Acids In Soil Solution Research Articles

Impact of preferential flow on soil chemistry of a podzol

Preferential flow paths are thought to affect the patterns of chemical properties of forest soils. However, little is known about their influence on podzols in coniferous forests. In our study we examined how soil chemical properties of a podzol in a Norway spruce stand are affected by preferential flow. We did three tracer experiments with Brilliant Blue FCF and analyzed soil chemical parameters (exchangeable cations, pH, total C, total N and C:N ratio) of preferential flow paths and soil matrix. For statistical analysis, we used mixed-effects models to account for a hierarchical sampling of our data. We found 5.0gkg−1 more C, 0.24gkg−1 more N, a C:N ratio larger by 2, smaller pH values (0.16 pH units), 32% more Ca and 57% more Mg in preferential flow paths than in soil matrix. Compared to the adjacent soil matrix, the content of Al did not differ significantly. However, 67% more Fe were found in preferential flow paths. These distinct chemical properties are probably due to root exudates, transport of solutes and dissolved organic carbon and percolation of acid soil solution from organic horizons along preferential paths. We attribute the increase of Ca and Mg to their transport via preferential flow paths after the application of lime some years ago. We conclude that a lower pH might enhance the release of Fe (and possibly Al) and thus increase podzolisation. In addition, our results show that soil liming could affect both the topsoil and the subsoil via transport of basic cations along preferential flow paths.

Characterization of soil low-molecular-weight organic acids in the Karst rocky desertification region of Guizhou Province, China

Soil low-molecular-weight (LMW) organic acids play important roles in the soil-forming process and the cycling of nutrients in Karst regions. In this study, we quantified the contents of LMW organic acids (including lactate, acetate, formate, malate, and oxalate) in soil solution over the Karst region of Guizhou Province, China using ion chromatography. The concentration of total LMW organic acids in topsoil solution ranged from 0.358 to 1.823 μmol·g−1, with an average of 0.912 μmol·g−1. The mean concentrations of lactate, acetate, formate, malate, and oxalate were 0.212±0.089, 0.302±0.228, 0.301±0.214, 0.014±0.018 and 0.086±0.118 μmol·g−1, respectively. There were also significant difference in the contents of these acids among four phases of rocky desertification, and their concentrations decreased with the aggravation of rocky desertification. The concentrations of the LMW organic acids were significantly positive correlated each other. Significant positive correlations were also observed among individual LMW organic acids in soil solution, and between them and soil available P, available K, exchangeable Ca, respectively. Furthermore, the concentrations of LMW organic acids were significantly positively correlated with inorganic anions (chlorides, nitrates, and sulfates) in Karst topsoil solution. Therefore, the concentrations of soil LMW organic acids might be one of driving force in the Karst rock desertification process in Guizhou Province.

Caracterização de espécies diploides de Lotus em resposta à toxidez por alumínio

Objetivou-se com este trabalho caracterizar espécies diploides, inclusive a espécie modelo Lotus japonicus, e linhas endogâmicas recombinantes do gênero Lotus, quanto à tolerância ao alumínio (Al) tóxico utilizando-se solo ácido e solução nutritiva. Os experimentos foram conduzidos em casa-de-vegetação, sendo testadas três espécies diploides (L. japonicus MG-20 e GIFU, L. filicaulis e L. burtii) e 180 linhas endogâmicas recombinantes. Nos experimentos com espécies diploides, utilizou-se a alfafa como testemunha sensível e, nos experimentos com linhas endogâmicas recombinantes, utilizou-se a espécie modelo GIFU. Nos experimentos em solo, foram avaliadas características morfológicas da parte aérea e da raiz e, nos experimentos em solução nutritiva, apenas o comprimento e crescimento radicular. As espécies modelo MG-20 e GIFU foram, em geral, as mais produtivas. Os resultados em solução nutritiva seguiram padrão de resposta semelhante ao observado nas avaliações em solo ácido, sendo a espécie MG-20 superior às demais em todas as concentrações de alumínio testadas. Das 180 linhas endogâmicas recombinantes testadas, 24 foram superiores e 39 inferiores à espécie GIFU. A grande diversidade observada nas espécies modelo e nas linhas endogâmicas recombinantes pode auxiliar na futura seleção de genótipos cultivados (tetraploides), uma vez que essas espécies possuem um grupo de marcadores moleculares desenvolvidos que podem ser utilizados na identificação de regiões responsáveis pela maior ou menor tolerância à toxidez por alumínio.

A new approach to study cadmium complexes with oxalic acid in soil solution

This study presents a new analytical approach for the determination of heavy metals complexed to low-molecular-weight-organic acids in soil solutions, which combines the sensitivity of differential pulse anodic stripping voltammetry (DPASV) with the molecular insight gained by electrospray ionization mass spectrometry (ESI–MS). The combination of these analytical methods allows the investigation of such complexes in complex matrixes. On the voltammograms of the soil solutions, in addition to the expected complexes of oxalic acid with cadmium and lead, respectively, also peaks belonging to mixed complexes of cadmium, lead, and oxalic acid (OAH 2) were observed. In order to verify the possible formation of complexes with OAH 2, aqueous solutions of OAH 2 with traces of Cd(II) were investigated as model systems. Signals corresponding to several distinct molecular complexes between cadmium and oxalic acid were detected in the model solutions using negative-ion ESI–MS, which follow the general formula [Cd n ( X, Y) (2 n+1) ] −, where n is the number of cadmium atoms, X = Cl −, and Y = OAH −. Some of these complexes were also identified in the ESI mass spectra taken from the soil solutions.

Dissolved carbon leaching from soil is a crucial component of the net ecosystem carbon balance

AbstractEstimates of carbon leaching losses from different land use systems are few and their contribution to the net ecosystem carbon balance is uncertain. We investigated leaching of dissolved organic carbon (DOC), dissolved inorganic carbon (DIC), and dissolved methane (CH4), at forests, grasslands, and croplands across Europe. Biogenic contributions to DIC were estimated by means of its δ13C signature. Leaching of biogenic DIC was 8.3±4.9 g m−2 yr−1 for forests, 24.1±7.2 g m−2 yr−1 for grasslands, and 14.6±4.8 g m−2 yr−1 for croplands. DOC leaching equalled 3.5±1.3 g m−2 yr−1 for forests, 5.3±2.0 g m−2 yr−1 for grasslands, and 4.1±1.3 g m−2 yr−1 for croplands. The average flux of total biogenic carbon across land use systems was 19.4±4.0 g C m−2 yr−1. Production of DOC in topsoils was positively related to their C/N ratio and DOC retention in subsoils was inversely related to the ratio of organic carbon to iron plus aluminium (hydr)oxides. Partial pressures of CO2 in soil air and soil pH determined DIC concentrations and fluxes, but soil solutions were often supersaturated with DIC relative to soil air CO2. Leaching losses of biogenic carbon (DOC plus biogenic DIC) from grasslands equalled 5–98% (median: 22%) of net ecosystem exchange (NEE) plus carbon inputs with fertilization minus carbon removal with harvest. Carbon leaching increased the net losses from cropland soils by 24–105% (median: 25%). For the majority of forest sites, leaching hardly affected actual net ecosystem carbon balances because of the small solubility of CO2 in acidic forest soil solutions and large NEE. Leaching of CH4 proved to be insignificant compared with other fluxes of carbon. Overall, our results show that leaching losses are particularly important for the carbon balance of agricultural systems.

Interaction between Al3+ and Acrylic Acid and Polyacrylic Acid in Acidic Aqueous Solution: A Model Experiment for the Behavior of Al3+ in Acidified Soil Solution

From the viewpoint of the phytotoxicity and mobility of Al(3+) released from soil minerals due to soil acidification, the interaction between Al(3+) and acrylic acid (AA) and polyacrylic acid (PAA) as a model compound of fulvic acid was investigated. The interaction was examined at pH 3 so as to avoid the hydrolysis of Al(3+). The interaction between Al(3+) and AA was weak. However, the interaction between Al(3+) and PAA was strong and depended on the initial (COOH in PAA)/Al molar ratio (R(P)) of the solution. For the range of 1/R(P), the interaction between Al(3+) and PAA can be divided into three categories: (1) 1:1 Al-PAA-complex (an Al(3+) combines to a carboxyl group), (2) intermolecular Al-PAA-complex (an Al(3+) combines to more than 2 carboxyl groups of other Al-PAA-complexes) in addition to the 1:1 Al-PAA-complex and (3) precipitation of intermolecular complexes. In conclusion, R(P) is an important factor affecting the behavior of Al(3+) in acidic soil solution.

A decade of monitoring at Swiss Long-Term Forest Ecosystem Research (LWF) sites: can we observe trends in atmospheric acid deposition and in soil solution acidity?

Trends in atmospheric acid deposition and in soil solution acidity from 1995 or later until 2007 were investigated at several forest sites throughout Switzerland to assess the effects of air pollution abatements on deposition and the response of the soil solution chemistry. Deposition of the major elements was estimated from throughfall and bulk deposition measurements at nine sites of the Swiss Long-Term Forest Ecosystem Research network (LWF) since 1995 or later. Soil solution was measured at seven plots at four soil depths since 1998 or later. Trends in the molar ratio of base cations to aluminum (BC/Al) in soil solutions and in concentrations and fluxes of inorganic N (NO(3)-N + NH(4)-N), sulfate (SO(4)-S), and base cations (BC) were used to detect changes in soil solution chemistry. Acid deposition significantly decreased at three out of the nine study sites due to a decrease in total N deposition. Total SO(4)-S deposition decreased at the nine sites, but due to the relatively low amount of SO(4)-S load compared to N deposition, it did not contribute to decrease acid deposition significantly. No trend in total BC deposition was detected. In the soil solution, no trend in concentrations and fluxes of BC, SO(4)-S, and inorganic N were found at most soil depths at five out of the seven sites. This suggests that the soil solution reacted very little to the changes in atmospheric deposition. A stronger reduction in base cations compared to aluminum was detected at two sites, which might indicate that acidification of the soil solution was proceeding faster at these sites.

Phosphorus in Soils of Temperate Forests: Linkages to Acidity and Aluminum

We used P fractionation techniques to study the accumulation, mobilization, and availability of soil P in six watersheds of the eastern United States and Europe, two of which included paired long‐term acidification experiments. Although total soil P concentrations varied widely among these watersheds, the proportions of P fractions were relatively uniform. The mean for the P fraction operationally defined as being associated with Al in the reference watersheds was 71% of total extractable P (SE ≤ 1%). Experimental whole‐watershed acidification resulted in significant depletion of Al‐P concentrations from the upper mineral soil in treated watersheds due to the dissolution of Al hydroxide by acidic solutions traveling along shallow flow paths. Acidic soil solutions mobilize both Al and P, leading to P depletion from the Al‐P fraction in the mineral soils. Across this suite of watersheds, lower pH appears to decrease Al/P ratios in the Al‐P fraction of these mineral soils through changes in Al solubility. Biocycling in these forests can play a critical role in linking subsurface mineral soil P to surface O horizon available P. In this study, sites with the lowest mineral subsoil Al/P ratios generally had the lowest mineral soil pH values and the highest O horizon available P concentrations. The net effect was to leave subsoil P more bioavailable at the lower pH values because of a lower Al/P ratio in the mineral subsoil at the pH range of 3.1 to 4.6 found in this study. These results suggest that changes in soil acidity due to management, air pollutants, or pedogenesis could shift P availability by altering acidity and the Al/P balance.

Interactive Effects of N Deposition, Land Management and Weather Patterns on Soil Solution Chemistry in a Scottish Alpine Heath

Nitrogen (N) deposition and land management practices can have profound impacts on the structure and functioning of alpine ecosystems occupying headwaters of major river systems. Such impacts have the potential to result in loss of N to surface waters and acidification, both of which could have serious consequences for water quality and downstream habitats. We present results from a 6-year study of Calluna-dominated alpine heathland in Scotland, designed to assess the interactive effects of N addition (0 and 50 kg N ha−1 y−l), simulated accidental fire and grazing on soil solution chemistry. Both N addition and to a lesser extent burning had significant effects on soil solution chemistry, whereas grazing had no significant impact. Soil solution nitrate (NO3 −) and ammonium (NH4 +) concentration showed a rapid response to N addition and N addition also resulted in acidification of soil solution. A ‘flush’ of base cations, which normally buffer soil from the acid effects of deposited N, accompanied the excess N released from the soil to soil solution. The N treatment had no effect on dissolved organic carbon (DOC), however, concentrations were significantly (14%) lower at the burned plots. In addition to treatment effects, temporal analysis of data from control plots demonstrated that soil solution chemistry was influenced by extremes in weather conditions. Peak NO3 − concentrations were observed in soil solution following the cold winter of 2000–2001 when there were frequent freeze/thaw events. A large pulse of base cations was lost from the soil following the dry year of 2003. These weather-induced responses potentially exacerbate the treatment effects observed in this study.

Local additional potential model for effect of strain rate on SCC of pipeline steel in an acidic soil solution

Stress corrosion cracking (SCC) behavior of X70 pipeline steel in an acidic soil solution was investigated by slow strain rate test, surface characterization, potentiodynamic polarization curve measurement and electrochemical hydrogen permeation technique. A local additional potential model (LAPM) was developed to illustrate the critical role of strain rate in SCC of the steel. According to LAPM, both density and mobility of local active spots on the steel surface, i.e., dislocation emergence point, increase linearly with strain rate. Generation of such active spots introduces an additional negative potential locally, affecting the electrochemical reaction and, consequently, the susceptibility of the steel to SCC. It is found that a maximum of the SCC susceptibility occurs at strain rate of 10 −6 s −1, which is associated with an enhanced hydrogen evolution due to the local additional potential (LAP) effect. When strain rate is sufficiently high to exceed 10 −6 s −1, the mobility of the dislocation emergence points is so fast that the reactive species in solution cannot combine with them for cathodic reaction, resulting in a decrease of the SCC susceptibility. Similarly, a maximum of hydrogen permeation current observed at the strain rate of 10 −6 s −1 is also attributed to the effect of strain rate on the density and mobility of dislocations in the steel. Diffusion of hydrogen atoms in a strained steel is through both body diffusion and dislocation diffusion, with the latter enhanced by an increasing strain rate. When strain rate is so high that the dislocation mobility is sufficiently fast, hydrogen atoms become incapable of catching up with the dislocations. As a result, the hydrogen diffusion is dominated by the body diffusion mode.

Vegetation cover regulates the quantity, quality and temporal dynamics of dissolved organic carbon and nitrogen in Antarctic soils

Populations of the two native Antarctic vascular plant species (Deschampsia antarctica and Colobanthus quitensis) have expanded rapidly in recent decades, yet little is known about the effects of these expansions on soil nutrient cycling. We measured the concentrations of dissolved organic carbon (DOC) and nitrogen (DON), amino acids and inorganic N in soils under these two vascular plant species, and under mosses and lichens, over a growing season at Signy Island in the maritime Antarctic. We recorded higher concentrations of nitrate, total dissolved nitrogen, DOC, DON and free amino acids in soil under D. antarctica and C. quitensis than in lichen or moss dominated soils. Each vegetation cover gave a unique profile of individual free amino acids in soil solution. Significant interactions between soil type and time were found for free amino acid concentrations and C/N ratios, indicating that vascular plants significantly change the temporal dynamics of N mineralization and immobilization. We conclude that D. antarctica and C. quitensis exert a significant influence over C and N cycling in the maritime Antarctic, and that their recent population expansion will have led to significant changes in the amount, type and rate of organic C and N cycling in soil.

Mobility and speciation of rare earth elements in acid minesoils and geochemical implications for river waters in the southwestern Iberian margin

This paper discusses the abundance, fractionation and chemical speciation of the rare earth elements (REE) released during two contrasting water–soil interactions, using acid sulfate and circumneutral soil samples from an abandoned mine land watershed in SW Spain. Our simulative experiment shows that the REE mobility is strongly dependent on the soil solution acidity. The acid solution extracts (pH = 3.1–3.7) extracted from the minesoils display overall REE concentrations much higher (up to three orders of magnitude) than those of the near-neutral soil extracts. The middle REE (MREE) were preferentially removed when compared to light REE (La N /Sm N = 0.07) and heavy REE (Gd N /Yb N = 2.49). The origin of this MREE-enriched signature is attributed to dissolution and/or solid–liquid exchange reactions involving iron oxy-hydroxides particles and surface coatings. The REE were found to behave conservatively under the strong acid conditions of the soil solutions, with sulfate complexes (mainly LnSO 4 +) being the largely dominant aqueous species (75–80%) despite the competitive effects of aluminium. Free metal ions (Ln 3+) accounted for most other species in solution (12–16%). All other ligands analysed (phosphate, nitrate, chloride, fluoride and bicarbonate) were not predicted to be significant complexers of REE, according to speciation calculations. The results of this study have implications for the REE geochemistry of the rivers draining the mine sites of the Iberian Pyrite Belt. The acid sulfate soils represent a major readily leachable MREE reservoir for the Tinto–Odiel fluvial system, which reflect the geochemical signature of the soil–water interaction in the mine lands watersheds.

Effect of inclusions on initiation of stress corrosion cracks in X70 pipeline steel in an acidic soil environment

The effect of inclusions on the initiation of stress corrosion cracking (SCC) X70 pipeline steel was investigated in an acidic soil solution using slow strain rate test, scanning electron microscopy and energy-dispersive X-ray techniques. The results demonstrated that stress corrosion cracks are not initiated in X70 steel when it is under anodic polarization. At cathodic polarization, hydrogen evolution is enhanced, and hydrogen is actively involved in SCC processes. Two types of inclusions exist in the steel and play different role in crack initiation. The inclusions enriching in Al are brittle and incoherent to the metal matrix. Microcracks and interstices are quite easily to be resulted in at the boundary between inclusions and metal. There is no crack initiating at inclusions containing mainly Si.

Soil morphological control on saline and freshwater lake hydrogeochemistry in the Pantanal of Nhecolândia, Brazil

Joint pedological, geochemical, hydrological and geophysical investigations were performed to study the coexistence of saline and freshwater lakes in close proximity and similar climatic conditions in the Nhecolândia region, Pantanal wetlands in Brazil. The saline lakes are concentrically surrounded by green sandy loam horizons, which cause differential hydrological regimes. Mg-calcite, K-silicates, and amorphous silica precipitate in the soil cover, whereas Mg-silicates and more soluble Na-carbonates are concentrated in the topsoil along the shore of the saline lake. In saline solutions, some minor elements (As, Se) reach values above the water quality recommendations, whereas others are controlled and incorporated in solid phases (Ba, Sr). Locally, the destruction of the sandy loam horizons generates very acidic soil solution (pH ~ 3.5) through a process not yet understood. The soil distributions indicate that some freshwater lakes are former saline lakes. They are invaded by freshwater after destruction of the sandy loam green horizons, then the freshwater becomes enriched in K +, SO 4 2 −, Fe, Al, and a stream of minor and trace elements. The formation of these green sandy loam horizons in the saline environment and their destruction in the non-saline one emphasizes the dynamic nature of this environment.

Arsenic in Rice (Oryza sativa L.) Related to Dynamics of Arsenic and Silicic Acid in Paddy Soils

Paddy rice is a global staple food which in some circumstances can contain high levels of the toxic element arsenic (As). In order to elucidate factors influencing As dissolution in the soil solution during paddy rice cultivation, rice (Oryza sativa L. "Selenio") was cultivated to maturity in six paddy soils in the greenhouse in 2005 and 2006. Concentrations of Mn, Fe, As, P, and silicic acid in soil solution and As concentrations in rice straw and polished rice grain were determined. There was a close relationship between Fe and As concentrations in the soil solution, suggesting that the major part of dissolved As originated from reduced iron-(hydr)oxide. However, in addition to the factors causing As dissolution in the soil, other factors influenced the uptake of As by rice. The inhibitory effect of indigenous silicic acid in the soil solution on As uptake was clearly shown. This implied that soils with high plant available Si contents resulted in low plant As contents and that Si application to soils may decrease the As content of rice.

Properties of organic matter precipitated from acidic forest soil solutions

From solutions of acidic forest soils, up to 90% of the organic matter (OM) can be precipitated by Al. Precipitation of the OM contributes to its resistance to microbial decay, so the process should be of relevance for C cycling and sequestration. However, little is known about the properties and the composition of the precipitated OM. Therefore, we investigated the size of precipitated OM flocs and determined the chemical components which were preferentially precipitated. We used four different OM solutions and precipitated OM at different Al/C ratios and pH values. Results of 13C NMR (nuclear magnetic resonance), 1H NMR and UV/vis spectroscopy clearly showed preferential precipitation of aromatic components with a high content of carboxylic groups at all pH and Al/C ratios. This selective precipitation was supported by FTIR measurements which additionally revealed that binding mechanisms between OM and Al were independent of pH and Al/C values. However, we observed greater Al/C ratios for OM precipitated at pH 4.5 than at 3.8, which could be related to the amount of Al(OH) 2+ cations in solution or the formation of small Al-hydroxide primary particles. The diameter of precipitated OM flocs ranged from 3 to 110 μm, with smaller size at pH 3.8 (ave. 16.6 μm) than at pH 4.5 (ave. 27.6 μm). We observed that the Al cations formed on average 2–3 bonds to the organic molecules. As a consequence, the spatial accessibility of the OM should be considerably reduced in these flocs, leading to additional stabilization, besides the intrinsic stability of the precipitated organic compounds. We conclude that the fate of precipitated OM might be similar in many soils, regardless of the parent dissolved organic matter (DOM) because of equalization of OM properties upon precipitation.

Stress corrosion cracking behavior of X70 pipe steel in an acidic soil environment

Stress corrosion cracking (SCC) behavior of X70 pipe steel was investigated in an extracted acidic soil solution by slow strain rate test (SSRT), potentiodynamic polarization curve measurements and surface analysis technique. The SCC process and mechanism of X70 steel in the acidic soil solution is mixed-controlled by both anodic dissolution and the hydrogen involvement. With the different applied potentials, the dominance of SCC process changes. At a relatively less negative potential, the steel SCC is based primarily on the anodic dissolution mechanism. When the applied potential is shifted negatively, hydrogen is involved in the cracking process, resulting in a transgranular cracking mode. With the further negative shift of applied potential, the SCC of the steel follows completely a hydrogen-based mechanism, with a river-bed shaped brittle feature of the fracture surface. Heat treatment alters the microstructure of the steel, resulting in a change of SCC susceptibility. In particular, the quenched steel with a bainite microstructure has a high susceptibility to SCC in the acidic soil, while the as-received steel with a ferrite matrix have a low SCC susceptibility.

Organic acid accumulation under flooded soil conditions in relation to the incorporation of wheat and rice straws with different C:N ratios

Crop residues are important agricultural resources and incorporating wheat straw into rice fields is becoming an alternative to open-field burning after wheat harvest in rice–wheat rotation systems. Organic acids are important soil constituents that are believed to be linked to many biological and environmental processes in the soil, including nutrient cycling, phytotoxicity, metal solubility and greenhouse gas formation. A number of studies have focused on the impact of wheat straw incorporation on organic acid accumulation under flooded soil conditions, but information on the relationship between organic acid accumulation and the properties of wheat straw, especially the C:N ratio, and the response of organic acid accumulation to N application is rare. In this study, incubation experiments were conducted to investigate the difference in organic acid (formic, acetic, propionic and butyric acids) accumulation in soil solution under flooded conditions between wheat and rice straw incorporation, and the relationship between the C:N ratio of the straw materials and organic acid accumulation. Results showed that the concentration of organic acids in the soil solution increased with the rate of straw incorporated. The overall accumulation of organic acids was higher when soil was incorporated with wheat straw than with rice straw. The NH+ 4 concentration in soil solution decreased more with wheat straw incorporation because of its higher C:N ratio. The addition of urea-N significantly enhanced CH4 flux and reduced the concentration of organic acids in soil solution in the wheat straw treatment, whereas CH4 flux and the concentration of organic acids in the rice straw treatment were less sensitive to the addition of urea-N. The practical implication of the results obtained in this study to N management in rice fields is also discussed.

Characteristics of amino acid uptake in barley

Plants have the ability to take up organic nitrogen (N) but this has not been thoroughly studied in agricultural plants. A critical question is whether agricultural plants can acquire amino acids in a soil ecosystem. The aim of this study was to characterize amino acid uptake capacity in barley (Hordeum vulgare L.) from a mixture of amino acids at concentrations relevant to field conditions. Amino acids in soil solution under barley were collected in microlysimeters. The recorded amino acid composition, 0–8.2 μM of l-Serine, l-Glutamic acid, Glycine, l-Arginine and l-Alanine, was then used as a template for uptake studies in hydroponically grown barley plants. Amino acid uptake during 2 h was studied at initial concentrations of 2–25 μM amino acids and recorded as amino acid disappearance from the incubation solution, analysed with HPLC. The uptake was verified in control experiments using several other techniques. Uptake of all five amino acids occurred at 2 μM and below. The concentration dependency of the uptake rate could be described by Michaelis–Menten kinetics. The affinity constant (K m) was in the range 19.6–33.2 μM. These K m values are comparable to reported values for soil micro-organisms.

Water-soluble organic matter and soil solution acidity in the main soil types of the central forest state biosphere reserve

The dynamics of the soluble organic carbon (CWSO) and pH in soil solutions of the main soil types of the Central Forest State Biosphere Reserve were described. Possible reasons for the pH variation were considered. It was found that different soils are characterized by specific levels of pH and CWSO. The structure of the soil solution acidity and its changes with depth were analyzed, and the relationship between the acidity and the content of water-soluble organics substances (WSOs) was determined. The predominantly hydrophilic nature and polydispersity of WSOs in soil solutions were revealed, as well as a decrease in the proportion of high-molecular soil fractions with depth. It was found that the mobility of metals in soils depends on the amphiphilic properties of WSOs to which they are bound, the metal features, and the soil type. The possibility of selective absorption of metals bound to the hydrophobic WSO fraction was shown.