Human impact on erosion patterns and sediment transport in the Yangtze River

• 40Ar/39Ar ages of detrital muscovite grains from the Yangtze River basin were dated.
• Muscovite data suggest that one tributary (the Min River) is the major contributor to the sands currently found in the delta.
• The sediment contribution calculated from muscovite and current sediment load data suggest an “old” and “young” erosion pattern, respectively.
• Human impact supersedes long-time natural factor control of erosion in the Yangtze River basin since ~ 1900 yr B.P.

Sediment load in rivers is an indicator of erosional processes in the upstream river catchments. Understanding the origin and composition of the sediment load can help to assess the influence of natural processes and human activities on erosion. Tectonic uplift, precipitation and run-off, hill slopes and vegetation can influence erosion in natural systems. Agriculture and deforestation are expected to increase the sediment yield, but dams and reservoirs can trap much of this sediment before it reaches the ocean. Here, we use major element composition and 40Ar/39Ar ages of detrital muscovites to constrain the sediment contribution of various tributaries to sedimentation in the Yangtze delta. The sediment contribution calculated from muscovite data was compared with that estimated from current sediment load data from gauging stations. Muscovite data show that the main contributor to the Yangtze delta sands is the Min River, while the current sediment load suggests that the Jinsha and Jialing rivers are the most important current contributors to delta sediments. We suggest that this difference reflects an “old” and “young” erosion pattern, respectively as medium grained muscovite could be transported much slower than suspended sediment load in the complex river-lake systems of the Yangtze River basin. These two different erosion patterns likely reflect enhanced human activity (deforestation, cultivation, and mining) that increasingly overwhelmed long-time natural factors controls on erosion since ~ 1900 cal years B.P.