Variations Of Dissolved Organic Matter Research Articles

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.

Spatiotemporal dynamics of dissolved organic matter and disinfection by-products formation potential of Shengzhong Lake in southwest China.

The quality and quantity of dissolved organic matter (DOM) in lakes as well as its environmental effects associated with the unintended disinfection by-products (DBPs) have received continuous attention. This work investigated the spatiotemporal dynamics of DOM in Shengzhong Lake in southwest China and the formed DBPs during the chlorine disinfection process. The results showed that lake water in summer had significantly higher dissolved oxygen and dissolved organic carbon than that in winter. In contrast, DOM in winter demonstrated an obviously higher aromaticity and molecular weight than that in summer. Four fluorescence components, i.e., terrestrial humic-like substances (C1), protein-like substances (C2), and microbial humic-like substances (C3 and C4), were identified, and their relative abundance followed in the order of C3 > C4 > C2 > C1 in winter and C4 > C3 > C1 > C2 in summer. The formation potential of trihalomethanes and haloacetic acids in winter was higher and lower than that in summer, which was mainly ascribed to the content of aromatic and hydrophobic substances. Compared to the significant seasonal dynamic, the spatial variation of DOM and the formed DBPs was not obvious. This work sheds light on the spatial-temporal distribution of DOM and the potentially formed DBPs in Shengzhong Lake, and will be helpful for understanding the biogeochemical cycle of carbon and assessing the drinking water safety.

Applying fluorescence spectroscopy and DNA pyrosequencing with 2D-COS and co-occurrence network to deconstruct dynamical DOM degradation of air-land-water sources in an urban river

In an urban river, comprehending the interplay between dissolved organic matter (DOM) and atmospheric, terrestrial, and aquatic sources is crucial. This encompassed investigating temporal variations in DOM and its association with the bacterioplankton community to gain profound insights into the biogeochemical dynamics and biodegradability of DOM. DOM was extracted from PM2.5, soil, sediment, bait, and terrestrial/aquatic plant residuals collected along the Wenyuhe River in Beijing, China - a region predominantly supplied with reclaimed water. Subsequently, mixed microbial communities from the river were introduced into DOM samples originating from each source and incubated for 10 days. Principal component analysis (PCA) applied to reassembled excitation-emission matrix (EEM) data revealed two distinct clusters: cluster 1 comprising soil, sediment, and PM2.5 samples; and cluster 2 consisting of bait as well as terrestrial/aquatic plant residuals. According to parallel factor analysis, C1 (microbial humic-like) and C2-C3 (fulvic-like) dominated the DOM from soil, sediment, and PM2.5. These components were continuously degraded during incubation, except for PM2.5. DOM from bait and terrestrial/aquatic plants contained representative components of C6 (phenolic-like) and C7 (tryptophan-like), which underwent extensive decomposition. Interestingly, DOM in PM2.5 contained aliphatic compounds and polycyclic aromatic hydrocarbons (PAHs) but exhibited weak degradation with the complete disappearance of C6 and C7. Rhodococcus was a unique species capable of degrading PAHs, which might be particularly important considering the specificity of PM2.5 pollution. Based on two-dimensional correlation spectroscopy (2D-COS), variations in DOM components such as C6, and C7 were significantly larger compared to those of C1, C2, C3, and C5 (terrestrial humic-like) from bait samples, sediments, and residual terrestrial plants. MW-2D-COS analysis revealed that DOM from bait samples and terrestrial/aquatic plants experienced substantial degradation by the second day while DOM from soil or sediment decomposed mainly on the fourth day. Notably, the decomposition of DOM fractions in PM2.5 occurred throughout the entire four-day period. Co-occurrence network analysis classified sources of DOM into two clusters similar to PCA results: cluster 1 showed significant microbial degradation of fulvic-like compounds while cluster 2 demonstrated deep microbial decomposition of tyrosine-like and phenolic compounds. Therefore, the artificial loading of DOM into rivers not only expands the chemical diversity within DOM but also perturbs bacterioplankton diversities.

Spatial and molecular variations in forest topsoil dissolved organic matter as revealed by FT-ICR mass spectrometry

Forest soils cover about 30 % of the Earth's land surface and play a fundamental role in the global cycle of organic matter. Dissolved organic matter (DOM), the largest active pool of terrestrial carbon, is essential for soil development, microbial metabolism and nutrient cycling. However, forest soil DOM is a highly complex mixture of tens of thousands of individual compounds, which is largely composed of organic matter from primary producers, residues from microbial process and the corresponding chemical reactions. Therefore, we need a detailed picture of molecular composition in forest soil, especially the pattern of large-scale spatial distribution, which can help us understand the role of DOM in the carbon cycle. To explore the spatial and molecular variations of DOM in forest soil, we choose six major forest reserves located in different latitudes ranging in China, which were investigated by Fourier transform-ion cyclotron resonance mass spectrometry (FT-ICR MS). Results show that aromatic-like molecules are preferentially enriched in DOM at high latitude forest soils, while aliphatic/peptide-like, carbohydrate-like, and unsaturated hydrocarbon molecules are preferentially enriched in DOM at low latitude forest soils, besides, lignin-like compounds account for the highest proportion in all forest soil DOM. High latitude forest soils have higher aromatic equivalents and aromatic indices than low latitude forest soils, which suggest that organic matter at higher latitude forest soils preferentially contain plant-derived ingredients and are refractory to degradation while microbially derived carbon is dominant in organic matter at low latitudes. Besides, we found that CHO and CHON compounds make up the majority in all forest soil samples. Finally, we visualized the complexity and diversity of soil organic matter molecules through network analysis. Our study provides a molecular-level understanding of forest soil organic matter at large scales, which may contribute to the conservation and utilization of forest resources.

Adsorption behavior of antibiotics with different structures onto vivianite in the presence of dissolved organic matter during the phosphorus recovery process

Formation of vivianite is a promising strategy to recover phosphorus from urban sewage and livestock wastewater, in which both various antibiotics and dissolved organic matters are contained. In this study, the interaction relationship and mechanism between vivianite, antibiotics and DOM were analyzed through the variations of DOM and antibiotics concentrations in supernatant, combined with characterization analysis and theoretical calculation. It’s found that the adsorption of three kinds of antibiotics onto vivianite following the order: tetracycline (TC) (∼90%) > ciprofloxacin (CIP) (∼15%) > sulfamethoxazole (SMX) (∼5%). The presence of fulvic acid (FA) greatly enhanced the adsorption of CIP, SMX to about 90%, 17% respectively, while there was no significant change in the adsorption of TC probably due to its good adsorption in the absence of FA. Interestingly, further analysis demonstrated that the FA will enhance the adsorption of antibiotics to vivianite because of the non-bonding interaction between FA molecules adsorbed on the surface of vivianite and antibiotics, and make the vivianite form better crystal without significant influences on phosphorus recovery. In addition, this study found that the adsorption of different kinds of antibiotics by vivianite was significantly related to the molecular weight of dissolved organic matter (DOM) in the actual livestock wastewater. Interestingly, the promotion of SMX adsorption is more likely to occur in the presence of DOM with small molecular weight (<5 kDa), while the introduction of DOM with larger molecular weight has greater promotion effect on CIP adsorption. The results gained in this study will expand the knowledge about the fate of antibiotics and recovery of phosphorus from urban sewage and livestock wastewater in the formation of vivianite.

The enhance mechanism of DOM on tetracyclines degradation by electrochemical technology: A improvement of treatment processes

Tetracyclines (TC) is a typical broad-spectrum antimicrobial agent, and excessive use of TC can lead to a large accumulation of residual tetracycline in water. DOM is organic substances that can pass through the 0.45 μm filter. While dissolved organic matter (DOM) is one of the most significant substances in water, which has an important effect on water treatment. In this study, ultraviolet and visible spectrophotometry (UV–Vis) is applied to explore DOM to the effect of the electrochemical degradation. Three-dimension excitation emission matrix fluorescence spectroscopy (3D-EEM) is used to identify the component variation of DOM after the electrochemical oxidation (EO). Liquid chromatograph mass spectrometer (LC-MS) is used to confirm the degradation pathway of TC whether spontaneous or electrochemical oxidation. High performance liquid chromatography (HPLC) suggests the ROS production by DOM in the electrochemical oxidation under different conditions. Results show that DOM can promote the degradation of TC in the electrochemical oxidation. Tailwater DOM containssubstances can produce persistent free radicals, which can promote the degradation under light and dark conditions, natural source DOM can produce more free radicals under light. Therefore, TC wastewater should be added tailwater to promote the degradation of TC before the further water treatment. Otherwise, TC can be degraded to differentpathways (light, electricity, and degrade spontaneously). This study provides a significant idea for practical water treatment of tetracyclines, and promotes the practical application of electrochemical technology.

Hydrological Controls on Dissolved Organic Matter Composition throughout the Aquatic Continuum of the Watershed of Selin Co, the Largest Lake on the Tibetan Plateau.

Alpine river and lake systems on the Tibetan Plateau are highly sensitive indicators and amplifiers of global climate change and important components of the carbon cycle. Dissolved organic matter (DOM) encompasses organic carbon in aquatic systems, yet knowledge about DOM variation throughout the river-lake aquatic continuum within alpine regions is limited. We used optical spectroscopy, ultrahigh-resolution mass spectrometry (Fourier transform ion cyclotron resonance mass spectrometry), and stable water isotopic measurements to evaluate linkages between DOM composition and hydrological connection. We investigated glacial influences on DOM composition throughout the watershed of Selin Co, including upstream glacier-fed rivers and downstream-linked lakes. We found that the dissolved organic carbon concentration increased, whereas specific ultraviolet absorbance (SUVA254) decreased along the river-lake continuum. Relative to rivers, the downstream lakes had low relative abundances of polyphenolic and condensed aromatic compounds and humic-like substances but increased relative abundances of aliphatics and protein-like compounds. SUVA254 decreased while protein-like components increased with enriched stable water isotope δ2H-H2O, indicating that DOM aromaticity declined while autochthonous production increased along the flow paths. Glacier meltwater contributed to elevated relative abundances of aliphatic and protein-like compounds in headwater streams, while increased relative abundances of aromatics and humic-like DOM were found in glacier-fed lakes than downstream lakes. We conclude that changes in hydrological conditions, including glacier melt driven by a warming climate, will significantly alter DOM composition and potentially their biogeochemical function in surface waters on the Tibetan Plateau.

Seasonal Variations of Dissolved Organic Matter in Urban Rivers of Northern China

Dissolved organic matter (DOM) is ubiquitously present in aquatic environments, playing an important role in the global carbon cycle and water quality. It is necessary to reveal the potential sources and explore spatiotemporal variation of DOM in rivers, especially in urban zones impacted by human activities. It was designed to aim to explore spatiotemporal variations of DOM in urban rivers and ascertain the influencing factors. In this study, dissolved organic carbon (DOC) concentrations, UV-Vis absorption spectroscopy, and 3D fluorescence spectroscopy combined with parallel factor analysis were utilized to characterize DOM composition in urban rivers (the Jiyun, Chaobai, and Yongding rivers) in Tianjin city, northern China. The results showed that DOC (1.28 to 25.85 mg·L−1), generally, was at its highest level in spring, followed by summer, and lowest in autumn and winter, and that the absorption parameters E250:365 (condensation degree/molecular weight, 7.88), SUVA254 (aromaticity, 3.88 L mg C−1 m−1), a355 (content of chromophores, 4.34 m−1), a260 (hydrophobicity, 22.02 m−1), and SR (molecular weight, 1.08) of CDOM (chromophoric DOM) suggested that DOM is mainly composed of low-molecular-weight fulvic acid and protein-like moieties, and had the capability of participating in pollutant migrations and transformations. The results demonstrated significant seasonal differences. Generally, high DOC content was detected in rivers in urban suburbs, due to anthropogenic inputs. Three fluorescence components were identified, and the fluorescence intensity of the protein class reached the highest value, 294.47 QSU, in summer. Different types of land use have different effects on the compositions of riverine DOM; more protein-like DOM was found in sections of urban rivers. The correlation between DOC concentration and the CDOM absorption coefficient was found to be unstable due to deleterious input from industrial and agricultural wastewater and from domestic sewage from human activities. HIX and BIX elucidated that the source of CDOM in three river watersheds was influenced by both terrestrial and autochthonous sources, and the latter prevailed over the former. Geospatial data analysis indicated that CDOM in autumn was sourced from plant detritus degradation from forest land or from the urban green belt; construction land had a great influence on DOC and CDOM in riparian buffer areas. It was revealed that DOM in the watershed is highly impacted by nature and human activities through land use, soil erosion, and surface runoff/underground percolation transport; domestic sewage discharge constituted the primary source and was the greatest determiner among the impacts.

Response of dissolved organic matter chemistry to flood control of a large river reservoir during an extreme storm event

With the frequent occurrence of extreme floods under global climate change-induced storm events, reservoir operation has been highlighted for river flood control, complicating the transport and transformation of riverine dissolved organic matter (DOM), one of the largest reactive carbon pools on earth. In particular, the response of riverine DOM chemistry to reservoir flood control during extreme storm events is still unclear. To fill this knowledge gap, the mechanism of DOM variation in Yangtze River with the world's largest Three Gorges Reservoir (TGR) operation during an extreme storm event was explored. Optical and molecular properties of DOM varied significantly from upstream to downstream in non-TGR area, while no significant variation in DOM chemistry was observed in TGR area. The results uncovered a short time transformation of DOM from non-TGR area to TGR area, demonstrating that although storm event induced chemodiversity bloom of riverine DOM, flood control of TGR “re-constrained” DOM to more similar chemistry mainly under the influence of turbidity involved DOM transformation (e.g., adsorption/desorption and flocculation). Furthermore, combined with the hydrological information, we found that although TGR temporarily blocked dissolved organic carbon (DOC) flow during the flood event, the abundance of biologically recalcitrant DOC increased in TGR, which would contribute to its further transportation to downstream watershed. This study emphasizes the impact of TGR on extreme storm event-induced DOM dynamics, which also hints a better understanding of the crucial role of anthropogenic activity in affecting carbon cycling under extreme climate change.

Innovative approach to reveal source contribution of dissolved organic matter in a complex river watershed using end-member mixing analysis based on spectroscopic proxies and multi-isotopes

Dissolved organic matter (DOM) in river watersheds dynamically changes based on its source during a monsoon period with storm event. However, the variations in DOM in urban and rural river watersheds that are dominated by point and non-point sources have not been adequately explored to date. We developed an innovative approach to reveal DOM sources in complex river watershed systems during pre-monsoon, monsoon, and post-monsoon periods using end-member mixing analysis (EMMA) by combining multi-isotope values (δ13C-DOC, δ15N-NO3 and δ18O-NO3) and spectroscopic indices (fluorescence index [FI], biological index [BIX], humification index [HIX], and specific UV absorbance [SUVA]). Several potential end-members of DOM sources were collected from watersheds, including top-soils, groundwater, plant group (fallen leaves, riparian plants, suspended algae), and different effluents (cattle and pig livestock, agricultural land, urban, industry facility, swine treatment facility and wastewater treatment facility). Concentrations of dissolved organic carbon, dissolved organic nitrogen, NO3-N, and NH4-N increased during the monsoon period with an increase in the input of anthropogenic DOM, which have higher HIX values owing to the flushing effect. The results of EMMA indicate that soil and agricultural effluents accounted for a substantial contribution of anthropogenic DOM at varying rates based on seasons. We also found that results of EMMA based on combining spectroscopic indices and δ13C-DOC isotope values were more accurate in tracing DOM sources with respect to land-use characteristics compared to applying only spectroscopic indices. The positive relationship between FI, BIX and δ15N-NO3 were revealed that nitrate would be decomposed from DOM affected by intensive agricultural activities. In addition, consistent with the EMMA results, the molecular composition of the DOM was clearly evidenced by a large number of CHON formulas, accounting for over 50% of the total characterized compounds, including pesticides and pharmaceuticals used in agriculture farmland and livestock. Our results clearly demonstrated that EMMA based on combing multi-stable isotopes and spectroscopic indices could be trace the DOM source, which is important for understanding changes in the DOM quality, and application of nitrate isotopes and molecular analysis supports in-depth interpretation. This study provides easy and intuitive techniques for the estimation of the relative impacts of DOM sources in complex river watersheds, which can be verified in various ways rather than relying on a single technique approach.

Changes in soil dissolved organic matter optical properties during peatland succession

• Topsoil and subsoil DOM respond differently to aboveground vegetation succession. • Succession increases the content of humic-like substances in topsoil DOM. • The content of protein-like material of the subsoil is stable under succession. • pH is a key factor affecting changes in fluorescence properties of topsoil DOM. Dissolved organic matter (DOM) is the most active component in the soil environment. Understanding the chemical diversity of DOM and the interaction of the physicochemical properties of the soil are key to managing peatland under succession. In this study, we aimed to understand the effects of peatland succession on soil DOM. We collected soil samples (topsoil: 0–10 cm, subsoil: 10–20 cm) from peatland during different stages of peatland succession in mid–high latitude northern regions, determined the changes in quantity and quality of DOM using fluorescence spectroscopy and parallel factor analysis. We found that peatland succession altered the effectiveness of soil nutrients and water content. During the succession, the content of humus-like substances in the DOM of the topsoil increased and the content of protein-like material decreased, whereas the content of substances in the subsoil remained stable. pH was the key factor affecting the change in the composition of the DOM in the topsoil during peatland succession. The variation of DOM in the subsoil may be related to the vegetation composition. The results suggest that fluorescent DOM components respond significantly to changes in peatland succession, and DOM properties are driven by soil pH and vegetation composition during peatland succession. In conclusion, our results reveal the optical changes and factors that influence DOM in peatlands under succession. This suggests that DOM can be modified by simultaneous changes of the physicochemical properties in the soil and the vegetation cover.

Impact of environmental factors and tributary contributions on tidal dissolved organic matter dynamics

Riverine dissolved organic matter (DOM) transport was a key step in the carbon biogeochemical cycle while we had limited understanding of its contribution to the estuary DOM dynamics. This study focused on the river downstream-to-tidal estuary DOM variation and the control of environmental factors on it. The contributions of three tributaries with varing urbanization degrees to the tidal DOM dynamics were evaluated. Though more aromatics were introduced to the urban tributary, the A250/A365 values and fluorescent index values indicated the DOM molecular size was uniformly reduced due to the enhanced microbial degradation during transport. The tidal DOM showed less varied spectroscopic indexes than the tributary DOM, but tidal cycles strongly impacted the fluorescent DOM quantified by the fluorescence regional integration (FRI). Salinity range can differentiate the fluorescent DOM variation patterns in river tributaries (e.g., <2.5, positive correlations; >2.5, negative correlations) and tidal cycles (>10, negative correlations). For tidal DOM, the high salinity decreased more humic-related components, resulting in increased proportions of protein-related components in high tides. The dissolved oxygen and nitrogen contents were negatively correlated with salinity, suggesting the microbial contributions and anthropogenic inputs in tributaries increased the tidal DOM quantity. The less urbanized tributaries contributed more to the low-tide DOM compositions/properties while the dynamic contribution of the urban tributary impacted more the tidal DOM dynamics. Our results highlighted the uneven declines of FRI values of different components by freshwater-saltwater mixing in estuaries and suggested the different functioning of urban, agro-urban, and suburban tributaries contributed to tidal DOM dynamics.

Effects of bisphenols and perfluoroalkylated substances on fluorescence properties of humic and amino acids substances of dissolved organic matter: EEM-PARAFAC and ATR-FTIR analysis

Abiotic, biotic, and sparingly the xenobiotic factors are considered to influence the compositional variation of dissolved organic matter (DOM) in aquatic environments. Increasing discharge of xenobiotics into water bodies necessitates the need to investigate their effects on the key components of DOM. The effects of bisphenols (BP) and perfluoroalkylated substances (PFAS) on the fluorescence characteristics of pure humic substances (HS) and amino acids (AA) of DOM were examined by using excitation-emission matrix-parallel factor analysis (EEM-PARAFAC) and the attenuated total reflection Fourier-transform infrared (ATR-FTIR) spectroscopy in this work. The results showed that interactions of fulvic acid (FA), humic acid (HA), and tryptophan (Trp) with the xenobiotic compounds could generate some fluorescence components like both HS and AA components, whereas the interactions with tyrosine (Tyr) could only generate AA fluorescence components. In addition, it was revealed that the fluorescence intensity of HS decreases by 50–70% and 18–25% in the treatments of HA and FA, respectively, at low concentration (2.5 × 10−3 mg/L) of BP, while this increases by 350–425% and 18–25% at the same concentration of PFAS. However, both BP and PFAS increase the fluorescence intensity of AA. The findings suggest that the xenobiotic compounds are important factors affecting the compositional variation of DOM, especially in the anthropogenically-impacted water bodies.

Spectroscopic properties and driving factors of dissolved organic matter in the Yellow River Delta

AbstractRiver deltas are hot spots of biogeochemical cycling. Understanding sources and driving factors of dissolved organic matter (DOM) in river deltas is important for evaluating the role of river deltas in regulating global carbon flux. In this study, spectroscopic properties of soil DOM were analyzed in both freshwater and tidal areas of the Yellow River Delta. Five fluorescent components of soil DOM (two humic-like DOM, two protein-like DOM and one possible contaminant) were identified by parallel factor analysis and further confirmed by comparison with an online database. Concentration, spectroscopic properties and sources of soil DOM and its components differed between freshwater and tidal areas. DOM concentration was much higher in freshwater areas than in tidal areas. In freshwater areas, soil DOM was mainly derived from phytoplankton and microorganisms, while it was mainly derived from microorganisms and human activities in tidal areas. These differences in DOM between both areas were strongly driven by environmental factors, especially soil carbon (C), nitrogen (N) and its stoichiometric ratio C/N. These explained 80.7% and 69.6% of variations in DOM and chromophoric DOM (CDOM), respectively. In addition, phytoplankton also contributed to soil DOM, CDOM and fluorescent components C1–C4 as identified by significant positive correlations between them. These results imply that both the concentration and composition of soil DOM are strongly driven by soil properties and phytoplankton density in the Yellow River Delta.

Land Use Overrides Stream Order and Season in Driving Dissolved Organic Matter Dynamics Throughout the Year in a River Network.

Anthropogenic land use has increased nutrient concentrations and altered dissolved organic matter (DOM) character and its bioavailability. Despite widespread recognition that DOM character and its reactivity can vary temporally, the relative influence of land use and stream order on DOM characteristics is poorly understood across seasons and the entire flow regime. We examined DOM character and 28-day bioavailable dissolved organic carbon (BDOC) across a river network to determine the relative roles of land use and stream order in driving variability in DOM character and bioavailability throughout the year. DOM in 1st-order streams was distinct from higher stream orders with lower DOC concentrations, less aromatic (specific ultraviolet absorbance at 254 nm (SUVA254)), more autochthonous (fluorescence index), and more recently produced (β/α) DOM. Across all months, variability in DOM character was primarily explained by land use, rather than stream order or season. Land use and stream order explained the most DOM variation in transitional and winter months and the least during dry months. BDOC was greater in watersheds with less aromatic (SUVA254) and more recent allochthonous DOM (β/α) and more development and impervious surface. With continued development, the bioavailability of DOM in the smallest and most impacted watersheds is expected to increase.

Effect of permanganate oxidation on the photoreactivity of dissolved organic matter for photodegradation of typical pharmaceuticals

Permanganate has been widely used in the remediation of contaminated water due to its relatively strong oxidation properties and ease of use. The ubiquitous dissolved organic matter (DOM) in natural waters causes a significant sink of permanganate in treatments, which further impacts the photoformation of reactive species and the removal of trace pollutants by DOM. Significantly, the effect of permanganate oxidation on the photoreactivity of DOM remains unknown. The present paper investigated for the first time the photophysical and photochemical properties variation of DOM from different sources after permanganate oxidation. Results showed that the permanganate oxidation caused a decrease in UV absorbance, fluorescence intensity, aromaticity, and molecular weight for all tested DOM samples, as well as photoformation rate of DOM triplet states (3DOM⁎), singlet oxygen (1O2), and hydroxyl radical (OH) under simulated sunlight. Quantum yield of 1O2 showed positively linear correlations with both triplet quantum yield coefficient (fTMP) and E2/E3 (ratio of absorbance at 254 and 365 nm) for all the DOM samples before and after permanganate oxidation. The quantum yield of OH exhibited no significant correlation with fTMP or E2/E3. Permanganate oxidation inhibited the DOM-photosensitized indirect photodegradation of pollutants that do not absorb sunlight (e.g., decreased by 15–29%). For the tested pollutants that undergo direct photolysis under sunlight, their photodegradation was promoted (e.g., increased by 1–19%) in the permanganate oxidized DOM solutions due to the decrease of light-screening effect by DOM. These findings suggest that permanganate oxidation affects the photoreactivity of DOM and the corresponding photochemical fate of organic pollutants in natural waters.

Discharge and Temperature Controls of Dissolved Organic Matter (DOM) in a Forested Coastal Plain Stream

Streams in the southeastern United States Coastal Plains serve as an essential source of energy and nutrients for important estuarine ecosystems, and dissolved organic matter (DOM) exported from these streams can have profound impacts on the biogeochemical and ecological functions of fluvial networks. Here, we examined hydrological and temperature controls of DOM during low-flow periods from a forested stream located within the Coastal Plain physiographic region of Alabama, USA. We analyzed DOM via combining dissolved organic carbon (DOC) analysis, fluorescence excitation–emission matrix combined with parallel factor analysis (EEM-PARAFAC), and microbial degradation experiments. Four fluorescence components were identified: terrestrial humic-like DOM, microbial humic-like DOM, tyrosine-like DOM, and tryptophan-like DOM. Humic-like DOM accounted for ~70% of total fluorescence, and biodegradation experiments showed that it was less bioreactive than protein-like DOM that accounted for ~30% of total fluorescence. This observation indicates fluorescent DOM (FDOM) was controlled primarily by soil inputs and not substantially influenced by instream production and processing, suggesting that the bulk of FDOM in these streams is transported to downstream environments with limited in situ modification. Linear regression and redundancy analysis models identified that the seasonal variations in DOM were dictated primarily by hydrology and temperature. Overall, high discharge and shallow flow paths led to the enrichment of less-degraded DOM with higher percentages of microbial humic-like and tyrosine-like compounds, whereas high temperatures favored the accumulation of high-aromaticity, high-molecular-weight, terrestrial, humic-like compounds in stream water. The flux of DOC and four fluorescence components was driven primarily by water discharge. Thus, the instantaneous exports of both refractory humic-like DOM and reactive protein-like DOM were higher in wetter seasons (winter and spring). As high temperatures and severe precipitation are projected to become more prominent in the southeastern U.S. due to climate change, our findings have important implications for future changes in the amount, source, and composition of DOM in Coastal Plain streams and the associated impacts on downstream carbon and nutrient supplies and water quality.

Bulk Chemical and Optical Spectroscopy Characterisations of Dissolved Organic Matter Extracted from the Tropical Coastal Sediment

The study of organic matter characterisation in coastal sediment is useful for understanding how dissolved organic matter (DOM) reactivity influences the fate of pollutants in the aquatic environment. However, there is little information available on the structural properties of DOM in coastal sediment. Chemical analysis, UV-Visible (UV-Vis) absorbance, fluorescence, and Fourier-transform infrared (FTIR) spectroscopy were used in this work to characterise and compare the components of water-extractable organic matter (WEOM) fractions from sediment from an estuary, a coastal area, and a port in Peninsular Malaysia, Malaysia. The elemental analysis (H/C and C/N ratios) of the three samples differed, which coincided with the findings of optical indices estimated from UV-Visible and fluorescent spectroscopy analyses. WEOM had an average output of 7.05 to 8.47 mg/L and was very dominating with heavy fraction organic carbon (HFOC). In DOM-KS and DOM-K sediments, the allochthonous component with a high degree of condensation and the aromatic compound was the dominating composition. Meanwhile, the DOM-KT possessed a high autochthonous composition as well as carboxylic and phenolic content. Correlation analysis indicates that the aromaticity index SUVA254 and humification index (HIX) have positive correlations. The combined results of the chemical and spectroscopic analyses indicate that different coastal ecosystems, with the integration of various human and land activities, produce variations in DOM in the coastal area.

Dynamic variations in DOM and DBPs formation potential during surface water treatment by ozonation-nanofiltration: Using spectroscopic indices approach

The combination of ozone and nanofiltration (NF) in drinking water treatment represents a potentially effective method of separating dissolved organic matter (DOM), and thereby reducing the potential formation of disinfection by-products (DBPs). This study has evaluated UV-absorbance and fluorescence-based optical descriptors, such as absorbance slope index (ASI), humification index (HIX), and the sum of fulvic-like and humic-like components (C1 + C2), etc., to track the variation of DOM constituents and DBP formation potential during the treatment of surface water samples by ozonation and nanofiltration (NF90 and NF270). Pre-ozonation markedly reduced the DOM molecular weight (MW) in the range of 5000–9000 Da by transforming the DOM into carboxylate-rich hydrophilic fractions, thereby mitigating the fouling of NF membranes. Among all the PARAFAC components, the humic-like component (C2) showed a predominant behavior against pre-ozonation and nanofiltration experiments. However, amino acid or microbial protein-like component (C3) was particularly associated with irreversible fouling of both membranes, compared to reversible fouling. C1 + C2 was found to be strongly correlated with both ASI and HIX, suggesting that C1 + C2 can be a useful surrogate for the humic-like content of the DOM. Principal DBPs detected after the chlorination were chloroform, bromodichloromethane and dichloroacetic acid, and DBP formation potential reduced with increased ozonation. A strong correlation between these DBPs and spectroscopic indices indicated that the humic content was an important factor in the formation of DBPs. In contrast, increasing ozonation not only shifted the DBP formation potential towards brominated precursors, but also resulted in increased brominated species of haloacetic acids. However, both NF membranes achieved approximately 90% removal of DBP precursors, for all of the detected DBPs, which was attributed to size exclusion and electrostatic interaction effects.

Anthropogenic Influences on Dissolved Organic Matter in Three Coastal Bays, North China

Coastal bays bear anthropogenic influence strongly, and thus dissolved organic matter (DOM) in coastal bays, which is an important component of global carbon cycling, could be heavily affected by anthropogenic inputs. Utilizing absorbance, fluorescence spectroscopy, and stable carbon isotope (δ13C), this study analyzed the characteristics and distribution of DOM in three coastal bays (Jiaozhou Bay, Sishili Bay, and Taozi Bay), located in North China. The results showed that there was always a high concentration of DOM near the river mouth in all three bays and the DOM concentration decreased along the salinity gradient in Jiaozhou Bay, indicating the riverine inputs are the main factor that causes the variation of DOM in these coastal bays. The effects of inflowing rivers on DOM in coastal bays differed with their watershed characteristics (i.e., agricultural/urban). In addition, humic-like DOM components were found to be positively correlated with the apparent oxygen utilization, suggesting microbial activities could contribute to the DOM in this region. There was generally a higher averaged concentration of fluorescent DOM in surface water than that in bottom water in Jiaozhou Bay. In contrast, higher humic-like DOM was found in bottom water than that in surface water in Sishili Bay and Taozi Bay, which could be attributed to aquaculture activities and biological production. Moreover, photodegradation/photobleaching, dumping, and sewage discharge had their effects on DOM in coastal bays. This study demonstrates that DOM in coastal bays is regulated by multiple sources (rivers, aquaculture, dumping, and sewage) and processes (biological production and photodegradation), and anthropogenic activities have their influences on optical and isotopic characteristics of DOM in coastal bays.