Seasonal and event dynamics of spatial soil moisture patterns at the small catchment scale

Abstract

[1] Our understanding of short-and long-term dynamics of spatial soil moisture patterns is limited due to measurement constraints. Using new highly detailed data, this research aims to examine seasonal and event-scale spatial soil moisture dynamics in the topsoil and subsoil of the small spruce-covered Wüstebach catchment, Germany. To accomplish this, univariate and geo-statistical analyses were performed for a 1 year long 4-D data set obtained with the wireless sensor network SoilNet. We found large variations in spatial soil moisture patterns in the topsoil, mostly related to meteorological forcing. In the subsoil, temporal dynamics were diminished due to soil water redistribution processes and root water uptake. Topsoil range generally increased with decreasing soil moisture. The relationship between the spatial standard deviation of the topsoil soil moisture (SD ) and mean water content () showed a convex shape, as has often been found in humid temperate climate conditions. Observed scatter in topsoil SD () was explained by seasonal and event-scale SD () dynamics, possibly involving hysteresis at both time scales. Clockwise hysteretic SD () dynamics at the event scale were generated under moderate soil moisture conditions only for intense precipitation that rapidly wetted the topsoil and increased soil moisture variability controlled by spruce throughfall patterns. This hysteretic effect increased with increasing precipitation, reduced root water uptake, and high groundwater level. Intense precipitation on dry topsoil abruptly increased SD but only marginally increased mean soil moisture. This was due to different soil rewetting behavior in drier upslope areas (hydrophobicity and preferential flow caused minor topsoil recharge) compared with the moderately wet valley bottom (topsoil water storage), which led to a more spatially organized pattern. This study showed that spatial soil moisture patterns monitored by a wireless sensor network varied with depth, soil moisture content, seasonally, and within single wetting and drying episodes. This was controlled by multiple factors including soil properties, topography, meteorological forcing, vegetation, and groundwater.

Effects of vegetation restoration on the spatial distribution of soil moisture at the hillslope scale in semi-arid regions

“…Compared with topsoil, temporal dynamics in deeper soil layers were diminished due to lower infiltration of precipitation and to root water uptake (Rosenbaum et al, 2012). Due Note: TWI represents topographic wetness index; the canopy length was measured perpendicularly to the contour and the canopy width was measured along with contour.…”

Measurement and Simulation of Soil Water Contents in an Experimental Field in Delta Plain

“…This indicates that only when the rainfall intensity is high enough can the soil water content at depths of more than 100 cm increase remarkably or quickly. Additionally, the soil water content at a depth of 60 cm in May was generally greater than that in March, which suggested that evaporation was less able to influence the deep soil layer with the onset of the rainy season and intermittent rains could make the soil water content at depths less than 60 cm change with the seasons [20,53], forming an annual cycle similar to a cosine curve (Figure 5a). However, soil water content and shallow groundwater table tend to be steady values when the rainfall was more intense or heavier.…”

“…The differences between Figure 4a,b suggested that the soil water content was more sensitive to rainfall than evapotranspiration and that the effects of rainfall could reach deeper soil layers. Therefore, soil water contents above the 20 cm depth are essentially controlled by rainfall and evapotranspiration [20] and those below the 40 cm depth are mainly controlled by rainfall and shallow groundwater in this field. during the 12-day evaporation period.…”

“…These may be caused by the shallow groundwater table in the field being connected to the water table of the whole plain. Many influential factors can make the shallow groundwater table change out of the control of the direct atmospheric boundary such as irrigations for huge regions of farmland and irregular precipitation in space and time [20,53].…”

“…Meteorological factors such as rainfall, evaporation, temperature, wind speed and direction were measured by the meteorological station. The measurements of soil water content at different depths (10,20,40,60 and 100 cm) of soil profile were performed by the soil water sensors (TDR100, Campbell Scientific) and were recorded at intervals of 10 min in terms of volumetric water content obtained from the TDR signal through the universal calibration curve of Topp et al [29]. The phreatic water table was recorded continuously with a time step of 5 min by the groundwater observation well.…”