Soil Humic Acids Research Articles

Temperature Dependence of Dissolved Organic Matter Fluorescence.

The temperature dependence of organic matter fluorescence apparent quantum yields (Φf) was measured for a diverse set of organic matter isolates (i.e., marine aquatic, microbial aquatic, terrestrial aquatic, and soil) in aqueous solution and for whole water samples to determine apparent activation energies ( Ea) for radiationless decay processes of the excited singlet state. Ea was calculated from temperature dependent Φf data obtained by steady-state methods using a simplified photophysical model and the Arrhenius equation. All aquatic-derived isolates, all whole water samples, and one soil-derived fulvic acid isolate exhibited temperature dependent Φf values, with Ea ranging from 5.4 to 8.4 kJ mol-1 at an excitation wavelength of 350 nm. Conversely, soil humic acid isolates exhibited little or no temperature dependence in Φf. Ea varied with excitation wavelength in most cases, typically exhibiting a decrease between 350 and 500 nm. The narrow range of Ea values observed for these samples when compared to literature Ea values for model fluorophores (∼5-30 kJ mol-1) points to a similar photophysical mechanism for singlet excited states nonradiative inactivation across organic matter isolates of diverse source and character. In addition, this approach to temperature dependent fluorescence analysis provides a fundamental, physical basis, in contrast to existing empirical relationships, for correcting online fluorescence sensors for temperature effects.

Soil aggregates: a scale to investigate the densities of metal and proton reactive sites of organic matter and clay phases in soil

SummaryDetermining site density of reactive sites of metals in the main soil phases remains a challenging task. This study aimed to show that densities of reactive sites in soil may be assessed by a fractionation procedure based on soil being spatially organized as aggregates. The method is described with copper as a model trace element and a common silty loam soil after applying a low energy fractionation method to maintain the integrity of soil aggregates. The reactivity of five soil size fractions (> 250, 250–63, 63–20, 20–2 and < 2 μm) to protons and copper was quantified by acid–base titrations. The total proton sorption capacities were assigned to the total concentration of copper reactive sites and fitted to a linear combination of the relevant reactivity data of each phase, namely the total contents of organic carbon, copper and acid‐extractable aluminium. Acid–base reactivity was linearly related to the distribution of copper, and differences between fractions were used to reconstruct the distribution of acid–base and copper‐complexing sites among the clay, organic and weakly reactive residual phases. In accordance with our hypothesis that key reactive phases are mainly organic materials and clays, we used this procedure to determine the site densities of (i) two size classes of particulate organic matter, (ii) strongly reactive organic matter (e.g. soil humic and fulvic acids) and (iii) clay. The site densities and the distributions of copper obtained were used to validate our conceptual model for predicting global soil reactivity to metals.Highlights Precise site densities of key soil reactive phases are often lacking in transfer modelling We applied specific experimental methods of aggregate analysis and partial leaching of Al phases Site densities of the various types of organic matter were assessed using variably amended soils Soil aggregate analysis is powerful for determining base parameters in element transfer modelling

Is the adsorption of soil organic matter to haematite (α‐Fe2O3) temperature dependent?

SummarySoil organic matter interactions with minerals are a key determinant in the long‐term protection and sequestration of carbon in soils and sediments. Climate warming could potentially alter the dynamics of the Earth's largest carbon pools through processes controlling the formation of mineral–organic associations (MOAs). We studied the adsorption of Elliott soil humic acid (HA) and fulvic acid (FA) to the iron oxide mineral haematite (α‐Fe2O3) at temperatures from 15 to 35°C through batch sorption experiments. The ΔG°, ΔH° and ΔS° of sorption were derived for HA and FA and suggested that formation of MOAs was spontaneous and exothermic. The Langmuir sorption coefficients for HA and FA decreased with warming, but the maximum sorption capacities were not temperature dependent. The decrease in sorption coefficient was less when the temperature was increased from 30 to 35°C than from 15 to 30°C. Our infrared, ultraviolet and visible spectroscopy analysis of the bound and unbound HA and FA revealed preferential adsorption of oxygen‐ and hydrogen‐substituted aromatic and aliphatic carbon, which was independent of temperature. The adsorption of a hydrophobic probe molecule, Rose Bengal, to haematite increased with warming. Our results suggest that (i) MOAs in warmer climates might be less sensitive to temperature changes, (ii) the amount of iron oxide‐associated organic matter might remain unchanged with warming and (iii) hydrophobic interactions with iron oxides may be temperature dependent.Highlights How does temperature affect the formation of soil organic matter–iron oxide associations? Warming can change the sorption of organic matter on to minerals thus altering carbon dynamics Warming decreases sorption coefficients, but does not affect maximum sorption capacities The amount of iron oxide-associated organic matter might remain unchanged with warming

Fungistatic Activity of Multiorigin Humic Acids in Relation to Their Chemical Structure.

Humic acid (HA) has an inhibitory effect on phytopathogenic fungi, but the structure-activity relationship remains unclear. HAs were extracted from 14 different materials, and their fungistatic activities and elemental C, N, S, and O contents were measured. Cross-polarization magic-angle spinning 13C nuclear magnetic resonance (CPMAS 13C NMR) was used to measure the organic carbon composition. The results showed that all HAs suppressed phytopathogenic fungi growth, with Yunnan lignite HAs showing the highest inhibition (85.3%) against Physalospora piricola. The soil and compost HA aromaticity (ARO) was <50%, except for black soil HAs, while the ARO of all coal HAs was >60%. The ARO of meadow and moss peat HAs was <50%, while the ARO of woody peat HAs was 50.61%. Mantel test and redundancy analysis (RDA) were applied to evaluate the structure-activity relationship. The Mantel test revealed that the N, S, O, N/O, carbonyl C, aromatic C-O, and anomeric C contents were significantly correlated with fungistatic activity. The RDA analysis showed that the S content was positively correlated with fungistatic activity, while the O content was negatively correlated. The carbonyl C content had a positive correlation with fungistatic activity, while the anomeric C and aromatic C-O content had a negative correlation. A high S content and an active composition (carbonyl C) in HAs would lead to a high degree of fungistatic activity. Phytotoxicity test indicated all HAs were beneficial to plant growth. This work identified the basic properties of HAs from various raw materials that control their fungistatic activities.

EFFECT OF SOME STIMULANTS ON FRUIT SET, YIELD AND FRUIT QUALITY OF HOLLYWOOD AND PIONEER PLUM CULTIVARS

The deterioration in area of plum orchards, in addition to the lack of productivity, resulted in an insufficient yield of plum. Some stimulants were investigated in this study during 2016 and 2017 seasons to improve fruit set; yield and fruit quality of Hollywood and Pioneer plum cultivars. Trees were treated with sprayed by with 1.0 and 1.5 ml/l of Daiblon k10 (contains 10% w∕w free amino acids and 10% w∕w potassium) or 4.0 and 6.0 ml/l of Essential Egy (contains mineral nutrients; natural Organic substance and 4.5 % L-amino acids). Other trees were treated with Humic acid as Actosol® (6.0 % w ∕ v potash and 20 % w ∕v Humate) at 5.0 ml/l /tree as spray foliar treatment or 30 ml/l /tree as soil application beside (control). The treatments were done at three times (at 30 % of flowering; 70% flowering and at full bloom) in each season. All trees were grown in sandy soil at El- Nubaria region, Behera Governorate, Egypt. A complete randomized block design was used with three replicates and each one was represented by one tree. During this investigation fruit set (%); yield (kg/tree); some physical and chemical fruit properties, as well as some mineral contents of leaves, were determined. Results cleared that the highest of both fruit number and yield (Kg∕ tree) were obtained when trees of Hollywood were sprayed with Essential Egy at 4.0 ml/l while the highest values of fruit set% and SSC were gained when trees were sprayed with 6.0 ml/l of Essential Egy. Spraying trees with Humic acid caused the highest leaf N and K content. All treatments under study gave variable effects on of total chlorophyll content. With regard to Pioneer cultivar, results showed that Essential Egy at 6.0 ml/l significantly increased fruit set %; fruit number per tree, yield (kg/tree and P content compared with Essential Egy at 0.4 ml/l which significantly increased SSC. Humic acid soil application significantly increased leaf N and P content. Spraying trees with Humic acid recorded the highest significant N and K content. Daiblon K10 at 1.0 ml/l gave the maximum total chlorophyll content. Thus, it can be recommended that spraying Hollywood and Pioneer cultivars with Essential Egy at 4.0 ml/l or 6.0 ml/l at three times (30 % of flowering; 70 % of flowering and at the full bloom) will increase plum yield and improve fruit quality

Aluminum complexation by soil humic acids, with special reference to chelating ability

Aluminum complexation by soil humic acids, with special reference to chelating ability

Effect of addition of organic materials and irrigation practices on soil quality in olive groves

Abstract The effect of addition of organic materials (shredded pruning residues, composted olive mill by-products) on spatial distribution of soil chemical and microbial properties in irrigated and rainfed olive groves was investigated. Most of the soil parcels were subjected to reduced tillage or no tillage practices. Soil sampling took place in 40 olive groves in the region of Messinia, south-western Peloponnese, Greece during a 5-year period (2012–2017). The results showed significant increases in soil organic matter, humic acids and nitrate content at the end of the study period, compared to the first year of the soil sampling campaign. On the other hand, the relatively low amount of fresh organic materials that was applied to the soil produced unfavorable results. Differences between irrigated and rainfed soil parcels were not significant, for most of the soil properties, since the area receives much higher loads of rain than the average rainfall, as registered in the main olive growing regions of Greece. The area underneath the tree canopy favors an environment that enhances soil fertility, compared to the area out of the tree canopy. Changes of soil properties according to depth showed that the surface soil in olive orchards has the potential to sequester carbon and nutrients.

Abundant Nonprotonated Aromatic and Oxygen-Bonded Carbons Make Humic Substances Distinct from Biopolymers

The nature of humic substances (HSs) extracted from soil organic matter and their distinction from degrading plant material has recently been called into question. Quantitative solid-state 13C nuclear magnetic resonance (NMR) analyses, in good agreement with elemental analysis, show that HSs are distinct from common biopolymers, refuting claims to the contrary made based on 1H-detected NMR spectra of the same standard peat humic acid as studied here. Aromatic carbons not bonded to hydrogen or oxygen, which are rare (≤10%) in common biomolecules, constitute a large fraction (28%–33%) of prairie soil and peat humic acids. Oxygen-bonded nonprotonated carbons such as aryl ketones, nonprotonated alkyl C–O, and abundant COOH groups are also characteristic of humic and fulvic acids but not observed in plant biopolymers. These distinctive structural differences between HSs and biopolymers challenge the recent proposal that HSs are unremarkable intermediates in a continuum of degrading biomolecules.

Evaluation of amendment addition and tree planting as measures to remediate contaminated soils: The Guadiamar case study (SW Spain)

Soil pollution is one of the main environmental concerns at a global scale, and different measures have been proposed for its prevention and remediation. In this paper we evaluate two measures – amendment addition and tree planting – applied to remediate soils contaminated by trace elements (TE). The Guadiamar study site (SW Spain) is a well-known example of a large-scale cleaning and remediation program intended to rehabilitate about 3000 ha of soils affected by a mine-spill in 1998. Firstly, we present the results of a long-term experiment in which two types of amendments – sugar beet lime (SL) and biosolid compost (BC) – were added to the spill-affected soil. Three different treatments were established: SL, BC, and NA (non-amended control). The experiment has been running since 2002 and new soil samples were taken in 2016. In general, the amendments increased soil pH and total organic carbon, and reduced TE availability. The available TE concentrations (CaCl2 extraction) decreased drastically with time in all cases, but the evolution differed among treatments. The treatment effectiveness was evaluated by measuring plant biomass, TE concentrations in plant shoots, and soil-plant transfer. Secondly, we present results detailing the effects of seven tree species (three - Populus alba, Celtis australis, and Fraxinus angustifolia - were deciduous and four - Quercus ilex, Olea europaea, Ceratonia siliqua, and Pinus pinea - evergreen) on remediated soils. In 2014 (about 15 years after planting) we measured TE concentrations in leaves and roots and related them with TE concentrations (total and available) in soil. There were significant differences among the studied tree species in the uptake and accumulation of TE in leaves and roots. Soil pH differed among tree species and with respect to adjacent non-planted sites. There was a negative exponential relationship between soil pH and availability of Cd, Cu, and Zn. The bioconcentration factor (BCF, root:soil) and the translocation factor (TF, leaf:root) were calculated to evaluate the potential of each tree species to stabilize TE in soil. Finally, we propose the phytoremediation of TE-contaminated soils as a three-stage process, including addition of soil amendments, planting of trees, and monitoring of TE dynamics.

Sorption of uranyl ions on TiO2: Effects of pH, contact time, ionic strength, temperature and HA

Sorption of U(VI) onto TiO2 as functions of pH, ionic strength, contact time, soil humic acid (SHA), solid-to-liquid ratio and temperature was studied under ambient conditions using batch and spectroscopic approaches. The sorption of U(VI) on TiO2 was significantly dependent on pH and ionic strength. The presence of SHA slightly enhanced the sorption of U(VI) on TiO2 below pH4.0, while it inhibited U(VI) sorption in the higher pH range. U(VI) sorption on TiO2 was favored at high temperatures, and the sorption process was estimated to be endothermic and spontaneous. Reduction of U(VI) to lower valent species was confirmed by X-ray photo-electron spectroscopy analysis. It is very interesting to find that U(VI) sorption on TiO2 was promoted in solutions with higher back-ground electrolyte concentrations. In the presence of U(VI), higher back-ground electrolyte made more TiO2 particles aggregate through (001) facets, leading more (101) facets to be exposed. Therefore, the reduction of U(VI) was enhanced by the exposed (101) facets and more U(VI) removal was observed.

Lanthanides and Actinides in Humic Acids of Soils and Paleosols of Forest-Steppe Conditions in the Southern Urals

This article analyzes the lanthanum, cerium, samarium, europium, terbium, ytterbium, lutetium, uranium, and thorium content in humic acids within soil and paleosol surface horizons from the southern steppe in the Southern Urals. Research demonstrates similar accumulation levels of these elements in paleosols isolated from both the active medium between 3.6 and 3.3 thousand years ago and in recent background soils. Despite the lack of significant differences, research has shown a growing content among the rarest metals in the series “the buried paleosols–man-modified paleosols of settlement–recent background soils”. Research has detected the lowest content of La, Ce, Sm, Eu, Yb, Lu, and Th in preparations of humic acids of recent background soils. This reveals a close content to most elements in humic acids of paleosols buried under barrows and ancient settlement paleosols. Additionally, it indicates the virtual absence of anthropogenic impact on binding lanthanides and actinides by humic acids in ancient times. The contribution of humic acids into the common pool for each element was evaluated using a special approach. Research showed that there was less than half the share of elements associated by humic acids of paleosols than in the recent background chernozems in the total pool of lanthanides and actinides. This article considers the prospects of using humic acids of recent and ancient soils in identifying behavioral patterns of metal complexes through time.

Influence of pH, soil humic acid, ionic strength and temperature on sorption of U(VI) onto attapulgite

The surface property of attapulgite was investigated by N2-BET surface area and zeta potential analysis in this paper. Solution pH had a remarkable effect on the sorption process, indicated an inner-sphere complexation. Humic acid (HA) in the solution enhanced U(VI) sorption significantly at pH 9.0. The characteristic fluorescence changes of HA indicated that a strong chemical reaction occurred between the functional groups in HA and UO22+. The sorption was a spontaneous and endothermic process with increased entropy, and the increase in temperature would benefit the sorption.

Proton and Copper Binding to Humic Acids Analyzed by XAFS Spectroscopy and Isothermal Titration Calorimetry

Proton and copper (Cu) binding to soil and lignite-based humic acid (HA) was investigated by combining X-ray absorption fine structure (XAFS) spectroscopy, isothermal titration calorimetry (ITC), and nonideal-competitive-adsorption (NICA) modeling. NICA model calculations and XAFS results showed that bidentate and monodentate complexation occurred for Cu binding to HA. The site-type-specific thermodynamic parameters obtained by combining ITC measurements and NICA calculations revealed that copper binding to deprotonated carboxylic-type sites was entropically driven and that to deprotonated phenolic-type sites was driven by entropy and enthalpy. Copper binding to HA largely depended on the site-type and coordination environment, but the thermodynamic binding mechanisms for Cu binding to the specific site-types were similar for the different HAs studied. By comparing the site-type-specific thermodynamic parameters of HA-Cu complexation with those of low molar mass organic acids, the Cu coordination could be further specified. Bidentate carboxylic-Cu complexes made the dominating contributions to Cu binding to HA. The present study not only yields molecular-scale mechanisms of ion binding to carboxylic- and phenolic-type sites of HA but also provides the new insight that the universal nature of site-type-specific thermodynamic data enables quantitative estimation of the binding structures of heavy metal ions to humic substances.

Riparian reforestation with a single exotic species restores soil aggregation and porosity but not humic substances

AbstractA degraded riparian area in the Uberaba River basin (Brazil) was restored by local landowners using a monoculture of the exotic species Syzygium cumini (L.) Skeels over 15 years. To assess this riparian restoration, we compared this experimental site (ES) with a disturbed site (DS) and a preserved site (PS) with regard to soil organic matter, humic and fulvic acids (HA and FA), glomalin, soil aggregation and porosity. The results did not show significant differences between ES and PS with regard to soil aggregation and porosity. The cation exchange capacity and the HA and FA contents of ES were significantly different from those in PS and DS. Whereas the HA content of ES was less than that in PS, FA was significantly increased. The order of aromatic composition of humic substances by site was PS &gt; ES &gt; DS and contrasted with the aliphatic composition, which was DS &gt; ES &gt; PS. A principal component analysis based on all variables demonstrated that ES was closer to PS than to DS but that there was no overlap among sites, as PS was driven by humic aromatic substances and the experimental site by fulvic and aliphatic compounds. We concluded that there was a functional recovery of ecosystem services related to soil aggregation and porosity, but the qualitative differences in organic matter formation between the restored and preserved sites were not consistent with ES being fully restored.

Молекулярно-масовий розподіл молекул гумінових кислот ґрунту під впливом посліду і компостів

Молекулярно-масовий розподіл молекул гумінових кислот ґрунту під впливом посліду і компостів

Comparative effects of different maize straw returning modes on soil humus composition and humic acid structural characteristics in Northeast China

ABSTRACTIn order to evaluate the effects of different maize straw returning modes on humus composition and humic acid (HA) structural, a field experiment was designed to have five treatments, i.e. Treatment CK (no straw returned), Treatment EIS (straw incorporated evenly into the soil using the crashing-ridging technique), Treatment SP (straw plowed into the soil), Treatment SM (straw returned as mulch) and Treatment SG (straw returned as pellets). Our results showed that Treatment EIS significantly increased the content of soil organic carbon (SOC), soil humus substances (HEC), soil humic acid carbon (HAC) and fulvic acid carbon (FAC) by 27.8%, 47.6%, 63.3% and 33.8%, respectively, as compared with CK. Among all the straw returning treatments, Treatment EIS was the most significant in effect of increasing the content of HEC, HAC and FAC. Moreover, Treatment EIS altered the composition of humus more significantly than all the other treatments, by increasing the proportion of alkyl C and the ratio of aliphatic C/aromatic C. These results suggest that straw returning accelerated the accumulation of soil organic C and various components of humus, significantly improved the structure of soil HA, with the practice of EIS in particular.

Stimulatory effect of magnetite on the syntrophic metabolism of Geobacter co-cultures: Influences of surface coating

Magnetite-mediated direct interspecies electron transfer (DIET) can facilitate syntrophic metabolism in natural microbial communities and also promote the performance of the engineered systems based on syntrophic interactions. In this study, the stimulatory effect of bare synthetic magnetite (Mt), humic acid coated magnetite, and SiO 2 coated magnetite (Mt-SiO 2 ) on DIET in defined co-cultures of Geobacter metallireducens / Geobacter sulfurreducens were studied. Magnetite coated with Aldrich humic acid (HA) and Elliott Soil humic acid (HA ES ), respectively, were prepared, and the two kinds of humic acid influenced the ability of Mt to promote syntrophic metabolism of the co-cultures in a similar way. When weight concentration was the same, pure humic acid presented the stimulatory effect on DIET similar to bare magnetite. However, the presence of HA coating on magnetite surface caused 50% and 61%, respectively, decrease in the rates of ethanol consumption ( R e ) and succinate production ( R s ) in DIET processes. Pure HA in the same weight concentration as the HA coating in Mt-HA induced the similar metabolism rates as Mt-HA. In the Mt-HA mediated DIET, most electrons from ethanol metabolism were transferred to G. sulfurreducens selectively through the HA coating, and magnetite core hardly contributed to DIET processes. The SiO 2 coating on magnetite resulted in 81% and 89%, respectively, decreases in R e and R s , mainly because the non-conductive SiO 2 layer hindered electron transfer between magnetite core and bacteria. After eight-day incubation with the co-cultures, bare magnetite nanoparticles formed relatively larger and more compact aggregates with cells than Mt-HA and Mt-SiO 2 , due to the different surface charge between bare and coated Mt. The generation of dissolved Fe(II) and HCl-extractable Fe(II) due to microbial reduction of magnetite by G. metallireducens and vivianite formation were observed along with DIET processes in all DIET experiments. Based on these results, different pathways of electron transfer in defined co-cultures of Geobacters with bare and coated magnetite nanoparticles were proposed. The findings in this study demonstrate the significant effects of surface properties on the ability of magnetite to stimulate DIET, which needs to be considered in order to comprehensively understand the role and mechanisms of mineral-mediated DIET in natural and engineered systems.

Humus substances and soil aggregates in the soils with different texture

Humus substances (HS) influence the incorporation of carbon into soil aggregates in many ways. In this study the influence of HS and their fractions in the soil on the proportions of carbon (total organic, labile, non-labile) in water-resistant macro-aggregates (WSA) and differences between the amount of carbon in WSA in coarse-grained (CGS) and fine-grained (FGS) soils with dependence on the proportions of HS in the soil were determined. The experiment included three soils (Haplic Chernozem, Haplic Luvisol, Eutric Cambisol), each of them with two different soil textures (CGS, FGS) from four ecosystems (forest, meadow, urban, and agro-ecosystem). In CGS, higher proportions (52 and 50%) of smaller (&amp;lt; 1 mm) dry-sieved macro-aggregates (DSA) and also WSA were determined, while in FGS, higher proportions (51 and 53%) of larger DSA (&amp;gt; 7 mm) and WSA (&amp;gt; 2 mm) were detected. A negative correlation was recorded between the content of organic carbon in the fractions of WSA and the amount of extracted humic acids (HA) in CGS, and fulvic acids (FA) in FGS. In CGS, the correlation between the carbon content in WSA and HA bound with Ca&lt;sup&gt;2+&lt;/sup&gt; and Mg&lt;sup&gt;2+&lt;/sup&gt;, which forms humates (HA2), was negative. In FGS, a negative correlation was recorded between the carbon content in WSA and free aggressive FA (FA1a) and free FA and those, which are bound with monovalent cations and mobile R&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;3&lt;/sub&gt; (FA1) in the soil. In the case of FA1a, a negative correlation was recorded in FGS and also in CGS, however this influence was more marked in CGS than in FGS (by about 21% higher correlation). In CGS, the influence of HA and FA in soil on the content of labile carbon in aggregates was stronger than in FGS. In CGS, a higher proportion of carbon in aggregates was detected in the case of lower stability of HS and HA and, on the contrary, in FGS, a higher content of carbon in aggregates was detected in the case of their higher stability.

Differences in humic acids structure of various soil types studied by DRIFT spectroscopy

The method of diffuse reflectance infrared spectroscopy (DRIFT) proved to be useful for studying the soil organic matter structure. The aim of this study was to compare DRIFT spectra of humic acids (HAs) separated from various soils and to identify their specific nature. Samples of agricultural soils (Dystric Cambisol, Haplic Chernozem, Greyic Phaeozem, and Haplic Luvisol) were collected from humic (A) horizons. Soil samples of reclaimed dumpsites (Haplic Technosol (molic) and (calcic)) were taken from the upper part of the soil profile. Samples of forest soils were collected from surface organic (H) horizons of Cambisols in spruce (Picea abies L. Karst.) and beech (Fagus silvatica L.) forests. The selected soil types differ in pH, carbon content, texture, and humus quality. An extraction of HAs was performed using a mixture of 0.5 M NaOH and 0.1 M Na&lt;sub&gt;4&lt;/sub&gt;P&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;7&lt;/sub&gt;. The separated HAs were freeze-dried and analyzed using a DRIFT spectrometer (Thermo Nicolet Nexus) without KBr dilution. There were found differences in relative aromaticity among the agricultural soils HAs. The most aromatic character was observed in HAs from Chernozems and the least in Cambisols. Preservation of the natural structure of Chernozem HAs during the reclamation process was documented on the HAs spectra from Haplic Technosols (molic). By using the DRIFT spectra of HAs of forest H horizons, it is possible to identify the fragments of decomposed material (gymnosperms or angiosperms). HAs isolated from these horizons represent a certain interstage between lignin and the matured soil humic acids.

Effect of Soil Fulvic and Humic Acids on Pb Binding to the Goethite/Solution Interface: Ligand Charge Distribution Modeling and Speciation Distribution of Pb.

The effect of adsorbed soil fulvic (JGFA) and humic acid (JGHA) on Pb binding to goethite was studied with the ligand charge distribution (LCD) model and X-ray absorption fine structure (XAFS) spectroscopy analysis. In the LCD model, the adsorbed small JGFA particles were evenly located in the Stern layer, but the large JGHA particles were distributed over the Stern layer and the diffuse layer, which mainly depended on the JGHA diameter and concentrations. Specific interactions of humic substances (HS) with goethite were modeled by inner-sphere complexes between the -FeOH20.5+ of goethite and the -COO- of HS and by Pb bridges between surface sites and COO- groups of HS. At low Pb levels, nearly 100% of Pb was bound as Pb bridges for both JGFA and JGHA. At high Pb levels and low HS loading, Pb-goethite almost dominated over the entire studied pH range, but at high HS loading, the primary species was goethite-HS-Pb at acidic pH and goethite-Pb at alkaline pH. Compared with JGFA, there was a constant contribution of Pb bridges of about 10% for JGHA. The linear combination fit of EXAFS, using Pb-HS and Pb-goethite as references, indicated that with increased HS loading more Pb was bound to adsorbed HS and less to goethite, which supported the LCD calculations.