Carbon transportation, transformation, and sedimentation processes at the land-river-estuary continuum.

In terrestrial ecosystems, carbon (C) transportation and C pool transformation processes both occur at the land-river-estuary continuum. Moreover, C budget and C balance processes are generally critical in achieving the C neutrality of terrestrial ecosystems. This study analyzes key C transportation processes at multiple interfaces that collectively constitute the land-river-estuary continuum, discusses C transportation and sedimentation processes at the land-river interface, and reveals aquatic plant C sequestration coupling processes and associated productivity. Transformation mechanisms of inorganic-organic C pools are also investigated here as well as a systematic evaluation of C transport flux within the different interfaces that constitute the land-river-estuary continuum. Results show that the net C sink of terrestrial ecosystems was 1.70 Pg C yr, wherein the gross primary productivity (GPP) of global terrestrial vegetation reached 123 Pg C yr, while rock weathering also consumed 0.30 Pg C yr of atmospheric carbon dioxide (CO). Subsequently, the C transported by the land-river-estuary continuum reached 1.70 Pg C yr. During this process, 0.20 Pg C is deposited and buried in inland water and 1.00 Pg C escapes from inland water systems each year. Therefore, only 0.85 Pg C is transported to the estuary. Finally, this study clarifies control mechanisms of C transportation and transformation processes at the land-river-estuary continuum. The aim of this study is to provide an important scientific basis for the quantitative analysis of C sources and sinks at the land-river-estuary continuum and C neutrality of the biosphere.