Ecosystem effects of intraspecific variation in a colour polymorphic amphibian.

An emerging consensus suggests that evolved intraspecific variation can be ecologically important. However, evidence that evolved trait variation within vertebrates can influence fundamental ecosystem-level processes remains sparse. In this study, we sought to assess the potential for evolved variation in the spotted salamander (Ambystoma maculatum) to affect aquatic ecosystem properties. Spotted salamanders exhibit a conspicuous polymorphism in the colour of jelly encasing their eggs-some females produce clear jelly, while others produce white jelly. Although the functional significance of jelly colour variation remains largely speculative, evidence for differences in fecundity and the morphology of larvae suggests that the colour morphs might differ in the strength or identity of ecological effects. Here, we assessed the potential for frequency variation in spotted salamander colour morphs to influence fundamental physiochemical and ecosystem properties-dissolved organic carbon, conductivity, acidity and primary production-with a mesocosm experiment. By manipulating colour morph frequency across a range of larval densities, we were able to demonstrate that larva density and colour morph variation were ecologically relevant: population density reduced dissolved organic carbon and increased primary production while mesocosms stocked with white morph larvae tended to have higher dissolved organic carbon and conductivity. Thus, while an adaptive significance of jelly coloration remains hypothetical, our results show that colour morphs differentially influence key ecosystem properties-dissolved organic carbon and conductivity.

Iron Promotes the Retention of Terrigenous Dissolved Organic Matter in Subtidal Permeable Sediments.

Marine permeable sediments are important sites for organic matter turnover in the coastal ocean. However, little is known about their role in trapping dissolved organic matter (DOM). Here, we examined DOM abundance and molecular compositions (9804 formulas identified) in subtidal permeable sediments along a near- to offshore gradient in the German North Sea. With the salinity increasing from 30.1 to 34.6 PSU, the DOM composition in bottom water shifts from relatively higher abundances of aromatic compounds to more highly unsaturated compounds. In the bulk sediment, DOM leached by ultrapure water (UPW) from the solid phase is 54 ± 20 times more abundant than DOM in porewater, with higher H/C ratios and a more terrigenous signature. With 0.5 M HCl, the amount of leached DOM (enriched in aromatic and oxygen-rich compounds) is doubled compared to UPW, mainly due to the dissolution of poorly crystalline Fe phases (e.g., ferrihydrite and Fe monosulfides). This suggests that poorly crystalline Fe phases promote DOM retention in permeable sediments, preferentially terrigenous, and aromatic fractions. Given the intense filtration of seawater through the permeable sediments, we posit that Fe can serve as an important intermediate storage for terrigenous organic matter and potentially accelerate organic matter burial in the coastal ocean.

Spectral characterization of the impact of modifiers and different prepare temperatures on snow lotus medicinal residue-biochar and dissolved organic matter.

This study involved the production of 20 biochar samples derived from secondary medicinal residues of Snow Lotus Oral Liquid, processed within the temperature range of 200-600 °C. Additionally, four medicinal residues, including dissolved organic matter (DOM), from 24 samples obtained using the shaking method, served as the primary source material. The investigation focused on two key factors: the modifier and preparation temperature. These factors were examined to elucidate the spectral characteristics and chemical properties of the pharmaceutical residues, biochar, and DOM. To analyze the alterations in the spectral attributes of biochar and medicinal residues, we employed near-infrared spectroscopy (NIR) in conjunction with Fourier-infrared one-dimensional and two-dimensional correlation spectroscopy. These findings revealed that modifiers enhanced the aromaticity of biochar, and the influence of preparation temperature on biochar was diminished. This observation indicates the stability of the aromatic functional group structure. Comparative analysis indicated that Na2CO3 had a more pronounced structural effect on biochar, which is consistent with its adsorption properties. Furthermore, we utilized the fluorescence indices from UV-visible spectroscopy and excitation-emission-matrix spectra with the PARAFAC model to elucidate the characteristics of the fluorescence components in the DOM released from the samples. The results demonstrated that the DOM released from biochar primarily originated externally. Aromaticity reduction and increased decay will enhance the ability of the biochar to bind pollutants. Those results confirmed the link between the substantial increase in the adsorption performance of the high-temperature modified charcoal in the previous study and the structural changes in the biochar. We investigated the structural changes of biochar and derivative DOM in the presence of two perturbing factors, modifier and preparation temperature. Suitable modifiers were selected. Preparation for the study of adsorption properties of snow lotus medicinal residues.

Naturalization of treated wastewater by a constructed wetland in a water-scarce Mediterranean region.

The effluents from conventional wastewater treatment plants (WWTP), even if accomplishing quality regulations, substantially differ in their characteristics with those of waters in natural environments. Constructed wetlands (CWs) serve as transitional ecosystems within WWTPs, mitigating these differences and restoring natural features before water is poured into the natural environment. Our study focused on an experimental surface-flow CW naturalizing the WWTP effluent in a semiarid area in Eastern Spain. Despite relatively low pollutant concentrations entering the CW, it effectively further reduced settled organic matter and nitrogen. Dissolved organic matter (DOM) reaching the CW was mainly protein-like, yet optical property changes in the DOM indicated increased humification, aromaticity, and stabilization as it flowed through the CW. Flow cytometry analysis revealed that the CW released less abundant but more active bacterial populations than those received. MiSeq Illumina sequencing highlighted changes in the prokaryotic community composition, with phyla Proteobacteria, Bacteroidetes, Firmicutes, and Actinobacteria dominating the CW outflow. Functional prediction tools (FaproTax and PICRUSt2) demonstrated a shift towards microbial guilds aligned with those of the natural aquatic environments, increased aerobic chemoheterotrophs, photoautotrophs, and metabolic reactions at higher redox potentials. Enhanced capabilities for degrading plant material correlated well with changes in the DOM pool. Our findings emphasize the role of CWs in releasing biochemically stable DOM and functionally suited microbial populations for natural receiving environments. Consequently, we propose CWs as a naturalization nature-based solution (NBS) in water-scarce regions like the Mediterranean, where reclaimed discharged water can significantly contribute to ecosystem's water resources compared to natural flows.

[Dynamic Changes of Dissolved Organic Matter Derived from Algal Decomposition and the Environmental Effects in Eutrophic Lakes].

The global occurrences of lake eutrophication have led to algal bloom and the subsequent algal decomposition, releasing high amounts of algae-derived dissolved organic matter (DOM) into the lake water. Algae-derived DOM could regulate the quantity and composition of DOM in lake water and further impact the biogeochemical cycles of multiple elements. In this study, the dynamic changes in the quantity and quality of DOM during algal decomposition under different eutrophic scenarios (e.g., from oligotrophication to severe eutrophication) were monitored, and the corresponding environmental effects (e.g., microbial responses and greenhouse gas emissions) caused by algal decomposition were further explored. The results showed that algal decomposition significantly increased the DOM levels, bioavailability, and intensities of fluorescent components in the water. The total DOM levels gradually decreased, whereas the average molecular weight increased along the decomposition process. Furthermore, unsaturated hydrocarbon and aliphatic compounds were preferentially utilized by microorganisms during algal decomposition, and some refractory molecules (e.g., lignin, condensed hydrocarbons, and tannin with high O/C values) were synchronously generated, as evidenced by the results from ultra-high-resolution mass spectrometry. The dominant bacterial species during algal decomposition shifted from Proteobacteria (46%) to Bacteroidetes (42%). In addition, algae addition resulted in 1.2-5 times the emissions of CO2 and CH4 from water, and the emission rates could be well predicted by the optical index of a254 in water. This study provides comprehensive perspectives for understanding the environmental behaviors of aquatic DOM and further paves the ways for the mitigation of lake eutrophication.

Effect of pyrolysis temperature and molecular weight on characterization of biochar derived dissolved organic matter from invasive plant and binding behavior with the selected pharmaceuticals.

A comprehensive understanding of the characteristics of biochar released-dissolved organic matter (BDOM) derived from an invasive plant and its impact on the binding behavior of pharmaceuticals is essential for the application of biochar, yet has received less attention. In this study, the binding behavior of BDOM pyrolyzed at 300-700 °C with sulfathiazole, acetaminophen, chloramphenicol (CAP), and carbamazepine (CMZ) was investigated based on a multi-analytical approach. Generally, the pyrolysis temperature exhibited a more significant impact on the spectral properties of BDOM and pharmaceutical binding behavior than those of the molecular weight. With increased pyrolysis temperature, the dissolved organic carbon decreased while the proportion of the protein-like substance increased. The highest binding capacity towards the drugs was observed for the BDOM pyrolyzed at 500 °C with the molecular weight larger than 0.3 kDa. Moreover, the protein-like substance exhibited higher susceptive and released preferentially during the dialysis process and also showed more sensitivity and bound precedingly with the pharmaceuticals. The active binding points were the aliphatic C-OH, amide II N-H, carboxyl CO, and phenolic-OH on the tryptophan-like substance. Furthermore, the binding affinity of the BDOM pyrolyzed at 500 °C was relatively high with the stability constant (logKM) of 4.51 ± 0.52.

Urban and agricultural influences on the coastal dissolved organic matter pool in the Algoa Bay estuaries.

While anthropogenic pollution is a major threat to aquatic ecosystem health, our knowledge of the presence of xenobiotics in coastal Dissolved Organic Matter (DOM) is still relatively poor. This is especially true for water bodies in the Global South with limited information gained mostly from targeted studies that rely on comparison with authentic standards. In recent years, non-targeted tandem mass spectrometry has emerged as a powerful tool to collectively detect and identify pollutants and biogenic DOM components in the environment, but this approach has yet to be widely utilized for monitoring ecologically important aquatic systems. In this study we compared the DOM composition of Algoa Bay, Eastern Cape, South Africa, and its two estuaries. The Swartkops Estuary is highly urbanized and severely impacted by anthropogenic pollution, while the Sundays Estuary is impacted by commercial agriculture in its catchment. We employed solid-phase extraction followed by liquid chromatography tandem mass spectrometry to annotate more than 200 pharmaceuticals, pesticides, urban xenobiotics, and natural products based on spectral matching. The identification with authentic standards confirmed the presence of methamphetamine, carbamazepine, sulfamethoxazole, N-acetylsulfamethoxazole, imazapyr, caffeine and hexa(methoxymethyl)melamine, and allowed semi-quantitative estimations for annotated xenobiotics. The Swartkops Estuary DOM composition was strongly impacted by features annotated as urban pollutants including pharmaceuticals such as melamines and antiretrovirals. By contrast, the Sundays Estuary exhibited significant enrichment of molecules annotated as agrochemicals widely used in the citrus farming industry, with predicted concentrations for some of them exceeding predicted no-effect concentrations. This study provides new insight into anthropogenic impact on the Algoa Bay system and demonstrates the utility of non-targeted tandem mass spectrometry as a sensitive tool for assessing the health of ecologically important coastal ecosystems and will serve as a valuable foundation for strategizing long-term monitoring efforts.

Photo-induced leaching behaviors and biodegradability of dissolved organic matter from microplastics and terrestrial-sourced particles.

Recent studies have increasingly focused on the occurrence of plastic leachate and its impacts on aquatic ecosystems. Nonetheless, the environmental fate of this leachate in the presence of abundant natural organic matter (NOM)-a typical scenario in environments contaminated with plastics-remains underexplored. This study investigates the photo-induced leaching behaviors of dissolved organic matter (DOM) from terrestrial-sourced particles (forest soil and leaf litter) and microplastics (MPs), specifically polystyrene (PS) and polyvinyl chloride (PVC), over a two-week period. We also examined the biodegradability and spectroscopic characteristics of the leached DOM from both sources. Our results reveal that DOM from microplastics (MP-DOM) demonstrates more persistent leaching behavior compared to terrestrial-derived DOM, even with lesser quantities per unit of organic carbon. UV irradiation was found to enhance DOM leaching across all particle types. However, the photo-induced leaching behaviors of fluorescent components varied with the particle type. The MP group exhibited a broader range and higher biodegradability (ranging from 19.7% to 61.6%) compared to the terrestrial-sourced particles (ranging from 3.7% to 16.5%). DOM leached under UV irradiation consistently showed higher biodegradability than that under dark conditions. Furthermore, several fluorescence characteristics of DOM, such as the protein/phenol-like component (%C2), terrestrial humic-like component (%C3), and humification index (HIX)-traditionally used to indicate the biodegradability of natural organic matter-were also effective in assessing MP-DOM (with correlation coefficients R2 = 0.6055 (p = 0.003), R2 = 0.5389 (p = 0.007), and R2 = 0.4640 (p = 0.015), respectively). This study provides new insights into the potential differences in environmental fate between MP-DOM and NOM in aquatic environments heavily contaminated with MPs.

Chemodiversity in freshwater health.

Dissolved organic matter may offer a way to track and restore the health of fresh waters.

Spectroscopic studies of the role of dissolved organic matter in acenaphthene photodegradation in liquid water and ice.

The effect of concentration and origin of dissolved organic matter (DOM) on acenaphthene (Ace) photodegradation in liquid water and ice was investigated, and the components in DOM which were involved in Ace photodegradation were identified. The DOM samples included Suwannee River fulvic acid (SRFA), Elliott soil humic acid (ESHA), and an effluent organic matter (EfOM) sample. Due to the production of hydroxyl radical (•OH) and triplet excited-state DOM (3DOM*) which react with Ace, DOM had promotion effects on Ace photodegradation. However, the promotion effects of DOM were prevailed over by their suppressing effect of DOM including screening light effect, intermediates reducing effect and RS quenching effect, and thus, the photodegradation rates of Ace decreased in the presence of the three DOM with concentrations of 0.5-7.5 mg C/L in liquid water and ice. ESHA had higher light absorption and thus had higher screening light effect on Ace photodegradation in liquid water than SRFA and EfOM. At each DOM concentration, ESHA exhibited higher promotion effect on Ace photodegradation than SRFA and EfOM, in liquid water and ice. The binding of Ace with DOM was indicated by decreases in fluorescence intensity of Ace when coexisted with DOM. However, the binding of Ace to DOM played an unimportant role in suppressing Ace photodegradation. The photodegradation behavior of fluorophores in Ace with DOM present in ice was not similar to that in liquid water. C-O, C═O, carboxyl groups O-H and aliphatic C-H functional groups in DOM were involved in the interaction of DOM with Ace. The presence of Ace seemed to have no influence on the photodegradation behavior of functional groups in DOM.

Dissolved organic matter (DOM) is independently stratified in thermally stratified water bodies.

Thermal stratification often occurs in deep-water bodies, including oceans, lakes, and reservoirs. Dissolved organic matter (DOM) plays a critical role in regulating the dynamics of aquatic food webs and water quality in aquatic ecosystems. In the past, thermal stratification boundaries have been sometimes used exclusively to analyze the vertical distribution of DOM in thermally stratified water bodies. However, the validity of this practice has been challenged. Currently, there is limited understanding of the formation mechanism and stratification of the vertical distribution of DOM in thermally stratified water bodies, which hinders the analysis of the interactions between DOM and vertical aquatic ecological factors. To address this gap, we conducted a comprehensive study to extensively collect the vertical distribution of DOM in thermally stratified water bodies and identify the primary factors influencing this distribution. We found that DOM was independently stratified in thermally stratified water bodies (including two cases in unstratified water bodies), and that the formation mechanisms and statuses of DOM stratification were different from those of thermal stratification. The boundaries and numbers of DOM stratification were generally inconsistent with those of thermal stratification. Therefore, it is more accurate to divide DOM into different layers according to its own vertical profile, and analyze DOM characteristics of each layer based on its own stratification instead of thermal stratification. This study sheds light on the relationship between DOM and thermal stratification and provides a novel approach for analyzing DOM vertical distribution characteristics and their impact on aquatic ecosystems. This finding also holds significant implications for the design and implementation of environmental management programs aimed at preserving the health and functionality of aquatic ecosystems.

Algae removal and algal organic matter chemistry modulated by KMnO4-PAC in simulated karst water.

In this study, we examined the modulation of algae removal and algal organic matter (AOM) chemistry by potassium permanganate and poly-aluminum chloride (KMnO4-PAC) in simulated karst water. Specifically, we verified the compositional changes of AOM sourcing from Chlorella sp. and Pseudanabaena sp. in response to the presence of divalent ions (Ca2+ and Mg2+). Aromatic protein and soluble microbial products were identified as the primary AOM components. Divalent ions accelerated dissolved organic carbon (DOC) and UV254 removal, particularly with Pseudanabaena sp. greater than Chlorella sp. (P < 0.05). Surface morphology analysis manifested that the removal of filamentous Pseudanabaena sp. was more feasible in comparison to globular Chlorella sp.. Our results highlight the significance of divalent ions in governing chemical behaviors and subsequent removal of both algae and AOM. This study upscales the understanding of the interactions among divalent ions, algae and AOM during preoxidation and coagulation process in algae-laden karst water.

Effects of dissolved organic matter and halogen ions on phototransformation of pharmaceuticals and personal care products in aquatic environments.

Photochemical reactions contribute to the attenuation and transformation of pharmaceuticals and personal care products (PPCPs) in surface natural waters. Nevertheless, effects of DOM and halogen ions on phototransformation of PPCPs remain elusive. This work selected disparate PPCPs as target pollutants to investigate their aquatic phototransformation processes. Results show that PPCPs containing multiple electron-donating groups (-OH, -NH2, -OR, etc.) are more reactive with photochemically produced reactive intermediates (PPRIs) such as triplet DOM (3DOM*), singlet oxygen (1O2), and reactive halogen species (RHSs), relative to PPCPs containing electron-withdrawing groups (-NOR, -COOR, -OCR, etc.). The generation of RHSs as a result of the coexistance of DOM and halide ions changed the contribution of PPRIs to the photochemical conversion of PPCPs during their migration from fresh water to seawater. For PPCPs (AMP, SMZ, PN, NOR, CIP, etc) with highly reactive groups toward RHSs, the generation of RHSs facilitated their photolysis in halide ion-rich waters, where Cl- plays a critical role in the photochemical transformation of PPCPs. Density functional theory (DFT) calculations showed that single electron transfer and H-abstraction are main reaction pathways of RHSs with the PPCPs. These results demonstate the irreplaceable roles of PPRIs and revealing the underlying reaction mechanisms during the phototransformation of PPCPs, which contributes to a better understanding of the environmental behaviors of PPCPs in complex aquatic environments.

Structure and composition of dissolved organic matters in sludge by ultrasonic treatment.

The leaching of dissolved organic matter (DOM) from the sludge into the liquid phase is induced by ultrasound. However, there is limited investigation into the structure and molecular composition of sludge DOM in this process. The molecular structure and composition of sludge DOM in ultrasonic treatment were comprehensively elucidated in this study. The sludge dissolved organic carbon (DOC) and three-dimensional fluorescence spectroscopy (3D-EEM) image had most significant change at 15-min ultrasonic time and 1.2 W/mL ultrasonic density, respectively. Gas Chromatography-Mass Spectrometry (GC-MS) analysis indicated that ultrasonic treatment of sludge reduced the macromolecules to small molecules in DOM. Then, electrospray ionization Fourier-transform ion cyclotron resonance mass spectrometry (ESI FT-ICR-MS) analysis revealed that lignin, tannins, and carbohydrates were the main components of sludge DOMs after ultrasound treatment. analysis revealed that lignin, tannins, and carbohydrates were the main components of sludge DOMs after ultrasound treatment. Furthermore, through the Van Krevelen analysis, the major components were CHO (48.50%) and CHOS (23.20%) in the DOM of ultrasonicated sludge. This research provides the basis for the practical application of ultrasonic treatment of sludge and provides basic information for DOM components.

Leaching behaviors of dissolved organic matter from face masks revealed by fluorescence EEM combined with FRI and PARAFAC.

Despite numerous studies investigating the occurrence and fate of microplastics, no effort has been devoted toward exploring the characteristics of dissolved organic matter (DOM) leached from face masks mainly made of plastics and additives used in large quantities during the COVID-19 pandemic. By using FTIR, UV-vis, fluorescence EEM coupling with FRI and PARAFAC, and kinetic models of leaching experiments, we explored the leaching behaviors of face mask-derived DOM (FM-DOM) from commonly used face masks including N95, KN95, medical surgical masks, etc. The concentration of FM-DOM increased quickly at early 0-48 h and reached equilibrium at about 48 h measured in terms of dissolved organic carbon and fluorescence intensity. The protein-like materials ranged from 80.32 % to 89.40 % of percentage fluorescence response (Pi,n) were dominant in four types of FM-DOM analyzed by fluorescence EEM-FRI during the leaching experiments from 1 to 360 h. Four fluorescent components were identified, which included tryptophan-like components, tyrosine-like components, microbial protein-like components, and fulvic-like components with fluorescence EEM-PARAFAC models. The multi-order kinetic model (Radj2 0.975-0.999) fitted better than the zero-order and first-order kinetic model (Radj2 0.936-0.982) for all PARAFAC components of FM-DOM based on equations derived by pseudo kinetic models. The leaching rate constants (kn) ranged from 0.058 to 30.938 and the half-life times (T1/2) ranged from 2.73 to 24.87 h for four FM-DOM samples, following the solubility order of fulvic-like components (C4) > microbial protein-like components (C3) > tryptophan-like components (C1) > tyrosine-like components (C2) for FM-DOM from four types of face masks during the leaching experiment from 0 to 360 h. These novel findings will contribute to the understanding of the underappreciated environment impact of face masks in aquatic ecosystems.

Dissolved organic nitrogen is a key to improving the biological treatment potential of landfill leachate.

Biological treatment is one of the most promising efficient, low-carbon and affordable approaches for the treatment of recalcitrantly degradable wastewater, such as landfill leachate. However, even the macroscopic molecular level analysis of dissolved organic matter (DOM) is limiting to the enhancement of biological treatment efficacy, and there is an urgent need for deeper exploration of DOM to gain insights into the key constraining substances. In the present study targeting at piercing leachate organic at molecular level, nitrogen-containing dissolved organic matter (DOMN) was identified to be the bottleneck that govern the biotreatment potential. The conclusion was made based on two series of experiments that compared the same anoxic-aerobic membrane bioreactor process (A process) operated stably at different regions, and compared with C process that coupling A process with a circulation aeration membrane bioreactor to improve aeration efficiency. The results confirmed that the relative abundance of DOMN was absolutely dominant among the three categories of DOM in all biologically treated samples, contributing to 60.36 %-65.81 % in removed-DOM, 60.33 %-70.95 % in refractory-DOM and 63.14 %-71.36 % in derived-DOM. Specifically, the high latitude A process had much lower DOMN removal rate than the low latitude A process (p < 0.05) and much higher refractory and derivatization rates than the low latitude A process (p < 0.05). DOM had similar results. No statistically significant differences were observed in the proportion of the three categories of DOM (DOMN), the elements composition, and the subcategory composition of the C process compared to the A process, in which the DOM (DOMN) derivation rate of NEC1-C (31.92 % and 33.41 %) was much higher than that of NEC1-A (20.88 % and 22.19 %). However, the AIwa and AImodwa of the derived-DOM (DOMN) were significantly higher in the C process than in the A process, which implied that excessive aeration did not enhance the biological treatment potential of the A process, but instead led to the proliferation of microorganisms and the secretion of extracellular polymer substances, which resulted in the derivation of more complex compounds. The results of the correlation analysis indicated that there were some regional differences in the molecular information of DOMN driven by climate temperature. In addition, it was worth mentioning that the nominal oxidation state of carbon (NOSCwa) of derived-DOMN in different regions of A process was noticeably higher than the corresponding DOM (p < 0.0001), implying that the derived-DOMN were still highly biodegradable, in other words, there was still great room for improving the biological treatment potential of landfill leachate. The present study provided a deeper insight and analysis of landfill leachate at the molecular level (DOMN) through multiple practical engineering cases, with a view to providing a theoretical basis for efficient optimization of biological treatment.

Interaction of reed litter and biochar presences on performances of constructed wetlands.

Constructed wetlands (CWs) are frequently used for effective biological treatment of nitrogen-rich wastewater with external carbon source addition; however, these approaches often neglect the interaction between plant litter and biochar in biochar-amended CW environments. To address this, we conducted a comprehensive study to assess the impacts of single or combined addition of common reed litter and reed biochar (pyrolyzed at 300 and 500 °C) on nitrogen removal, greenhouse gas emission, dissolved organic matter (DOM) dynamics, and microbial activity. The results showed that combined addition of reed litter and biochar to CWs significantly improved nitrate and total nitrogen removal compared with biochar addition alone. Compared to those without reed litter addition, CWs with reed litter addition had more low-molecular-weight and less aromatic DOM and more protein-like fluorescent DOM, which favored the enrichment of bacteria associated with denitrification. The improved nitrogen removal could be attributed to increases in denitrifying microbes and the relative abundance of functional denitrification genes with litter addition. Moreover, the combined addition of reed litter and 300 °C-heated biochar significantly decreased nitrous oxide (30.7 %) and methane (43.9 %) compared to reed litter addition alone, while the combined addition of reed litter and 500 °C-heated biochar did not. This study demonstrated that the presences of reed litter and biochar in CWs could achieve both high microbial nitrogen removal and relatively low greenhouse gas emissions.

Potential retention of dissolved organic matter by soil minerals during wetland water-table fluctuations.

Wetlands export large amounts of dissolved organic carbon (DOC) downstream, which is sensitive to water-table fluctuations (WTFs). While numerous studies have shown that WTFs may decrease wetland DOC via enhancing DOC biodegradation, an alternative pathway, i.e., retention of dissolved organic matter (DOM) by soil minerals, remains under-investigated. Here, we conducted a water-table manipulation experiment on intact soil columns collected from three wetlands with varying contents of reactive metals and clay to examine the potential retention of DOM by soil minerals during WTFs. Using batch sorption experiments and Fourier transform ion cyclotron resonance mass spectrometry, we showed that mineral (bentonite) sorption mainly retained lignin-, aromatic- and humic-like compounds (i.e., adsorbable compounds), in contrast to the preferential removal of protein- and carbohydrate-like compounds during biodegradation. Seven cycles of WTFs significantly decreased the intensity of adsorbable compounds in DOM (by 50 ± 21% based on fluorescence spectroscopy) and DOC adsorbability (by 2-20% and 1.9-12.7 mg L-1 based on batch sorption experiment), to a comparable extent compared with biodegradable compounds (by 11-32% and 1.6-15.2 mg L-1). Furthermore, oxidation of soil ferrous iron [Fe(II)] exerted a major control on the magnitude of potential DOM retention by minerals, while WTFs increased mineral-bound lignin phenols in the Zoige soil with the highest content of lignin phenols and Fe(II). Collectively, these results suggest that DOM retention by minerals likely played an important role in DOC decrease during WTFs, especially in soils with high contents of oxidizable Fe. Our findings support the 'iron gate' mechanism of soil carbon protection by newly-formed Fe (hydr)oxides during water-table decline, and highlight an underappreciated process (mineral-DOM interaction) leading to contrasting fate (i.e., preservation) of DOC in wetlands compared to biodegradation. Mineral retention of wetland DOC hence deserves more attention under changing climate and human activities.

Mass variations and transfer process of shrimp farming pollutants in aquaculture drainage systems: Effects of DOM features and physicochemical properties.

The expansion of aquaculture produces increasing pollutant loads, necessitating the use of drainage systems to discharge wastewater into surface water. To assess the mass variations and transfer process of aquaculture wastewater, an entire aquaculture drainage investigation lasting for 48 h was conducted, focusing on the nutrients, heavy metals, dissolved organic matter (DOM), and physicochemical properties of drainage in a commercial shrimp farm. The findings revealed that early drainage produced more heavy metals, total nitrogen (TN), dissolved organic nitrogen (DON), and feed-like proteins from aquaculture floating feed and additives, whereas late drainage produced more PO43--P and total dissolved phosphorus (TP). A few pollutants, including DON, Cu, and feed-like proteins, were effectively removed, whereas the contents of TN, dissolved inorganic nitrogen, and Zn increased in the multi-level aquaculture drainage system. Limited dilution indicated that in-stream transfer was the main process shaping pollutant concentrations within the drainage system. In the lower ditches, NO3--N, heavy metals, and feed-like proteins exhibited evident in-stream attenuation, while TN and NH4+-N underwent significant in-stream enrichment processes, especially in ditch C, with the transfer coefficient values (vf) of -1.74E-5 and -2.04E-5. This indicates that traditional aquaculture drainage systems serve as nitrogen sinks, rather than efficient nutrient purge facilitators. Notably, DOM was identified as a more influential factor in shaping the in-stream transfer process in aquaculture drainage systems, with an interpretation rate 40.79% higher than that of the physiochemical properties. Consequently, it is necessary to eliminate the obstacles posed by DOM to pollutant absorption and net zero emissions in aquaculture drainage systems in the future. ENVIRONMENTAL IMPLICATIONS: Nutrients, heavy metals, and dissolved organic matter are hazardous pollutants originating from high-density aquaculture. As the sole conduit to natural waters, aquaculture drainage systems have pivotal functions in receiving and purifying wastewater, in which the in-stream transfer process is affected by ambient conditions. This field study investigated the spatial variations, stage distinctions, effects of physicochemical properties, and dissolved organic matter (DOM) features. This finding suggests that the aquaculture drainage system as a nitrogen sink and DOM source. While the DOM is the key factor in shaping the in-stream transfer process, and obstacles for pollutant elimination. This study helps in understanding the fate of aquaculture pollutants and reveals the drawbacks of traditional aquaculture drainage systems.

Quenching residual H2O2 from UV/H2O2 with granular activated carbon: A significant impact of bicarbonate.

UV/H2O2 has been used as an advanced oxidation process to remove organic micropollutants from drinking water. It is essential to quench residual H2O2 to prevent increased chlorine demand during chlorination/chloramination and within distribution systems. Granular activated carbon (GAC) filter can quench the residual oxidant and eliminate some of the dissolved organic matter. However, knowledge on the kinetics and governing factors of GAC quenching of residual H2O2 from UV/H2O2 and the mechanism underlying the enhancement of the process by HCO3- is limited. Therefore, this study aimed to analyse the kinetics and influential factors, particularly the significant impact of bicarbonate (HCO3-). H2O2 decomposition by GAC followed first-order kinetics, and the rate constants normalised by the GAC dosage (kn) were steady (1.6 × 10-3 L g-1 min-1) with variations in the GAC dosage and initial H2O2 concentration. Alkaline conditions favour H2O2 quenching. The content of basic groups exhibited a stronger correlation with the efficiency of GAC in quenching H2O2 than did the acidic groups， with their specific kn values being 8.9 and 2.4 min-1 M-1, respectively. The presence of chloride, sulfate, nitrate, and dissolved organic matter inhibited H2O2 quenching, while HCO3- promoted it. The interfacial hydroxyl radical (HO•) zones were visualised on the GAC surface, and HCO3- addition increased the HO• concentration. HCO3- increased the concentration of persistent free radicals (PFRs) on the GAC surface, which mainly contributed to HO• generation. A significant enhancement of HCO3- on H2O2 quenching by GAC was also verified in real water. This study revealed the synergistic mechanism of HCO3- and GAC on H2O2 quenching and presents the potential applications of residual H2O2 in the H2O2-based oxidation processes.