Glaciers could mean life and death for salmon during heatwave
As climate change continues to worsen, heatwaves like killed hundreds of people It became more common and extreme last summer as it rolled across the Pacific Northwest.These heat waves can cause mass death fish in the stream become too hot for them. However, some salmon have found a surprising savior in this battle for survival: glaciers.
Rising temperatures and extreme heat events have brought disaster to Pacific Northwest communities. Heat-related illness and death are becoming more common, and environmental resource managers are dealing with summer droughts that make water allocation more difficult. Warming river temperatures and low flows put cold-water species such as salmon at a higher risk of heat stress, disease and even population mortality, and heat waves are sometimes the tipping point between what salmon can tolerate and lethal river temperatures.
Glaciers can mitigate some of these effects by producing cold meltwater for streams and rivers that receive meltwater. In this way, they create buffers against high temperatures and low flows. However, the exact contributions of glaciers to rivers and the impact of climate change on those contributions remain questions that can only be answered by long-term studies.
Mauri Pelto, Director North Cascade Glacier Climate Project (NCGCP), has devoted his entire research career to answering similar questions. A professor of environmental science at the Nichols College, he founded the NCGCP in 1984 to monitor the long-term response of glaciers to climate change. Along with an ever-changing research team that includes undergraduates, graduate students and his own children, he has been studying these glaciers and tracking changes in their mass, endpoint locations and runoff for nearly four years. While the primary focus of Project Pelto is tracking and understanding glacier retreat, his work also includes working with community partners to study the potential impact of glacier retreat on wildlife, including salmon, ice worms, and goats.
A post shared by Mauri Pelto.
This latest research From NCGCP, published in the journal water In April, an analysis was made of how the contribution of glacier runoff to streams during heatwaves can alter stream conditions and potentially protect salmon populations from the risk of heat stress-related hazards in the river. The research team compared two sections of the Nooksack River in northwest Washington — the glacier-covered North Fork and the glacier-free South Fork — and tracked stream temperature, discharge and glacier runoff over 24 high temperature events over the past decade.
The study quantified the effects of glacier runoff on river temperature and flow during heatwaves, confirming trends familiar to water managers. Thermal events typically result in increased water flow temperature and reduced water flow. However, in glacialized streams, the glaciers melt faster, contributing more cold runoff to the stream, buffering the temperature and water volume rate. While this general trend is understood, these differences have never been quantified, making it difficult to accurately predict the impact a heatwave might have on the river and the species that live in it.
The North Fork Nooksack River is fed by glaciers and snowfields on Mt. Baker, Mt. Shuksan, and Goat Mountain, and glacial runoff subsidizes the stream during the hot, dry summer months. Image credit: Patrick McNally/Frick
The new study found that during heatwaves, the amount of water in glacier-free streams like the South Prongs decreased by about 20 percent, while those in glaciers like the North Prongs increased by 20 percent. The amount of water in a river or stream affects the amount of dissolved oxygen and water temperature and discharge levels, all of which affect salmon populations.
Pelto told GlacierHub that the effect of glacier runoff on stream temperature during heatwaves was not as dramatic as the difference in water volume, but still significant. In the forks without glaciers, the water temperature rose by about 2 degrees Celsius, while in the forks with glaciers it rose by only 1 degree Celsius. However, Pelto noted, “streams without glaciers are already starting to be at higher temperatures, so it does end up being a bigger problem for salmon.”
For salmon, the difference between the two forks is already clear.The South Fork consistently exceeds the tolerance temperature for salmon (about 19 degrees Celsius), and last summer, there was a Mass die-off of 2,500 Chinook salmon The Nuuksack River in South Fork after a heatwave. The salmon themselves didn’t die from the heat, Pelto explained, but “their systems are stressed, which makes it easier for algae or bacterial explosions to injure them.” In the North Fork, where stream temperatures didn’t rise nearly as much, salmon survived the heatwave. Unscathed.
Salmon, such as Nooksack’s Spring Chinook salmon, are important for cultural, survival and economic purposes. Many indigenous tribes, such as the Nooksack Indian tribe and fishing communities, depend on these populations. Source: Pacific Northwest National Laboratory /Frick
As the glaciers retreat and disappear, more rivers will begin to resemble the South Prong. That means salmon populations will be more vulnerable to the negative impacts of heatwaves and high temperature events, and mass die-offs like last summer’s could become more common.
Salmon is important culture, the economic and ecological resources of the Pacific Northwest, and their loss would have devastating effects on the region. Understanding quantifiable ways in which glaciers buffer river temperatures and discharge rates will allow fisheries managers to protect salmon and prioritize at-risk salmon populations in the future.
