Assessing the extraction and quantification of amorphous silica in soils of forest and grassland ecosystems

Abstract

SummaryMany studies have highlighted the importance of the Amorphous Silica (ASi) pool to the overall mass balance in the biogeosphere. In order to advance our knowledge of measurements and quantification of this pool, it is necessary to compare the ability of different extractants to dissolve ASi in soils and to test methods developed in the aquatic sciences to soils systems. The methods used in this work included three acid extraction techniques (0.2 M NH 4 -oxalate, 0.1 M NH 4 -citrate and 0.5 M NH 4 -acetate) and two alkaline extraction techniques (0.094 M Na 2 CO 3 and 0.5 M NaOH), which are more commonly used for the measurement of ASi in aquatic sediments. Our results indicate that the amount of Si extracted from phytolith samples with the acid methods was two orders of magnitude less than the amount of extracted by alkaline extractions. When applied to natural soil samples, these extractions show that the acid techniques are only able to extract loosely-bound components such as adsorbed Si and Si bound in amorphous matrices with Al and Fe. While Na 2 CO 3 or NaOH extracted the same amount of ASi in Podzols, Na 2 CO 3 was able to extract only part of the ASi extracted with NaOH in Chernozems. Pretreatment of the samples with 0.1 M HCl before the Na 2 CO 3 extraction did not increase amounts of ASi extracted. The present work suggests that alkaline methods used commonly for ASi on aquatic sediment samples can be used on a wide variety of soils.

Anthropogenic impact on amorphous silica pools in temperate soils

“…A generally higher solubility of the amorphous Si fraction as compared to the mineral phase makes it more easily available for biological (re-)cycling on shorter time scales . The reliability of the method has been shown for forested soils (Saccone et al, 2007), arable soils and wetland soils (Struyf and Conley, 2009). Approximately 30 mg of dried soil (<2 mm) was mixed in 40 ml of 0.094 M Na 2 CO 3 solution and digested for 5 h at 85 • C. A 1 ml aliquot was removed from the sample bottle after 3, 4 and 5 h and neutralized with 9 ml of 0.021 M HCl, before DSi determination (CSi d ) by the automated molybdate-blue method (Grasshoff et al, 1983).…”

The contribution of tephra constituents during biogenic silica determination: implications for soil and palaeoecological studies

“…Melzer et al, 2012;Saccone et al, 2007;Sommer et al, 2013). The magnitude overlaps with Si Alk content attributed to tephra, the initial rapid dissolution of clay minerals and/or complete dissolution of nanocrystalline fractions in our experiments (Fig.…”

“…In addition, the sequential Na 2 CO 3 extraction is a rather simple method and the results show a high recovery of the biogenic Si fraction (Meunier et al, 2014;Saccone et al, 2007). The main advantage of the method is that a relatively large number of samples can be measured in a relatively short time span.…”

“…The inheritance of glass shards in some types of aeolian material might partly explain high Si Alk in aeolian deposits measured by other studies (e.g. 4 wt % SiO 2 ; Saccone et al, 2007).…”

Landscape elements and river chemistry as affected by river regulation – a 3-D perspective

“…These vegetation types are adapted to regularly flooding and thus have a character of a wetland. Moreover, grasses and sedges are known to contain significant amount of amorphous silica in their biomass (Saccone et al, 2007). In a recent study, Struyf and Conley (2009) have shown that especially these arctic wetlands are impressive storages of amorphous silica (ASi) that are either diatom frustules or phytoliths (Piperno, 1988).…”