Extractable Organic Matter Research Articles

Optimizing soil dissolved organic matter extraction by grey relational analysis

Dissolved organic matter (DOM) in soil plays an important role in the fate and transport of contaminants. It is typically composed of many compounds, but the effect of different extraction factors on the abundance of different DOM components is unknown. In this study, DOM was extracted from three soils (paddy field, vegetable field and forest soils) with various extraction time, liquid to solid ratios (LSRs), extractant types, and extractant concentrations. The LSR had a significant effect on DOM content, which increased by 0.5–4.0 times among the three soils when LSR increased from 2:1 to 10:1 (P < 0.05). Dissolved organic matter content increased by 4%–53% when extraction time increased from 10 to 300 min (P < 0.05). Extractant concentration had different effects on DOM content depending on the extractant. Higher concentrations of KCl promoted DOM extraction, while higher concentrations of KH2PO4 inhibited DOM extraction. Therefore, grey relational analysis was used to further quantitatively evaluate the effect of extraction time, LSR, and extractant concentration on DOM, using KCl as an extractant. For the paddy field and forest soils, the impact of these three factors on DOM extraction efficiency was in the following order: KCl concentration > LSR > extraction time. However, the effect was different for the vegetable field soil: LSR > extraction time > KCl concentration. Taking all these factors into account, 1.50 mol L−1 KCl and an LSR of 10:1 with a shaking time of 300 min was recommended as the most appropriate method for soil DOM extraction.

The Albedo of Ryugu: Evidence for a High Organic Abundance, as Inferred from the Hayabusa2 Touchdown Maneuver.

The Hayabusa2 mission successfully collected samples from the asteroid Ryugu last year and will return these to Earth in December 2020. It is anticipated that the samples will enable the analysis of terrestrially uncontaminated organic matter and minerals. Such analyses are in turn expected to elucidate the evolution of organic matter through Solar System history, including the origination and processing of biogenically important molecules, which could have been utilized by the first organisms on Earth. In anticipation, studies have made predictions concerning the properties of Ryugu, including its composition. The spectral characteristics of Ryugu, such as albedo, have been employed to relate the asteroid to members of the carbonaceous chondrite group that have been identified on Earth. However, the recent Hayabusa2 touchdown highlights a disparity between the color of surfaces of displaced platy fragments, indicating a brightening trend for the surface exposed to space compared to that facing into the body. Here we present a mass balance calculation with reference to data from the literature, which indicates that Ryugu may contain a significantly higher abundance of organic matter (likely >50%) than the currently most accepted meteorite analogues. A high organic content may result in high levels of extractable organic matter for the second touchdown site, where the spacecraft sampled freshly exposed material. However, high abundances of insoluble aromatic/graphitic rich organic matter may be present in the first touchdown site, which sampled the surface of Ryugu that had been exposed to space. Moreover, we suggest that the potentially high organic abundance and the rubble-pile nature of Ryugu may originate from the capture of rocky debris by a comet nucleus and subsequent water-organic-mineral interactions and sublimation of water ice.

Interaction of dietary rumen undegradable protein level and supplemental rumen-protected conjugated linoleic acid on performance of growing goat kids

Abstract This study aimed to investigate the effects of dietary rumen undegradable protein (RUP) level and supplemental rumen protected conjugated linoleic acid (rpCLA) on performance, nutrient digestibility, rumen fermentation, urinary purine derivatives and plasma metabolites in growing kids. Thirty-two Kurdish kids (13.06 ± 1.08 kg BW) were fed diets differing in RUP level (low = 250 vs. high = 350 g/kg of dietary CP) supplemented either with 15 g/kg rpCLA or 12 g/kg of hydrogenated soybean oil (HSO). The experiment was lasted for 100 days including a 20-d of adaptation period. Goat kids fed diet containing high RUP supplemented with rpCLA had the lowest dry matter intake, but the greatest average daily gain and feed efficiency compared to the other groups (P ≤ 0.05). The interaction of dietary RUP level and rpCLA supplementation had no effect on organic matter, crude protein and ether extract digestibility and ruminal fermentation parameters (P > 0.05). Goat kids fed diet containing high RUP supplemented with HSO had the greatest plasma concentration of triglycerides compared to the other groups (P ≤ 0.05). Urinary uric acid and allantoin concentrations were not influenced by the experimental diets (P > 0.05). In conclusion, feeding diet containing high RUP level supplemented with 15 g/kg rpCLA improved production performance of growing goat kids.

Effect of enzyme supplementation and extruding process on the digestibility of nutrients and phenolic acids of defatted rice bran based diets in ileal-cannulated growing pigs

To improve the efficiency of nutrient utilization in defatted rice bran (DRB) used as animal feed ingredient, the effects of enzyme supplementation and extruding process on the coefficient of apparent ileal digestibility (CAID) and apparent total tract digestibility (CATTD) of nutrients and nutraceutical phenolic acids were evaluated using growing pigs (initial body weight = 18 ± 1.2 Kg) permanently fitted with ileal T-cannula. The extruded DRB ingredient (EDRB) was prepared by extruding the DRB ingredient at 130–135 °C using a single-screw extruder. The enzyme preparation contained cellulase, xylanase, phytase, and ferulic acid esterase. Eight cannulated pigs were allocated according to a 4 × 4 double Latin square arrangement. In each period, 1 of 4 tested diets, i.e., DRB basal diet, EDRB basal diet, and their enzyme added counterparts were randomly distributed to 2 pigs (1 pig form each square). The feces were sampled on the 6th and 7th day, and the ileal digesta were collected on the 8th, 9th and 10th day in each period. The results shown that pigs fed EDRB containing diets exhibited higher CAID values of dry matter (DM), organic matter (OM), gross energy (GE), and ether extract (EE) (P <0.001), and CATTD values of DM, OM, GE, crude protein (CP) and EE (P <0.002) comparing with that of DRB containing items. The CATTD values of most NSP fractions and their constituent residues in EDRB diets were positively affected by the extruding process; however, only the CAID values of insoluble arabinose and xylose were increased (P < 0.05). Enzyme inclusion improved the CAID of DM, OM, GE, ash, Ca, total phosphorus (TP) and phytate phosphorus (PP, P <0.05), and the CATTD of ash, Ca, TP, PP, and Mg (P <0.05). The added enzyme increased the digestion of NSP fractions in the foregut of pigs whereas the effect was not obvious in the large intestine of pigs except for insoluble arabinose. The enzyme addition did not show any effect on the CAID and CATTD of CP, and the CAID of amino acids in the rice bran containing diets. On the contrary, the CAID of amino acids were decreased and the CATTD of CP was increased by the extruding process. To sum up, the extruding temperature adopted in this study (130–135 °C) was too high for DRB processing with the aim of improving the efficiency of amino acids utilization, while it was helpful to improve the digestion of most of gross nutrients and NSP fractions over the whole digestive tract of pigs.

Optical Properties of the Extractable Organic Matter Fractions in Typical Chernozems of Long-Term Field Experiments

The extractable fractions of organic matter (OM) differing in their mobility—water-extractable organic matter, labile humic substances, and humic substances—have been isolated from different-sized aggregates of a typical chernozem (Haplic Chernozem (Loamic, Pachic)). The first two fractions characterize the active OM pool, and the latter fraction characterizes the slow OM pool. Overall, the extractable OM fractions make it possible to assess the content and qualitative composition of the active and slow OM pools and, in an indirect manner, of the passive OM pool. The content of dissolved organic carbon in the extracts is used to quantify the yield of fractions, and the spectral characteristics of light absorption in the ultraviolet and visible ranges attest to their qualitative composition. The main attention is focused on the OM recovery in the chernozems after an extreme regime (permanent tilled fallow) and on the differences in the OM of soil aggregates in dependence on their size. A large part of plant residues entering the soil during the recovery of the chernozem after the extreme conditions of tilled fallow is fixed in the passive OM pool. The qualitative composition of active pools is restored much faster than their quantity typical of the undisturbed cenoses. The optical descriptors E2/E3 of labile humic substances and E4/E6 of humic substances significantly depends on the size of aggregates.

Impact of natural disturbance, forest management and vegetation cover on topsoil biochemical characteristics of Tatra Mts. (Slovakia)

Perturbations caused by windstorms usually lead to the harvesting and clearcutting of fallen trees and wood debris, especially in the areas of managed forest ecosystems. Induced shifts in soils due to management practices play a crucial role in the restoration and maintaining of key ecosystem services. This paper focuses on topsoil chemical properties in relation to vegetation type (trees, shrubs and herbs) evolving at windstorm damaged (in 2004) areas with former Norway spruce (Picea abies) forests in the Tatra Mts. region (Slovakia). We assessed the content of topsoil organic matter fractions (extractives, holocellulose (HC) and lignin (Lig)), carbon in microbial biomass (Cmic), soil organic matter (SOM) and the content of elements N, C, H and S. The study plots represent different types of post-windthrow disturbance history/regime: wooden debris extraction (EXT), wooden debris not extracted (NEX), wooden debris extraction followed by wildfire (FIR), affected by the windstorm in 2014 with the subsequent wooden debris extraction (REX) and unaffected (REF). Our results revealed significant differences among sites in the content of dichloromethane extractives (EXT vs. REX and FIR), acetone extractives (NEX vs. EXT, FIR and REF), ethanol extractives (FIR vs. EXT, NEX and REF), water extractives (FIR vs. REX, NEX) and Cmic (EXT vs. NEX, FIR and REF). The topsoil of Vaccinium myrtillus and Picea abies showed a higher ratio of C/N, N/Lig, and Lig/HC compared to Rubus idaeus, Avenella flexuosa, Calamagrostis villosa, and Larix decidua. The content of N, C, H and S varied between topsoil with shrubs (Vaccinium myrtillus, Rubus idaeus) and grasses (Avenella flexuosa, Calamagrostis villosa). A positive correlation between soil organic matter (SOM) and polar extractives (r=0.81) and a negative correlation between SOM and HC (r=−0.83) was revealed. The carbon content in microbial biomass (Cmic) is positively correlated with acid soluble lignin (ASL) (r=0.85). We also identified a strong correlation between Klason lignin (KL) and the Lig/HC ratio (r=0.97).

The role of residual bitumen on the pore structure of organic-rich shales from low to over mature: Insight from shale and coal samples after the hydrous pyrolysis

The role of residual bitumen on the pore structure of organic-rich shales is related to maturity. However, the studies about the role of the soluble and insoluble residual bitumen on the pore structure of organic-rich shales from low to over mature are deficient. In this study, non-extracted and extracted organic-lean shale, organic-rich shale and coal samples after the hydrous pyrolysis are used to investigate the role of residual bitumen on the pore structure of the organic-rich shales from low to over mature.The specific surface areas of shale and coal samples from low to over mature increase after the solvent extraction. For the organic-lean shale samples from low to over mature and the organic-rich shale samples (lower than 1.51% Ro), the increments of the specific surface area are in proportion to the extractable organic matter (EOM) contents. For the coal samples from low to over mature and the organic-rich shale samples (higher than 1.51% Ro), there is no positive relationship between the increments of the specific surface area and the EOM contents. The increments of pore volumes are obvious in the organic-rich shale samples from mature to high mature and coal samples at wet gas and dry gas stage.The blocking of soluble residual bitumen on inorganic nano-pores depends on the EOM content and will reach the top at the maximum EOM content or the oil peak while the blocking of soluble residual bitumen on organic nano-pores does not depend on the EOM content and will reach the top at over mature. From low mature to mature, the soluble residual bitumen only blocks inorganic nano-pores. From high to over mature, the blocking on inorganic nano-pores gradually becomes weak while the blocking on organic nano-pores gradually increases. The scanning electron microscopy observations and the thermal evolutions of the specific surface area/pore volume of the non-extracted organic-rich shale and coal samples indicate that the organic nano-pores of the insoluble residual bitumen are undeveloped from low mature to mature and more and more developed from high to over mature.

Influence of extractable organic matters on pore structure and its evolution of Chang 7 member shales in the Ordos Basin, China: Implications from extractions using various solvents

To explore the effect of extractable organic matters on pore structure and its evolution of shales, a suite of lacustrine Chang 7 shales with various maturities from the Ordos Basin, China were extracted using acetone, tetrahydrofuran (THF), carbon disulfide (CS2), and benzene, respectively. Fractionations of extracted organic matters were employed to examine group components. Low-pressure nitrogen and carbon dioxide adsorptions were used to characterize the pore structure before and after extraction.The results showed that the asphaltene comes to be significantly extractable in the presence of THF, which may be attributed to that THF has remarkable ability of decreasing the interaction between asphaltene and shale matrix. The micropores with a diameter ranging from 0.3 nm to 0.86 nm in the samples with high TOC content (>15.6%) clearly increased after extractions, thus soluble organic matters of shales may be mainly stored in the micropores with the diameter range above. On the contrary, mesopores have not obvious changes after extractions. Comparably, CS2 has greater access to release micropores and mesopores than other solvents, which may be related to that CS2 is easier to enter the most inner spots due to its smallest dynamic diameter and strip molecular structure. THF has greater access to release micropores due to its ability of reducing molecular size of asphaltene fraction and dissolving abundant asphaltene with small molecular diameter. TOC exerts a stronger control on mesopores and micropores than minerals, mesopores and micropores mainly exist in organic matters of the studied samples. Effect of soluble organic matters on pore structure was much less than maturity, suggesting the generation and cracking of liquid hydrocarbons aren't the major influence factor of evolution of porosity in studied samples.

Effect of Marine Macroalga Enteromorpha sp. Enriched with Zn(II) and Cu(II) ions on the Digestibility, Meat Quality and Carcass Characteristics of Growing Pigs

In the present study, the effect of macroalga Enteromorpha sp. enriched with Zn(II) and Cu(II) ions on daily amounts of feces and urine excreted by growing pigs, apparent fecal nutrient digestibility and daily nitrogen balance and retention, meat quality and the slaughter value of carcasses was examined. The duration of feeding experiments was 87 days. In the control group, the requirement for zinc and copper was covered by inorganic salts, whereas in the experimental group algae enriched with these elements via biosorption were supplemented. No effect of Enteromorpha sp. on the increase in digestibility of dry matter, dry organic matter, crude protein, crude fat and nitrogen-free extractives was observed. Statistically significant differences concerned only the digestibility of crude ash. The daily amount of excreted feces and urine did not differ significantly between groups. Meat from pigs in the algal group was characterized by a lower water absorption and drip loss and contained less fat and more protein than meat from the control group. Furthermore, a slight darkening of the meat was observed. The weight of the liver was lower in pigs from the algal group. Enriched macroalga Enteromorpha sp. may be introduced into pig nutrition as a feed material as an alternative to inorganic salts.

Trends in thermal maturity indicators for the organic sulfur-rich Eagle Ford Shale

Thermal maturity is critical to evaluate petroleum systems and to interpret biomarker results for paleoenvironmental and geobiology studies. Many thermal maturity indices were developed for marine source rocks containing type II kerogen, but their behavior in organic sulfur-rich source rocks requires more investigation. Here, we present geochemical analyses of whole and extracted rock, isolated kerogen, and extractable organic matter across a natural thermal maturity sequence of the Upper Cretaceous Eagle Ford Shale to evaluate the behavior of maturity parameters in organic sulfur-rich source rocks. The samples have similar mineralogy and trace element composition, minimizing potential facies effects on thermal maturity parameters. Atomic H/C ratios of isolated kerogen, extractable organic matter yield, and programmed pyrolysis results show that the samples range from the pre-oil through dry gas generation windows. Programmed pyrolysis data and kerogen elemental ratios show that the immature samples host both type IIS (atomic Sorg/C > 0.04) and sulfur-rich type II kerogen (kerogen Sorg/C: 0.03–0.04) while samples with lower kerogen Sorg/C ratios (kerogen Sorg/C < 0.02) are more mature. The vitrinite reflectance values corresponding to the onset of oil generation in the Eagle Ford are comparable to other type II petroleum systems. Likewise, the organic sulfur-rich Eagle Ford follows a similar hydrogen index (HI) and kerogen H/C trend as other marine type II source rocks. Hopane and sterane stereoisomer maturity ratios are anomalously elevated at low thermal maturities, so they should not be applied in organic sulfur-rich petroleum systems to infer thermal maturity. However, some biomarker ratios, including those that are more commonly used as source parameters, strongly track thermal maturity in this case study with limited facies variability.

Resveratrol protects against PM2.5-induced heart defects in zebrafish embryos as an antioxidant rather than as an AHR antagonist

Resveratrol (RSV), a natural polyphenolic compound commonly found in food, has antioxidant and aryl hydrocarbon receptor (AHR) antagonist effects. We have recently demonstrated that AHR mediated reactive oxygen species (ROS) generation contributes to the cardiac developmental toxicity of ambient fine particle matter (PM2.5). Thus, we hypothesized that RSV protects against the cardiac developmental toxicity of PM2.5 by inhibiting ROS generation and AHR activity. To test this concept, we exposed zebrafish embryos to extractable organic matter (EOM) from PM2.5 in the presence or absence of RSV. We found that RSV significantly counteracted EOM-induced cardiac malformations in zebrafish embryos. The EOM-induced ROS production, DNA damage and apoptosis in the heart of zebrafish embryos were also counteracted by RSV supplementation. Furthermore, RSV attenuated EOM-induced changes in the expression of genes involved in cardiac development (nkx2.5, sox9b, axin2), oxidative stress (nrf2a, nrf2b, gstp1, gstp2, sod1, sod2, cat) and apoptosis (p53, bax). However, RSV did not suppress EOM-induced AHR activity. In conclusion, our data indicates that RSV protects against the PM2.5-induced heart malformations by inhibiting oxidative stress rather than through AHR antagonism.

Bio-geochemical evolution and critical element mineralization in the Cretaceous-Cenozoic coals from the southern Far East Russia and northeastern China

A total of 23 coal and two carbonaceous shale samples of the Early Cretaceous-Miocene, collected from different basins in the Primorye and Sakhalin regions of Russia, and the Hunchun basin of northeastern China, were used in this study for determination of major oxides (by AES and XRF), trace elements (by ICP-MS), sulfur, carbon, carbon isotopes, and major components of extractable organic matter (wet-chemical and gas-chromatographic analyses). Interpretation of the obtained data was intended to elucidate geodynamic and other geological processes controlling bio-geochemical compositions and critical element mineralization of the studied coals. The data suggest that inorganic matter in the studied coals was derived mainly from the Paleozoic granites and the Cenozoic felsic and intermediate tuffs. The Early Eocene and, in particular, Oligocene epochs represent the two major mineralization events in the regions, resulting in enrichment of Ge, W, Be, Mo, Sb, Sr, Ba, REY (rare earth elements and Y), Th, and U in the coals. The two events were related respectively to the Indo-Eurasian collision followed by plate reorganization in the Pacific and the opening of the Sea of Japan. The geodynamic changes were probably associated with mantle-derived volcanic activity and intensive degassing, which enhanced the capability of surficial and ground waters to leach and redistribute trace metals. Organic matter played a significant role in the system of mineralization, starting from weathering of source rocks and ending at the coal diagenetic stage. Organic acids significantly accelerated leaching and transportation of the metals, while they, together with sulfate-reducing bacteria, kerogen, alcohols + ketones, and n-alkanols in particular, played an important role in metal precipitation, mainly through reactions of cation exchange and adsorption.

Study of organic pollution in superficial sediments of Meliane river catchment area: aliphatic and polycyclic aromatic hydrocarbons.

Organic contaminants can be accumulated in aquatic systems even at trace concentrations with potential threats to the environment and human health. The present study has been performed to evaluate the effects of organochlorines and polyaromatic hydrocarbons on surface sediments of the Meliane river catchment. Their determination provides an essential scientific approach for a better understanding of the expected sources and the processes of bioaccumulation. The concentrations of saturated hydrocarbons in extractable organic matter of the dry sediment were found ranging from 0.58 to 3 83μgkg-1 and PAHs content ranged from 63 to 131μgkg-1. These results indicated the adherence of Oued Meliane to the pollution of the Tunis Gulf. The fraction of saturated hydrocarbons extracted from the sediments of Oued Meliane included a majority of organic compounds of biogenic nature with a small oil input. In addition, characterization with the TAR index and the LMW/HMW index confirmed that terrigenous inputs in this fraction are more abundant than aquatic inputs. The characterization of PAHs fraction has shown its pyrolitic origin with a predominance of high molecular weight PAHs.

Effect of electron irradiation on some physical, chemical and digestion properties of pistachio by-products

In the present study pistachio by-products (PB) were treated with various doses of electron irradiation (10–100 kGy). The results indicated that applied doses of electron irradiation had no effect on organic matter (OM), crude protein (CP) and ether extract content of PB. Irradiation increased (P < 0.01) total phenol content; while decreased cell wall compartment, tannin (P = 0.05) and condensed tannin (P = 0.03) contents. Irradiation decreased (P = 0.04) water binding capacity (WBC), but increased (P < 0.05) solubility of dry mater (DM), OM and protein of PB with increasing in irradiation dose. Electron irradiation effectively increased rapidly degradable fraction (a) and decreased potentially degradable fraction (b) of DM and OM of PB in the rumen of sheep compared to the control. The FTIR spectra of samples revealed similar pattern without any changes in the functional group status with a decrease in relative transmittance of peaks in irradiated groups. In conclusion, this study showed that electron irradiating can effectively change physical and chemical; and digestive properties of PB.

Implications for peat formation in Maritsa-West Basin, SE Bulgaria: Insights from organic petrology, palynology and biomarker assemblage

The paper reports the results of the organic petrological, palynological and geochemical characterization of lignite samples from the Kipra lignite seam (Late Miocene, Maritsa-West Basin, Bulgaria). The bulk of the organic matter (OM) is represented by highly gelified detrohuminite with locally abundant leaf-derived ulminite. Liptinite group is characterized by predominance of microsporinite and liptodetrinite, locally with cutinite and fluorinite. Terpene resinite and suberinite are rare. Low TPI and high GI indices indicate peat formation from vegetation with low preservation potential, deposited under water-logged environment of marsh- or fen-type. The palynological results reveal a vegetational community representing different habitats (i.e. mesophytic, marginal and aquatic). The relatively poor preservation of the palynomorphs, however, suggests vegetation that was more diverse during peat formation. Although gymnosperm palynomorphs predominate, the gymnosperm organic matter contribution was probably minor as indicated by the low contents of sesqui- and diterpenoid biomarkers. Because of the absence of triterpenoid biomarkers of neither oleanane, nor lupane or ursane-type, it is considered that angiosperms that do not synthesize their precursors predominated, or the depositional environment had unfavorable characteristics, which prevented the transformation of the triterpenoid precursors.The extractable organic matter yield from the Kipra lignite is low, and dominated by saturated compounds, while polar compounds and asphaltenes occur in low amounts. Aromatic compounds are completely absent. The saturated hydrocarbons are mainly composed of n-alkanes, accompanied by minor amounts of branched- (including isoprenoids) and cycloalkanes, sesqui- and diterpenoids, steroids and hopanoids. Straight chain alkanes are prevailed by long-chain homologues, but show rather mature distribution with CPI ~ 1. Biological (e.g. bacterial) activities and/or environmental control are considered as the main factor/s controlling the observed uncommon n-alkane distributions. A rather uncommon pentacyclic terpenoid, i.e. onocerane I, was tentatively identified in one sample, based on its characteristic fragmentation pattern. Based on its presence, a very specific plant community is considered, and/or specific palaeoenvironmental conditions occurred at least temporarily during the peat formation. However, the responsible plants could not be identified. The low amounts of hopanoid biomarkers, together with the low amounts of n-alkanones, are consistent with limited aerobic biodegradation of the plant remains. The mature 22S/(22S + 22R) C30 hopane ratio (~ 0.55), as well as the random huminite reflectance values (~0.3–0.4%), which are more than twice higher than previously reported, argue for a local increase of coalification degree, presumably due to increased thermal influx around major faults.

Generation of hydroxyl radical during chlorination of hydroxyphenols and natural organic matter extracts

The generation of hydroxyl radicals (•OH) during the chlorination of air saturated solutions of different hydroxyphenols (hydroquinone, resorcinol, catechol, gallic and tannic acids) at pH 7 has been determined by the formation of phenol (in presence of benzene in excess) or 2-hydroxyterephthalic acid (in presence of terephthalic acid). Formation of •OH was only detected during the chlorination of o- or p-hydroxyphenols, compounds that react with chlorine by electron transfer forming the corresponding semiquinones/quinones. In aerated solutions, oxygen is reduced by the semiquinone to the superoxide radical, O2•−, which reacts with HOCl to •OH. Compared to the studied o-hydroxyphenols, the lower reactivity of hydroquinone towards chlorine favours the reaction between chlorine and O2•−, and its •OH formation potential is ∼50 times higher. The extent of •OH generated increased with the concentration of the hydroxyphenol and chlorine, but the •OH yield (moles formed per mole of hydroxyphenol eliminated), decreased due to the formation of the quinone, that acts as O2•− scavenger. The yield was almost not affected by the pH (6 ≤ pH ≤ 7.5), whereas a strong impact of dissolved O2 was observed. The •OH production was null in absence of O2 and 2.5–3 times higher at oxygen saturated conditions compared to air-saturated. Contrary to chlorination, during bromination of hydroquinone •OH was not formed, which can be attributable to a much faster consumption of the oxidant, with no chance for O2•− to react with bromine.Formation of •OH during the chlorination of different NOM extracts (SRHA, SRFA, PLFA and Nordic Lake NOM) and water from Lake Greifensee (Switzerland) was also studied using terephthalic acid as •OH scavenger. For SRHA, SRFA and Nordic Lake NOM (all of allochthonous origin and presenting high electron-donating capacity, EDC), •OH yields expressed as moles formed per mole of DOC0 (%), were between 1.1 and 2.0, similar to that of hydroquinone (∼1.5). For PLFA and Lake Greifensee water (autochthonous, lower EDC) much lower •OH yields were observed (0.1–0.3). Both chlorination rate and EDC, the later favouring the formation/stabilization of O2•−, seem to be key factors involved in •OH generation during the chlorination of NOM. A mechanism for these findings is proposed based on kinetic simulations of hydroquinone chlorination at pH 7.

High-pH and anoxic conditions during soil organic matter extraction increases its electron-exchange capacity and ability to stimulate microbial Fe(III) reduction by electron shuttling

Abstract. Soil organic matter (SOM) is redox-active, can be microbially reduced, and transfers electrons in an abiotic reaction to Fe(III) minerals, thus serving as an electron shuttle. The standard procedure to isolate organic matter (OM) from soil involves the use of alkaline and acidic solutions and the separation of humic acids (HAs) and fulvic acids (FAs). This process potentially leads to unwanted changes in SOM chemical and redox properties. To determine the effects of extraction conditions on the redox and electron-shuttling properties of SOM extracts, we prepared HA, FA, and water-extractable organic matter (OM) extracts, applying either a combination of 0.1 M NaOH and 6 M HCl or ultrapure water (pH 7), from soil samples collected from the subsoil (0–15 cm, A horizon, pH 6.5–6.8) in Schönbuch forest, Baden-Württemberg, Germany. Both chemical extractions (NaOH∕HCl) and water extractions were done in separate experiments under either oxic or anoxic conditions. Furthermore, we applied the NaOH∕HCl treatment to a subsample of the water-extractable OM to separate HA and FA from the water-extractable OM. When comparing the amount of carbon extracted from soil by different extraction methods, we found that FA and HA chemically extracted from the soil can make up to 34 %–40 % of the soil organic carbon pool while the water-extractable OM only represents 0.41 %–2.74 % of the total soil organic carbon. The higher extraction efficiency of the chemical extraction is probably due to the deprotonation of carboxyl and phenol functional groups under high pH. Anoxic extraction conditions also led to more extracted carbon. For water-extractable OM, 7 times more C was extracted under anoxic conditions compared to oxic conditions. This difference was probably due to the occurrence of microbial reduction and dissolution of Fe(III) minerals in the soil during the anoxic water extraction and thus the concomitant release of Fe(III) mineral-bound organic matter. To compare the redox activity of different SOM extracts, the electron-exchange capacity (EEC) of all extracted HA, FA, and water-extractable OM was analyzed and our results showed that, under anoxic extraction conditions, the HA chemically isolated from the water-extractable OM had 2 times higher EEC values compare to the water-extractable OM itself, suggesting the potential formation of redox-active aromatic functional groups during the extraction with NaOH under anoxic conditions by condensation reactions between amino acids, aldehydes, and hydroxyl- and catechol-containing molecules. We also performed a microbial Fe(III) reduction experiment with all extracts and found that higher EEC of extracts in turn resulted in a higher stimulation of microbial Fe(III) mineral reduction by electron shuttling, i.e., faster initial Fe(III) reduction rates, and in most cases also in higher reduction extents. Our findings suggest that OM extracted with water at neutral pH should be used to better reflect environmental SOM redox processes in lab experiments and that potential artefacts of the chemical extraction method and anoxic extraction condition need to be considered when evaluating and comparing abiotic and microbial SOM redox processes.

Organic sulfur: A spatially variable and understudied component of marine organic matter

AbstractSulfur (S) is a major heteroatom in organic matter. This project evaluated spatial variability in the concentration and molecular‐level composition of organic sulfur along gradients of depth and latitude. We measured the concentration of total organic sulfur (TOS) directly from whole seawater. Our data reveal high variability in organic sulfur, relative to established variability in total organic carbon or nitrogen. The deep ocean contained significant amounts of organic sulfur, and the concentration of TOS in North Atlantic Deep Water (NADW) decreased with increasing age while total organic carbon remained stable. Analysis of dissolved organic matter extracts by ultrahigh resolution mass spectrometry revealed that 6% of elemental formulas contained sulfur. The sulfur‐containing compounds were structurally diverse, and showed higher numbers of sulfur‐containing elemental formulas as NADW moved southward. These measurements of organic sulfur in seawater provide the foundation needed to define the factors controlling organic sulfur in the global ocean.

Climate, carbon content, and soil texture control the independent formation and persistence of particulate and mineral-associated organic matter in soil

Understanding the mechanisms controlling the formation and persistence of soil organic matter (SOM) is important for managing soil health and sustainable food production. The formation of SOM and the degree to which it is protected from decomposition are important for determining the long-term persistence of SOM. We used soils collected in a 13C-labelled litter decomposition study established at agricultural sites in Canada to understand the formation and persistence of newly-formed SOM. The ten agricultural sites spanned a wide range of soil carbon contents, texture, and climatic conditions. We fractionated the soil to isolate water extractable organic matter (WEOM), free light POM (fPOM), sand-sized and occluded particulate organic matter (oPOM), and silt and clay sized particles, referred to as mineral-associated organic matter (MAOM). Quantitative isotope tracing was used to determine the litter-derived C in all fractions. We performed these analyses early (six months after incubation) and later (five years after incubation) in the decomposition process to evaluate factors that control the formation and persistence of POM and MAOM. After six months litter-derived C was found in all fractions, but after five years it had declined in all fractions except the MAOM. Formation of MAOM was related to high mean annual precipitation and low sand content, whereas occluded POM formation was related to high soil C content. Persistence of MAOM and POM during the incubation were associated with low soil temperature and high soil C content. There was no consistent indication that formation of MAOM occurred from the decomposition of POM, suggesting that MAOM and POM are formed by two separate pathways. This has important implications for SOC models, which assume that plant-derived C passes through a sequence of pools, becoming more stable along the way.

A diverse uncultivated microbial community is responsible for organic matter degradation in the Black Sea sulphidic zone.

SummaryOrganic matter degradation in marine environments is essential for the recycling of nutrients, especially under conditions of anoxia where organic matter tends to accumulate. However, little is known about the diversity of the microbial communities responsible for the mineralization of organic matter in the absence of oxygen, as well as the factors controlling their activities. Here, we determined the active heterotrophic prokaryotic community in the sulphidic water column of the Black Sea, an ideal model system, where a tight coupling between carbon, nitrogen and sulphur cycles is expected. Active microorganisms degrading both dissolved organic matter (DOM) and protein extracts were determined using quantitative DNA stable isotope probing incubation experiments. These results were compared with the metabolic potential of metagenome‐assembled genomes obtained from the water column. Organic matter incubations showed that groups like Cloacimonetes and Marinimicrobia are generalists degrading DOM. Based on metagenomic profiles the degradation proceeds in a potential interaction with members of the Deltaproteobacteria and Chloroflexi Dehalococcoidia. On the other hand, microbes with small genomes like the bacterial phyla Parcubacteria, Omnitrophica and of the archaeal phylum Woesearchaeota, were the most active, especially in protein‐amended incubations, revealing the potential advantage of streamlined microorganisms in highly reduced conditions.