Military training areas have to sustain the intensive usage of tracked and wheeled vehicles and the dismounted movement of soldiers. The periodic nature of training activities causes heavy loads, including a high number of loading repetitions on the soil; this makes the mechanical strength and recovery of soil a consequential issue. In many cases, the preparation of new training areas involves field preparations, e.g. earthmoving or deforestation activities that lead to serious disturbance of soil, especially its natural mechanical strength. The goal of this study was to investigate the potential methods to determine the conditions of previously disturbed military training areas. Soil measurements were carried out two years after deforestation works. Within this study, soil samples were collected and the mechanical strength of soil was determined in July and November 2020, with the aim to characterize soil conditions during dry and wet periods. Soil bulk density as well as cone penetrometer and dynamic cone penetrometer measurements were carried out.  In chemical parameters of soil, the total carbon content was measured as an indicator of uniformity by mixing organic matter in the soil surface (25 cm) layer. As the development of plant cover and especially its tight root system is very important for increasing the mechanical strength of soil, the content of plant available nutrients (P, K, Mg and Ca) was also measured. To evaluate the uniformity of blended upper soil layer, the soil was divided into 5 different layers of 5 cm thick each. The bulk density was determined for each layer. The chemical parameters of soil were determined for each layer separately and a diagram of element content in profile was created according to obtained results. This presentation will address the preliminary results of field measurements.

How to cite: Vennik, K., Tõnutare, T., and Krebstein, K.: Evaluation of the Mechanical Strength of Disturbed Military Training Areas based on the Physical and Chemical Parameters of Soil, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-2557, https://doi.org/10.5194/egusphere-egu21-2557, 2021.

Soil disturbance will remarkably alter physical properties of the soil  and the recovery of the structure as well as mechanical strength recovery will take  years. Typically deforestation works, e.g. needed for the establishment of open military training areas, seriously influences soil mechanical state. Deforestation works involve processes like felling of trees, uprooting of stumps followed by levelling of ground. For the establishment of more favourable conditions for grass cover development, tree stumps and felling residues are mixed into the soil with a rotary thriller. Therefore, the final disturbed ground  has low density and high porosity resulting in low mechanical strength. On the  contrary, military training includes high intensity movement by soldiers and trafficking by vehicles. Thus, these types of activities presume stable soil conditions with a high mechanical strength. The aim of our research was to investigate soil density status of disturbed grassland with computed tomography. The soil samples were collected from the undisturbed area and from the grassland which was treated with the rotary thriller 2 years ago. The undisturbed soil samples were collected using plastic cylinders (of 10 cm diameter and 20 cm height) in 3 repetitions.  For comparison, smaller soil samples (5.3 cm diameter and 4 cm height) were obtained at 0, 5, 10, 15, 20, 30 cm depths  for determining the soil bulk density. In the  laboratory, the high resolution industrial computed tomography system Yxlon FF 35 CT was used with the larger soil samples. The soil samples were analyzed using the software Volume Graphics VGSTUDIO MAX 3.2.  Our results indicated the possibility of determination of distribution of pores in the soil and the changes in the porosity of soils depending on the soil treatment and the type.

How to cite: Krebstein, K., Tõnutare, T., Vennik, K., Virro, I., Tõnutare, T., Kõlli, R., and Soobik, L.: Usage of computed tomography for investigation of the soil porosity in disturbed grassland , EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-13023, https://doi.org/10.5194/egusphere-egu21-13023, 2021.

The variation of water content has a significant effect on the engineering behaviour of clayey soils. This is in particular of high importance to infrastructure projects such as open pit mine rehabilitation. During the construction of open pit mines, the natural ground water level needs to be lowered for the feasibility of mining activities. This dewatering causes significant shrinkage and development of cracks amongst the deposits of cohesive soils. In order to design a rehabilitation plan, it is critical to investigate the shrinkage and desiccation cracks occurred within and around open pit mines as the result of dewatering. This study aims at identifying the shrinkage and crack development patterns using an experimental approach and utilizing image analysis. Three different types of clays were studied to this end. Physical properties including liquid limit, plastic limit and linear shrinkage of clays were determined. Soil samples were put in circular moulds of 150 mm diameter and 5 to 25 mm thickness. The variation of water content, while desiccating, was monitored. In addition, a digital camera was used to capture the initiation and propagation of desiccation cracks. Crack and shrinkage intensity factors were determined and analysed against various soil properties. The results obtained in this study could potentially lead to developing models to predict crack propagation patterns in various soils. This will ultimately result in more realistic and reliable future designs of infrastructures, such as mine rehabilitation.

How to cite: Yaghoubi, M. and Baumgartl, T.: Evaluation of Shrinkage and Desiccation Crack Propagation Patterns in Clays for the assessment of their suitability in landform rehabilitation, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-6736, https://doi.org/10.5194/egusphere-egu21-6736, 2021.

Soil texture is an essential factor for effective land management in agricultural production. Knowledge of soil texture and particle size at field scale can aid with on-going soil management decisions. Standard soil physical and gravimetric methods for particle size analysis are time-consuming and X-ray fluorescence spectrometry (XRF) provides a rapid and cost-effective alternative. The objective of this study was to explore the use of XRF as a predictor for particle size. An extensive archive of Irish soils with particle size and soil texture data was used to select samples for XRF analysis. Regression and correlation analyses on XRF determined results showed that the relationship between Rb and % clay varied with soil type and was dependent on the parent material. There was a strong relationship (R > 0.62, R²>0.30, p<0.05) between Rb and clay for soils originating from bedrock such as limestones and slate. Contrastingly, no significant relationship (R<0.03, R²=0.00, p>0.05) exists between Rb and % clay for soils originating from granite and gneiss. Furthermore, there was a significant negative correlation (p<0.05) between Rb and % sand. The XRF is a useful technique for rough screening of particle size distribution in soils originating from certain parent materials. Thus, this may contribute to the rapid prediction of soil texture based on knowledge of the particle size distribution.

How to cite: Croffie, M., Williams, P. N., Fenton, O., Fenelon, A., and Daly, K.: X-ray fluorescence spectrometry for rapid screening of particle size in soils, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-5307, https://doi.org/10.5194/egusphere-egu21-5307, 2021.

The redox potential (Eh) is a master variable affecting speciation and fate of nutrients and pollutants in aqueous environments. To date, direct potentiometric measurements using redox electrodes are the only viable means of monitoring Eh in-situ and continuously. While some scholars indicated the quantitative value of this direct Eh measurement, many have argued that because there are often discrepancies between the measured Eh and the measured speciation of redox active species in solution, the electrode measurements can be regarded as qualitative at best. The ambiguity regarding the quantitative power of potentiometric Eh measurements has led many to disregard this important analytical tool. The question is raised – are there environments in which redox electrodes give a more reliable representation of the redox state than others? We investigated this question in a simplified system of solubilized Fe in different concentrations and various ratios of FeCl₃ to FeSO₄. HCl and KCl were added to achieve different pH value (in the range of 2-4) and ionic strength levels (10-100 mM). The solutions were maintained stirred and were monitored continuously and simulatenously using 7 permanently installed redox electrodes with a data logger. The electrode readings were compared with the Eh calculated by external measurement of Fe speciation and the known solution inputs. In the initial solution, where only the ferrous iron form was added, a standard deviation of ~10mV was found between the electrodes used in this study; additions of Ferric iron to these solutions led to a decrease in standard deviation between electrodes down to ~2mV and concurrently to a convergence between electrode readings and the Nernst-based calculated Eh. The increased deviation in low ferric iron concentrations occurred regardless of the measuring device or if an external reference electrode was used. These findings suggest that potentiometric measurements have an effective range for which they can be used, which has been widely overlooked in the literature.  We examined different indices to define the effective range. Using the standard deviation as the index of the effective range, it was determined that in the tested solutions deviations increased when Fe⁺³ molar activity was <20 nM at an ionic strength of 10-20mM; but the rise occurred at a lower value (<5nM) in solutions with ionic strength ~100mM. The increased effective range at higher ionic strength points towards electron shuttling as a possible effector of the electrode range; if so, it is postulated that in natural systems, electron shuttling by organic matter may greatly increase electrode effective range. We believe that once the understanding that potentiometric redox measurements have an effective range is further established and explored it may be a game changer which will promote both the development of methods to define the effective range and technical improvements to increase electrode effective range so that potentiometric redox measurements can be more widely utilized as a quantitative tool.

How to cite: Yalin, D. and Shenker, M.: New perspective on the powers and limitations of potentiometric redox measurements, a possible game changer, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-9830, https://doi.org/10.5194/egusphere-egu21-9830, 2021.

The purpose of this work is to investigate the accumulation of metals in urban soils of the main geochemical landscapes of the urban environment and in plants growing in these areas. The paper presents the results of a study of the accumulation of metals (Cu, Pb, As, Co, Cr, V, Zn, Mn, Sr, Ni, Ca, Fe) in the accumulative soil horizon of the main functional zones of Kaliningrad (agricultural landscape, residential, industrial and municipal). As a control, we used the landscape of recreation and recreation. The accumulation of elements in the soil and leaves of plants during the growing season and calendar period (year) was studied. The content of TM was determined in the leaves of woody, shrubby and herbaceous plants (22 species) of the urban environment of the city of Kaliningrad.

The metal content in the samples was determined by X-ray fluorescence analysis on the Spectroscan Max-G device. Soil samples were taken from the upper accumulative horizon with a thickness of 0 to 10 cm by the envelope method. The content of TM in the samples was determined by X-ray fluorescence analysis on the device " Spectroscan Max-G "("Spektron", Russia). Soil samples for analysis were prepared in accordance with the M049-P/10 method.

In urban soils, a significant excess of background concentrations of lead, manganese, zinc, copper, strontium and nickel (Pb>Cu>Zn>Mn>Sr>Ni) was found. The maximum content of pollutants in urban soils was observed in industrial and residential multi-storey areas with increased transport load. It is shown that the pH of the soil has the greatest influence on the distribution of metals in the accumulative horizon.

The absorption of elements by plants is species-specific. The highest total level of metals (Mn, Fe, Zn, Sr, Br, Rb) was observed in the leaves of woody plants: holly maple, hanging birch and heart-shaped linden. Of the studied elements, the plants most accumulated manganese and iron. The accumulation of manganese in the leaves is more characteristic of woody plants than of shrubs or grasses. The maximum content of Mn was found in the leaves of holly maple (79.5%), in the leaves of other plants, manganese accumulated significantly less actively (2.7 - 35.6%). The predominant accumulation of iron was observed in the leaves of white clover, wrinkled rose and crowned chub, its content in the leaves was 81.0—83.8 %. Among woody species, the maximum concentration of iron was found in the leaves of heart-shaped linden (69.9 %) and hanging birch (53.4%). Among the species that actively accumulate Zn — black poplar (32.5 %), in the leaves of other plants, the zinc content is 2.2 — 16.8% of the total pollutants. The highest content of strontium was found in samples of meadow clover (19.1 %), in the leaves of other plants the proportion of metal was significantly lower (1.8—11.4%). Analysis of the accumulation of metals in the leaves of the studied plants revealed a positive correlation between the content of Fe and Sr (r = 0.71).

How to cite: Chupakhina, N., Maslennikov, P., Feduraev, P., Skrypnik, L., and Chupakhina, G.: Determination of the content of heavy metals in soils and plants of urban ecosystems (Kaliningrad, Russia), EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-6610, https://doi.org/10.5194/egusphere-egu21-6610, 2021.

In order to predict concentrations in green plants from kinetic data as well as from mobile soil fractions from geogenically enriched areas, soils from historic mining and smelting sites in Styria (Austria) were used to grow lettuce in pot experiments. Lettuce is known for high accumulation of Ni and Cd in the shoots as well, but in our case, uptakes remained low. Addition of a mixed metal salt solution resulted in high Ni concentrations in the plants, contrary to Cd and Pb. Effects of mineral fertilizers and metal salt additions upon plant metal uptake and N resp C/N shifts were monitored and combined with results from batch-extraction as well as with release rates and released amounts obtained by a modified EUF (electro-ultra-filtration) method.

The release obtained by EUF in 0,002M DTPA was modelled by linear, logarithmic, parabolic (√) and quadratic dependence versus time, from original as well as from cumulated datasets. As expected, addition of soluble salts increased the release, whereas addition of PK fertilizer lowered the release of the metals from soil. Thus, food contamination hazards can be lowered by adequate agricultural activities. Plant uptake by nickel got clearly enhanced by metal salt additions, whereas effects of added cadmium and lead were lower. Correlations between plant uptake and release rates resp. released amounts were in the same range, whatever model was used.

How to cite: Sager, M., Jelecevic, A., and Liebhard, P.: Modelling plant uptake of Cd, Ni and Pb from mobile fractions and release rates obtained by the EUF-method, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-6283, https://doi.org/10.5194/egusphere-egu21-6283, 2021.

Biochar has been described as relatively stable form of C with long mean residence time due to its predominantly aromatic structure. Addition of biochar can sequester C in the soil, albeit the effect of biochar on native soil organic C decomposition, whether it stimulates or reduces the decomposition of native soil organic matter, requires further understanding. The aim of this research was to study the long-term impact of biochar (BC) on the composition of soil organic matter (SOM) in Fragi-Stagnic Albeluvisol. The work was compiled on the basis of field experiment, set up on a production field in 2011. The experiment was drawn up of two treatments and four replicates, where on half of the replicates slow-pyrolysis hardwood BC (51.8% C, 0.43% N) produced at 500-600 °C was applied 50 Mg ha^-1. The soil samples were collected from 0-10 cm soil layer in autumn 2020. The air-dried samples were sieved through a 2-mm sieve and divided into two fractions: the particulate organic matter (POM) fraction (soil particles larger than 0.063 mm) and the mineral-associated organic matter (MAOM) (<0.063 mm) by density fractionation method. The soil organic carbon (SOC) and total nitrogen (Ntot) concentrations of bulk soil and fractions were measured. The chemical composition of SOM was studied using ¹³C nuclear magnetic resonance (NMR) spectroscopy. Bulk soil samples and fractions were pretreated with 10% HF solution before NMR spectroscopy analysis. Two indices were calculated: the ratio of alkyl C/O-alkyl C, which describes the degree of SOM decomposition and soil hydrophobicity (HI): (aromatic-C+alkyl-C)/O/N-Alkyl-C.

The addition of BC to the soil increased the SOC concentration but did not influence the Ntot concentration and the soil C/N ratio increased from 11.6 to 16.7. The distribution of POM and MAOM was not affected by the BC and POM proportion accounted for an average of 57–58%. The SOC concentrations of POM and MAOM fractions were higher in the BC variant. The BC increased the proportion of aromatic-C in the SOM, as the proportion of aromatic-C in initial BC was high (almost 92%). Initially the BC is inherently highly hydrophobic and increased the HI of bulk soil, POM, and MAOM fractions. The HI increased in line: MAOM<bulk<POM (1.51<1.67<1.97). An increase in HI inhibits the decomposition of SOM and it was also confirmed by a decreased ratio of alkyl-C/O-alkyl-C after the BC addition. The decomposition degree was lowest in POM fraction where SOC concentration was more than doubled due to BC. The suppressed decomposition was caused by the limitation of soil Ntot concentration and increased C/N ratio.

In conclusion, the effect of BC on the composition of SOM was still evident after 10 years of increasing SOC concentration and soil hydrophobicity and decreasing SOM decomposition degree promoting C sequestration to the soil.

This work was supported by the Estonian Research Council grant PSG147.

How to cite: Pärnpuu, S., Kauer, K., and Raave, H.: The long-term effect of biochar on composition of soil organic matter , EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-11639, https://doi.org/10.5194/egusphere-egu21-11639, 2021.

The aim of this research was to study the effect of different plants on soil organic matter (SOM) composition. The composition of SOM was studied in a field experiment established in 1964 on a carbonaceous glacial till soil with very low initial SOC concentration (1.28 g kg^-1). The effects on SOM composition of bare fallow, barley, grasses, and clover-grasses mixture, were studied using 13C nuclear magnetic resonance (NMR) spectroscopy which is a common tool to characterize SOM. In 2014 the soil samples were collected from 0-5 cm soil layer, air-dried samples sieved through a 2-mm sieve and pretreated with 10% HF solution before NMR spectroscopy analysis. Samples of bulk soil and density fractionated mineral fraction (John et al., 2005) were analyzed. Also, a sample from barley treatment collected in 1966 was analyzed.

O/N-alkyl C was the most abundant C type at the start of the experiment and also in all treatments after 50 years. During 50 years the proportions of O/N-alkyl C and alkyl C increased but contributions of carboxyl C and aromatic C decreased. The ratio of alkyl C/O-alkyl C, which describes the degree of soil organic matter decomposition, decreased from 0.47 (in 1966) to 0.40-0.44 in treatments with plants. In bare fallow treatment, the SOM decomposition stage did not change a lot during the time. In soil mineral fraction the differences between treatments appeared more clearly and the degree of decomposition decreased in line: bare fallow>barley>clover-grasses>grasses (0.49>0.40>0.36>0.34) and this was due to higher O/N-alkyl-C content in treatments with plants. The higher O/N-alkyl C contribution in soil heavy fraction can be attributed to microbially synthesized carbohydrates (Yeasmin et al., 2020) and depended on the amount and properties of C input into the soil in different treatments.

In conclusion, the SOM composition was influenced by plant composition and the effect was more pronounced in soil mineral fraction. The SOM degree of decomposition was higher in treatment with annual crop (barley during 50 years). Under perennial grasses and clover-grasses mixture, the soil organic matter decomposition degree was lower.

This work was supported by the Estonian Research Council grant PSG147.

References

John, B., Yamashita, T., Ludwig, B., & Flessa, H. (2005). Storage of organic carbon in aggregate and density fractions of silty soils under different types of land use. Geoderma, 128(1–2), 63–79. https://doi.org/10.1016/j.geoderma.2004.12.013

Yeasmin, S., Singh, B., Smernik, R. J., & Johnston, C. T. (2020). Effect of land use on organic matter composition in density fractions of contrasting soils: A comparative study using 13C NMR and DRIFT spectroscopy. Science of the Total Environment, 726, 138395. https://doi.org/10.1016/j.scitotenv.2020.138395

How to cite: Kauer, K. and Pärnpuu, S.: NMR spectroscopy approach to study soil organic matter formation under different plant composition during 50 years, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-12110, https://doi.org/10.5194/egusphere-egu21-12110, 2021.

A grand challenge for mankind is to fight climate change, which involves both reducing and reverting CO₂ emissions. Soils store more carbon (C) than the atmosphere and biosphere combined, and it is microorganisms that govern whether C compounds remain in the soil, or whether they are decomposed and released to the atmosphere as CO₂. The microbial influence on C cycling range from the way they decompose soil organic matter (SOM) to their contributions on the formation of soil aggregates that are particularly important for physical C stabilization in soils. However, the relationship between the microbial activity, SOM properties and physicochemical microenvironment, including complexity of soil structure (i.e., arrangement of pore space in and between soil aggregates), and how each of these factors contribute to the prolonged residence of C in soils, is not well understood. Therefore, the aim of this work has been to develop and make use of an analytical approach for studying the influence of pore space architecture on microbial SOM decomposition and dynamics by integrating two novel tools in soil sciences – microfluidic chips, which mimic soil structure, and infrared (IR) spectroscopic imaging, which provides detailed information about chemical properties of materials within these chips.

We have used several microchip designs to simulate different levels of complexity of soil pore space. The hypothesis is that the more complex the chip structures – the less decomposition of SOM will be observed, as more of it will be ‘hidden’ from its decomposers within hard-to-reach spaces. For the IR spectroscopic imaging, macro attenuated total reflection (ATR) accessory has been used. In this mode, an ATR element of high refractive index is put in contact with a sample – the microchip - and total internal reflection signal at the boundary between the element and the sample is recorded. The signal is detected with an imaging focal plane array (FPA) detector and carries information about IR absorptions in the sample. With IR spectra serving as fingerprints for identifying molecules, spatially and temporally resolved observation of chemistry and chemical changes of a SOM substrate initially filling the microchip structures and undergoing decomposition by subsequently inoculated microbial cultures can be made. Our pilot data suggests feasibility of the approach for analysis of complex substrates such as lignin, maize leaves or SOM from real soils and its dependence on the complexity of chip. Evaluating molecular changes in parts of the larger molecules or of the compound mixture under decomposition could even contribute to quantifying, e.g., N mining within the compounds. Eventually, knowing the influence of spatial structure on the decomposition rate and pathways can help us understand how important is the spatial heterogeneity when we study organic matter degradation in soils.

How to cite: Pucetaite, M., Arellano, C., Ohlsson, P., Persson, P., and Hammer, E.: Macro ATR-FTIR imaging for better understanding of organic matter dynamics in soil, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-14325, https://doi.org/10.5194/egusphere-egu21-14325, 2021.

UV spectroscopy is extensively used for the quantitative analysis of natural macromolecules because of simplicity. As a qualitative method it is not very selective. The absorption spectra of organic macromolecules are generally broad bands without distinct peaks decreasing with the increasing wavelength making thus impossible to draw conclusions about exact chemical composition. However certain optical properties enable to obtain information about the organic matter transformation and changes in soils.

In present study soil samples from different depths were investigated by UV spectroscopic methods to measure the absorbance ratios at several wavelengths that could be related to chemical properties of the organic matter, for example the aromaticity, average molecular mass, functional groups, etc. The aim was to study the changes in structural characteristics of humic acids in soil profiles by using their UV absorbance ratios (A254/A436, A280/A350, A470/A664, A254/A354, A254/A204). The top layer of the soil was also characterized by comparing the structure of humic and fulvic acids and unfractionated dissolved organic matter. The spectra and molecular masses were additionally obtained by high performance size exclusion chromatography (HPSEC) with diode array detection.

Our results showed that there is a systematic change in the absorbance ratios at different wavelengths of humic- and fulvic acids and dissolved organic matter spectra in the soil profile that indicates to structural changes in the soil in time. The comparison of all fractions indicated that fulvic acid and unfractionated organic matter are structurally more similar to each other than to humic acid. Although the values obtained by two studied methods (UV spectroscopy and HPSEC) did not give the same values for the absorbance ratios, the correlations are mostly comparable and therefore, both methods can be used to estimate the changes of structural properties in soil.

How to cite: Lepane, V., Otsep, H., Szajdak, L. W., and Szczepanski, M.: Techniques involving UV absorption spectroscopy for estimation of structural changes in soil organic matter, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-15909, https://doi.org/10.5194/egusphere-egu21-15909, 2021.