Ideas and perspectives : carbon leaks from flooded land : do we need to replumb the inland water active pipe?

Gwenaël Abril (1) , Alberto Vieira Borges (2)

1 BOREA - Biologie des Organismes et Ecosystèmes Aquatiques
2 Université de Liège

At the global scale, inland waters are a significant source of atmospheric carbon (C), particularly in the tropics. The active pipe concept predicts that C emissions from streams, lakes and rivers are largely fuelled by terrestrial ecosystems. The traditionally recognized C transfer mechanisms from terrestrial to aquatic systems are surface runoff and groundwater drainage. We present here a series of arguments that support the idea that land flooding is an additional significant process that fuels inland waters with C at the global scale. Whether the majority of CO 2 emitted by rivers comes from floodable land (approximately 10 % of the continents) or from well-drained land is a fundamental question that impacts our capacity to predict how these C fluxes might change in the future. Using classical concepts in ecology , we propose, as a necessary step forward, an update of the active pipe concept that differentiates floodable land from drained land. Contrarily to well-drained land, many wetlands (in particular riparian and littoral wetlands) combine strong hydrological connectivity with inland waters, high productivity assimilating CO 2 from the atmosphere, direct transfer of litter and exudation products to water and waterlogged soils, a generally dominant allocation of ecosystem respiration (ER) below the water surface and a slow gas-exchange rate at the water-air interface. These properties force plants to pump atmospheric C to wetland waters and, when hydrol-ogy is favourable, to inland waters as organic C and dissolved CO 2. This wetland CO 2 pump may contribute disproportionately to CO 2 emissions from inland waters, particularly in the tropics where 80 % of the global CO 2 emissions to the atmosphere occur. In future studies, more care must be taken in the way that vertical and horizontal C fluxes are conceptualized along watersheds, and 2-D models that adequately account for the hydrological export of all C species are necessary. In flooded ecosystems, significant effort should be dedicated to quantifying the components of primary production and respiration by the submerged and emerged part of the ecosystem community and to using these metabolic rates in coupled hydrological-biogeochemical models. The construction of a global typology of wetlands that includes productivity, gas fluxes and hydrological connectivity with inland waters also appears necessary to adequately integrate continental C fluxes at the global scale.

Domaines: Géochimie; Interfaces continentales, environnement

Gwenaël Abril, Alberto Vieira Borges. Ideas and perspectives : carbon leaks from flooded land : do we need to replumb the inland water active pipe?. Biogeosciences, 2019, 16 (3), pp.769-784. ⟨10.5194/bg-16-769-2019⟩. ⟨hal-02104953⟩