Net landscape carbon balance of a tropical savanna: Relative importance of fire and aquatic export in offsetting terrestrial production. (13th August 2020)

• Record Type: Journal Article
• Authors: Duvert, Clément; Hutley, Lindsay B.; Beringer, Jason; Bird, Michael I.; Birkel, Christian; Maher, Damien T.; Northwood, Matthew; Rudge, Mitchel; Setterfield, Samantha A.; Wynn, Jonathan G.
• Is Part Of: Global change biology. Volume 26:Number 10(2020)
• Page Start: 5899
• Page End: 5913
• Publication Date: 2020-08-13
• Subjects: carbon dioxide -- fire‐related emissions -- fluvial carbon transport -- inland waters -- land carbon sink -- methane -- net ecosystem carbon budget -- seasonal wetland; Climatic changes -- Environmental aspects -- Periodicals; Troposphere -- Environmental aspects -- Periodicals; Biodiversity conservation -- Periodicals; Eutrophication -- Periodicals; 551.5
• DOI: 10.1111/gcb.15287
• Languages: English
• ISSNs: 1354-1013

Abstract

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 (ΣFaq ). Here, we determined the NLCB of a lowland catchment (~140 km 2 ) in tropical Australia over 2 years by evaluating net terrestrial productivity (NEP), fire‐related C emissions and ΣFaq (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 ΣFaq (−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 ΣFaq significantly offset NEP during the wet season, with a disproportionate contribution by single major monsoonal events—up to 39% of annual ΣFaq was exported in one event. We hypothesize that wetter and hotter conditions in the wet–dry tropics in the future will increase ΣFaq 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. Abstract : We examine the role of fire and aquatic export in offsetting the terrestrial carbon sink in a fire‐prone, monsoonal savanna area of the wet‐dry tropics. We find that while the area is a large carbon sink, fire emissions and aquatic export via rivers and seasonal wetlands reduce this sink by 13% and 7%, respectively. Aquatic export offsets the sink during the wetter months, whereas fire can shift the landscape to net carbon export during the dry season.