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Characterizing the transformation of aquatic humic substances exposed to ultraviolet radiation using excitation–emission matrix fluorescence spectroscopy and PARAFAC
摘要： It is important to understand the change in aquatic humic substances (AHS) induced by light due to the upward trend in ultraviolet (UV) radiation reaching the surface of the Earth. Changes in the quantity and quality of AHS in AHS-rich wetland water exposed to UV-A or UV-B light were determined using 3-dimensional excitation–emission matrix (EEM) fluorescence spectroscopy combined with parallel factor analysis (PARAFAC) and a resin isolation method. The dissolved organic carbon and AHS-carbon concentrations decreased via photodegradation with UV-A or UV-B exposure. The decreases in both carbon concentrations were greater when exposed to UV-B than when exposed to UV-A. Three AHS-like components were detected by EEM-PARAFAC: AHS-1, AHS-2, and AHS-3. AHS-1 and AHS-3 were degraded more by UV-A and UV-B exposure, respectively. AHS-2 was degraded slightly by UV-A exposure, whereas exposure to UV-B generated AHS-2 in the presence of low-molecular-weight compounds, and then underwent photodegradation. AHS-1 exposed to UV-A and AHS-3 exposed to UV-A or UV-B photoflocculated at day 14. The humification index indicated that UV-A exposure led to the preferential photodegradation of AHS, whereas UV-B exposure not only caused AHS degradation but also the degradation or photoflocculation of other compounds with simple structures. AHS changed little in the dark, demonstrating that bacterial effects on AHS were relatively unimportant. The processes of humification and flocculation are important in removing and sequestering carbon from its active cycle. Therefore, the degradation and transformation of AHS exposed to UV can have a major impact on aquatic ecosystem processes.
关键词： photochemical degradation,ultraviolet radiation,aquatic humic substances (AHS),EEM-PARAFAC,dissolved organic matter (DOM)
更新于2025-09-23 15:21:01
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FDOM Conversion in Karst Watersheds Expressed by Three-Dimensional Fluorescence Spectroscopy
摘要： A karst system, formed by the dissolution of carbonate rocks, is usually susceptible to contamination. Little is known about the composition of natural dissolved organic matter (DOM) in groundwater systems, especially in karstic groundwater. To reveal the characteristics of DOM in a karst aquifer, the Yufuhe River Basin, a typical karst watershed in northern China, was selected. DOM fluorescence (FDOM) was measured with the excitation-emission matrices (EEMs) spectroscopy technique. Parallel factor analysis (PARAFAC) was used to analyze the karst hydrogeological factors that affect FDOM biogeochemical behavior. Three fluorescent components, i.e., tyrosine-like, tryptophan-like, and ultraviolet fulvic acid were found. Their fluorescence properties were closely related to human activity and subterranean hydrology. Fluorescence properties suggested that FDOM in the Yufuhe River karst aquifer was predominant from anthropogenic activity. In addition, due to the effect of karstic heterogeneous hydrological conditions, FDOM showed obvious differentiation in the recharge, flow path, and discharge systems. The FDOM fluorescence intensity (FI) was weak in surface water and groundwater at the upper reaches (recharge area). In the middle of the flow path area, the percentage of tyrosine-like and tryptophan-like substances degraded and fulvic acid rose gradually. However, after infiltrating into the lower reaches (discharge area) of the deep karst aquifer system, the fulvic acid matter was consumed and protein-like matter accumulated.
关键词： dissolved organic matter fluorescence (FDOM),groundwater,three-dimensional fluorescence spectroscopy,karst aquatic system,Yufuhe River
更新于2025-09-23 15:21:01
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Fluorescence as a Surrogate for the Release of Intracellular Material From Cyanobacteria
摘要： Water treatment plants that apply preoxidation before physical cell removal can compromise cyanobacterial cell integrity and cause the release of intracellular organic matter (IOM) containing toxic or odorous metabolites. In this study, fluorescence was evaluated as a surrogate for IOM released from cyanobacterial cells following oxidation with ozone, chlorine, chlorine dioxide, or monochloramine. Oxidation of 200,000 cells/mL of Microcystis aeruginosa led to a significant increase in both the fluorescence index (FI) and the fluorescent dissolved organic matter (FDOM) intensity (excitation wavelength, 370 nm; emission wavelength, 460 nm). FI and FDOM proved impractical for detecting weakly fluorescing IOM released from Oscillatoria sp. and Lyngbya sp., indicating that the viability of fluorescence monitoring is cyanobacteria-specific. For strongly fluorescing IOM, FI and FDOM can serve as qualitative surrogates for the concomitant release of metabolites. Elevated FI and FDOM were not sensitive to the concentration of microcystin-LR but can provide an early warning that a utility’s source water is at risk for metabolite release and accumulation.
关键词： fluorescence index,cyanobacteria,Microcystis aeruginosa,fluorescent dissolved organic matter,intracellular organic matter,microcystin-LR
更新于2025-09-19 17:15:36
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Evaluation of Machine Learning Approaches to Predict Soil Organic Matter and pH Using vis-NIR Spectra
摘要： Soil organic matter (SOM) and pH are essential soil fertility indictors of paddy soil in the middle-lower Yangtze Plain. Rapid, non-destructive and accurate determination of SOM and pH is vital to preventing soil degradation caused by inappropriate land management practices. Visible-near infrared (vis-NIR) spectroscopy with multivariate calibration can be used to effectively estimate soil properties. In this study, 523 soil samples were collected from paddy ?elds in the Yangtze Plain, China. Four machine learning approaches—partial least squares regression (PLSR), least squares-support vector machines (LS-SVM), extreme learning machines (ELM) and the Cubist regression model (Cubist)—were used to compare the prediction accuracy based on vis-NIR full bands and bands reduced using the genetic algorithm (GA). The coef?cient of determination (R2), root mean square error (RMSE), and ratio of performance to inter-quartile distance (RPIQ) were used to assess the prediction accuracy. The ELM with GA reduced bands was the best model for SOM (SOM: R2 = 0.81, RMSE = 5.17, RPIQ = 2.87) and pH (R2 = 0.76, RMSE = 0.43, RPIQ = 2.15). The performance of the LS-SVM for pH prediction did not differ signi?cantly between the model with GA (R2 = 0.75, RMSE = 0.44, RPIQ = 2.08) and without GA (R2 = 0.74, RMSE = 0.45, RPIQ = 2.07). Although a slight increase was observed when ELM were used for prediction of SOM and pH using reduced bands (SOM: R2 = 0.81, RMSE = 5.17, RPIQ = 2.87; pH: R2 = 0.76, RMSE = 0.43, RPIQ = 2.15) compared with full bands (R2 = 0.81, RMSE = 5.18, RPIQ = 2.83; pH: R2 = 0.76, RMSE = 0.45, RPIQ = 2.07), the number of wavelengths was greatly reduced (SOM: 201 to 44; pH: 201 to 32). Thus, the ELM coupled with reduced bands by GA is recommended for prediction of properties of paddy soil (SOM and pH) in the middle-lower Yangtze Plain.
关键词： soil organic matter,paddy soil,vis-NIR spectra,pH,machine learning approaches
更新于2025-09-19 17:15:36
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Natural organic matter inhibits aggregation of few-layered black phosphorus in mono- and divalent electrolyte solutions
摘要： Extensive synthesis and applications of few-layered black phosphorus (BPs) are accompanied by increasing concern over its stability and potential risk. However, the colloidal stability of BPs under environmentally relevant conditions remains unclear. Hence, we investigated the influences of two representative electrolytes (i.e., NaCl and CaCl2) and natural organic matter (NOM) on the aggregation behavior of BPs. Ca2+ ions exhibited a stronger destabilization effect on BPs than Na+ due to their stronger surface charge screening as well as intersheet bridging by the complexes of Ca2+ ions and oxidized phosphorus (POx) species on the BPs surface. Apart from the Ca2+-induced enhanced aggregation in the presence of high concentration of Ca2+, the aggregation behavior of BPs in the two electrolytes at different concentrations and their ratios of critical coagulation concentrations (CCCs) generally followed classical colloidal theory such as the Schulze–Hardy rule. Moreover, in the presence of 10 mg C/L NOM the CCC values of BPs in NaCl and CaCl2 solutions were both three times higher than that obtained without NOM, and the aggregation kinetics of BPs in these electrolytes containing NOM were qualitatively consistent with extended DLVO theory. Specifically, NOM significantly improved the stabilization of BPs in CaCl2 solutions via steric repulsion and isolation of Ca2+ ions from interaction with POx species on the surface of BPs. This stabilization mechanism derived from “NOM corona” structures was elucidated by a wide spectrum of characterization and quantification techniques. These findings provide new insights into evaluating the stability and fate of this nanomaterial in natural aquatic environments.
关键词： few-layered black phosphorus,colloidal stability,NOM corona,aggregation,electrolytes,natural organic matter
更新于2025-09-19 17:15:36
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Simulated photo-degradation of dissolved organic matter in lakes revealed by three-dimensional excitation-emission matrix with regional integration and parallel factor analysis
摘要： Simulated photo-degradation of fluorescent dissolved organic matter (FDOM) in Lake Baihua (BH) and Lake Hongfeng (HF) was investigated with three-dimensional excitation-emission matrix (3DEEM) fluorescence combined with the fluorescence regional integration (FRI), parallel factor (PARAFAC) analysis, and multi-order kinetic models. In the FRI analysis, fulvic-like and humic-like materials were the main constituents for both BH-FDOM and HF-FDOM. Four individual components were identified by use of PARAFAC analysis as humic-like components (C1), fulvic-like components (C2), protein-like components (C3) and unidentied components (C4). The maximum 3DEEM fluorescence intensity of PARAFAC components C1eC3 decreased by about 60%, 70% and 90%, respectively after photo-degradation. The multi-order kinetic model was acceptable to represent the photo-degradation of FDOM with correlation coefficient (Radj2) (0.963e0.998). The photo-degradation rate constants (kn) showed differences of three orders of magnitude, from 1.09(cid:1) 10(cid:3)6 to 4.02 (cid:1) 10(cid:3)4 min(cid:3)1, and half-life of multi-order model (Tn1=2) ranged from 5.26 to 64.01 min. The decreased values of fluorescence index (FI) and biogenic index (BI), the fact that of percent fluorescence response parameter of Region I (PI,n) showed the greatest change ratio, followed by percent fluorescence response parameter of Region II (PII,n), while the largest decrease ratio was found for C3 components, and the lowest Tn1=2 was observed for C3, indicated preferential degradation of protein-like materials/components derived from biological sources during photo-degradation. This research on the degradation of FDOM by 3DEEM/FRI-PARAFAC would be beneficial to understanding the photo-degradation of FDOM in natural environments and accurately predicting the environmental behaviors of contaminants in the presence of FDOM.
关键词： Fluorescence regional integration,Parallel factor analysis,Photo-degradation,Fluorescent dissolved organic matter,Multi-order kinetic models,Three-dimensional excitation-emission matrix
更新于2025-09-16 10:30:52
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[IEEE 2019 10th Workshop on Hyperspectral Imaging and Signal Processing: Evolution in Remote Sensing (WHISPERS) - Amsterdam, Netherlands (2019.9.24-2019.9.26)] 2019 10th Workshop on Hyperspectral Imaging and Signal Processing: Evolution in Remote Sensing (WHISPERS) - Closed-Loop Moving Windows Wavelength Selection Method With Application To Near-Infrared Spectroscopic Analysis
摘要： Wavelength selection plays a very important role in near-infrared (NIR) spectroscopy, which has always been an important research direction. Based on the reverse-deletion waveband idea, the closed-loop moving window-partial least squares (closed-loop MW-PLS) method was proposed, which can eliminate interference wavelengths and enable flexible multi-band wavelength selection. NIR analysis of soil organic matter was taken as an example to evaluate the performance of closed-loop MW-PLS. And the MW-PLS was also used for comparison. The proposed algorithm traversed all the sub-bands of the original range to perform forward and backward optimization. The forward optimization was just the original MW-PLS. Therefore, the closed-loop MW-PLS completely covered the MW-PLS. The results of soil organic matter indicated that the close-loop MW-PLS was strictly superior to original MW-PLS, and the method extension was meaningful and had no increase in operational complexity. We believe that the closed-loop MW-PLS method will have a wider application.
关键词： soil,organic matter,closed-loop moving window-partial least squares,wavelength model optimization,Near-infrared spectroscopic analysis
更新于2025-09-12 10:27:22
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Applications of Laser-Induced Breakdown Spectroscopy for Soil Analysis, Part I: Review of Fundamentals and Chemical and Physical Properties
摘要： Laser-induced breakdown spectroscopy (LIBS) has become a prominent analytical technique in recent years for real-time characterization of soil properties. However, only a few studies of soil chemical and physical properties have been reported using LIBS until recently. The aims of this article are to: (1) provide the basic principles of LIBS for soil analysis and (2) present the use of LIBS for soil pH, soil texture, and humification degree of soil organic matter (SOM). The second article will cover soil classification and soil elemental analysis, including plant nutrients, carbon (C), and toxic elements. LIBS is a multi-element analytical technique based on atomic spectroscopy that employs a high-energy laser pulse focused onto a sample surface to create a transient plasma. It is a spectroscopic analytical technique that requires very little or no sample preparation, examines each sample in seconds, and offers a flexible platform for the examination of a broad array of elements in the sample. LIBS also can be used to infer soil chemical and physical properties if a relationship exists between the chemical composition and the soil properties. With proper calibration, LIBS has a great potential for real-time in-field soil analysis and precision farming that could lead to improved soil management and agricultural production, and reduced agricultural environmental impacts.
关键词： humification degree of soil organic matter,soil texture,precision agriculture,soil sensing,soil analysis,soil pH
更新于2025-09-11 14:15:04
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A Self-Adaptive Model for the Prediction of Soil Organic Matter Using Mid-Infrared Photoacoustic Spectroscopy
摘要： Fast quantification of soil organic matter (SOM) is important in crop production and soil fertility evaluation. Fourier-transform infrared (FTIR) spectroscopy has been widely utilized for rapid, cost-effective, and non-destructive SOM determination. However, the lack of accuracy has limited the application of FTIR spectroscopy to quantitative SOM prediction because the models are built from a typical database, resulting in large errors in new independent samples. In this study, using 933 paddy soil samples collected in Lishui, China, a “self-adaptive” model was designed for predicting SOM content, in conjunction with Fourier-transform mid-infrared photoacoustic spectroscopy (FTIR-PAS). The resulting FTIR-PAS spectra afforded abundant soil information, reflected in O–H, N–H, and C–H vibrations (4000–2800 cm?1), C=O and C–H vibrations (2500–1200 cm?1), and the fingerprint region (1200–500 cm?1). The self-adaptive model was established by: (i) identification of soil samples, selected by Euclidean distance, with soil spectra to similar the target (unknown) soil sample and ranking of the Euclidean distance values in ascending order; (ii) selection of the optimal parameters to build a partial least squares (PLS) model based on an optimal calibration sample subset; and (iii) prediction and validation of the unknown soil sample. The predictive capabilities of the self-adaptive model and conventional PLS model were compared; the self-adaptive and conventional PLS models had R2 values of 0.9293 and 0.5796, root mean square errors of prediction of 1.65 and 3.26 g kg?1, and ratios of percentage deviation (RPD) of 3.18 and 1.62, respectively. Therefore, the self-adaptive model showed greater potential for application, having significantly enhanced applicability while improving the accuracy of prediction.
关键词： Fourier-transform mid-infrared photoacoustic spectroscopy,partial least squares,paddy soils,self-adaptive model,soil organic matter
更新于2025-09-11 14:15:04
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8.78% Efficient All‐Polymer Solar Cells Enabled by Polymer Acceptors Based on a B←N Embedded Electron‐Deficient Unit
摘要： Mono-cardboard waste digestion in batch tests associated with different impact factors was investigated. The maximum methane generation was 394 mL/gVSadd with the best F/M of 0.5 at mesophilic conditions. The highest methane content reached 75% in the dynamic water bath feeding with an average particle size of 1?3 mm. Hydrolysis and methanogenesis were significantly different between static and dynamic states, especially at particle size over 3 mm. The modified Gompertz model (R2 > 0.98) and the modified Aiba model (R2 > 0.88) were the most appropriate models for methane generation among the six kinds of models. At different TS, the variation of dissolved organic matters reflects the metabolic rate of the microbial community. The soluble microbial product-like and protein-like components half split by excitation?emission factors significantly negatively corresponded to biomethane production. Moreover, a rapid loss of matrix-parallel methanogenesis was observed with high organics concentration. A strong correlation between the F/M ratio and the CH4 generation ability was observed with an optimized F/M of 0.5. The maximum energy production was also investigated based on the optimized particle size of 2?5 mm and F/M of 0.5, in which long-term stability was maintained.
关键词： dissolved organic matter,kinetic models,methane production,EEM-PARAFAC,Mono-cardboard digestion
更新于2025-09-11 14:15:04