CO2 emissions from Chinese inland waters under global change

Abstract

Outgassing of carbon dioxide (CO2) from inland waters into the atmosphere is an important component of the global carbon cycle. Yet, fluxes of this evasion pathway remain uncertain due to the lack of spatially and temporally resolved CO2 measurements and water surface area estimates. Here we present seasonal and annual fluxes of CO2 emissions from Chinese inland waters (streams, rivers, lakes and reservoirs) and evaluate their changes over the past three decades. We estimate that the CO2 efflux from Chinese inland waters was 138±31 Tg C yr–1 in the 1980s and it declined to 98±19 Tg C yr–1 in the 2010s, with 88–93% of the emissions from streams and rivers. This significant decrease was likely caused by a combination of anthropogenic perturbations, including the conversion of flowing rivers to reservoirs, widespread eutrophication, and the implementation of reforestation programmes. However, we also report increased evasion rates from the Tibetan Plateau inland waters, which we relate to expanded surface area and enhanced lateral carbon export due to climate warming. We suggest that the CO2 emissions from Chinese inland waters have greatly offset the terrestrial carbon sink and are therefore a key component of China’s carbon budget.