Excitation-emission Matrix Fluorescence Research Articles

Characterization and source of fluorescent dissolved organic matter in the Western Arctic Ocean: new insights from the 2019 summer study

Increase in river discharge and seasonal primary production and decline in sea ice coverage in the Arctic Ocean in summer can significantly affect the distribution and composition of dissolved organic matter (DOM). This study aimed to enhance the current available knowledge about the impacts of environmental changes on the characteristics of DOM in the rapidly changing Arctic Ocean. Seawater samples were collected from the western Arctic Ocean during the summer of 2019 and analyzed for fluorescent DOM (FDOM), dissolved organic carbon (DOC), and stable oxygen isotope (δ18O) content in conjunction with biophysical properties. We identified two humic-like (C1 and C2) and one protein-like (C3) components using fluorescence excitation-emission matrix coupled with parallel factor (EEM–PARAFAC) analysis. Remarkably high intensities of humic-like FDOM were found in the upper halocline layer (32 < salinity < 33.5 psu, at depths between 50–200 m) with high inorganic nutrient concentrations and low N* values, indicating that the humic-like FDOM was supplied from the shelf sediment. Furthermore, shoaling of the upper halocline layer brought high levels of humic-like FDOM to the euphotic zone, resulting in an increased probability of photodegradation of humic-like FDOM due to exposure to solar radiation in the surface layer. Tryptophan-like FDOM was positively correlated with river water fraction (friver) and riverine DOC but not with chlorophyll-a (Chl-a) and heterotrophic bacterial abundance, indicating river discharge as a potential additional source of tryptophan-like FDOM. The correlation coefficients between tryptophan-like FDOM and river water parameters (friver and riverine DOC) differed across the Chukchi Sea, Chukchi Borderland, and East Siberian Sea, implying that the influence of river discharge on tryptophan-like FDOM is region-dependent. An increase in river discharge in future might lead to a greater supply of tryptophan-like FDOM, impacting the dynamics of DOM cycling in the western Arctic Ocean.

Remote sensing identification of urban water pollution source types using hyperspectral data

Owing to accelerated urbanisation, increased pollutants have degraded urban water quality. Timely identification and control of pollution sources enable relevant departments to effectively perform water treatment and restoration. To achieve this goal, a remote sensing identification method for urban water pollution sources applicable to unmanned aerial vehicle (UAV) hyperspectral images was established. First, seven fluorescent components were obtained through three-dimensional excitation-emission matrix fluorescence spectroscopy of dissolved organic matter (DOM) combined with parallel factor analysis. Based on the hierarchical cluster analysis of the seven fluorescence components and three spectral indices, four pollution source (PS) types were determined, namely, domestic sewage, terrestrial input, agricultural and algal, and industrial wastewater sources. Second, several water colour and optical parameters, including the absorption coefficient of chromophoric DOM at 254 nm, humification index, chlorophyll-a concentration, and hue angle, were utilised to develop an identification method with a recognition accuracy exceeding 70% for the four PSs that is suitable for UAV hyperspectral data. This study demonstrated the potential of identifying PSs by combining the fluorescence characteristics of DOM with the optical properties of water, thus expanding the application of remote sensing technologies and providing more comprehensive and reliable information for urban water quality management.

Metal behavior and soil quality changes induced by the application of tailor-made combined biochar: An investigation at pore water scale

The remediation performance of biochar varies based on the biomass used for its production. Further innovation involves developing tailor-made biochar by combining different raw materials to compensate for the limitations of pure biochar. Therefore, tailor-made combined biochar produced from the co-pyrolysis of pig manure and invasive Japanese knotweed (P1J1), as well as biochars produced from these feedstocks separately, i.e., pure pig manure (PM) and pure Japanese knotweed (JK), were applied to Pb and As contaminated soil to evaluate the biochar-induced changes on soil properties, microbial activity, DOM, and metal and metalloids solubility at the soil pore water scale. Biochar application reduced soluble Pb, whereas enhanced the As mobility; the increased soil pH after biochar addition played a fundamental role in reducing the Pb solubility, as revealed by their significant negative correlation (r = −0.990, p < 0.01). In contrast, the release of dissolved P strongly influenced As mobilization (r = 0.949, p < 0.01), especially in P-rich PM and P1J1 treatments, while JK showed a marginal effect in mobilizing As. Soils treated with PM, P1J1, and JK mainly increased Gram-negative bacteria by 56 %, 52 %, and 50 %, respectively, compared to the control. Fluorescence excitation-emission matrix spectroscopy combined with parallel factor analysis identified three components in pore water DOM, C1 (long wavelength humic-like), C2 (short wavelength humic-like), and C3 (protein-like), which were dominant respectively in the P1J1, JK, and PM-added soil. A principal component analysis (PCA) confirmed that the PM and P1J1 had similar performance and were more associated with releasing P and Mg and specific DOM components (C1 and C3). Meanwhile, P1J1 supplemented soil OM/OC and K, similar to JK. The results of this study suggest that combined biochar P1J1 can comprehensively enhance soil quality, embodying the advantages of pure PM and JK biochar while overcoming their shortcomings.

Remediation potential of magnetic biochar in lead smelting sites: Insight from the complexation of dissolved organic matter with potentially toxic elements

Magnetic biochar has been widely used in potentially toxic elements (PTEs) polluted soils due to its magnetic separation capability and synchronous immobilization for multiple metals. However, the contribution of magnetic biochar to soil dissolve organic material (SDOM) and its binding behavior with PTEs needs to be further clarified prior to its remediation application on lead smelting sites. In this study, multi-spectral techniques of excitation-emission matrix (EEM) fluorescence spectroscopy and two-dimensional FTIR correlation spectroscopy (2D-FTIR-COS) were used to explore the evolution characteristics of SDOM in the lead smelting site under the remediation of magnetic biochar, and to further analyze its affinity and binding behavior with Pb and As. Results showed that magnetic biochar significantly increased SDOM content and decreased Pb and As available content. EEM and parallel factor analysis (EEM-PARAFAC) and Self-Organizing map analysis showed that humus-like and aromatic DOM increased and microbial-derived SDOM decreased after magnetic biochar cultivation. Furthermore, 2D-FTIR-COS correlation spectroscopy analysis indicated that BDOM had a stronger binding affinity to Pb, while SDOM has a stronger binding affinity to As. The binding sequences of different DOMs to PTEs varied greatly, the carboxyl and amide groups of SDOM and BDOM showed a remarkable and rapid response. Our results enhance the insights of magnetic biochar on soil function and PTEs remediation potential, providing novel information for its environmental remediation application.

A novel ion exchange-electrodialysis hybrid system to treat rare-earth oxalic precipitation mother liquid: Contamination reduction, efficient Y3+ recovery, and acid separation

A novel ion exchange process combined with selective electrodialysis (SED) process has been demonstrated to not only efficiently recover low concentration rare-earth elements (REEs) and separate hydrochloric acid, but also significantly reduce membrane fouling. Two resins with different functional groups were selected for pretreatment and recovery of Y3+ from Y rare-earth oxalic precipitation (Y REOP) mother liquor. CH-93 resin showed a Y recovery rate of over 94 %, and the Y recovery efficiency remained above 90 % after 5 cycles. The mother liquor treated with resin (R-T) and the untreated mother liquor (W-R-T) were subjected to acid separation via SED, and membrane fouling was systematically evaluated. Compared with W-R-T group, the hydrochloric acid recovery efficiency of R-T group increased by 21.01 % (12 V), and the unit energy consumption decreased by 54.30 % (12 V). The results of 3D fluorescence excitation-emission matrix (3D-EEM) and fluorescent region integration (FRI) showed the dissolved organic matter (DOM) on AEM and CEM in R-T group both decreased by >45 %. The AEM of W-R-T group showed the highest fluorescence intensity ratio in V region (36 %), indicating humic acid-like substances were the main cause of AEM fouling. Generally, this study provides a new approach for the resource utilization of REOP mother liquor.

Fluorescence-based indicators predict the performance of conventional drinking water treatment processes: Evaluation based on the changes in the compositions of dissolved organic matter

This study investigated the treatability of dissolved organic matter (DOM) by the selected lab-scale drinking water treatment processes using fluorescence excitation-emission matrix (EEM) analysis. The fluorescence ratio Peak 3/Peak 2 was established from well-defined fluorescence peak intensity of humic-like components (Ex/Em: 225 nm/425 nm) and protein-like components (Ex/Em: 230 nm/345 nm). Peak 3/Peak 2 predicted the aromatic characteristics of DOM and their origins in the different natural surface water feeding the different drinking water treatment plants. The drinking water treatment processes confirmed the treatability of DOM using Peak 3/Peak 2 and was well-confirmed by specific UV260 absorbance relative to dissolved organic carbon (DOC) (SUVA) and fluorescence-based indices. Peak 3/Peak 2 was demonstrated to have a strong correlation with SUVA and DOC removal for the water after treatment by coagulation, adsorption, and chlorination. Compared to the humification index and fluorescence index, Peak 3/Peak 2 is better for indicating the DOM composition in terms of treatability. These findings can broaden the use of fluorescence spectroscopy in water treatment applications, by developing the fluorescence ratio to evaluate the performance of drinking water treatment plants.

DOM accumulation in the hyporheic zone promotes geogenic Fe mobility: A laboratory column study

Hyporheic zone (HZ) systems have a natural purification capacity, and they are commonly used to provide high quality drinking water. However, the presence of organic contaminants in HZ systems in anaerobic environments causes the aquifer sediments to release metals (e.g., Fe) at levels above drinking water standards, which affects the quality of groundwater. In this study, the effects of typical organic pollutants (dissolved organic matter (DOM)) on Fe release from anaerobic HZ sediments were investigated. Ultraviolet fluorescence spectroscopy, three-dimensional excitation-emission matrix fluorescence spectroscopy, excitation–emission matrix spectroscopy coupled with parallel factor analysis and Illumina MiSeq high-throughput sequencing were used to determine the effects of the system conditions on Fe release from HZ sediments. Compared with the control conditions (low traffic and low DOM as a baseline), the Fe release capacity was enhanced by 26.7 % and 64.4 % at low flow rate (85.8 m/d) and high organic matter concentration (1200 mg/L), which was consistent with the residence-time effect. The transport of heavy metals under different system conditions varied with the influent organic composition. The influent organic matter composition and fluorescence parameters (the humification index, biological index and fluorescence index) were closely related to the release of the Fe effluent, while these factors had less influence on Mn and As. From 16S rRNA analysis of the aquifer media at different depths at the end of the experiment, under low flow rate and high influent concentration conditions, reduction of Fe minerals by Proteobacteria, Actinobacteriota, Bacillus, and Acidobacteria promoted the release of Fe. These functional microbes play an active role in the Fe biogeochemical cycle in addition to reducing Fe minerals to promote Fe release. In summary, this study reveals the effects of the flow rate and influent DOM concentration on the release and biogeochemistry of Fe in the HZ. The results presented herein will contribute to a better understanding of the release and transport of common groundwater contaminants in the HZ and other groundwater recharge environments.

Transformation of organic carbon through medium pressure (polychromatic) UV disinfection of wastewater effluent during wet weather events

An observed decrease in total organic carbon (TOC) and dissolved organic carbon (DOC) concentrations following wastewater disinfection with medium pressure (MP, polychromatic) ultraviolet (UV) irradiation during wet weather flows is investigated. When antecedent rainfall in the previous 7-days was >2 in (5 cm), TOC and DOC concentrations decreased dramatically following MP-UV disinfection. Organic carbon surrogate measurements of biological oxygen demand (BOD), TOC, DOC, turbidity, UVA – 254 nm, SUVA (specific UVA), scanning UV–Visible spectra (200–600 nm), fluorescence excitation-emission matrix (EEM) spectra, and light scattering data are presented for wastewater resource recovery facility (WRRF) influent, secondary effluent (pre-UV-disinfection), and MP-UV-disinfected (final effluent) samples. TOC and DOC in wastewater influent and secondary effluent (i.e., pre-UV disinfection) correlated with antecedent rainfall conditions. The percent TOC and DOC removal through secondary treatment (i.e., from influent to effluent pre-UV) and the percent TOC and DOC removal through MP-UV disinfection (i.e., from effluent pre-UV to effluent post-UV) were compared and the latter approached 90 % through MP-UV disinfection during high antecedent rainfall conditions. Spectroscopy (UV, visible, or fluorescence) was performed on samples after filtration through 0.45 μm filters, i.e., the operationally defined DOC fraction of aquatic carbon. Scanning UV–visible spectra indicated transformation of an unidentified wastewater component into light-scattering entities regardless of antecedent rainfall conditions. The types of organic carbon (diagenetic, biogenic, or anthropogenic) and the significance of wet weather are discussed. An organic carbon contribution via infiltration and inflow was attributed as a source-of-interest in this research.

Oil species identification based on fluorescence excitation-emission matrix and transformer-based deep learning

After oil spills are found at sea, the identification on oil species can help determine the source of leakage and form the plan of post-accident treatment. Since the fluorometric characteristics of petroleum hydrocarbon reflect its molecular structure, the composition of oil spills could potentially be inferred using the fluorescence spectroscopy method. The excitation-emission matrix (EEM) includes additional fluorescence information in the dimension of excitation wavelength, which could be useful to identify oil species. This study proposed an oil species identification model using transformer network. The EEMs of oil pollutants are reconstructed into sequenced patch input that consists of the fluorometric spectra obtained under the different excitation wavelengths. The comparative experiments show that the proposed model can reduce the incorrect predictions and achieve higher identification accuracies than the regular convolutional neural networks that have been used in the previous studies. According to the structure of transformer network, an ablation experiment is also designed to evaluate the contributions of different input patches and seek for the optimal excitation wavelengths for oil species identification. The proposed model is expected to identify oil species, and even other fluorescent materials, based on the fluorometric spectra collected under multiple excitation wavelengths.

Reduction of byproduct formation and cytotoxicity to mammalian cells during post-chlorination by the combined pretreatment of ferrate(VI) and biochar

Ferrate [Fe(VI)] can efficiently degrade various pollutants in wastewater. Biochar application can reduce resource use and waste emission. This study investigated the performance of Fe(VI)/biochar pretreatment to reduce disinfection byproducts (DBPs) and cytotoxicity to mammalian cells of wastewater during post-chlorination. Fe(VI)/biochar was more effective at inhibiting the cytotoxicity formation than Fe(VI) alone, reducing the cytotoxicity from 12.7 to 7.6 mg-phenol/L. The concentrations of total organic chlorine and total organic bromine decreased from 277 to 130 μg/L and from 51 to 39 μg/L, compared to the samples without pretreatment. Orbitrap ultra-high resolution mass spectrometry revealed that the number of molecules of DBPs decreased substantially from 517 to 229 by Fe(VI)/biochar, with the greatest reduction for phenols and highly unsaturated aliphatic compounds. In combination with the substantial reduction of 1Cl-DBPs and 2Cl-DBPs, 1Br-DBPs and 2Br-DBPs were also reduced. Fluorescence excitation-emission matrix coupled with parallel factor analysis suggested that fulvic acid-like substances and aromatic amino acid was obviously reduce likely due to the enhanced oxidation of Fe(IV)/Fe(V) produced by Fe(VI)/biochar and adsorption of biochar. Furthermore, the DBPs generated by electrophilic addition and electrophilic substitution of precursors were reduced. This study shows that Fe(VI)/biochar pretreatment can effectively reduce cytotoxicity formation during post-chlorination by transforming DBPs and their precursors.

Selective associations of organic matter components with ferrihydrite: Implications for Fe-organic matter preservation in tidal flat wetlands

The association of organic matter (OM) with iron (Fe) is a critical mechanism to preserve OM in intertidal coastal ecosystems such as salt marshes and mangroves. The present study aimed to investigate the influence of the organic carbon to Fe molar ratio (OC/Fe), ionic strength, and OM composition on Fe-OM association. Fe-OM was prepared using humic acids extracted from salt marsh and mangrove sediments by the adsorption process in the OC/Fe molar ratios of 0.01–1.0 and by the coprecipitation process in the OC/Fe molar ratios of 0.1–9.9. Sample properties were studied by X-ray diffraction, scanning electron microscopy, ultraviolet–visible spectroscopy, attenuated total reflection Fourier transform infrared spectroscopy, three-dimensional fluorescence excitation emission matrix spectroscopy, and pyrolysis–gas chromatography/mass spectrometry. The results showed that selective associations of OM components with ferrihydrite were affected by the association mode (e.g., adsorption and coprecipitation), OC/Fe molar ratio, OM composition and ionic strength. Abundant aliphatic compounds could be adsorbed on ferrihydrite. Moreover, ferrihydrite was prone to preserve humic-like fluorescent components through the adsorption process. The protein-like fluorescent components and aliphatic compounds had high affinity for ferrihydrite during coprecipitation with low OC/Fe molar ratios. An increase in the OC/Fe molar ratio resulted in coprecipitation of aromatic compounds with ferrihydrite. Salinity-induced flocculation caused more amount of aromatic and polycyclic aromatic compounds to associate with ferrihydrite during the coprecipitation process. Compared to the salt marsh OM, more N-compounds and less aliphatic compounds in the mangrove OM were coprecipitated with ferrihydrite. This study provided important insights into the mechanisms of OM preservation with ferrihydrite in tidal wetland ecosystems.

Multi-tracer evidence for the presence of autochthonous organic carbon and the role of biological carbon pump in two river–reservoir ecosystems on the Chinese Loess Plateau

The biological carbon pump (BCP) effect of dissolved inorganic carbon (DIC)-enriched karst surface waters is an important carbon sink mechanism that has substantial implications for the study of global missing carbon sinks and carbon cycling. However, the operation of the BCP is not established well in wider inland waters, particularly not in the surface waters of the Chinese Loess Plateau (CLP) that are also DIC-enriched but have high turbidity. In this study, we combined analyses of stable isotopes (δ2H, δ18O, and δ13C) and C/N ratios, ultraviolet absorption spectroscopy, and excitation-emission matrix fluorescence approaches to investigate the sources and compositions of particulate organic carbon (POC) and dissolved organic carbon (DOC) in two river–reservoir ecosystems [the Wulihe (WLH)-river to WLH-reservoir and Honghe (HH)-river to HH-reservoir] on the CLP. Both DOC and POC signals from autochthonous production gradually increased from the river inflow to the reservoir areas along the river flow, particularly during the wet season with the same duration of rain and heat. The WLH-reservoir had higher δ2H, δ18O, and δ13C values, more protein-like fluorescence components, higher chlorophyll-a and DOC concentrations, and lower CO2 efflux than the HH-reservoir. Our results showed that the BCP intensity of the WLH-reservoir was higher than that of the HH-reservoir, probably because of the longer water residence time of the WLH-reservoir. Although the amount of autochthonous dissolved organic matter (Auto-DOM) produced by the BCP in the surface water on the CLP was lower than that in the karst regions of southwest China (CKR), the proportion of Auto-DOM in the CLP was close to that in the CKR, indicating the significance of Auto-DOM in the surface water on the CLP. Furthermore, the BCP-derived Auto-DOM correlated negatively with the partial pressure of CO2, and the WLH-reservoir with a higher BCP effect exhibited CO2 influx in the wet season (−1.47 ± 0.02 g m−2 d−1), indicating that the enhanced BCP process contributed to the water–air interface carbon sink. This study highlighted that enhanced BCP could generate carbon sinks in DIC-enriched but high-turbidity surface waters, providing the underlying theory for extending the BCP carbon sink model to a wider range of surface waters flowing through areas of soil carbonate.

Anti-interference and non-destructive identification of textile fabrics using front-face excitation-emission matrix fluorescence spectroscopy combined with multi-way chemometrics

The identification of trace textile fabrics discovered at crime scenes plays a crucial role in the case of forensic investigations. Additionally, in practical situations, fabrics may be contaminated, making identification more challenging. To address the aforementioned issue and promote the application of fabrics identification in forensic analysis, front-face excitation-emission matrix (FF-EEM) fluorescence spectra coupled with multi-way chemometric methods were proposed for the interference-free and non-destructive identification of textile fabrics. Common commercial dyes in the same color range under different materials (cotton, acrylic, and polyester) that cannot be visually distinguished were investigated, and several binary classification models for the identification of dye were established using partial least squares discriminant analysis (PLS-DA). The identification of dyed fabrics in the presence of fluorescent interference was also taken into consideration. In each kind of pattern recognition model mentioned above, the classification accuracy (ACC) of the prediction set was 100%. The alternating trilinear decomposition (ATLD) algorithm was executed to separate mathematically and remove the interference, and the classification model based on the reconstructed spectra attained an accuracy of 100%. These findings indicate that FF-EEM technology combined with multi-way chemometric methods has broad prospects for forensic trace textile fabric identification, especially in the presence of interference.

Influences of Anthropogenic Pollution on the Dynamics of Sedimentary Fulvic Acid Fractions as Revealed via Spectroscopic Techniques Combined with Two-Dimensional Correlation Spectroscopy

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

The spectral resolution of DOM in urban rivers affected by different non-point source intensities using self-organizing maps.

UV-Vis, three-dimensional excitation-emission matrix fluorescence spectroscopy (EEMs) and a self-organizing map (SOM) were used to study changes in the composition and constituent concentrations of dissolved organic matter (DOM) in the water column of two urban rivers with different non-point source inputs during spring and summer. The level of humification and the relative molecular mass of DOM were remarkably higher in the summer than in the spring (P < 0.01) in both rivers. The SOM model showed that the fluorescence intensity of the spring component was lower than in summer in water bodies with higher levels of non-point source inputs, while the opposite was true for water bodies with lower levels of non-point source inputs. Principal component analysis (PCA) showed that nutrients like nitrogen and phosphorus promoted autogenous processes in these water bodies. Seasonal variations and differing intensities of non-point source inputs had remarkable effects on urban river waters (R2 = 0.775, P < 0.001). Non-point source inputs increased the concentrations of humus-like fractions and promoted autogenesis in the water bodies.

Effects of paddy irrigation-drainage system on water quality and productivity of small rivers in the Himi region of Toyama, Central Japan

The aim of this study was to clarify the impact of differences between historical and recently introduced irrigation and drainage management systems on water quality in the rivers around paddy fields. We investigated the seasonal variation in nutrients concentration and dissolved organic carbon (DOC) components in single- (used for intake only) and dual-purpose (used for both intake and drainage) channels during a 4-year period in the Himi region of Toyama, Central Japan. The system of dual-purpose channel has traditionally been used in the region of this study. A total of 197 three-dimensional excitation-emission matrix (3DEEM) fluorescence spectra of DOM in waters were applied for the parallel factor analysis (PARAFAC) modeling. Based on the 3DEEM and PARAFAC, the abundance of terrestrial humic-like components in the dual-purpose channel was significantly higher than that in the single-purpose channel. The even long-chain n-fatty acids derived associated with rice cropping in sediments of the dual-purpose channels were 22−30-fold higher than that of the single-purpose channel. In addition, the turbidity values of the river waters had significantly positive linear correlations with concentrations of K+, DOC, and humic-like components. These observations indicate that the dissolved nutrient concentrations in the river water were higher in the dual-purpose channel compared to those of the single-purpose channel, which may be supplied by leaching from the inflow of soil particles from the paddy fields. During the mid-irrigation period, the quantity of epiphytic chlorophyll a on artificial substrate tiles in the dual-purpose channel were 3.1–4.1-fold higher than that in the single-purpose channel. This study clear that the input of paddy drainage during the irrigation season significantly changes the DOC components in river waters and irrigation management is strongly linked to the primary production in agricultural channels. Therefore, it is important to consider the impact of the introduction of different irrigation and drainage management systems on water quality and productivity in order to maintain the riverine ecosystems around rice paddies, which are based on historical water use systems.

Rapid measurement of brown tide algae using Zernike moments and ensemble learning based on excitation-emission matrix fluorescence.

Accurate real-time prediction of microalgae density has great practical significance for taking countermeasures before the advent of Harmful algal blooms (HABs), and the non-destructive and sensitive property of excitation-emission matrix fluorescence (EEMF) spectroscopy makes it applicable to online monitoring and control. In this study, an efficient image preprocessing algorithm based on Zernike moments (ZMs) was proposed to extract compelling features from EEM intensities images. The determination of the highest order of ZMs considered both reconstruction error and computational cost, then the optimal subset of preliminarily extracted 36 ZMs was screened via the BorutaShap algorithm. Aureococcus anophagefferens concentration prediction models were developed by combining BorutaShap and ensemble learning models (random forest (RF), gradient boosting decision tree (GBDT), and XGBoost). The experimental results show that BorutaShap_GBDT preserved the superior subset of ZMs, and the integration of BorutaShap_GBDT and XGBoost achieved the highest prediction accuracy. This research provides a new and promising strategy for rapidly measuring microalgae cell density.

Metal–organic cage as fluorescent probe for LiPF6 in lithium batteries

Lithium hexafluorophosphate (LiPF6), the most commonly used lithium battery electrolyte salt, is vulnerable to heat and humidity. Quantitative and qualitative determination the variation of LiPF6 have always relied on advanced equipment. Herein, we develop a fast, convenient, high-selective fluorescence detection method based on metal–organic cages (MOC), whose emission is enhanced by nearly 20 times in the presence of LiPF6 with good stability and photobleaching resistance. The fluorescent probe can also detect moisture in battery electrolyte. We propose and verify that the luminescence enhancement is due to the presence of hydrogen bond-induced enhanced emission effect in cages. Fluorescent excitation-emission matrix spectra and variable-temperature nuclear magnetic resonance spectroscopy are employed to clarify the role of hydrogen bonds in guest-loaded cages. Density functional theory (DFT) calculation is applied to simulate the structure of host-guest complexes and estimate the adsorption energy involved in the system. The precisely matched lock-and-key model paves a new way for designing and fabricating novel host structures, enabling specific recognition of other target compounds.

Deciphering riverine dissolved organic matter biodegradation: Evidence from three-dimensional fluorescence

Biological degradation contributes significantly to aquatic dissolved organic matter (DOM) turnover. Yet to date, the specific biological pathways involved in DOM degradation are still obscure. Here, we show how DOM changes in response to 28-d incubation in a karst river, via the combined fluorescent excitation-emission matrix (EEM) with parallel factor analysis (PARAFAC) and peak picking. Tyrosine-, tryptophan- and UV humic-like components were identified as the primary DOM in original waters. Notable decreases of protein-like components were observed after 15 ℃ incubation, suggesting preferential consumption of biogenic DOM. Elevated temperature (30 ℃), however, caused significant decreases in visible humic-like and terrestrial fulvic-like components, but an increase in UV humic-like components in comparison to 15 ℃ incubation (p < 0.05). Humification index (HIX) decreased dramatically after 15 ℃ incubation, indicating that biological processes regulated river DOM properties. Our results highlight the significant biogenic signals in karst rivers, and evidence that fluorescence measurement can decipher riverine DOM biodegradation as a useful approach.

Fast quantification and kinetic study of 9-hydroxyfluorene in soil samples based on multi-way calibration methods coupled with excitation-emission matrix fluorescence

Fast quantification and kinetic study of 9-hydroxyfluorene in soil samples based on multi-way calibration methods coupled with excitation-emission matrix fluorescence