Dissolved Oxygen in Loon Lake

One may ask “What on earth is dissolved oxygen (DO) and what does it have to do with Loon Lake?”

Well, DO is something that is really important and it amounts to the equivalent of the life blood of our lake. You may remember, from high school days, that water is composed of hydrogen ions and hydroxyl ions to produce H~2~O. 

DO is oxygen that occupies the spaces between molecules of water.

A good way to visualize this concept is to think about a box of blue balls that represent water molecules. Interspersed throughout the box of blue balls are a few red balls that represent oxygen.

DO gets into Loon Lake by several methods: bubbling streams flowing into the lake; rainfall; as a byproduct of aquatic plant photosynthesis; winds blowing across the surface of the lake; and finally water flowing over the ground. Water flowing through the ground contains little or no oxygen and contributes very little.

Interestingly, while winds can add oxygen to our lake, winds can also cause an upwelling of lower water levels that are already low in DO levels, causing lower oxygen levels throughout an entire water column. 

It’s important to know that the concentration of oxygen is inversely proportional to the water temperature. What this means is that on hot summer days, the concentration of dissolved oxygen decreases in water at the top of the water column. And a lake can have a real problem if there isn’t much oxygen already contained in the water at the lower levels of the water column. If this combination of lower oxygen levels persists, a lake can begin to experience a die off of fishes and other organisms.

DO is consumed by fish and zooplankton and is needed by them to survive. It is also reduced by the biological decay of organic material such as decaying plants and animals or wastes from animals and humans. DO concentrations are lowest in the bottom portions of the water column because the decomposition of algae and other organic material uses up oxygen as part of that process.

So for a lake and it’s inhabitants to be healthy, the concentration of DO must remain within acceptable guidelines.

The Canadian water quality guidelines for the lowest acceptable DO concentrations are 6 and 5.5 mg/L for the early and other life stages, respectively, in warm-water ecosystems; and 9.5 and 6.5 mg/L for the early and other life stages, respectively, in cold-water ecosystems. These guidelines were derived from the U.S. Environmental Protection Agency’s “slight production impairment” estimates (USEPA 1986), with an additional safety margin of 0.5mg/L to estimate threshold DO concentrations.

Ontario’s Ministry of the Environment did a DO study in our lake in October 2014. One of the results of the study indicated that the DO level was 7.03 mg/L at a depth of 19 meters. And, as expected, the concentrations increased going toward the surface of the lake and decreased going toward the bottom of the lake. 

One could ask “what does this mean to me?” Well, if you were a fisher, you would try to fish where the DO concentrations are higher. And a good location would be near weed beds because a product of photosynthesis is oxygen!

In August 2016, I will be creating a DO profile in Loon Lake, using the Ministry of the Environment’s equipment and I will be repeating the profile immediately after ice-out 2017. Once those results are complied, I will be writing a report on the effect of winter ice cover on the DO levels in Loon Lake’s water column and submitting the report, along with my test results, to the MOEE.

My report will be published on my Blog.