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

湖泊沉积物是古环境信息的重要档案，在促进对过去气候和人与环境相互作用的科学认识方面发挥了关键作用。本论文旨在通过使用哥斯达黎加拉古纳宗丘的六个岩心网络来描述湖泊沉积物的空间变化，以评估湖泊沉积物研究中的一些常见假设。之前的古环境研究已经在宗丘建立了史前农业的记录。这项研究将以农业影响为地层标志，分析有机碳和稳定同位素组成的空间变化。每个岩芯将接受一套地球化学分析，包括大宗沉积物和特定于化合物的稳定碳同位素分析，以描绘史前农业的程度，使用特定于化合物的技术进行有机质表征和来源确定，以及分析稳定的氢同位素比率以提供水分平衡记录。通过地化分析创建的记录将增加来自农业区间的玉米花粉计数。这些数据将被组合在一起，以创建高分辨率的、空间上明确的有机碳组成记录。从这个数据集可以量化空间变化的程度。如果空间差异被证明是显著的，它可能会改变目前被接受的湖泊沉积物采样方法，并改进对依赖有机质分析的替代物的解释。这些记录之间的空间和时间上的一致将提供强有力的证据，证明多个核心可以在空间上清晰地重建史前农业。这些信息将对考古学家具有明显的实用价值，并将有助于理解湖泊与其周围分水岭之间的联系，这是朝着在湖泊沉积物中分离人为信号和气候信号的目标迈出的重要一步。了解人类与环境之间的关系对于准备应对当前的全球变化情景至关重要。这项研究的跨学科方面(地理学、地球化学学、考古学)将提供向广大受众交流成果的机会，并促进不同领域的科学家之间的合作。在这个项目中建立的记录可能对当地土地管理者、生态学家和保护生物学家特别有帮助，因为他们试图了解森林再生并将这一知识应用于重新造林退化的土地。关于热带山地前雨林的干扰和干扰恢复的详细信息特别重要，因为拉古纳宗丘附近地区不仅是哥斯达黎加生物多样性最丰富的地区之一，也是森林砍伐最严重的地区之一。

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.