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Controlling factors for the spatial variability of soil magnetic susceptibility across England and Wales

Controlling factors for the spatial variability of soil magnetic susceptibility across England and Wales
Controlling factors for the spatial variability of soil magnetic susceptibility across England and Wales
We review the nature and importance of soil factors implicated in the formation of secondary ferrimagnetic minerals in soils and palaeosols worldwide. The findings are examined with respect to temperate regions through a comprehensive analysis of over 5000 samples of surface soil from England and Wales taken from a 5×5 km grid. Over 30 soil and environmental attributes are considered for each sample as proxies for soil forming factors. Measurements of low field magnetic susceptibility (mass specific) and frequency dependent susceptibility (mass specific and percentage) on each sample provide estimates of the concentration and grain size of ferrimagnetic minerals.
Maps of soil magnetism across England and Wales show non-random distributions and clusters. One subset of data is clearly linked to contamination from atmospheric pollution, and excluded from subsequent analyses. The concentration of ferrimagnetic minerals in the non-polluted set is broadly proportional to the concentration of minerals falling into the viscous superparamagnetic domain size range (~15–25 nm). This set shows clusters of high magnetic concentrations particularly over specific parent materials such as schists and slates, mudstones and limestones.
Bivariate analyses and linear multiple regression models show that the main controlling factors are parent material and drainage, the latter represented by soil drainage classes and particle size. Together these two factors account for ~30% of the magnetic variability in the complete dataset. A second group of factors, including climate (mean annual rainfall), relief (slope and altitude), and organisms (land use, organic carbon and pH) have subordinate control. Climate as represented by mean annual temperature and pedogenic time is deemed not relevant at these spatio-temporal scales.
The findings are consistent with a largely abiotic system where the role of iron-reducing bacteria appears minor. At coarse spatial and temporal scales, secondary ferrimagnetic mineral formation is controlled by the weathering capacity to supply Fe to the surface soil. At finer scales, soluble Fe precipitates as ferrihydrite before transformation in response to periodically anaerobic conditions into other minerals including nanoscale magnetite.
soil magnetism, magnetic susceptibility, frequency-dependence, soil forming factors, england and wales
0012-8252
158-188
Blundell, A.
1966d0f0-724d-40d9-b104-5495f7018794
Dearing, J.A.
dff37300-b8a6-4406-ad84-89aa01de03d7
Boyle, J.F.
1148a73e-ce47-41d8-9dc2-3bc88537cbea
Hannam, J.A.
62b17b22-42da-4d8c-9333-1300d69c358a
Blundell, A.
1966d0f0-724d-40d9-b104-5495f7018794
Dearing, J.A.
dff37300-b8a6-4406-ad84-89aa01de03d7
Boyle, J.F.
1148a73e-ce47-41d8-9dc2-3bc88537cbea
Hannam, J.A.
62b17b22-42da-4d8c-9333-1300d69c358a

Blundell, A., Dearing, J.A., Boyle, J.F. and Hannam, J.A. (2009) Controlling factors for the spatial variability of soil magnetic susceptibility across England and Wales. Earth-Science Reviews, 95, 158-188. (doi:10.1016/j.earscirev.2009.05.001).

Record type: Article

Abstract

We review the nature and importance of soil factors implicated in the formation of secondary ferrimagnetic minerals in soils and palaeosols worldwide. The findings are examined with respect to temperate regions through a comprehensive analysis of over 5000 samples of surface soil from England and Wales taken from a 5×5 km grid. Over 30 soil and environmental attributes are considered for each sample as proxies for soil forming factors. Measurements of low field magnetic susceptibility (mass specific) and frequency dependent susceptibility (mass specific and percentage) on each sample provide estimates of the concentration and grain size of ferrimagnetic minerals.
Maps of soil magnetism across England and Wales show non-random distributions and clusters. One subset of data is clearly linked to contamination from atmospheric pollution, and excluded from subsequent analyses. The concentration of ferrimagnetic minerals in the non-polluted set is broadly proportional to the concentration of minerals falling into the viscous superparamagnetic domain size range (~15–25 nm). This set shows clusters of high magnetic concentrations particularly over specific parent materials such as schists and slates, mudstones and limestones.
Bivariate analyses and linear multiple regression models show that the main controlling factors are parent material and drainage, the latter represented by soil drainage classes and particle size. Together these two factors account for ~30% of the magnetic variability in the complete dataset. A second group of factors, including climate (mean annual rainfall), relief (slope and altitude), and organisms (land use, organic carbon and pH) have subordinate control. Climate as represented by mean annual temperature and pedogenic time is deemed not relevant at these spatio-temporal scales.
The findings are consistent with a largely abiotic system where the role of iron-reducing bacteria appears minor. At coarse spatial and temporal scales, secondary ferrimagnetic mineral formation is controlled by the weathering capacity to supply Fe to the surface soil. At finer scales, soluble Fe precipitates as ferrihydrite before transformation in response to periodically anaerobic conditions into other minerals including nanoscale magnetite.

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More information

Published date: 2009
Keywords: soil magnetism, magnetic susceptibility, frequency-dependence, soil forming factors, england and wales
Organisations: Environmental Processes & Change

Identifiers

Local EPrints ID: 68597
URI: https://eprints.soton.ac.uk/id/eprint/68597
ISSN: 0012-8252
PURE UUID: e235216f-3945-4e8c-9b07-e28dc0b82f43
ORCID for J.A. Dearing: ORCID iD orcid.org/0000-0002-1466-9640

Catalogue record

Date deposited: 11 Dec 2009
Last modified: 06 Jun 2018 12:44

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