A new hypothesis for the origin of Amazonian Dark Earths

Lucas C. R. Silva (), Rodrigo Studart Corrêa, Jamie L. Wright, Barbara Bomfim, Lauren Hendricks, Daniel G. Gavin, Aleksander Westphal Muniz, Gilvan Coimbra Martins, Antônio Carlos Vargas Motta, Julierme Zimmer Barbosa, Vander de Freitas Melo, Scott D. Young, Martin R. Broadley and Roberto Ventura Santos
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Lucas C. R. Silva: University of Oregon
Rodrigo Studart Corrêa: University of Brasília
Jamie L. Wright: University of Oregon
Barbara Bomfim: University of Oregon
Lauren Hendricks: University of Oregon
Daniel G. Gavin: University of Oregon
Aleksander Westphal Muniz: Brazilian Agricultural Research Corporation - CPAA/Embrapa Amazônia Ocidental
Gilvan Coimbra Martins: Brazilian Agricultural Research Corporation - CPAA/Embrapa Amazônia Ocidental
Antônio Carlos Vargas Motta: University of Paraná
Julierme Zimmer Barbosa: Federal Institute of Southeast Minas Gerais
Vander de Freitas Melo: University of Paraná
Scott D. Young: University of Nottingham
Martin R. Broadley: University of Nottingham
Roberto Ventura Santos: University of Brasília

Nature Communications, 2021, vol. 12, issue 1, 1-11

Abstract: Abstract Amazonian Dark Earths (ADEs) are unusually fertile soils characterised by elevated concentrations of microscopic charcoal particles, which confer their distinctive colouration. Frequent occurrences of pre-Columbian artefacts at ADE sites led to their ubiquitous classification as Anthrosols (soils of anthropic origin). However, it remains unclear how indigenous peoples created areas of high fertility in one of the most nutrient-impoverished environments on Earth. Here, we report new data from a well-studied ADE site in the Brazilian Amazon, which compel us to reconsider its anthropic origin. The amounts of phosphorus and calcium—two of the least abundant macronutrients in the region—are orders of magnitude higher in ADE profiles than in the surrounding soil. The elevated levels of phosphorus and calcium, which are often interpreted as evidence of human activity at other sites, correlate spatially with trace elements that indicate exogenous mineral sources rather than in situ deposition. Stable isotope ratios of neodymium, strontium, and radiocarbon activity of microcharcoal particles also indicate exogenous inputs from alluvial deposition of carbon and mineral elements to ADE profiles, beginning several thousands of years before the earliest evidence of soil management for plant cultivation in the region. Our data suggest that indigenous peoples harnessed natural processes of landscape formation, which led to the unique properties of ADEs, but were not responsible for their genesis. If corroborated elsewhere, this hypothesis would transform our understanding of human influence in Amazonia, opening new frontiers for the sustainable use of tropical landscapes going forward.

Date: 2021
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DOI: 10.1038/s41467-020-20184-2

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