pH Violations in the Lower Deschutes River: Why It's Happening and Why It Matters
Figure 1. Round Butte Dam and the Selective Withdrawal Tower.
The statement has often been made that the selective water withdrawal (SWW) tower has created “natural” conditions on the lower Deschutes River. A look at the available pH data does not support this claim. On the contrary, pH levels in the lower Deschutes tells the story of how river conditions have declined following tower operations.
What is pH?
What is pH, and what does it mean to be “acidic” or “basic”? As an example, things with a lower pH, like grapefruit juice and vinegar, are acidic, while things with a higher pH, like bleach and drain cleaner, are basic (alkaline). A pH level of 7 is neutral, a pH less than 7 is acidic, and a pH greater than 7 is basic (or alkaline). pH is the expression of the concentration of hydrogen ions and it is measured on a negative logarithmic scale of 0-14. This means that a pH level of 9 has a hydrogen ion concentration 10 times less than a pH level of 8. The optimal pH range for most aquatic organisms is within a couple of units above and below 7 (neutral) pH.
pH and Aquatic Life
It is detrimental to aquatic organisms' biological functions if pH is excessively low or high. pH levels above 9.0, particularly for prolonged periods, are harmful to salmonids and cause damage to skin, gills, olfactory organs and eyes in addition to decreased reproduction and growth. Additionally, toxicity of pollutants (ammonia, metals) increases as pH levels increase. While the lower Deschutes is currently not listed for any aquatic life toxics, the fact that current pH levels in the lower Deschutes are above 8.5 for most of the year and commonly reach 9.0 and above during summer months is cause for concern, especially if any of the concentration of these pollutants were to increase.
Even more pertinent to the lower Deschutes, due to the sensitive relationship and balance between water chemistry and aquatic food webs, even moderately elevated pH can be an indicator that overall river health is poor. This is largely due to the link between pH, nutrient levels, and algal growth (Figures 2-3). As algal growth increases from added nutrients, the chemical reactions from photosynthetic activity cause the concentrations of hydrogen ions in the water to decrease, which causes pH levels to increase. Increased algal growth of certain species now prevalent in the lower Deschutes also reduces the habitat and food sources of macroinvertebrates. (Nutrient levels in the Deschutes basin will be covered in its own post in the near future.)
Figures 2-3. Algae in the lower Deschutes. Left: Algae on rocks, one mile below the Pelton Reregulating Dam. Right: Algae growing on one of DRA’s data sondes near Warm Springs after only one month of being in the water.
Post-SWW Violations of Oregon’s pH Standard
Since the Clean Water Act was amended in 1972, state environmental agencies have been responsible for establishing specific standards of water quality parameters, including pH, within each drainage. In the Deschutes Basin, the Oregon Department of Environmental Quality (DEQ) set the maximum pH standard at 8.5 in order to protect aquatic organisms from the harmful effects high pH outlined above.
Since the Selective Water Withdrawal Tower began operation in Lake Billy Chinook in late 2009, pH levels have risen in the Lower Deschutes River and have consistently exceeded DEQ’s 8.5 maximum standard. In 2022 alone, DRA’s data collected at river mile 99.7 (approximately 0.3 miles downstream of the reregulating dam) show 170 days that pH levels violated the 8.5 standard out of 234 days of data collection. Unfortunately, this has been the norm since the DRA started collecting seasonal continuous pH data in the lower river starting in 2016. Furthermore, a comparison of long-term pH data collected by Oregon DEQ before and after tower operations in the lower Deschutes at the Warm Springs Bridge from 1989-2022 show an immediate and sustained increase in exceedances of the 8.5 standard upon commencement of SWW operations (Figure 3).
The only realistic explanation for the increase in pH after 2009 is SWW Tower operations. This is largely due to the strong relationship pH has to nutrients and the relative increase of nutrients entering the lower Deschutes due to surface water releases from Lake Billy Chinook when tower operations began. This issue will be covered in depth in a future post. In summary, the nutrient issues in the lower Deschutes, as represented by the elevated pH levels, have caused negative shifts at the base of the river ecosystem and is also correlated to the increase in fish disease that has been observed over the last decade. The pH and nutrient issues are only part of the LDR’s water quality problems attributed to the SWW tower operations.
Figure 3. DEQ pH measurements taken from similar times of day and month from 1989 - 2022 (pre- and post-SWW Tower) on the LDR at the HWY26 bridge in Warm Springs. pH above 8.5 occurred in ~3% of measurements (n=89) from 1989-2009 (pre-SWW Tower) compared to 29% of measurements (n=70) from 2010-2022 (post-SWW Tower). Source: ODEQ Ambient Water Quality Monitoring System. Data source: DEQ Ambient Water Quality Monitoring System database
What can be done? Fortunately, conditions could be improved by simply increasing the proportion of cool, clean bottom water released by the SWW Tower. Rather than releasing 80-100% warm nutrient rich surface water from Lake Billy Chinook for the majority of the year, PGE could simply maximize cool, clean bottom releases outside of the peak juvenile salmonid outmigration period of March-June and thereby improve water quality conditions without any impact to power production or anadromous fish reintroduction. The DRA will continue to advocate for the immediate relief that cooler, cleaner bottom-water will provide to the lower Deschutes River.
Current and upcoming pH issues in the lower Deschutes
You can access the current water quality conditions, including pH, on the lower Deschutes River, on our Public Portal. pH, temperature, and dissolved oxygen data is collected and uploaded to the portal every 10 minutes at each of our two monitoring stations in the lower Deschutes near Warm Springs and Maupin. For more information, please read the Public Portal Help Sheet and reference our lower Deschutes River Updates.
If you have been following the DRA’s recent posts, you know that Oregon Department of Environmental Quality (DEQ) is proposing the relaxation of the pH standard from 8.5 to 9.0 in the Crooked River and Trout Creek basins as part of their 2022 Aquatic Life Use updates. The DRA strongly opposes these changes and have submitted a comment addressing this and other concerns outlined in our recent blog post. The public comment period closed on June 23. After DEQ addresses public comments, it will need approval by the Oregon Environmental Quality Commission this Fall and it will then be submitted to the U.S. EPA for consultation and final approval. The proposed updates will not take effect until final approval. This process may take through the end of 2024.
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