3.3.2 Speed of flow/turbulence
To get nutrients and dissolved oxygen to all parts of a body of water, good mixing is important. We have had one example in the thermal stratification in deep lakes in summer (Figure 7), where poor mixing and reduced sunlight lead to the bottom layers not being supplied with the necessary conditions for plant growth. The same principle applies to rivers and streams. Fast-moving turbulent streams mix and agitate the water, aiding the transfer of oxygen from the atmosphere to the river, and carry nutrients more efficiently to the plants and animals in the river. Small, rapidly flowing streams are nearly always saturated with dissolved oxygen; large sluggish rivers may have oxygen concentrations well below saturation conditions.