A few weeks ago we covered the topic of using CO2 as a barrier to fish movement. For a refresher, you can read about it here, but the basic idea is that some river locks may be infused with CO2, creating a plume of CO2 water that is released when the lock is open and which deters fish from moving upstream. Because we had additional questions and comments (and it’s a tricky topic), we interviewed Dr. Caleb Hasler, a post-doctoral researcher at the University of Illinois. Caleb is heavily involved in researching the impacts of CO2 on fish.

Q: Will any barrier work to prevent Asian carp from getting to the Great Lakes? It would seem that no matter what we engineer, at some point these fish will get to the Great Lakes. 

Any non-physical barrier should not be considered to be 100% effective at preventing Asian carp (Bighead, Silver, and Black Carp) from getting to the Great Lakes. For fish, there are variations in size and behavior that may limit a “one barrier for all” approach. However, installing different types of barriers should reduce the likelihood that Asian carp will get to the Great Lakes and that is why understanding the potential for CO2 to be an effective barrier is important.

Q: What are the characteristics of the CO2 plume that will emerge from a lock? Does it stay together as a blob of water, or does it diffuse into the rest of the river?

Great question, and one that is currently being addressed by hydrologists and modelers. From simple experiments we have completed, gentle aeration causes CO2 to be released from water that has had CO2 injected. Therefore, we think that upon release from a lock, the CO2 will be quickly off-gassed close to the lock. Several other characteristics of water and the presence of CO2-using biota may influence off-gassing, so it will be interested to see the results of the hydrology models currently being completed.

Q: Adding CO2 to water lowers the pH, and this is well known in marine environments as ocean acidification. How much will pH be impacted in rivers? Will they be acidified? Would river acidification impact fish and other animals?

Definitely adding CO2 to freshwater will cause acidification, however, this acidification is termed “weak” acidification (not to be confused with “strong” acidification, similar to acid rain). We expect that in the water where the CO2 is injected, there will be approximately a drop in pH from (roughly) 7.5 to 6.5. We have recently completed a review paper on the potential impacts of elevated CO2 in freshwater (Freshwater biota and rising pCO2? Ecology Letters), and it seems that many freshwater systems already experience a range of CO2 and pH values across daily and seasonal time scales, thus, freshwater organisms are likely adapted to small changes in pH. Our lab is currently completing studies on freshwater fishes and mussels to see what behavioral and physiological changes may occur when animals are exposed to elevated CO2 and weak acidification. Stay tuned!

Q: We hear a lot about problems related to too much CO2 in the atmosphere. If we pump large amounts of CO2 into water, won’t it eventually off-gas into the environment and contribute to greenhouses gases, which are already high?

On average, freshwater systems are currently (and have been for a long time) supersaturated with CO2, meaning they already off-gas CO2 to the atmosphere and transport a lot of CO2 to the ocean. Should CO2 be injected into water as a barrier, this will likely lead to higher levels of CO2 in the surrounding air of a localized area for brief periods of time (i.e., around the lock, immediately after injection), but significantly increasing GHGs is unlikely given the large volume of gases already in the atmosphere and the large contribution of other sources of GHGs.

Q: Are other chemical barriers (other gases) under investigation? Why CO2?

Dr. Suski has reviewed this topic in detail in a paper published in 2012 (Non-physical barriers to deter fish movements, Environmental Reviews 20: 1–12). So far, CO2 has been the most effective gas barrier tested, however, we did complete studies this summer using ozone. Ozone was difficult to use because it quickly changes into oxygen when it meets other substances in water and requires a large amount of ozone in order to reach levels that may influence fish. CO2 has been deemed appropriate because it has been shown to cause avoidance behavior in several species and size classes of fish, is relatively simple to inject, and so far has shown great promise in influencing Asian carp movement.

Please contact Caleb Hasler with any questions, or follow him on twitter @CalebHasler