Human and natural controls on erosion in the Lower Jinsha River, China. (February 2019)

• Record Type: Journal Article
• Authors: Schmidt, Amanda H.; Denn, Alison R.; Hidy, Alan J.; Bierman, Paul R.; Tang, Ya
• Is Part Of: Journal of Asian earth sciences. Volume 170(2019)
• Page Start: 351
• Page End: 359
• Publication Date: 2019-02
• Subjects: 10Be -- Landslides -- Erosion -- Yangtze River -- Sediment yield; Earth sciences -- Asia -- Periodicals; Sciences de la terre -- Asie -- Périodiques; Earth sciences; Asia; Periodicals; 555.05
• DOI: 10.1016/j.jseaes.2018.10.017
• Languages: English
• ISSNs: 1367-9120

Abstract

Highlights: Long-term sediment generation rates scale with mean basin slope throughout the lower Jinsha River. The ratio of contemporary sediment yield to long-term sediment generation is an average of five. People are raising sediment yield with agriculture and deforestation and lowering it with dams. Percent of basins with landslides is positively correlated to modern sediment yield. Abstract: The lower Jinsha River has the highest sediment yield rates of the entire Yangtze watershed; these high yields have previously been attributed to a mix of the local geologic setting as well as intensive human land use, particularly agriculture. Prior studies have not quantified long-term background rates of sediment generation, making it difficult to know if modern sediment yield is elevated relative to the long-term rate of sediment generation. Using in situ 10 Be in detrital river sediments, we measured sediment generation rates for tributaries to the lower Jinsha River. We find that the ratio of modern sediment yield to long-term sediment generation rate is 5.9 ± 2.8 (mean, 1 SD, n = 5), which is significantly higher than that elsewhere in western China and implies contemporary rates of sediment export far exceed long-term rates of sediment generation by weathering on hillslopes (1.9 ± 1.6 [median, 1 SD, n = 20]; [Schmidt et al., 2017]). Long-term (thousand year) rates of sediment generation correlate best with the steepness of the upstream watershed, a result found around the world. In contrast, modern sediment yield and the ratio of sediment yield to sediment generation rates correlate best with agricultural land use and distance to the nearest dam. Modern (1950s–1980s) sediment yield and the ratio of sediment yield to sediment generation rate also correlate well with percent of the watershed containing landslides observable today. The significantly higher modern sediment yield, lack of correlation between percent of the basin with landslides and long-term rates of sediment generation, and widespread deforestation and agriculture in the region suggest that landslide scars observable today are at least in part a result of human-induced land use change. Thus, we conclude that a mix of geologic setting and human activity control high contemporary sediment yield rates in the region.