Establishing a terrestrial proxy based on fluorescent dissolved organic matter from sediment pore waters in the East China Sea

Imprint of incomplete combustion processes on the water column of the anthropogenic-pressured Baltic Sea

This study evaluates the distribution and sources of thermogenic organic matter in the Baltic Sea water column, focusing on polycyclic aromatic hydrocarbons (PAH), dissolved black carbon (DBC), and the imprint of thermogenic organic matter on the dissolved organic matter (DOM) pool. The spatial patterns and complex interactions between land-based and atmospheric sources were assessed from Kiel Bay to Pomeranian Bight within the water column with the combined targeted and untargeted approaches. The findings emphasize the significant influence of terrestrial inputs from the Oder River and autochthonous production composing DOM. In the Pomeranian Bight, PAH and DBC concentrations strongly correlate with land-based discharge, while shipping emissions play a more prominent role in the Arkona Sea. The sea surface microlayer shows unique characteristics in DOM composition, with potential combustion products as an important source revealed by PAH and DOM analyses. Ultrahigh-resolution mass spectrometry identified combustion products, in the DOM pool, providing insights into anthropogenic impacts. This research contributes to a better understanding of the complex dynamics of thermogenic organic matter in coastal environments, highlighting the interplay between land-based sources, shipping emissions, and in-situ processes in the Baltic Sea region.

Unveiling the effects of dissolved organic matter (DOM) extracted from coastal algae and river on the photooxidation of arsenite

The coastal environment is an important ecosystem connecting land and sea, and arsenite (As(III)) in coastal seawater can seriously affect human health through the food chain. However, the effects of dissolved organic matter (DOM) extracted from coastal algae and rivers on As(III) photooxidation remain unclear. Results show that coastal algal DOM (CA-DOM) is significantly more effective than Suwannee River natural organic matter (SRNOM) in photooxidation of As(III), with a rate 8.3 times higher after correcting for light screening effects. CA-DOM accelerates As(III) photooxidation mainly through the 3DOM⁎ pathway, contributing 78.7 % to the process, whereas 3NOM⁎ contributes only 37.2 % for SRNOM. CA-DOM consists primarily of low-excited tyrosine and tryptophan-like protein substances, whereas SRNOM consists of humic and fulvic acid-like substances. Thus, CA-DOM exhibits a higher steady-state concentration of 3DOM⁎, and the 3DOM⁎ reacts much faster with As(III) than the 3NOM⁎. The increase in CA-DOM concentration can significantly accelerate the photooxidation of As(III), whereas the effect of SRNOM concentration is negligible. Increased salinity can accelerate As(III) photooxidation for all types of DOM. Our results provide new insights into the role of DOM from different sources in the photooxidation of As(III) in the natural environment or engineering applications.

Spatial distribution studies on sedimentary organic matter along the shoreline of Arabian Sea: insights from Kollam, Southwest Coast, India

The present study was aimed at investigating the source, quality, and quantity of organic matter and labile fraction of biochemical constituents in the surficial sediments of Arabian Sea Shoreline at Kollam, India, which gives an input into the processes associated with the subsurface geochemistry pattern. About 15 surface sediment samples were collected from the five beaches for this study during January 2021. The samples were analyzed for CHN, total organic carbon (TOC), and labile fraction such as carbohydrates (CHO), proteins (PRO), and lipids (LIP). The TOC/TN ratio revealed that the source organic matter (OM) in the samples was primarily of marine origin and autochthonous, except TM3 at Thirumullavaram. Thirumullavaram is a sheltered beach, and it has low hydrodynamic process. The high organic matter content in TM3 (13.9) may be the originated from the terrestrial input. The hierarchical cluster analysis revealed that TM3 indicate that unique character to other stations. Principal component analysis revealed that three components accounted for 78% of the total variance. PC1 variance was associated with carbon-based organic compounds. PC2 was predominantly influenced by CHO and LOM, suggesting that PC2 may encompass variability associated with these nutritional profiles. PC3 was influenced by LIP and LIP/CHO, showing it may be a lipid-related component. The PRO to CHO ratio is < 1, exhibiting old aged organic matter deposited in sediments and the meso-oligotrophic status. The LIP to CHO ratio, recorded as < 1, exhibits the poor quality of energetic (food) OM in sediments. The sediment samples exhibit the following trend CHO > PRO > LIP.

Sediment porewaters serve as a transient organic carbon pool at the land-ocean interface

The organic carbon (OC) cycle at the land-ocean interface is an important component of the global carbon budget, yet the processes that control the transfer, transformation, and burial of OC in these regions remain poorly understood. In this work, we examined sedimentary OC (SOC) in short core sediments, dissolved inorganic carbon (DIC), dissolved organic carbon (DOC), and chromophoric dissolved organic matter (CDOM), as well as other solutes in sediment porewaters of the Changjiang Estuary and adjacent East China Sea (ECS) shelf. The main goal of this work is to investigate the variation of the sources and composition of different forms of carbon in estuarine sediments associated with different sedimentary regimes, to further understand the role of sediment porewater in carbon sequestration at the land-ocean interface. Concentrations of Fe2+ and Mn2+ in porewaters of the muddy sediments are much higher than those in the sandy sediments, and SO42- decreases with depth in the deep sediment layer, indicating the degradation of SOC in mobile muds is mainly driven by suboxic and/or anoxic diagenetic processes (e.g., iron-manganese reduction). The accumulation of DIC in the muddy sediment is higher compared to the sandy sediment, indicating relatively complete SOC remineralization. The DOC in porewaters of the muddy areas is mainly composed of highly degraded and low molecular weight humic-like substances (C1), whereas in the sandy area, porewater DOC is mainly composed of less degraded and high molecular weight protein-like substances (C2 and C3). The average DOC stock (28.5 t/km2) in the upper 30 cm sediment porewaters is significantly higher than that of DIC (12.5 t/km2) in sandy area, but less in muddy areas (17.0 t/km2 of DOC vs. 25.4 t/km2 of DIC). The total DOC stock in sediment porewaters of the sandy area accounted for ∼61 % of DOC stock in water column of the ECS, indicating that the porewater is an important DOC pool in the ECS. However, this DOC pool is rather transient due to its high reactivity and mobility, especially in sandy area. Nevertheless, compared with other marine environments, the carbon stock of DOC (average of 43.8 t/km2) in porewaters of stable sedimentary environments is much higher than that of DIC (average of 21.7 t/km2). This work further supports the notion that sedimentary regime plays an important role in OC cycling at the land-ocean interface and highlights the significance of sediment porewaters as a vast carbon pool in marine ecosystems.

Characterization and spatiotemporal variations of fluorescent dissolved organic matter in leachate from old landfill-derived incineration residues and incombustible waste

Dissolved organic matter (DOM) influences the bioavailability and behavior of trace metals and other pollutants in landfill leachate. This research characterized fluorescent dissolved organic matter (FDOM) in leachate from an old landfill in Japan during a 13-month investigation. We employed excitation-emission matrix (EEM) fluorescence spectroscopy with parallel factor analysis (PARAFAC) to deconvolute the FDOM complex mixture into three fluorophores: microbial humic-like (C1), terrestrial humic-like (C2), and tryptophan-like fluorophores (C3). These FDOM components were compared with findings from other studies of leachate in landfills with different waste compositions. The correlations among EEM-PARAFAC components, dissolved organic carbon (DOC) concentration, and ultraviolet-visible and fluorescence indices were evaluated. The FDOM in leachate varied spatially among old and extended leachate collected in the landfill and leachate treatment facility. The FDOM changed temporally and decreased markedly in August 2019, November 2019, and April 2020. The strong positive correlation between HIX and %C2 (r = 0.87, ρ = 0.91, p < 0.001)) implies that HIX may indicate the relative contribution of terrestrial humic-like components in landfill leachate. The Fmax of C1, C2, and C3 and the DOC concentration showed strong correlations among each other (r > 0.72, ρ > 0.78, p < 0.001) and positive correlations with leachate level (r > 0.41, p < 0.001), suggesting the importance of hydrological effects and leachate pump operation on FDOM.

Co-influence of biochar-supported effective microorganisms and seasonal changes on dissolved organic matter and microbial activity in eutrophic lake

DOM (dissolved organic matter) play a crucial role in lakes' geochemical and carbon cycles. Eutrophication evolution would influence nutrient status of waters and investigating the DOM variation helps a better understanding of bioremediation on environmental behavior of DOM in eutrophic lakes. In our study, the contents, compositions and characteristics of systematic DOM&SOM (sediment organic matter) were greatly influenced by seasonal changes. But the effective bioremediations obviously reduced the DOM concentration and thus mitigated the eutrophication outbreak risks in water bodies due to the increased MBC (microbial biomass carbon), microbial activity and metabolism. In early summer, the overall DOM in each treatment were readily low levels and derived from both autochthonous and exogenous origins, dominated by fulvic acid-like. In midsummer, the DOM contents and characteristics in each treatment increased significantly as phytoplankton activity improved, and the majority of DOM were humic acid-like and mainly of biological origin. The greatest differences of enzymes, MBC, microbial metabolism and DOM&SOM removal among different treatments were observed in summer months. In autumn, the systematic DOM&SOM slightly reduced due to the deceased microbial activity, in which the microbial humic acids were main component and derived from endogenous sources. Additionally, the gradually decreased SOM with cultivated time in each treatment was a result of microbiological conversion of SOM into DOM. For various treatments, BE, BE.A, BE.C and BE.E increased the MBC, enzymatic and microbial activities due to the application of biochar-supported EMs. Among these, BE and BE.A, especially BE.A with oxygen supplement, achieved the most desirable effect on reducing systematic DOM&SOM levels and increasing enzymatic and microbial activities. The group of EM also reduced the levels of DOM&SOM as improved degradation of EMs for DOM. However, BC, BE.C and BE.E finally did not achieved the desirable effect on reducing DOM&SOM due to the suppression of microbial activities, respectively, from high dose of biochar, weakening of dominant species and additional introduction of EMs in low liveness.

Dissolved organic nitrogen cycling revealed at the molecular level in the Bohai and Yellow Sea

Marginal seas play a crucial role in the cycling of dissolved organic nitrogen (DON) between the terrestrial and marine environments. However, very few studies have considered the molecular transformation of DON in marginal seas, leaving the DON molecular modifications in its cycling largely unknown. Therefore, this study examined DON cycling in the Bohai Sea and Yellow Sea, two semi-closed marginal seas in northern China, using stable isotopes (δ15N and δ13C), optical characteristics, and molecular compositions. Compared to the Yellow Sea, the Bohai Sea had a weaker exchange with the open ocean, resulting in higher concentrations, lower δ15N, and more recalcitrant properties in DON. The DON cycling showed significant differences inside and outside the Yellow Sea Cold Water (YSCW). Degradation was the major sink of DON in the YSCW, during which more highly unsaturated compounds and carboxyl-rich alicyclic molecules were produced. Nitrogen atoms were found to be removed from the molecules with more N atoms to those with fewer ones during the DON degradation. This study discovered the molecular modifications in DON cycling and highlighted the intrinsic mechanisms in the cycling of DON in marginal seas.

Interactions between dissolved organic matter and the microbial community are modified by microplastics and heat waves

Dissolved organic matter (DOM) exists widely in natural waters and plays an important role in river carbon cycles and greenhouse gas emissions through microbial interactions. However, information on DOM-microbe associations in response to environmental stress is limited. River environments are the main carriers of microplastic (MP) pollution, and global heat waves (HWs) are threatening river ecology. Here, through MP exposure and HW simulation experiments, we found that DOM molecular weight and aromaticity were closely related to initial microbial communities. Moreover, MP-derived DOM regulated microbial community abundance and diversity, influenced microorganism succession trajectories as deterministic factors, and competed with riverine DOM for microbial utilization. SimulatedHWs enhanced the MP-derived DOM competitive advantage and drove the microbial community to adopt a K-strategy for effective recalcitrant carbon utilization. Relative to single environmental stressor exposure, combined MP pollution and HWs led to a more unstable microbial network. This study addresses how MPs and HWs drive DOM-microbe interactions in rivers, contributes to an in-depth understanding of the fate of river DOM and microbial community succession processes, and narrows the knowledge gap in understanding carbon sinks in aquatic ecosystems influenced by human activities and climate change.

Explore variations of DOM components in different landcover areas of riparian zone by EEM-PARAFAC and partial least squares structural equation model

Dissolved organic matter (DOM) plays key roles in species-distribution of contaminants and the biogeochemical cycle of carbon in ecosystems. Riparian zone is the representative of water-land ecotone and controls the DOM exchange between water and land. However, the variance of DOM in different landcover areas of an urban river riparian zone is unknown. In this study, fluorescence excitation-emission matrix (EEM) spectroscopy coupled with parallel factor analysis (PARAFAC) and partial least squares structural equation model (PLS-SEM) was applied to character dissolved organic matter (DOM) fractions in four types of landcover riparian areas (natural forest, artificial forest, semi-natural grassland, and cropland) of Puhe River and trace latent factors. Soil samples were collected at 0-20 cm, 20-40 cm, 40-60 cm, and 60-80 cm. The results showed that soil DOM components and humification varied between forests with grassland and cropland samples, and soil humification was obviously higher in the forest samples than that in the grassland and cropland samples. In the natural and artificial forest soils, the humic/fulvic-like were the dominant fractions of DOM, whose variations were smaller than the protein-like with soil depths. However, the tyrosine-like was the representative component in the grassland and cropland soils, whose variation was smaller than the humus substances. According to the PLS-SEM, the DOM components and humification were affected by soil physiochemical properties and DOM sources. The humification in the forest soils had a positive correlation with tryptophan-like, which derived from blended source of the autochthonous and terrigenous. Nevertheless, a positive correlation was observed between humification and humus substances, which could derive from microbial degradation of tyrosine-like, in the grassland and cropland soils. Moreover, the soil physiochemical properties were negatively related to DOM components in all soil samples, which could affect indirectly soil humification. Therefore, EEM combined with PARAFAC and PLS-SEM might be an effective method to investigate DOM fractions and trace the latent factors in different landcover areas of the riparian zone.

Photochemical behavior of constructed wetlands-derived dissolved organic matter and its effects on Bisphenol A photodegradation in secondary treated wastewater

Free water surface flow (FWS) constructed wetlands (CWs) have been broadly applied for polishing secondary treated effluents. Dissolved organic matter derived from FWS CWs (WDOM) plays key roles in contaminants transformations. Conversely, photodegradation could shape the quantity and quality of WDOM, thereby affecting its roles in the photolysis of organic micropollutants (OMPs). Nevertheless, whether and how solar irradiation-induced photodegradation modify the properties of WDOM, and the effects of WDOM on the photodegradation of OMPs remain unclear. This study elucidates the photochemical behavior of two WDOM isolated from field-scale FWS CWs for effluent polishing under simulated sunlight irradiation using spectroscopic tools and high-resolution mass spectra. Furthermore, the roles of WDOM in the photodegradation of Bisphenol A (BPA), as a representative endocrine-disrupting compound (EDC), were comprehensively investigated. Solar irradiation was demonstrated to lower the molecular weight and aromaticity of WDOM, as well as weaken its light absorption. Ultrahigh-resolution mass spectra further confirmed that aromatic and unsaturated structures were susceptible to solar irradiation-induced photodegradation reactions. Subsequently, less aromatic and more saturated structures eventually formed under sunlight irradiation, consistent with the result from spectroscopic characterization. The reactive species produced from WDOM significantly enhanced the photodegradation of BPA with the k_obs noticeably increasing 4-fold compared with the k_obs for direct photolysis. Additionally, ³WDOM* was identified as the dominant reactive species leading to the photolysis of BPA in the presence of WDOM. These findings improve understanding of the phototransformation behavior of WDOM under sunlight irradiation and the roles that WDOM plays in the photochemical fate of coexisting OMPs in CWs treatment systems.

Feasibility of source identification by DOM fingerprinting in marine pollution events

Accurate source identification is the first step of pollution control in environmental emergency management, especially in marine pollution events. Dissolved organic matter (DOM) absorption and fluorescence (excitation-emission matrices, EEMs) analyses were applied to trace contaminant sources for a pollution event that occurred along the coast of Laizhou Bay, Bohai Sea. Parallel factor analysis (PARAFAC) of the EEMs identified four fluorescent components: terrestrial humic-like (C1), tryptophan-like (C2), and a mixture of terrestrial and marine humic-like (C3) and tyrosine-like (C4) components. The relationships among C1 to C4 and quality indices indicated that the DOM originated from terrestrial input and biological activity. The EEMs-PARAFAC results accompanied by the optical characteristics of DOM and fingerprinting demonstrated that the marine pollution event occurred was from enterprise emissions. The numerical simulation confirmed the reliability of EEMs-PARAFAC modeling for DOM fingerprinting of pollution sources in polluted regions. This study provided a feasible method for source recognition in marine pollution events.

Photobleaching reduces the contribution of dissolved organic carbon to glacier melting in the Himalayas and the Tibetan Plateau

Dissolved organic carbon (DOC) makes an important contribution to glacier melting in the Himalayas and the Tibetan Plateau (HTP). Photobleaching can effectively reduce the light absorption ability of DOC, further changing its impact on glacier melting, which is not yet well researched in the HTP. Therefore, snowpit samples from the Bayi, Ganglongjiama (GLJM), Jiemayangzong (JMYZ) and Demula (DML) glaciers were collected to study the influence of photobleaching on the light absorption ability of DOC and its impact on glacier melting. The results showed that the DOC concentration of snowpit samples, which was affected by the melting state and photobleaching, decreased from the northern HTP to the southern HTP. At an early stage of melting, the mass absorption cross-section value at 365 nm (MAC₃₆₅) values showed a negative correlation with DOC concentrations in the snowpit at the JMYZ and DML glaciers, indicating that colored DOC tended to be concentrated in the snowpit during the melting process. With the aggravation of ablation, some snowpit samples in the GLJM and Bayi glaciers had both low concentrations and MAC₃₆₅ values of DOC due to the reduced influence of photobleaching on the light absorption ability of DOC. Similarly, two fluorescence components (one protein-like component and one humic-like component) were identified in the extracted DOC at the JMYZ and DML glaciers, while those components were not detected in the GLJM glacier. Based on the sources of fluorescent DOC and five-day backward air mass trajectories, long-distance transport of pollutants from South Asia was an important source of snowpit DOC in the southern HTP. In this study, photobleaching can effectively remove colored and fluorescent DOC from snowpit samples in the HTP, further reducing the radiation forcing and glacier melting caused by DOC.

Novel Insights into Dissolved Organic Matter Processing Pathways in a Coastal Confined Aquifer System with the Highest Known Concentration of Geogenic Ammonium

High levels of geogenic ammonium in groundwater is a highly neglected nitrogen pool in coastal aquatic systems. Although organic matter (OM) mineralization is known to significantly influence geogenic ammonium enrichment, the detailed mechanism underlying ammonium enrichment based on dissolved organic matter (DOM) characterization in coastal aquifer systems remains unclear. In this study, we characterized the optical and molecular signatures of DOM coupled with hydrogeochemistry and multiple isotopes (H/O/C/N) to elucidate in detail the mechanisms underlying the anomalously high ammonium in the coastal confined aquifer system of the Pearl River Delta, which exhibits the highest reported geogenic ammonium concentration in groundwater on the Earth. We identified three DOM fluorescent components, a marine humic-like component (C1) and two other humic-like components (C2 and C3). The autochthonous OM was first processed to the C1 component, which was further transformed to C2 and C3 components. In terms of molecular classes, the processing pathway from bacterial- or algal-derived OM to aliphatic compounds and highly unsaturated-low O compounds was identified, and highly unsaturated-low O compounds were accumulated as the main products. Compounds containing two or three N atoms were processed, and compounds with one N atom gradually accumulated, which was further degraded into CHO compounds. The ammonium (up to 179 mg/L as N) was gradually enriched due to the decomposition of CHO+3N to CHO+2N, CHO+1N, and CHO compounds. Owing to the longer residence time and less frequent fresh water flushing, the produced ammonium was retained in the aquifer as a "long-term result". The contrasting DOM characteristics, together with the differing depositional and hydrogeological conditions, give rise to the higher levels of geogenic ammonium in coastal confined aquifer systems compared with inland alluvial-lacustrine confined aquifer systems. To our knowledge, this is the first study to characterize DOM and its relationship with geogenic ammonium in coastal aquifer systems.

Remediation of contaminated dredged harbor sediments by combining hydrodynamic cavitation, hydrocyclone, and persulfate oxidation process

A pilot-scale hybrid treatment system consisting of hydrodynamic cavitation (HC), hydrocyclone separator (HS), and sodium persulfate (PS), was employed for removing polycyclic aromatic hydrocarbons (PAHs) from dredged harbor sediments. The effectiveness of PAH degradation was studied by varying the inlet pressure (0-2.0 bar), PS dosage (or Σ[PAH] to [PS] mole ratio of 1:1-1:10³) at HS inflow velocity of 2.85 m/s, slurry concentration of 10%, and reaction time of 60 min. The degradation rate of PAH in the overflow (OF) sediment was significantly lower than that of the underflow (UF) sediment. After an inlet pressure increase of 0.5 bar and ΣPAH: [PS] molar ratio of 1: 10, the PAH removal was 87% and 55% in the UF and OF, respectively, by the combined HC-PS-HS unit. Without PS, the PAHs removal was 46% and 40% in the UF and OF, respectively. The removal efficiency for 6-, 5-, 4-, 3-, and 2-ring PAHs was 100%, 93%, 93%, 92%, and 82% in the UF and 55%, 61%, 67%, 47%, and 36% in the OF by the combined HC-PS-HS system. FEEM spectroscopy clarified that aromatic protein-based components (tryptophan- and tyrosine-like combined) were gradually degraded and transformed into soluble microbial metabolites when organic matter content declined during the combined HC-PS-HS treatment. This study provides new insights into the combined HC-PS-HS system for PAH degradation in dredged sediments.

Hydrodynamic cavitation activation of persulfate for the degradation of polycyclic aromatic hydrocarbons in marine sediments

Hydrodynamic cavitation (HC) coupled with persulfate (PS)-based that resulted in the synergistic degradation of polycyclic aromatic hydrocarbons (PAHs) in contaminated marine sediments. The effects of HC injection pressure and Σ[PAH]: [PS] on the rate and extent of PAH degradation were studied in the pressure range of 0.5-2.0 bar, PS concentration rage of 2 × 10^-4 to 2 × 10^-2 M or Σ[PAH]: [PS] of 1:10-1000, and reaction time of 20-60 min. A pseudo-first-order rate law fitted PAHs removal kinetics well. The degradation rate constant increased with injection pressure, reaching the maximum level at 0.5 bar, then decreased at injection pressure became greater than 0.5 bar. The results showed that PAH removal was 84% by the combined HC and PS process, whereas, HC alone only achieved a 43% removal of PAHs in marine sediments under the optimal inlet pressure of 0.5 bar at PS concentration of 2 × 10^-2 M in 60 min. The HC‒PS system effectively removed PH, PY, FLU, BaA, and CH at 91, 99, 91, 84, and 90%, respectively. The maximum removal of 6-, 5-, 4-, 3-, and 2-ring PAHs was 89, 87, 84, 76, and 34%, respectively. Major reactive oxygen species (ROSs), namely, SO₄^-• and HO•, were responsible for PAHs degradation. Results clearly highlighted the feasibility of HC-PS system for the clean-up of PAHs-laden sediments in particular and other recalcitrant organic contaminants in general.

Distribution, sources, and ecological risks of potentially toxic elements in the Laizhou Bay, Bohai Sea: Under the long-term impact of the Yellow River input

Potentially toxic element (PTE) contamination is a common environmental issue in offshore regions worldwide. Water and sediment samples were collected from the Yellow River downstream and adjacent Laizhou Bay to investigate the residues, sources, and ecological risks of 11 typical PTEs (As, Cd, Co, Cr, Cu, Mn, Ni, Pb, Sc, V, and Zn). The results indicated that the concentrations of PTEs in the sediments decreased from the Yellow River Estuary to the inner Laizhou Bay under the long-term effect of the Yellow River input. Principal component analysis (PCA) identified three potential sources: natural origins, coastal anthropogenic activities (e.g., oil exploration and steel refining), and marine production (e.g., marine aquaculture and transportation). Among the PTEs, Cd was the most significant contaminant, with a contamination factor (CF) of 2.06 ± 0.78. Furthermore, Cd was the most sensitive factor used in evaluating the overall ecological risk using Monte Carlo analysis, with a contribution of up to 96%. Although the overall contamination and risk levels were low in the bay, a higher pollution load index (PLI) and risk index (RI) adjacent to the Yellow River Estuary indicated that the Yellow River remained the primary contributor to the PTEs contamination in the bay.

Spectroscopic fingerprinting of dissolved organic matter in a constructed wetland-reservoir ecosystem for source water improvement-a case study in Yanlong project, eastern China

The coupling between constructed wetlands and reservoir (CWs-R) afforded a novel ecosystem to improve the water quality and increase the emergency storage capacity of micro-polluted river drinking water source. In this study, spectroscopic characteristics of DOM in YL CWs-R ecosystem were first systematic studied based on a three-year field monitoring to investigate the chemical composition, sources and track the involved biogeochemical processes in the ecosystem. Three humic-like components (C1, C2, and C4, em >380 nm) and one protein-like component (C3, em < 380 nm) were identified by PARAFAC model. Significant spatiotemporal variations in concentration and composition of FDOM were observed in YL CWs-R ecosystem. The improved water transparency (SD) and, the increased hydraulic retention time (HRT) along YL CWs-R ecosystem enhance photochemical processes, leading to significant decreases in the intensities of humic-like components in effluent (P < 0.05) with lower degrees of aromaticity, molecular weights, and humification (decrease in HIX and increases in S_R and BIX). In contrast, no significant spatial difference was observed for protein-like component (P > 0.05), which implies that the biodegradation and production of protein-like component may balance each other in the CWs-R ecosystem. The ecological pond unit plays a major role in the removal and transformation of DOM, especially in summer, while wetland purification unit contributes little to DOM reduction. In addition, the decay of aquatic macrophytes in wetland purification unit and the risk of algal bloom in the ecological pond unit might become important autochthonous sources of DOM, especially in summer and autumn. These findings are critical for further understanding the transformation processes of DOM in large-scale CWs-R ecosystems, and could provide important implications to improve sustainable safety of drinking water sources.

Chemically unidentified dissolved organic carbon: A pivotal piece for microbial activity in a productive area of the Northern Patagonian shelf

The biochemical composition and fluorescence properties of DOM were assessed in relation to phytoplankton and major aquatic bacterial clades in a regenerative area of the Argentine Shelf. DOM was mainly of autochthonous biological origin, containing humic- and protein-like substances of medium degree of unsaturation and diagenesis. Biochemical-DOM accounted for 25% of total DOC, being dissolved combined amino acids (DCAA) the dominant fraction followed by free carbohydrates. Phytoplankton was the main source of serine, alanine, and valine, and particulate carbohydrates. Gammaproteobacteria abundance correlated negatively with ammonium and positively with DCAA, suggesting a coupling between ammonium consumption and refractory amino acid production. A preferential utilization of alanine, leucine and threonine as nitrogen source was inferred from the distribution of Cytophaga-Flavobacteria-Bacteroidete in relation with dissolved free amino acids (DFAA). Notably, Alpha- and Betaproteobacteria correlated with the large pool (75%) of chemically unidentified DOC and not with DCAA or dissolved combined carbohydrates. Particularly, Alphaproteobacteria (∼40% of EUB total heterotrophic bacteria) either significantly contribute to the production of the "humic", refractory fraction of marine DOM, or the latter impairs resource control on their abundance. Spatial heterogeneity inherent to coastal-shelf areas drives important regional variability in the biochemical properties of DOM.