In rivers, a transition occurs from the highest course to the medium and lowest course. When a river transitions to less steep land, it gets wider and slower and contains more oxygen, nutrients, and fewer algae blooms.
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A river is composed of three main courses:
- The highest course is near the source.
- The medium course, where there is a low slope. There is a decrease in the speed of the waters, the erosive effect, and the dragging capacity. The flow increases due to the contribution of tributaries. The valley widens.
- The low course is near the mouth, where the slope is low, and the river speed decreases notoriously. There are wider valleys -plains- and wide meanders. The most characteristic feature of this part of the river is the deposit of the last materials that have been uprooted and transported in the previous phases. Hight sedimentation degree.
When a river transitions to less steep land, getting wider and slower, it contains more oxygen, more nutrients, and fewer algae blooms.
This occurs because sunlight reaches the bottom in those areas with less steepness. As the current is not that strong, many vegetable species can grow and photosynthesize, attaching to the bottom and not being pulled up by the stream.
The existence of more vegetable species -especially near the shore- means a higher photosynthetic rate, which also means more oxygen available. As we already know, during the photosynthesis process, oxygen is released from water molecules. So, the more photosynthetic species grow in these rivers, the more oxygen is available.
More plants growing in shadower areas also means more refuge available for invertebrates and small vertebrates. Many animal species can find shelter and a source of food in fewer steep lands, especially small species.
As biodiversity increases, it also increases organic matter and nutrients available for plants and animals. Sediments might accumulate in the bottom.
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