Uncertainties in the determination of water storage changes of a shallow groundwater site using profile probe-measured volumetric water contents.

Water resource management of areas with shallow groundwater tables often aims at improving soil water retention and storage and at reducing greenhouse gas emissions. However, methods to quantify the effect of management measures in the field are rare. One possibility is to monitor the volumetric water content in a soil profile, to calculate the water storage change, and to upscaling the point data to the field. But how exact are the estimated values on sites with organic soils and shallow groundwater conditions? And can soil water storage changes be estimated from water content data obtained with profile probes? To test this, an EnviroScan profile probe was installed in a soil monolith of a weighable groundwater lysimeter to monitor the volumetric water contents at eight depths. The water storage changes obtained from profile probe data were compared with the reference storage change from the lysimeter. A soil specific calibration was useful especially for soil layers with higher organic matter content. Water storage changes estimated from profile probe data largely reflected the reference hydrograph of the lysimeter except for intensive drying and rapid infiltration periods. The results suggest that profile probe data can be used to quantify soil water retention; by installing multiple probes, the approach allows extending such point observation to larger lowland areas with shallow groundwater tables.