Anthropogenic impact on amorphous silica pools in temperate soils

Abstract

Abstract. Human land use changes perturb biogeochemical silica (Si) cycling in terrestrial ecosystems. This directly affects Si mobilisation and Si storage and influences Si export from the continents, although the magnitude of the impact is unknown. A major reason for our lack of understanding is that very little information exists on how land use affects amorphous silica (ASi) storage in soils. We have quantified and compared total alkali-extracted (PSi a ) and easily soluble (PSi e ) Si pools at four sites along a gradient of anthropogenic disturbance in southern Sweden. Land use clearly affects ASi pools and their distribution. Total PSi a and PSi e for a continuous forested site at Siggaboda Nature Reserve (66 900 ± 22 800 kg SiO 2 ha −1 and 952 ± 16 kg SiO 2 ha −1 ) are significantly higher than disturbed land use types from the Råshult Culture Reserve including arable land (28 800 ± 7200 kg SiO 2 ha −1 and 239 ± 91 kg SiO 2 ha −1 ), pasture sites (27 300 ± 5980 kg SiO 2 ha −1 and 370 ± 129 kg SiO 2 ha −1 ) and grazed forest (23 600 ± 6370 kg SiO 2 ha −1 and 346 ± 123 kg SiO 2 ha −1 ). Vertical PSi a and PSi e profiles show significant (p < 0.05) variation among the sites. These differences in size and distribution are interpreted as the long-term effect of reduced ASi replenishment, as well as changes in ecosystem specific pedogenic processes and increased mobilisation of the PSi a in disturbed soils. We have also made a first, though rough, estimate of the magnitude of change in temperate continental ASi pools due to human disturbance. Assuming that our data are representative, we estimate that total ASi storage in soils has declined by ca. 10 % since the onset of agricultural development (3000 BCE). Recent agricultural expansion (after 1700 CE) may have resulted in an average additional export of 1.1 ± 0.8 Tmol Si yr −1 from the soil reservoir to aquatic ecosystems. This is ca. 20 % to the global land-ocean SiCorrespondence to: W. Clymans (wim.clymans@ees.kuleuven.be) flux carried by rivers. It is necessary to update this estimate in future studies, incorporating differences in pedology, geology and climatology over temperate regions, but data are currently not sufficient. Yet, our results emphasize the importance of human activities for Si cycling in soils and for the land-ocean Si flux.

A Review of the Stable Isotope Bio-geochemistry of the Global Silicon Cycle and Its Associated Trace Elements

“…Modern day anthropogenic factors have a strong influence on the global Si cycle, for example through increases in CO 2 , temperature and changes in hydrological regimes and erosion, variations in agriculture and land use, eutrophication and changes in nutrient stoichiometry in coastal regions, and river damming (e.g., Rickert et al, 2002;Struyf et al, 2004Struyf et al, , 2010Laruelle et al, 2009;Clymans et al, 2011;Carey and Fulweiler, 2012). Anthropogenic perturbations of the global biogeochemical Si cycle are due to the gradual aggradation or depletion of the amorphous SiO 2 pool held in continental soils (Barão et al, 2015;Vandevenne et al, 2015) and aquatic sediments (Frings et al, 2014b) in response to these changing environmental forcings (Struyf and Conley, 2012) and river damming (Conley et al, 1993).…”

How big is the influence of biogenic silicon pools on short-term changes in water-soluble silicon in soils? Implications from a study of a 10-year-old soil–plant system

“…Furthermore, evidence arises that BSi pools are in disequilibrium at decadal timescales due to disturbances and perturbations by humans, e.g., by changes in forest management or farming practices (Barão et al, 2014;Keller et al, 2012;Vandevenne et al, 2015). As a consequence, BSi accumulation and BSi dissolution are not balanced, which influences Si cycling in terrestrial biogeosystems, not only on decadal but also on millennial scales (Clymans et al, 2011;Frings et al, 2014;Sommer et al, 2013;Struyf et al, 2010). Sommer et al (2013), for example, found the successive dissolving of a relict phytogenic Si pool to be the main source of dissolved Si in soils of a forested biogeosystem.…”

“…Due to the fact that the continuous decomposition of this relict phytogenic Si pool is not compensated by an equivalent buildup by recent vegetation the authors concluded that a BSi disequilibrium occurred on a decadal scale. On a millennial scale Clymans et al (2011) estimated the total amorphous Si storage in temperate soils to be decreased by approximately 10 % since the onset of agricultural development about 5000 years ago. This decrease does not only have consequences for land-ocean Si fluxes but also influences agricultural used landscapes, because Si is a beneficial element for many crops (e.g., Epstein, 2009;Ma and Yamaji, 2008).…”

Biomass uptake and fire as controls on groundwater solute evolution on a southeast Australian granite: aboriginal land management hypothesis

“…Following extensive land clearance in the area after 1869 there has been a decrease in the regularity of bush fires, but the intensity of the fires has increased, and elements continue to be removed from the system through this process. In addition, nutrient species are exported by crop harvesting and grazing (Clymans et al, 2011;Heckman et al, 2003). Thus while modern agriculture is a significantly different land management practice to that of pre-European Aboriginals, the outcome of nutrient depletion of groundwater in the study area is the same.…”