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What is temperature?

Temperature is the measure of how much heat energy is in a substance. There are no such things as “hot things” or “cold things,” that is only what our bodies experience. In actuality, this experience comes from the seemingly “hotter” object having more heat energy, than the “colder” object. What causes the heat energy? Well, we can’t see it with our eyes, but it is actually molecules being bounced around. When we experience something warm, the molecules of the substance are moving fast, if it’s a hot substance….even faster! Cold sensations to our skin are the result of slow moving molecules, or less heat energy. When our skin is warmer than the object we are touching, the “cold” object slows down the molecules on our skin…making us feel cold at the contact point. The same is true for when we touch “hot” things. The faster moving molecules on the hot substance we are connecting with speed up the molecules at the contact point…making us experience the object as warmer than our skin. We measure this energy with tools such as thermometers as a gauge of how much heat energy is in a substance.

Why is temperature important for the health of our watershed?

Temperature plays an important role in all fields of science, including physics, chemistry, and biology. Many physical properties of materials (solid, liquid, gas) depend on the temperature. It affects the solubility of a substance too! It’s like the difference between putting sugar in iced tea versus putting sugar in hot tea. The hot tea makes the sugar dissolve quickly while in the iced tea you have stir it a while before it will dissolve. Solubility is how readily things will be dissolved in a substance. This impacts the health of our watersheds because all the living things breathing in water need oxygen to survive. The colder the water, the more oxygen it can hold while a liquid. The water temperatures here in the northwest are generally very cold and many of the animals and insects that live in these cold waters have adapted to live in water that has sufficient oxygen. But when water temperature starts to increase, the water holds less oxygen and living organisms have a difficult time breathing.

Temperature also plays an important role in determining the rate and extent to which chemical reactions occur In living organisms sometimes temperatures only a few degrees higher can result in harmful reactions with serious consequences. This is one reason why the human body has a number of fancy ways to keep its temperature at 37 °C, or 98.6°F. For salmon, water temperatures above 68°F are dangerous. It can stress them out, making them more vulnerable to disease and a 77°F water temperature can even kill them. Sometimes water temperatures will rise naturally, as the result of a warm spring or summer. However, when humans increase the temperature of water by changing its flow direction, or dumping warm water into waterways, this is called thermal pollution. This kind of pollution can have the same kind of drastic impacts on the health of a watershed that chemical pollution can have.