Temperature
Why are we concerned?
Temperature changes can affect all aquatic life. For example, warm water holds less dissolved oxygen than cold water and triggers more plant growth and higher respiration rates. The lowered oxygen levels of warmer waters are further reduced when plants and animals die and decay.
Although most aquatic life has adapted to survive within a range of water temperatures, some fish species, (trout, for example) require cooler waters. The metabolic rate of organisms, or the rate at which they convert food into energy, also increases with higher water temperatures, resulting in even greater demands on oxygen.
Research also shows that extreme temperature fluctuations can make fish and insects more susceptible to disease, parasites and the harmful effects of toxic waste.
The background science
Stable water temperature is a critical factor in maintaining the health of a stream and its inhabitants. Temperatures over 78˚ F, (25.6˚ C) for example, are usually fatal to brook trout, which need waters in the range of 55˚- 65˚ F (12.8˚-18.3˚ C) in order to thrive. Other fish such as the smallmouth bass can survive an upper limit of 86˚ F (30˚ C) and carp can live in even warmer waters. So as temperature increases, cool water species will gradually be replaced by warm water ones.
The common causes of warmer stream temperatures include:
- Thermal pollution from industries discharging heated water into streams
- Runoff from heated surfaces such as parking lots, roofs, roads
- Mill ponds and impoundments with large surface areas that absorb heat
- Removing trees that shade and cool the stream
- Suspended soil particles (turbidity) that absorb the sun's heat
- Sediment that fills the stream making it more shallow
For additional information, check out the fact sheet "Temperature: Its Role in Aquatic Habitats"
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