The multiscale signature of ecohydrological fluctuations on soil biogeochemical cycles

Abstract

Numerous soil ecosystem services, ranging from carbon sequestration to crop production, derive from a delicate interaction between hydrologic fluctuations due to rainfall intermittency and biogeochemical cycles. This coupling propagates from the soil surface, where high frequency soil moisture variability drives the alternation between oxic and anoxic soil conditions, to the bedrock, where infrequent percolation pulses impact mineral dissolution. This dissertation discusses how combining stochastic biogeochemical models, observations, and dimensional analysis helps shed light on this complex coupling and to derive parsimonious models governing such dynamics.

Particular emphasis is placed on the iron cycle in the soil root zone and the dissolution of silicate minerals in the deeper regolith because of their environmental relevance for soil carbon storage, CO2 emissions, and plant productivity. While in the first part of the dissertation the focus is on the temporal aspect of the interaction between hydrology and biogeochemistry, in the second part the focus shifts towards the spatial one. Age theory is introduced as a framework for dealing with spatial heterogeneities and up-scaling reaction rates and transport processes. We conclude by outlining how these approaches may be useful for developing an environmental control theory for sustainable ecosystem management under changing climates and increasing food, water and energy demands.