea, suggesting that fluorescent DOM is produced in situ in the Japan Sea. Furthermore, we find that the amount of fluorescent DOM at a given apparent oxygen utilization is greater in the deep water of the Japan Sea than it is in the North Pacific, where the highest level of fluorescent DOM in the open ocean was previously observed. We conclude that the repeated renewal of the deep water contributes to the accumulation of fluorescent DOM in the interior of the Japan Sea.
Background and Purpose
Stereotactic thalamotomy has been an effective surgical procedure in the treatment of medically refractory essential tremor (ET), however, little is known about the bilateral effects of unilateral ventralis intermedius (Vim) thalamotomy and Vim deep brain stimulation (DBS). We studied the lateralized effects of unilateral Vim thalamotomy and Vim DBS in ET patients.
Methods
Vim thalamotomy was performed in 6 patients and Vim DBS in 6. Patients were evaluated preoperatively and at 3 and 6 months postoperatively using the Clinical Rating Scale for Tremor (CRST).
Results
The contralateral Part A (tremor localization/severity rating) and Part B (specific motor tasks/function rating) subscores, and axial subscores of CRST significantly improved after unilateral Vim thalamotomy or Vim DBS. On the side ipsilateral to surgery, ET patients demonstrated no significant improvements in the Part A and Part B subscores of CRST. The Part C (functional disabilities resulting from tremor) subscores and total scores of CRST were significantly improved after surgery.
Conclusions
Vim thalamotomy and DBS may be equally effective for the management of contralateral and axial tremor in ET patients, but both interventions may not improve tremor on the side ipsilateral to surgery.
The fluorescence of dissolved organic matter (DOM) is suppressed by a phenomenon of self-quenching known as the inner filter effect (IFE). Despite widespread use of fluorescence to characterize DOM in surface waters, the advantages and constraints of IFE correction are poorly defined. We assessed the effectiveness of a commonly used absorbance-based approach (ABA), and a recently proposed controlled dilution approach (CDA) to correct for IFE. Linearity between corrected fluorescence and total absorbance (A(Total); the sum of absorbance at excitation and emission wavelengths) across the full excitation-emission matrix (EEM) in dilution series of four samples indicated both ABA and CDA were effective to an absorbance of at least 1.5 in a 1 cm cell, regardless of wavelength positioning. In regions of the EEMs where signal to background noise (S/N) was low, CDA correction resulted in more variability than ABA correction. From the ABA algorithm, the onset of significant IFE (>5%) occurs when absorbance exceeds 0.042. In these cases, IFE correction is required, which was the case for the vast majority (97%) of lakes in a nationwide survey (n = 554). For highly absorbing samples, undesirably large dilution factors would be necessary to reduce absorbance below 0.042. For rare EEMs with A(Total) > 1.5 (3.0% of the lakes in the Swedish survey), a 2-fold dilution is recommended followed by ABA or CDA correction. This study shows that for the vast majority of natural DOM samples the most commonly applied ABA algorithm provides adequate correction without prior dilution.
An online repository of published organic fluorescence spectra has been developed, which can be searched for quantitative matches with any set of unknown spectra. It fills a critical gap by increasing access to measured and modelled (PARAFAC) spectra, and linking across studies and systems to reveal "global" fluorescence trends. Fluorescence spectroscopy offers an inexpensive, non-destruc-tive method for obtaining sensitive measurements of a diverse group of organic compounds that contain uorophores. This technology is now widely used to characterise naturally-occur-ring organic matter in natural and articial aquatic systems with the purpose of understanding how the uorescent frac-tion of carbon is partitioned between different organic matter fractions, and inferring the processes responsible for its formation and removal. 1–5 With Excitation–Emission Matrix (EEM) spectroscopy, uorescence emission is measured over a range of excitation wavelengths to produce three-dimensional uorescence landscapes (Fig. 1). Each EEM represents total uorescence from an unknown number of underlying uo-rophores which in ideal conditions uoresce independently following Beers Law, but under non-ideal conditions may interact. 6 Over the past ten years it has become common practice to decompose EEM datasets mathematically using PARAllel FACtor analysis (PARAFAC). 7–9 PARAFAC reduces the EEM dataset into a small number of building blocks – referred to as 'underlying components' – each with a characteristic excitation and emission spectrum (Fig. 1). Each EEM in a dataset is modelled by a simple recipe in which the same building blocks are combined in varying amounts, reecting their variable concentrations. There are now well over 100 published PARAFAC models of dissolved and natural organic matter (both referred to hereaer as NOM) and over 500 published PARAFAC components. 9,10
Inland waters transport large amounts of dissolved organic matter (DOM) from terrestrial environments to the oceans, but DOM also reacts on route, with substantial water column losses by mineralization and sedimentation. For DOM transformations along the aquatic continuum, lakes play an important role as they retain waters in the landscape allowing for more time to alter DOM. Although DOM losses are significant at the global scale, little is known about how the reactivity of DOM varies across landscapes and climates. The reactivity of DOM is inherently linked to its chemical composition. We used fluorescence spectroscopy to explore DOM quality from 560 lakes distributed across Sweden, and encompassed a wide climatic gradient typical of the boreal ecozone. Six fluorescence components were identified using parallel factor analysis (PARAFAC). The intensity and relative abundance of these components were analyzed in relation to lake chemistry, catchment and climatic characteristics. Land cover, particularly the percentage of water in the catchment, was a primary factor explaining variability in PARAFAC components. Likewise, lake water residence time influenced DOM quality. These results suggest that processes occurring in upstream water bodies, in addition to the lake itself, have a dominant influence on DOM quality. PARAFAC components with longer emission wavelengths, or red-shifted components, were most reactive. In contrast, protein-like components were most persistent within lakes. Generalized characteristics of PARAFAC components based on emission wavelength could ease future interpretation of fluorescence spectra. An important secondary influence on DOM quality was mean annual temperature, which ranged between -6.2 and +7.5 °C. These results suggest that DOM reactivity depends more heavily on the duration of time taken to pass through the landscape, rather than temperature. Projected increases to runoff in the boreal region may force lake DOM towards a higher overall amount and proportion of humic-like substances. This article is protected by copyright. All rights reserved.
Many alpine areas are experiencing deglaciation, biogeochemical changes
driven by temperature rise, and changes in atmospheric deposition. There
is mounting evidence that the water quality of alpine streams may be
related to these changes, including rising atmospheric deposition of
carbon (C) and nutrients. Given that barren alpine soils can be severely
C limited, atmospheric deposition sources may be an important source of
C and nutrients for these environments. We evaluated the magnitude of
atmospheric deposition of C and nutrients to an alpine site, the Green
Lake 4 catchment in the Colorado Rocky Mountains. Using a long-term
dataset (2002-2010) of weekly atmospheric wet deposition and snowpack
chemistry, we found that volume weighted mean dissolved organic carbon
(DOC) concentrations were 1.12 ± 0.19 mg l-1, and
weekly concentrations reached peaks as high at 6-10 mg l-1
every summer. Total dissolved nitrogen concentration also peaked in the
summer, whereas total dissolved phosphorus and calcium concentrations
were highest in the spring. To investigate potential sources of C in
atmospheric deposition, we evaluated the chemical quality of dissolved
organic matter (DOM) and relationships between DOM and other solutes in
wet deposition. Relationships between DOC concentration, fluorescence,
and nitrate and sulfate concentrations suggest that pollutants from
nearby urban and agricultural sources and organic aerosols derived from
sub-alpine vegetation may influence high summer DOC wet deposition
concentrations. Interestingly, high DOC concentrations were also
recorded during "dust-in-snow" events in the spring, which may reflect
an association of DOM with dust. Detailed chemical and spectroscopic
analyses conducted for samples collected in 2010 revealed that the DOM
in many late spring and summer samples was less aromatic and
polydisperse and of lower molecular weight than that of winter and fall
samples. Our C budget estimates for the Green Lake 4 catchment
illustrated that wet deposition (9.9 kg C ha-1
yr-1) and dry deposition (6.9 kg C ha-1
yr-1) were a combined input of approximately 17 kg C
ha-1 yr-1, which could be as high as 24 kg C
ha-1 yr-1 in high dust years. This atmospheric C
input approached the C input from microbial autotrophic production in
barren soils. Atmospheric wet and dry deposition also contributed 4.3 kg
N ha-1 yr-1, 0.15 kg P ha-1
yr-1, and 2.7 kg Ca2+ ha-1
yr-1 to this alpine catchment.
PARAllel FACtor analysis (PARAFAC) is increasingly used to decompose fluorescence excitation emission matrices (EEMs) into their underlying chemical components. In the ideal case where fluorescence conforms to Beers Law, this process can lead to the mathematical identification and quantification of independently varying fluorophores. However, many practical and analytical hurdles stand between EEM datasets and their chemical interpretation. This article provides a tutorial in the practical application of PARAFAC to fluorescence datasets, demonstrated using a dissolved organic matter (DOM) fluorescence dataset. A new toolbox for MATLAB is presented to support improved visualisation and sensitivity analyses of PARAFAC models in fluorescence spectroscopy.
We present the results of a mesocosm experiment investigating the production and utilization of autochthonous dissolved organic matter (DOM) by the plankton community under different inorganic nutrient regimes. Fluorescence spectroscopy combined with parallel factor analysis was applied to study the dynamics of autochthonous DOM. Seven independent fluorescent fractions were identified, differing in their spectral characteristics, production rates, and sensitivity to photochemical and microbial degradation processes. Five different humic fractions, a marine protein, and a peptide fluorescence were found. The five humic fractions were produced microbially, with the greatest production occurring under combined Si- and P-limiting conditions. The two proteinaceous fractions were produced during exponential growth of phytoplankton, irrespective of biomass composition. Photodegradation was an important sink for the microbially derived humic material, and the marine protein material was susceptible to both photo- and microbial degradation. © 2005, by the American Society of Limnology and Oceanography, Inc.
Sea ice plays a dynamic role in the air-sea exchange of CO2. In addition to abiotic inorganic carbon fluxes, an active microbial community produces and remineralizes organic carbon, which can accumulate in sea ice brines as dissolved organic matter (DOM). In this study, the characteristics of DOM fluorescence in Antarctic sea ice brines from the western Weddell Sea were investigated. Two humic-like components were identified, which were identical to those previously found to accumulate in the deep ocean and represent refractory material. Three amino-acid-like signals were found, one of which was unique to the brines and another that was spectrally very similar to tryptophan and found both in seawater and in brine samples. The tryptophan-like fluorescence in the brines exhibited intensities higher than could be explained by conservative behavior during the freezing of seawater. Its fluorescence was correlated with the accumulation of nitrogen-rich DOM to concentrations up to 900 μmol L -1 as dissolved organic carbon (DOC) and, thus, potentially represented proteins released by ice organisms. A second, nitrogen-poor DOM fraction also accumulated in the brines to concentrations up to 200 μmol L-1 but was not correlated with any of the fluorescence signals identified. Because of the high C:N ratio and lack of fluorescence, this material is thought to represent extracellular polymeric substances, which consist primarily of polysaccharides. The clear grouping of the DOM pool into either proteinaceous or carbohydrate-dominated material indicates that the production and accumulation of these two subpools of DOM in sea ice brines is, to some extent, decoupled.
Drinking water lakes are threatened globally and therefore in need of protection. To date, few studies have been carried out to investigate how the composition and dynamics of chromophoric dissolved
organic matter (CDOM) in drinking water lakes are influenced by inflow rate. Such CDOM can lead to
unpleasant taste and odor of the water and produce undesirable disinfection byproducts during drinking
water treatment. We studied the drinking water Lake Qiandao, China, and found that the concentrations of
suspended particulate matter (SPM) in the lake increased significantly with inflow rate (p < 0.001).
Similarly, close relationships between inflow rate and the CDOM absorption coefficient at 350 nm a(350)
and with terrestrial humic-like fluorescence C3 and a negative relationship between inflow rate and the
first principal component (PC1) scores, which, in turn, were negatively related to the concentrations and
relative molecular size of CDOM (p < 0.001), i.e. the concentration and molecular size of CDOM entering
the lake increased proportionately with inflow rate. Furthermore, stable isotopes (δD and δ18O) were depleted in the upstream river mouth relative to downstream remaining lake regions, substantiating that
riverine CDOM entering the lake was probably driven by inflow rate. This was further underpinned by
remarkably higher mean chlorophyll-a and in situ measured terrestrial CDOM fluorescence (365/480 nm)
and apparent oxygen utilization (AOU), and notably lower mean PC1 and CDOM spectral slope (S275-295)
recorded in the upstream river mouth than in the downstream main lake area. Strong negative correlations
between inflow rate and a(250):a(365), S275-295, and the spectral slope ratio (SR) implied that CDOM input
to the lake in rainy period was dominated by larger organic molecules with a more humic-like character.
Rainy period, especially rainstorm events, therefore poses a risk to drinking water safety and requires
higher removal efficiency of CDOM during drinking water treatment processes
Computation of 2D Spectra from Discrete DataUnevenly Spaced DataDisrelation SpectrumComputational Efficiency
Chemical characteristics of PM2.5 in Xi'an in wintertime of 2006, 2008, and 2010 were investigated. Markers of OC2, EC1, and NO3-/SO42- ratio were calculated to investigate the changes in PM2.5 emission sources over the 5-year period. Positive matrix factorization (PMF) model was used to identify and quantify the main sources of PM2.5 and their contributions. The results showed that coal combustion, motor vehicular emissions, fugitive dust, and secondary inorganic aerosol accounted for more than 80% of PM2.5 mass. The importance of these major sources to the PM2.5 mass varied yearly: coal combustion was the largest contributor (31.2%±5.2%), followed by secondary inorganic aerosol (20.9%±5.2%) and motor vehicular emissions (19.3%±4.8%) in 2006; the order was still coal combustion emissions (27.6%±3.4%), secondary inorganic aerosol (23.2%±6.9%), and motor vehicular emissions (20.9%±4.6%) in 2008; while coal combustion emission further decreased (24.1%±3.1%) with fugitive dust (19.4%±5.5%) increasing in 2010. The changes in PM2.5 chemical compositions and source contributions can be attributed to the social and economic developments in Xi'an, China, including energy structure adjustment, energy consumption, the expansion of civil vehicles, and the increase of urban construction activities.
Daily PM2.5 samples were collected at an urban site in Beijing during four one-month periods in 2009-2010, with each period in a different season. Samples were subject to chemical analysis for various chemical components including major water-soluble ions, organic carbon (OC) and water-soluble organic carbon (WSOC), element carbon (EC), trace elements, anhydrosugar levoglucosan (LG), and mannosan (MN). Three sets of source profiles of PM2.5 were first identified through positive matrix factorization (PMF) analysis using single or combined biomass tracers - non-sea salt potassium (nss-K(+)), LG, and a combination of nss-K(+) and LG. The six major source factors of PM2.5 included secondary inorganic aerosol, industrial pollution, soil dust, biomass burning, traffic emission, and coal burning, which were estimated to contribute 31±37%, 39±28%, 14±14%, 7±7%, 5±6%, and 4±8%, respectively, to PM2.5 mass if using the nss-K(+) source profiles, 22±19%, 29±17%, 20±20%, 13±13%, 12±10%, and 4±6%, respectively, if using the LG source profiles, and 21±17%, 31±18%, 19±19%, 11±12%, 14±11%, and 4±6%, respectively, if using the combined nss-K(+) and LG source profiles. The uncertainties in the estimation of biomass burning contributions to WSOC due to the different choices of biomass burning tracers were around 3% annually and up to 24% seasonally in terms of absolute percentage contributions, or on a factor of 1.7 annually and up to a factor of 3.3 seasonally in terms of the actual concentrations. The uncertainty from the major source (e.g. industrial pollution) was on a factor of 1.9 annually and up to a factor of 2.5 seasonally in the estimated WSOC concentrations.
As the widespread application of online instruments penetrates the environmental fields, it is interesting to investigate the sources of fine particulate matter (PM2.5) based on the data monitored by online instruments. In this study, online analyzers with 1-h time resolution were employed to observe PM2.5 composition data, including carbon components, inorganic ions, heavy metals and gas pollutants, during a summer in Beijing. Chemical characteristics, temporal patterns and sources of PM2.5 are discussed. On the basis of hourly data, the mean concentration value of PM2.5 was 62.16±39.37μgm(-3) (ranging from 6.69 to 183.67μgm(-3)). The average concentrations of NO3(-), SO4(2-), NH4(+), OC and EC, the major chemical species, were 15.18±13.12, 14.80±14.53, 8.90±9.51, 9.32±4.16 and 3.08±1.43μgm(-3), respectively. The concentration of PM2.5 varied during the online-sampling period, initially increasing and then subsequently decreasing. Three factor analysis models, including principal component analysis (PCA), positive matrix factorization (PMF) and Multilinear Engine 2 (ME2), were applied to apportion the PM2.5 sources. Source apportionment results obtained by the three different models were in agreement. Four sources were identified in Beijing during the sampling campaign, including secondary sources (38-39%), crustal dust (17-22%), vehicle exhaust (25-28%) and coal combustion (15-16%). Similar source profiles and contributions of PM2.5 were derived from ME2 and PMF, indicating the results of the two models are reasonable. The finding provides information that could be exploited for regular air control strategies.
Atmospheric bioaerosol particles were collected using a bioaerosol sampler from Oct. 2013 to Aug. 2014 in the coastal region of Qingdao. The total microbes were measured using an epifluorescence microscope after staining with DAPI (4',6-diamidino-2-phenylindole). The concentration of total airborne microbes showed seasonal variation, with the highest value in winter and the lowest in summer. The mean concentration of total microbes was 6.55×10(5)Cells/m(3) on non-hazy days. The total microbe concentration increased to 7.09×10(5) and 9.00×10(5)Cells/m(3) on hazy and foggy days, respectively. The particle sizes of the total microbes presented a bimodal distribution on sunny days, with one peak at 1.1-2.1μm and another at 4.7-7.0μm. The size distribution of total microbes showed an increase in the fine fraction on hazy days and an increase in the coarse fraction on foggy days. However, the size distribution became unimodal during a heating period. Spearman correlation analysis showed that temperature and O3 had a significant negative correlation with the airborne microbe concentration, while PM2.5, SO2, NO2, CO and the air quality index (AQI) had significant positive correlations with the airborne microbe concentration during hazy days. The increased number of airborne microbes will affect the air quality on hazy days.
A novel semi-continuous excitation emission matrix (EEM) fluorescence and absorbance monitoring system has been developed. Full EEMs were collected simultaneously with absorbance spectra every 20 min during 24 h solar-simulated irradiation experiments, and the kinetic change of fluorescence of Suwannee River natural organic matter IHSS standard material (SRNOM) at various pH values was investigated. Parallel factor analysis (PARAFAC) was then used to isolate the photo-labile and pH-influenced fluorescent components of SRNOM. Kinetic analysis showed increasing rates of fluorescence loss with increasing pH. This has significant implications for the photo-degradation of dissolved natural organic matter during estuarine mixing, when large increases of pH are common. The influence of pH on fluorescence and photo-degradation kinetics emphasizes the need for pH to be monitored and accurately controlled during laboratory experiments. It is also highly recommended that when constructing PARAFAC models or monitoring changes in fluorescence data between samples of different origins, that the pH be held constant to remove any potential artifacts or misinterpretation of data.
Copyright © 2015 Elsevier Ltd. All rights reserved.
The biochemical composition of dissolved organic matter (DOM) strongly influences its biogeochemical role in freshwater ecosystems, yet DOM composition measurements are not routinely incorporated into ecological studies. To date, the majority of studies of freshwater ecosystems have relied on bulk analyses of dissolved organic carbon and nitrogen to obtain information about DOM cycling. The problem with this approach is that the biogeochemical significance of DOM can only partially be elucidated using bulk analyses alone because bulk measures cannot detect most carbon and nitrogen transformations. Advances in fluorescence spectroscopy provide an alternative to traditional approaches for characterizing aquatic DOM, and allow for the rapid and precise characterization of DOM necessary to more comprehensively trace DOM dynamics. It is within this context that we discuss the use of fluorescence spectroscopy to provide a novel approach to tackling a long-standing problem: understanding the dynamics and biogeochemical role of DOM. We highlight the utility of fluorescence characterization of DOM and provide examples of the potential range of applications for incorporating DOM fluorescence into ecological studies in the hope that this rapidly evolving technique will further our understanding of the biogeochemical role of DOM in freshwater ecosystems.
Dissolved organic matter (DOM) is known to form strong complexes with heavy metals and thus governs the distribution, toxicity, bioavailability, and the ultimate fate of heavy metals in the environment. The relevant aspects of metal-organic interactions remain unclear because the metal binding functionalities in DOM are substantially non-uniform and the availability of the models is limited. In this work, two-dimensional correlation spectroscopy (2DCOS) integrated with synchronous fluorescence and infrared absorption spectroscopy was used to explore the binding process of copper to DOM. A series of heterogeneous binding sites in humic acid (HA), a representative DOM, and the subsequent subtle changes of these sites within the molecular interactions were elucidated by 2DCOS method. The band assignments and the correspondence between the results obtained by two spectral probes (synchronous fluorescence and infrared absorption spectra) were verified by hetero-2DCOS. Our results showed that, during the copper binding process, the carboxyl and polysaccharide groups gave the fastest responses to copper binding. Then, fluorescence quencing of fluorescent humic-like moieties occurred with vibrational change of the related functionalities, i.e., phenolic and aryl carboxylic groups, which further induces the fluorescence quenching of fulvic-like fractions. Finally, small amounts of amide and aliphatic groups participated in the copper binding after the fluorescence of the protein-like fraction decreased. With these promising results, a comprehensive picture of structural changes of HA during copper binding process was developed, highlighting the superior potential of 2D-heterospectral correlation spectroscopy in studying complex interactions in environment.
We aim to identify the key success factors of the Japanese business intelligence (BI) market, by analyzing the “product architectures” of the winners' BI software and consulting services. Market share is used as the definition of win. Results highlight the following features of winners' architectures: the software and consulting services' architectures were “closed” at first, and consulting services' architecture changed from “closed” to “open” first, followed by that of the software. The losers' product architectures had the opposite dynamics: the software's architecture became “open” first, followed by that of the consulting services. These results indicate that differences in the dynamics of product architectures could be the dominant success factors in the BI market.
Heterogeneous distributions of copper-binding sites within extracellular polymeric substances (EPS) were examined by using a fluorescence quenching titration method combined with two-dimensional correlation spectroscopy (2D-COS). The binding properties were compared for two types of the EPS extracted from the sludge formed under aerobic and anaerobic conditions. The quenching behaviors of the synchronous fluorescence spectra upon the addition of copper were similar for the two EPS. Protein-like fluorescence was substantially quenched by the copper addition while the changes of fulvic- and humic-like fluorescence were not obvious, suggesting that protein molecules were largely involved in binding copper for both EPS types. The logarithmic stability constants calculated at the wavelengths corresponding to the highest peaks were 4.73 and 4.22 for the aerobic and the anaerobic EPS, respectively. However, the 2D-COS revealed the possibility of the presence of multiple sites for copper binding within the protein-like fluorescent structures of the anaerobic EPS. No such heterogeneous distribution in the binding sites was found for the aerobic EPS. For the anaerobic EPS, the spectral change preferentially occurred in the wavelength order of 297 nm → 290 nm → 268 nm, exhibiting a range of the logarithmic values from 4.43 to 4.13. The extent of the binding affinities exactly followed the sequential orders interpreted from the 2D-COS results. Our study clearly demonstrated that fluorescence quenching combined with 2D-COS could be successfully used to provide a better understanding of the chemical heterogeneity associated with metal-binding sites within EPS.
Despite the wide use of absorption and fluorescence spectroscopy for tracking the sources of dissolved organic matter (DOM), there are limited studies on evaluating their source discrimination capabilities at variable solution chemistry (pH, NaCl, Ca(2+), and DOM concentration). For this study, we compared the applicability of several well-known spectroscopic indices via end member mixing analysis based on two contrasting DOM sources (Suwannee River fulvic acid and an algal DOM). The absorption coefficients and the intensities of fluorescent components from parallel factor analysis (PARAFAC) showed linear relationships with increasing algal carbon fraction in the mixture of the two DOMs. In contrast, although they still behaved conservatively, spectral ratio indices such as spectral slopes, ratios of PARAFAC components, humification index, and fluorescence index changed in nonlinear patterns with the mixing ratios. The indices based on PARAFAC results exhibited strong discrimination capabilities, as indicated by high susceptibility to the changes in DOM sources relative to the analytical precision. While variable NaCl concentrations had limited effects, most fluorescence indices were considerably affected by other solution chemistry such as pH, Ca(2+), and DOM level. Our study demonstrated that the applicability of the source discrimination indices should be critically examined especially in the environments with notable changes in the solution chemistry. The solution chemistry effects could be minimized by adjusting samples to a constant condition prior to the measurements or otherwise the effects should be fully taken into account in interpreting the field observations.
Organic matter (OM) causes many problems in drinking water treatment. It is difficult to monitor OM concentrations and character during treatment processes due to its complexity. Fluorescence spectroscopy is a promising tool for online monitoring. In this study, a unique dataset of fluorescence excitation emission matrixes (EEMs) (n = 867) was collected from all treatment stages of five drinking water treatment plants (WTPs) situated in diverse locations from subtropical to temperate climate. The WTPs incorporated various water sources, treatment processes and OM removal efficiencies (DOC removal 0%-68%). Despite these differences, four common fluorescence PARAFAC components were identified for characterisation of OM concentration and treatability. Moreover, fluorescence component ratios showed site-specific statistically significant correlations with OM removal, which contrasted with correlations between specific UV absorbance at 254 nm (SUVA) and OM removal that were not statistically significant. This indicates that use of fluorescence spectroscopy may be a more robust alternative for predicting DOC removal than UV spectroscopy. Based on the identified fluorescence components, four optical locations were selected in order to move towards single wavelength online OM monitoring.
PM2.5 samples have been collected in urban Shanghai, China, during April (spring), July (summer), October (autumn) 2012, and January (winter) 2013, respectively. Seventeen organosulfates (OSs) derived from isoprene, α-/β-pinene, and presumably aromatic precursors were quantified using a high-performance liquid chromatogram coupled to a triple quadrupole mass spectrometer. During our sampling days, the total concentration of detected OSs ranged between 0.0209 and 60.8 ng m−3 (sodium octyl sulfate and benzyl sulfate as standards). The seasonal average concentration of OSs was the highest (26.2 ng m−3) in summer 2012 and the lowest (0.510 ng m−3) in spring 2012, accounting for 0.471‰ and 0.00965‰ of the corresponding PM2.5 mass, respectively. Isoprene- and α-/β-pinene-derived OSs showed a clear seasonal fluctuation with a peak in summer, whereas OS derived from aromatic precursors was less variable in most seasons. The share of aromatic OS in the total measured OSs was the highest (63.5%) in winter 2013 and the lowest (2.94%) in summer 2012, suggesting that aromatic OS could serve as an important component of the OS species in urban Shanghai. In addition, a number of OSs demonstrated distinct diurnal profiles, reflecting diverse formation mechanisms with multiple atmospheric oxidants in an urbanized area like Shanghai.
Particulate matter (PM) air pollution poses a formidable public health threat to the city of Beijing. Among the various hazards of PM pollutants, microorganisms in PM2.5 and PM10 are thought to be responsible for various allergies and for the spread of respiratory diseases. While the physical and chemical properties of PM pollutants have been extensively studied, much less is known about the inhalable microorganisms. Most existing data on airborne microbial communities using 16S or 18S rRNA gene sequencing to categorize bacteria or fungi into the family or genus levels do not provide information on their allergenic and pathogenic potentials. Here we employed metagenomic methods to analyze the microbial composition of Beijing's PM pollutants during a severe January smog event. We show that with sufficient sequencing depth, airborne microbes including bacteria, archaea, fungi, and dsDNA viruses can be identified at the species level. Our results suggested that the majority of the inhalable microorganisms were soil-associated and nonpathogenic to human. Nevertheless, the sequences of several respiratory microbial allergens and pathogens were identified and their relative abundance appeared to have increased with increased concentrations of PM pollution. Our findings may serve as an important reference for environmental scientists, health workers, and city planners.
Rainwater is not only a critical source of drinking and agricultural water but it plays a key role in the fate and transport of contaminants through their removal by wet deposition. Rainwater is a complex mixture of organic compounds yet despite its importance its spatial and temporal variability are not well understood and less than 50% of the organic matter has been characterized. In-depth analytical approaches were used in this study to characterize the seasonal variation in rainwater composition. Rainwater samples were collected over a one-year period in Scarborough, Ontario, Canada. The seasonal variation of atmospheric organic carbon (AOC) in rainwater was analyzed by excitation-emission matrix spectroscopy (EEMs), 1D and 2D NMR with compound identification by spectral database matching, GC–MS, FT-ICR-MS, and GC × GC-TOFMS. This combination of techniques provided four complementary datasets, with less than 10% overlap, of anthropogenic and biogenic AOC. NMR with database matching identified over 100 compounds, primarily carboxylic acids, carbohydrates, and nitrogen-containing compounds. GC × GC-TOFMS analysis identified 344 compounds in two rain events with 33% of the compounds common to both events. FT-ICR-MS generated a seasonally dependent profile of 1226–1575 molecular ions of CHO, CHOS, and CHON elemental composition. FT-ICR-MS and GC × GC-TOFMS datasets were compared using van Krevelen diagrams (H/C vs. O/C), the H/C ratio vs. mass/charge (m/z), and the carbon oxidation state/carbon number matrix. Fluorescence patterns were correlated with NMR results resulting in the identification one seasonally-dependent component of chromophoric dissolved organic matter (CDOM). This study demonstrated the importance of using of an integrated analytical approach to monitor the compositional variation of AOC.
The goal of the research presented here was to determine the impact of photochemistry on the abundance and spectral qualities of chromophoric dissolved organic matter (CDOM) in precipitation. The relationship between sunlight and CDOM in rainwater was complex with both production and photobleaching of optical properties occurring simultaneously in different regions of the fluorescence excitation emission spectra (EEMs) over relatively short time scales. Spectral slope was inversely correlated with the observed changes in total integrated fluorescence suggesting that photo-induced modifications in the molecular weight of CDOM were occurring along with fluctuations in its optical properties. Atmospheric condensate collected near a high traffic roadway had a response to sunlight similar to authentic rainwater suggesting some fraction of the CDOM in atmospheric waters is derived from local anthropogenic gas phase sources. There was a dramatic increase in fluorescence in two samples photolyzed with photosynthetically active radiation only (PAR; 400–700 nm) compared to analogous samples exposed to full spectrum sunlight indicating that this less energetic light is capable of producing photochemically labile compounds in rainwater. The observed temporal variability in the molecular level response of CDOM to sunlight is important because it may alter the spectral attenuation and the amount of solar radiation reaching the earth’s surface.
The distributions of fluorescent components in dissolved organic matter (DOM) from Ise Bay, Japan, were determined by excitation emission matrix (EEM) fluorescence spectroscopy combined with parallel factor analysis (PARAFAC). Three terrestrial humic-like, one marine humic-like, and three non-humic-like fluorescent components were identified by PARAFAC, and the environmental dynamics of individual fluorescent components in the bay area were evaluated. The observed linear relationships between salinity and abundance of two of the three humic-like components in the bay area indicate a terrestrial origin and conservative mixing behavior of these components. On the other hand, nonconservative mixing for the other terrestrial and the marine humic-like components was observed, indicating that the sources of these were other than solely riverine inputs. Thus, in addition to riverine sources, this terrestrial humic-like component may receive inputs from biogeochemical reworking of terrestrial DOM and/or particulate organic matter, while the most likely sources for the marine humic-like component are estuarine biological activity and/or microbial reworking of plankton-derived DOM. From the spatial distributions in the bay area as well as their relationships with salinity, two of the non-humic-like components were suggested to be of autochthonous estuarine origin and likely represent biologically labile components. Microbial degradation processes were suggested to be important factors driving the dynamics of another non-humic-like component. This study exemplifies the potential applicability of EEM-PARAFAC in studies of fluorescent DOM dynamics in estuaries.
Excitation emission matrix fluorescence spectroscopy combined with PARAFAC analysis provides a fast and ef- fective method of characterizing the fluorescent fraction of dissolved organic matter (DOM). Fluorescence mea- surements can be used as a tracer for quantitative and qualitative changes occurring in the DOM pool as a whole. An earlier study found that the fluorescence signal could be modeled by five fractions. This study presents an analysis on a considerably larger data set (.1,200 samples) resulting from a 1-yr sampling program in Horsens Estuary, Denmark. Eight fluorescent fractions were identified. Four biogenic terrestrial, two anthropogenic, and two protein-like fractions were identified. Analysis of covariation between the components identified source-specific fractions and the presence of common factors controlling the composition of terrestrial DOM exported from different catchments.
Concentrated human activity and limited atmospheric mixing create a high potential for airborne pollutant impacts to alpine lakes developed as mountain resorts. Lake Tahoe is a major alpine resort straddling the California–Nevada border, receiving more than two million visitors each year. The lake’s clarity has declined substantially since the inception of intense development in the Tahoe basin in the 1970s. The 2002–2004 Lake Tahoe Atmospheric Deposition Study (LTADS) was conducted as part of a multi-agency effort to develop a water quality management plan for the lake. Estimating aerosol deposition to the lake requires detailed knowledge of the spatial and temporal patterns of aerosol concentration, size distribution, and chemical composition over the entire basin – and developing a management plan requires also that the sources of the aerosols be known with considerable specificity. In lieu of the intensive measurement network implied by this level of detail, we hypothesized that a set of measurements to characterized the temporal, spatial, and size distribution patterns of particles in ambient air and in local emissions in the vicinity of Lake Tahoe could be used to extrapolate long time series of simple measurements to an annual aerosol deposition computation. Here we report the results of our detailed aerosol measurement campaign. Our results show that there are strong systematic and repeating gradients in aerosol loading that occur as functions of location, land use, traffic activity, and time of day, and that road dust is a major source of aerosols around the lake. In addition, we observed strong consistency of particle size distributions as a function of source type, largely independent of particle concentrations. Finally, we demonstrated the use of particle counters to directly observe downwind dispersion and deposition of particles. Together, these findings support the use of imputed location- and time-specific size distributions in annual aerosol deposition calculations, even though particle size distributions were not directly measured in the LTADS baseline monitoring program, and that program was conducted at only a limited set of sites in the Tahoe basin.Two companion articles in this journal issue describe the overall findings of the LTADS study (Dolislager et al., “Overview of the Lake Tahoe Atmospheric Deposition Study”) and the results of measurements taken on the lake itself (VanCuren et al., “Air Pollution in the Shore Zone of a Large Alpine Lake – 2 – Local and Regional Pollutant Distribution over Lake Tahoe California–Nevada”).