Discovery Magazine

Analysis and Detection of Amazonian Terra Preta Sites

Hyperspectral images generated from satellite-borne sensors provide information in many wavelengths. The hyperspectral imaging can be used to determine nutrient levels in plant leaf tips, and thereby provide information about the soil in which the plant is growing. Terra Preta soils (Amazonian black earths) are soils created by pre-Columbian peoples living in Amazonia. Some of these terra preta soils may be as much as 5,000 years in age, but most were produced about 1,000-2,000 years ago. Terra preta soils were formed by adding nutrients from ash, fish meal and feces to the natural soil. These enrichments made terra pretas agriculturally superior to the natural soils. Considerable uncertainty exists as to the full extent of these modified soils, and hyperspectral imaging offers a new airborne tool to identify their extent from space. In this proposal, remote-sensing, ground-truthed by fieldwork, will attempt to identify elevated nutrient staus and the presence of tera preta in poorly known areas of Amazonia.

Another aspect of this study is to incorporate existing soils data from published sources. The soil profiles with characteristics of terra preta will be mapped as will those that do not contain this modified soil. Until now, most maps prepared by archaeologists signal where terra preta was found, but they do not report their negative data, of where a search was made but no terra preta was discovered. Once the soils data are mapped, 20 environmental attributes will be used to characterize the environment where terra preta has been located. Models will be constructed of where terra preta is likely to occur, but has yet to be found. Additional soils analysis will be conducted to test whether the terra preta truly does fall in this geographic range. Terra preta is the strongest evidence available that indigenous people lived a non-nomadic existence and tended crops on a long-term basis; as we refine the maps of terra preta we are also discovering the geographic extent of long-term agriculture in Amazonia.

This fusion of hyperspectral imaging and field ecology complements ongoing research by Bush and his students to map pre-Columbian land use in western Amazonia.