Nature Lab

Watershed Health

Dissolved Oxygen in Warmwater Headwater Streams

When MDC Watershed Ecologist Darren Thornhill began his study of dissolved oxygen (DO) in warmwater headwater streams, he was looking for a pattern. DO is critical to the survival of aquatic organisms. While a daily oxygen curve has been established for large bodies of water like lakes and ponds, not much is known about the natural fluctuations of DO in small headwater streams.

“The majority of streams in Missouri are headwater streams, which leads to the incredible diversity of aquatic organisms in the state,” Thornhill says. “We wanted to look at DO levels in streams surrounded by high-quality habitat to determine how to best protect this important habitat.”

In 2020 and 2021, MDC staff measured DO and other water quality parameters in headwater streams at 34 sites on conservation areas in Missouri’s prairie ecoregions. At each site, technicians collected data two to four times each year from June to September.

“DO is related to water temperature,” explains Thornhill. “The warmer the water, the lower the concentration of oxygen. So, we focused on the hottest, driest time of year to see what these highest quality streams produce during the worst conditions for oxygen.”

Information about DO levels and their daily fluctuations in healthy prairie streams could provide a reference for what to aim for when restoring habitat. But no single pattern emerged from the study.

“We saw that high-quality habitat in the watershed lends to high water quality,” says Thornhill. “But no stream had a DO profile exactly the same as another. Each stream is an individual, unique in what it provides to those species that use it. So, we need to protect each stream because there isn’t another one like it.”

Dissolved Oxygen Study

Objectives:

• Find typical range of DO in headwater streams in high-quality habitat during summer
• Determine if DO levels are related to other water quality parameters and stream habitat
• Try to determine a daily DO cycle for these streams

Methods:

• DO and other water quality factors measured at 34 sites
• Three adjacent pools at each site measured 2–4 times from June to September
• Measurements taken every hour from sunrise (when DO is lowest) to noon (when DO is highest)
• Stream structure and vegetation assessed

Findings:

• DO in warmwater headwater streams is highly variable from stream to stream and day to day
• Every stream has a unique DO profile

MDC staff collected baseline data on dissolved oxygen (DO) in headwater streams across Missouri’s prairie region in 2020 and 2021.

Learn more at short.mdc.mo.gov/4Qb.