Dietrich et al. (2025) Uncertainties in the determination of water storage changes of a shallow groundwater site using profile probe-measured volumetric water contents

Identification

• Journal: Environmental Monitoring and Assessment
• Year: 2025
• Date: 2025-12-04
• Authors: Ottfried Dietrich, Horst H. Gerke
• DOI: 10.1007/s10661-025-14847-0

Research Groups

• Working Group “Lowland Hydrology and Water Management”, Research Area 2 “Land Use and Governance”, Leibniz Centre for Agricultural Landscape Research (ZALF), Müncheberg, Germany
• Working Group “Silicon Biogeochemistry”, Research Area 1 “Landscape Functioning”, Leibniz Centre for Agricultural Landscape Research (ZALF), Müncheberg, Germany

Short Summary

This study evaluates the suitability of a capacitive soil moisture profile probe for estimating soil water storage changes at a shallow groundwater site, comparing probe data (with default and soil-specific calibrations) against reference lysimeter measurements. It found that soil-specific calibration improved accuracy, especially for organic soils, and profile probes can quantify water storage changes well, particularly over longer periods, despite limitations during rapid hydrological events or when water levels are above the surface.

Objective

• To evaluate the suitability of a capacitive soil moisture profile probe for the estimation of soil water storage change on a shallow groundwater site.
• To assess the possibilities and limits of this method for application on shallow groundwater sites as a basis to improve quantification and evaluation of water retention measures in landscapes.

Study Configuration

• Spatial Scale: Field experiment conducted in the Spreewald wetland (51° 52′ N, 14° 2′ E), Germany. Investigations used a weighable groundwater lysimeter monolith with an area of 1 m² and a vertical thickness of 2.0 m. The EnviroScan profile probe measured a soil volume of approximately 0.1 m radius around the well.
• Temporal Scale: Data collected from 1 December 2018 to 30 November 2019 (1 year). Lysimeter data were measured every 10 minutes, weather station data every 1 minute. Analyses were primarily conducted with daily values, with hourly data used for sensor calibration.

Methodology and Data

• Models used:
  • EnviroScan profile probe (Sentek) with capacitive sensors.
  • Diviner probe (used as a reference for soil-specific calibration).
  • Weighable groundwater lysimeter (used as a reference for actual water storage change).
  • Calibration function for volumetric water content (θv): θv = A * SF^B + C (power function).
  • FAO Penman-Monteith method for grass reference evapotranspiration.
  • Water balance equation for actual evapotranspiration (ETa): ΔS = P − ETa + Rin − Rout.
• Data sources:
  • Lysimeter mass change measurements.
  • Volumetric water content measurements from EnviroScan and Diviner probes at eight depths (0.1 m, 0.2 m, 0.3 m, 0.4 m, 0.5 m, 0.6 m, 0.9 m, and 1.2 m).
  • Automatic weather station data (precipitation, net radiation, soil heat flux, air temperature, relative air humidity, wind speed).
  • Soil physical properties from samples (bulk density, organic carbon content, texture).

Main Results

• Soil-specific calibration significantly improved the accuracy of volumetric water content measurements, particularly for the top soil horizon (0-0.4 m, degraded fen peat with 10.1% organic content). For this horizon, the Root Mean Square Error (RMSE) was reduced from 0.0467 m³/m³ (default) to 0.0322 m³/m³ (soil-specific), and the Nash–Sutcliffe model efficiency (NSE) improved from 0.8404 to 0.9242.
• Water storage changes estimated from soil-specific calibrated profile probe data largely reflected the reference lysimeter hydrograph, with a correlation coefficient (R²) of 0.98, an index of agreement (IoA) of 0.99, an RMSE of 0.01082 m, and an NSE of 0.94 for the annual cumulative storage change.
• Deviations between probe and lysimeter measurements were observed during intensive drying and rapid infiltration periods (e.g., heavy rainfall events), attributed to differences in measurement volume and potential macropore flow.
• The first soil horizon (0-0.4 m) contributed most to the annual water storage change. The second (0.4-0.55 m, loamy sand) and third (0.55-1.8 m, sand) horizons showed minimal water content changes due to their properties, high groundwater levels, and limited plant water extraction.
• Daily water storage changes exhibited greater inaccuracies compared to cumulative changes, especially on days with precipitation (RMSE of 0.00523 m for precipitation ≥ 0.002 m/d versus 0.00182 m for no precipitation).
• The study period (2018-2019) was slightly drier than the 30-year average, with a climatic water budget deficit of -0.141 m.

Contributions

• Provides a direct, field-scale validation of capacitive soil moisture profile probe data for quantifying water storage changes in shallow groundwater sites using a weighable groundwater lysimeter.
• Emphasizes the critical need for soil-specific calibration of capacitive probes, especially for soils with high organic matter content, to achieve accurate volumetric water content estimations.
• Evaluates the practical possibilities and limitations of using profile probes for monitoring water retention measures in lowland areas, highlighting their utility for longer-term assessments despite short-term inaccuracies.
• Demonstrates how soil horizon properties and sensor depth distribution influence the accuracy of water storage change estimations in heterogeneous soil profiles.

Funding

• Projekt DEAL
• Authority of Environment, Health and Consumer Protection of the Federal State of Brandenburg

Citation

@article{Dietrich2025Uncertainties,
  author = {Dietrich, Ottfried and Gerke, Horst H.},
  title = {Uncertainties in the determination of water storage changes of a shallow groundwater site using profile probe-measured volumetric water contents},
  journal = {Environmental Monitoring and Assessment},
  year = {2025},
  doi = {10.1007/s10661-025-14847-0},
  url = {https://doi.org/10.1007/s10661-025-14847-0}
}