Doctoral Dissertation Research: Interpreting Prehistoric Agriculture from Isotope and Pollen Indicators in Neotropical Lake Sediments: Do Multiple Cores Enhance Spatial Resolution?

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Lake sediments are important archives of paleoenvironmental information and have played a key role in advancing scientific understanding of past climates and human-environment interactions. This dissertation project seeks to evaluate some common assumptions in lake sediment research by using a network of six cores from Laguna Zoncho, Costa Rica to characterize spatial variations in lake sediments. Previous paleoenvironmental work has established a record of prehistoric agriculture at Zoncho. This study will use the agricultural impacts as stratigraphic markers to analyze spatial variation in organic carbon and stable isotope composition. Each core will be subjected to a suite of geochemical analyses including bulk sediment and compound-specific stable carbon isotope analysis to delineate the extent of prehistoric agriculture, organic matter characterization and source determination using compound-specific techniques, and analysis of stable hydrogen isotope ratios to provide a record of moisture balance. The record created by the geochemical analyses will be augmented with maize pollen counts from the agricultural intervals. The data will be combined to create a high-resolution, spatially explicit record of organic carbon composition. From this dataset it will be possible to quantify the extent of spatial variation. If spatial variation proves significant, it may transform the currently accepted approach to lake-sediment sampling and improve the interpretation of proxies that rely on organic matter analysis. Spatial and temporal coincidence between the records will provide strong evidence that multiple cores can create a spatially explicit reconstruction of prehistoric agriculture. This information will have obvious utility to archaeologists and will contribute to understanding of the linkages between a lake and its surrounding watershed, an important step toward the goal of separating anthropogenic and climate signals in lake sediments.Understanding relationships between humans and their environment are critical to preparing for current global change scenarios. The interdisciplinary aspect of this research (geographic, geochemical, archaeological) will provide an opportunity to communicate results to a wide audience and promote collaboration between scientists in different fields. The record constructed in this project may be particularly helpful to local land managers, ecologists, and conservation biologists as they seek to understand forest regeneration and apply this knowledge to reforesting degraded lands. The detailed information on disturbance and disturbance recovery in tropical premontane rainforest is especially important because the area near Laguna Zoncho is not only one of the most biologically diverse sectors of Costa Rica, but also one of the most deforested.