Listening to the Stream
Can you hear the stream crossing the meadow ? Can you hear the dragonfly hovering above the fresh water ?
If you come closer and look deep into the water, you may see some of its inhabitants. Look at these fishes, frogs and crayfishes ; yet, most of the stream dwellers are hidden under rocks. To see them, you should move the river ground — also called « benthos ». Then, you might find all types of insects and worms. Many are larvae waiting to become adult and go out of the water.
Flora is also pretty strange since mosses, small algae and diatoms are dominating this world. They can only live where the water is not too deep so the light can still reach the bottom of the river.
Living in this running water is like being on another planet. The temperature is almost constant, the current is strong and water is everywhere.
The quantity of oxygen is highly variable between the day and the night. During the night, algae don’t photosynthesis and don’t produce oxygen. For this reason, oxygen saturates the stream during the day but is scarce during the night…
A stream usually has few resources to live on. Although some plants grow in the water and can be eaten, most of the stream nutrients come from outside. Dead leaves, dead wood and dead animals fall in the water and are transported by the current. All those dead bodies are shredded and decomposed by insects and bacteria. Many animals filter, collect and eat floating particles ; only a few are predators.
A stream is not only the habitat of a huge diversity of aquatic invertebrates, but it also has important functions in the landscape.
- Rivers regulate the flux of water by absorbing the rain, recharging the groundwater reserves and hydrating soils during summer drought.
- This running water is a network which allows animals to move and run away from bad conditions. It also disperses plant offspring in remote places.
- Do not forget that streams are simply beautiful so hikers enjoy to walk along them.
A stream can have different shapes and properties depending on the regional slope, geology and precipitation pattern.
For example, mountainous regions often have straight, narrow and fast streams running through a U shaped valley formed by a retreating glacier ; while, lowland regions often have meandering slow and large streams going through a flat alluvial valley.
Scientists even classify rivers depending on their order of apparition and their width. An alpine stream is a « first stream » because it is first point where water appeared. In Spanish, it’s called « nacimiento del agua », which means the water birth place. It’s the source of the water. The stream generated from this first stream is a second stream, then comes the third and so on.
Concerning the width, wider is the stream and higher is its number type : 12 is the maximum. For example, the Seine in Paris has a width ranging from 30 to 200 m. So it is a type 8-12.
All this water is very useful to humans. For this reason, it needs to be protected against degradation and pollutants, heavy metals and hormones for instance. The quality of the stream is assessed thanks to its biodiversity and its chemo-physical properties such as pH and nutrient content.
The use of the water has to be sustainable and its management prevents floods and droughts. Only this way human will continue to live well drinking water and eating veggies without worry.
I hope you enjoyed this crashcourse about stream ecology. Thanks to M. Dieterich for his course and thanks to my classmates for their love.
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