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Several characteristics of the water cycle have the potential to cause sudden (abrupt) changes of the water cycle. [7]: 1148 The definition for "abrupt change" is: a regional to global scale change in the climate system that happens more quickly than it has in the past, indicating that the climate response is not linear.
Soil erosion (especially from agricultural activity) is considered to be the leading global cause of diffuse water pollution, due to the effects of the excess sediments flowing into the world's waterways. The sediments themselves act as pollutants, as well as being carriers for other pollutants, such as attached pesticide molecules or heavy metals.
Thermal pollution is the rise or drop in the temperature of a natural body of water caused by human influence. Thermal pollution, unlike chemical pollution, results in a change in the physical properties of water. A common cause of thermal pollution is the use of water as a coolant by power plants and industrial manufacturers. [1]
Water pollution also reduces the ecosystem services such as drinking water provided by the water resource. Sources of water pollution are either point sources or non-point sources. [155] Point sources have one identifiable cause, such as a storm drain, a wastewater treatment plant, or an oil spill. Non-point sources are more diffuse.
Nonpoint source pollution is the leading cause of water pollution in the United States today, with polluted runoff from agriculture and hydromodification the primary sources. [ 44 ] : 15 [ 21 ] Regulation of Nonpoint Source Pollution in the United States
Human activity has had an impact on the water cycle. Infrastructure, like dams, have a clear, direct impact on the water cycle by blocking and redirecting water pathways. Human caused pollution has changed the biogeochemical cycles of some water systems, and climate change has significantly altered weather patterns. [ 13 ]
As it has low water solubility, it tends to stay at the water surface, so organisms that live there are most affected. DDT found in fish that formed part of the human food chain caused concern, but the levels found in the liver, kidney and brain tissues was less than 1 ppm and in fat was 10 ppm, which was below the level likely to cause harm.
A practical definition of water pollution is: "Water pollution is the addition of substances or energy forms that directly or indirectly alter the nature of the water body in such a manner that negatively affects its legitimate uses." [1]: 6 Water is typically referred to as polluted when it is impaired by anthropogenic contaminants.