Dissolved Oxygen

What a living, breathing lake needs: DISSOLVED OXYGEN

by Dr. Nate Bosch, director of the Lilly Center for Lakes & Streams photo by the Lilly Center for Lakes & Streams

Did you know that dissolved oxygen is an indicator of water quality in your lake?

When enough dissolved oxygen is present, a lake, pond, or stream can support a wide variety of aquatic critters! Fish (like bluegill, sunfish, and catfish) and zooplankton (like daphnia, cyclops, and rotifers— which are food for the fish) all need dissolved oxygen to breathe.

Dissolved oxygen needs to be recharged. Those molecules get used quickly and lakes need the right circumstances to keep enough in stock for their inhabitants. Moving water, for instance, has more dissolved oxygen than stagnant water. This is because fresh oxygen gets mixed into the water via wind or wave action, like chocolate chips being folded into cookie batter. Cold water also typically holds more dissolved oxygen than warm water, which means fish can overwinter in a lake, assuming spring comes quickly enough to remove ice from the lake’s surface and allow wind to mix in a fresh supply of oxygen. Bacteria, however, are known to mastermind ways to diminish dissolved oxygen. They like to live in the bottom sediment of local lakes— and especially in areas that receive deposits of organic matter! Tree leaves and lawn clippings, and dead weeds, algae, and fish all cause dissolved oxygen to get used up as they decay. Bacteria use this dissolved oxygen to grow speedily, leaving very little for other forms of life like the fish and zooplankton. This can be especially problematic in the summer when a pond or lake is not mixing from top to bottom. The cool water near the bottom of the lake loses most of its oxygen due to these bacteria.

All lakes are in some stage of eutrophication (the process by which they will eventually be ‘filled in’). Did you know that what you choose to do on your property can speed up or slow down eutrophication? It is a natural process that leads to yet another valuable water resource: wetlands. But for those of us who live on or close to a Kosciusko County lake, we would like our lakes to be filled with healthy, dissolved oxygen-balanced water rather than filling in with organic matter and sediment. There is much more to discover about your lake! Visit lakes.grace.edu/field-notes to equip yourself with knowledge about zebra mussels, freshwater food chains, bluegreen algae, and more.

Here are three ways to keep your lake’s dissolved oxygen storage room stocked: 1. Get rid of yard waste correctly. Do not dump it in your lake. Organic matter will decay and decrease dissolved oxygen, but it could also lead to a growth spurt for unwanted algae and weeds. 2. Decorate your shoreline with native plants. Unlike invasive species, native species often better absorb nutrients to reduce overabundant weed and algae growth and help keep more dissolved oxygen in the bottom waters of your lake. 3. Use less fertilizer. Specifically, try to use phosphorus-free fertilizer. When fertilizer gets washed into a lake, it acts as a stimulant and leads to more weed and algae growth.

The Lilly Center for Lakes & Streams at Grace College conducts research, provides resources, engages and educates residents, and collaborates with local organizations to make the lakes and streams of Kosciusko County clean, healthy, safe, and beautiful. To date, the Lilly Center has conducted scientific research on over 30 streams and 40 lakes. The Lilly Center is driven to create a legacy of stewardship by equipping community members, visitors, and future generations to understand and enjoy the county’s natural beauty. For more information, visit lakes.grace.edu.