Geochemical Monitoring System and Network for Complex Subsurface Matrices

To effectively manage vegetation resources, it is critical to extend our knowledge and understanding of complex biogeochemical subsurface systems. Reactive transport models have become popular tools for predicting geochemical and biogeochemical processes in complex subsurface matrices, including the vadose zone and groundwater, but their accuracy and predictive power are limited by our capability to collect chemical information from the field. Advanced, in-situ sensing systems are needed to cost- effectively collect accurate and relevant information about nutrients and other chemicals in the soil and saturated zone. The author proposes to develop a stand-alone in-situ system for continuous monitoring of carbon and nitrogen compounds in the vadose zone and groundwater. Specifically, this system will collect information in real time about key geochemical parameters, so that reactive transport models can simulate biogeochemical processes in complex subsurface matrices. The proposed monitoring system will incorporate a family of optical sensor elements, all of them based on the same optical technique, connected to a single compact unattended optoelectronic unit, and will be capable of collecting measurements of pH, oxygen, carbon dioxide, nitrates, phosphates, which are key parameters for understanding interactions among gases, water, microbes, and rock soils across spatial scales. The sensor family proposed in based on phase-resolved luminescence detection. Sensor elements based on this technique for measuring nitrate will be developed, and sensor elements for oxygen and pH previously developed for medical and defense applications will be adapted for underground monitoring. A multi- parameter probe will be assembled and characterized, and a compact device will be fabricated, and the first demonstrator will be evaluated in the field for groundwater monitoring. Adaptations for application in the vadose zone will be identified. An economical and uncomplicated system for measuring the properties of groundwater and its interaction with soil will directly benefit climate science, and will also have commercial applications in agriculture and water quality monitoring.