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Main question: Differentiate the major drivers and chronology of erosion and aggradation in the fluvial and fluviokarst landscapes of the southern and central Maya Lowlands

Types of evidence used: From 1991-2007 we sampled and analyzed water and soil chemistry and excavated scores of trenches in transects across the major sinks of the Maya Lowlands, from upland natural karst and anthropogenic depressions to footslopes, to alluvial fans, to flood-plains, and to the wetlands of the coastal plain of northern Belize.

Conclusions: The majority of evidence, reconstructed from sediment chemistry,artifacts, ecofacts, and from modern analogs, shows that human induced deforestation and erosion was the main cause of accelerated erosion and aggradation in all sinks except those located on the coastal plain floodplains and depressions. Here the aggraded sediments are dominantly gypsum rich sediments with thin Histosols and short-term paleosols, rather than the carbonate and silicate clays that we found in the upland sediments and slope soils. This fourth mechanism of aggradation corresponds to sea level rise inducing wetland and peat formation and forcing up water tables nearly saturated with sulfate and calcium. The sediment chemistry parallels the groundwater chemistry over a 100 km expanse across the coastal plain to the sea. Eroded sediment and human manipulation contributed to this aggradation but because gypsum, which comes from groundwater, overshadows the mineralogy, evaporite formation from rising water tables is the probable explanation for coastal plain aggradation. Thus, aggradation has several causes in this region, but the two main drivers are different ones for adjacent geomorphic landscapes, though they are deceptively similar to the naked eye