Sediment in rivers plays an essential role in the river and watershed ecosystems. A recent paper (Science, 24 June 2022, p. 1447-1452) reported widespread decreases in river sediment fluxes for major rivers in the North Hemisphere and concluded that these decreases mainly resulted from dam construction. 

 Generally, the spatial and temporal variations in river sediment are regulated by climate change and human activities, including precipitation, land cover and land use, damming, and dredging activities. In addition to dams, what is the contribution of changes in land cover to the decrease in sediment flux in rivers? 

 Recently, a research team led by Dr. CAO Zhigang and Prof. DUAN Hongtao (Nanjing Institute of Geography and Limnology, Chinese Academy of Sciences, China) and Prof. YANG Hong (University of Reading, the UK), collected long-term in-situ sediment flux data from seven major rivers in China. The team found that large dams on the Yangtze River, Zhu River, and Yellow River significantly reduced the sediment fluxes in the first 5-10 years following dam construction. However, the sediment fluxes in these rivers did not continue to decrease as before but even increased. 

 Their findings were published in Science Bulletin on October 30, 2023. 

 “Besides dams, there must be other factors that continuously reduce sediment fluxes after dams have been operational for many years,” said Prof. DUAN. 

 The researchers further used satellites to obtain a long-term dataset of vegetation coverage and suspended sediment concentration in China’s major rivers. The team found that vegetation cover in river catchments significantly increased in the 1980s and correlated well with the variations in sediment concentration. 

 “The variations in sediment fluxes in estuaries resulted from the combined effects of dams and land cover change in the watershed,” said Dr. CAO. 

 “Undoubtedly, anthropogenic activities have altered the landscape in the watershed in various ways. Our analysis demonstrated a significant relationship between vegetation cover in the watershed and river sediment, suggesting that the greening of Chinese land mainly induced by afforestation in the watersheds significantly reduces sediments in rivers,” said Prof. YANG. 

 This study illustrates that greener land exerted essential controls on reducing soil erosion and sediment loads into China's rivers. To a certain extent, while the influence of dam construction on river sediment was dramatic, the impact of land use change was even more profound. 

In the past two decades, China has implemented several massive ecological restoration programs, including afforestation and the “Grain for Green” project, which significantly increased terrestrial vegetation. Greening land is another crucial strategy to reduce sediments in rivers, and it can also increase carbon sequestration and enhance other ecological services. 

 See the article: 

Remarkable effects of greening watershed on reducing suspended sediment flux in China major rivers 

https://doi.org/10.1016/j.scib.2023.08.036

Contact 

 TAN Lei 

 Nanjing Institute of Geography and Limnology 

 E-mail: ltan@niglas.ac.cn