Extreme Temperatures, Soil Moisture, and Flooding Drive Methane Fluxes in the Kati Thanda-Lake Eyre Basin, Central Australia

Drylands and dry inland waterways are increasingly recognized as important contributors to global carbon cycling, but little is known about their response to flooding. Using soil chambers and the headspace equilibrium method, methane concentrations were measured in the Kati Thanda-Lake Eyre Basin (KTLEB) from 2024 through 2025 to establish a seasonal baseline for methane flux across upland, floodplain, and river channels (dry and inundated). A subsequent rainfall event in 2025 induced significant flooding in the KTLEB which allowed us to characterize key conditions before, during, and after an episodic flood pulse.

Under dry conditions methane uptake occurred across all terrestrial sites during the winter (avg: -0.107 ± 0.056 mg/m^-2/d^-1) but many switched to producing methane in the summer (avg: 0.278 ± 0.124 mg/ m^-2/d^-1). Methane flux from inundated river channels averaged 2.5 ± 0.4 mg/ m^-2/d^-1 and 6.4 ± 1.4 mg/ m^-2/d^-1 during the winter and summer, respectively. Water-air methane fluxes from the inundated river channels were significantly higher than sediment-air methane fluxes, regardless of landscape position (upland, floodplain or dry river channel).

Wetting from rain just prior to the flood had little effect on methane fluxes. However, methane fluxes during the flooding event initially reached 40 ± 3.9 mg/m m^-2/d^-1 before rapidly decreasing to 5.6 ± 0.5 mg/ m^-2/d^-1. As floodwater receded, re-exposed floodplain soil produced the highest methane fluxes (max: 172, avg: 42.3 ± 22.7 mg/ m^-2/d^-1). Three months later, methane fluxes from the soil and water returned to near their pre-flood rate. This work advances our understanding of seasonal dynamics, including episodic flooding, on methane fluxes in drylands.