TY - JOUR

T1 - Estimation of Recharge from Long-Term Monitoring of Saline Tracer Transport Using Electrical Resistivity Tomography

AU - Haarder, Eline Bojsen

AU - Jensen, Karsten Høgh

AU - Binley, Andrew

AU - Nielsen, Lars

AU - Uglebjerg, T.B.

AU - Zibar, Majken Caroline Looms

PY - 2015

Y1 - 2015

N2 - The movement of a saline tracer added to the soil surface was monitored in the unsaturated zone using cross-borehole electrical resistivity tomography (ERT) and subjected to natural rainfall conditions. The ERT data were inverted and corrected for subsurface temperature changes, and spatial moment analysis was used to calculate the tracer mass, position of the center of mass, and thereby the downwardly recharging flux.We conducted a field experiment at the agricultural field site Voulund within the Danish hydrological observatory, HOBE, with the purpose of estimating recharge using geophysical methods. In September 2011, a saline tracer was added across a 142-m2 area at the surface at an application rate mimicking natural infiltration. The movement of the saline tracer front was monitored using cross-borehole electrical resistivity tomography (ERT); data were collected on a daily to weekly basis and continued for 1 yr after tracer application. The ERT data were inverted and corrected for temperature changes in the subsurface, and spatial moment analysis was used to calculate the tracer mass, position of the center of mass, and thereby the downwardly recharging flux. The recovered mass was underestimated by the ERT data by up to 50%. Mass balance errors are widely recognized and are a result of variable resolution of the tomographic models and smoothing applied in the inversion routine. The results were nonetheless in very good agreement with pore water samples collected and analyzed from five cores extracted within the tracer application area during the same period. Recharge during the 7.5 mo from September 2011 to the end of April 2012 was estimated to be about 500 mm using the ERT data. This value is in good accord with recharge estimates made based on drainage data from buried lysimeters located only meters away from the cross-borehole ERT array. This suggests that long-term automated ERT monitoring of a surface-applied tracer is a promising technique for estimating groundwater recharge.

AB - The movement of a saline tracer added to the soil surface was monitored in the unsaturated zone using cross-borehole electrical resistivity tomography (ERT) and subjected to natural rainfall conditions. The ERT data were inverted and corrected for subsurface temperature changes, and spatial moment analysis was used to calculate the tracer mass, position of the center of mass, and thereby the downwardly recharging flux.We conducted a field experiment at the agricultural field site Voulund within the Danish hydrological observatory, HOBE, with the purpose of estimating recharge using geophysical methods. In September 2011, a saline tracer was added across a 142-m2 area at the surface at an application rate mimicking natural infiltration. The movement of the saline tracer front was monitored using cross-borehole electrical resistivity tomography (ERT); data were collected on a daily to weekly basis and continued for 1 yr after tracer application. The ERT data were inverted and corrected for temperature changes in the subsurface, and spatial moment analysis was used to calculate the tracer mass, position of the center of mass, and thereby the downwardly recharging flux. The recovered mass was underestimated by the ERT data by up to 50%. Mass balance errors are widely recognized and are a result of variable resolution of the tomographic models and smoothing applied in the inversion routine. The results were nonetheless in very good agreement with pore water samples collected and analyzed from five cores extracted within the tracer application area during the same period. Recharge during the 7.5 mo from September 2011 to the end of April 2012 was estimated to be about 500 mm using the ERT data. This value is in good accord with recharge estimates made based on drainage data from buried lysimeters located only meters away from the cross-borehole ERT array. This suggests that long-term automated ERT monitoring of a surface-applied tracer is a promising technique for estimating groundwater recharge.

U2 - 10.2136/vzj2014.08.0110

DO - 10.2136/vzj2014.08.0110

M3 - Journal article

VL - 14

JO - Vadose Zone Journal

JF - Vadose Zone Journal

SN - 1539-1663

IS - 7

ER -