Dissolved Organic Matter Extracts Research Articles

Seasonal changes in the content of dissolved organic matter in arable soils

PurposeThe aim of this paper has been to determine the seasonal changes in the content of dissolved organic matter (DOM) in the soils under agricultural use based on assaying changes in dissolved organic carbon (DOC) and dissolved nitrogen (DNt) as well as determining the factors which can define the DOM in soils.Materials and methodsThe research has involved the soils under agricultural use sampled in the Kujawsko-Pomorskie province (Poland). Phaeozems and Luvisols were sampled from the depth of 0–30, 30–60, and 60–100 cm, November 2011 through September 2013, in November, March, May, July, and September. The soil samples were assayed for the grain size composition, pH, dry weight content, content of total organic carbon, and total nitrogen. Dissolved organic matter was extracted with 0.004 mol dm3 CaCl2; in the DOM extracts, the content of dissolved organic carbon (DOC) and dissolved nitrogen (DNt) were assayed. The research results were statistically verified.Results and discussionIt has been demonstrated that in the first year of research, the content of dissolved organic carbon in the soils was changing throughout the year. The highest differences in the content of that carbon fraction occurred across the soil sampled in autumn and the soil sampled in spring. In the second year of research, an inverse dependence was noted. DOC was migrating to deeper layers of the soil profile; yet, the migration got more intensive in summer. The content of dissolved nitrogen was not changing significantly throughout the year. Higher DNt content in the surface layer, in general, resulted in a higher content of dissolved nitrogen in deeper profile layer, which could have been due to leaching of the nutrient deep down the soil profile.ConclusionsThe content of dissolved organic carbon was significantly related to the content of total organic carbon and total nitrogen. Significant changes in the content of dissolved forms of nitrogen were reported in the profile of Phaeozems due to mineral fertilization and irrigation. The soils where irrigation and higher nitrogen rates had been applied demonstrated a higher content and share of soluble forms of nitrogen, as compared with the soils non-irrigated and the soils where lower nitrogen rates had been supplied.

Bulk optical characterization of dissolved organic matter from semiarid wheat-based cropping systems

Dissolved organic matter (DOM) plays a critical role in the cycling of nutrients and long-term agricultural sustainability. The composition of DOM in soil is likely altered due to management, yet there is limited knowledge on the effect of long-term cropping on DOM chemical character. Here, we characterized water extractable DOM composition along a gradient of soil organic carbon (SOC) affected by differing cropping and tillage intensity in a semiarid climate of the northern Great Plains, USA. Soil samples (0–10, 10–20, 20–30 cm) were collected from conventional till-fallow winter wheat (Triticum aestivum L.; Ftill-W), no-till spring pea/oilseed-wheat (Pisum sativum L.; Pg/O-W), and no-till continuous wheat (W-W) fields, and analyzed using UV/Vis absorbance and excitation-emission matrix fluorescence spectroscopy. The concentration of DOM decreased with depth and was significantly greater (P<0.05) under W-W or Pg/O-W than Ftill-W. The absorbance at 254 nm (Abs254), a proxy for DOM aromatic nature, indicated that aromaticity decreased with depth and lower biomass-C inputs (i.e. W-W≥ Pg/O-W ≥Ftill-W). Multidimensional parallel factor (PARAFAC) analysis revealed humic-like (C1, C2), monolignol-like (C3), and protein/tannin-like (C4) components with varying fluorescence intensities as a function of cropping system and soil depth. DOM humification, indicated by the humification index (HIX), increased significantly with depth (P<0.05) and was higher for Ftill-W (2.95) than W-W (2.61) or Pg/O-W (2.28). Overall, DOM became depleted of plant-derived constituents and was enriched by more decomposed, condensed substances in Ftill-W, as compared to W-W or Pg/O-W soils. DOM composition is strongly affected by cropping intensity and such changes are important drivers controlling SOC accretion in arable soils.

Composition and Transformation of Dissolved Organic Matter in the Baltic Sea

The processing of terrestrial dissolved organic matter (DOM) in coastal shelf seas is an important part of the global carbon cycle, yet, it is still not well understood. One of the largest brackish shelf seas, the Baltic Sea in northern Europe, is characterized by high freshwater input from sub-arctic rivers and limited water exchange with the Atlantic Ocean via the North Sea. We studied the molecular and isotopic composition and turnover of solid-phase extractable (SPE) DOM and its transformation along the salinity and redox continuum of the Baltic Sea during spring and autumn. We applied ultrahigh-resolution mass spectrometry and other geochemical and biological approaches. Our data demonstrate a large influx of terrestrial riverine DOM, especially into the northern part of the Baltic Sea. The DOM composition in the central Baltic Sea changed seasonally and was mainly related to autochthonous production by phytoplankton in spring. Especially in the northern, river-dominated basins, a major fraction of riverine DOM was removed, likely by bio- and photo-degradation. We estimate that the removal rate of terrestrial DOM in the Baltic Sea (Bothnian Bay to the Danish Straits/Kattegat area) is 1.6 – 1.9 Tg C per year which is 43 to 51% of the total riverine input. The export of terrestrial DOM from the Danish Straits/Kattegat area towards the North Sea is 1.8 – 2.1 Tg C per year. Due to the long residence time of terrestrial DOM in the Baltic Sea (total of ca. 12 years), seasonal variations caused by bio- and photo-transformations and riverine discharge are dampened, resulting in a relatively invariant DOM molecular and isotopic signature exported to the North Sea. In the deep stagnant basins of the Baltic Sea, the DOM composition and dissolved organic nitrogen concentrations changed seasonally, likely because of vertical particle transport and subsequent degradation releasing DOM. DOM in the deep anoxic basins was also enriched in sulfur-containing organic molecules, pointing to abiotic sulfurization of DOM under sulfidic conditions.

How representative are dissolved organic matter (DOM) extracts? A comprehensive study of sorbent selectivity for DOM isolation

Solid phase extraction (SPE) has become a widespread method for isolating dissolved organic matter (DOM) of diverse origin such as fresh and marine waters. This study investigated the DOM extraction selectivity of 24 commercially available SPE sorbents under identical conditions (pH = 2, methanol elution) on the example of Suwannee River (SR) water and North Sea (NS) water by using DOC analysis and Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS). Proton nuclear magnetic resonance (1H NMR) spectroscopy was employed to assess leaching behavior, and HLB sorbent was found to leach substantially, among others. Variable DOC recoveries observed for SR DOM and NS DOM were primarily caused by the respective molecular composition, with subordinated and heterogeneous contributions of relative salinity. Scatter of average H/C and O/C elemental ratios and gross alignment in mass-edited H/C ratios according to five established coarse SPE characteristics was near identical for SR DOM and NS DOM. FTMS-based principal component analysis (PCA) provided essentially analogous alignment of SR DOM and NS DOM molecular compositions according to the five established groups of SPE classification, and corroborated the sorption-mechanism-based selectivity of DOM extraction in both cases. Evaluation of structural blanks and leaching of SPE cartridges requires NMR spectroscopy because FT-ICR mass spectrometry alone will not reveal inconspicuous displacements of continual bulk signatures caused by leaching of SPE resin constituents.

Environmental Drivers of Dissolved Organic Matter Molecular Composition in the Delaware Estuary

Estuaries as connectors of freshwater and marine aquatic systems are hotspots of biogeochemical element cycling. In one of the best studied temperate estuaries, the Delaware Estuary (USA), we investigated the variability of dissolved organic matter (DOM) over five sampling cruises along the salinity gradient in August and November of 3 consecutive years. Dissolved organic carbon (DOC) concentrations were more variable in the upper reaches of the estuary (245±49 µmol L-1) than at the mouth of the estuary (129±14 µmol L-1). Bulk DOC decreased conservatively along the transect in November but was non-conservative with increased DOC concentrations mid-estuary in August. Detailed analysis of the solid-phase extractable DOM pool via ultrahigh resolution mass spectrometry (Fourier-transform ion cyclotron resonance mass spectrometry, FT-ICR-MS) revealed compositional differences at the molecular level that were not reflected in changes in concentration. Besides the mixing of terrestrial and marine endmember signatures, river discharge levels and biological activity were found to impact DOM molecular composition. DOM composition changed less between August and November than along the salinity gradient. Relative contributions of presumed photolabile DOM compounds did not reveal non-conservative behavior indicative of photochemical processing; suggesting that on the timescales of estuarine mixing photochemical removal of molecules plays a minor role in the turbid Delaware Bay. Overall, a large portion of molecular formulae overlapped between sampling campaigns and persisted during estuarine passage. Extending the analysis to the structural level via the fragmentation of molecular masses in the FT-ICR-MS cell, we found that the relative abundance of isomers along the salinity gradient did not change, indicating a high structural similarity of aquatic DOM independent of the origin. These results point towards a recalcitrant character of the DOM supplied by the Delaware River. We demonstrate that in addition to bulk DOC quantification, detailed information on molecular composition is essential for constraining sources of DOM and to identify the processes that impact estuarine DOM, thereby controlling amount and composition of DOM eventually discharged to the ocean through estuaries.

Probing the Photosensitizing and Inhibitory Effects of Dissolved Organic Matter by Using N,N-dimethyl-4-cyanoaniline (DMABN).

Dissolved organic matter (DOM) can act as a photosensitizer and an inhibitor in the phototransformation of several nitrogen-containing organic contaminants in surface waters. The present study was performed to select a probe molecule that is suitable to measure these antagonistic properties of DOM. Out of nine studied nitrogen-containing aromatic compounds, 4-cyanoaniline, N,N-dimethyl-4-cyanoaniline (DMABN), sotalol (a β-blocker) and sulfadiazine (a sulfonamide antibiotic) exhibited a marked photosensitized transformation that could be substantially inhibited by addition of phenol as a model antioxidant. The photosensitized transformation of DMABN, the selected probe compound, was characterized in detail under UV-A and visible irradiation (λ > 320 nm) to avoid direct phototransformation. Low reactivity of DMABN with singlet oxygen was found (second-order rate constant <2 × 107 M-1 s-1). Typically at least 85% of the reactivity of DMABN could be inhibited by DOM or the model antioxidant phenol. The photosensitized transformation of DMABN mainly proceeded (>72%) through demethylation yielding N-methyl-4-cyanoaniline and formaldehyde as primary products. In solutions of standard DOM extracts and their mixtures the phototransformation rate constant of DMABN was shown to vary nonlinearly with the DOM concentration. Model equations describing the dependence of such rate constants on DOM and model antioxidant concentrations were successfully used to fit experimental data.

Chemical differences of aquatic humic substances extracted by XAD-8 and DEAE-cellulose

Chemical characteristics of dissolved organic matter (DOM) extracted from an ombrotrophic bog in northern Minnesota by two methods – XAD-8 and DEAE-cellulose – were compared using 13C NMR spectroscopy, excitation–emission matrix fluorescence spectroscopy (EEMS), and Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS). DOM extracted with XAD-8, a relatively hydrophobic sorbent, had a larger 13C NMR signal in the aromatic carbon region, but DOM extracted by DEAE-cellulose, a weak anion exchanger, had a larger signal in the carboxylic carbon region. DOM extracts prepared by the two methods were similar in their overall chemical characteristics that serve as proxies for organic matter sources. For example, only small differences were observed in the fluorescence index (FI) values of the extracts, and all values were within the range expected for terrestrially-derived DOM. EEMS spectra of both extracts had “humic-like” peak A areas smaller than that of standard reference Suwannee River fulvic acid. Of 2801 distinct chemical formulas assigned during FT-ICR MS analysis of the two extracts, 66% were present in both; 15% were unique to the XAD-8 extract, and 19% were unique to the DEAE-cellulose extract. Van Krevelen plots showed that the DEAE-cellulose extract had more tannin-like and condensed aromatic entities and formulas with higher O/C ratios, whereas the XAD-8 extract had more lignin-like material and formulas with higher H/C ratios. Overall, differences in chemical characteristics of the extracts reflect the mechanisms by which the extractants operate.

Mechanism of ofloxacin fluorescence quenching and its interaction with sequentially extracted dissolved organic matter from lake sediment of Dianchi, China.

The wide use and occurrence of antibiotics in water environments have caused wide concerns. Ofloxacin (OFL) was selected as a target antibiotic, and the interaction between OFL and sequential extracted dissolved organic matter (DOM) from the sediment of Dianchi, a hypertrophic lake in Southwest China, was explored using fluorescence quenching technology. The method of fuorescence quenching was used to characterize the interaction between OFL and sequentially extracted DOM. The result indicated that static and dynamic quenching both existed in the interaction. The interaction in the background water (0.01mol/L NaCl and 200mg/L NaN3) became increasingly weak with the further extraction of DOM. A low non-linear factor N value (0.53∼0.63) of Freundlich model was observed, indicating a non-linear interaction between OFL and DOM. Elemental characterization and infrared spectrum analysis showed an enhanced OFL-DOM binding with the decrease in humic acid (HA) polarity. The effect of ion strength was tested in the OFL-DOM interaction to show the impact of usually existing metal ions in water environment on the OFL behavior. The result showed that K(+) had little influence, but Cu(2+) had a significant promotion (p < 0.05) in the OFL-DOM interaction in background water, indicating that divalent metal ions, which have the bridge bond or complexation capacity, are more active in the OFL-DOM interaction than monovalent ions, with no bridge bond or complexation capacity. This work would be useful in the fate and risk assessment of antibiotics in water environments.

Extending the analytical window for water-soluble organic matter in sediments by aqueous Soxhlet extraction

Dissolved organic matter (DOM) in marine sediments is a complex mixture of thousands of individual constituents that participate in biogeochemical reactions and serve as substrates for benthic microbes. Knowledge of the molecular composition of DOM is a prerequisite for a comprehensive understanding of the biogeochemical processes in sediments. In this study, interstitial water DOM was extracted with Rhizon samplers from a sediment core from the Black Sea and compared to the corresponding water-extractable organic matter fraction (<0.4μm) obtained by Soxhlet extraction, which mobilizes labile particulate organic matter and DOM. After solid phase extraction (SPE) of DOM, samples were analyzed for the molecular composition by Fourier Transform Ion-Cyclotron Resonance Mass Spectrometry (FT-ICR MS) with electrospray ionization in negative ion mode. The average SPE extraction yield of the dissolved organic carbon (DOC) in interstitial water was 63%, whereas less than 30% of the DOC in Soxhlet-extracted organic matter was recovered. Nevertheless, Soxhlet extraction yielded up to 4.35% of the total sedimentary organic carbon, which is more than 30-times the organic carbon content of the interstitial water. While interstitial water DOM consisted primarily of carbon-, hydrogen- and oxygen-bearing compounds, Soxhlet extracts yielded more complex FT-ICR mass spectra with more peaks and higher abundances of nitrogen- and sulfur-bearing compounds. The molecular composition of both sample types was affected by the geochemical conditions in the sediment; elevated concentrations of HS- promoted the early diagenetic sulfurization of organic matter. The Soxhlet extracts from shallow sediment contained specific three- and four-nitrogen-bearing molecular formulas that were also detected in bacterial cell extracts and presumably represent proteinaceous molecules. These compounds decreased with increasing sediment depth while one- and two-nitrogen-bearing molecules increased, resulting in a higher similarity of both sample types in the deep sediment. In summary, Soxhlet extraction of sediments accessed a larger and more complex pool of organic matter than present in interstitial water DOM.

Methylmercury photodegradation in surface water of the Florida Everglades: importance of dissolved organic matter-methylmercury complexation.

Photodegradation is the major pathway of methylmercury (MeHg) degradation in many surface waters. However, the mechanism of MeHg photodegradation is still not completely understood. Dissolved organic matter (DOM) is expected to play a critical role in MeHg photodegradation. By using several techniques, including N2/O2 purging and the addition of stable isotope (Me(201)Hg), scavengers, competing ligands, and a singlet oxygen ((1)O2) generator, the role played by MeHg-DOM complexation in MeHg photodegradation of Everglades surface water was investigated. DOM appeared to be involved in MeHg photodegradation via the formation MeHg-DOM complexes based on three findings: (1) MeHg was quickly photodegraded in solutions containing DOM extracts; (2) degradation of MeHg did not occur in deionized water; and (3) addition of competing complexation reagents (dithiothreitol-DTT) dramatically prohibited the photodegradation of MeHg in Everglades water. Further experiments indicated that free radicals/reactive oxygen species, including hydroxyl radical (·OH), (1)O2, triplet excited state of DOM ((3)DOM*), and hydrated electron (e(-)aq), played a minor role in MeHg photodegradation in Everglades water, based on the results of scavenger addition, (1)O2 generator addition and N2/O2 purging. A pathway, involving direct photodegradation of MeHg-DOM complexes via intramolecular electron transfer, is proposed as the dominant mechanism for MeHg photodegradation in Everglades water.

Molecular evidence for rapid dissolved organic matter turnover in Arctic fjords

Dissolved organic matter (DOM) in the ocean comprises one of the largest active carbon pools on earth. Deep water formation at high latitudes carries DOM from the active surface layers to the deep ocean. However, information on sources and fate of DOM in the Arctic Ocean is limited. To reveal the relevance of autochthonous DOM production and transformation in Arctic fjord systems to the global deep ocean DOM pool, we performed a comprehensive study on the molecular composition of DOM and the composition of the associated microbial communities in four selected fjords of Svalbard. At various water depths, a total of 34 samples were taken in fall 2010 for the determination of bulk concentrations of dissolved organic carbon (DOC) and total dissolved nitrogen (TDN), for the molecular characterization of solid-phase extractable DOM as well as for microbial community fingerprinting.While TDN concentration and the composition of the microbial community showed a clear distinction between surface and bottom water samples, bulk DOC (~60μmol C L−1) and dissolved black carbon (~1.8% of DOC) as a marker for terrestrial input were uniformly distributed. In-depth molecular-level analyses of the DOM composition using ultrahigh resolution mass spectrometry via Fourier-transform ion cyclotron resonance mass spectrometry (FT-ICR-MS) revealed insignificant variation of the relative abundance of 11630 molecular masses that were detected in the water samples.From these findings we conclude that DOM produced during the spring/summer bloom is rapidly transformed within the short, but productive warm season by the specialized resident microbial community. Thus, in fall the DOM pool mainly consists of semi-refractory and refractory material, most of which has been introduced from Arctic Ocean water inflow. Assuming that our findings are representative for high latitude marine systems in general, the contribution of autochthonous seasonal DOC production in plankton bloom situations to the DOC pool in regions of deep water formation might be marginal.

Soil structural indices' dependence on irrigation water quality and their association with chromophoric components in dissolved organic matter

SummaryIrrigation with treated wastewater (TWW) may affect soil structure and stability and the characteristics of dissolved organic matter (DOM) of the soil solution. The objectives of our study were (i) to evaluate the impact of TWW irrigation, as compared with fresh water (FW) irrigation, on aggregate stability and saturated hydraulic conductivity (indices of soil structure stability) and (ii) to determine whether these indices can be associated with the chromophoric indicators of water‐extractable DOM in TWW‐ and FW‐irrigated soils. We studied aggregate stability and soil hydraulic conductivity (HC) of four different soil types irrigated with either TWW (for at least 5 years) or FW. The results were linked to earlier published data on the concentration scores of fluorescent chromophoric DOM components (obtained from excitation‐emission matrices of flouorescence coupled with parallel factor analysis), dissolved organic carbon (DOC) concentration and absorbance at 254 nm (Abs254). These were all obtained from water extracts of the same soils as those used in the current study. Irrigation with TWW decreased aggregate stability, in comparison to irrigation with FW, in the sandy clay and clay soils, while in the loamy sand TWW increased aggregate stability. The apparent steady state HCs in the TWW‐irrigated samples in the loamy sand, sandy clay and clay soils were similar to, or significantly less than, those obtained in the FW‐irrigated samples. In the sandy loam the opposite trend was noted. Results of principal component and classification analyses showed that the aggregate stability indices were directly associated with soil organic matter and DOM attributes in the coarse‐textured soils, while in the fine‐textured soils inverse associations were noted. Only in the fine‐textured soils were the HC attributes associated (directly) with some of the DOM characteristics. Our results suggest that structural indices of fine‐textured soils are more sensitive than those of coarse‐textured soils to the composition of water extractable DOM.

Impacts of Sampling Dissolved Organic Matter with Passive Capillary Wicks Versus Aqueous Soil Extraction

Quantitative characterization of dissolved organic matter (DOM) in soil and vadose zone solution is needed to interpret mechanisms of nutrient and C cycling as well as bio‐weathering processes. Passive capillary wick samplers (PCaps) are useful for soil solution sampling because they can provide measures of water and associated DOM‐constituent flux in the unsaturated zone, however potential impacts of the wick material on DOM chemical properties has not been investigated yet. We therefore conducted experiments where aqueous soil extracts were transported along PCap fiberglass wicks in flow‐through experiments. Results indicated limited dissolved organic carbon (DOC) sorption and DOM fractionation, and related parameters (total dissolved nitrogen [TDN], DOM fluorescence components) also remained largely unaffected. We note that this experiment does not account for the extent to which soil hydrologic processes may be affected by PCap field installations. However, given that the wicks did not fractionate significantly DOM, we compared field‐based PCap DOM solution collected in situ with laboratory‐based aqueous soil extraction (ASE) of DOM from the same soils to assess differences in DOM quality. Spectroscopic analysis of DOM in ASE solutions showed lower O‐H stretch/carboxlyate band intensity ratios, more pronounced aliphatic C‐H stretching (Fourier Transform Infrared analysis), higher specific ultraviolet‐absorbance (SUVA254) values as well as greater abundance of fluorescence components in the region attributed to fulvic acids. We conclude that difference in molecular properties of DOM derived from laboratory ASE vs. PCap field collection of the same soils is attributable to differential disturbance effects of the two methods of soil solution collection.

Dissolved organic matter reduces algal accumulation of methylmercury

Dissolved organic matter (DOM) significantly decreased accumulation of methylmercury (MeHg) by the diatom Cyclotella meneghiniana in laboratory experiments. Live diatom cells accumulated two to four times more MeHg than dead cells, indicating that accumulation may be partially an energy-requiring process. Methylmercury enrichment in diatoms relative to ambient water was measured by a volume concentration factor (VCF). Without added DOM, the maximum VCF was 32 × 10(4) , and the average VCF (from 10 to 72 h) over all experiments was 12.6 × 10(4) . At very low (1.5 mg/L) added DOM, VCFs dropped by approximately half. At very high (20 mg/L) added DOM, VCFs dropped 10-fold. Presumably, MeHg was bound to a variety of reduced sulfur sites on the DOM, making it unavailable for uptake. Diatoms accumulated significantly more MeHg when exposed to transphilic DOM extracts than hydrophobic ones. However, algal lysate, a labile type of DOM created by resuspending a marine diatom in freshwater, behaved similarly to a refractory DOM isolate from San Francisco Bay. Addition of 67 µM L-cysteine resulted in the largest drop in VCFs, to 0.28 × 10(4) . Although the DOM composition influenced the availability of MeHg to some extent, total DOM concentration was the most important factor in determining algal bioaccumulation of MeHg.

Study on the spectral and Cu (II) binding characteristics of DOM leached from soils and lake sediments in the Hetao region

Dissolved organic matter (DOM) is the most active component in environmental system and its chemical and structural characteristics most likely influence its biodegradation. Four surface soil (0-20 cm) and three core sediment samples (0-10 cm) were collected from Wuliangsuhai Lake. The objectives of this study were to investigate the spectral properties and humification degree of DOM and to determine and discuss comparatively the complexing capacities and stability constants of DOM by Cu (II) in the Hetao region. In this study, fluorescence spectra and fluorescence quenching methods were used to evaluate the humification degree of DOM and calculate the complexing capacities and the stability constants between DOM and Cu (II). Two defined peaks, at wavelengths of 260∼300 nm (peak I) and 300∼350 nm (peak II), could be identified for soil DOM at a Δλ value of 30 nm. In sediment DOM extracts, a third peak (III) was observed near 364 nm. The results show that there is a significant difference in the structure of DOM because of different sources. The humification degree is significantly higher for soil samples than those of sediment samples. The FT-IR spectra of DOM show that structure in sediment DOM is more functional groups than those in soil DOM. DOM has a stronger Cu binding affinity in soils than in sediment in the Hetao region, which may lead to potentially significant influence on the migration and transformation of Cu (II).

Characterization of dissolved organic matter across the Subtropical Convergence off the South Island, New Zealand

Dissolved organic matter (DOM) was investigated along a gradient across the Subtropical Convergence (STC) off the South Island, New Zealand. Ultrahigh resolution electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR-MS), excitation emission matrix fluorescence (EEM) spectroscopy, and molecular lignin analysis techniques were used to study this DOM. The analysis revealed a group of compounds found only in the coastal DOM samples, which were also characterized by an elevated terrestrial DOM fluorescence pattern and elevated lignin content if compared to the offshore samples. This group exhibited a high degree of carbon unsaturation, as evident from high double bond equivalence minus oxygen values (DBE-O > 9) and maximum fluorescence intensity. Sulfur-containing molecular formulae for summer DOM samples were much more abundant across the entire transect of the STC compared to winter and exhibited distinctly different hydrogen:carbon and oxygen:carbon elemental ratios, suggesting a possible correlation between biological activity and sulfur compounds. The molecular formulae common to all STC samples were compared with those calculated for DOM extracted from freshwater collected from a stream discharging into Doubtful Sound (West Coast, New Zealand). ESI-FT-ICR-MS measurements undertaken in negative electrospray ionization (ESI−) mode indicated that 30% of the molecular formulae were present in both types of DOM, while in positive ESI mode (ESI+) over 90% of the formulae were present in all samples. Hence, a significant portion of the molecular formulae assigned to the solid-phase extractable DOM pool (SPE-DOM) appear to be identical in oceanic and freshwater samples.

Humic-rich peat extracts inhibit sulfate reduction, methanogenesis, and anaerobic respiration but not acetogenesis in peat soils of a temperate bog

To understand why anaerobic ombrotrophic peats can be very low in methane after drainage related afforestation, we analyzed the competition of sulfate reducing, humus reducing, and methanogenic microorganisms by incubating ombrotrophic peats of the Mer Bleue bog, Ontario. Sulfate, sulfide, and sulfate containing peat dissolved organic matter (DOM) from an afforested site were added in reduced and oxidized redox state. Sulfate and acetate concentrations were analyzed, bacterial sulfate reduction (BSR) and CO2 and CH4 production quantified, and results analyzed by ANOVA. DOM was characterized by Fourier transformed infrared and fluorescence spectroscopy and analyzed for trace elements. CH4 production (116 nmol cm−3 d−1) and BSR rate (102 nmol cm−3 d−1) were similar in ‘controls’. BSR in treatments ‘sulfate’ (73 nmol cm−3 d−1) and ‘sulfide’ (118 nmol cm−3 d−1) did not significantly differ from ‘controls’ but addition of DOM significantly diminished BSR down to 0.4 nmol cm−3 d−1 (Kruskal Wallis test, p < 0.05). CH4 production decreased with sulfate (16%, not significant) and sulfide addition (40%, p < 0.05) and CO2 production increased (treatment ‘sulfate’, p < 0.05). Addition of all DOM extracts (67 mg L−1) almost completely suppressed methanogenesis and CO2 production (p < 0.05), but acetate accumulated compared to the control (p < 0.05). The DOM applied contained carboxylic, aromatic and phenolic moieties and metal contents typical for peat humic substances. We conclude that a toxic effect of the intensely humified DOM occurred on both methanogenic and sulfate reducing bacteria (SRB) but not on fermenting microorganisms. As yet it is not clear what might cause such a toxic effect of DOM on SRB and archaea.

Dissolved Organic Matter Extracted With Water and a Saline Solution From Different Soil Profiles

The organic matter fraction present in soil solution and passing a filter of pore size of 0.45 μm is operationally defined as dissolved organic matter (DOM). In this work, DOM was extracted with either water or a saline solution from the various horizons of four different soil profiles, either cultivated or not, and characterized by chemical analysis and spectroscopic techniques such as emission fluorescence spectroscopy and Fourier transform infrared spectroscopy. Water and a saline solution extracted different amounts of DOM. These results imply that the effect of colloidal dispersion exerted by water resulted in a higher release and solubilization of organic matter compared with colloidal flocculation exerted by the saline solution. Thus, the extractant used for DOM extraction from soil must be taken into due account for its effect on the nature of DOM extracted. Our results corroborate the need to standardize extraction methods. Fluorescence emission spectra provided evidence of a variation in DOM composition as a function of depth along the soil profile, which was possibly related to adsorption of aromatic molecules on soil colloids. Finally, land use also seemed to influence the chemical nature of DOM along the soil profile.

Characterisation of dissolved organic matter in water extracts of thermally altered plant species found in box - ironbark forests

This study investigated the chemical structure of extracted dissolved organic matter (DOM) derived from thermally altered plant material found in the box–ironbark environments of central Victoria, namely: Eucalyptus tricarpa, Pinus pinaceae, Isolepsis nodosa, Acacia pycnantha, and Cassinia arcuata. Samples taken from the plants were burnt at 150, 300, and 400°C, under oxidising and reducing conditions in order to represent the variable combustion undergone by plants during bushfire events. The extraction of DOM from the burnt residues into water was conducted over 96 h. During the extraction period, solution concentrations of DOM were measured using HPLC and TOC methods, while the chemistry of the extracted DOM was characterised using ATR-IR. The nature of the extracted DOM depended on the originating species and whether burnt under oxidising or reducing conditions. DOM derived from the residues of the Australian native trees and shrubs (E. tricarpa, A. pycnantha, and C. arcuata) were generally more aromatic and conjugated than the materials extracted from herbaceous I. nodosa and introduced dendrophyte P. pinaceae. When burnt under reducing conditions, fire residues were less polar, indicated by the fact that they were significantly less soluble and ATR-IR spectra spectroscopy showed little OH stretching compared with the extracts obtained under oxidising conditions. Water extracts from the burnt residues sorbed strongly to the mineral goethite, but had less affinity for the kaolinite surface.

Intake of dissolved organic matter from deep seawater inhibits atherosclerosis progression

Dissolved organic matter (DOM) in seawater can be defined as the fraction of organic matter that passes through a filter of sub micron pore size. In this study, we have examined the effect of DOM of deep seawater (DSW) from Pacific Ocean on platelet aggregation and atherosclerosis progression. DSW was passed through a series of filters and then through an Octadecyl C18 filter; the retained substance in ethanol was designated as C18 extractable DOM (C18-DOM). Our studies showed that C18-DOM treatment inhibited platelet aggregation, P-selectin expression and activity of COX-1 significantly. C18-DOM increased the expression of anti-atherogenic molecule namely heme oxygenase-1 in endothelial cells and all these data showed that C18-DOM is exhibiting aspirin-like effects. Moreover our in vivo studies showed that C18-DOM feeding slowed remarkably the progression of atherosclerosis. Our study demonstrated a novel biological effect of oceanic DOM, which has several important implications, including a possible therapeutic strategy for atherosclerosis.