WHAT ARE THE NATURAL INFLUENCES ON WATER QUALITY?
Water quality is affected by a range of natural influences, primarily geological, hydrological, and climatic influences. All of these can affect the quantity and the quality of surface water. Within these major influences, other natural processes like weathering of rocks, depositions due to wind, leaching from soil, run-off due to hydrological factors, snowmelt, and biological processes in the aquatic environment, also affect a watershed. These natural processes cause changes in the pH and alkalinity of the water and can cause nutrient overload.
Large phenomenons, like flooding, can dilute the concentration of dissolved substances in the water, whereas a drought could increase those concentrations. Heavy rainfall can enhance decomposition and flush large amounts of organic matter into streams. On the other hand, a low flowing river can cause a temperature increase and a decreased concentration of dissolved oxygen. Seasonal variations in surface run-off have a strong effect on river discharge and subsequently on the concentration of pollutants in river water. Many rocks and minerals in the Earth's crust contain fluoride which can be leached out by natural weathering and rainwater and can cause contamination of surface water and groundwater.