Global importance of Amazonian white-sand peat carbon

White sand ecosystems (WSE)- known locally as Campinarana, Campinarana florestada (in Brazil) or Caatinga Amazonica (Venezuela) are typically thin-stemmed, nutrient scarce, low canopy ecosystems located on sandy soils (podzols) distributed across the Amazon basin. It has been previously documented that WSEs can form histosol layers capable of storing significant carbon, but existing studies are limited in geographic scope and quantity of data points. Notably a new study measured up to 2m of peat in Colombian WSEs, but we lack a wider understanding of the distribution and dynamics of peat forming WSEs across Amazonia.

Here we undertake a simple spatial analysis, overlapping a recently published Amazon peat map with previously published WSE distributions. We combine this with recent carbon density data and insights gained from an in-depth study of Colombian white sand peatlands (WSP) by Winton et al. (in review).

We estimate a total white sand peatland area of 78,832 (40,403 – 117,133) km² across the Amazon basin, corresponding to 26% of all white sand ecosystems. The greatest concentration is in the Rio Negro basin in Brazil. We predict that 39%, 26%, 15% and 6% of Amazon basin WSE forests are underlain by peat in Venezuela, Brazil, Colombia and Peru respectively. We in turn estimate a total carbon stock of 3.86 (0.64–7.48) Pg C in the WSPs of the Amazon basin, comparable to that of the largest known peatland region in the South America- the Pastaza-Maranon Foreland Basin.

We conclude that WSPs are critically understudied ecosystems and represent a fundamental gap in our understanding of the Amazon basin carbon cycle. Crucially, no existing studies appear to be located in the most concentrated areas of peat, with Colombia being the only substantial WSP region to be densely sampled. Our results can inform future research priorities in WSPs.