z-logo
open-access-imgOpen Access
Magnetic Resonance Monitoring and Numerical Modeling of Soil Moisture during Evaporation
Author(s) -
Merz Steffen,
Balcom Bruce J.,
Enjilela Razieh,
Vanderborght Jan,
Rothfuss Youri,
Vereecken Harry,
Pohlmeier Andreas
Publication year - 2018
Publication title -
vadose zone journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.036
H-Index - 81
ISSN - 1539-1663
DOI - 10.2136/vzj2016.10.0099
Subject(s) - loam , evaporation , moisture , water content , richards equation , soil water , soil science , isothermal process , water vapor , porous medium , silt , chemistry , porosity , environmental science , materials science , geotechnical engineering , geology , thermodynamics , composite material , geomorphology , physics , organic chemistry
Core Ideas Evaporative drying of soil columns was monitored in high resolution using NMR. Soil moisture data were used for validating a water, vapor, and heat flow model. The Richards approach was insufficient under Stage II conditions. NMR is a feasible technique for soil moisture measurements under Stage II conditions. Evaporation from bare soil surfaces can be restrained to a great extent with the development of a dry layer at the soil surface where capillary hydraulic conductance ceases and water flow proceeds only by gas phase transport. Model calculations and preliminary experiments with model porous media have shown that this surface layer can be very thin. An accurate characterization of these processes is required, which is provided by noninvasive magnetic resonance (MR) methods. The evaporative drying of a silt loam and a sandy loam was monitored at high spatial resolution in laboratory experiments. The MR data were used to assess the performance of two numerical models: (i) the Richards equation, which considers isothermal liquid water flow, and (ii) a coupled soil water, heat, and vapor flow numerical model. The experimental results reveal two distinct drying regimes for both soil types where, at the onset of the second evaporation stage, a dry surface zone developed with increasing thickness over time. This layer revealed that water loss inside the soil coincided with a relatively low evaporation rate as the liquid continuity to the soil surface vanished. The modeling results clearly demonstrated the need to consider heat and vapor flow. It was shown, as a proof of principle, that MR relaxation time spectra may serve as a proxy to follow desaturation processes where spatially resolved transverse relaxation can reveal a secondary evaporation front.

The content you want is available to Zendy users.

Already have an account? Click here to sign in.
Having issues? You can contact us here