Silicon fractionation in Mollic Fluvisols along the Central Elbe River, Germany

Abstract

Quantification of Si in its different forms in soil is a prerequisite to understand the geochemical distribution and fate of Si along with their driving biogeochemical processes. However, different Si fractions in floodplain soils have not been quantified yet, and little is known about the processes driving Si fractionation in these soils. The aim of this study was to clarify the processes that drive formation and distribution of Si among fractions in floodplain soils. We obtained and quantified these fractions using a sequential Si extraction method (Georgiadis et al., 2013) in three Mollic Fluvisols along the Central Elbe River. The highest Si proportion apart from the residual fraction was found in minerogenic amorphous silica (up to 5.6% of total Si), followed by Si occluded in pedogenic oxides and hydroxides (up to 0.7% of total Si). Silicon from biogenic amorphous silica amounted to 0.02-0.6% of total Si. The smallest proportion of Si was found in the mobile Si fraction and made up about 0.01% of the total Si. The results of this study demonstrate the importance of the soil water budget on the accumulation of easy-to-mobilise Si, Si occluded in pedogenic oxides and hydroxides and amorphous silica. Reductive dissolution of Fe and Mn oxides may induce Si release into the soil solution, subsequent oxidizing conditions may induce Si accumulation by adsorption, co-precipitation and occlusion of Si on/with newly formed Fe and Mn oxides. Accumulation of bio-opal after flooding may induce larger amounts of biogenic amorphous silica in floodplain soils than in terrestrial soils. Finally, floodplain soils may accumulate larger amounts of Si bound to occluded particulate SOM than terrestrial soils, which experience less input of particulate SOM than floodplain soils. Literatur

Contrasting biogeographic patterns of bacterial and archaeal diversity in the top- and subsoils of temperate grasslands

“…Soil texture was examined by laser diffraction using Malvern Mastersizer 2000 (Malvern Instruments Ltd., UK) after removal of organic matter and calcium carbonates (59). Dithionite-extractable iron (Fe d ) and aluminum (Al d ) were extracted from soil using the citrate-bicarbonate-dithionite (CBD) method (61, 62) and subsequently determined on an inductively coupled plasma-atomic emission spectrometer (ICP-AES, ICAP6300, Thermo Scientific, USA).…”

Silicon Fractionation of Soluble Silicon in Volcanic Ash Soils That May Affect Groundwater Silicon Content on Jeju Island, Korea

“…These results are attributable to the fact that, since there is no boundary between mobile and loosely adsorbed Si in the soils, some loosely adsorbed Si was already desorbed from the soils at sequential extraction step 1 with CaCl 2 [25]. Consequently, the sum of the two fractions is a readily soluble, easy-to-mobilize Si fraction in Si pools from the soils [25,51]. As mentioned earlier, Jeju Island's Andisols, which have a high content of soil components that absorb monosilicic acid, have a larger amount of readily soluble Si in subsoil horizons compared with mainland Korea's Inceptisols.…”

Pedogenesis, clay mineralogy, and silicon geochemistry in hypersaline tidal flat soils on the Brazilian coast

“…A positive correlation between clay content and Sialk (r=0.79, n=18, p<0.01, Fig. 6b) support this idea, indicating that amorphous Si is accumulating in the clay fraction (Georgiadis et al, 2014(Georgiadis et al, , 2017. This process is favored in soils under constant flooding events due to constant hydration of colloidal amorphous particles, which inhibits the formation of larger particles (Huang and Vogler, 1972) and favors Si concentration in microsites (Drees et al, 1989;Singh and Gilkes, 1993).…”

“…The interplay of some specific soil conditions is essential to understand the Si dynamics in terrestrial and aquatic ecosystems (Cornelis et al, 2014;Georgiadis et al, 2017), such as ion activities, pH, and salinity (Drees et al, 1989). In general, the solubility of silica increases in soils affected by salts and under high pH values (Loucaides et al, 2008).…”

“…As a result, these conditions increase the complexity and difficulty in understanding chemical reactions involving Si in these ecosystems. For example, periodic flooding and alternating redox conditions lead to formation of redox concentrations, which favor adsorption and co-precipitation of Si with Fe oxyhydroxides under oxic conditions (Georgiadis et al, 2017). On the other hand, the release of Si during dissolution of Fe oxyhydroxides when soils are sub-oxic can promote precipitation of Sialk due to an increase of H4SiO4 concentration in the soil solution (Saccone et al, 2007).…”