Connected flow paths as first order control on critical zone water flows: coincidence or self-organized optimality?

Abstract

This study proposes a theoretical framework that links hydrological dynamics to thermodynamics, with emphasis on dynamics and dissipation of free energy and production of entropy in the critical zone. Based on this theory we analyse simulations with a physically based hydrological model in the Weiherbach and the Malalcahuello catchments to learn about free energy dynamics and entropy production in these different hydro-climatic and hydropedological settings. Results for the Weiherbach catchment suggest the existence of a thermodynamic optimal hillslope structure as a result of co-evolution of biotic patterns and the soil catena. This optimum structure allowed acceptable un-calibrated reproduction of observed rainfall-runoff behaviour when being used in a catchment model – in fact it came close to the best fit. Results corroborate furthermore that connected network-like structures – vertical preferential pathways and the river network in this case – act as dissipative structures by accelerating flow against driving gradients, which implies accelerated entropy production. For the Malalcahuello catchment we found that maximum drainage is the functional optimum hillslope structure. This is explained by the very wet, energy limited climate, the presence of non- cohesive highly permeable ash soils and the different mechanism causing preferential flow.