Distribution Of Dissolved Organic Matter Research Articles

Autochthonous sources and biogeochemical processes drive the spatiotemporal variation of DOM composition and optical indicators in a karst river

Dissolved organic matter (DOM), as a large carbon pool, is key to biogeochemical cycles, especially in some unique areas. Karst rivers typically exhibit unique biogeochemical characteristics and different human inputs; whether and how these special differences affect DOM distribution, transport and composition are not clear. Here, 134 samples were obtained from the Daning River, a typical karst river located in the mountain landscapes of the Yangtze River, during both the dry and wet seasons. Multiple methods including UV–visible absorption, three-dimensional fluorescence spectroscopy parallel factor analysis (PARAFAC), principal component analysis (PCA) and correlation analysis were used to research the molecular compositions, optical properties and origins of DOM. During the wet season, there was higher aromaticity and intensity of UV absorbing functional groups in DOM. The higher Fmax of the protein-like component in the wet season suggested more biological sources in DOM. PCA indicated that autochthonous sources and biodegradation were the main sources of DOM during the two seasons. During the dry season, forest showed the opposite effect on DOM quality when compared to farmland and urban. The findings demonstrated that monsoonal climate and biogeochemical processes were the primary reasons for the differences in DOM components and sources, which benefits the understanding of carbon biogeochemical processes in the karst rivers. More importantly, the analysis of DOM composition and sources can provide valuable insights into identifying potential contaminants and understanding water quality variations, which is beneficial to the concrete implementation of water protection.

Optical signatures of dissolved organic matter in the Siberian Rivers during summer season

Rivers are the main way of mobilizing, transforming and transporting of dissolved organic carbon to the ocean, thus largely determining the features of the carbon cycle on the Arctic shelf and in the Arctic Ocean as a whole. Seasonal variations in dissolved organic matter (DOM) fluxes from land to sea have been well documented in the Siberian river’s deltas, yet remarkably little is known about how DOM varies with hydrograph within the rivers main stems. The distribution of DOM and its optical characteristics as well as the CO2 fluxes between river water and the atmosphere in the main channel and tributaries of Siberian rivers such as the Lena, the Ob and the Anadyr in summer (July) were studied. The aim of this study was to investigate spatial changes in dissolved organic carbon (DOC) concentrations and DOM composition based on its absorption properties along the riverine main stem, to compare the dynamics of DOC concentration and DOM properties in different Siberian rivers and to reveal the main factors determining its variability, to evaluate the relationship of DOM with carbonate chemistry of riverine waters. The observed spatial variability of the investigated parameters in the river channel was strongly influenced by the river hydrograph along with landscape and geographical features of its catchment area. The phase of river runoff differed significantly in the same time period in different river sections, thus largely determining the quantitative and qualitative variations in the composition of DOM. In the Ob River the inflow of water from its largest tributary, the Irtysh River, is also an important factor of spatial variations. During the summer low-flow period, less aromatic DOM was found in river waters; it was more photodegraded with a relatively low molecular weight of compounds, compared to the high-water period. Such dynamics is one of the factors that alter the carbonate chemistry of waters as well as the magnitude and direction of CO2 fluxes between river water and the atmosphere.Higher DOC concentrations and higher aromatic DOM were found in the Ob River waters compared to the waters of ‘permafrost’ rivers – the Lena and the Anadyr rivers, which was caused by higher soil organic carbon content and its greater availability determined by the state of permafrost located in the river’s watersheds. A strong correlation between DOC concentrations and the colored fraction of DOM was established, thus confirming the possibility of using the latter as a proxy of DOC concentrations in Siberian rivers. The unique information obtained on the properties and variability DOM, which enters the rivers in different flow phases along the main stem, allows a more accurate evaluation of the effect of changing climate on biogeochemical cycles in the Arctic.

Interactions between particulate organic matter and dissolved organic matter in a weak dynamic bay revealed by stable isotopes and optical properties

Few studies have incorporated the tools of stable isotopes and optical properties to study the biogeochemical process of organic matter (OM), including particulate organic matter (POM) and dissolved organic matter (DOM), which prevents our comprehension of the interactions between POM and DOM in the marine environment. In this study, the origin, distribution, and fate of POM and DOM in Tieshangang Bay, a weak dynamic bay were investigated by measuring δ13C and δ15N of POM, dissolved organic carbon (DOC), and absorption and fluorescence of DOM (CDOM and FDOM). In the upper bay, POM source was mainly originated from terrestrial discharge, whereas the high fluorescence index (FI) indicated that external aquatic organism activity dominated DOM sources. In contrast, in the outer bay, the slightly increased δ13C and enriched δ15N of POM and enhanced fluorescence intensities of protein-like DOM components indicated the considerable contributions of the in situ biological activities to OM. A net addition of DOC and optical components of DOM occurred in both the upper and outer bays. The decomposition of terrestrial POM was responsible for the addition of DOM due to the weak dynamics in the upper bay, whereas the enhanced primary production and the strong decomposition of freshly produced POM jointly contributed to the addition of DOM in the outer bay. Our study suggests that hydrodynamics regulate the biogeochemistry and interactions of POM and DOM in the weak dynamic bay.

DOM influences Hg methylation in paddy soils across a Hg contamination gradient

Rice paddies provide optimum conditions for Hg methylation, and paddy soil is a hot spot for Hg methylation and the predominant source of methylmercury (MeHg) accumulated in rice grains. The role of dissolved organic matter (DOM) in controlling Hg bioavailability and methylation in rice paddy systems remains unclear. Paddy soils from eight various cultivation sites in China were chosen to investigate the variations in soil DOM and the influence of DOM concentration and optical characteristics on Hg methylation in rice paddy systems. In the present study, 151 rhizosphere soil samples were collected, and UV–Vis absorption and fluorescent spectroscopy were used to identify the optical properties of DOM. The relationship between MeHg and DOM's optical property indices revealed the production of MeHg consumes lower molecular weight DOM. Moreover, the correlation between DOM concentration and its optical characteristics highlighted the significant role of humic components on MeHg variability in paddy soil. Variation and correlation results demonstrated the allochthonous origin of DOM in the Hg-contaminated soil, with a higher molecular weight and humic character of DOM, as well as the dominant role of autochthonous DOM in promoting Hg methylation in uncontaminated soil. The current study indicated that soil organic matter and its dissolved fractions tend to limit Hg bioavailability and subsequently diminish MeHg production in contaminated paddy soils. Furthermore, the leading roles of allochthonous DOM in protecting MeHg from degradation and autochthonous DOM signatures in enhancing MeHg production in paddy soils. Overall, these findings provide insight into the correlative distributions of DOM and Hg along a Hg concentration gradient in paddy soil, thereby highlighting their potential role in controlling Hg bioavailability and regulating Hg methylation in the soil ecosystems.

Size exclusion chromatography and stable carbon isotopes reveal the limitations of solid phase extraction with PPL to capture autochthonous DOM production

The study of the elemental and carbon isotopic composition of dissolved organic matter (DOM) is of great interest in deciphering the origin and transformations of organic matter in estuarine and coastal environments. Styrene-divinylbenzene copolymer (PPL) sorbent is currently the most commonly used material for the isolation of DOM from environmental samples. It is notably used for the development of molecular formula-based indices used to study DOM reactivity. However, any extraction procedure (including with PPL) will fractionate the DOM. If this fractionation is not well constrained it can lead to biased interpretations of the biogeochemical processes affecting DOM. In this work we investigate the fractionation effects of the PPL sorbent on the size class distribution of DOM and the carbon isotopic composition of the PPL retentate. The use of size exclusion chromatography, that does not require a pre-concentration step, allows a precise study of the fractionation of DOM (including aromaticity) by the PPL resin. Extractions performed on two types of humic substances dissolved in artificial seawater, using the PPL resin, showed high extraction yield (> 85%) and the stable isotopic carbon composition (δ13C) of these compounds was successfully recovered. These results indicate that salinity is not a parameter affecting extraction yield on PPL sorbent. For a hydrophilic compound (atropine) the extraction efficiency was low (33%) and δ13C signature was underestimated. Size exclusion chromatography measurements, in samples collected along a salinity gradient, demonstrate that the PPL sorbent strongly fractionates DOM. Although the DOM size class distributions in freshwaters and marine waters were initially different, their retentates were marked by similar size class distributions. This work demonstrates that PPL resin captures DOM compounds with less nitrogenous content and it seems to have a lower affinity for aromatic compounds of marine origin than of terrigenous origin. The study of DOM distribution in a macro-tidal estuary demonstrated the limitations of PPL resin extraction in capturing an internal N-rich DOM production event at the time of sampling. Futhermore, the isotopic composition of the PPL resin retentate appears to depend on the extraction efficiency of the more hydrophobic compounds which changed along the salinity gradient. This study recommends careful interpretations of data that only rely on PPL extractions, particularly for works tracking the origin of DOM in estuaries and comparing DOM composition across ocean biogeochemical domains.

Insights into surface circulation and mixing in James Bay and Hudson Bay from dissolved organic matter optical properties

Hudson Bay and James Bay are fed by numerous rivers, which also deliver large amounts of dissolved organic matter (DOM). The objective of this study is to assess Hudson Bay wide DOM spatial distribution using ultraviolet-visible light absorption and excitation-emission matrix fluorescence spectroscopies. Overall, a five-component PARAFAC model was validated using 1060 discrete samples collected over nine field campaigns between 2009 and 2018 and including the first samples from James Bay ( n = 112). Regional and seasonal variations were observed. Particularly striking was a 9-fold difference in concentration between coastal and marine zones of these bays, which implies limited mixing between those regions. Seasonal variations in absorption coefficient at 355 nm and terrestrial humic-like components were found only in east Hudson Bay, revealing a regional disparity in seasonal DOM behaviour. The summer intensities and relative abundances of DOM revealed that cyclonic circulation transports terrestrial DOM around James Bay following its eastern shores before being transported northward along the western coast of Belcher Islands. The vertical distribution of DOM indicated that fluorescent DOM is delivered to the deeper layer by winter convective mixing in northern Hudson Bay. • Limited mixing between the coastal and marine regions of the bay is observed. • The strong terrestrial signal of east James Bay is found in northern Belcher Island. • DOM is delivered to the deeper layer by winter convection in northern Hudson Bay.

Geochemical Features of Ground Ice from the Faddeevsky Peninsula Eastern Coast (Kotelny Island, East Siberian Arctic) as a Key to Understand Paleoenvironmental Conditions of Its Formation

Understanding paleoenvironmental conditions of the permafrost formation allows us to estimate the permafrost carbon pool and its behavior upon thawing in a changing climate. In order to classify different types of ground ice and to reconstruct paleoenvironments, we examined geochemical data of ice wedges (IWs), tabular ground ice (TGI), and lens ice from the eastern coast of the Faddeevsky Peninsula (East Siberian Arctic). We analyzed isotope and ion composition, molecular composition of the gas phase, bulk biogeochemical parameters and dissolved organic matter (DOM) composition in ground ice samples. IWs formed in the Late Pleistocene under the coldest winter conditions and in the Holocene in proximity to the sea. The Holocene IWs have the highest mean d-excess (11–13‰) and a heavier isotope composition by an average of 6‰ compared with the Late Pleistocene IWs. We observe predominance of sea-salt fractions in ion composition of the Holocene IWs, while the Late Pleistocene IW shows enrichment in non-sea-salt component of SO42− (nssSO42−), which is probably associated with mineral leaching of deposits. Higher dissolved organic carbon (DOC) content in the Late Pleistocene IW (to 17.7 mg/L) may indicate more favorable vegetation conditions or lower degree of organic matter mineralization compared to Holocene IWs and TGI. CH4 concentrations were relatively low with a maximum value of 2.27 μmol/L. DOM composition, supposed to record the paleoenvironment of the freezing process, was for the first time tried as a biomarker for paleoenvironmental reconstructions of ground ice formation. Parallel factor (PARAFAC) analysis of EEM (Excitation-Emission matrix) of fluorescent DOM decomposes four components: P1–P3, which are related to allochthonous humic-like constituents, and P4, which is relevant to autochthonous fraction associated with microbial activity. The distribution of fluorescent DOM tracked the variability in both paleoclimate conditions of the IW formation (discriminating the Holocene and the Late Pleistocene IWs) and types of ground ice (IW and TGI), which demonstrates the potential of the used approach.

Response of dissolved organic matter to thermal stratification and environmental indication: The case of Gangnan Reservoir

Dissolved Organic Matter (DOM), an important part of the carbon cycle in reservoir ecosystems, has a great impact on aquatic environment to recognize the conversion process of different media DOM. The distribution, spectral characteristics, and sources of DOM in Gangnan Reservoir during thermal stratification were analyzed using ultraviolet-visible absorption spectroscopy and excitation-emission matrix spectroscopy. Three humic-like components (C2, C3, and C4) and two protein-like components (C1 and C5) were identified. The proportions of the humic-like components increased with the progression of thermal stratification (C2 and C3 were dominant), whereas the protein-like components decreased in proportion, and the trend in the interstitial water was constant (C3 and C4 were dominant). The proportion of the humic-like components in the sediments was highest during the stationary period of thermal stratification (C2 and C3 were dominant). C2 and C3 were significantly correlated in the water body and interstitial water (P < 0.001), while C1 and C5 were correlated in the sediment (P < 0.05). In the water body, C2 and C3 were negatively correlated during the formative period of thermal stratification (slope = −1.85; R2 = 0.52), strongly positively correlated during the stationary period (slope = 0.76; R2 = 0.94), and positively correlated during the weakening period of thermal stratification (slope = 0.46; R2 = 0.30). With the progression of thermal stratification, the relative contribution of endogenous substances decreased gradually, whereas the humification degree increased in the water body and interstitial water. The protein-like components and key physicochemical factors (Fe, Mn, TN, TP, and CODMn) were significantly correlated during the formative period (P < 0.05), and humic-like components and key physicochemical factors (NO2−-N and TN) were significantly correlated during the stationary and weakening periods (P < 0.05). C1, C4, and C5 indicated NO3−-N during the formative period; C2 and C3 indicated NO3−-N during the stationary period; and C2 and C4 indicated NO3−-N during the weakening period in the water body. These findings enhance the understanding the mutual transformation processes of DOM in reservoir ecosystems and could guide water quality management.

Characteristics of chromophoric dissolved organic matter in the Northern Andaman Sea

The dissolved organic matter (DOM) in the ocean is a large carbon pool that plays an important role in the global carbon cycle. Investigation of the characteristics and behaviors of DOM in some areas facilitates a better understanding of biochemical processes in the water column. In February 2020, water samples were collected to characterize the distribution and optical properties of DOM from the Northern Andaman Sea and the Northeastern Bay of Bengal. A high dissolved organic carbon (DOC) concentration appeared in the Northern Andaman Sea, which is strongly affected by the DOM contents of the Irrawaddy and Salween Rivers. A barrier layer that resulted from the freshwater input was observed above the thermocline. This layer was believed to have had a consistent effect on the concentration of DOM in the surface water and contributed to the differences in DOC concentration on each side of the Preparis Channel. Based on the fluorescence excitation emission matrix and parallel factor analysis, four fluorescent components were identified, including three humic-like components (C1, C2, and C4 with their maximal Ex/Em at ≤240/418 nm, 315/384 nm, and 270 (360)/442 nm and represented as peaks A, M, and A+C, respectively) and one protein-like component (C3 with maximal Ex/Em at 275/334 nm and represented as peak T). The humic-like components were mainly derived from terrestrial inputs. Low levels of humic-like components were confined in the upper water, with strong photodegradation in the euphotic zone. C3 was a typical tryptophan-like component that represented freshly produced autochthonous DOM. The correlation between C3 and biological index and apparent oxygen utilization suggested that it was highly bioavailable and not easy to be preserved in the deep sea. Overall, our results showed the distributions of DOM in the Northern Andaman Sea and the Northeastern Bay of Bengal and revealed the behaviors and controlling factors for DOM in the upper water.

Distribution of Biodegradable Dissolved Organic Matter and Its Affecting Factors in a Typical Peri-urban Watershed in Yangtze River Delta

Dissolved organic matter (DOM) plays key roles in the carbon biogeochemical cycle, and biodegradable dissolved organic matter (BDOM) is one of the key fractions of DOM. Rapid urbanization and intensive human activities substantially influence the distribution of DOM at the watershed scale. Identifying the spatial and temporal variability in BDOM has become an important and urgent issue of water quality control in rapid urbanization areas. However, limited studies have been conducted to explore the role of human activities on the occurrence and distribution of BDOM in peri-urban watersheds. In this study, the spatial and temporal distribution of BDOM and related affecting factors were investigated in a typical peri-urban watershed (Zhangxi watershed) located at Ningbo City in Yangtze River Delta. Water samples were collected in wet and dry seasons in 2019 based on topographic features, land use, and intensity of human activities. The BDOM were characterized by fluorescence excitation-emission matrix and parallel factor analysis (EEM-PARAFAC), and land use patterns were analyzed using the Source-Sink Landscape Model. The results of this study showed that the BDOM concentrations ranged from 0.57 to 6.80 mg·L-1. Obvious spatial and temporal heterogeneities of BDOM were found at the watershed scale, and significantly higher concentrations of BDOM were observed in the wet season than those in the dry season. Furthermore, relatively high concentrations of BDOM were found in areas with relatively higher intensive human activities. Two fluorescent components (a terrestrial humic-like substance and protein-like substance) were observed using the PARAFAC model. The results of spatial analysis showed that terrestrial humic-like fluorescent components were closely positively correlated with anthropogenic parameters (percentages of agricultural and urban land and ratio of source and sink landscapes). The results showed that the occurrence and distribution of BDOM were strongly influenced by human activities, which could provide scientific guidance for water quality control and related land management in peri-urban aquatic ecosystems.

Distinct differences in surface-water dissolved organic matter between the East China Sea and Okinawa Trough: Source and hydrological effects

Cross-shelf transport plays an important role in marine carbon cycles. In this study, we examined the concentration and optical composition of dissolved organic matter (DOM) in 33 surface water samples collected along a transect from the East China Sea (ECS) to the Okinawa Trough (OT) in spring 2021. Compared to OT waters, ECS waters are characterized by higher dissolved organic carbon (DOC) concentration (111.55 ± 13.30 vs. 72.52 ± 5.01 μmol L−1), chromophoric DOM concentration (0.44 ± 0.15 vs. 0.12 ± 0.03 m−1 for a350), aromaticity (1.07 ± 0.11 vs. 0.64 ± 0.08 L mg−1C m−1 for SUVA254), and humification index (1.04 ± 0.25 vs. 0.58 ± 0.07). Fluorescence components C1, C3, and C4 displayed similar regional trends with the highest intensity in the inner shelf, followed by the outer shelf and then OT, whereas C2 had the highest intensity in the outer shelf, followed by the inner shelf and then OT. Comparison of the inner and outer ECS shelves revealed similar DOC concentrations, but different optical parameters (i.e., a350, S275–295, HIX, BIX, C1-C4 intensity). Our study suggests that: 1) active carbon cycling alters surface water DOM compositions in the ECS shelf, which is not reflected by total DOC concentrations, likely due to an offset effect between terrestrial DOM removal and marine DOM production; and 2) DOM is well mixed in the ECS shelf, but hardly passes across the OT owing to the strong barrier effect of the Kuroshio Current during the sampling season. Investigation of DOM biogeochemistry in other seasons and different water depth is necessary as the Changjiang Diluted Current and Kuroshio Current are weaker in winter and stronger in summer, respectively, which affects the spatial and temporal distribution of water DOM in the ECS-OT regions.

Investigating the vertical distribution of dissolved organic matter in 5-m soil profiles in farmland and typical woodland on the southern loess plateau

With the implementation of the ‘Grain-for-Green’ program on the Chinese Loess Plateau (CLP), drought-tolerant deep-rooted plants have been increasingly introduced to the northwest in China. However, the vertical features of dissolved organic matter (DOM) in deep soil profiles on CLP during the ‘Grain-for-Green’ program is still not well understood. In the study, ultraviolet–visible (UV–Vis) spectroscopy and three-dimensional fluorescence excitation-emission matrices (3D-EEMs) with parallel factor analysis (PARAFAC) were used to characterize DOM in 5-m profile of farmland and forestland (Pinus tabulaeformis and Robinia pseudoacacia) in the southern CLP. The results demonstrated that the average dissolved organic carbon (DOC) content of the surface layer of farmland (119.3 mg kg−1 soil) was lower than that of forestland (Pinus tabulaeformis 175.5 mg kg−1 soil; Robinia pseudoacacacia 166.4 mg kg−1 soil). The DOC content gradually decreased with increasing soil depth and reached stability after 2 m depth. Three substances, including tryptophan-like substances (C1) and two humic acid-like substances (C2, C3), were detected from all samples. Tryptophan-like substances (C1) significantly increased with soil depth while humic acid-like substances (C2, C3) significantly decreased particularly in farmland. The humic acid-like content of surface soils (Robinia pseudoacacia) was relatively higher, but the difference between the two vegetation soils was not significant. The freshness index (β/α) values of DOM as well as biological index (BIX) values were significantly higher in farmland than that in forestland, and the humification index (HIX) values were lower than in forestland soils, indicating that the change of soil DOM in farmland was more active than that in forestland and more dependent on local terrestrial sources. These results could contribute to a better understanding of the vertical distribution and features of soil DOM during the ‘Grain-for-Green’ program of CLP.

Fluorescence characteristics and source analysis of DOM in groundwater during the wet season in the CKDu zone of North Central Province, Sri Lanka

The dissolved organic matter (DOM) should be purified for safe drinking water due to disinfection by-products (DBPs) produced by disinfectants reaction with DOM. Current research on groundwater in the chronic kidney disease with unknown etiology (CKDu) zone of the North Central Province (NCP) in Sri Lanka has focused mainly on aquatic chemistry, with limited attention paid to the spatial distribution, compositional sources and factors of DOM. Therefore, the structure, composition, source and spatial distribution of the DOM of two kinds of groundwater samples collected from dug well and tube well in the NCP during the wet season were determined, compared and analyzed by analytical tools such as parallel factor analysis (PARAFAC). Results show that the average concentrations of TOC in these two groundwater samples are generally higher than 5.0 mg/L, and the concentration of TOC in the groundwater of the shallow weathered aquifer is higher than that of the deep hard rock aquifer, while its distribution of the two aquifers are on contrary. The DOM in the dug well has three types and four components, including humus-like component C1 (33.36%) and C2 (38.60%), protein-like component C3 (13.09%) and heterogeneous organic component C4 (14.95%). In the tube well, two types and two components of the DOM are determined, including humus-like component CⅠ (69.80%) widely existing in natural water and soluble microbial by-product CⅡ (30.20%) produced by microbial community activities. In the dug well, DOM is mainly exogenous input, the higher ion concentration in water affected the fluorescence intensity of humus and protein components. And in the tube well, DOM has obvious endogenous characteristics, and higher pH value may inhibit the production of protein like fluorescent substances to a certain extent.

Biophysical controls on spatial and summer/winter distributions of total and chromophoric dissolved organic matter in the Taiwan Strait

This study examined the physical and biogeochemical processes that determine the spatial and summer/winter distributions of dissolved organic matter (DOM) and chromophoric dissolved organic matter (CDOM) in the Taiwan Strait (TS). The hydrological conditions in the TS varied between early summer and winter because of differences in terrestrial input as well as input from the poleward South China Sea Water (SCSW) during the warm summer and the strong, nutrient-rich, equatorward China Coastal Water (CCW) in winter. Concentrations of dissolved organic carbon (DOC) ranged from 60 to 100 μM-C in early summer and from 70 to 144 μM-C in winter. The average stoichiometric ratio of DOC : DON:DOP was high (353:49:1) in the land-source impacted zones and low (168:21:1) in the SCSW-laden areas, both of which are higher than the Redfield ratio. The concentrations of DOC and nutrients were higher in the western TS (on the coast of China) than in the eastern TS (on the coast of Taiwan), and the highest concentrations were mostly found in the Minjiang River plume, reflecting the profound effects of freshwater input in early summer and CCW inflow in winter. The absorption and emission characteristics of the CDOM varied to a large extent with locations because of the mixing of the shelf water with different source waters. Although the absorption coefficient (aCDOM(325)) and fluorescence intensity of the terrestrial humic-like CDOM (Ft: Ex/Em= 260/400-460) were both strongly inversely correlated with salinity, as an optical tracer, Ft may be more effective than aCDOM(325) in examining the mixing among source waters, given that aCDOM(325) may be subject to various photobleaching effects in the TS. Ft was also significantly correlated with the concentrations of terrestrially derived nitrate and nitrite (N+N) and silicate. The results of factor analysis elucidated the complexity of the hydrological and biological processes that affect the distributions of DOM and CDOM in the TS.

Spatial Complexity in Dissolved Organic Matter and Trace Elements Driven by Hydrography and Freshwater Input Across the Arctic Ocean During 2015 Arctic GEOTRACES Expeditions

AbstractThis study traces dissolved organic matter (DOM) in different water masses of the Arctic Ocean and its effect on the distributions of trace elements (TEs; Fe, Cu, Mn, Ni, Zn, Cd) using fluorescent properties of DOM and the terrigenous biomarker lignin. The Nansen, Amundsen, and Makarov Basins were characterized by the influence of Atlantic water and the fluvial discharge of the Siberian Rivers with high concentrations of terrigenous DOM (tDOM). The Canada Basin and the Chukchi Sea were characterized by Pacific water, modified through contact with productive shelf sediments with elevated levels of marine DOM. Within the surface layer of the Beaufort Gyre, meteoric water (river water and precipitation) was characterized by low concentrations of lignin and tDOM fluorescence proxies as DOM is removed during freezing. High‐resolution in situ fluorescence profiles revealed that DOM distribution closely followed isopycnals, indicating the strong influence of sea‐ice formation and melt, which was also reflected in strong correlations between DOM fluorescence and brine contributions. The relationship of DOM and hydrography to TEs showed that terrigenous and marine DOM were likely carriers of dissolved Fe, Ni, Cu from the Eurasian shelves into the central Arctic Ocean. Chukchi shelf sediments were important sources of dCd, dZn, and dNi, as well as marine ligands that bind and carry these TEs offshore within the upper halocline in the Canada Basin. Our data suggest that tDOM components represent stronger ligands relative to marine DOM components, potentially facilitating the long‐range transport of TE to the North Atlantic.

(Anti)estrogenic activity impacted by complex environmental matrices: A DOM and multiphase distribution approach

The presence of estrogenic endocrine disruptors in aquatic environments has been a concern and bioassays are recommended tools for their monitoring. However, the physicochemical properties of contaminants and the environmental matrix features may influence the resultant response. This study aimed to assess this influence on the Yeast Estrogen Screen (YES) assay. Mixtures of 17β-estradiol (E2) and humic acid (HA) were evaluated through the Schild approach aiming to investigate the interactions between estrogens and dissolved organic matter (DOM). Moreover, environmental samples from municipal landfill leachate and wastewater treatment plant (WWTP) influents and effluents were screened for (anti)estrogenic activity at both dissolved and particulate phases. Finally, results were statistically confronted with physicochemical parameters through principal component analysis (PCA). The HA test concentrations strongly reduced the E2 response, even at low levels. Humic substances may not only reduce estrogen bioavailability, but also interfere with the assay mechanism through enzymatic inhibition thus masking the sample estrogenic potential. Landfill leachate had total E2-Eq in the range 1282–2591 ng L−1, while WWTP influent and effluent were in the range 12.1–41.4 and <DL–2.3 ng L−1, so estrogenicity was reduced 92% in average. Particulate phase was responsible for 33–100% of measured E2-Eq between matrices, though cytotoxicity occurred in some extracts. Antiestrogenic activity was observed in both phases and might also have masked the estrogenicity of samples. PCA did not resulted in positive correlations supporting a multiphase distribution pattern of estrogenic compounds. Nevertheless, the solids and organic matter characteristics supported the data interpretation. In conclusion, the in vitro YES assay is subjected to factors intrinsic to the environmental sample that can influence on the measured estrogenic response. Therefore, results interpretation should be performed together with organic matter characterization parameters, cytotoxicity and antiestrogenic activity evaluation.

Influence of the conservation mode of seawater for dissolved organic carbon analysis

Marine dissolved organic matter (DOM) is one of the largest exchangeable organic carbon reservoir on the planet. The main proxy to track the distribution of DOM in the aquatic environments remains dissolved organic carbon (DOC). Thereby the optimal protocol for long-term DOC preservation in seawater samples must be defined. In this context, we monitored bulk DOC concentrations and its size class distribution in filtered seawater samples during yearlong experiments. With different conservation mode, we tested two types of commonly used materials (borosilicate brown glass and high-density polyethylene, HDPE) and three conditioning protocols (untreated, acidified at pH 2 and frozen at −20 °C). Offshore samples collected along the entire water column of the Pacific Ocean and stored in HDPE bottles were also analysed after 2 years of storage at pH of 2 and compared to frozen samples. Results demonstrated that bulk DOC concentrations can be accurately determined in untreated samples for one month and for years in frozen samples as well as in acidified samples, when samples are stored in acid cleaned HDPE bottles or flame sealed glass ampoules. Storage in brown glass vials with Bakelite caps seems more uncertain. The study of the size class distribution of DOC reveals the possibility to study DOM for 1 month in filtered samples with no additional treatment and for years in frozen samples when stored in acid cleaned HDPE bottles. Significant changes in DOC size fractionation were observed when samples were acidified. The high molecular weight (HMW) compounds and the humic substances from the upper 1000 m were significantly degraded at pH 2, incorporating DOC in the low molecular weight (LMW) fractions. These experiments provide preservation guidelines for future studies that aim either to study bulk DOC or the chemical properties marine DOM. It is recommended to store seawater in HDPE vials at −20 °C for DOM study, or at pH 2 for bulk DOC measurements.

Unravelling relationships between fluorescence spectra, molecular weight distribution and hydrophobicity fraction of dissolved organic matter in municipal wastewater

The characteristics of dissolved organic matter (DOM) in the influent and secondary effluent from 6 municipal wastewater treatment plants (WWTPs) were investigated with a size exclusion chromatogram (SEC) coupled with multiple detectors to simultaneously detect ultraviolet absorbance, fluorescence, dissolved organic carbon (DOC) and dissolved organic nitrogen (DON) as a function of molecular weight (MW). The SEC chromatograms showed that biopolymers (>6 kDa) and humic substances (0.5–6 kDa) comprised the significant fraction in the influent, while humic substances became the abundant proportion in the secondary effluent. Direct linkages between MW distribution and hydrophobicity of DOM in the secondary effluent were further explored via SEC analysis of XAD resin fractions. DON and DOC with different hydrophobicity exhibited significantly distinct MW distribution, indicating that it was improper to consider DOC as a surrogate for DON. Different from DOC, the order of averaged MW in terms of DON was hydrophobic neutral ≈ transphilic neutral > hydrophobic acid > transphilic acid > hydrophilic fraction. Fluorescence spectral properties exhibited a significant semi-quantitative correlation with MW and hydrophobicity of DOC, with Pearson's coefficients of −0.834 and 0.754 (p < 0.01) for biopolymer and humic substances. Meanwhile, regional fluorescence proportion was demonstrated to indicate the MW and hydrophobicity properties of DON at the semi-quantitative level. The fluorescence excitation-emission matrix (EEM) could be explored to provide a rapid estimation of MW distribution and hydrophobic/hydrophilic proportion of DOC and DON in WWTPs.

Insight into disinfection byproduct formation potential of aged biochar and its effects during chlorination.

Biochar can achieve multiple benefits including solid waste management, polluted water remediation, carbon sequestration, and emission reduction. However, various environmental factors (such as temperature variations and dry-wet alternation) and microbial activity may lead to the fragmentation, dissolution, and oxidation of biochar. These accelerate the dissolution of biochar-derived dissolved organic matter (DOM) and then influence disinfection byproducts formation potential (DBPFP) throughout the water treatment process. In this paper, biochars from six biomass feedstocks with five aging processes were prepared, and the DBPFP of biochar and its derived DOM were first studied systematically. Different aging processes might increase the DBPFP of biochar by increasing DOM content and changing the fraction distribution of DOM derived from biochar. Especially, the DBPFP of biochar increased apparently with the chemical aging process. Coexisting with the environmental concentration of humic acid, even aged biochar showed the potential to reduce DBPFP and integrated toxic risk value of the mixed system. In this study, the DBPFP of biochar-derived DOM during the disinfection process is confirmed, and the results can give information to the selection of biomass feedstocks of biochar and its service life in the water treatment process.

Association between greenhouse gases and dissolved organic matter composition in the main rivers around Taihu Lake

River ecosystems receive a large amount of organic matter, which will increase the production of greenhouse gases (GHGs), including carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O). Despite extensive research on the distribution of greenhouse gases and dissolved organic matter (DOM), little is known about the associations between greenhouse gases and DOM compositions. In this study, the distributions of GHGs (CO2, CH4 and N2O) and DOM in the overlying water of the main rivers around Taihu Lake were investigated. The results showed that the concentration of GHGs was positively correlated with dissolved organic carbon concentrations. Three-dimensional excitation-emission matrix fluorescence spectroscopy techniques were employed to identify the source of the DOM, which was related to protein-like and humic-like components. The DOM was a combination of terrigenous and endogenous origins. The GHGs (except CO2) were significantly associated with DOM composition. These results emphasize the importance of the relationship between GHGs (CO2, CH4 and N2O) and DOM compositions in river ecosystems.