What Is Dissolved Oxygen? 9 Things (2022) You Must Know

Sometimes people have a hard time believing that there can be too much of a good thing.

For example, you need water to live.

You need to actively work to stay hydrated each day.

However, you can become overhydrated, which can lead to dangerously low levels of sodium in your blood.

Another example of this is oxygen.

Oxygen is widely considered the key to life.

Most organisms on Earth cannot survive without it, even if they are underwater.

However, dissolved oxygen can pose threats to aquatic organisms, and that’s what will be discussed in this blog.

Let’s get started. 

1. What is dissolved oxygen?

Dissolved oxygen (DO) is the amount of oxygen that is present in water.

There are a few different sources of oxygen for water bodies, including the atmosphere and aquatic plants.

Running water (i.e., swift-moving stream) dissolves more oxygen than still water (i.e., pond or lake).

2. Why is it important to evaluate dissolved oxygen?

In order to breathe, all aquatic animals require dissolved oxygen.

So, low levels of oxygen (hypoxia) or no oxygen levels (anoxia) will occur when excess organic materials like large algal blooms are decomposed by microorganisms.

This is because the decomposition process consumes oxygen.

Additionally, low oxygen levels often occur at the bottom of the water column and affect the organisms that live in the sediments.

It can be normal for certain dissolved oxygen levels to fluctuate periodically, seasonally, and even as part of the natural daily ecology of the aquatic resource.

That said, when dissolved oxygen levels decrease, sensitive animals may relocate, decline in health, or die.

Evaluating the dissolved oxygen levels in an ecosystem is vital to ensuring that all organisms have what they need to continue to thrive.

3. What can dissolved oxygen tell us about the condition of water?

Dissolve oxygen is an important measure of water quality and serves as a direct indicator of an aquatic resource’s ability to support aquatic life.

When doing a NARS (National Aquatic Resource Survey) Survey, levels of dissolved oxygen are measured with a calibrated water quality probe meter.

Measurements with temperature and pH are often combined with these as well.

Each organism often has its own dissolved oxygen tolerance range, and often dissolved oxygen levels below 3 milligrams per liter (mg/L) are deemed concerning.

Waters with levels below 1 mg/L are considered hypoxic and usually devoid of life.

4. What is oxygen saturation?

Oxygen saturation is a relative measure of the concentration of oxygen that is dissolved or carried in a given medium as a proportion of the maximal concentration that can be dissolved in that medium at the given temperature.

5. What is the environmental impact of dissolved oxygen?

As a rule of thumb, the total dissolved oxygen concentrations in water should not exceed 110 percent.

When you exceed this concentration, it can be harmful to aquatic life.

For example, fish in water that contains excessive dissolved oxygen (or other gases) may suffer from “gas disease.”

However, this is a very rare occurrence.

The bubbles or emboli block the flow of blood through blood vessels, which can cause death.

External bubbles known as emphysema can also occur and be seen on fins, skin, or other tissue.

Aquatic invertebrates are also impacted by gas bubble disease but at levels higher than those lethal to fish.

Overall, having adequate dissolved oxygen is necessary for good water quality.

Oxygen is a necessary element in all forms of life.

Natural stream purification processes require adequate oxygen levels to provide for aerobic life forms.

When dissolved oxygen levels in the water drop below 5.0 mg/l, aquatic life will be under stress.

The lower the concentration of dissolved oxygen, the greater the stress.

Oxygen levels that remain below 1-2 mg/l for a few hours can result in large fish kills.

6. What is thermal stratification?

Occurring from late spring to early fall, thermal stratification is a seasonal phenomenon in temperate regions.

In the summertime, the epilimnion (the upper layer of water in the water) of the Great Lakes is warmed significantly by the sun.

During this process, cooler water separates and forms two additional layers (metalimnion and hypolimnion) that are heavier or denser.

However, during the wintertime, no stratification occurs as the lake is cool and more uniform in water temperature.

7. How does oxygen enter a lake?

Building on thermal stratification, oxygen can enter a lake in three different routes.

The main mechanism through which it does this is by atmospheric diffusion.

Atmospheric diffusion is where the oxygen in the air is absorbed by surface water due to a difference in oxygen concentration.

Another way oxygen can enter a lake is by aquatic plants photosynthesizing and releasing oxygen in the water.

A third way is when rivers and streams bring oxygenated water into the lake.

If the lake is stratified, the lower layer of the water (the hypolimnion) receives little oxygen from atmospheric diffusion, and it is too dark to support oxygen-producing plant life.

Additionally, as riverine input has only minimal impacts on the oxygen content of large water bodies like Lake Erie, it receives very little dissolved oxygen during summer thermal stratification.

8. How do you define the trophic status of a lake?

The trophic status of a lake is the way by which you designate its nutrient or growth status.

Lakes are often described by their productivity levels.

Here are the primary trophic categories you should keep in mind.

bulletOligotrophic: An oligotrophic lake has low nutrient concentrations and low plant growth (i.e., Lake Superior).

It is usually considered to have low productivity.

bulletEutrophic: A eutrophic lake has high nutrient concentrations and high plant growth (e.g., Lake Erie).

It is considered to have high productivity.

bulletMesotrophic: Mesotrophic lakes fall somewhere between eutrophic and oligotrophic lakes.

They are considered to have average productivity.

A eutrophic lake like Lake Erie has large algae blooms growing at the surface during the summer.

The algae need large amounts of nutrients in order to form these blooms.

As the algae die, the bloom sinks to the bottom and is decomposed by bacteria.

This decomposition process — the biological separation of a substance into simpler elements — requires oxygen.

Oxygen consumption and low oxygen input in the hypolimnion combine to create extremely low levels during thermal stratification.

Then, when dissolved oxygen levels drop below 2 mg/l, water is described as hypoxic.

If it approaches 0mg/l, it becomes anoxic.

These zones with either hypoxic or anoxic water are known as dead zones because few organisms can survive there.

Organisms that are in dead zones will either suffocate or leave the area.

According to Michigan water quality standards, a minimum oxygen concentration of 7 mg/l is needed for cold-water fish, and a minimum oxygen concentration of 5 mg/l is needed for warm water fish.

9. How can you help your lake stay healthy?

If you’re a landowner, you may be facing unhealthy water conditions and wondering what you can do.

Fortunately, there are a lot of ways that you can help protect the health of your lake and its inhabitants.

Many of these begin right on your property regardless of whether you live on the shoreline or not.

Here are our top tips:

bulletMaintain proper oxygenation in the lake

As noted above, oxygen is a critical element to the quality of water in a lake.

It’s necessary for the life and well-being of animals and bacteria that decompose organic matter.

To maintain oxygen circulation in your lake, you need to keep the water properly aerated.

This will allow your water to stay healthy, and it will also lessen the presence of algae while counteracting anoxic conditions that affect the water’s ability to support life.

To keep your lake aerated, follow these steps.

1. Use natural aeration that relies on natural resources for oxygen circulation in the lake.

You can do this by putting plants on the surface of the lake and its surroundings, which release oxygen in the water and promotes proper aeration.

Natural aeration will also happen when the wind blows into the water.

It promotes movement and allows for oxygen to go into the lake.

2. Try surface aeration with special tools.

This is the process of using tools that work on the surface to help pull and propel it into the air.

It will allow it to get in contact with oxygen.

Surface aeration tools include fountains, floating surface aerators, and paddlewheel aerators.

3. Submerged aeration is a method that promotes oxygen circulation underneath the water’s surface.

This process oxygenates the water with onshore pumps and air compressors.

bulletApply bacterial treatment in the lake

Treatments with natural bacteria can help maintain the quality of water and amount of dissolved oxygen in your lake.

They help reduce the nutrients in the water that algae and weeds feed on.

Moreover, natural bacteria aids in breaking down muck and sludge and fighting off bad odor in the water.

bulletIntegrate phytofiltration in your maintenance program

Phytofiltration is the process of filtering pollutants, harmful substances, or excessive nutrient levels in the lake with the use of plants and trees.

The most common way of doing this is by using surface plants to help promote oxygenation, absorb nutrients, and block sunlight.

When you do this, algae growth is reduced.

You can also do this by planting vegetation along the shoreline of the lake.

This will allow the vegetation to act as a filter and prevent any form of pollutant from coming in contact with the water.

At the same time, they block sunlight prevent shoreline erosion, and provide food and shelter for animals.

We do not recommend uprooting any existing plants along the lake’s shoreline.

This can cause erosion and damage to the water.

Leave them in place and allow them to grow alongside any new plants that you want around the plant’s edge.

bulletUse natural products for your gardening needs

Maintaining your plants properly is a vitally important factor in keeping your lake healthy.

You should ensure that your vegetation is pest-free and utilize gardening products that are free from chemicals.

bulletObserve proper maintenance of your septic tanks

If you have a septic tank, did you know that it can affect the cleanliness and dissolved oxygen levels of your lake?

You need to make sure it’s maintained properly, so your lake isn’t at risk of getting polluted or contaminated.

Here are some of the best ways to ensure that your septic system continues to work well.

  1. Conserve water
  2. Avoid flushing non-biodegradable materials in your toilet
  3. Use eco-friendly soaps
  4. Fix leaks
  5. Schedule regular inspections and have the tank pumped out if needed
  6. Keep maintenance records and system maps
  7. Don’t place anything heavy on top of the drain field lines

bulletUse lake dyes

Using aqua dyes can help you to prevent algae growth.

Some people mistakenly believe that this alone is for aesthetic appeal because it adds more pigment to the water.

However, this pigment acts as a shade and blocks the sunlight from penetrating underneath the surface.

As a result, algae growth is reduced because there’s not enough sunlight available for their photosynthesis.

So, if algae growth is a big issue for your lake and you want to improve both that and its appearance, consider using lake dyes!

AquaDyes is a great place to start as they have an entire catalog of dye products for your lake that are eco-friendly, safe, and easy to use.

bulletKeep a safe distance between the lake’s shorelines and structures

If you’re building structures around your lake (i.e., a dock or house), make sure that the vegetation along and near its shoreline won’t be disrupted.

Taking down trees, uprooting plans, or creating deep excavations to create a structure near a lake can endanger the quality of water.

So, make sure that you do the proper planning and ensure that there’s sufficient distance between the shoreline and your structure.

Final Thoughts

Dissolved oxygen is one of the largest factors in ensuring the health of lake water.

Maintaining your lake requires a lot of hard work and effort.

However, it is completely feasible to understand how to care for the organisms in your lake and prevent dead zones without oxygen.

Just follow our tips above and be mindful of your actions.

Removing vegetation to create structures for your enjoyment can jeopardize water quality and nature overall.

Additional Resources

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Disclaimer: we are not lawyers, accountants or financial advisors and the information in this article is for informational purposes only. This article is based on our own research and experience and we do our best to keep it accurate and up-to-date, but it may contain errors. Please be sure to consult a legal or financial professional before making any investment decisions.

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