Net landscape carbon balance of a tropical savanna: relative importance of fire and aquatic export in offsetting terrestrial production

Duvert, Clément, Hutley, Lindsay B., Beringer, Jason, Bird, Michael I., Birkel, Christian, Maher, Damien T., Northwood, Matthew, Rudge, Mitchel, Setterfield, Samantha A., and Wynn, Jonathan G. (2020) Net landscape carbon balance of a tropical savanna: relative importance of fire and aquatic export in offsetting terrestrial production. Global Change Biology. (In Press)

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Abstract

The magnitude of the terrestrial carbon (C) sink may be overestimated globally due to the difficulty of accounting for all C losses across heterogeneous landscapes. More complete assessments of net landscape C balances (NLCB) are needed that integrate both emissions by fire and transfer to aquatic systems, two key loss pathways of terrestrial C. These pathways can be particularly significant in the wet-dry tropics, where fire plays a fundamental part in ecosystems and where intense rainfall and seasonal flooding can result in considerable aquatic C export (sigma F-aq). Here, we determined the NLCB of a lowland catchment (similar to 140 km(2)) in tropical Australia over 2 years by evaluating net terrestrial productivity (NEP), fire-related C emissions and sigma F-aq (comprising both downstream transport and gaseous evasion) for the two main landscape components, that is, savanna woodland and seasonal wetlands. We found that the catchment was a large C sink (NLCB 334 Mg C km(-2) year(-1)), and that savanna and wetland areas contributed 84% and 16% to this sink, respectively. Annually, fire emissions (-56 Mg C km(-2) year(-1)) and sigma F-aq (-28 Mg C km(-2) year(-1)) reduced NEP by 13% and 7%, respectively. Savanna burning shifted the catchment to a net C source for several months during the dry season, while sigma F-aq significantly offset NEP during the wet season, with a disproportionate contribution by single major monsoonal events-up to 39% of annual sigma F-aq was exported in one event. We hypothesize that wetter and hotter conditions in the wet-dry tropics in the future will increase sigma F-aq and fire emissions, potentially further reducing the current C sink in the region. More long-term studies are needed to upscale this first NLCB estimate to less productive, yet hydrologically dynamic regions of the wet-dry tropics where our result indicating a significant C sink may not hold.

Item ID: 64234
Item Type: Article (Research - C1)
ISSN: 1365-2486
Keywords: carbon dioxide, fire-related emissions, fluvial carbon transport, inland waters, land carbon sink, methane, net ecosystem carbon budget, seasonal wetland
Copyright Information: © 2020 John Wiley & Sons Ltd
Funders: Australian Research Council (ARC), Terrestrial Ecosystem Research Network (TERN), National Science Foundation (USA)
Projects and Grants: ARC DP160101497
Date Deposited: 02 Sep 2020 07:34
FoR Codes: 04 EARTH SCIENCES > 0402 Geochemistry > 040202 Inorganic Geochemistry @ 50%
04 EARTH SCIENCES > 0406 Physical Geography and Environmental Geoscience > 040608 Surfacewater Hydrology @ 50%
SEO Codes: 96 ENVIRONMENT > 9603 Climate and Climate Change > 960307 Effects of Climate Change and Variability on Australia (excl. Social Impacts) @ 40%
96 ENVIRONMENT > 9611 Physical and Chemical Conditions of Water > 961103 Physical and Chemical Conditions of Water in Fresh, Ground and Surface Water Environments (excl. Urban and @ 60%
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