Aquatic carbon fluxes dampen the overall variation of net ecosystem productivity in the Amazon basin: An analysis of the interannual variability in the boundless carbon cycle. (15th April 2019)

• Record Type: Journal Article
• Authors: Hastie, Adam; Lauerwald, Ronny; Ciais, Philippe; Regnier, Pierre
• Is Part Of: Global change biology. Volume 25:Number 6(2019)
• Page Start: 2094
• Page End: 2111
• Publication Date: 2019-04-15
• Subjects: Amazon -- boundless carbon cycle -- carbon -- CO2 evasion -- ENSO -- floodplains -- interannual variation -- NEP; Climatic changes -- Environmental aspects -- Periodicals; Troposphere -- Environmental aspects -- Periodicals; Biodiversity conservation -- Periodicals; Eutrophication -- Periodicals; 551.5
• DOI: 10.1111/gcb.14620
• Languages: English
• ISSNs: 1354-1013

Abstract

Abstract: The river–floodplain network plays an important role in the carbon (C) cycle of the Amazon basin, as it transports and processes a significant fraction of the C fixed by terrestrial vegetation, most of which evades as CO2 from rivers and floodplains back to the atmosphere. There is empirical evidence that exceptionally dry or wet years have an impact on the net C balance in the Amazon. While seasonal and interannual variations in hydrology have a direct impact on the amounts of C transferred through the river–floodplain system, it is not known how far the variation of these fluxes affects the overall Amazon C balance. Here, we introduce a new wetland forcing file for the ORCHILEAK model, which improves the representation of floodplain dynamics and allows us to closely reproduce data‐driven estimates of net C exports through the river–floodplain network. Based on this new wetland forcing and two climate forcing datasets, we show that across the Amazon, the percentage of net primary productivity lost to the river–floodplain system is highly variable at the interannual timescale, and wet years fuel aquatic CO2 evasion. However, at the same time overall net ecosystem productivity (NEP) and C sequestration are highest during wet years, partly due to reduced decomposition rates in water‐logged floodplain soils. It is years with the lowest discharge and floodplain inundation, often associated with El Nino events, that have the lowest NEP and the highest total (terrestrial plus aquatic) CO2 emissions back to atmosphere. Furthermore, we find that aquatic C fluxes display greater variation than terrestrial C fluxes, and that this variation significantly dampens the interannual variability in NEP of the Amazon basin. These results call for a more integrative view of the C fluxes through the vegetation‐soil‐river‐floodplain continuum, which directly places aquatic C fluxes into the overall C budget of the Amazon basin. Abstract : We apply the ORCHILEAK model to analyse the interannual variability in the boundless carbon cycle of the Amazon basin. We show that the export of carbon to, and CO2 evasion from, the river‐floodplain network is highly interannually variable‐ greatest during wet years and lowest during droughts. However, overall net ecosystem productivity (NEP) and carbon sequestration are also highest during wet years, partly due to reduced decomposition in water‐logged floodplain soils. Furthermore, we find that aquatic carbon fluxes display greater variation than terrestrial fluxes, and that this variation dampens the interannual variability in NEP of the Amazon by moderating terrestrial variation.