MEASURING SOIL GAS FLUX IN DYNAMIC COASTAL ENVIRONMENTS WITH LOW-COST INSTRUMENTATION

Coastal tidal wetland environments are capable of sequestering carbon and regulating carbon dioxide (CO₂) flux, which influences the global climate. Traditional methods of directly measuring CO₂ flux involve collecting grab samples via expensive closed-chambered instrumentation placed over the sediment surface. An accessible soil gas well was designed and deployed to collect continuous and automated data of CO₂ flux in dynamic coastal environments with an overall cost that is four times lower than traditional methods.

Soil gas wells are constructed with polyvinyl chloride (PVC) pipes and contain a sensor to collect CO₂ gas concentrations. The well is constructed with a screen interval below the ground surface, allowing intake of the surrounding sediment. The well casing extends above the sediment surface and water column to protect the gas sensor from rising water levels. A flotational backflow check valve in the PVC well was designed to protect the gas sensor from king tides and storm surge. A release valve at the top of the well limits pressure build-up within the casing.

The CO₂ gas sensor is powered via a marine battery and solar panel. CO₂ gas concentrations and flux readings are acquired through cellular communication with the gas sensor, allowing remote access for data monitoring. The power and communication systems are deployed on a treated wooden platform above mean high tide water levels. The equipment is fastened to a dock float and post extensions, permitting equipment to rise in unusually high waters and gravitate when returning to steady-state water levels.

The economical soil gas well design provides insight into spatiotemporal fluctuations of CO₂ flux in remote tidal wetlands. Fluctuations of concern for analysis being conducted in North Inlet – Winyah Bay, SC includes variations of CO₂ flux during daily high tides, acute high-energy events, and disparities among geomorphic locations within the tidal wetland. The well design allows for easy manipulation to include sensors for other greenhouse gas (GHG) species of concern (e.g., methane, nitrous oxide). Dissemination of low-cost soil gas flux wells will expand GHG data sets by advancing accessibility to researchers, ultimately enhancing the global GHG flux projection of tidal wetlands.