Increased Terrestrial Carbon Export and CO₂ Evasion From Global Inland Waters Since the Preindustrial Era

Global carbon dioxide (CO2) evasion from inland waters (rivers, lakes, and reservoirs) and carbon (C) export from land to oceans constitute critical terms in the global C budget. However, the magnitudes, spatiotemporal patterns, and underlying mechanisms of these fluxes are poorly constrained. Here, we used a coupled terrestrial-aquatic model to assess how multiple changes in climate, land use, atmospheric CO2 concentration, nitrogen (N) deposition, N fertilizer and manure applications have affected global CO2 evasion and riverine C export along the terrestrial-aquatic continuum. We estimate that terrestrial C loadings, riverine C export, and CO2 evasion in the preindustrial period (1800s) were 1,820 +/- 507 (mean +/- standard deviation), 765 +/- 132, and 841 +/- 190 Tg C yr(-1), respectively. During 1800-2019, multifactorial global changes caused an increase of 25% (461 Tg C yr(-1)) in terrestrial C loadings, reaching 2,281 Tg C yr(-1) in the 2010s, with 23% (104 Tg C yr(-1)) of this increase exported to the ocean and 59% (273 Tg C yr(-1)) being emitted to the atmosphere. Our results showed that global inland water recycles and exports nearly half of the net land C sink into the atmosphere and oceans, highlighting the important role of inland waters in the global C balance, an amount that should be taken into account in future C budgets. Our analysis supports the view that a major feature of the global C cycle-the transfer from land to ocean-has undergone a dramatic change over the last two centuries as a result of human activities.