Agricultural land use doubled sediment loads in western China's rivers

Abstract

Land use changes, such as deforestation and agricultural expansion, increase soil erosion on the scale of hillslopes and small drainage basins. However, the effects of these changes on the sediment load in rivers is poorly quantified, with a few studies scattered globally, and only 10 data points in the world's most populous nation, China. At 20 different sites in western China, we compare contemporary fluvial sediment yield data collected daily over 4 to 26 years between 1945 and 1987 (median=19years) to long-term measures of sediment generation based on new isotopic measurements of in situ 10 Be (beryllium-10) in river sediments. We find that median sediment yield at these sites exceeds background sediment generation rates by a factor of two (from 0.13 to 5.79 times, median 1.85 times) and that contemporary sediment yield is statistically significantly different from long-term sediment generation rates (p < 0.05). Agricultural land use is directly and significantly proportional to the ratio of contemporary sediment yield to long term sediment generation rates (Spearman correlation coefficient rho=0.52, p < 0.05). We support these findings by calculating erosion indices, which compare the delivery of meteoric 10 Be to each watershed with the export of meteoric 10 Be bound to riverine sediment. Erosion indices are also directly and significantly proportional to agricultural land use (rho=0.58, p < 0.05). Together, these data sets suggest that upstream agricultural land use has significantly increased sediment supply to rivers in western China, likely increasing turbidity and decreasing ecosystem services such as fisheries.