GREENHOUSE GAS PRODUCTION IN THE UPPER FLORIDAN AQUIFER: IMPLICATIONS FOR CARBON BIOGEOCHEMICAL CYCLING

Karstic groundwater systems are significant yet critically understudied sources and sinks of greenhouse gases, such as carbon dioxide and methane. These gases are often produced by microbes which may respond to varying temporal flow conditions linked to heterogeneous permeability of karst aquifers. To evaluate the correlation between greenhouse gas emissions and discharge, gas samples were collected using headspace extraction techniques from the Santa Fe River Sink-Rise system in north-central Florida, USA. The samples were analyzed for their CO₂ and CH₄ concentrations using Cavity Ring Down Spectrometry. Greenhouse gas concentrations increase along the conduit flow path from River Sink to River Rise reflecting greenhouse gas production in the subsurface. The total respective fluxes of CO₂ and CH₄ measured over the sampling period at the River Rise is approximately 3 kg/s and 0.02 kg/s. The generated CO₂ and CH₄ evades to the atmosphere when the water discharges back to the surface. These results reflect the potential importance of karst groundwater systems to atmospheric greenhouse gas concentrations.