Terrestrial-aquatic isotope sensor for in-situ field measurements

Ecological and biogeochemical processes occurring along coastal interfaces are poorly understood on a mechanistic level and critically underrepresented in current models, impeding our ability to make informed resource management decisions. Stable isotope ratio measurements, e.g., 13C/12C, can provide detail about pathways and sources by adding specificity and attribution information that concentration measurements alone are unable to capture. Currently, isotope measurements are obtained by collecting a relatively small number of samples and analyzing those off-site using a laboratory device. The proposed field sensor will open up the ability to significantly increase the temporal and spatial resolution of the measurements enabling a far more detailed study of shifting conditions, along with the ability to capture transients. We propose the development of a novel field sensor for in-situ monitoring of stable isotope ratios in terrestrial-aquatic interface (TAI) regions. The sensor utilizes mid-infrared (Mid-IR) laser absorption spectroscopy to uniquely identify and quantify molecular species (e.g., CH4, CO2, and their isotopologues). The concept uses a novel hollow fiber gas cell, which enables high sensitivity in a compact form factor appropriate for remote field use. The proposed work leverages recent development of both CO2 isotope sensors for laboratory rhizosphere analysis along with related CH4 isotope sensors for in-situ deep-sea vent/seep analysis. For this effort, we are proposing to apply, optimize, and specifically engineer these new developments to address needs at coastal TAI field sites. This will include further reductions in size, weight, and power (SWaP), along with networking and integration of complimentary sensors for “smart” utilization. The effort will be done in collaboration with DOE field scientists, who will both guide the development and test the resulting sensor systems. In Phase I, a methane isotope system will be assembled utilizing a new sampling front end that will be specifically optimized for TAI applications. A brassboard sensor package will be produced to prove the basic concept. The brassboard will be tested by DOE scientists to baseline the performance and explore aspects in need of further development. Results and user feedback from the testing will be utilized to design a higher Technology Readiness Level (TRL) system to be produced in Phase II. The resulting sensors will also be utilized for a range of commercial applications related to natural gas (e.g., methane) leak and attribution analysis.