Optode Films for Real-Time Soil, Rhizosphere, and Subsurface Monitoring

To effectively manage vegetation, water, and ultimately climate resources, it is critical to extend knowledge and understanding of complex hydro-biogeochemical subsurface systems. Reactive transport models are promising tools for predicting hydro-biogeochemical processes in watersheds and complex subsurface matrices, including the vadose zone, rhizosphere, and groundwater, but their accuracy and predictive power are limited by our capability to collect chemical information from the field. Spaciotemporal information about distribution of nutrients and other chemicals in complex matrixes at a submillimeter scale has the potential to accelerate and elevate our understanding of biogeochemical processes, and significantly improve modeling tools; instrumentation that can provide such information is needed. We propose to develop a family of optode films interrogated by a luminescence-based imaging system for monitoring carbon and nitrogen compounds in the rhizosphere, vadose zone, and groundwater, in real time and with spatial resolution. This system will collect information about key hydro-biogeochemical parameters, so that reactive transport models can simulate hydro-biogeochemical cycles in watersheds and complex subsurface matrices. The proposed monitoring system will incorporate a family of optode chemical sensors, all of them based on the same optical technique, interrogated by the same imaging system, that will be capable of collecting measurements of pH, oxygen, carbon dioxide, nitrates, and phosphates, key parameters for understanding spatiotemporal interactions among gases, water, microbes, and rock soils. In Phase I, emission lifetime-based optode sensors for nitrate and pH will be developed, and sensor elements for oxygen and carbon dioxide previously developed for medical and defense applications will be adapted for subsurface monitoring. High resolution imaging of our optodes for spatiotemporal measurement of hydro-biogeochemical parameters will be demonstrated. A preliminary design for a first demonstrator imaging system will be developed, and adaptations for application in the vadose zone and other complex subsurfaces will be identified. An economical and uncomplicated system for measuring key chemical parameters in watershed and subsurface hydro-biogeochemical cycles will directly benefit climate science, and will also have commercial applications in agriculture and water quality monitoring.