Answer:
All terrestrial and aquatic animals need oxygen to survive. Many aquatic macroinvertebrate species depend on oxygen-rich water. Without sufficient oxygen they may disappear. Even a small change in dissolved oxygen concentration can affect the composition of aquatic communities. Many fish require a certain dissolved oxygen range in order to survive
Aquatic life- animals living in water use up dissolved oxygen. Bacteria take up oxygen as they decompose materials. Dissolved oxygen levels drop in a water body that contains a lot of dead, decomposing material.
Elevation- the amount of oxygen in elevation increases. Since streams get much of their oxygen from the atmosphere, streams at higher elevations will generally have less oxygen.
Salinity (saltiness)- Salty water holds less oxygen than fresh water.
Temperature- cold water holds more dissolved oxygen than warm water.
Turbulence- more turbulence creates more opportunities for oxygen to enter streams.
Vegetation- riparian vegetation directly affects dissolved oxygen by releasing oxygen into the water during photosynthesis. It indirectly affects dissolved oxygen concentrations because vegetation shading a stream may decrease water temperatures, and as temperature decreases dissolved, oxygen increases.
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