Temporal stability of soil matric potential in the Shale Hills Critical Zone Observatory

This study utilized a 6-yr database consisting of catchment-wide soil matric potential (MP) measurements at 62 locations from the surface down to 1.0 m depth within the 7.9-ha Shale Hills Critical Zone Observatory in Pennsylvania. The objectives were to: (1) assess the temporal stability of soil MP spatial distribution pattern; and (2) examine the temporal variability of soil MP across the catchment. Our results showed that spatial variability of soil MP increased parabolically with decreasing catchment-wide average MP across all measurement depths and different seasons. This relationship is different from the exponential relationship between soil moisture content spatial variability and catchment-averaged volumetric soil moisture, which could be attributed to the nonlinearity of the soil water retention curve. Moreover, the spatial variability of soil MP was also found to be related to topographical characteristics as higher variation of MP was observed in the valley sites. Based on the analysis of Mean Relative Difference, the spatial pattern of soil MP varied among different depths and no one single location had the same ranking more than two layers, indicating the lack of soil moisture correspondence between layers. The spatial pattern of soil MP was more stable over time under wet conditions, but less stable during the drying periods. The results of this study can help optimal design and plan for monitoring and sampling, and provide insights regarding hydropedological processes at the pedon, hillslope, and catchment scales. Spatial variability of soil matric potential in relation to catchment-wide mean matric potential at each of the five depths and the profile.