Fulvic Acid Fractions Research Articles

Linking the electron transfer capacity with the compositional characteristics of dissolved organic matter during hyperthermophilic composting

Redox-active functional groups in dissolved organic matter (DOM) can mediate reductions in organic pollutants and the passivation of heavy metals, which are related to the humification process of composting. Hyperthermophilic composting (HTC) has been shown to promote changes in the composition and structure of DOM and accelerate humification. However, how HTC affects the redox properties of DOM remains unclear. Here, we fractionated DOM into humic acid (HA), fulvic acid (FA) and hydrophilic (HyI) fraction to study their electron transfer capacities (ETC) and the relationship between ETC and compositional characteristics using electrochemical method and excitation-emission matrix-parallel factor analysis. HTC accelerated the formation of component 3 containing quinone-like moieties, which mainly existed in the HA, improving the electron accepting capacity (EAC) of DOM. The rapid degradation of component 4 containing tryptophan-like substances of HA, FA and HyI strengthened the electron donating capacity of DOM in HTC. Partial least squares path model also showed that compositional changes and the stronger ETC of DOM in HTC had a positive effect on the maturity degree, revealing that the EAC of HA could be used as a maturity index for compost. This study advances our understanding of the humification process and the contamination control mechanism of HTC.

The influence of humic and fulvic acids on Cd bioavailability to wheat cultivars grown on sewage irrigated Cd-contaminated soils

The soil cadmium (Cd) contamination is a ubiquitous environmental problem that has resulted from intense irrigation with wastewater. This pot trial was conducted with aim to produce safe food with Cd tolerant wheat cultivar in wastewater irrigated soils. For this purpose, two wheat cultivars NARC-2011 (Cd tolerant) and Shafaq-2006 (Cd sensitive) were screened out and selected, after conducting a pilot trial of twelve local wheat cultivars against Cd stress. Both cultivars were grown in naturally contaminated soils with Cd concentrations (4.18, 3.23, 2.29 and 1.25 mg kg−1). After harvesting, NARC-2011 showed significant photosynthetic attributes, grain biochemical parameters and yield. Additionally, Cd concentrations in edible grains of NARC-2011 cultivars were found within standard limits (200 mg kg−1), in all contaminated soils. Furthermore, a marked decrease in Cd bioavailability was noted with cultivar NARC-2011, where contribution of mobile Cd fractions (exchangeable and reducible) percentage was decreased, while immobile Cd fractions percentage increased (oxidizable and residual). Fourier transform infrared (FTIR) spectroscopy reflects the maturity and stability of humic and fulvic like acid fractions and revealed that humification of these compounds after prolonged sludge enriched wastewater irrigation lowered the Cd availability. The wheat cultivar NARC-2011 (Cd tolerant) could be opted to grow on soils irrigated with wastewater for a long time, as Cd bioavailability decreased with ageing due to stabilized humic substances and varietal tolerance.

CARBON AND NITROGEN IN SOILS AND HUMIC FRACTIONS OF DIFFERENT PEDOFORMS IN THE ATLANTIC FOREST BIOME

Relief is a soil formation factor that can modify the distribution of soil organic matter (SOM) fractions in a landscape. The objective of this study was to evaluate the effect of the relief on SOM fractions, considering their distribution in different topographic positions, segments, in two pedoforms (concave and convex) in areas covered with forest in the Atlantic Forest biome. The two pedoforms were selected in adjacent areas and divided into segments considering the topographic variation. The carbon and nitrogen origins were evaluated in the extract up to 100 cm of depth. Soil samples from the 0-5, 5-10, and 10-20 cm layers were collected for chemical characterization and fractioning (granulometric and chemical) of the SOM. The soil density in the 0-5 and 5-10 cm layers was determined to calculated the carbon stocks. The isotopic composition showed predominance of 13C. The highest organic carbon and particulate carbon contents were found in the convex pedoform. The distribution of humic fractions showed that the larger part of the humidified carbon was in the humin fraction. The humin and fulvic acid fractions were higher in the convex pedoform. The carbon stocks were, in general, higher in the convex pedoform, decreasing as the soil depth increased; and nitrogen stocks presented no differences. The higher carbon and nitrogen contents were found in the convex pedoform and in the lower region of the concave pedoform.

Spectroscopic characterization of humic and fulvic acids in soil aggregates, Brazil

Agricultural management methods affect organic compounds in the soil. The aim of this study was to characterize humic and fulvic acids using infrared spectroscopy and nuclear magnetic resonance (NMR) in aggregates collected from areas under different crop and soil management systems. Soil samples were collected at depths of 0.00–0.10 m in a trial set up in 1989 with four management systems (no-till, no-till with chiseling every three years, disk harrowing and heavy disking) under two production systems (succession and rotation). In the laboratory, the soil was sieved and separated into two fractions: particle size of 2 mm or more, and less than 2 mm. From each of the samples an aliquot was extracted and the humic and fulvic acids purified for FTIR, UV-VIS and NMR-1H analysis. The results obtained showed that the structural characterization of the humic and fulvic acid fractions were linked to organic matter left on the soil surface, especially where the agricultural system involved species diversity. Aggregates ≥2 mm produce higher NMR, UV-VIS and FTIR spectral magnitudes in aromatic and aliphatic structures than those <2 mm. Aggregates collected from soil under no-till retained their aromatic and aliphatic chemical structures, resulting in higher spectral amplitude.

Formation and mobility of soil organic carbon in a buried humic horizon of a volcanic ash soil

A buried humic horizon (14C age between 5.4 and 6.8 kyr BP) of a volcanic ash soil in Aomori, Japan, which was collected from the depth between 147 and 187 cm at 5 cm-interval (total eight sub-horizon samples), was investigated to clarify the degree of biological transformation and mobility of soil organic carbon (SOC) fractions. The SOC fractions were prepared from each sub-horizon sample by extraction and precipitation procedures with controlling pH of the extracted solution, resulting in humin, humic acid (HA), and four fulvic acid (FA) fractions (two hydrophilic FA fractions: FA1 and FA2, and two hydrophobic FA fractions: FA3 and FAIHSS). The prepared SOC fractions were characterized by 14C age and stable isotopic ratios of 13C (δ13C) and 15N (δ15N). The hydrophilic FA fractions showed the highest δ13C and δ15N values, indicating that these SOC fractions had been most enriched with 13C and 15N by biological metabolic processes. On the other hand, the HA fraction showed the lowest δ13C and δ15N values, therefore this fraction would have been less-metabolized, although HA fraction has been regarded as well-processed in general. The 14C age of the HA fraction was almost same as the deposition age of the corresponding sub-horizon, indicating that the C in the HA fraction would have been fixed in situ right after photosynthesis by plants at the early stage of soil formation and chemically stabilized at soil surface, by fire event, etc. The average rates of vertical translocation of the SOC fractions were low (humin and HA fractions: <1 mm per century, FA fractions: 1–4 mm per century), implying that the vertical translocation of SOC would not be the main mechanisms for forming thick humic horizons. The present study showed strong evidence of the in situ formation of SOC on soil surface, and successive up-building accumulation of soil particles containing SOC would contribute to the formation of the thick humic horizons.

Morphogenetic Diagnostics and Nomenclature of Alluvial-Meadow Soils in the Subtropical Semiarid Area, Floodplain of the Kur River, Azerbaijan

Abstract—The aim of this study was to evaluate morphologic features, diagnostic qualifiers and enhance classification of alluvial-meadow soils in the floodplain of the Kur River within Azerbaijan. For this purpose, several soil pits were placed in the representative test areas and multiple soil samples collected within field campaigns (2014–2015). Based on the field and laboratory test data, the detailed soil maps of the test areas were compiled, and diversity of alluvial-meadow soils was classified as suborders (subtypes): alluvial-meadow primitive; alluvial-meadow layered (flaggy); alluvial-meadow dark and alluvial-meadow irrigated. It was found out that in the floodplains, local soil variability was predominantly attributed to not only alluvial sediments, but also water table, mineralization rate and salt content of underground water as well flood water play an important role. The mineralization of ground water is weak (1.40–3.70 g/L) and the concentration of hydro-carbonates (HCO3) varies from 0.56 to 0.92 g/L. No salinization indication found in the profile of alluvial-meadow primitive and alluvial-meadow layered soils, while weak concentration (solid content = 0.40–0.54%) was found at a depth of 80–150 cm in the alluvial-meadow dark soil. Unlike other subtypes, alluvial-meadow dark soil is characterized with the higher biomass (green weight of top = 41.5 c/h and green weight of underground = 142.3 c/h), high mobility of humus substances with predominance of the 1st fraction of humin (20.0–28.1%) and fulvic acids (14.6–22.3%). The ratio of Ch.a : Cf.a reaches 1.18–1.32. For the alluvial-meadow irrigated soil, the second fraction of humin acid (9.3–10.2%) and total content of humin acid ranges from 45.6 to 50.3%. The ratio of Ch.a : Cf.a is larger (1.37–1.50). Depending on the litho logy of alluvial sediments, the content of SiO2 and R2O3 varies in the ranges of 53.0–57.2 and 9.6–26.0%, respectively. For the alluvial-meadow dark soil, decomposition of alum silicates in alkaline hydrolysis is typical (8.7–9.0). The content of SiO2 and R2O3 varies between 47.8 and 50.6%, and 19.7 and 21.6%, respectively. In the topsoil, of the irrigated soils in associated to washing out the content of Ca and CaO content (12.2–13.1%) increases in deeper horizons.

Binding Mechanism Between Fulvic Acid and Heavy Metals: Integrated Interpretation of Binding Experiments, Fraction Characterizations, and Models

In this study, nine fulvic acid fractions (FAs) were obtained by a progressively extracting method from lake sediment and used as adsorbent for binding metal ions. The characterization indicated that former FA fractions had stronger polarity, more O-bearing functional groups, and less aliphaticity. And the results of EEM-PARAFAC indicated that there were four components in FAs, i.e., two humic-like components and two fulvic-like ones. The sorption experiments showed sorption capacity of selected metal ions onto FAs decreased with increasing extractions, and the analysis of binding stability for selected metal ions onto FAs were ranked as FAs-Cu>FAs-Pb>FAs-Cd. For all extracted FAs, the principal component analysis for sorption capacity showed that O-bearing functional groups and molecular weight were dominant factors for FAs binding metal ions. Furthermore, the characterization results of nine FAs pre- and post-adsorption indicated that the phenolic groups of FAs had a greater contribution to bind Pb2+ over than Cd2+ and Cu2+, while carboxyl and N-bearing groups had a stronger affinity for Cu2+ than others. The study has the potential significance to insight the FA and metal ions cycling processes in lakes.

Fate of 2,4,6-Tribromophenol in Soil Under Different Redox Conditions.

Fate of 2,4,6-tribromophenol (TBP) in environmental matrices is obscure. We used 14C-tracer to investigated mineralization, transformation, and non-extractable residue (NER)-formation of TBP in a soil under continuously oxic, continuously anoxic, and anoxic-oxic alteration conditions. In all cases, TBP rapidly dissipated, mineralized to CO2, and formed NERs in the soil. Considerable amounts of transformation products (2-12%) were detected during the incubation. Marked mineralization (13-26%) indicated that soil microorganisms used TBP as their energy source. About 62-70% of the initial radioactivity was transformed into NERs, being mainly attributed to binding to humic and fulvic acid fractions. TBP transformation was significantly faster under oxic conditions than under anoxic conditions, and was boosted when the soil redox changed from anoxic to oxic state. The results provide new insights into fate of TBP in soil and suggest the importance to evaluate the stability of NERs for risk assessment of TBP in soil.

Dynamics of soil aggregation and organic carbon fractions over 23 years of no-till management

Evaluation of aggregate formation in no-till farming systems and the effects on soil organic matter can provide relevant insights into soil carbon storage, nutrient cycling, and soil susceptibility to erosion. However, there is little information on the soil aggregate formation pathways in no-till systems. This study aimed to investigate the effect of no-tillage duration on soil aggregates and soil organic matter compared with undisturbed soil in the rainy and dry season. The following experimental sites were analyzed: NT7 (no-till management for 7 years), NT14 (no-till management for 14 years), NT23 (no-till management for 23 years) and AF, a preserved fragment of Atlantic Forest (reference area). Aggregate formation pathway was analysed/described according to the morphological pattern using a stereo microscope (LEICA M125), in magnification ranges between 20x and 40 × . Physical fractionation of organic matter was carried out by granulometric size separation, and humic substances were separated into humic acid, fulvic acid, and humin fractions by differential solubility. No-till management affected the dynamics of soil aggregation and organic matter fractions. In the long term, no-till farming reduced biological aggregation (52.5 ± 4.5 % in AF to 19.2 ± 3.1 % in NT23), and increased physicochemical aggregation (21,2 ± 2.1 % in AF to 47.2 ± 5.1 % in NT23), may be because the traffic-induced compaction resulting from seeding. However, over the years, no-till farming increased soil particulate organic carbon (POC), mineral-associated organic matter (MAOM) and humin contents because of the constant input of crop residues to surface layers. Our results suggest that the morphological classification analysis of soil aggregates was sensitive to changes in land use over time, consisting as an indicator practical, affordable, repeatable, and easily understood and interpreted, which may be used to ascertain changes in physical soil conditions.

Soil organic carbon storage and quality are impacted by corn cob biochar application on a tropical sandy loam

Humic substances, which are integral components of total organic carbon (TOC), influence soil quality. The study aimed to investigate whether humic and non-humic fractions exhibit early, consistent, and measurable changes and affect TOC sensitivity and storage in a tropical sandy loam soils amended with corn cob biochar. There were four treatments with four replicates established in a randomized complete block design. Composite soil samples were taken from plots without biochar (CT), from plots incorporated with 15 t biochar ha−1 (BC-15), and 30 t biochar ha−1 without or with phosphate fertilizer (BC-30 and BC-30+P). The TOC, and humin, humic acid (HA), and fulvic acid (HA) fractions of soil organic carbon were determined for each treatment. The optical densities (400–700 nm) were measured on the soil-free extracts by spectrophotometry; the densities measured at 465 and 665 nm were used to calculate the E465/E665 ratios. The BC-30 and BC-30+P plots recorded the highest TOC, humin, humic acid (HA), and fulvic acid (FA) contents with respect to the lowest in the CT. The total exchangeable carbon stratification was significantly higher in all the biochar-treated plots relative to the CT. Spectral analysis showed higher values of E465/E665 (5.02 and 5.15) in the CT and BC-15-treated soils, respectively, compared with the BC-30 and BC-30+P-amended soils with E465/E665 ratios of 2.76 and 2.98, respectively. Corn cob biochar applied to a tropical sandy loam: • increased the concentrations of HA and FA and led to increased stratification of TOC, with a stronger effect on HA compared with FA; • significantly lowered E465/E665 at the high biochar application rate of 30 t ha−1, implying the dominance of high molecular weight humic acid-like substances, and increased degree of aromaticity of the TOC.

Resistance of Soil Organic Matter in “Humic A Horizons” of the Mountainous Region in the State of Rio De Janeiro

Soils with high organic carbon content, such as those with A horizon, occur in different regions of Brazil. This study aimed to determine the quantitative and qualitative characteristics of organic matter regarding the humic A horizon under different land uses in Bom Jardim, in Rio de Janeiro State, Brazil. Samples from forest, pasture, Eucalyptus plantation, coffee cultivation, olericulture, and also passion fruit soils were sampled and analyzed. In October 2011, undisturbed samples from humic A horizons, were collected for soil density analysis. In addition, disturbed samples were collected for the determination of organic carbon (C-org) content, total carbon, humic substance fractions contents and natural abundance of (13)Carbon (delta C-13). Low C-org contents were observed in areas under olericulture, pasture and passion fruit cultivation. The fulvic acid fraction was higher than other fractions, regardless of land use. The small variability in delta C-13 indicated maintenance of original C-org and suggest high resistance of Soil Organic Matter in humic A horizons.

Effects of hydrophobicity-based fractions of Pony Lake fulvic acid on the colloidal stability and dissolution of oppositely charged surface-coated silver nanoparticles

Environmental contextThe fate of silver nanoparticles (AgNPs) in aqueous systems could be influenced by the hydrophobicity of natural organic matter. We observed that the aggregation and dissolution of oppositely charged AgNPs were controlled by the selectivity and dynamics of sorption processes involving the nanoparticle surface and hydrophobic groups on natural organic matter. These findings will be helpful to understand the fate and effects of coated AgNPs in natural systems. AbstractThe fate of silver nanoparticles (AgNPs) released into aquatic environments is significantly affected by natural organic matter (NOM). However, current studies are still insufficient to understand interactions between NOM and AgNPs because they do not explicitly consider the heterogeneity of NOM. We investigated how NOM components with different properties (hydrophobicity, molecular weight, aromaticity, and polarity of functional groups) interact with AgNPs coated with citrate (Cit) and branched polyethylenimine (BPEI) and influence their colloidal stability and dissolution. Pony Lake fulvic acid (PLFA) selected as a model NOM was fractionated into hydrophobic (HPO) and transphilic (TPI) fractions. Sorption of PLFA molecules with a high content of polar functional groups bound to the aromatic rings onto nanoparticles was more favourable in the case of the TPI fraction, which most likely resulted in higher aggregation for both AgNPs and stronger protection of BPEI-AgNPs against dissolution compared with the HPO fraction. Additionally, in contrast to the Cit-AgNPs, resorption of Ag+ ions released from BPEI-AgNPs and/or sorption of Ag+-PLFA complexes to the nanoparticles was most likely a dynamic process, as suggested by the time-dependent changes in the molecular weight of the PLFA fractions sorbed to the BPEI-AgNP surface. These observations suggest that the accessibility of the AgNP surface for the hydrophobicity-based fractions of NOM as well as their colloidal stability and dissolution are controlled by the type and charge of coating materials and by the molecular weight, aromaticity, and content of polar functional groups of NOM.

Soil Organic Matter Black Box

Soil Organic Matter Black Box

Mercury and dissolved organic matter dynamics during snowmelt runoff in a montane watershed, Provo River, Utah, USA

The mechanisms of Hg and dissolved organic matter (DOM) transport from watersheds to streams remain unclear, especially in snowmelt dominated montane systems. We characterized total Hg concentrations and DOM characteristics during snowmelt by weekly and/or monthly sampling at three locations in the upper Provo River, northern Utah, over two water years (2016 and 2017). Total Hg concentrations increased from <1 ng/L during baseflow to >7 ng/L during the snowmelt period (April–June), with decreasing concentrations from upstream to downstream. Filtered THg concentrations accounted for 65–75% of the unfiltered concentrations, suggesting that Hg is primarily transported in the dissolved phase. Annual THg loading in the upper Provo River was approximately 1 kg/yr, with ~90% of the flux occurring during the snowmelt period. Filtered THg concentrations were strongly correlated with in-situ fluorescence DOM (fDOM) measurements, allowing for the development of high-resolution proxy THg concentrations. Further, DOM characteristics, evaluated using excitation-emission matrices (EEMs) and parallel factor analysis (PARAFAC), identified the dominance of soil humic and fulvic acid fractions of DOM during runoff. Total Hg concentrations were low in snowpack but elevated in ephemeral streams during snowmelt runoff, indicating that Hg originated from shallow soil water rather than snow. Concentration—discharge relationships revealed clockwise hysteresis patterns, suggesting that Hg was flushed from soils on the rising limb of the hydrograph. Our results demonstrate that a majority of Hg transport occurs with a flux of DOM during the short snowmelt season as shallow soils are flushed by meltwater. The snowmelt-driven Hg pulse is a substantial source to downstream reservoirs and potentially contributes to a fish consumption advisory.

The role of humic-like substances as atmospheric surfactants in the formation of summer-heavy rainfall in downtown Tokyo

In order to study the impact of organic aerosols in the formation of UHR (hereafter UHR = urban-induced heavy rain), we analyzed humic-like substances (hereafter HULIS) that serve as major atmospheric surfactants as well as the major inorganic ions in rainwater collected on an event basis at the Nishi-Waseda Campus of Waseda University in Shinjuku, Tokyo. Fulvic and humic acid fractions in HULIS was determined by the DEAE (Diethylaminoethyl cellulose) -UV method. The total wet deposition flux of HULIS in UHR was 33.5 times higher than that found in a normal rainfall and 57.3 times higher than that found in THR (hereafter THR = typhoon heavy rain). The accumulation of HULIS to acidic anions such as NO3− and SO42− in UHR compared to other types of rain indicates that HULIS in UHR accelerated the growth of cloud droplets via reduction of surface tension, which likely led to the rapid development of cumulonimbus clouds.

Assessment the Effect of Compost Amendments on Soil Characteristics and Barley Plant

This study aimed to evaluate the effects of three different types of commercial compost, i.e., Animal Manure Compost (AMC), Crop Manure Compost (CMC) and Town Refuse Compost (TRC) on some chemical and spectroscopic characteristics of sand soil, as well as growth and yield barley plant (Hordum vulgar cv. Giza 123). They were individually applied at rate of 2% (oven-dry basis) and incubated for 56 days, and then Humic Acids (HA) and Fulvic Acids (FA) fractions were extracted and analyzed using total acidity and UV-Vis spectroscopy. From UV-Vis absorption spectra the absorbance ratios E4/E6 have been calculated. Soil pH, EC, and organic carbon content were determined. In addition, compost-N mineralization and nitrification rates were assessed. The results showed that the soil treated with organic amendment had higher values of organic matter, EC and available N as Compared with the unamend soil. Soil compost amendments had positive effect on mineralization, as the Net-N release increased with incubation time. The E4/E6 ratios of HA fraction in soil treatments ranged from 3.2 to 7.6, while the E4/E6 ratios of FA were higher than that of HA values (4.3-9.5). On the other hand, total acidity of function group for FAs was much greater than that for HAs (0.6-10.6 meq g−1 fulvic material). The results showed that addition of composts significantly (at P≤0.05) increased barley grain, straw weight and total yield compared to control (no compost application).

Experimental and modeling study of proton and copper binding properties onto fulvic acid fractions using spectroscopic techniques combined with two-dimensional correlation analysis

Fulvic acid (FA) significantly influences the bioavailability and fate of heavy metals in environments, while its acid-base characters and metal binding processes are still unclear. Here, spectroscopic techniques combined with multiple models (e.g., NICA-Donnan model) and two-dimensional correlation spectroscopy (2D COS) were applied to explore the proton and copper binding properties of FA sub-fractions (FA3-FA13). The charge densities, average contents of carboxylic and phenolic groups, average dissociation constants pKa1 and pKa2 of sub-fractions ranged 0–16 meq∙g∙C−1, 5.03–9.58 meq∙g∙C−1, 2.52–4.67 meq∙g∙C−1, 4.15–4.33 and 8.52–9.72, respectively. FA sub-fractions had a relatively narrow distribution of carboxyl group and a broad distribution of phenolic group. FA sub-fractions also exhibited roughly two phenolic hydroxyl groups per every 1–3 phenyl rings. Differential absorbance spectra (DAS) derived Gaussian bands were associated to the inter-chromophore interactions, the changes of molecular conformations and functional groups with copper addition. Differential spectra slopes (DSlope275-295&325-375) were more significant with higher copper concentration and copper amounts bonded to carboxylic groups. UV–Vis and fluorescence spectra with 2D heterospectral COS revealed the copper binding heterogeneities and sequential orders of chromophores and fluorophores, quantitatively confirming by the order of conditional stability constants (log KCu: 4.64–5.56). Salicylic-/polyhydroxyphenolic, hydroxyl and amino groups were strongly associated to the basic units for fluorophores. Sequential changes followed the order of humic-like→fulvic-like materials for FA3/FA5, humic-like→fulvic-like→tryptophan-like materials for FA7, and humic-like→tryptophan-like→fulvic-like→tyrosine-like materials for FA9/FA13. Spectroscopic techniques combined with various models (especially for 2D COS) are beneficial to elucidate the binding heterogeneity and sensitivity for metal-organic matters at the functional group level.

Modeling the quenching of fluorescence from organic matter in Amazonian soils

Knowledge of the interactions of soil organic matter (SOM) with metal species is important in order to obtain information concerning the fates of the metals in environment, whose reactive functional groups present in SOM can provide high complexation capacity. The aim of this study was to evaluate the interactions involving humic acids (HA) and fulvic acids (FA), extracted from Amazonian soils, with Cu(II) and Al(III) ions, using fluorescence quenching spectroscopy. The obtained results showed that the data for the humic fractions of the Amazonian Spodosols could be fitted with one to one complexation model, which provided the best representation of the changes in fluorescence quenching after addition of Cu(II) or Al(III) ions. It was found that the HA presented fewer complexation sites and lower stability constants, compared to the FA samples. Furthermore, the FA showed selective interaction with the metals, while the HA fraction was less selective and could be associated its homogeneous structure. The results showed that the humic acids required 10 times more carbon in their structures than fulvic acids for complexing a metal atom. This behavior can be associated to the fact that the Fulvic Acid fraction has higher mobility and greater interaction during the profile when compare humic acids. Hence, given the diversity of metals to which the HA has affinity, this soil fraction appears to be mainly responsible for soil fertility, while the FA fraction has higher mobility and greater interaction with water.

Aerobic denitrification performance of strain Acinetobacter johnsonii WGX-9 using different natural organic matter as carbon source: Effect of molecular weight

The aim of this study was to investigate the effect of natural organic matter (NOM) including humic acid (HA) and fulvic acid (FA), intracellular organic matter (IOM) extracted from Microcystis aeruginosa (MA) and Chlorella sp. (CH), and their different molecular weight (MW) fractions on the aerobic denitrification performance of bacterial strain WGX-9 by monitoring nitrogen removal efficiency and testing changes in organic matter with HA, FA, MA-IOM and CH-IOM as the sole carbon source. Strain WGX-9 was identified as Acinetobacter johnsonii and exhibited excellent aerobic denitrification capability. The nitrate removal efficiency with IOM as the sole carbon source was relatively higher than that with NOM as the sole carbon source. The prepared NOM and extracted IOM samples were separated into six fractions with MW cut-offs of 100, 30, 10, 5 and 1 kDa. The fraction of MW > 100 kDa contributed the largest amount to the MW distribution, accounting for 77.11%, 29.00%, 44.97% and 24.81% of HA, FA, MA-IOM, and CH-IOM, respectively. Nitrate removal efficiency was improved with decreasing MW of organic matter. For example, nitrate removal efficiency was 26.50%, 32.41%, 27.88% and 43.89% using HA, FA, MA-IOM, and CH-IOM fractions of MW > 100 kDa as the carbon source, whereas with MW < 1 kDa, it increased to 36.67%, 37.88%, 60.90%, and 68.90%, respectively. This is probably because the smaller MW fraction is more suitable for bacterial growth. These results demonstrate that the strain WGX-9 can utilize lower MW organic matter, which lays the foundations for nitrogen removal in actual drinking water reservoirs.

The Molecular Composition of Humic Substances Isolated From Yedoma Permafrost and Alas Cores in the Eastern Siberian Arctic as Measured by Ultrahigh Resolution Mass Spectrometry

AbstractOngoing climate change is making the large pool of organic matter (OM) stored in Arctic permafrost vulnerable to mobilization; thus, garnering a deeper understanding of molecular transformations within the abundant pool of soil OM, specifically humic substances, is crucial. Here we present the first high‐resolution mass‐spectrometry examination of molecular compositions of humic acid (HA) and fulvic acid (FA) isolated from organic‐rich deep yedoma (Pleistocene age ice‐rich permafrost) and alas (thermokarst deposit formed during permafrost thaw) cores. The FA fractions were dominated by oxygen‐rich unsaturated compounds, whereas the HA fractions were mostly composed of relatively reduced saturated and aromatic moieties. A substantial increase in contribution of both CHO‐only and N‐containing aliphatic compounds was observed in the HA fractions of the yedoma OM with depth, whereas the alas HA fractions were depleted in aliphatics but enriched with condensed and hydrolyzable tannins. The observed differences in compositional space of the immobile OM stored in the deep yedoma versus alas deposits were consistent with evolution of OM during thermokarst lake genesis, implying intense microbial degradation of N‐rich OM released from the yedoma deposits and accumulation of highly degraded, plant‐derived OM. The patterns of molecular transformations of OM were apparent in compositional space of the least degraded HA fractions as compared to much more oxidized FA fractions. This shows great promise of molecular exploration of the alkali‐extracted OM, comprising up to 50% of the total organic carbon in deep permafrost both for paleoreconstructions and predictions of climate feedback to released OM due to permafrost thaw.