ANTHROPOGENIC LANDSCAPE MODIFICATION ON A MAYA LOWLANDS TROPICAL CATENA

Ongoing geoarchaeological investigations in the Three Rivers Region since 1995 indicate the ancient Maya greatly altered their surrounding landscape to maximize agricultural productivity; these modifications include the building of terraces and drainages, truncating backslopes, and aggrading footslopes. At the urban site of La Milpa and its immediate surroundings, terrace and drainage construction peaked during the Late Classic period (ca. 550 – 850 A.D.), a time of heightened population pressure and increasing environmental instability. Geochemical characterization and carbon isotope (δ¹³C) analysis were used in association with archaeological excavations to understand the nature of human alteration of the landscape. A catena was excavated across an 8m-high limestone slope in tropical forest area that was culturally modified to support and stabilize a high volume of sediment. Using major elemental concentrations across the catena, we derived a measure (Ca + Mg) / (Al + Fe + Mn) of the relative age of soil catenas. At the crest, on the inside of the terrace, we found low (Ca + Mg) / (Al + Fe + Mn) ratios in a Ab horizon and high ratios in the C, AC, and A horizons above, indicating the relative youth of the horizons associated with terrace use. Further, carbon isotopes (δ¹³C) provided strong evidence for C₄ species in the ancient terrace soil (of which Zea mays, or maize, is the principal plant associated with ancient Maya habitation) but only evidence for C₃ species (like tropical trees) on the backslopes and other crest-shoulders, suggesting the use of the terrace for crop agriculture or that backslope soils eroded and then developed since Maya abandonment. This research sheds light into human impacts on landscapes during periods of terrace construction and use, the result of a strategy to stabilize cultivable sediment and maximize crop yields at a time when food security represented a challenge for the communities of the Three Rivers Region.