The physical, chemical and biological structures and processes controlling biogeochemical reaction, flow and transport in natural landscapes interact at multiple space and time scales and are difficult to quantify. The current paradigm of hydrological and biogeochemical theory is that process descriptions derived from observations at small scales can be applied to predict at much larger scales, as long as some effective values of the scale dependent parameters can be identified. However, this paradigm is known to be flawed and increasingly frequent calls have been made for new theories that will better link small-scale process understanding with large-scale predictions. Furthermore, natural systems evolve in time in a way that is hard to observe in short-run laboratory experiments or in natural landscapes with unknown initial conditions and time-variant forcing. This project will use carefully designed wetting and drying experiments using stable water isotope tracers at the hillslope scale to determine the structure of flow paths, as well as to quantify water transit time distributions along those flow paths. Chemical analysis of pore waters and hillslope outflow will determine mineral weathering kinetics during these wetting-drying cycles which will be related to observed water transit times. Detailed numerical modeling with a coupled systems model will be used to simulate the flow and reactive transport and the evolution of the porous medium through data assimilation and inverse modeling.
This project will observe the way water, rock and life interact and create the organized structure of the soil. These observations will be made at an unprecedented spatial and temporal resolution using the Landscape Evolution Observatory (LEO) at Biosphere 2. LEO consists of three large artificial landscapes built in a climate controlled environment that contain over 1,800 sensors to measure how water flows through these landscapes and interacts with the soil minerals and microbiological ecosystems. The research outcome will contribute to a new generation of modeling tools for quantifying contaminant transport in a changing environment. The result will reconcile the discrepancies between observations of flow and transport phenomena at lab and field scales. Two PhD students and several undergraduate students will be trained in novel hydrologic-geochemical experimentation and Earth systems modeling, and their research will be shared with the 100,000 people that visit Biosphere 2 each year.
