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NATURAL FACTORS REGULATING WATER QUALITY
If there was no human influence, water quality would be determined by the weathering of bedrock minerals, by atmospheric processes of evapotranspiration and the deposition of dust and salt by wind, by the natural leaching of organic matter and nutrients from soils, and by hydrological factors that lead to runoff.Surface runoff is extremely variable. It is influenced by latitude, local differences in elevation (orography), and location on continents. In equatorial and monsoon regions, runoff exceeds 2000 mm/year or 63 litres km-2 s-1. In regions where runoff is less than 25 mm/year, rivers are not perennial unless fed by wetter basins further upstream.
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