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类-环境相互作用的科学认识方面发挥了关键作用。 本论文项目旨在评估一些常见的假设，在湖泊沉积物研究中使用的网络，从拉古纳宗乔，哥斯达黎加，以表征湖泊沉积物的空间变化。 先前的古环境工作已经在宗乔建立了史前农业的记录。 本研究将利用农业影响作为地层标志，分析有机碳和稳定同位素组成的空间变化。 将对每个岩芯进行一套地球化学分析，包括大量沉积物和特定化合物的稳定碳同位素分析，以划定史前农业的范围，使用特定化合物技术确定有机物的特性和来源，并分析稳定氢同位素比率，以提供水分平衡记录。 地球化学分析所创造的记录将增加农业间隔的玉米花粉计数。 这些数据将被合并，以创建一个高分辨率的，空间上明确的有机碳组成记录。 从这个数据集，将有可能量化空间变化的程度。 如果空间变化证明是重要的，它可能会改变目前接受的方法，湖泊沉积物采样，并改善依赖于有机物分析的代理解释。 这些记录之间的时空重合将提供强有力的证据，证明多个岩心可以在空间上清晰地重建史前农业。 这些信息将有明显的实用性，考古学家，并将有助于了解湖泊及其周围的流域之间的联系，朝着分离湖泊沉积物中的人为和气候信号的目标迈出了重要一步。了解人类与环境之间的关系是至关重要的，为当前的全球变化情景做好准备。 这项研究的跨学科方面（地理，地球化学，考古学）将提供一个机会，向广大受众传达结果，并促进不同领域科学家之间的合作。 本项目中构建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，并将这些知识应用于退化土地的造林。 关于热带山前雨林的干扰和干扰恢复的详细资料特别重要，因为拉古纳宗乔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，而且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.