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What Is Dissolved Oxygen and How Does It Affect the Quality of Water?
Wednesday, July 24, 2019

Did you know that both fish and plants need dissolved oxygen in the water so that they can survive?

Fish and plants both need about 5 mg/l of dissolved oxygen in the water in or to survive and grow. However, higher levels such as 8 mg/l can help with better results for your plants and help encourage a healthy lake for fish.

But what is dissolved oxygen? Keep on reading to find out more about dissolved oxygen and why it is so important.

What is Dissolved Oxygen?

According to Business Dictionary, dissolved oxygen definition is the 'amount of oxygen dissolved (and hence available to sustain marine life) in a body of water such as a lake, river, or stream.'

Dissolved oxygen is the most important indicator of water quality. This allows you to understand whether the water is able to support a balanced aquatic ecosystem of plants and animals.

Dissolved oxygen in water can happen one of two ways. The first way is when oxygen dissolves in surface water due to the aerating actions of winds. The second way oxygen dissolves in water is as a byproduct of aquatic plant photosynthesis.

Water molecules contain an oxygen atom, however, this oxygen isn't needed by aquatic organisms living in natural waters. The oxygen that the fish and zooplankton need to survive is oxygen water that is dissolved.

Why is Dissolved Oxygen Important?

Dissolved oxygen in water is essential to the survival of the wildlife who inhabit the stream, lake, or river. When dissolved oxygen becomes too low, fish and other aquatic organisms cannot survive.

How Come Some Water Doesn't Have as Much Dissolved Oxygen?

One reason why dissolved oxygen can change from bodies of water is because of the speed at which the water moves. Rapidly moving water, such as rivers or streams, seem to contain a lot of dissolved oxygen. Whereas, water that is stagnant, such as a large lake, doesn't contain as much dissolved oxygen.

Another reason why some water might have more or less dissolved oxygen is that wastewater that contains organic pollutants can harm the dissolved oxygen in the water.

Another reason why some water might have less dissolved oxygen is because of the time of year and temperature. In summer months, when the temperature is particularly hot, this can affect how stagnant the water is.

Water near the surface of the lake becomes too warm for aquatic life, whilst water near the bottom has too little oxygen and so organisms struggle to survive. This can lead to the loss of many fish and other wildlife who rely on the lake.

How Can You Measure Dissolved Oxygen?

Measure dissolved oxygen in bodies of water by using field and lab meters. Modern meters are small and are now electronic, but they still use a probe to test the water.

Dissolved oxygen is dependent on the temperature, so make sure your mete has been calibrated properly before each use.

Interestingly, a USGS study found that a weekly sampling of a body of water may not have more power to determine multi-year trends than bimonthly sampling.

Test Your Water

Now that you understand what is dissolved oxygen and how important it is, make sure you regularly check your water to ensure that your aquatic organisms can survive.

Learn more about what is dissolved oxygen and how you can monitor it and detect it in your water.

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