We had an interesting find this year regarding algae and chemical testing at Duck Creek at Myers Park in Stillwater. I vaguely remember that algae could affect pH levels but have never saw it happen until recently, and I learned a lot from this instance. Here is the story:
Oklahoma State University students monitored Duck Creek at Myers Park on 2/22/2024 at 5:30 p.m. and recorded a pH of 9.8- WOW! I saw this when I QA’d their data at the end of February, and it really had me worried. I passed all their data on to ODEQ and also contacted Zack Henson, the Watershed Quality Manager for the City of Stillwater. I emailed Zack all the information on March 4th and that evening he did some investigating. Zack took a total of six pH readings within a half-mile distance of the creek between Highway 51 and W. 12th Ave., with the Blue Thumb (BT) monitoring site at Myers Park in the middle (see map). Duck Creek was transformed into a concrete channel between Hwy-51 and W 9th Ave, and four of Zack’s pH measurements were within this stretch. Here, he found that pH readings steadily increased from 7.76, where the concrete channel began, to 9.45 where it ended. On the south side of W 9th Ave where the BT volunteers monitor, the pH slightly decreased to 9.18. A quarter mile downstream at W 12th Ave, the pH dropped to a more normal level of 7.64 where the stream returned to more natural habitat.
 Before sunrise on March 6th, Zack went back to Myers Park and got a pH reading of 7.62 where it was 9.18 the previous evening. What caused this? It is likely a combination of the algae, the concrete channel and warmer water temperature that influenced the pH.
Algae are photosynthetic organisms that use sunlight, water, and carbon dioxide (CO2) to produce energy through the process of photosynthesis. During the day, photosynthesis occurs and algae take in CO2 while releasing oxygen as a byproduct. The exchange of gases during photosynthesis can influence the pH of the water by increases or decreases in the concentration of CO2, and it is the presence of dissolved CO2 in the water which creates carbonic acid that ultimately lowers pH. When algae photosynthesize and consume CO2, the decrease of CO2 in the water leads to a decrease in carbonic acid that results in an increase in pH (more alkaline or basic). At night, respiration happens, photosynthesis stops and algae releases CO2 thus increasing the concentration of carbonic acid and lowering pH (more acidic). This cycle creates diel fluctuations in pH. The extent to which algae can influence the pH of water depends on various factors, including the amount and type of algae present, water temperature, the rate of photosynthesis, the availability of nutrients, and the buffering capacity of the water. In some cases, excessive algae growth, such as algal blooms, can significantly alter the pH of water bodies, leading to increased alkalinity.
It's important to note that changes in pH due to algae growth can have implications for the overall ecosystem. Algae blooms and subsequent changes in pH can affect aquatic life, including fish and other organisms, as they may be sensitive to pH variations. Additionally, alterations in pH can impact the solubility and availability of nutrients and other substances in the water, potentially influencing the overall water quality.
So, this monitoring site at Myers Park might not be properly representing the entirety of Duck Creek, but it is easy to access for the student monitors and has been very educational with this recent find- and Blue Thumb is all about education. Now that we know this can happen, we will keep a watchful eye out and will also inform future student monitors of this case. You just never know what you will find until you investigate. My thanks to Zack Henson for jumping on this and doing the investigating. Blue Thumb appreciates you, Zack!
Kim Shaw
Data Quality Assurance Officer
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