Water quality

9.5.3 Sediments

Sediments result from erosion of exposed soil surfaces, with much eroded soil being deposited in basins throughout the world, including in Africa, Asia and Latin America. Deforestation, poor agricultural and livestock practices, intensive fuelwood harvesting, mining, urbanization and unplanned settlements are major causes of soil vulnerability to erosion, and stormgenerated run-off carries soil into downstream waterbodies (Annex 9-1). Sediment-associated pollutants can have human health impacts, and interfere with water uses and aquatic organism metabolism and habitats (UNEP 2017). Artificial channels from dams and urban development can change sediment flow paths, lead to erosion and reduce sediment available to build up banks, river deltas and beaches along coastlines, causing aquatic ecosystem changes (Blum and Roberts 2009, Syvitski et al. 2009; Yang et al. 2011; Cloern and Jassby 2012; Adams et al. 2016; Yihdego, Khalil and Salem 2017).