Salinity refers to the saltiness of water caused by the dissolution of minerals in rocks, soils and decomposing plant material. The level of salinity in a river, for instance, depends on the geological and climatic environments through which the river flows. Salinity increases downstream, as salts are continuously added through natural and anthropogenic processes such as mining, industry and agriculture, but are only minimally removed through technological interventions or diluted by precipitation (du Preez et al. 2000).
High levels of salinity can lead to the "salinisation of irrigated soils, diminished crop yields, increased scale formation and corrosion in domestic and industrial water pipes, and changes in the biotic communities." 1 000 mg/L is considered moderate salinity and is generally tolerated by humans; however, at levels above 3 000 mg/L (high salinity) fatal intestinal damage and renal damage can occur (DEAT 2009).
Salt can accumulate on the surface as a crust, or in soil, when evapotranspiration exceeds precipitation.
Source: Reed 2009
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Water quality in all reaches of the Limpopo River in Botswana and South Africa is dominated by high levels of sodium and chloride (LBPTC 2010). Although naturally occurring geological characteristics contribute to salinity to some extent, poorly managed irrigation systems are the primary cause of high levels of soil and water salinity in the basin. Large-scale commercial irrigation systems utilise equipment and systems to manage salinity; however, smaller scale operations do not have access to this sophisticated equipment (FAO 2004) and as a result up to 10 % of soils in South Africa are saline.