Sensitivity of bulk sedimentary stable carbon isotopes to prehistoric forest clearance and maize agriculture

The stable carbon isotope compositions (δ13C) of tropical lake sediments and soils have been used to reconstruct the occurrence of prehistoric maize cultivation and its relative importance through time. This study assesses some of the possible variables affecting the response of lake sediment bulk organic carbon isotope (δ13CTOC) values to variations in the scale of prehistoric maize cultivation and the potential of this proxy to yield quantitative estimates of the scale of prehistoric maize agriculture in small tropical watersheds. High resolution analyses of δ13CTOC values, maize pollen concentrations, and mineral influx were conducted on sediments deposited during a ∼220 year period of prehistoric maize agriculture in the watershed of Laguna Castilla, a small lake in the mid-elevations of the Cordillera Central, Dominican Republic. Close correspondence between δ13CTOC values and maize pollen concentrations in the Laguna Castilla sediment record indicates a close relationship between the isotopic values and the scale of prehistoric maize cultivation. Correlations between the δ13CTOC signature and mineral influx indicate that the isotope record is also sensitive to variations in allochthonous carbon delivery. This study establishes that sedimentary δ13CTOC values can provide a highly sensitive proxy of the spatial scale of prehistoric maize agriculture in small tropical watersheds, but emphasizes the need for a better understanding of sediment dynamics and carbon cycling in anthropogenically modified landscapes before this proxy can be widely employed in diverse archaeological settings.