Lake Sediment Records Examining the Spatial and Temporal Connections of Human Activity and Climate Change in Southwestern China

In regions of the world with long histories of human occupation, both natural environmental change and anthropogenic activities have impacted lake sediment dynamics over several millennia. The Yunnan Plateau of southwestern China is primarily impacted by the Indian Summer Monsoon (ISM) whose variability controls hydrologic balance. Despite the importance of the ISM as a critical water resource, we lack continuous terrestrial records of the ISM over a wide enough spatial gradient to understand its variability over multi-decadal time scales. Yunnan also has an extensive history of settlement, agriculture, and mineral resource extraction next to lakes, creating challenges in separating the impacts of recent disturbance from earlier activities. This dissertation will 1) establish records of anthropogenic impacts to lake sediment dynamics, 2) create records of hydrologic balance from lakes to understand ISM variability over the Holocene/Pleistocene, and 3) examine the intersection between climate variability and human activity around lakes to examine societal responses to changing water availability.\ud Utilizing a multi-proxy approach, including sedimentology and stratigraphy, stable isotopes of authigenic carbonate minerals and organic matter, and trace element geochemistry, this research characterizes the nature, timing, and magnitude of both anthropogenic disturbance and climate variability to four lakes in Yunnan: Xing Yun, Erhai, Chenghai, and Dian. Results show that prior to ~2,000 years BP, shifts in hydrologic balance are generally in phase with insolation forcing. Several abrupt drops in ISM strength are inferred over the Holocene and agree with other records of ISM variability from the Tibetan Plateau. Over the last 2,000 years, records of climatic change are overwritten by pre-industrial human activities including soil erosion, eutrophication, heavy metal pollution, and hydrologic modification. The scale of such activities is either equal or greater than modern-day impacts, suggestive of a several millenia legacy that likely contributes to contemporary environmental challenges