Humic Acid Fractions Research Articles

Evaluation by Multivariate Statistical Methods of Relationship with Physicochemical Properties of Humic Acid and Some Soil

Humic acid is a very important component for soil. In particular, It is an important factor for regulation of plant nutrients. In this study, HA (humic acid) contents of soil samples taken from 12 different locations were determined by appropriate method. After extracting the humic acid from the soil samples, the remaining soil elements concentrations were determined by ICP-OES method. In addition, the element concentrations in the humic acid fraction were determined by the same method. In soil samples were determined organic matter (OM), pH, EC, clay, silt and sand. The relationships between all variables were evaluated by multivariate statistical analysis such as correlation, simple linear regression, PCA (Principal Component Analysis). Spearman rho coefficient was taken into consideration in the correlation analysis. Simple linear regression analysis showed significant regression model between HA and OM, pH, HAfMn (HAf: humic acid fraction), HAfSe, HAfP, TfCd (Tf:soil fraction), TfMn, TfPb, TfSe. In the PCA analysis, 4 factors were found to explain 88.23% of the total change. P1:OM, TPb, TSe, HA P2:TAs, TSb, TBa, TMn, TFe P3: TCd, TP, pH, TSn, Silt, TAl P4: Kil, sand, TBe, EC. In the correlation analysis (N: 12), HA was significant positive with TfSe (r= 0.615, P <0.05), and significant negative with HAfBe (r= -0.786, P <0.01) and significant positive with HAfMn (r= 0.918, P <0.01) and significant negative with HAfSn (r= -0.700, P <0.05) and significant positive with HAfSe (r= 0.704, P <0.05) and significant positive with HAfP (r= 0.700, P <0.05) correlation was found.

Effect of Soil Organic Matters in Dredged Soils to Utilization of their Mixtures Made with a Steel Slag.

Dredged soils have been used as construction materials by alkaline activation with steel slag (steel slag-dredged soil mixtures) at harbors. Such mixtures develop strength chiefly by calcium silicate hydrate (C-S-H) formation by the pozzolanic reaction. However, the strength of such mixtures is unpredictable, and in some cases, mixtures have been too soft for the intended engineering application. An identification of strength development indicators would accelerate evaluation processes for strength development to facilitate and promote the utilization of such materials. This paper focuses on the relationship between the characteristics of soil organic matters in dredged soils and the strength development of the mixtures by a comparison of eight dredged soils collected from eight different Japanese harbors. The characteristics of the soil organic matters were identified to determine as indicators of mixtures with weak strength development, i.e., enriched sulfur content in extracted soil organic matter (humic acid) fraction, and the N/C ratio of humic acid similar to land humic acid standards. Increases in the validated fraction of dredged soils and steel slag by replacing fractions disadvantageous to construction resources would contribute to reduce waste production, which would lower the environmental impact of the use, aiming to achieve sustainable utilization of such materials.

Characterizing Humic Substances from Native Halophyte Soils by Fluorescence Spectroscopy Combined with Parallel Factor Analysis and Canonical Correlation Analysis

Soil is one of the principal substrates of human life and can serve as a reservoir of water and nutrients. Humic substances, indicators of soil fertility, are dominant in soil organic matter. However, soil degradation has been occurring all over the world, usually by soil salinization. Sustainable soil productivity has become an urgent problem to be solved. In this study, fluorescence excitation-emission matrices integrated with parallel factor analysis (PARAFAC) and canonical correlation analysis (CCA) were applied to characterize the components of fulvic acid (FA) and humic acid (HA) substances extracted from soils from the Liaohe River Delta, China. Along the saline gradient, soil samples with four disparate depths were gathered from four aboriginal halophyte communities, i.e., the Suaeda salsa Community (SSC), Chenopodium album Community (CAC), Phragmites australis Community (PAC), and Artemisia selengensis Community (ASC). Six components (C1 to C6) were identified in the FA and HA substances. The FA dominant fractions accounted for an average of 45.81% of the samples, whereas the HA dominant fractions accounted for an average of 42.72%. Mature levels of the HA fractions were higher than those of the FA fractions, so was the condensation degree, microbial activity, and humification degree of the FA fractions. C1 was associated with the ultraviolet FA, C2 was referred to as visible FA, C3 and C4 were relative to ultraviolet HA, C5 represented microbial humic-like substances (MH), and C6 referred to visible HA. C1, C2, C5 and C6 were latent factors of the FA fractions, determined using the CCA method and could possibly be used to differentiate among the SSC, CAC, PAC and ASC samples. C3, C4, C6 and C5 were latent factors of the HA fractions, which might be able to distinguish the ASC samples from the SSC, CAC and PAC samples. Fluorescence spectroscopy combined with the PARAFAC and CCA is a practical technique that is applied to assess the humic substance content of salinized soils.

Transformations of phenolic compounds in meadow soils

The aim of the research has been to determine the role of phenolic compounds in the processes of transformations of organic matter in meadow soils, leading to the formation of humic substances. The research has been performed based on the plant material and soil sampled from Europe’s unique complex of permanent grasslands irrigated continuously for 150 years applying the slope-and-flooding system, the Czerskie Meadows. Phenolic compounds were isolated from the plant material samples (hay, sward and roots) and soils (horizon A, AE and Bsv) and from the fraction of humic and fulvic acids. It was found that the contents of phenolic compounds decrease in the following order: hay > sward > roots > A horizon soil > AE horizon soil > Bsv horizon soil > A horizon fulvic acids > AE horizon fulvic acids > Bsv horizon fulvic acids > A horizon fulvic acids > AE horizon fulvic acids > Bsv horizon fulvic acids. A significantly higher share of cinnamyl than vanillyl and syringyl compounds in the extracts of fulvic acids and slightly higher in the hydrolysates of humic acids confirms the effect of the chemical composition of the plant material undergoing decomposition on the properties of the emerging humic substances.

Carbon and Nitrogen Balance in an Oxisol Influenced by Sewage Sludge and Mineral Fertilization

ABSTRACT Most conventional agricultural production systems have difficulty maintaining carbon (C) and nitrogen (N) stocks in soils. However, the use of organic sources in fertilization, such as sewage sludge, can reverse these processes of degradation of soil organic matter. The objective of this study was to evaluate C and N stocks and balance in organic matter fractions of a Oxisol under pineapple after fertilization with sewage sludge and mineral fertilizers. A randomized block experimental design was used with four replications in a 2 × 2 factorial arrangement, corresponding to two pineapple cultivars (‘Vitória’ and ‘Smooth Cayenne’) and two fertilization tips (sewage sludge and mineral fertilizers). Soil samples were collected at the depths of 0–20, 20–40, and 40–60 cm to characterize the stocks of total organic carbon (TOC), total nitrogen (TN), labile carbon (LC), carbon in the fulvic acid fraction (FAF), in the humic acid fraction (HAF), and in the humin fraction (HUM), and the humification index (HI). Fertilization with sewage sludge increased the carbon and nitrogen stocks in the labile and stable fractions of the soil compared to the soil that received only mineral fertilization and compared to the condition at the beginning of cultivation. The increase in the TOC stock was 8 t ha−1, with accumulated storage of 148 t ha−1 in the 0–60 cm depth. The TN stock increased 2 t ha−1, with accumulated storage of 15 t ha−1 in the 0–60 cm depth. Therefore, fertilization with sewage sludge contributed to the agricultural sustainability of the soil.

The NMR and spectral study on the structure of molecular size-fractionated lignite humic acid

In this study, high pure humic acid (HA) extracted from lignite was fractionated into four fractions according to their molecular weights by the ultrafiltration method. The structural characteristics of various HA fractions were investigated by UV–Vis,FTIR, and 3D fluorescence spectra and 13 C/ 1 H-NMR tests. The experiment results showed that the HA fractions with the molecular weight ＞50 KDa are major, containing 70.89%. The active hydrogen proportion declined from 43.96% to 21.27% with the increase of HA molecular weight, meaning the decrease of the large HA molecules’ acidic group content. On the other hand, 80.93% of the aromatic nucleus content and 12.5% of the alkyl carbon (aliphatic structure) were observed in the large HA molecules that are much higher than those in the small HA molecules. The NMR and spectra studies indicated that the small HA molecules have more acidic groups such as hydroxy, carboxyl. Meanwhile, the large HA molecules have more aromatic and aliphatic structures. The above research indicated that the HA fractions with low molecular weight could provide more active sites for the interaction between HA and iron minerals. Moreover, the carbon chain and aromatic nucleus in the high molecular weight HA fractions could keep the space structure of HA stable. • High pure lignite humic acid was fractionated successfully by ultrafiltration. • The differences of composition and structure of various HA fractions were investigated. • The structure proportion of HA was quantized by integral and PARAFAC method. • The smaller HA molecular had more abundant oxygen-bearing groups. • The larger HA molecular had more aromatic structures.

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.

PHOTOCATALYTIC ACTIVITY OF IN-SITU FE-DOPED TIO2 FOR NATURAL ORGANIC MATTER REMOVAL

Humic acids represent a major fraction of natural organic matter (NOM) in aquatic environments. Having undefined composition and complex ill-defined structures, their presence in natural waters is undesirable. In this study, solar photocatalytic activity of synthesized Fe-doped TiO2 photocatalysts was investigated for the degradation of a 100 kDa molecular size fraction of humic acid. For this purpose, catalysts comprised of 5 different molar ratios of Fe/Ti were prepared by in-situ sol gel method and characterized by FTIR and Raman spectroscopy. Optimum loadings of the catalysts were determined and the kinetics of humic acid removal was investigated focusing on UV–vis spectroscopic parameters. Moreover, fluorescence techniques such as excitation-emission matrix (EEM) were also acquired for elucidating induced structural changes of humic acid during photocatalytic degradation. Results revealed that, using photocatalysts prepared by in-situ sol-gel method 20 to 25% removal of humic acid could be attained after photocatalytic treatment of 120 min.

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.

Insight into the influence of humic acid and sodium alginate fractions on membrane fouling in coagulation-ultrafiltration combined system

Membrane fouling has become the one of main obstacles for the widespread application of membrane technology in water treatment processes. Coagulation as pretreatment is proven to be effective for the alleviation of membrane fouling. In this study, the influence of humic acid (HA)/sodium alginate (SA) fractions in the structure and resistance of cake layer on the membrane surface was investigated. The presence of SA at an appropriate fraction could facilitate the formation of large and loosely branched flocs and thereby form a more permeable cake layer on the membrane surface due to good bridging and charge neutralization abilities of SA molecules. The particle image velocimetry (PIV) technique was employed for monitoring the dynamic formation process of cake layer under different HA/SA fractions. The cake layer with a higher thickness was observed to be rapidly formed on the membrane surface at the presence of SA in water. According to the theoretical analysis, the membrane fouling in coagulation-ultrafiltration (UF) combined system demonstrated to be highly dependent on the size and intra-porosity of flocs. The fractal dimension of flocs might have an impact on the resistance of cake layer through affecting the porosity of aggregated flocs. The SA molecules could be used as the coagulant aid for effective alleviation of membrane fouling and the improvement of filtration performance in a coagulation-UF combined system.

Dynamics, thermodynamics, and mechanism of perfluorooctane sulfonate (PFOS) sorption to various soil particle-size fractions of paddy soil

Soil is an important sink for perfluorooctane sulfonate (PFOS) that is a typical persistent organic pollutant with high toxicity. Understanding of PFOS sorption to various particle-size fractions of soil provides an insight into the mobility and bioavailability of PFOS in soil. This study evaluated kinetics, isotherms, and mechanisms of PFOS sorption to six soil particle-size fractions of paddy soil at environmentally relevant concentrations (0.01–1 μg/mL). The used soil particle-size fractions included coarse sand (120.4–724.4 mm), fine sand (45.7–316.2 mm), coarse silt (17.3–79.4 mm), fine silt (1.9–39.8 mm), clay (0.5–4.4 mm), and humic acid fractions (8.2–83.7 mm) labeled as F1~F6, respectively. PFOS sorption followed pseudo-second-order kinetics related to film diffusion and intraparticle diffusion, with speed-limiting phase acted by the latter. PFOS sorption isotherm data followed Freundlich model, with generally convex isotherms in larger size fractions (F1~F3) but concave isotherms in smaller size fractions (F4 and F5) and humic acid fraction (F6). Increasing organic matter content, Brunner−Emmet−Teller surface area, and smaller size fractions were conducive to PFOS sorption. Hydrophobic force, divalent metal ion-bridging effect, ligand exchange, hydrogen bonding, and protein-like interaction played roles in PFOS sorption. But hydrophobic force controlled the PFOS sorption, because its relevant organic matter governed the contribution of the soil fractions to the overall PFOS sorption. The larger size fractions dominated the PFOS sorption to the original soil because of their high mass percentages (~80%). This likely caused greater potential risks of PFOS migration into groundwater and bioaccumulation in crops at higher temperatures and ce values, based on their convex isotherms with an exothermic physical process.

Method of Tillage with the Factor Determining the Quality of Organic Matter

The aim of this paper has been to determine the importance of the strip-till method for the content of carbon and the quality of organic matter as compared with plough and ploughless tillage. The question to answer has been to what extent strip-till can contribute to carbon sequestration and thus be part of the strategy of counteracting climate change. The research involved soil where conventional tillage (CT), strip-till (ST), and reduced tillage (RT) were applied. These systems differ completely in the way they affect the post-harvest residue, i.e., “plant residue management”. For air-dry soil samples, the following analyses were made: the content of total organic carbon (TOC) and total nitrogen (Nt), content of dissolved organic carbon (DOC) and dissolved nitrogen (DNt), and the fractional composition of humus. In the surface layer the content of TOC ranged from 11.96 (CT) to 13.88 g kg−1 (RT) and DOC ranged from 209.9 (CT) to 230.5 mg kg−1 (ST). The share of the fraction of fluvic acids (0–15 cm layer) changed from 15.51% (RT) to 18.81% (ST), the share of the fraction of humic acids was 9.36% (ST) to 11.60%, and humins were 68.90% (CT) to 72.6% (RT). These results demonstrated that the tillage system determines the properties of the organic matter of soil. In the surface layer (0–15 cm) and in the 30–50 cm layer the properties of the soil organic matter under strip-till had a greater similarity to the soil under ploughless tillage than under conventional tillage. Ploughless tillage and strip-till considerably limited the leaching of carbon and nitrogen from the surface layer to the 30–50 cm layer. Strip-till, similarly to ploughless tillage, is the tillage method which can be crucial for the process of carbon sequestration.

Characterizing humic substances from a large-scale lake with irrigation return flows using 3DEEM-PARAFAC with CART and 2D-COS

The study was intended to determine whether the composition or distribution of humic substances from lake sediment could be characterized by spectroscopic data with chemometrics methods. The research materials were humic substances extracted from sediment samples collected in heavily polluted areas in Wuliangsuhai Lake. Humic substance extraction was performed using the method proposed by the International Humic Substances Society (IHSS). In extracted humic substances, the three-dimensional excitation–emission matrix (3DEEM) was determined, and parallel factor analysis (PARAFAC) with classification and regression trees (CART) and two-dimensional correlation spectra (2D-COS) was used to analyze spectroscopic data. Both the fulvic acid (FA) and the humic acid (HA) samples had five PARAFAC components (C1–C5), which contained Vis fulvic-like component (C1), Vis humic-like component (C2), UV humic-like component (C3), microbial fluorescent component (C4), and UV fulvic-like component (C5). This indicated the ubiquity of the humic substance components in the environment. For the CART analysis, C1 was the key factor used to differentiate FA and HA, while C1–C4 were the key parameters used to distinguish the humic substance samples in the eight units. Using 2D-COS and hetero 2D-COS, the PARAFAC components were formed with the increasing of sediment depth in the following order: C3 → C2 → C5 → C4 → C1, which suggested that the relatively labile structure appeared earlier than the relatively stable structure with the greater depth of the sediment. The Vis fulvic-like could be a key factor used to discriminate the FA and the HA fractions, while the latent factors of different depths of sediment were not identical. The order of the humic substance formations was Vis humic-like → UV humic-like → Vis fulvic-like → microbial fluorophore → UV fulvic-like.

Visible-light-excited humic acid for peroxymonosulfate activation to degrade bisphenol A

In this study, a novel peroxymonosulfate (PMS) activation method by visible light (VL) excited humic acid (HA) was developed and applied to degradation of bisphenol A (BPA). Results showed that, in HA (2 mg/L)/PMS (1 mM)/VL system, the degradation rate of BPA could reach 95.4% within 30 min, which was much higher than that of HA/VL system (9.4%) and PMS/VL system (15.5%). Meanwhile, the concentration of HA was also decreased in this process and the original structure of HA was obviously destroyed. Reaction mechanism accounting for the effect of HA on BPA degradation in the PMS/HA/VL system was explicated by the quenching experiments, electron paramagnetic resonance (EPR) detection and HA fractionation experiments. Results showed that singlet oxygen (1O2), hydroxyl radical (OH) and sulfate radical (SO4−) were all involved in the system, and 1O2 was the primary reactive species responsible for BPA degradation. The aromatic constituents of HA made the dominant contribution to the generation of reactive species, in which the phenolic groups played the role of electron-donor, and the quinone moieties acted as the electron shuttles could accelerate the electron-transfer between HA and PMS, which thus activated PMS to form the reactive species for BPA degradation. As HA is ubiquitous in nature, this study may provide a new insight into the in situ water treatment with the assistance of PMS.

Fire lead to disturbance on organic carbon under sugarcane cultivation but is recovered by amendment with vinasse

Sugarcane burning has been widely practiced in Brazil and worldwide. In the long term, this farming practice can cause soil erosion, reduction in organic carbon (OC) and consequently, changes in the structure of soil organic matter (SOM). Such changes may be difficult to reverse. This study aimed to assess the medium- and long-term effects of sugarcane burning on SOM characteristics, both in terms of quantity and structural quality and evaluate the application of vinasse as a strategy to attenuate fire-induced changes in burned soil. The experiment was conducted in a 50-year-old sugarcane field on soils classed as Cambissolo Háplico (Inceptisol). Four plots were sampled: a) burning of sugarcane for harvest for 37 years (SCB37); b) renewal of the sugarcane field and burning for harvest for 3 years (SCB3); c) renewal of the sugarcane field without burning for harvest for 3 years (SCWB), and d) renewal of the sugarcane field and burning for harvest with the application of vinasse for 3 years (SCV). Chemical and physical characterization of SOM was performed by solid-state spectroscopy (UV–vis, ATR-FTIR e 13C NMR CP/MAS) and chemometric techniques. The results showed that sugarcane burning drastically impacts SOM content and its chemical structure, however, the application of vinasse preserves and restores the soil from the fire effects. Content of soil OC, particulate OC, mineral-associated OC, humic acid, humin and light fraction OM that were affected by fire, had an increase and recovery of contents by the vinasse application. Solid state spectroscopy showed that labile structures were lost in humic acids (HA) by fire and recalcitrant structures were preserved. The application of vinasse incorporated fragments of lipids and carbohydrates in HA structure. Burning sugar cane straw affects the integrity of soil organic matter but can be restored by applying vinasse.

Humic acids derived from Leonardite to improve enzymatic activities and bioavailability of nutrients in a calcareous soil

Understanding the role of humic substances in soils is important for developing and utilizing organic fertilizers or soil amendments for sustainable agriculture. The objective of this study was to determine the effects of different fractions of humic acids derived from Leonardite on enzymatic activities and bioavailability of nutrients in a soil. The experiment was carried out by mixing different factions of humic acids with a soil and incubated for 70 d. The treatments included five factions of humic acids (HS1 (low molecular weight), HS2 (medium molecular weight), HS3 (large molecular weight, SED (sediment of fractions), HS (mixture of HS1, HS2, and HS3)), raw Leonardite (IM) and a control (no addition of humic acid). Experimental results showed that application of humic acids significantly improved acid and alkaline phosphatase activities, especially with HS1. Humic substances with high molecular weights significantly inhibit urease activity, and the optimal application rate was 600 kg/hm2 of humic substances with the high molecular weights. Concentrations of NH4+-N were decreased with increasing humus applications. All treatments (HSmix, HS1, HS2, HS3, IM, SED) did not affect the soil contents of Ca, although soil concentrations of K, P, Cu, Zn were increase significantly when small molecular weight humus (HS1) was applied. Keywords: humic acid, molecular weight, Leonardite, enzyme, nutrient content DOI: 10.25165/j.ijabe.20201303. Citation: Sun Q, Liu J L, Huo L F, Li Y C, Li X, Xia L R, et al. Humic acids derived from Leonardite to improve enzymatic activities and bioavailability of nutrients in a calcareous soil. Int J Agric & Biol Eng, 2020; 13(3): 200–205.

Role of humus substances in chemical soil pollution during deposit exploitation in Priokhotye and Priamurye

Here we analyze how the mining enterprises of Priokhotye and Priamurye affect the state of soils. It is established that during 3–5 years of operation of the ZIF (gold mining factory) there is occurred in the soil an increase in total concentrations of Fe, Mn, Pb, Cu and Zn with respect to the background level. We show that sulfate-containing minerals of mining raw materials and waste play a role in the formation of wastewater composition and chemical contamination of soils. The background-forming elements (Fe and Mn) were found to determine the nature of the distribution of soluble forms of Cu, Pb, Zn and Co in the soil profile, while the content of aggressive fractions of humic acids intensifies their migration activity. The distribution of chemical elements in the soil profile is controlled by the content and quality of organic matter. The degree of activation of geochemical processes in situ in the soils against the background of a low temperature gradient does not prevent the migration of pollutants via the subsurface flow down the slope. The conditions of the migration of the elements and the processes of their concentration in the soils were analyzed. The migration activity of multi-charged cations (Fe3+, Mn7+) was shown to determine the behavior of low-charged cations (Cu(1−2)+, Zn2+, Pb2+). The levels of contamination of the soils characterized by the excess of concentrations of elements over their regional geochemical background were studied. The spatial heterogeneity of chemical element concentrations in soils is considered as a function of migration activity of elements. The mechanisms of chemical contamination of soils that present the risks of soil degradation in the absence of recultivation are described. The basic principles of the regime of natural resources management in the areas of mining activity for the territory of Priokhotye and Priamurye are formulated.We publish fragment of the map, original geochemical studies and a new data, focusing on the different aspects of this case study. We are publishing this for the first time.

Speciation of Radium-226 in the Components of Terrestrial and Aqueous Northern Taiga Ecosystems in a Former Radium Production Site

Abstract—The paper considers the content and geochemical mobility of 226Ra in surface waters, bottom sediments, and radioactively contaminated soils (podzolic and alluvial–soddy) of the northern taiga subzone in the area of former radium production site. It is established that the level or radioactive contamination and specific activity of geochemically mobile radium in the podzolic soil is higher, while its migration with surface waters is lower (0.03 Bq/L) than in the alluvial–soddy soil. The drainage waters of the latter are characterized by the maximum radium content (0.55 Bq/L), which is mainly concentrated in the suspended matter (98%) and humic acids (97%) fractions. In the river waters, radium is mainly accumulated in the suspended fraction and fulvic acid compounds. It is shown that under low-temperature and high-water current conditions and a weak sorption capacity of bottom material, the specific activity of the radioactive element in the riverine sediments in the zone of anthropogenic impact is higher than the average background value (0.3–1.8 against 0.2 mBq/g). Sedimentation of radionuclide in the geochemically mobile and weakly mobile species is most intense within contaminated sites. The radium content in the “carbonates”, “sesqui-oxides and -hydroxides” and, especially, “exchangeable” fractions extracted from soils was higher than in other fractions. A cumulative fraction of “water soluble”, “organic matter”, and “amorphous silicates” groups accounts for 0.4–3.7 and 1.6–7.4% of radionuclide content in the podzolic and alluvial–soddy soils, respectively, and was characterized by the predominance of “organic matter” fraction. The fraction of geochemically mobile radium is negatively correlated with its bulk specific activity (r = –0.81), which is noted as trend for bottom sediments. The contribution of insoluble residue in the radionuclide specific activity was 23.5–95.5 and 7.8–69.4% in the podzolic and alluvial–soddy oils, respectively.

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.