Dissolved Oxygen in the water
Today we are going to touch on dissolved oxygen data on the USGS stream conditions site. Dissolved oxygen is another good indicator for overall stream health. This is a measure of the amount of oxygen present in the water that is available for aquatic life. All aquatic animals need oxygen to survive. Rapid water in streams and rivers will have Co a higher amount of dissolved oxygen than stagnant water. Areas where groundwater discharge (water that flows into streams from underground) also contributes to higher dissolved oxygen levels. Things that will lower the dissolved oxygen levels are, high water temperatures, bacteria, and fertilizer runoff.
High water temperatures will squeeze out oxygen molecules from between the water molecules. Trout are particular susceptible to the relationship between warm water and dissolved oxygen. At high water temperatures trout become particularly stressed because there is less oxygen available to keep up with their increased metabolic rate. This is why it is not acceptable to fish for trout at water temperatures above 68 degrees. The stress put on them is too high and the lack of oxygen makes it difficult for them to recover.
Bacteria levels also lower the oxygen levels. Sewage runoff will increase bacteria levels in the water which will consume the available oxygen. Runoff from fertilizer that was spread on a farmer’s field or a person’s lawn will also effect the oxygen levels in a negative manner. This fertilizer will increase the amount of plant growth in a waterway and when this plant growth begins to die and decay it will increase the bacteria levels in the water.
Oxygen levels greater than 9 mg/l will support abundant aquatic life. Fish will be healthy enough to spawn and reproduce and there will be plenty of oxygen for aquatic insect like mayflies and stoneflies to reproduce in the waterway providing an abundant source of food for fish. When oxygen levels drop below 5 mg/l however it becomes increasingly difficult for fish to survive and reproduce and at levels below 3 mg/l aquatic life cannot survive.
Below is a graph showing both the water temperature and the dissolved oxygen. This is how you can use the graph options to analyze the data and understand how changes in one parameter effect another parameter. You can clearly see in this graph the relationship between water temperature and dissolved oxygen.
I hope you learned something in this post. If nothing else understand that our waterways need us to keep them clean and healthy to enable our future generations to enjoy them as much as we do. Stay tuned for the next post where we will discuss PH.
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