Aromatic Dissolved Organic Matter Research Articles

Pollutant-removal and DOM characteristics in an urban stormwater wetland

ABSTRACT Stormwater wetlands play a crucial role in the urban environment, providing many ecosystem services. In this work, a stormwater wetland was developed to study the effects on the removal of pollutants and the characteristics of dissolved organic matter (DOM) under different operating conditions, such as hydraulic retention time (HRT) and water depth. The results showed that the stormwater wetland exhibited excellent pollutant-removal performance, such as NH4 +_N, TN, TP, COD, and suspended solids (SS). The removal rates for these substances reached 79.1%, 73.2%, 89.0%, 84.3%, 80.4%, and 73.77, respectively, with 24 h of HRT and 15 cm of water depth. An increase in HRT can improve the removal rates of TN, TP, COD, and TOC. The removal rates for these parameters decreased with increasing water depth, though, except for TP; the UV–VIS spectral parameters indicated that an obvious decrease occurred in the degrees of humification and aromaticity of DOM with increasing HRT and water depth after the stormwater wetland treatment. Parallel factor (PARAFAC) analysis identified six fluorescent components (one combination of freshly produced biologically labile matter and a tryptophan-like component, one fulvic-like, one humic-like, and three tryptophan-like), whose fluorescence intensity was weakened after the stormwater wetland treatment. The lowest intensity appeared with 24 h of HRT and 15 cm of water depth. This study could be beneficial for understanding and managing stormwater wetlands, thus alleviating the impacts of pollutants on urban environments.

Sources and Spatial Variation of Dissolved Organic Matter in Summer Water of Inflow Rivers Along Chaohu Lake Watershed

The sources and spatial variations of dissolved organic matter (DOM) in summer water of inflow rivers (FL, HB, QY, ZH, and NF) along the Chaohu Lake watershed were analyzed using the ultraviolet-visible absorption spectrum (UV-vis) method and three-dimensional excitation emission matrix fluorescence spectroscopy-parallel factor analysis (EEM-PARAFAC). The specific ultraviolet absorbance of DOM at 254 nm in the NF river was lower than in other rivers, and the spectral slope ratio (SR) of the NF river was higher than that of the HB river. This showed that the urban runoff inputs reduce the aromaticity of DOM in the NF river water, but has little effect on the molecular weight. The high fluorescence index (FI) and biological index, and the low humification index, indicated the main autochthonous sources of the DOM in the NF river. Four humic-like components (C1-C4), comprising terrestrial organic matter (C1, C3, and C4) and microbial degradation products (C2), and two protein-like components (C5 and C6) were identified as the main sources of DOM in the inflow rivers along the Chaohu Lake watershed. The dissolved organic carbon and DOM fluorescence components in the river water exhibited spatial variation along the direction of flow. The DOM in water from FL, HB, QY, and ZH was sourced from soil runoff inputs, whereas in NF water, it was mainly sourced from urban runoff and wastewater treatment plant effluents.

Microbial Roles in Dissolved Organic Matter Transformation in Full-Scale Wastewater Treatment Processes Revealed by Reactomics and Comparative Genomics.

Understanding the degradation of dissolved organic matter (DOM) is vital for optimizing DOM control. However, the microbe-mediated DOM transformation during wastewater treatment remains poorly characterized. Here, microbes and DOM along full-scale biotreatment processes were simultaneously characterized using comparative genomics and high-resolution mass spectrometry-based reactomics. Biotreatments significantly increased DOM's aromaticity and unsaturation due to the overproduced lignin and polyphenol analogs. DOM was diversified by over five times in richness, with thousands of nitrogenous and sulfur-containing compounds generated through microbe-mediated oxidoreduction, functional group transfer, and C-N and C-S bond formation. Network analysis demonstrated microbial division of labor in DOM transformation. However, their roles were determined by their functional traits rather than taxa. Specifically, network and module hubs exhibited rapid growth potentials and broad substrate affinities but were deficient in xenobiotics-metabolism-associated genes. They were mainly correlated to liable DOM consumption and its transformation to recalcitrant compounds. In contrast, connectors and peripherals were potential degraders of recalcitrant DOM but slow in growth. They showed specialized associations with fewer DOM molecules and probably fed on metabolites of hub microbes. Thus, developing technologies (e.g., carriers) to selectively enrich peripheral degraders and consequently decouple the liable and recalcitrant DOM transformation processes may advance DOM removal.

Wildfire-Derived Pyrogenic Carbon Modulates Riverine Organic Matter and Biofilm Enzyme Activities in an In Situ Flume Experiment.

Wildfires produce large amounts of pyrogenic carbon (PyC), including charcoal, known for its chemical recalcitrance and sorption affinity for organic molecules. Wildfire-derived PyC can be transported to fluvial networks. Here it may alter the dissolved organic matter (DOM) concentration and composition as well as microbial biofilm functioning. Effects of PyC on carbon cycling in freshwater ecosystems remain poorly investigated. Employing in-stream flumes with a control versus treatment design (PyC pulse addition), we present evidence that field-aged PyC inputs to rivers can increase the dissolved organic carbon (DOC) concentration and alter the DOM composition. DOM fluorescence components were not affected by PyC. The in-stream DOM composition was altered due to leaching of pyrogenic DOM from PyC and possibly concurrent sorption of riverine DOM to PyC. Decreased DOM aromaticity indicated by a lower SUVA245 (−0.31 unit) and a higher pH (0.25 unit) was associated with changes in enzymatic activities in benthic biofilms, including a lower recalcitrance index (β-glucosidase/phenol oxidase), suggesting preferential usage of recalcitrant over readily available DOM by biofilms. The deposition of particulate PyC onto biofilms may further modulate the impacts of PyC due to direct contact with the biofilm matrix. This study highlights the importance of PyC for in-stream biogeochemical organic matter cycling in fire-affected watersheds.

Mechanistic Investigation of Enhanced Photoreactivity of Dissolved Organic Matter after Chlorination.

Chlorine is commonly used in disinfection processes in wastewater treatment plants prior to discharge of the effluents into receiving waters. Effluent organic matter and humic substances constitute up to 90% of dissolved organic matter (DOM) in receiving water, which induces photogeneration of reactive species (RS) such as excited triplet state of DOM (3DOM*), singlet oxygen (1O2), and hydroxyl radical (•OH). The RS plays an important role in the attenuation of trace pollutants. However, the effect of chlorine disinfection on the photoreactivity of the DOM has remained unclear. Here, we investigated the physicochemical properties and subsequent RS variation after chlorination of DOM. Solid-state 13C cross-polarization/magic angle-spinning NMR and Fourier transform ion cyclotron resonance mass spectrometry verified that the aromaticity, electron-donating capacity (EDC), and average molecular weight of DOM decreased markedly after chlorination. It was found for the first time that the photoproduction of 3DOM*, 1O2, and •OH increased markedly after chlorination of DOM upon irradiation of simulated sunlight. The quantum yields of 3DOM*, 1O2, and •OH were positively correlated with E2/E3 (ratio of the absorbance at 254 to 365 nm) while negatively correlated with EDC before and after chlorination. These findings highlight the synergetic effect of chlorine disinfection on the photosensitization of DOM under irradiation of sunlight, which will promote the removal of trace pollutants in surface waters.

Dynamic changes in size‐fractionated dissolved organic matter composition in a seasonally ice‐covered Arctic River

AbstractArctic rivers are sensitive to climate and environmental change, but the biogeochemical response remains poorly understood. Monthly size‐fractionated dissolved organic matter (DOM) samples from the lower Yukon River were characterized using UV–visible, fluorescence, and Fourier transform‐infrared (FT‐IR) spectroscopy techniques. The EEM‐PARAFAC analysis revealed three major fluorescent DOM components, including two humic‐like components (C480 and C400) and one protein‐like component (C310), with their relative importance following the order of C480 ≥ C400 > C310 in the high‐molecular‐weight DOM (1 kDa–0.4 μm) and C400 > C480 > C310 in the low‐molecular‐weight DOM pool (< 1 kDa). Transformation in DOM and change in sources were manifested in major fluorescent components and optical properties, including biological index (BIX), humification index (HIX), spectral slope (S275–295) and specific UV absorbance at 254 nm (SUVA254). These changes occurred within different DOM size‐fractions and among ice‐covered, spring freshet, and open seasons. Joint analysis of EEM and FT‐IR spectra using a data fusion technique showed that humic‐like DOM is mostly associated with C─H, C═C, and C─O bonds, while protein‐like DOM is correlated more with C─N and N─H related structures. DOM aromaticity and the ratios of HIX to BIX and protein‐like to humic‐like components may be used as a compelling proxy to measure change in source waters and to infer permafrost dynamics. Our results provide insight into the seasonal variation in DOM composition for different size‐fractions in the lower Yukon River, and a baseline dataset against which future changes can be understood in the context of arctic basin biogeochemical cycling.

Spatio‐temporal changes in dissolved organic matter composition along the salinity gradient of a marsh‐influenced estuarine complex

AbstractThe interconnected estuarine complex of the Altamaha River and adjacent sounds located in Georgia (USA) functions as a hotspot for organic matter transformation as it is transported to the Atlantic Ocean. Here, we investigated how dissolved organic matter (DOM) composition changes both spatially and seasonally along the estuary and how it influences bacterial processing. Surface samples were collected during high tide at fifteen stations throughout the estuary in April, July, October 2017, and January 2018. Bulk, optical, and molecular analyses were conducted on samples before and after dark incubations to assess DOM sources and transformation patterns in the system. The dominant driver of change in DOM composition was found to be the terrigenous‐marine gradient in organic matter sources. Six distinct clusters were identified based on the terrigenous signature of the DOM pool, explaining 45% of the variance in DOM composition in the system. Bacterial consumption of dissolved organic carbon (DOC) was strongly influenced by DOM composition, with increased degradation rates for DOM with a larger terrigenous character. However, changes in optical properties suggested that less aromatic DOM that co‐varied with the terrigenous material was preferentially degraded. The passage of Hurricane Irma in September 2017 resulted in a 27% ± 7% increase in DOC content, likely due to inundation associated with storm surge and increased local precipitation, and DOC biodegradation was 17% ± 8% higher than during summer. These effects lasted for at least one month after the storm, revealing that hurricanes can have a large impact on DOM composition and cycling in coastal systems.

Release Mechanisms of Carbon Source and Dissolved Organic Matter of Six Agricultural Wastes in the Initial Stage

As carbon sources for the denitrification process, agricultural wastes have some problems, such as excess release of organic carbon; unclear release characteristics of nitrogen, phosphorus, and colorimetric substances; and unclear components, release mechanisms, and potential effects of the released dissolved organic matter (DOM) in the start-up period. To resolve those problems, rice straw, wheat straw, corn stalk, corncob, soybean stalk, and soybean hull were selected as denitrification carbon sources to investigate the release mechanisms and potential influences of the organic matter, secondary pollutants, and DOM. The results showed that the six agricultural wastes could be used as the denitrification carbon source. The carbon content in the wheat straw was the highest and the secondary pollution risk from the corncob was the lowest. For the six carbon sources, the second-order kinetic equation and Ritger-Peppas equation were followed during the 1-120 h carbon release process. The fitting results demonstrated that corncob was more suitable for use as the denitrification carbon source because of its moderate cm value and longer t1/2 value, and the release mechanisms of the six types of carbon sources were mainly controlled by the diffusion process. The NH4+-N, TN, and TP contents in the immersion water of the rice straw were higher than those of the five other agricultural wastes, and there was heavy chromaticity in the immersion water of the wheat straw and corn stalk. The amounts of nitrogen, phosphorus, and chromatic substances released from the corncob were the lowest. The leachates of the corncob and soybean hull had higher biodegradability and lower risks of secondary pollution than those of the other sources. The aromaticity and molecular weight of DOM increased as the reaction time increased, and the humification of DOM was low. Five components were identified by PARAFAC. The main component was protein-like matter, which was mainly composed of tyrosine-like and tryptophan-like substances. There was less humic acid-like matter in the immersion water. The component characteristics of DOM might have had an adverse effect on the subsequent water treatment process. These results could provide theoretical support for the impact on effluent water quality and risk assessment when the agricultural wastes are used as an additional denitrification carbon source at the start-up stage.

Seasonal transformations of dissolved organic matter and organic phosphorus in a polymictic basin: Implications for redox-driven eutrophication

Redox-driven internal phosphorus (P) loading from lake sediments is a key process for propagating and sustaining cyanobacterial blooms in freshwater lakes. Missisquoi Bay in Lake Champlain, VT regularly experiences cyanobacterial blooms driven by internal P loading as well as from seasonal transitions, but the response of dissolved organic matter (DOM) to these changing conditions has previously not been investigated in this system and seldom in other redox-dynamic freshwaters. In this study, Fourier transform-ion cyclotron resonance mass spectrometry (FT-ICR MS) has been employed to explore the seasonal transformation and distribution of DOM, including organic P (DOP), from spring 2017 to winter 2018 along with high-frequency geochemical monitoring. DOM was largely composed of allochthonous compounds with unique molecules from seasonal autochthonous sources and greater proportions of N,S-containing formulae after the early summer bloom season and during the winter. DOM compositions from spring to late summer was more aliphatic during the early bloom season, while DOM between late summer to winter was more aromatic with greater similarities between the two seasons. In contrast, DOP compositions from all seasons were highly dissimilar and suggested a compartmentalized water column, where riverine DOP compounds that were degraded during transport and in surface waters were largely absent in the benthic DOP. Additional sediment core incubation experiments were implemented to study the effects of short-term oxygen limitation on DOM and DOP composition to better constrain potential redox-based drivers of their mobility between sediment and the water column. Short-term incubations suggested an increase in aliphatic DOM and new DOP compounds, with little change in aromatic DOM, suggesting selective mobilization driven by microbial iron(III) and manganese(IV) reduction. Together, these detailed FT-ICRMS data show, for the first time, how DOM and DOP from various sources respond to changing physical and geochemical conditions in redox-dynamic freshwaters, demonstrating how these compounds cycle in freshwater settings and likely impact nutrient bioavailability.

Carbon, nitrogen and phosphorus stoichiometry controls interspecific patterns of leaf litter-derived dissolved organic matter biodegradation in subtropical plantations of China

Leaching of leaf litter is the primary source of dissolved organic matter (DOM) in forest soils. However, the interspecific variations of litter-derived DOM characteristics and biodegradation and their controlling factors remain unclear in subtropical plantations. Using fresh leaf litter of two broadleaf trees (Liquidambar formosana and Schima superba) and two coniferous trees (Pinus massoniana and P. elliottii) in subtropical plantations of China, we assessed the effects of tree species on the amounts and properties of litter-derived DOM with a short-term leaching experiment, and examined the interspecific variation of DOM biodegradation using a 56-day laboratory incubation method. Broadleaf tree litter generally leached higher amounts of dissolved organic carbon (DOC), dissolved total nitrogen (DTN), and dissolved total phosphorus (DTP) than coniferous tree litter. Compared with coniferous trees, broadleaf trees had higher DOM aromaticity and molecular weight, but lower DOC:DTP and DTN:DTP ratios in the litter leachates. Despite greater DOM aromaticity and molecular weight, broadleaf trees had higher litter-derived DOM biodegradation than coniferous trees because of the relatively lower DOC:DTP and DTN:DTP ratios. These results indicate the distinct patterns of litter-derived DOM characteristics and biodegradation between broadleaf and coniferous trees, and also highlight the predominant role of C:N:P stoichiometry in driving the interspecific variation of litter-derived DOM biodegradation in subtropical plantations of China.

Revealing the characteristics of dissolved organic matter in urban runoff at three typical regions via optical indices and molecular composition

Dissolved organic matter (DOM) plays a major role in ecological systems and influences the fate and transportation of many pollutants. Despite the significance of DOM, understanding of how environmental and anthropogenic factors influence its composition and characteristics is limited, especially in urban stormwater runoff. In this article, the chemical properties (pollutant loads, molecular weight, aromaticity, sources, and molecular composition) of DOM in stormwater extracted from three typical end-members (traffic, residential, and campus regions) were characterized by UV–visible (UV–vis) spectroscopy, excitation-emission matrix spectroscopy combined with parallel factor analysis (EEM-PARAFAC), and ultra-performance liquid chromatography quadrupole time-of-flight mass spectrometry (UPLC-Q-TOF-MS). There are three findings: (1) The basic properties of DOM in stormwater runoff varied obviously from three urban fields, and the effect of initial flush was also apparent. (2) The DOM in residential areas mainly came from autochthonous sources, while allochthonous sources primarily contributed to the DOM in traffic and campus areas. However, it was mainly composed of terrestrial humic-like components with CHO and CHON element composition and HULO and aliphatic formulas. (3) The parameters characterizing DOM were primarily related to terrestrial source and aromaticity, but their correlations varied. Through the combination of optical methods and UPLC-Q-TOF spectrometry, the optical and molecular characteristics of rainwater are effectively revealed, which may provide a solid foundation for the classification management of stormwater runoff in different urban regions.

Photodegradation of dissolved organic matter of chicken manure: Property changes and effects on Zn2+/Cu2+ binding property

Untreated livestock manure contains high concentrations of dissolved organic matter (DOM), which can enter the environment through leaching and eluviation, showing an important impact on the environment. In this research, fresh chicken manure from a large-scale chicken farm was collected as the source of DOM. The infrared spectrum of the original DOM was characterized. TOC analysis, UV spectrum and 3D fluorescence spectrum were used to measure the properties of DOM before and after photodegradation. Infrared spectroscopy results show that chicken manure DOM may contain aliphatic and aromatic compounds, alcohols, phenols, polysaccharides and some protein substances; In three systems, the order of TOC removal rates of DOM was water + UV system (85%) > > water + simulated sunlight system (7.2%) > ice + simulated sunlight system (4.5%); Changes of UV spectra, fluorescence spectra, molecular weight distribution and pH value show that, in three systems, as the illumination time increased, photodegradation reduced pH value of the systems, aromaticity and humus contents of DOM, while increased the proportion of medium and/or small molecular weight components of DOM. The amounts of all these changes were proportional to DOM photodegradation rates in the system. The binding ability of DOM with Cu2+ and Zn2+ in water solution decreased significantly after the photodegradation.

Characteristics, Sources, and Seasonal Variability of Dissolved Organic Matter (DOM) in the Ganges River, Bangladesh

This study investigated seasonal variability of sources and fluorescence characteristics of dissolved organic matter (DOM) in the Ganges River using three-dimensional excitation-emission matrix (3DEEM) spectroscopy and parallel factor analysis (PARAFAC). 3DEEM and PARAFAC identified five fluorophores (Peak: A, C, M, T, W) and four fluorescent components, i.e., detergent, fulvic acid (M-type), fulvic acid (C-type), and protein-like, respectively, showing high fluorescence characteristics in the pre-monsoon (March-June) and monsoon (July-October) compared to the post-monsoon (November-February) period. Dissolved organic carbon (DOC) and Specific ultraviolet absorbance (SUVA254) were in the range 1.85-4.7 mg/L and 1.23-5.51 L/mg-m, respectively. DOM components were both fresh and microbial-derived throughout the year. Local hydrological and physicochemical conditions supported the autochthonous and aromatic DOM production in post-monsoon, and richness of terrestrial-derived natural and anthropogenic DOM in the pre-monsoon and monsoon periods. The molecular weight of DOM decreased from the mid of pre-monsoon and continued till monsoon with the increase of terrestrial-derived DOM and photo-irradiation as well as microbial activity. Tryptophan-like fluorescence (TLF) showed high intensity throughout the peak-flow pre-monsoon and monsoon periods, demonstrating a high to intermediate risk of microbial contamination of the Ganges River. The seasonal variability of DOM characteristics suggests that the source and biogeochemistry of DOM in the Ganges Rivers might be sensitive to local hydrology and climate. • DOC concentrations and DOM fluorescence intensity attained their highest values at the beginning of monsoon and showed high seasonal variability. • The compositions of DOM carried by the Ganges River varied at different times of the year, and fresh, autochthonous and less aromatic DOM dominated in the late pre-monsoon and monsoon. • PARAFAC model identified four fluorescent DOM components (detergent-, fulvic- (M like), fulvic- (C like) and protein-like) which showed high seasonal variability with rainfall and river discharge.

Relationships between dissolved black carbon and dissolved organic matter in streams

Black carbon (BC) is a pyrolyzed product derived from incomplete combustion. A major fraction of BC produced by landscape fires is initially deposited onto onsite soils. Atmospheric deposition of soot is known to be an important source of soil BC, especially in watersheds that are not affected by landscape fires. The transport of the dissolved fraction of oxidized BC in soil, defined as dissolved black carbon (DBC), to streams is considered one of the important loss pathways of BC in soil, but the mechanism is not well documented. We measured the quantity and quality of DBC, determined by a benzenepolycarboxylic acid method, and the quantitative and qualitative parameters of bulk dissolved organic matter (DOM) in streams in Hokkaido, northern Japan, whose catchments were not affected by landscape fire for at least 110 years. DBC with relatively low polycondensed signatures occurred in the streams, irrespective of differences in watershed characteristics and seasons, suggesting that atmospheric deposition of soot into the catchment is probably a major source of stream DBC. The DBC concentration was linearly related to the dissolved organic carbon (DOC) concentration, irrespective of the differences in watershed characteristics and seasons. Furthermore, the polycondensation degree of DBC was observed to correlate with the qualitative parameters of bulk DOM. Such quantitative and qualitative relationships between DBC and bulk DOM imply that the transfer mechanism from soils to streams of soot-derived polycondensed DBC is linked with that of higher plant-derived, high-molecular-weight aromatic DOM.

Amount and biodegradation of dissolved organic matter leached from tree branches and roots in subtropical plantations of China

Dissolved organic matter (DOM) plays a crucial role in biogeochemical cycles and ecosystem functions in forests. However, our understanding of wood litter-derived DOM amounts and biodegradation in forest ecosystems remains limited. In this study, we collected branches and roots with varying diameters (2.0–5.0 mm and 5.0–12.0 mm in diameter) from four common tree species (Liquidambar formosana, Schima superba, Pinus massoniana, and Pinus elliottii) in subtropical plantations of southern China. We measured the amounts of dissolved organic carbon (DOC), dissolved total nitrogen (DTN), and dissolved total phosphorus (DTP), and DOM aromaticity in the litter leachates from a short-term leaching experiment. Here, the specific ultraviolet absorbances at 254 nm and 350 nm were used to indicate DOM aromaticity. We subsequently performed a 28-day incubation experiment to investigate wood litter-derived DOM biodegradation. Our results showed that, irrespective of tree species, branches often leached lower amounts of DOC with lower aromatic content than roots at each diameter class. For both branches and roots, DOC quantity generally increased with decreasing diameter class, but aromatic content showed an opposite trend. Moreover, DOM biodegradation increased with increasing diameter class, and branches had greater DOM biodegradation than did roots. In addition, DOM biodegradation exhibited no significant relationship with DOC:DTN and DOC:DTP ratios, but correlated negatively with DOM aromaticity. These observations highlight the crucial roles of organ type and diameter in regulating wood litter-derived DOM amount and biodegradation, and suggest that DOM chemistry rather than stoichiometry drives the variation of wood-derived DOM biodegradation in subtropical plantations of China.

Hydrological seasonality largely contributes to riverine dissolved organic matter chemical composition: Insights from EEM-PARAFAC and optical indicators

Dissolved organic matter (DOM) chemodiversity shows spatial and temporal variations in aquatic systems due to different biogeochemical process and complex sources. However, there remains a large gap on DOM compositions and source proportion, as well as factors driving DOM chemical compositions and source variations in monsoonal rivers of China. Here, 126 water samples were collected from monsoonal rivers in both dry and wet seasons in the ThreeGorgesReservoir (TGR) region, an area characterized by monsoonal climate. We therefore consequently investigated the temporaland spatial variations of DOM compositions and sources using UV–Visible absorption and fluorescence excitation emission matrix (EEM)-parallel factor analysis (PARAFAC) as well as principal component analysis (PCA). There was higher degree of humification, aromaticity and lignin substances of DOM in the wet season than in the dry season. EEM-PARAFAC analysis identified four fluorescent components of DOM in the dry season and three components in the wet season. More protein-like component (tryptophan-like) was identified in the dry season when compared to the wet season, demonstrating that biological and autochthonous sources were the primary source of DOM in the dry season. PCA and the percentage of components also demonstrated more autochthonous sources and weaker terrestrial sources of DOM in the dry season. The spatial distribution of DOM optical properties demonstrated the higher protein abundance and lower molecular weight in urban land use and farmland area along the river bank. The findings demonstrated that hydrological seasonality and anthropogenic activities were key drivers for the DOM compositions and sources variations, which will improve our understanding on the crucial role of DOM in biogeochemical cycle, as well as help to guide water quality protection in the monsoonal rivers.

Effect of UV/chlorine treatment on photophysical and photochemical properties of dissolved organic matter

Dissolved organic matter (DOM) is a ubiquitous component in effluents, DOM discharged with an effluent can affect the composition and properties of natural DOM in the receiving waters. As the photophysical and photochemical properties of effluent DOM can be changed by wastewater treatment processes, the effect of UV/chlorine treatment on the photophysical and photochemical properties of DOM was investigated using Suwannee River fulvic acid (SRFA) and Suwannee River natural organic matter (SRNOM) as representatives. Results showed that the absorbance of the two DOM was significantly decreased. The evolution trends of three representative photophysical parameters upon increase of chlorine dosages were observed. Also, a decrease in DOM aromaticity, molecular weight and electron-donating capacity was observed upon increasing chlorine dosage. Quantum yields of excited triplet state of DOM (3DOM*), singlet oxygen (1O2) and hydroxyl radicals (·OH) first decreases and then increased in the UV/chlorine systems upon increasing chlorine dosages due to the different reaction pathways of the two DOM. Moreover, 3DOM* can not only be regarded as a “controller” of other reactive intermediates, but also effectively promote the photodegradation of bezafibrate, which is classified as a persistent organic contaminant. This study gives deep insights into effects of UV/chlorine on the photophysical and photochemical properties of DOM, and is helpful for understanding the dynamic roles of DOM in the photodegradation of micropollutants.

Contrasting the Optical Characterization of Dissolved Organic Matter in Water and Sediment from a Nascent River-Type Lake (Chongqing, China)

Carbon cycling in rivers is altered by the creation of impoundments through dam construction. This paper seeks to identify the source and composition of dissolved organic matter (DOM) in both water and sediment in Lake Longjing by contrasting the optical characterization of DOM. By comparing the dissolved organic carbon (DOC) concentrations, we show that the sediment (53.7 ± 16.6 mg/L) acts as a DOC source to the overlying water (23.1 ± 1.4 mg/L). The estimated DOC flux in the original reservoir region (88.3 mg m−2 d−1) is higher than that in the newly submerged region (26 mg m−2 d−1), whereas the latter has larger contribution to the DOC annual load because of its larger sediment area. Spectroscopic analysis suggested that pore waters had higher aromaticity and lower proportion of fresh DOM than those in surface waters and benthic overlying waters. Through Parallel Factor Analysis, four fluorescent components were identified, i.e., two terrestrial humic-like components, one protein-like, and one microbial humic-like. Spearman correlation and Non-Metric-Multidimensional Scaling (NMDS) analysis manifested that fluorescent DOM in surface sediments is mainly contributed by autochthonous source, the others by allochthonous source. Due to the high sensitivity of the fluorescent intensity of the protein-like component, it is a useful indicator to reveal the changes of source of DOM.

Resource aromaticity affects bacterial community successions in response to different sources of dissolved organic matter

Microbe-mediated transformation of dissolved organic matter (DOM) contributes substantially to the carbon dynamics and energy flow of aquatic ecosystems; yet, the temporal dynamics of bacterial communities in response to diverse DOM sources are scarcely known. Here, we supplied four distinct sources of DOM (algae-derived, macrophyte-derived, sewage-derived, and soil-derived) to the same bacterial community to track the effects of these DOM sources on the carbon processing and successional dynamics of bacterial communities. Although by the end of the incubation the proportion of bio-degraded DOM was significantly lower in the soil-derived DOM treatment than for the other sources, rapid initial metabolism of protein-like and aliphatic compounds and increasing aromaticity and humification degree of DOM during the incubation period were observed for all sources. The role of stochastic processes in governing the community assembly decreased substantially from 61.4% on the first day to 16.7% at the end of the incubation. Moreover, stronger deterministic selection and lower temporal turnover rate were observed for the soil-derived than the other DOM sources, indicating stronger environmental filtering by the more aromatic DOM. Significant correlations were also observed between the humification index (HIX) of DOM and bacterial community diversities, co-occurrence patterns, habitat niche breadths, and the contribution of deterministic ecological processes. In addition, we demonstrated that taxa with different abundance patterns all play crucial but different roles in the response to DOM variation. Our results indicate the importance of DOM aromaticity as a predictor of the outcome of different DOM sources on bacterial community dynamics.

Dissolved Organic Matter in Continental Hydro-Geothermal Systems: Insights from Two Hot Springs of the East African Rift Valley

Little is known about the quantity and quality of dissolved organic matter (DOM) in waters from continental geothermal systems, with only a few reports available from the Yellowstone US National Park. In this study, we explored the chemodiversity of DOM in water samples collected from two geothermal hot springs from the Kenyan East African Rift Valley, a region extremely rich in fumaroles, geysers, and spouting springs, located in close proximity to volcanic lakes. The DOM characterization included in-depth assessments performed by negative electrospray ionization Fourier-transform ion cyclotron resonance mass spectrometry (FT-ICR-MS). Reduced, saturated and little aromatic DOM compounds were dominant in the hot spring waters collected from either the Ol Njorowa gorge (ON) or the south shore of the soda-saline Lake Elementaita (ELM). Oxygen-poor and sulfur-bearing DOM molecules prevailed in ON, probably reflecting abiotic sulfurization from sulfide-rich geofluids. Nitrogen-bearing aliphatic and protein-like molecules were abundant in ELM, possibly perfusing through the organic-rich sediments of the adjacent Lake Elementaita. Notably, the heat-altered DOM of ancient autochthonous derivation could represent an overlooked source of aliphatic organic carbon for connected lentic environments, with a potential direct impact on nutrient cycling in lakes that receive geothermal water inputs.