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Mongolia

Quantifying Long-Term Human Impacts to the Landscape using Soils and Sediments on the Yunnan Plateau of Southwestern China

Human activities including agriculture (e.g. irrigation, drainage, terracing), metallurgy (e.g. mining, processing, smelting), and deforestation have altered cycles of erosion and sedimentation for thousands of years. In the Yunnan province of southwestern China, where written records are incomplete, it is unclear when, where, and how much disturbance occurred. Moreover, the Yunnan Plateau inherits a legacy of metal contamination beginning with Bronze Age metallurgy. Lake sediments offer a means to investigate both the history of erosion/sedimentation and ancient metallurgy using geochemical signatures combined with stable isotopic compositions and physical properties of the sediment to identify sediment source. Reconstruction of parallel historical processes allows examination of the interactions among processes, particularly assessment of the remobilization of legacy contamination and contributions to legacy effects. However, proper interpretation of lacustrine sediment records requires comprehensive understanding of the catchment processes that control erosion/sedimentation and sediment transport (both fluvial and aeolian). In particular, in regions sensitive to variable monsoonal strength including the Yunnan, it is important to differentiate between “natural” and human-induced processes as climate change can substantially impact the landscape and therefore the sediment record. The proposed research will focus on a set of lakes and their catchments to clarify these processes and interactions, enhance regional models, and develop widely applicable analytical frameworks that can be applied to the greater region as well as other locations around the world.

One of the challenges in understanding human impacts on sediment dynamics is the difficulty in measuring a clear baseline. This is growing even more challenging with the increasing recognition of the importance of legacy sediment in fluvial systems. In areas with long periods of human habitation, these challenges are greater. In addition, while sediment transport is fundamental to the fate and remobilization of legacy metal contamination, careful examination of sediment and metal dynamics is relatively rare, particularly over extended temporal periods. The proposed research builds on a growing body of data to reconstruct histories of regional climate, human manipulation of lake levels, nutrient status changes, and legacy contamination loadings in a set of adjacent lakes on the Yunnan Plateau of southwestern China. Soil and sediments in the contributing areas will be similarly characterized to develop an understanding of potential contributors to modern sediment loads. When combined, these records provide the means to partition sediment contamination in lakes between direct loading during periods of historical metallurgical activity and sediments historically contaminated during these periods, but remobilized later due to other human activities. This distinction clarifies our understanding of the role of legacy contamination in contemporary catchment process.

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