Monitoring spatiotemporal soil moisture variability in the unsaturated zone of a mixed forest using electrical resistivity tomography
17
Citation
70
Reference
10
Related Paper
Citation Trend
Abstract:
Abstract European forests are suffering considerably from the consequences of the droughts of recent years, and the exact reasons and influencing factors for this are still not fully understood. This study was conducted to characterize the changes and dynamics of soil moisture in a mixed forest in northern Bavaria within 1 year. Since electrical resistivity correlates well with soil water content, we used two‐dimensional electrical resistivity tomography (ERT) monitoring and time‐lapse analyses to supplement punctual measurements by sensors and soil analyses to show soil moisture changes throughout a whole year (2020–2021). While the topsoil dries out significantly from summer to autumn down to a depth of about 3 m, a clear increase in soil water content and a decrease in resistivity below 3 m can be observed during winter period. Anomalies in the topsoil (0–1 m) showing lower resistivities than the surrounding substrate could be related to tree positions by additional terrestrial laser scans. A significant relationship could be found between tree crown projection area and resistivity in 1–2 m depth. We found a trend that mean resistivity below pine is lower as below beech. ERT data were also used to estimate the soil water content via Archie's law and the results correlate strongly with the measured values, but the degree of correlation varies depending on the depth level. ERT as a noninvasive method, in combination with additional data, for example, on the vitality status of individual trees, could help to better understand root water uptake and water supply to trees, especially during periods of drought.Keywords:
Topsoil
Electrical Resistivity Tomography
Subsoil
Electrical resistivity tomography (ERT) has been suggested as a noninvasive approach for measuring cracks in Vertisols; however, its use has been limited, in part due to a lack of knowledge of the interactions between soil water content and electrical resistivity in cracking soils. In this study, we examined the relationship between soil water content and electrical resistivity for a Vertisol under cracked and noncracked conditions. Electrical resistivity was measured on soil clods, where desiccation does not result in cracking. Results showed that soil matrix electrical resistivity could be predicted from soil water content using an empirical model (RMSE = 8.3 Ωm and r 2 = 0.84). On a 4.5‐ by 5‐m area of a Vertisol, in situ measurements of bulk soil electrical resistivity and soil water content were made using three‐dimensional ERT and neutron soil moisture meter, respectively. Using the empirical model from soil clod measurements and field measured soil water content, we predicted the electrical resistivity of the in situ soil. When cracks were absent, measured soil electrical resistivity fell within the prediction intervals of the empirical model. When cracks were present, average measured electrical resistivity between the 0.2‐ and 0.8‐m depth exceeded predicted electrical resistivity by 15,200 Ωm. The increased electrical resistivity measured on cracked soil cannot solely be attributed to lower soil water content. We, therefore, concluded that cracking directly increased the bulk soil electrical resistivity. Additionally, these data showed that for soils with and without cracks, in situ measurements of soil electrical resistivity could not predict soil water content within the accuracy of the neutron soil moisture meter. Observed differences between in situ electrical resistivity of the soil matrix and bulk soil indicate that ERT might be utilized to nondestructively map soil cracking.
Vertisol
Electrical Resistivity Tomography
Cite
Citations (12)
Subsoil
Topsoil
Plough
Soil resistivity
Electrical Resistivity Tomography
Cite
Citations (36)
Abstract European forests are suffering considerably from the consequences of the droughts of recent years, and the exact reasons and influencing factors for this are still not fully understood. This study was conducted to characterize the changes and dynamics of soil moisture in a mixed forest in northern Bavaria within 1 year. Since electrical resistivity correlates well with soil water content, we used two‐dimensional electrical resistivity tomography (ERT) monitoring and time‐lapse analyses to supplement punctual measurements by sensors and soil analyses to show soil moisture changes throughout a whole year (2020–2021). While the topsoil dries out significantly from summer to autumn down to a depth of about 3 m, a clear increase in soil water content and a decrease in resistivity below 3 m can be observed during winter period. Anomalies in the topsoil (0–1 m) showing lower resistivities than the surrounding substrate could be related to tree positions by additional terrestrial laser scans. A significant relationship could be found between tree crown projection area and resistivity in 1–2 m depth. We found a trend that mean resistivity below pine is lower as below beech. ERT data were also used to estimate the soil water content via Archie's law and the results correlate strongly with the measured values, but the degree of correlation varies depending on the depth level. ERT as a noninvasive method, in combination with additional data, for example, on the vitality status of individual trees, could help to better understand root water uptake and water supply to trees, especially during periods of drought.
Topsoil
Electrical Resistivity Tomography
Subsoil
Cite
Citations (17)
Electrical Resistivity Tomography
Topsoil
Bedrock
Vertical electrical sounding
Cite
Citations (59)
Abstract. Understanding the role of vegetation in the interface between the atmosphere and groundwater is the most decisive key in analyzing the processes involved in water transfer. The main effect of vegetation is its root water uptake, which significantly modifies the processes involved in water transfer in the vadose zone. This paper focuses on mapping temporal and spatial changes in soil moisture using electrical resistivity tomography (ERT). The main objective is to assess how electrical resistivity (ER) is useful for mapping water distribution along a heterogeneous toposequence crossed by a hedgerow. Ten ERT were performed over the studied period for a 28 m long toposequence and compared to matric potential and groundwater level measurements. Soil volumetric water content (VWC) was predicted with two methods: (i) from ER using the Waxman and Smits model (ii) and from matric potential using an experimental retention curve fitted by a Van Genuchten model. Probability density functions (PDFs) of our set of data show that the largest change in mean ER and matric potential was observed in the topsoil layer. We then analyzed the consistency between ER and point measurements in this layer by extracting the arrays at the junction of ER grids and point measurements. PDFs of ER maps at each monitoring time (from T01 to T10) were also calculated to select the most contrasting distributions, corresponding to the wettest (T06) and driest states (T10). Results of ER were consistent with matric-potential measurements, with two different behaviors for locations inside and outside the root zone. A consistent correlation between VWC values from the Waxman and Smits model and those obtained from the retention curve was observed outside the root zone. The heterogeneous soil system inside the root zone shows a different pattern in this relationship. A shift in the relationship between ER and soil moisture for the locations outside and inside the root zone highlights the nonstationarity between wet and dry periods inside the root zone. The equivocal behavior of this relationship shows the limitation of using ER to predict soil moisture in a heterogeneous soil system. Such systems were actually related to the high hedgerow root density and also to a particular topographical context (ditch and bank) that is encountered in Brittany and throughout northwestern Europe.
Topsoil
Electrical Resistivity Tomography
Water potential
Pedotransfer function
Cite
Citations (13)
Subsoil
Topsoil
Infiltration (HVAC)
Soil horizon
Cite
Citations (34)