The boundary where the fresh water layer meets the salt water layer below is called the pycnocline. The pycnocline acts as a physical barrier that prevents the two layers from mixing together. During the summer, when algae-consuming bacteria are most active, the pycnocline cuts off oxygen-deprived bottom waters from oxygen-rich surface waters. This can create large areas of low- or no-oxygen at the bottom of the Bay.
The bottom of the Bay is not flat—rather, it has varying shallow and deep areas. This phenomenon often takes place each summer in:. Because larger fish require more oxygen to survive, they will die of oxygen depletion before small fish and other organisms in the same environment.
They might also be quicker to display symptoms of oxygen depletion. Aquaculturists and fish owners should monitor DO levels on a routine basis using a portable or inline DO controllers, transmitters, or analyzers. By tracking changes in DO levels, you can identify when DO is getting dangerously low and make adjustments to your aquatic environment to increase the amount of oxygen present. If your water quality monitor reveals low DO, there are a variety of things you can do to boost DO levels in your aquatic environment.
They include:. If you frequently monitor DO levels, you should be able to correct for small changes without having to take more intensive measures such as replacing the water. To compare different water-quality monitors and find the right DO tester for your needs , click the link below to learn more about Jenco Instruments and to locate a distributor.
Regularly-published posts about water quality industry, applications, instruments, how-to's and more. Recognizing Symptoms of Low DO in Fish Fish that fall victim to low DO levels will often seem lethargic and will spend more time at the surface of the water gulping air or in front of an aerator.
Dissolved oxygen DO is one of the most important indicators of water quality. It is essential for the survival of fish and other aquatic organisms. Oxygen dissolves in surface water due to the aerating action of winds. Oxygen is also introduced into the water as a byproduct of aquatic plant photosynthesis. When dissolved oxygen becomes too low, fish and other aquatic organisms cannot survive. The colder water is, the more oxygen it can hold.
As the water becomes warmer, less oxygen can be dissolved in the water. Salinity is also an important factor in determining the amount of oxygen a body of water can hold; fresh water can absorb more oxygen than salt water. Oxygen levels also may be reduced when there are too many bacteria or algae in water see Biochemical Oxygen Demand. After the algae complete their life cycle and die, they are consumed by bacteria.
During this decay process the bacteria also consume the oxygen dissolved in the water. This can lead to decreased levels of biologically available oxygen, in some cases leading to fish kills and death to other aquatic organisms.
Virtually all the oxygen we breath is manufactured by green plants. If water is too warm, there may not be enough oxygen in it. When there are too many bacteria or aquatic animal in the area, they may overpopulate, using DO in great amounts.
Oxygen levels also can be reduced through overfertilization of water plants by run-off from farm fields containing phosphates and nitrates the ingredients in fertilizers. Under these conditions, the numbers and size of water plants increase. Then, if the weather becomes cloudy for several days, respiring plants will use much of the available DO. When these plants die, they become food for bacteria, which in turn multiply and use large amounts of oxygen.
And this depleting all the oxygen. How much DO an aquatic organism needs depends upon its species, its physical state, water temperature, pollutants present, and more. For example, at 5 o C 41 o F , trout use about milligrams mg of oxygen per hour; at 25 o C 77 o F , they may need five or six times that amount. Fish are cold-blooded animals. They use more oxygen at higher temperatures because their metabolic rates increase.
Numerous scientific studies suggest that parts per million ppm of DO is the minimum amount that will support a large, diverse fish population.
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