Using Time-Lapse 3D Electrical Resistivity Tomography to Image the Seasonal Heterogeneous Change in Near-Surface Resistivity in the Reynolds Creek Critical Zone Observatory
Abstract
At the Reynolds Creek Critical Zone Observatory (RCCZO), located in southwest Idaho, long term monitoring of soil moisture using in situ moisture probes has shown that during the dry summer only the shallow soils(<30 cm) respond to rainfall events, as shown in Figure 1, while the deeper soils are recharged only during the wet winter. This is not an uncommon observation in semi-arid environments but how this response to rainfall varies spatially at the plot scale has yet to be measured. To investigate this process, we installed 7x8 m2 electrical resistivity tomography (ERT) arrays at two field sites, Low Elevation Sage (LES) at 1406 m in elevation and Mid Elevation Sage (MES) at 1653 m in elevation. We monitored the two sites weekly during the spring and fall of 2015 and 2016 to capture the dry down and wet up of the soils. Controls for the geophysical data were obtained from soil moisture probes adjacent to the ERT arrays at 5, 15, 30, 60 and 90 cm of depth. The inverted resistivity grids show that the region that readily responds to rainfall varies both within a plot and between sites. MES's rainfall responsive zone is shallow partially continuous layer (see Figure 2), while LES's is deeper and bowl shaped (see Figure 3). Further the inverted grids at MES, Figure 2, show rainfall responsive, vertical tube structures which are likely hydraulically conductive pathways to the deeper vadose zone. This spatial heterogeneity cannot be captured by the existing moisture probe data. Our results imply that spatially limited hydraulically conductive pathways may link the shallow soils to the deeper vadose zone even during the seasonal dry periods where these regions are thought to be disconnected.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2016
- Bibcode:
- 2016AGUFM.H13K1559N
- Keywords:
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- 1813 Eco-hydrology;
- HYDROLOGYDE: 1835 Hydrogeophysics;
- HYDROLOGY