Aromatic Dissolved Organic Matter Research Articles

Feasting on terrestrial organic matter: Dining in a dark lake changes microbial decomposition.

Boreal lakes are major components of the global carbon cycle, partly because of sediment‐bound heterotrophic microorganisms that decompose within‐lake and terrestrially derived organic matter (t‐OM). The ability for sediment bacteria to break down and alter t‐OM may depend on environmental characteristics and community composition. However, the connection between these two potential drivers of decomposition is poorly understood. We tested how bacterial activity changed along experimental gradients in the quality and quantity of t‐OM inputs into littoral sediments of two small boreal lakes, a dark and a clear lake, and measured the abundance of operational taxonomic units and functional genes to identify mechanisms underlying bacterial responses. We found that bacterial production (BP) decreased across lakes with aromatic dissolved organic matter (DOM) in sediment pore water, but the process underlying this pattern differed between lakes. Bacteria in the dark lake invested in the energetically costly production of extracellular enzymes as aromatic DOM increased in availability in the sediments. By contrast, bacteria in the clear lake may have lacked the nutrients and/or genetic potential to degrade aromatic DOM and instead mineralized photo‐degraded OM into CO2. The two lakes differed in community composition, with concentrations of dissolved organic carbon and pH differentiating microbial assemblages. Furthermore, functional genes relating to t‐OM degradation were relatively higher in the dark lake. Our results suggest that future changes in t‐OM inputs to lake sediments will have different effects on carbon cycling depending on the potential for photo‐degradation of OM and composition of resident bacterial communities.

Phosphorus mobility in dam reservoir affected by redox oscillations: An experimental study

The internal sedimentary phosphorus (P) load of aquatic systems is able to support eutrophication, especially in dam–reservoir systems where sedimentary P stock is high and where temporary anaerobic conditions occur. The aim of this study therefore is to examine the response of sedimentary P exposed to redox oscillations. Surface sediments collected in the Champsanglard dam–reservoir (on the Creuse River, France) were subjected to two aerobic phases (10 and 12 days) alternated with two anaerobic periods (21 and 27 days) through batch incubations. The studied sediment contained 77 ± 3 μmol/g DW of P, mainly associated with the ascorbate fraction (amorphous Fe/Mn oxyhydroxides). The used sediment was rich in organic matter (OM) (21% ± 1%) with primarily allochthone signature. Our results showed that redox oscillations enhance dissolved inorganic phosphorus release at sediment/water interface. During the first anaerobic stage, the P release was mainly controlled by the dissolution/precipitation of iron minerals. The more pronounced increase of P release during the second anaerobic stage (44%) was due to various mechanisms related to the change in quality of dissolved organic matter (DOM), namely a higher SUVA254 and humification indices. The release of more refractory DOM (rDOM) served to lower the microbial metabolism activity, possibly favored iron oxyhydroxide aggregation and thus limiting iron reduction. In addition, rDOM is able to compete for mineral P sorption sites, leading to a greater P release. In reservoir with predominant allochthone OM input, the release of more aromatic DOM therefore plays an important role in P mobility.

The Effects of Flue Gas Desulphurization Gypsum on the Properties of Dissolved Organic Matter and Bacterial Community During Composting

Composting is a process that converts organic materials including solid wastes into humus-like substances. Additives play an important role in regulating composting performances. This work investigated the influences of flue gas desulphurization gypsum (FGDG) on the properties and evolution of dissolved organic matter (DOM) during the co-composting of dairy manure, sugarcane leaf and pressmud (the sludge from sugar factory effluent) with the combination techniques of elemental analysis, particle size, zeta potential, UV–Vis spectroscopy and FT-IR technology. The results revealed that FGDG amendment reduced carbon loss and facilitated nitrogen emission in compost DOM, increased the aromaticity of DOM and compost maturity, enhanced the absorbance of –OH, –CHO, –COOH and C–O in polysaccharides. Additionally, the adding of FGDG was an inhibitive factor to the whole bacterial diversity during composting. These findings provided new insights into the evolution and properties of DOM and the microbial community during the composting process with FGDG amendment.

Effects of long-term green manure application on the content and structure of dissolved organic matter in red paddy soil

Dissolved organic matter (DOM) plays important roles in soil biogeochemistry activity and nutrients transportation in soils, but studies regarding the long-term effects of green manures on the content and structure of DOM in red paddy soil have not been reported yet. A long-term green manure experiment established in 1982 was utilized to test the DOM contents in different treatments, and the spectral characteristics of DOM were investigated by using ultraviolet-visible (UV-Vis) spectrometry and Fourier transform infrared (FTIR) spectrometry. The experiment included four cropping systems: rice-rice-milk vetch (RRV), rice-rice-rape (RRP), rice-rice-ryegrass (RRG) and rice-rice-winter fallow (RRF), among them, milk vetch, rape, and ryegrass are popular winter green manure species in southern China. The results showed that the content of dissolved organic carbon (DOC), which is widely used to estimate the concentration of DOM, was significantly promoted after the incorporation of green manures compared with the other sampling stages. The contents of aromatic groups and the degree of humification of DOM increased in RRV and RRP, suggesting more complex compositions of the soil DOM after long-term application of milk vetch and rape. The contents of phenol, alcohol and carboxylic acid group at the mature stage of early rice were significantly higher than those at the stage of after green manures turned over, especially for the RRV treatment. The absorption ratio of FTIR indicated that winter plantation of rape increased the aromatic-C/aliphatic-C ratio, and ryegrass increased the aromatic-C/carboxyl-C ratio. In conclusion, long-term planting of milk vetch and rape as green manures increased the degree of aromaticity, humification and average molecular weight of DOM, and made the DOM more stable in red paddy soil.

Impacts of soil improvement on the pollutant-removal performance and DOM characteristics using a simulation experiment

Abstract An experimental simulation device was used to evaluate the water purification performance of soil improved with two different conditioners, which were cornstalk and zeolite (CSZ), turf and quartz sand (CTS) in this study. The results showed that the removal rates for total suspended solids (TSS), chemical oxygen demand (COD), total nitrogen (TN), and total phosphorus (TP) reached 75.58%, 25.71%, 68.37%, and 64.67%, respectively, for CSZ, and 85.09%, 92.75%, 76.71%, and 98.33%, respectively, for CTS, suggesting that soil improvement showed higher water purification performance with the CTS conditioner than with the CSZ conditioner. The structure, composition, and source of dissolved organic matter (DOM) were probed using ultraviolet visible (UV–Vis) spectra and fluorescence spectra. The spectral parameters indicated that the CTS conditioner-improved soil showed a relatively high humification and aromaticity of DOM, and a relatively higher contribution of organic matter derived from microbial substances. In addition, the results of 2D-COS suggested that the binding sites and sequences can be significantly influenced by soil improvement, and vary between the two kinds of conditioners. The CTS-improved soil was more effective in reducing fluorescent DOM than was the CSW-improved soil. This study can provide a scientific foundation for the treatment of agricultural non-point source (NPS) pollution.

Characteristics of Dissolved Organic Matter (DOM) and Relationship with Dissolved Heavy Metals in a Peri-urban and an Urban River

Dissolved organic matter (DOM) is ubiquitous in the aquatic environment, playing an important role in the fate of heavy metals in aquatic systems. In this study, we characterized the DOM and heavy metals and their distribution in a peri-urban river and an urban river in Ningbo city. In addition, the relationship between DOM and dissolved heavy metals was also determined. Results showed that higher DOC, CDOM, and FDOM concentrations were found in the river with the higher urbanization level. Four fluorescence peaks were identified in the excitation-emission matrix (EEM) of DOM, including fulvic acid-like fluorescence peaks A and C and protein-like fluorescence peaks B and T. The higher fluorescence intensities of peak B and T were found in the urban river, and similar trends were also found for the degree of humification and aromaticity of DOM. Similarly, concentrations of heavy metals, such as As, Cu, and Mn, were significantly higher in the urban river. Moreover, DOM had significant positive correlations with Cu, Cr, Mn, As, Zn, and Pb in the urban river, while DOM only exhibited significant positive correlations with Mn, Pb, and Cu in the peri-urban river. In conclusion, urbanization level influenced the characteristics and concentrations of CDOM in rivers which were closely related to the distribution of heavy metals.

Inoculation with Compost-Born Thermophilic Complex Microbial Consortium Induced Organic Matters Degradation While Reduced Nitrogen Loss During Co-Composting of Dairy Manure and Sugarcane Leaves

This investigation was carried out on the effects of compost-born thermophilic complex microbial consortium (TCMC) composed of Ureibacillus suwonensis (TB42), Geobacillus thermodenitrificans (TB62) and Bacillus licheniformis (TA65) on co-composting of dairy manure and sugarcane leaves. The study assessed the TCMC influence on physicochemical parameters and dissolved organic matter (DOM) properties. Compared to the control (CP), the inoculated pile (CPT) showed a longer thermophilic phase, a faster organic matter degradation, a better Kjeldahl nitrogen preservation as well as a greater aromaticity and stability of DOM. Consequently, the inoculation with TCMC agent was effective in reducing the loss of nitrogen and accelerating maturity of compost.

Flux and Seasonality of Dissolved Organic Matter From the Northern Dvina (Severnaya Dvina) River, Russia

AbstractPan‐Arctic riverine dissolved organic carbon (DOC) fluxes represent a major transfer of carbon from land‐to‐ocean, and past scaling estimates have been predominantly derived from the six major Arctic rivers. However, smaller watersheds are constrained to northern high‐latitude regions and, particularly with respect to the Eurasian Arctic, have received little attention. In this study, we evaluated the concentration of DOC and composition of dissolved organic matter (DOM) via optical parameters, biomarkers (lignin phenols), and ultrahigh resolution mass spectrometry in the Northern Dvina River (a midsized high‐latitude constrained river). Elevated DOC, lignin concentrations, and aromatic DOM indicators were observed throughout the year in comparison to the major Arctic rivers with seasonality exhibiting a clear spring freshet and also some years a secondary pulse in the autumn concurrent with the onset of freezing. Chromophoric DOM absorbance at a350 was strongly correlated to DOC and lignin across the hydrograph; however, the relationships did not fit previous models derived from the six major Arctic rivers. Updated DOC and lignin fluxes were derived for the pan‐Arctic watershed by scaling from the Northern Dvina resulting in increased DOC and lignin fluxes (50 Tg yr−1 and 216 Gg yr−1, respectively) compared to past estimates. This leads to a reduction in the residence time for terrestrial carbon in the Arctic Ocean (0.5 to 1.8 years). These findings suggest that constrained northern high‐latitude rivers are underrepresented in models of fluxes based from the six largest Arctic rivers with important ramifications for the export and fate of terrestrial carbon in the Arctic Ocean.

Optical Properties of Dissolved Organic Matter and Their Relation to Mercury Concentrations in Water and Biota Across a Remote Freshwater Drainage Basin.

Dissolved organic matter (DOM) includes an array of carbon-based compounds that vary in size and structure and have complex interactions with mercury (Hg) cycling in aquatic systems. While many studies have examined the relationship between dissolved organic carbon concentrations ([DOC]) and methyl Hg bioaccumulation, few studies have considered the effects of DOM composition (e.g., protein-content, aromaticity). The goal of this study was to explore the relationships between total and methyl [Hg] in water, invertebrates, and fish and optically derived measures of DOM composition from 47 lake and river sites across a boreal watershed. Results showed higher aqueous total [Hg] in systems with more aromatic DOM and higher [DOC], potentially due to enhanced transport from upstream or riparian areas. Methyl [Hg] in biota were all positively related to the amount of microbial-based DOM and, in some cases, to the proportions of labile and protein-like DOM. These results suggest that increased Hg bioaccumulation is related to the availability of labile DOM, potentially due to enhanced Hg methylation. DOM composition explained 68% and 54% more variability in [Hg] in surface waters and large-bodied fish, respectively, than [DOC] alone. These results show that optical measures of DOM characteristics are a valuable tool for understanding DOM-Hg biogeochemistry.

American beech leaf‐litter leachate chemistry: Effects of geography and phenophase

AbstractThe decomposition of broadleaved tree leaves can contribute a substantial amount of energy to forested watersheds via dissolved organic matter (DOM), nutrients, and biological activity. Less is known about how these inputs may vary within a single tree species that is known to have two genetically distinct and geographically separate populations, or how these inputs may change throughout autumn senescence and abscission. It is often implicitly assumed that intraspecific differences in leaf‐litter leachate chemistry do not significantly differ geographically. We analyzed the morphological and chemical leaf traits and leachates from Fagus grandifolia (American beech) leaves (n = 360) during three phenophases: fresh green leaves, senescing leaves, and fallen leaves. During each phenophase, leaves were collected from four sites along a geographic transect stretching from Vermont to North Carolina (over 1400 km), with two sites representing each genetic population and differing climatic conditions. Leachates were analyzed for routine solutes and nutrients, as well as fluorescent and UV‐visible absorbance indices. Amounts of macro‐ and micronutrients were highly variable among sites and phenophases but tended to be lowest during the fallen‐leaf phase, while measured fluorescence and absorbance indices tended to increase during the senescing‐leaf phase and plateau. Results suggest significant differences in leached nutrients among sites, and optical properties and nutrients among phenophases. Aromaticity and molecular weight of DOM in leachates was generally low, and aromaticity and humification of leachates both increased over time with leaf age. These results also suggest that geographically (or genetically) separate populations of the same species do not experience senescence in the same way and that implicit assumptions of intraspecific uniformity of leaf‐litter leachate chemistry for a given tree species may be invalid.

模拟增温及隔离降雨对中亚热带杉木人工林土壤可溶性有机质的数量及其结构的影响

PDF HTML阅读 XML下载 导出引用 引用提醒 模拟增温及隔离降雨对中亚热带杉木人工林土壤可溶性有机质的数量及其结构的影响 DOI: 10.5846/stxb201704250749 作者: 作者单位: 福建师范大学,福建师范大学,福建师范大学,福建师范大学 作者简介: 通讯作者: 中图分类号: 基金项目: 国家自然基金面上项目（31570606）；福建省自然科学基金面上项目（2015J01120） Effects of experimental soil warming and precipitation reduction on the quantity and structure of soil dissolved organic matter of Cunninghamia lanceolata plantations in subtropical China Author: Affiliation: Fujian Normal University,Fujian Normal University,Fujian Normal University, Fund Project: 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:温度和水分影响森林生态系统的结构与功能，而全球变暖和降雨格局的改变是未来气候变化的趋势。我国中亚热带地区森林覆盖率大，碳库丰富，可溶性有机质（DOM）作为森林生态系统的重要组成部分，气候变化对它的数量和组成具有重要的影响。本文对我国湿润亚热带地区杉木人工林土壤进行模拟增温以及隔离50%的降雨试验，利用光谱技术手段研究增温及隔离降雨对土壤可溶性有机质（DOM）的数量及其结构的影响。试验设对照（CK）、增温（W）、隔离降雨（P）、增温与隔离降雨的交互作用（WP）4种处理。结果表明，与对照相比，土壤增温后，0-10cm和10-20cm土层的土壤可溶性有机碳（DOC）和可溶性有机氮（DON）增加，但其芳香性指数和腐殖化程度降低，增温加速DOM的流失，不利于土壤有机质的稳定。季节变化影响土壤的环境，导致隔离降雨有使DOM的数量增加或减少的趋势；在旱季（2014年10月和2015年1月），隔离降雨降低了土壤DOM的数量，但其芳香性指数和腐殖化程度增加，而进入雨季（2015年4月），隔离降雨有使DOM增加的趋势，但其组分中的芳香化合物较少。增温和隔离降雨的交互作用在一定程度上促进DOM的产生，其结构比对照简单。温度和降雨对DOM的影响较为复杂，在全球气候变化背景下，只有长期对其进行观测并探讨其他因素带来的影响才能深入了解气候变暖和降雨格局的变化对土壤碳、氮的影响。 Abstract:Temperature and moisture are important to the structure and function of forest ecosystems. In future decades, global warming and variations in precipitation patterns will be the major climatic characteristics. Global warming is suggested to accelerate the decomposition of soil organic matter (SOM), and thereby to increase the carbon flux. Altered rainfall amounts might affect plant growth and soil structure. As a crucial component of forests, dissolved organic matter (DOM) plays an important role in such ecological processes. It is central to the questions of carbon decomposition/sequestration in soils and nutrient availability to microorganisms and plants. Natural evergreen broad-leaved forests make up the typical vegetation in the subtropical zone of China, but large areas of natural forests have been transformed to Cunninghamia lanceolata plantations. Therefore, it is critical that we should explore the effects of warming and precipitation variations on the dynamic changes of DOM in these plantations. In this article, we investigated the effects of simulated soil warming, 50% precipitation reduction, and the combination of the two factors on the quantity and composition of soil DOM. There were four treatments (three replicates per treatment) effects studied:(1) no warming and natural precipitation; (2) warming and natural precipitation; (3) no warming and precipitation reduction; and (4) warming and precipitation reduction. The soil samples were collected in October 2014, January 2015, and April 2015, respectively. To learn more about the relationships of DOM with temperature and moisture, we also measured the soil microbial biomass carbon and microbial biomass nitrogen. The results showed that the quantity of DOM increased after soil warming in both 0-10cm and 10-20cm soil layers. In addition, the aromaticity and humification degree of DOM decreased after warming. In our study, soil warming could accelerate the loss of DOM and restrain the stability of carbon. The impacts of the precipitation reduction treatment on DOM production showed a seasonal pattern. In particular, the quantity of DOM was reduced but its aromaticity and humification degree were enhanced in the drought season (October 2014 and January 2015), whereas in the rainy season (April 2015), the quantity of DOM had increased since the growth of microorganisms and the content of aromatic compounds were reduced simultaneously. Under the combination of warming and precipitation reduction, the quantity of DOM increased because of accelerated decomposition of SOM. Moreover, the DOM structure became simpler through the interaction of the two factors. The effects of temperature and moisture on the quantity and structure of soil DOM are sophisticated. We will continue to estimate the impacts of warming and precipitation reduction on soil microbes, organic matter, and other elements with long-term observational data to attain a more profound comprehension about carbon and nitrogen cycling under global climate change. 参考文献 相似文献 引证文献

The properties and dynamic changes of DOM subfractions during food waste and sugarcane leaves co-composting.

The purpose of this research was to evaluate the properties and dynamic changes of humic acids (HA), fulvic acids (FA), hydrophobic neutrals (HoN), and hydrophilic (Hi) fractions of dissolved organic matter (DOM) during food waste and sugarcane leaves co-composting process. The pools of HA, FA, HoN, and Hi were separated from DOM by fractionation method, and characterized using spectroscopic (UV-vis, FTIR) and pyrolysis-GC/MS analyses. The least peaks in the HA pool were found in FTIR spectra with the simple structure in HA. The highest value of SUV254 was observed in HA, indicating that the HA pool played a dominant role in aromaticity of DOM. Hydrophobic compounds (HA, FA, HoN) had higher percentages of alkanes and cyclo-alkanes at the end of composting, while lower contents in the Hi pool. Both DOM and its subfractions increased the Chinese flowering cabbage (Brassica campestris L.) seed germination rate (SGR), whereas HA had a significant effect on promoting the root growth.

Reciprocal influences of dissolved organic matter and nanosized zero-valent iron in aqueous media

We investigated concurrent effects between nano-sized zero-valent iron (NZVI) and dissolved organic matter (DOM). Specific UV absorbance of DOM revealed that aromatic/hydrophobic moieties of DOM were bounded to NZVI surfaces. The DOM fluorescence emission peak shifted toward lower wavelength after NZVI exposure, which indicated removal of aromatic DOM fractions. This blue shift of the emission peak also attributes to the reduction of electron acceptors through NZVI-DOM charge transfer complexes. High molecular weight (103–104 Da) DOM fractions, which are suspected to be both aromatic and hydrophobic, were removed. X-ray absorption spectroscopy (XAS) elucidated that Fe(0) content in the 30-d aged NZVI in the presence of DOM (61.6%) was substantially higher than that in the absence of DOM (25.0%). Corrosion and oxidation of NZVI were mitigated due to interruption of electron transfer by surface bounded DOM and stabilization of Fe(II) by Fe-DOM complexes. The XAS also revealed that the evolution of the iron (oxyhydr)oxide shell of NZVI was significantly altered by complexed aromatic DOM.

Extreme flooding mobilized dissolved organic matter from coastal forested wetlands

Two intense rainfalls [Hurricane Joaquin (2015) and Hurricane Matthew (2016)], one year apart, provided a unique opportunity to examine changes in dissolved organic matter (DOM) dynamics in coastal blackwater rivers under extreme flooding conditions in the southeastern United States. Two sites along Waccamaw River (a coastal blackwater river) and the outflow of 18 sub-basins of Yadkin-Pee Dee Basin were sampled during and after the flooding events. The peaks of dissolved organic carbon (DOC) and nitrogen (DON) concentrations were observed 18 and 23 days after peak discharge in 2015 and 2016, respectively. Moreover, DOM aromaticity and abundance of humic substances significantly increased during the same period. Separation of discharge hydrograph into surface runoff and subsurface flow suggested that temporal changes were mainly due to contributions from subsurface flow flushing organic matter from wetlands and organic-rich riparian zones. The spatial analysis highlighted the key role of the forested wetlands as the only land use that significantly correlated with both DOM quantity (DOC and DON load) and DOM composition (i.e., aromaticity). The Yadkin-Pee Dee River basin alone exported more than 474 million kg DOC into the ocean during high-flow conditions from the 2016 event, indicating that such extreme short-term events mobilized enormous amounts of organic carbon and nitrogen to the ocean. Considering the predicted increase in frequency and intensity of extreme rainfall events in the eastern U.S., the results of this study can shed light on changes in DOM dynamics that may occur under such conditions in the near future.

Insights into the pollutant-removal performance and DOM characteristics of stormwater runoff during grassy-swales treatment

ABSTRACT The water purification performance of grassy swales for treating stormwater road runoff was evaluated using a simulated experimental device in two different seasons. The results showed that the removal rates for total suspended solids (TSS), chemical oxygen demand (COD), total nitrogen (TN), and total phosphorus (TP) reached 89.90%, 56.71%, 32.37%, and 19.67%, respectively, in summer, and 34.09%, 7.75%, 56.71%, and 13.33%, respectively, in winter, suggesting that grassy swales showed higher water purification performance in summer than in winter. Soil filtration in grassy swales also showed high removal rates of TSS, COD, TN and TP in summer (98.13%, 59.10%, 33.82%, and 24.59% respectively). The structure, composition and source of dissolved organic matter (DOM) were investigated using ultraviolet visible (UV–Vis) spectra and fluorescence spectra. The spectral parameters indicated a relatively high humification and aromaticity of DOM, and a relatively higher contribution of organic matter derived from microbial substances in summer than in winter. In addition, grassy-swale treatment showed a slight decrease in metal-ion concentrations at the surface, while the removal rates in the bottom samples were 38.42%, 40.59%, 33.81%, and 40.06% for Cu2+, Cd2+, Pb2+, and Zn2+, respectively. The results of 2D-COS suggested that grass swales treatment can change the binding sites and binding sequencing of DOM with heavy metals and further influence the metal speciation, mobility and biotoxicity.

The Optical, Chemical, and Molecular Dissolved Organic Matter Succession Along a Boreal Soil‐Stream‐River Continuum

AbstractSoils export large amounts of organic matter to rivers, and there are still major uncertainties concerning the composition and reactivity of this material and its fate within the fluvial network. Here we reconstructed the pattern of movement and processing of dissolved organic matter (DOM) along a soil‐stream‐river continuum under summer baseflow conditions in a boreal region of Québec (Canada), using a combination of fluorescence spectra, size exclusion chromatography and ultrahigh resolution mass spectrometry. Our results show that there is a clear sequence of selective DOM degradation along the soil‐stream‐river continuum, which results in pronounced compositional shifts downstream. The soil‐stream interface was a hot spot of DOM degradation, where biopolymers and low molecular weight (LMW) compounds were selectively removed. In contrast, processing in the stream channel was dominated by the degradation of humic‐like aromatic DOM, likely driven by photolysis, with little further degradation of either biopolymers or LMW compounds. Overall, there was a high degree of coherence between the patterns observed in DOM chemical composition, optical properties, and molecular profiles, and none of these approaches pointed to measurable production of new DOM components, suggesting that the DOM pools removed during transit were likely mineralized to CO2. Our first order estimates suggest that rates of soil‐derived DOM mineralization could potentially sustain over half of the measured CO2 emissions from this stream network, with mineralization of biopolymers and humic substances contributing roughly equally to these fluvial emissions.

Effects of Sulfide Concentration and Dissolved Organic Matter Characteristics on the Structure of Nanocolloidal Metacinnabar.

Understanding the speciation of divalent mercury (Hg(II)) in aquatic systems containing dissolved organic matter (DOM) and sulfide is necessary to predict the conversion of Hg(II) to bioavailable methylmercury. We used X-ray absorption spectroscopy to characterize the structural order of mercury in Hg(II)-DOM-sulfide systems for a range of sulfide concentration (1-100 μM), DOM aromaticity (specific ultraviolet absorbance (SUVA254)), and Hg(II)-DOM and Hg(II)-DOM-sulfide equilibration times (4-142 h). In all systems, Hg(II) was present as structurally disordered nanocolloidal metacinnabar (β-HgS). β-HgS nanocolloids were significantly smaller or less ordered at lower sulfide concentration, as indicated by under-coordination of Hg(II) in β-HgS. The size or structural order of β-HgS nanocolloids increased with increasing sulfide abundance and decreased with increasing SUVA254 of the DOM. The Hg(II)-DOM or Hg(II)-DOM-sulfide equilibration times did not significantly influence the extent of structural order in nanocolloidal β-HgS. Geochemical factors that control the structural order of nanocolloidal β-HgS, which are expected to influence nanocolloid surface reactivity and solubility, should be considered in the context of mercury bioavailability.

Compositional changes and molecular transformations of dissolved organic matter during the arctic spring floods in the lower Churchill watershed (Northern Manitoba, Canada)

The spring flood season in Northern aquatic systems is characterized by rapid changes in river discharge and fluxes of organic and inorganic species, yet remains under sampled. In this study, we examine the molecular characteristics and transformations of dissolved organic matter (DOM) during the Arctic spring season at three locations in the lower Churchill River watershed. Characteristics including dissolved organic carbon concentrations, optical properties (i.e. absorbance and, excitation-emission matrix fluorescence coupled with parallel factor analysis, EEM-PARAFAC) and molecular characterization using high resolution mass spectrometry (HR-MS) were assessed. As spring floods progressed, a significant reduction in DOM spectral slope (S275–295) and an increase in absorbance (a270) were observed suggesting an increase in DOM molecular weight and concentrations at all sampled locations. A maximum in HR-MS lignin-class compounds coincided with peak flow at all sampled locations, further validated with an increase in PARAFAC humic-like components and a minimum in S275–295. Principal component analyses revealed that both protein and aromatic humic-like material measured by HR-MS and EEM-PARAFAC, respectively, were significantly correlated (ANOVA, p < 0.05), demonstrating similarities in both techniques. Based on network analysis of HR-MS assigned formula, the highest peak flow day was characterized by a maximum in homologous DOM of C2H2O and C2H4 additions, suggesting structural similarities in newly deposited lignin and humic material. Overall, the progression of the spring freshet shifted the lower Churchill River watershed from an environment rich in proteins and lipids to an aquatic system more abundant in lignin, aromatic and humic DOM.

Comparison of the effects of chloramine and chlorine on the aromaticity of dissolved organic matter and yields of disinfection by-products

This study compared effects of chlorination and chloramination on the chromophores of dissolved organic matter (DOM) and attendant formation of disinfection by-products (DBPs) in raw and treated surface waters. Comparison of the differential absorbance spectra of chloraminated and chlorinated waters shows that interactions of chloramine with DOM chromophores result in changes that are in many respects similar to those observed for chlorine although the extent of degradation of DOM chromophores and the attendant decrease of DOM aromaticity by chloramine are less pronounced than that caused by free chlorine. The degradation of DOM chromophores caused by the examined disinfectants indicated that in both cases a gradual decrease of DOM took place. Decreases of DOM aromaticity estimated based on the changes of DOM absorbance at 254 or 280 nm were correlated with chlorine consumption in a similar way for both examined disinfectants. Correlations between changes of DOM absorbance and yields of dihaloacetic acids (DHAA) were also similar for chlorination and chloramination. This was interpreted to indicate that the generation of DHAA proceeds via the degradation of the reactive sites associated with DOM chromophores irrespective of whether these sites are engaged by chlorine or chloramine. Correlations between the decrease of DOM aromaticity and formation of other DBP (e.g. trihalomethanes - THM, trihaloacetic acids - THAA and dihaloacetonitriles - DHAN) for chloramine and chlorine were also observed but, as opposed to the observations for DHAA, the correlations between degradation of DOM aromaticity and yields of THM, THAA or DHAN were different for chlorination and chloramination.

Reactivity of Triplet Excited States of Dissolved Natural Organic Matter in Stormflow from Mixed-Use Watersheds.

Dissolved organic matter (DOM) quantity and composition control the rate of formation (Rf,T) of triplet excited states of dissolved natural organic matter (3DOM*) and the efficiency of 3DOM* formation (the apparent quantum yield, AQYT). Here, the reactivity of 3DOM* in stormflow samples collected from watersheds with variable land covers is examined. Stormflow DOM reflects variability in DOM quantity and composition as a function of land cover and may be important in controlling the fate of cotransported pollutants. Rf,T and AQYT were measured using 2,4,6-trimethylphenol in stormflow samples under simulated sunlight. The DOM source and composition was characterized using absorbance and fluorescence spectroscopies and high-resolution mass spectrometry. Rf,T and the total rate of light absorption by the water samples (Ra) increased with the dissolved organic carbon (DOC) concentration. AQYT was independent of DOC concentration, but varied with DOM source: developed land cover (4-6%) ≈ open water > vegetated land cover (3%). AQYT was positively related to an index for microbial/algal DOM content and negatively related to DOM molecular weight, DOM aromaticity, and the content of polyphenols. This work demonstrates that TMP is an effective probe for the determination of Rf,T and AQYT in whole water samples after accounting for the inhibition of TMP photodegradation by DOM.