Temperature

The temperature of the water in your river or lake is very important for water quality. The temperature of the water affects many physical, biological and chemical characteristics of a river or lake. Do you know why cool water can hold more oxygen than warm water? Because gases dissolve easier in cooler water!

Why is the temperature of water so important? For a number of reasons! Temperature affects:

• the amount of oxygen that can be dissolved in the water

• the rate of photosynthesis by algae and larger aquatic plants

• the metabolic rates of aquatic organisms

• the sensitivity of organisms to toxic wastes, parasites and diseases

One way that the temperature of water can increase in a river or lake is from thermal pollution. Thermal pollution is an increase in water temperature caused by adding relatively warm water to a body of water. Industries, such as nuclear power plants, may cause thermal pollution by discharging warmer water from their plant that was used to cool machinery. Thermal pollution may also come from stormwater running off warmed urban surfaces, such as streets, sidewalks and parking lots.

Why do we measure changes in the temperature of water? As water temperature rises, the rate of photosynthesis and plant growth (and decay) increases. As plants die, they are decomposed by bacteria that consume oxygen, increasing the biochemical oxygen demand in the water. The metabolic rate of organisms also rises with increasing water temperatures, resulting in an even greater oxygen demand.

Most aquatic organisms have adapted to survive within a range of water temperatures. Some organisms prefer cooler water, such as trout and stonefly nymphs, while others thrive under warmer conditions, such as carp and dragonfly nymphs. As the temperature of a river or lake increases, cool water species will be replaced by warm water organisms. Few organisms can survive in temperatures of extreme heat or cold.

Why is the temperature of the water so high?

What are the weather conditions today and the previous days before your sampling?

Check out the stream bank or shoreline - do you find any trees or bushes providing shade?

Can you find any sources of thermal pollution in the watershed? How can warm water impact the ecology of a river or lake?

Check out the streambank and watershed - can you find any obvious sources of soil erosion?

What is the cause(s) of your problem? What did you find that led you to this conclusion?

Now is the time to take ACTION!