4 research outputs found
Intentional creation of carbon-rich dark earth soils in the Amazon
Fertile soil known as Amazonian dark earth is central to the debate over the size and ecological impact of ancient human populations in the Amazon. Dark earth is typically associated with human occupation, but it is uncertain whether it was created intentionally. Dark earth may also be a substantial carbon sink, but its spatial extent and carbon inventory are unknown. We demonstrate spatial and compositional similarities between ancient and modern dark earth and document modern Indigenous practices that enrich soil, which we use to propose a model for the formation of ancient dark earth. This comparison suggests that ancient Amazonians managed soil to improve fertility and increase crop productivity. These practices also sequestered and stored carbon in the soil for centuries, and we show that some ancient sites contain as much carbon as the above-ground rainforest biomass. Our results demonstrate the intentional creation of dark earth and highlight the value of Indigenous knowledge for sustainable rainforest management
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Estimating soil carbon in southern Amazon late Holocene anthropogenic landscapes containing archaeological 'dark earth' Anthrosols
Amazonian dark earths (ADE) are anthropogenic soils with concentrated carbon and nutrients that formed mainly during the latter half of the Holocene, prior to the arrival of Europeans, but are still forming on a more limited scale up to the present in indigenous communities. ADE, a result of domestic, economic, and agricultural activities in and around human settlements, are noted for their extraordinary fertility and resilience and for the significant quantities of organic carbon, much in the form of charcoal. The deepest and most extensive areas of ADE are generally located on the bluffs of major rivers adjacent to floodplains, but significant areas of ADE have also been found in floodplains and in headwater and interfluvial areas. Our research aims to shed light on the distribution of modified soils in distinct regions of the Amazon in relation to landforms and the environment. Research on ADE has led to the development of a 'biochar' industry that promotes the incorporation of charcoal into the soil for the dual purpose of improving fertility and sequestering carbon, but the potential for large-scale carbon storage in anthropogenic soils is unclear, in part because the amount of carbon already stored in ADE is unknown as there is a notable lack of research attempting to quantify the carbon over the scale of a site or region. We undertook this challenge in the Upper Xingu region of southeastern Amazonia in partnership with the local Kuikuro indigenous community who have shared their valuable traditional knowledge on the creation and management of ADE. We used data from over 3500 soil samples from diverse contexts, both ancient and modern, that we collected and analyzed over the past two decades for organic carbon and a range of other chemical and physical properties that can serve as proxies for soil modification by humans. Dark earth samples from profiles down to 1 m depth in archaeological sites ranged from 20% to 150% more OC than unmodified forest soil and dark earth profiles in current and historic villages ranged from 20-90% more organic carbon. We used the results from soil sample transects to estimate the carbon in landuse zones within and surrounding modern, historic, and ancient settlement sites. In continuing work, we are attempting to use satellite remote sensing and AI to extrapolate our results across a larger region
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Remote sensing and machine learning reveal abundance and patterns of Amazonian dark earth
Amazonian dark earth (ADE) is anomalously fertile and carbon-rich soil created by past inhabitants of the Amazon basin. Despite its importance to cultural heritage and carbon sequestration, efforts to systematically map the distribution and extent of ADE are hindered by difficulties of access and field excavation. To circumvent these barriers, we use a machine-learning classifier applied to remote sensing imagery to predict the occurrence of ADE across the 26,000 km (super 2) Xingu Indigenous Territory (XIT). We compile training data derived from field excavation and mapping as well as spectrally distinct vegetation patches, with which we train a random-forest classifier on a two-season Landsat 5 composite image to produce classification maps for the XIT with predicted locations of ADE. We predict 710 km (super 2) of ADE within the XIT (approximately 2.7% of the landscape by area) and find a strong correspondence between ADE locations and topography, with sites located along the edges of bluffs adjacent to river floodplains and tributary streams. We further estimate that the XIT may hold 7 Mt of anthropogenic carbon within ADE deposits