Abril G. and Borges A.V. (2019) Ideas and perspectives: Carbon leaks from flooded land: do we need to replumb the inland water active pipe? Biogeosciences 16, 769–784.
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 fuelled by terrestrial ecosystems. The traditionally recognized C transfer mechanisms from terrestrial to aquatic systems are surface runoff and groundwater drainage. Based on classical concepts in ecology, and a literature survey, we highlight the importance of flooded land as a preferential source of terrestrial carbon to aquatic systems at the global scale. Contrarily to well-drained land, most wetlands combine strong hydrological connectivity with inland waters, high productivity assimilating CO2 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 hydrology is favourable, to inland waters as organic C and dissolved CO2. This wetland CO2 pump may contribute disproportionately to CO2 emissions from inland waters, particularly in the tropics where 80 % of the global CO2 emissions to the atmosphere occur. Studies in terrestrial and aquatic ecosystems could be reconciled by considering the occurrence of an efficient wetland CO2 pump to river systems. In future studies, wetland 2-D conceptual models must adequately account for the hydrological export of all C species. The construction of a global typology of wetlands that includes productivity, gas fluxes and hydrological connectivity with inland waters also appears necessary to quantify carbon exchange between continental surfaces and the atmosphere.
BOREA contact: Gwenaël Abril, gwenael.abril@mnhn.fr
