Rights statement: Accepted for publication in Water Resources Research. Copyright 2017. American Geophysical Union. Further reproduction or electronic distribution is not permitted.”
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Rights statement: © 2017. American Geophysical Union
Final published version, 2.37 MB, PDF document
Available under license: CC BY-NC: Creative Commons Attribution-NonCommercial 4.0 International License
Final published version
Research output: Contribution to Journal/Magazine › Journal article › peer-review
Research output: Contribution to Journal/Magazine › Journal article › peer-review
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TY - JOUR
T1 - Characterization of reactive transport by 3-D electrical resistivity tomography (ERT) under unsaturated conditions
AU - Wehrer, Markus
AU - Binley, Andrew
AU - Slater, Lee D.
N1 - © 2017. American Geophysical Union
PY - 2016/10
Y1 - 2016/10
N2 - The leaching of nitrate from intensively used arable soil is of major concern in many countries. In this study, we show how time lapse electrical resistivity tomography (ERT) can be used to characterize spatially heterogeneous processes of ion production, consumption, and transport in soils. A controlled release fertilizer was introduced into an undisturbed soil core in a laboratory lysimeter and subjected to infiltration events. The production of ions resulting from processes associated with nitrification and their transport through the soil core was observed by time lapse ERT and analysis of seepage water samples from a multicompartment sampler. ERT images show development and propagation of a high-conductivity plume from the fertilizer source zone. Molar amounts of nitrate produced in and exported from the soil core could be well reproduced by time lapse ERT using a spatial moment analysis. Furthermore, we observed that several shape measures of local breakthrough-curves (BTCs) of seepage water conductivity and nitrate derived by effluent analyses and BTCs of bulk conductivity derived by ERT are highly correlated, indicating the preservation of spatial differences of the plume breakthrough in the ERT data. Also differences between nitrate breakthrough and a conservative tracer breakthrough can be observed by ERT. However, the estimation of target ion concentrations by ERT is error bound and the smoothing algorithm of the inversion masks spatial conductivity differences. This results in difficulties reproducing spatial differences of ion source functions and variances of travel times. Despite the observed limitations, we conclude that time lapse ERT can be qualitatively and quantitatively informative with respect to processes affecting the fate of nitrate in arable soils.
AB - The leaching of nitrate from intensively used arable soil is of major concern in many countries. In this study, we show how time lapse electrical resistivity tomography (ERT) can be used to characterize spatially heterogeneous processes of ion production, consumption, and transport in soils. A controlled release fertilizer was introduced into an undisturbed soil core in a laboratory lysimeter and subjected to infiltration events. The production of ions resulting from processes associated with nitrification and their transport through the soil core was observed by time lapse ERT and analysis of seepage water samples from a multicompartment sampler. ERT images show development and propagation of a high-conductivity plume from the fertilizer source zone. Molar amounts of nitrate produced in and exported from the soil core could be well reproduced by time lapse ERT using a spatial moment analysis. Furthermore, we observed that several shape measures of local breakthrough-curves (BTCs) of seepage water conductivity and nitrate derived by effluent analyses and BTCs of bulk conductivity derived by ERT are highly correlated, indicating the preservation of spatial differences of the plume breakthrough in the ERT data. Also differences between nitrate breakthrough and a conservative tracer breakthrough can be observed by ERT. However, the estimation of target ion concentrations by ERT is error bound and the smoothing algorithm of the inversion masks spatial conductivity differences. This results in difficulties reproducing spatial differences of ion source functions and variances of travel times. Despite the observed limitations, we conclude that time lapse ERT can be qualitatively and quantitatively informative with respect to processes affecting the fate of nitrate in arable soils.
KW - nitrate leaching
KW - nitrogen cycle
KW - time-lapse electrical resistivity tomography
KW - ERT
KW - multicompartment sampler
KW - lysimeter
KW - SPECTRAL INDUCED POLARIZATION
KW - PREFERENTIAL FLOW PATHS
KW - BREAKTHROUGH CURVES
KW - SOLUTE TRANSPORT
KW - DEICING CHEMICALS
KW - DC RESISTIVITY
KW - ZONE TRANSPORT
KW - UNSTABLE FLOW
KW - VADOSE ZONE
KW - SOIL-WATER
U2 - 10.1002/2016WR019300
DO - 10.1002/2016WR019300
M3 - Journal article
VL - 52
SP - 8295
EP - 8316
JO - Water Resources Research
JF - Water Resources Research
SN - 0043-1397
IS - 10
ER -