The water
temperature of a
river is very important for
water quality. Most of the
physical,
biological, and
chemical characcteristics of a river are directly affecte by temperature. Temperature influences ammount of
oxygen that can be dissolved in water (see
dissolved oxygen), rate of
photosynthesis,
metabolic rates of
aquatic organisms, and sensitivity of organisms to
toxic wastes,
parasites, and
diseases.
Humans affect water temperature mainly through thermal pollution.This is caused by the addition of relatively
warm water to the river. This comes from
industries such as
power plants that may be discharging water used to
cool machinery. The
cutting down of trees also affects the temperature since thre trees help
shade to water.
As water temperature rises, the rate of photsynthesis and plant gwoth increases. More plants grow then die, which increases the
decomposition by bacteria that consume oxygen. Therefore, the need for oxygen in the water (see
Biochemical Oxygen Demand) is also increased.