The principle of ‘maximum energy dissipation’: a novel thermodynamic perspective on rapid water flow in connected soil structures

Abstract

Preferential flow in biological soil structures is of key importance for infiltration and soil water flow at a range of scales. In the present study, we treat soil water flow as a dissipative process in an open non-equilibrium thermodynamic system, to better understand this key process. We define the chemical potential and Helmholtz free energy based on soil physical quantities, parametrize a physically based hydrological model based on field data and simulate the evolution of Helmholtz free energy in a cohesive soil with different populations of worm burrows for a range of rainfall scenarios. The simulations suggest that flow in connected worm burrows allows a more efficient redistribution of water within the soil, which implies a more efficient dissipation of free energy/higher production of entropy. There is additional evidence that the spatial pattern of worm burrow density at the hillslope scale is a major control of energy dissipation. The pattern typically found in the study is more efficient in dissipating energy/producing entropy than other patterns. This is because upslope run-off accumulates and infiltrates via the worm burrows into the dry soil in the lower part of the hillslope, which results in an overall more efficient dissipation of free energy.

Threshold behaviour in hydrological systems as (human) geo-ecosystems: manifestations, controls, implications

“…The MEP principle emerges from the trade-off between thermodynamic "forces"/gradients and fluxes, because the latter depletes the former (Kleidon et al, 2006;Kleidon and Schymanski, 2008). Zehe et al (2009) recently showed that preferential pathways, when activated, are more efficient dissipators of Helmholtz free energy in cohesive soils, especially during dry summer conditions. Apparent preferential pathways offer additional degrees of freedom to the flow process and Zehe et al (2009) suggested that water flow in soils organises in such a way that dissipation of Helmhotz free energy becomes maximum (MED) for a given rainfall input, for a given soil and given soil structures.…”

“…This sudden change in behaviour manifests itself either in the form of an activity/triggering event as in the case of earthquakes (a hot spot in space as suggested by Rundle et al, 2006), or in the form of strongly increased reaction rates in biogeochemical systems (a hot moment in time as suggested by McClain et al, 2003), or as a qualitative change in the macroscopic dynamics as in the case of a laser (Haken, 1983). When the threshold is crossed, and associated processes or responses become considerably faster or slower, and/or the thermodynamic mixing is much more or much less efficient (Kleidon and Schymanski, 2008;Zehe et al, 2009). Examples of elementary threshold phenomena include phase transitions between the liquid, solid and gas phases of an element, or from laminar to turbulent flow, or from emission of normal light to laser light (Haken, 1983).…”

Form and function in hillslope hydrology: characterization of subsurface flow based on response observations

“…To do so, the measurements, which were originally taken in 0.1 m increments, were resampled at depths by linear interpolation. Due to the potentially short correlation length of soil moisture (Zehe et al, 2010), inverse distance interpolation between two locations is generally not appropriate. In the case of the vertical profiles, however, the integration depths of the probes exceeded the measuring increments.…”

Maximum entropy production in environmental and ecological systems

“…Zehe et al (2010) evaluate the effect of preferential flow associated with biogenic soil structures on hydrological fluxes using nonequilibrium thermodynamics. They show that these structures act to maximize dissipation of chemical potential gradients within the soil.…”