Intermittent Streams (Seasonal) flow during certain times of the year when smaller upstream waters are flowing and when groundwater provides enough water for stream flow.
Runoff from rainfall or other precipitation supplements the flow of seasonal stream. During dry periods, seasonal streams may not have flowing surface water. Larger seasonal streams are more common in dry areas.
Although they cease to exist as streams during the summer and fall, they are still inhabited by aquatic fauna. However, this fauna does not have an active aquatic life stage during the dry period.
In a very general way, the fauna of intermittent streams can be divided into two groups.
The Summer-Fall Association of the dry stream. The species are few and consist of those organisms that can survive in the remaining pools in spite of the rising water temperature. Or they may be small organisms that can burrow into the moist interstitial spaces below the stream bed where some water still remains.
The Winter-Spring Association composed of organisms characteristic of flowing water. They appear each year and make up a fairly stable permanent population. By possessing certain features in their life cycle, most members are pre-adapted to escape the unfavorable dry period.
For example, the old generation dies when the stream dries up and the population survives as small individuals existing in the moist substrate.
Some invertebrates survive the dry period in the egg stage. Species whose life cycle does not include inactive stages during the dry period are either forced from the area or die as the streams dry up.
End of Intermittent StreamsMore about Flowing Water…
Still Water (Lentic)
Liverworts and Mosses
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