Wetland geomorphology and paleoecology near Akab Muclil, Rio Bravo floodplain of the Belize coastal plain

Abstract

To understand wetland geomorphology and paleoecology, we collected a 2.6 m sediment core from a flooded swamp adjacent to the Maya archaeological site of Akab Muclil in the Maya Lowlands of northwestern Belize. The site of Akab Muclil has a known occupation that persisted from Early Maya Classic (1700–1350 BP) through the Terminal Maya Classic (1180–1050 BP) and into the Postclassic (1050–450 BP) and lies near a vast network of ancient Maya canal and field systems. We analyzed this core using a combination of paleoecological and geochemical techniques to determine the history of land use and natural change over time within this wetland. Accelerator Mass Spectrometry dating, pollen, charcoal analysis, micropaleontology, geochemical analysis, and magnetic susceptibility provide a suite of methods from which we interpret the geomorphic and ecological history of this wetland system. Four AMS dates from the length of the core provide us with an age model that runs from 1675 cal BP through the Maya Classic onward to the present. At the base of this system, soil composition and chemistry provide evidence that the system changed from a seasonally wet terrestrial soil to a perennially wet swamp, as the basal Mollisol soil lies buried by peats and calcareous sediments. This shift to a perennial wetland could be related to ancient Maya water management or a natural geomorphic change, though we suspect the former because of nearby ancient Maya large-scale geomorphic and hydrological manipulation in the form of intensive canalization and agriculture. Evidence of ancient Maya uses and impacts, including sedimentation, Zea mays pollen, and high charcoal counts occur from the lowest levels of the sequence through the Classic and into the Postclassic period. Above this level, the strata change to stable peats, laminated deposits of light gray/dark gray gypsum, authigenic carbonate, and layers of fibrist peat, with little evidence of human impact until recent increases in charcoal and phosphorous. This study, compared with other regional studies, indicates a later transition from terrestrial to wetland, later human impacts in the Postclassic, and a geomorphic impact record closely tied to the history of the adjacent site rather than broader land use trends.