For salmon, even small changes in their environment can lead to big changes in their ability to migrate. In the Yakima River, low dissolved oxygen concentrations in water are making it difficult for salmon to breathe and migrate upstream. This low oxygen concentration is likely caused by increased growth of a plant native to the river, water stargrass (Heteranthera dubia) but it could be caused by other organisms respiring in the river.
Sarah Roley, Assistant Professor at Washington State University Tri Cities, is studying the effects of removing stargrass with a commercial harvester to try to increase oxygen concentrations in the water so salmon can breathe more easily. Roley is one of the winners of the 2021 State of Washington State Water Research Center Seed Grants.
Although Roley has multiple funding sources for the experiments she is conducting, she said that without the seed grant she would not be able to complete all parts of the experiment. Additionally, the project benefits doctoral student Aaron Pelly by providing him with a research assistantship for the fall semester.
“I think really this important detail of figuring out where respiration is occurring, being able to really test if it’s water star grass, or is it the sediment, that we would not have been able to do without the WRC grant. So we would have had incomplete information”, Roley said. There is a very consistent oxygen concentration of oxygen in the atmosphere across the entire globe. However, the amount of oxygen in water varies greatly. Water oxygen concentrations are affected by organisms respiring or photosynthesizing and by the temperature of the water with warm water holding less oxygen.
Respiration is how living organisms produce energy, typically by the intake of oxygen, and photosynthesis is how plants use sunlight to synthesize food from carbon dioxide and water. At night, photosynthesis does not occur while respiration increases, both of which lead to decreased oxygen levels in the water. Fish use oxygen dissolved in water to breathe. Salmon are cold water fish and can’t migrate when water temperatures are too high, so they migrate at night when the temperatures are cooler. But at night the Yakima River doesn’t have enough oxygen for the fish.
Over the last few decades, water stargrass has proliferated in the Yakima River, Roley said. In some places, almost the entire width of the river is covered in stargrass. Increased respiration resulting from the huge increase in stargrass is the likely cause of the low oxygen levels. If large amounts of stargrass are removed from the Yakima river the oxygen levels in the water may increase to levels suitable for salmon migration. But another respiring organisms, such as microbes or algae, could be the cause of the decreased oxygen level. Pelly conducted previous research that suggests that water stargrass could be responsible for the low dissolved oxygen concentrations.
Pelly is a part of the seed grant program and will gain experience in field and laboratory techniques as well as data management by participating in the experiment. Roley and Pelly will remove stargrass from two locations in the lower Yakima River as well as monitor two control sites that are not harvested. The oxygen rate in the water, the amount of stargrass, stargrass respiration, sediment respiration and water column respiration will be measured before and after the stargrass harvest.
In areas without stargrass, sediment and water column respiration will be measured. Respiration will be measured using opaque, cylindrical chambers outfitted with a probe that measures dissolved oxygen. “This doesn’t happen very often, but sometimes it does happen, they will drift,” Roley said. “Meaning, say oxygen is at eight milligrams per liter, and they are starting to measure it at something lower than that or something higher than that then we check the calibration before and after. So if they aren’t accurate we can correct for that.”
Temperature and dissolved oxygen in the water will also be measured starting in early summer before the probes are removed during the stargrass harvest and redeployed after. The daily dissolved oxygen minimum as well as days above and below an oxygen threshold that salmon can tolerate will be measured. The probe will be calibrated frequently to ensure accuracy of the readings.
“This doesn’t happen very often, but sometimes it does happen, they will drift,” Roley said. “Meaning, say oxygen is at eight milligrams per liter, and they are starting to measure it at something lower than that or something higher than that then we check the calibration before and after. So if they aren’t accurate we can correct for that.”
The stargrass will be removed by a commercial harvester in late summer when water levels are low. Removing stargrass could be the key to helping salmon migrate through the Yakima river, but if it isn’t, the experiment will have successfully ruled out one reason for the increased respiration. Roley’s experiment will complement other research that is already occurring to help many agencies make better conservation decisions.
Author: Erin Mullins, WSU Undergrad Intern