Monitoring soil water content at a heterogeneous oil sand reclamation site using a cosmic-ray soil moisture probe

Abstract

Soil water content (SWC) measurements are important for numerous applications including climate and weather prediction, agriculture and irrigation activities, and monitoring the progress of reclamation on land disturbed by mining or other industrial activities. We assessed the SWC measurement accuracy of a cosmic-ray soil moisture probe (CRP) and explored the possibility of downscaling the CRP measurement to the plot scale. The experiments were conducted at a highly heterogeneous reclamation site in the Alberta Oil Sands near Fort McMurray, Alberta, Canada. The study site is unique because it consists of 36 one hectare plots composed of 12 different reclamation covers made up of various layering schemes of peat and coarse-textured soil. The one-hectare plots also contain different vegetation (species and density). A CRP was installed in the center of the reclamation study site and calibrated using soil core samples. CRP-measured SWC was compared to weighted average SWC measured from soil cores and a network of soil moisture probes within the CRP footprint over two summers. The CRP responded clearly to precipitation events with peaks in the measured SWC and the CRP estimates of SWC were very close to SWC estimated with soil cores and in-situ soil moisture probes with a RMSE of 0.027cm3cm−3 and 0.027cm3cm−3, respectively, over the two summers. We also attempted to downscale the CRP measurements from the 2014 season to the plot scale using HYDRUS-1D modeling and the known soil texture in order to unweight the CRP-measured SWC. The modeled SWC (optimized with the CRP measurements) within the CRP footprint was relatively close to the CRP-measured SWC with a RMSE of 0.047cm3cm−3. Overall, the CRP provided accurate average SWC measurements at the reclamation site despite the soil and vegetation heterogeneity.