Collaborative Research: Deciphering connections among land management, soil erosion, and sediment yield in large river basins

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Amanda Schmidt, Paul Bierman, Dylan RoodOberlin College, University of Vermont, University of California ? Santa BarbaraThis project will combine a daily record of sediment yield with isotopic inventories to decipher the connections among land use, soil erosion, and sediment yield in 4 large rivers draining the Tibetan Plateau. Sediment yield data, measured daily for 44 stations, each with up to 27 years of daily sediment concentration and discharge records, suggest that in these basins there is no systematic increase in sediment yield over time despite significant, and well-documented, land clearance. The investigators will combine the sediment yield data with analysis of 3 isotopic systems to understand why 30 years of extensive deforestation did not change sediment yield. Their isotopic analyses will document sediment sources, sinks, and rates of movement. They will use one isotopic system, in situ 10Be, to calculate background erosion rates integrated over millennial timescales; rates that can be compared to modern sediment yield data. A second isotopic system, meteoric 10Be, will be a tracer for sediment mixing from heavily disturbed and less-disturbed regions, and can additionally be combined with sediment yields to estimate soil loss. The third isotopic system, 137Cs and 210Pb, will allow investigators to determine how much sediment in transport comes from deep gully/landslide erosion and how much comes from near surface sediment sources. This project will provide background erosion rates that can be compared to modern sediment yield data. Furthermore, the work will provide a robust means of identifying sub-basins that are heavily disturbed and are losing soil, even if much of that soil is not making it into the river network. Geomorphic mapping, both in the field and through remote sensing, will determine where and how much eroded sediment is stored on the landscape as colluvium and in terraces. This project will provide information about how land-use affects soil erosion and sediment yield at different spatial and temporal scales, critical data for implementing meaningful land-use policies in mountainous regions around the world. The Chinese government is building a series of dams in the study area, the source of fresh water for nearly 2 billion people. Understanding the time scales over which sediment moves off slopes, into channels, and downstream is critical for determining the life span of these and other dams in mountainous areas worldwide. This project will bring together an early career faculty member at an exceptional undergraduate institution, a senior researcher who directs a state-of-the-art research facility, and an early career scientist at a research facility in order to achieve maximum enrichment of both undergraduate science education and pedagogical training for the doctoral students.