Filling the gap: Estimating Australia’s riverine carbon gas emissions

In order to understand aquatic carbon export in a changing world, we must first understand the baseline. Compared to North America and Europe, Australia has significantly fewer observations of CO₂ and CH₄ in streams and rivers, particularly in the tropical regions. We used synoptic sampling of 164 different headwater streams in three tropical sub-climates (humid, wet-dry and semi-arid) and the temperate region of Australia to try to better quantify the greenhouse gas (GHG) emissions from headwater streams in both spatial and temporal contexts. Across all four regions, CO₂ and CH₄ concentrations were 163.8  and 1.7 μmol L^-1, significantly higher than previously reported global medians for all stream orders, respectively. Significant spatial variation occurred between the tropical and temperate zones as well as across the tropical sub-climates. Temporally, while gas concentration varied only minimally, gas evasion varied significantly between seasons in the tropics, particularly in the semi-arid and wet-dry tropics where at least 85% and 54% of streams were seasonally ephemeral, respectively. This seasonal change in flow regime not only reduces surface areas of streams but the lower flow rate and velocity reduce the gas transfer velocity. These changes in surface area and gas transfer velocity show that hydrology drives seasonal changes rather than the availability of either gas. These data both demonstrate the need for spatially and temporally diverse (at both global and regional scales) training data for global upscaling efforts, as well as highlight Australia as a potential hotspot for GHG emissions on a global scale. 

Primary Presenter: Adam Rexroade, Charles Darwin University (rexroadea@gmail.com)

Authors:

Adam Rexroade, Research Institute for the Environment and Livelihoods, Charles Darwin University, Darwin, Northern Territory, Australia  (rexroade@cdu.edu.au)

Francesco Ulloa-Cedamanos, Research Institute for the Environment and Livelihoods, Charles Darwin University, Darwin, Northern Territory, Australia  (francesco.ulloacedamanos@cdu.edu.au)

Marcus Wallin, Department of Aquatic Sciences and Assessment, Swedish University of Agricultural Sciences, Upsala, Sweden  (Marcus.Wallin@slu.se)

Clément Duvert, Research Institute for the Environment and Livelihoods, Charles Darwin University, Darwin, Northern Territory, Australia  (clem.duvert@cdu.edu.au)