Arising from the Wetlands: Mechanisms and Chronology of Landscape Aggradation in the Northern Coastal Plain of Belize

Research on human and environmental interactions in the Maya Lowlands has included important case studies of ancient water and soil management, impacts of climatic fluctuations, and diverse agricultural adaptations over millennia. Studies also have shed light on landscape and soil formation, including past periods of soil erosion and aggradation of several parts of these tropical lowlands. This study uses water, soils, radiocarbon, and archaeological data to determine the quantity, timing, and causes of aggradation in Belize's Three Rivers region in a series of sinks from the karst uplands into the coastal plain. Water sources in the uplands have low quantities of dissolved ions including sulfate, but water in the coastal plain has high amounts of dissolved ions and is nearly saturated in sulfate and calcium. Soil and geomorphic findings come from twenty-two excavations that uncovered more than 1,200 m2 of stratigraphy, representing a broader region. These extensive data serve to characterize and date stratigraphy, and exposures and four main excavations from the uplands into the wetlands of the coastal plain serve to intensively characterize soil profiles. We found that this landscape in the early to middle Maya Preclassic (1200 BC to 350 BC) was on average 1.2 m lower and mantled by what is now a distinct paleosol. From the Late Preclassic (350 BC–AD 250) to Classic periods (AD 250–900), the landscape aggraded by an average of 1.2 m from four possible sources: river flooding, local erosion, ancient Maya landscape manipulation, and gypsum precipitation from a rise in a water table nearly saturated in calcium and sulfate ions. Soil erosion is the main driver of the clastic sedimentation on upland valleys and fans, but water table rise is the main driver on the wetlands of the coastal plain because the aggraded sediments here are dominantly composed of gypsum, in which the groundwater is saturated. This latter type of aggradation, by the natural rise of a water table saturated in calcium and sulfate, represents a different mechanism from the more typical erosion-induced aggradation. This study shows that the ancient Maya confronted more natural hazards in the Classic period than just the well-known droughts of the eighth through tenth centuries AD, and in this case the Maya adapted to an environmental change so large that they had to adjust their land use strategies from well-drained to perennial wetland conditions.