Predicting Hot Spots and Hot Moments of Biogenic Gas Accumulation and Release in a Subtropical Ecosystem Using Airborne Ground-Penetrating Radar
Authors
Xavier Comas1* (xcomas@fau.edu), Neil Terry 2, Caiyun Zhang 3
Institutions
1Department of Geosciences, Florida Atlantic University, Davie, FL; 2 New York Water Science Center, U.S. Geological Survey, Troy, NY; 3Department of Geosciences, Florida Atlantic University, Boca Raton, FL
Abstract
Peat soils are major terrestrial carbon stores and large natural producers of biogenic greenhouse gases (i.e., methane and carbon dioxide). These gases accumulate in the soil matrix to be subsequently released to the atmosphere, therefore directly influencing climate change. While recent advances have been made with regards to the prediction of carbon fluxes, many uncertainties still exist to properly understand the spatial distribution of hot spots and hot moments for the accumulation and release of biogenic gases. This can be attributed to the limitations in terms of effective noninvasive methods that can be deployed at scales of measurement relevant for the imaging and identification of such hot spots.
This project has been testing a prototype ground-penetrating radar (GPR) unit (the Geodrone 80 from Mala) mounted on a small unoccupied aircraft system (sUAS) to efficiently identify the presence of hot spots and hot moments in subtropical peat soils of the Everglades and explore how certain physical (i.e., soil structure) and biochemical properties (i.e., metabolic pathway) may influence its dynamics. Delays with drone acquisition and study site selection due to changes in drone legislation in Florida initially shifted efforts to laboratory simulations, where a set of high frequency antennas were suspended over a peat monolith (extracted from the Water Conservation Area, WCA1 in the Everglades) using a custom-made rail system that allowed for the antenna to move autonomously (simulating airborne measurements using a drone) that were able to successfully monitor changes in dielectric permittivity associated with biogenic gas build up and release over a period of several months. At the field scale, an initial set of drone measurements using Mala’s 80 MHz Geodrone were collected from two locations in the WCA2, Everglades. At each of these two locations, Geodrone flights were programmed to collect data in a grid over an approximate 100 m2 area. These preliminary airborne results via the Geodrone show promise for generating maps of static gas content distribution across the peat column as based on changes in EM wave travel time when peat thickness is known (or assumed constant over specific areas). Furthermore, these measurements will be expanded into time-lapse mode in order to define temporal changes in EM wave travel time across the peat column associated with the build-up and release of biogenic gases that will allow researchers to efficiently isolate the presence of hot spots for gas accumulation and release.