Water Temperature
Water temperature is an important parameter to study in streams, and it is
probably the number one reason why many streams and rivers may excede water
quality standards.
Most aquatic organisms need a constant water temperature in order to survive.
When the water temperature changes rapidly, many organisms become stressed,
which often leads to increased disease or makes them more susceptible to predation.
This is the reason one should slowly introduce tropical fish to an aquarium
after purchase. They need to become acclimatized to the water of their new homes.
Coldwater fish like trout and salmon are very much susceptible to sudden temperature
changes. Many aquatic insects and other invertebrates (clams, mussels, and worms)
which are found in cleaner habitats are often susceptible to sudden temperature
changes too. Those animals that live in a broader range of habitats such as
carp tend to be more resistant to such changes, although a change of 5-10 degrees
in a short time would also harm them.
Generally, the cooler the water, the better. More life forms are able to survive
in cooler water, although ice cold waters may also restrict the number of creatures
living there. As the water temperature increases, the water is able to hold
less oxygen. This probably is a major reason why fish and other susceptible
life forms are affected by increasing temperatures.View
the handout on the classroom wall to see which species of fish are able to live
in which temperature of water.
Sources of temperature change:
Probably the most frequent reason that the water temperature rises is due
to lack of shade. Deep shade is provided by large conifer trees along the stream
banks. The shade cools the air, and thus helps cool the water temperature. Dead
conifers fall into the streambed and decompose very slowly, providing hiding
places for organisms and providing small patches of shade at midstream to cool
the water. Broadleaf deciduous trees like cottonwoods, alders, and maples likewise
provide ample shade and a resulting cooling affect. Shrubbery along the streambank
also provides shade as well as protection from floods.
Lack of shade along a watercourse is especially critical during summer months,
where the water temperature may increase so high that many plants and animals
can't live. With increased deaths comes increased decomposition of the dead
animals, which increases such nutrients as phosphate (PO4) and nitrate (NO3)
in the water, leading to further water pollution. In addition, during the summer,
the volume of water in streams and rivers decreases, making it easier to heat
the water.
The velocity of the water also determines how fast the water warms. Slow streams,
or the water in pools, ponds, lakes, or in impoundments behind dams all suffer
greatly increased water temperatures, and thus less oxygen in the water.
Slichter