Displays

Dissolved organic matter (DOM) is ubiquitous in terrestrial and aquatic ecosystems where it serves several important functions. It plays a central role in the landscape carbon balance, connects the terrestrial and aquatic environments, and acts as a vector for both nutrients and contaminants. Herein DOM is defined as dissolved molecules and suspended colloidal objects with a size below 0.2 μm. Despite the high interest of DOM, the important connection between the chemical composition of DOM and its colloidal structure are poorly understood. An active discussion in this field of research is how different extraction procedures affect the properties of DOM. Historically, sodium hydroxide extraction has been widely applied but today water extraction, more resembling the natural process, is commonly used. Even when using water as the solvent, the protocol for DOM extraction can differ greatly resulting in the study of different material.

We have systematically investigated the effects of extraction temperature and time on the chemical and colloidal properties of DOM extracted with water from a boreal forest soil. Chemical composition was determined using elemental analysis, pH, z-potential and ¹H NMR while the colloidal structure was probed using a combination of dynamic and static light scattering (DLS, SLS) and small angle x-ray scattering (SAXS). Our results show that chemically the DOM is dominated by carbohydrates irrespective of extraction time and temperature.  Concentration and colloidal structure on the other hand are affected by these parameters. At high temperatures the concentration of all identified components increases, with the most notable difference in the carbohydrates. Also, with increasing extraction temperature the colloidal structure transforms from dense clusters to something resembling flexible polymer chains.

Contrast match experiments of DOM using small angle neutron scattering (SANS) have also been performed in preparation for studies on DOM-mineral interactions. The results show that the match point of DOM agrees with that of carbohydrates further confirming our results of the chemical composition. We believe our broad combination of complementary techniques is necessary to advance the understanding of DOM, in particular the correlation between chemical composition and colloidal properties. In the long-term it can help to reveal the importance of DOM size distribution and aggregation of DOM components for biogeochemically important processes in soil.

How to cite: Andersson, E., Meklesh, V., Persson, P., Tunlid, A., and Olsson, U.: Effect of extraction temperature and time on the chemical and colloidal properties of dissolved organic matter, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-21548, https://doi.org/10.5194/egusphere-egu2020-21548, 2020.

     Dissolved organic matter (DOM) is the most mobile and actively cycling fraction of soil carbon and acts as a carrier of nutrients and contaminants. It is consumed by microbes, photodegraded, or adsorbed in soils and sediments on its way to the ocean. Despite intensive research in the last two decades, the formation and fate of DOM in soils and its response to changes in land use and climate are poorly understood [1-3]. The changes in temperature and chemical composition of soils affect substantially the rates of microbial decomposition. It has previously been observed that afforestation had a positive effect on carbon stocks approximately 3 decades after land-use change [4]. The aim of this study was to identify the role of afforestation on the chemical composition and colloidal nature of DOM. We compared water extractable DOM from an organic horizon in three differently aged (35-, 61-, 90-years-old) Norway spruce stands growing in the same Tönnersjöheden area located at Simlångsdalen, south-west Sweden . Arable fields that were adjacent to each of these three forests served as control DOM samples and represented the soil material before afforestation. Chemical composition of DOM was inferred from ¹³C solid-state nuclear magnetic resonance (NMR), high-resolution ¹H NMR, infrared spectroscopy (DRIFT) and elemental analysis measurements. Colloidal properties of DOM were investigated using small-angle X-ray and dynamic light scattering methods together with electrophoretic mobility measurements. The dialysis experiment was additionally performed in order to investigate the high molecular fraction of DOM.

     Elemental analysis revealed an increase in the ratio between total organic C and total N with forest age and no differences between three field DOM extracts. ¹H and ¹³C NMR results showed that both field and forest DOM extracts were dominated by carbohydrates and also contained carboxylic and aliphatic compounds. The aromatic structures were not detected using NMR. However, some features of aromatics and phenolics were detected in IR spectra, especially in forest cold DOM. Scattering data showed that field and forest DOM contained locally stable colloidal aggregates of ca. 100 nm in radius. The structures of these aggregates are consistent with a combination of globular and cluster-like colloids. Field DOM contained slightly higher fraction of clusters than forest DOM. According to the dialysis experiment the half of DOM was presented in high molecular weight fraction (> 12-14 kDa). Overall, our data suggest that DOM extracted from forest and field organic soils had similar chemical and colloidal properties. The relative composition was dictated more by temperature at which DOM was extracted.

1. J. Lehmann, M. Kleber, Nature. 528, 60–68 (2015).
2. M. W. I. Schmidt et al., Nature. 478 (2011), pp. 49–56.
3. K. Kalbitz, S. Solinger, J.-H. Park, B. Michalzik, E. Matzner, Soil Sci. 165, 277–304 (2000).
4. T. G. Bárcena et al., Glob. Chang. Biol. 20, 2393–2405 (2014).

How to cite: Meklesh, V., Gentile, L., Olsson, U., Tunlid, A., and Persson, P.: Chemical composition and colloidal properties of dissolved organic matter in Norway spruce forest stands of different ages, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-15883, https://doi.org/10.5194/egusphere-egu2020-15883, 2020.

Predicted changes in land use in mountain ecosystems due to agricultural and climatic pressure have the potential to change the abiotic controls of soil organic matter storage (i.e. temperature, and humidity). Yet an integrated assessment of the impact of land use change on site abiotic varibles (temperature, humidity) and its relation to the molecular composition of carbon (C), nitrogen (N), sulphur (S) and phosphorus (P) is lacking. In this study, we used a natural land use gradient (forest [F], degraded forest [DF] and alpine pasture [AP]) within the Karwendel mountain range as a model system to  analyse the C, N,S and P dynamics. At these sites, we measured climatic variables (air temperature and humidity and soil temperature at three depths) through a whole year and determined significant changes in soil temperature after conversion to alpine pasture. Soils were sampled at the organic and mineral horizons of each site and thereafter analysed for its C, N, S and P total concentrations, pH and sugar and amino sugars content. Thereafter, the molecular composition of C,N,S and P in the soils  was analysed combining synchrotron-based X-ray absorption near edge structure (XANES) spectroscopy and liquid state ³¹P-NMR spectroscopy. Our results show that although forest to alpine pasture conversion led to losses of C no changes of N, P or S concentrations where observed. These analyses show that with conversion to alpine pasture the SOM changes to a more decomposed state (increase of Alkyl:O-Alkyl ratio), which is accompanied by an increase of Amidic and Pyrrolic-N and an increase of sulfate-S. Moreover, the nominal oxidation state (NOS) of each analysed element, calculated from the spectral data shows a decrease, which might be due to higher decomposition rates in alpine pasture.  This shows that molecular changes in C,N,S and P occur after land use change in the topsoil, and are majorly depended on the soil temperature.  Moreover, this indicates changes that soil microorganisms were affected by land use change, which will be explored further by aminosugar analysis and PLFA. Our results show the rapid molecular changes of soil C,N,S and P after to land use.

How to cite: Colocho Hurtarte, L. C., Wang, L., and Prietzel, J.: Reconciling the multiple impacts of land use change on soil carbon, nitrogen, phosphorus and sulphur cycles, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-20828, https://doi.org/10.5194/egusphere-egu2020-20828, 2020.

The objective was to examine whether near infrared spectroscopy (NIRS) can be used as an alternative, quick method to determine compost maturity. A crucial prerequisite was to use a suitable reference parameter that describes the maturity of compost well and is also predictable with NIRS. A sum parameter for maturity was developed, which was calculated from contents of dissolved organic carbon (DOC), nitrate nitrogen (NO₃-N), ammonium nitrogen (NH₄-N), oxygen consumption (with Oxitop® method) and from Solvita™-maturity index (with Solvita™ test), with the individual parameters weighted differently in the calculation.

For the calibration 476 compost samples were collected from 28 composting plants in Austria and Czech Republic. The dried and ground samples were physico-chemically analyzed using conventional methods and scanned with an AOTF-NIR spectrometer (wavelength range 1200-2150 nm). Most of the samples (360) originated from the composting plant of the City of Vienna (C1), the other samples (116) originated from smaller composting plants (C2) which employ different compost process technologies and methods. Besides, the samples differed in their input material composition due to seasonal effects (proportion of greenwaste, biowaste, wood, leaves, etc.) and in composting time.

Multivariate analyses were performed to model the data using the statistical programme Unscrambler^©. A principal component analysis (PCA) performed on the spectral data showed that samples differ tendentially according to their origin. Calibration models were developed for a) all samples (one overall model) and b) two groups of samples divided according to the PCA results. The first submodel S1 mainly consisted of samples from composting plant C1 and the second submodel S2 of samples from composting plants C2 and of several samples from C1. The performance of the overall model showed good results with correlation coefficients of r(cal)= 0.89 and r(val)= 0.82 and an average error of prediction of 1.24 (with the values of the sum parameter for compost maturity ranging from 0.5 to 12). The results of submodel S1 performed better with r(cal)= 0.91, r(val)= 0.89 and an average error of prediction of 0.95. The submodel S2 showed correlations of r(cal)= 0.89, r(val)= 0.82 and an average error of prediction of 1.36. The validation of the models showed that the use of submodels resulted in better predictions, especially for the C1 samples. For C2 samples the appropriate model needed to be selected as for some samples the overall model performed better. In general, prediction results of C1 samples were better than those of C2 samples due to a lower influence of factors such as different process technologies.

It is expected that prediction will still improve with further calibration and integration of samples of similar origin into the respective models.

The project INTEKO ATCZ42 was cofinanced by the EU through the European Regional Development Fund in the framework of INTERREG V-A Austria-Czech Republic and by the City of Vienna.

How to cite: Diethart, I., Erhart, E., Bonell, M., Fuchs, K., Haas, D., and Hartl, W.: Determination of compost maturity using near infrared spectroscopy (NIRS), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11423, https://doi.org/10.5194/egusphere-egu2020-11423, 2020.

Soils act as a major sink for atmospheric carbon (C) and, correctly managed, can help counterbalance the excessive CO₂ emissions. Organic C in soils can be physically stabilized and ‘hidden’ from its decomposers within soil aggregates and it is thought that soil fungi play a decisive role in “gluing together” and redistributing soil mineral particles and existing organic matter to form them (M. W. I. Schmidt et al., Nature 478(7367), 49–56, 2011). A significant contribution to the early aggregation process is adsorption of fungal exudates to the reactive surfaces of mineral particles. To uncover the mechanisms of C stabilization processes and to be able to increase the C sink potential of our soils, we need a deepened understanding of which fungi play key roles in the process, what mineral properties promote it, and what type of fungal exudates are involved.

For this purpose, we have grown saprotrophic and symbiotic (both arbuscular mycorrhizal (AM) and ectomycorrhizal (EM)) fungi under sterile conditions in contact with different principal soil components: quartz, goethite and muscovite, on top of X-ray transparent silicon nitride membrane windows and analyzed fungal hyphae by high lateral resolution synchrotron based scanning transmission X-ray microscopy (STXM) in combination with near edge X-ray fine structure (NEXAFS) spectroscopy at absorption edges of C(K), K(L), N(K) and Fe(L). We performed our experiments in the SM beamline at Canadian Light Source, Saskatoon, Canada and I08 beamline at Diamond Light Source, Oxfordshire, UK. In the resultant chemical images, we were able to differentiate the mostly proteinaceous hyphal material, the exudate layer constituting of mixtures of polysaccharides and proteins, and the organo-mineral interfaces consisting of a higher protein and carboxyl to sugar ratio than in the exudate layer. We also observed heterogeneous distributions of the exudate materials around the fungal hypha, indicating presence of exudation channels in the cell wall. Finally, we specifically analyzed NEXAFS spectra at Fe(L) absorption edge of goethite containing samples and were able to show changes in iron speciation in the mineral particles that were in contact with the fungal exudates. These results provide us with better insights to both nanoscale processes of fungal exudation and their role in the formation of organo-mineral interfaces subsequently responsible for soil aggregation.

How to cite: Pucetaite, M., Persson, P., and Hammer, E.: Nanoscale STXM imaging of soil fungal exudates and organo-mineral interfaces, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-4733, https://doi.org/10.5194/egusphere-egu2020-4733, 2020.

Understanding soil’s C sink potential is crucial to support soil management that increases its long-term carbon storage. Soil aggregate formation is known to be a main factor for long-term C sequestration, as C becomes physically protected, or “hidden”, within an increasingly complex three-dimensional structure.

The dynamic process of soil aggregation is however not yet clearly understood. Soil (micro) organisms are thought to play a decisive role in “gluing together” and redistributing particles. They also move existing organic material, and include own exudates and dead cells into aggregates. Fungi, and especially mycorrhizal fungi play a key role in physical organic matter stabilization as they transport carbon compounds over long distances and into narrow soil pores, but little is known about the chemical remnants they leave to soil aggregates.

We investigated the exudates of single hyphae of two saprotrophic and two mycorrhizal fungi (G. confluens, P. subvisciva, P. involutus, R. irregularis), with and without contact to three types of minerals (quarts, goethite, muscovite). We grew them in sterile cultures on Si₃N₄ windows and analysed hyphae, their exudate layers and the organo-mineral interfaces. STXM analysis was performed at CLS, Canada, Diamond, UK, at the C(K), K(L), N(K) and Fe(L) absorption edges, and we made complementary measurements with photothermal IR microspectroscopy at Soleil, France. We found differential composition of the exudates depending on fungal species and environmental conditions. In some cases, we could identify spatially resolved oscillating plumes of K exudates emitted from the hyphae, indicating possible exudation channels. Goethite particles in close vicinity to a hypha showed reduced Fe(2+) compounds, suggesting that oxidative processes may take place. We further investigated thin-polished samples of AMF hyphae grown in a sterile soil, and located polysaccharide-, lipid- and protein-compounds in the surrounding soil matrix.

Our results will help to better understand the processes of fungal soil aggregation and physical organic matter stabilization.

How to cite: Hammer, E. C., Persson, P., and Pucetaite, M.: STXM analysis of fungal soil aggregation, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-17614, https://doi.org/10.5194/egusphere-egu2020-17614, 2020.

The Tibetan Plateau is the third-largest glaciated area of the world and is one of the most sensitive regions due to climate warming, such as fast-melting permafrost, dust blow and overgrazing in recent decades. In the past 50 years, the warming rate on the Tibetan Plateau is higher than the global average warming rate with 0.40 ± 0.05 °C per decade. The climate warming is most distinct in the northeastern Tibetan Plateau, implying increasing air and surface temperatures as well as duration and depth of thawing. The main ecological consequences are a disturbed vegetation cover of the surface and a depletion of nutrient-rich topsoils (Baumann et al., 2009, 2014) coupled with an increase of greenhouse gas emissions, mainly CO₂ (Bosch et al., 2017). Due to the extreme environmental conditions resulting from the intense and rapid tectonic uplift, highly adaptive and sensitive ecosystem have developed, and the Plateau is considered to be a key area for the environmental evolution of Earth on regional and global scales, which is particularly sensitive to global warming (Jin et al., 2007; Qiu, 2008). Climate warming and land-use change can reduce soil organic carbon (SOC) stocks as well as soil nitrogen (N) and phosphorus (P) contents and soil quality. Many species showed their distributions by climate-driven shifts towards higher elevation. In Tibetan Plateau, however, the elevational variations of the alpine grassland are rare (Huang et al., 2018) and it is largely unknown how the grass line will respond to global warming and whether soils play a major role. With this research, the hypothesis is tested that soil quality, given by SOC, N and P stocks and content, is a driving factor for the position and structure of the grass line and that soil quality is one of the major controls of biodiversity and biomass production in high-mountain grassland ecosystems.

A Fourier transformation near and mid-infrared spectroscopy (FT-NMIRS) should be used to measure soil P fractions rapid and for large numbers of soil samples, and analyze environmental factors, including temperature, precipitation, soil development, soil fertility, and the ability of plants to adapt to the environmental impact of climate using FT-NMIRS.

We explored first near-infrared spectroscopy (NIRS) in soils from grassland on the Tibetan Plateau, northwestern China and extracted P fractions of 196 samples from Haibei Alpine Meadow Ecosystem Research Station, Chinese Academy of Sciences, at four depths increments (0-10 cm 10-20 cm 20-40 cm and 40-70 cm) with different pre-nutrient additions of nitrogen (N) an P. The fractionation data were correlated with the corresponding NIRS soil spectra and showed significant differences for depth increments and fertilizer amendments. The R² of NIRS calibrations to predict P in traditional Hedley fractions ranged between 0.12 and 0.90. The model prediction quality was higher for organic than for inorganic P fractions and changed with depth and fertilizer amendment. The results indicate that using NIRS to predict the P fractions can be a promising approach compared with traditional Hedley fractionation for soils in alpine grasslands on the Tibetan Plateau.

How to cite: Cao, Z., Kühn, P., and Scholten, T.: Soil and vegetation feedbacks on climate change in high mountain ranges of the Tibetan Plateau__using near and mid-infrared spectroscopy (FT-NMIRS) in soil properties, phosphorus (P) as example, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-17087, https://doi.org/10.5194/egusphere-egu2020-17087, 2020.

The possibilities of analytical instruments are growing rapidly and the precision of analysis is increasing pidevalt. On the parallel with the development of high tech instrumentation, we can find large number of solutions for analytical determinations using simple, non analytical equipment. One of the trends in the development of analytical techniques and solutions is to find possibilities for a simple and cheap method for providing analysis. This has been made possible due to rapid development of biochemical, chemical, physical sciences and computer technology during the last decade.  

In many scientific articles we can find solutions using digital cameras and smartphones as spectrometers and data collecting devices.  And it is not only a few single experiments. There is a already a term known in scientific literature as „lab on phone“.

This has raised a question such as in which cases do we have the confidence in the results obtained from the useage of smartphones and when is it required to have the precision of spectrometrial measurements.

We have been working on the development of a method for determination of plant available phosphorus from extracts obtained by Mehlich 3 method for some years. During our work many soils have been analysed by diferent methods: digital image analysis and spectroscopical analysis. In our presentation we compare the results of soil P analysis obtained by smartphone, Vis-spectrometry and atomic emission spectrometry.

How to cite: Tõnutare, T. and Oras, A.: The comparison of smartphone, Vis- and atomic emission spectrometers for soil P analysis by Mehlich 3 method , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-581, https://doi.org/10.5194/egusphere-egu2020-581, 2020.

The acidification process influences mostly soils used agriculturally. It causes yield decrease and loss of plant nutrients from soil via leaching and also rise in concentration of undesibrable, harmful for plant roots ions ( Al³⁺) in soil solution.

To overcome the negative effects of acidification to agricultural plant production, liming of agriculturally managed soils is widely in use. 40% of agriculturally used lands in Estonia needs periodic liming and approximately 130 000 tons of liming material will be needed for neutralizing acidic soils every year.  Typically different naturally occouring carbonatic materials , as limestone and dolomite, is used for this purpose.  In Estonia more than 9 million tons of ash has been produced as waste byproduct in Estonian power plants every year. Only 1,9% of this byproduct has been reused in building materials industry and agriculture. The amounts of oilshale ash used as liming material by farmers is increasing from year to year.  

The oilshale fly ash is higly alkaline material with high content of Ca (20 – 33% ), K ( 2,6 – 10%), Mg (2 – 4%) and several microlelement (Zn, Cu, Mo, Mn). Due to modernization of powerplants the new burning technology (CFB) was introduced. Therefore the the fly ash with new chemical and physical properties appeared on the market of liming agents for farmers.

The aim of the research was to investigate the change of water soluble plant nutrient  (P, K, Mg, Ca) content in acidic soils as a result of liming with oilshale fly ash.  Experiment was conducted as a pot experiment  with five different soils and three fly ashes and two types of granulated ashes and powdered limestone.  The influence of soil organic carbon, soil acidity, texture, to the water soluble  nutrient gradient in soil was investigated. 

The differences between oilshale ashes to the changes in nutrient gradient was found. The Nutrient gradient depends from oilshale ash as well from soil properties.   

How to cite: Ilves, M., Köster, T., Krebstein, K., and Tõnutare, T.: Determination the influence of liming with oilshale ashes to the changes of water extractable plant nutrients in acidic soils, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-20338, https://doi.org/10.5194/egusphere-egu2020-20338, 2020.

Due to increase of fertilizers prices and tightening of environmental protection requirements the need for efficient use of fertilizers has increased. At moment over the word huge number of different methods for determination of soil plant available phosphorus (PAP) are in use. Due to unequal extraction ability of extractants have each method own specific gradation to evaluate the soil P class. Allmost all widely used PAP extraction methods are developed in last century, mostly more than fifty years ago and often there is not possible to found information how the P status classes and fertilizer recommendations are determined for each method is determined.

The content of PAP in soil is difficult to estimate because soil pH has a strong effect to soil  - solution chemistry. Therefore extracting  soils with higly buffered solutions as for example Mehlich 3 can give overestimated results. The acidic Mehlich  3 extactant can solubilize relatively insoluble Ca- Fe- and Al phosphates. Also the AL (acetate-lactate) method uses the buffered extraction solution and may influence the amount of extracted PAP. The most realistic conditions for PAP extraction can give the extraction solution which mimic the soil environment that has actively growing roots. 

The aim of our research was to investigate the extraction of PAP with extragent similar by chemical composition to soil solution with root exudates proposed by Haney et al (2010).  The obtained results were compared with Mehlich 3 and AL methods results.    

Ref.: Haney, R.L., Haney, E.B., Hossner, L.R., Arnold, J,G. 2010. Modification to the New Soil Extractant H3A-1: A Multinutrient Extractant. Communications in Soil Science and Plant Analysis, 41:1513-1523.

How to cite: Tonutare, T., Kaldmae, G., Köster, T., Krebstein, K., and Rodima, A.: Comparison of Mehlich 3, AL and artificial root exudates containing extractants for soil phosphorus analysis, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-20904, https://doi.org/10.5194/egusphere-egu2020-20904, 2020.

The cation exchange capacity (CEC, cmol(+)/kg) is a measure of soil’s capacity to retain exchangeable cations. However, it is expensive to collect CEC across a heterogenous field and at different depths. To value-add to limited data, proximal sensed electromagnetic (EM) data has been coupled to CEC through linear regression (LR) models, because they measure apparent soil electrical conductivity (EC_a, mS/m). However, these LRs have been depth-specific. This approach was compared with one universal LR between estimates of true electrical conductivity (s, mS/m) and CEC from various depths, including topsoil (0-0.3 m), subsurface (0.3-0.6 m), shallow subsoil (0.6-0.9 m) and deeper subsoil (0.9-2.1 m). We estimated s from inversion of EM38 and EM31 EC_a either alone or in combination (joint-inversion), in horizontal (EC_ah) and vertical (EC_av) modes, using a quasi-3d (q3-d) inversion software (EM4Soil) and various parameters, including EM38 at two different heights (i.e. 0.2 or 0.4 m). In terms of performance, the LR correlation (R² > 0.60) was largest between deeper subsoil CEC and EM38 EC_ah at 0.2 m. However, the LR was unsatisfactory for CEC calibration in the topsoil (0.31), subsurface (0.37) and shallow subsoil (0.52). In comparison, a universal LR between CEC and σ was well correlated (0.72), when both EM38 (0.2 m) and EM31 EC_a in both modes, were inverted using a forward model (CF), inversion algorithm (S2) and small damping factor (λ = 0.03). The calibrations tested using a leave-one-out cross validation, showed CEC prediction was precise (RMSE, 2.35 cmol(+)/kg), unbiased (ME, -0.002 cmol(+)/kg) with good concordance (Lin’s, 0.83). To improve areal prediction, closer spaced transects need to be collected, while improved vertical resolution of CEC prediction we recommend DUALEM-421 EC_a data be acquired. 

How to cite: Zhao, D. and Triantafilis, J.: Mapping cation exchange capacity using a quasi-3d joint-inversion of EM38 and EM31 data , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-918, https://doi.org/10.5194/egusphere-egu2020-918, 2020.

X-ray fluorescence spectrometry (XRF) is a rapid and inexpensive method for soil analysis. Although, not as precise and accurate as mineral acid digestion-Inductively Coupled Plasma spectrometry for soil testing at present, the XRF method has the potential to be optimised. The objective of this study was to reduce moisture effects, particle size effects and spectra interferences on trace element and macronutrient analyses by improving soil sample preparation and XRF calibration, using bench top Energy-dispersive X-ray Fluorescence Spectrometry (EDXRF). The soil particle size effects study involved samples prepared as pressed powders, pressed pellets, and pressed pellets with a wax binder. After which, the recoveries of Al, Cr, Ni, Mn, Pb, Ca, Fe, K, Mg, P, S and Zn were evaluated as a measure of accuracy and precision. The XRF was calibrated with the fundamental parameters (FP) and matching library (FPML) methods to reduce spectral interferences and validated with certified reference materials. In addition, both XRF methods (FP and FPML) were compared with aqua regia digestion (acid digestion) -Inductively Coupled Plasma-Optic Emission Spectrometry (ICP-OES) using concordance correlation coefficient (CCC), whereby a value of 1 indicated good agreement between methods. There were significant differences (p<0.05) between the sample preparation methods and the pressed pellet with wax binder had the best accuracy and precision for all the elements. In addition, for the calibration study, the FPML gave better recoveries of Ni, Ca, Mg, S, P, Cr compared to the FP, however, for Fe, Zn, K and Mn the FP had better recoveries than the FPML. Furthermore, there was good agreement (CCC>0.80) between both XRF methods and ICP-OES for all elements except Al, P, Cu, K, S and Cr (CCC<0.60). Aqua regia digestion underestimated the total concentration of Al and K, thus, the XRF had better accuracy for predicting these elements. However, for Cr, S, Cu and P, the XRF overestimated the concentration of these elements in soil. This study has shown that the XRF is as accurate as the ICP-spectrometry for most elements when properly calibrated with the advantage of having a shorter sample preparation. Thus, environmental analysts can monitor soils frequently using the XRF without losing analytical results especially with Al and K and also incurring substantial costs in analyses as with traditional methods. 

Keywords: soil; elemental analysis; X-Ray Fluorescence; spectrometry; calibration

How to cite: Croffie, M., Williams, P. N., Fenton, O., Fenelon, A., Metzger, K., and Daly, K.: Determination of trace elements and macronutrients in agricultural soils using energy dispersive X-ray fluorescence as a rapid and precise analytical technique, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9564, https://doi.org/10.5194/egusphere-egu2020-9564, 2020.

In many contaminated sites and/or sites affected by a potentially toxic element (PTE) contamination, the spatial variability of soil contamination is a very complex issue.

This is because the history of contamination in a specific industrial site is often lost in time and with very different modifications occurring over time. It is even hidden in the case of illegal waste dumping, for which type, quantity and localization of contaminants are unknown. Thus it is not known in advance (i) the spatial distribution of contamination, (ii) the knowledge about how contaminants have been distributed over and beneath the soil, (iii) how far contaminants have been reworked during the life time of the contaminated site.

Despite these problems, it is self-evident that a detailed knowledge of the natural and the anthropogenic spatial variability of soil contamination and soil properties is of crucial importance in both site characterization and most importantly in site reclamation.

Here we claim that the analysis of soil trenches in combination with pXRF can strongly support the understanding about processes behind soil contaminant distribution and this information can then be used in the following study of contaminated site characterization.

This contribution focuses on how to acquire detailed knowledge of the spatial distribution of contamination in an agricultural area of southern Italy, 6 ha of farmland confiscated by the Italian Judiciary due to past illegal burial of industrial tannery wastes causing potential contamination by Cr, Zn and heavy hydrocarbons (C>12). After indirect geophysical and radiometric (i.e. soil gamma ray emissions) prospections, 8 sites for soil profiles and trenches (10 x 1.7 m wide) digging were identified.

Over these trenches both morphological (i.e. colour, structure, plant roots, etc.) and elemental total content analysis (Olympus p-XRF) were performed. This analysis enable to identify three type of soil contaminant deposition which affected to various degree the Ap, Bw and C horizons of the investigated Silandic Andosol. The highest Cr and Zn content was found in the B horizon, where levels of 25000 ppm were measured in soil-pockets of muddy-grey materials, very likely hosting the original processing residues.

How to cite: Terribile, F., Vingiani, S., Mileti, A., and Langella, G.: Soil morphometrics applied to soil trenches in a contaminated site, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-6452, https://doi.org/10.5194/egusphere-egu2020-6452, 2020.

Correlations between magnetic enhancement and heavy metal pollution in the urban soils of an industrial area in Shanghai

Mei Li, Zi-Chen He, Xue-Feng Hu

School of Environmental and Chemical Engineering, Shanghai University, Shanghai 200444, China

Fifty-three topsoil samples (0-5 cm) on the sides of highways surrounding the Bao Steel Company were collected in Baoshan District of Shanghai, Southeast China. Physical-chemical properties and magnetic susceptibility of the topsoils were analyzed. Close to the Yangtze River Estuary, the soils in the study area in the northern part of Baoshan District, Shanghai, were mostly derived from tidal sediments of the estuary. The topsoils were thus alkaline, with pH in a range of 8.0-8.6. The content of organic matter in the topsoils was in a range of 8.0-78.6 mg g^-1. The content of Fe in the topsoils varied greatly, possibly influenced by the industrial emissions from local metal smelters and power plants. The content of total Fe (Fe_t) in the topsoils was in a range of 21.0-68.6 mg g^-1, with an average of 33.7 mg g^-1; free Fe (Fe_d), 8.5-25.2 mg g^-1, with an average of 13.8 mg g^-1; amorphous Fe (Fe_o), 2.2-40.4 mg g^-1, with an average of 13.1 mg g^-1. Correspondingly, the magnetic signals of the topsoils were significantly enhanced and varied greatly from site to site. Magnetic susceptibility of the topsoils was in a range of 35.3-1722.7×10^-8 m³ kg^-1, with an average of 408.5×10^-8 m³ kg^-1. The topsoil with the maximum magnetic susceptibility, 1722.7×10^-8 m³ kg^-1, was coarse in grain size and located beside some machinery, cement and material factories. Magnetic susceptibility of the topsoils was significantly correlated with Fe_t, Fe_d and Fe_o (r=0.712, 0.777, 0.961, n=53; p<0.01). The contents of toxic heavy metals, Zn, Pb, Cr, Co, Mn and Ni, in the topsoils were also analyzed. It was found that heavy metals were highly accumulated in the topsoils. The contents of Mn, Cr and Ni in the topsoils were more than 2 times the background values in the soils of Shanghai, and Pb and Zn were more than 4 times the background values. Moreover, magnetic susceptibility of the topsoils was positively significantly correlated with the content of Zn, Mn and Ni (r=0.884, 0.819, 0.564, p<0.01; n=53). This suggests that magnetic susceptibility of the topsoils can be used to indicate the degree of heavy metal pollution to some extent. There are many iron smelting factories and coal-fired power plants in the study area, which emitted a high amount of Fe-containing magnetic particles. The small particles had a large surface area and often adsorbed toxic heavy metals. When the particles were settled down on the ground, both magnetic signals and heavy metal contents of the topsoils were enhanced simultaneously. Therefore, the magnetic techniques are a promising means to study and evaluate the pollution of urban soils.

How to cite: Li, M.: Correlations between magnetic enhancement and heavy metal pollution in the urban soils of an industrial area in Shanghai, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-1117, https://doi.org/10.5194/egusphere-egu2020-1117, 2020.

For technological control of hydrometallurgical processes, it is especially important to obtain data on element concentrations with an express method. Potentiometry on an ion-selective electrode makes it possible to determine concentrations in real time. We propose a method for calculation of silver concentrations for chloride solutions.

In chloride solutions, silver is present in several forms: the cation [Ag⁺] and the complexes [AgCl], [AgCl₂]^-, [AgCl₃]^2-, [AgCl₄]^3-. The ion-selective electrode is calibrated using an AgNO₃ solution that contains exclusively Ag⁺ cations; therefore, it actually determines only the cation content. However, in chloride solutions the cationic form of silver is present in a minimum concentration. Complexes with chloride anions have an opposite charge and are not fixed during the analysis. The total silver concentration can be estimated by measuring the total chloride content in the sample. Using the reference data on the stability constants and information on the concentration of silver cations obtained with potentiometry on an ion-selective chlorine-silver electrode we developed a mathematical model in order to calculate the total silver concentration. Using this model, the total concentration of all the forms of silver was calculated. The data are summarized in Table 1.

Calculating the equilibrium concentration we found that in high-salinity solutions silver prevails in the form of [AgCl₄]^3-. All the other complexes are present in smaller quantities. This result shows that it is important to take into account the complexes formation in potentiometric measurements on ion-selective electrodes.

How to cite: Chupakhina, N., Novikov, O., Maslennikov, P., and Chupakhina, G.: Determination of the silver concentration with ion-selective electrode potentiometry, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5816, https://doi.org/10.5194/egusphere-egu2020-5816, 2020.