Critical zone biogeochemistry: Linking structure and function

Recent studies of the critical zone (CZ)-which extends from impermeable bedrock upward through fractured rock, saprolite, soil, and aboveground biomass-have begun to reveal how this zone functions as a single system, responsive on an event basis, but also evolving its structure over geologic timescales. In order to understand the interrelationships between biogeochemical dynamics and CZ structure, CZ observatories across the globe have been established that utilize a common set of measurements (i.e., measurements in situ in the x, y, z, and t domains) to enable the testing of relations among processes that are postulated to be tightly coupled in CZ function. In this context, CZ biogeochemistry is probed across a range of space and timescales (pore to watershed, hydrologic events to millennia) to better understand linkages between hydrology, biological activity, and geochemical reactions that can be incorporated into predictive models. In this chapter, we provide an overview of biogeochemistry through the lens of CZ science, and present our understanding of how tightly linked biogeochemical processes both drive and derive from landscape and ecosystem structure and evolution.