Deschutes River Alliance Reveals 2016 Science Plan

Our 2016 Science Plan is now posted to our website, under the Reports tab. Our annual science plans have evolved over the course of the past two years.  The first year was directed at determining if the changes (alterations in aquatic insect populations and nuisance algae proliferation) we had been observing in the lower Deschutes River began directly below the Pelton-Round Butte Dam Complex and continued to the mouth, or if there was a source downstream from the dams causing these changes.  These efforts confirmed that alterations in aquatic insect populations and the nuisance algal blooms begin immediately below the dams.

Algae at Disney Riffle, 1 mile below the Pelton-Round Butte Dam Complex. Photo by Greg McMillan.

As a consequence, in 2015 we realized we needed to understand the quality of water released from the Selected Water Withdrawal Tower in the Lake Billy Chinook reservoir, which largely controls the water quality in the lower river.  To determine that, we began to conduct water quality sampling in Lake Billy Chinook.  We’ve been sampling both surface water and water at depth since the beginning of June 2015.

We’ve learned a few fundamental facts about Lake Billy Chinook:

  • The water at the bottom of Round Butte Dam forebay is roughly twenty degrees (Fahrenheit) cooler at depth than at the surface during the summer.
  • The pH at the surface in the forebay and Crooked River Arms approaches 10 (highest recorded pH was 9.9). We did a search of the scientific literature and determined that the maximal pH salmonids can tolerate for any prolonged period of time is 8.5.  The water at depth has a much more tolerable pH of 7 to 8.
  • We also learned the primary nutrient source (for both nitrogen- and phosphorous-based nutrients) in Lake Billy Chinook, is the Crooked River. The Middle Deschutes also makes a contribution to that nutrient load.  The Metolius is relatively low in nutrients, especially nitrogen-based nutrients.  These nutrients are what fuel algal blooms.

We have hypothesized that the massive algal blooms in Lake Billy Chinook have acted as a filter for nutrients.  The nutrients are consumed by the algae when they grow rapidly with exposure to warm temperatures and sunlight. The algae then die in late summer and fall.  As the reservoir cools in the fall, the previously warmer water at the surface cools and mixes with water at the bottom.  We believe that in the past this allowed the reservoir to sequester nutrients and prevent them from being discharged into the lower river at the rate they are today.

Our results this summer do indeed show a reduction in surface water nutrient levels as algae activity increases.  In the winter and spring, prior to the reservoir algae blooms, 100% surface water is being discharged into the lower river.  We believe that this is when the lower river likely becomes loaded with the nutrients that trigger the widespread nuisance algal growth we’ve all observed and slipped on!

This year we will begin sampling reservoir water at the surface and at depth in February.  This will allow us to determine if the nutrient cycling described above is indeed taking place.

We will also be continuing our aquatic insect sampling work at two locations below the dam complex, along with our aquatic insect hatch survey.

Lastly, we’ve been fortunate to be given funding for a high quality continuous water quality sampling and recording device that will be installed below the dam complex.  This will allow us to understand the hourly, daily, and seasonal changes in water quality discharged from the dam complex.

We wish to thank all of our supporters for making this work possible.  Without your continued contributions we would be unable to pursue answers to these critically important research questions.  Funding for our 2016 Science Plan is not yet complete.  We are grateful for any contributions you can provide to help us achieve these research goals.  Effective advocacy is founded on strong scientific research. Thank you!

Water quality monitoring on Lake Billy Chinook, 2015. Photo by Greg McMillan.

Water quality monitoring equipment, Lake Billy Chinook, 2015. Photo by Greg McMillan.


Deschutes River Alliance: Cooler, cleaner H2O for the lower Deschutes River. 

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