Amazon Basin forest pyrogenic carbon stocks: First estimate of deep storage

Publication date: 15 November 2017
Source:Geoderma, Volume 306
Author(s): Nina Koele, Michael Bird, Jordahna Haig, Ben Hur Marimon-Junior, Beatriz Schwantes Marimon, Oliver L. Phillips, Edmar A. de Oliveira, C.A. Quesada, Ted R. Feldpausch
Amazon Basin forest soils contain considerable soil organic carbon stocks; however, the contribution of soil pyrogenic carbon (PyC) to the total is unknown. PyC is derived from local fires (historical and modern) and external inputs via aeolian deposition. To establish an initial estimate of PyC stocks in non-terra preta forest with no known history of fire, to assess site and vertical variability, as well as to determine optimal sampling design, we sampled 37 one hectare forest plots in the Amazon Basin and analysed PyC via hydrogen pyrolysis of three individual samples per plot and of bulked samples to 200cm depth. Using our data and published total organic carbon stocks, we present the first field-based estimate of total PyC stock for the Amazon Basin of 1.10 Pg over 0–30cm soil depth, and 2.76 Pg over 0–100cm soil depth. This is up to 20 times higher than previously assumed. Three individual samples per 1ha are sufficient to capture the site variability of PyC in our plots. PyC showed significant, large-scale variability among plots. To capture 50% of the PyC in 200cm soil profiles, soil must be sampled to a depth of at least 71cm. PyC represents a significant (11%) portion of total organic carbon in soil profiles 0–200cm depth. This finding highlights the potentially important role that historical fire has played in modifying soil C stocks. Our data suggest that PyC is an important carbon pool for long-term storage, involved in millennial scale biogeochemical cycling, particularly in the subsurface soil.