Maize pollen concentrations in Neotropical lake sediments as an indicator of the scale of prehistoric agriculture

We evaluated the potential of maize pollen concentrations in lake sediment profiles to serve as indicators of the extent of prehistoric agriculture in neotropical lake basins using records from a network of five sediment cores recovered from Laguna Zoncho, Costa Rica. The watershed of this small (0.75 ha) lake in the Diquis archaeological region has a c. 3000 year history of prehistoric agriculture and subsequent forest recovery, as documented through previous studies of pollen, charcoal, diatoms, and phosphorus fractions in a single core recovered from the center of the lake. In our new network of cores, we compared maize pollen concentrations with two independent proxies for the scale of agriculture in the same cores: abundance of organic matter (OM), which is an indicator of soil erosion, and bulk sediment stable carbon isotope ratios of organic matter (delta C-13(OM)), which reflect the proportion of forested and cleared land within the watershed. In none of the five cores did maize pollen concentrations correspond with either OM or delta C-13(OM), suggesting that sedimentary maize pollen concentrations are not sensitive to the scale of maize agriculture in small neotropical watersheds. We found maize pollen in relatively high concentrations in two of the four cores taken near the lakeshore, but the others contained little or no maize pollen. The core from the center of the lake consistently recorded maize pollen, a finding that we attribute to sediment-focusing processes.