“…Alternatively, oxidation of POC biosphere during transit through river basins can fuel ecosystems downstream [Mayorga et al, 2005] and is a component of heterotrophic respiration, which is not included in ecosystem carbon budgets at the scale of forest plots [Malhi, 2012]. If the carbon is old, such as carbon stored over millennial time scales in soils [Galy and Eglinton, 2011;Hilton et al, 2015] and over longer time scales in sedimentary rocks as "petrogenic" POC (POC petro ) [Galy and Eglinton, 2011;Hilton et al, 2011a], its oxidation represents a source of CO 2 to the atmosphere not captured in most budgets [Bouchez et al, 2010;Hilton et al, 2014;Vihermaa et al, 2014Vihermaa et al, ]. et al, 2013Larsen et al, 2014], and because of the association between POC and clastic sediment, these locations also experience the highest measured rates of POC discharge [Milliman, 1995;Kao and Liu, 1997;Hicks et al, 2000;Lyons et al, 2002;Hilton et al, 2008a;Wheatcroft et al, 2010;Milliman and Farnsworth, 2011;Hilton et al, 2012;Stallard, 2012;Goñi et al, 2013;Hilton, 2017].…”