As California ponders water storage, a new study adds nuance to cold water conservation.
As drought-stricken California considers construction of new damsa new study reveals that many existing state structures— despite efforts to prioritize healthy water temperatures— are lacking in the cold-water ecosystems that depend on them.
The study, Posted in PLOS A, analyzed data from 77 cold-water streams across California to characterize their “thermal regime,” that is, their annual temperature fluctuations over a period of eight to 12 years. Salmon, trout, and a variety of other cold-water species are sensitive to disturbances in temperature patterns; the temperature range is as important to their life cycle as the amount of water flow. But across the state, according to the study, some dams have disrupted these rhythms up to 50 km from the affected rivers.
The Pine Flat Dam in Sanger, California releases water into the flow of the Kings River after being held in a reservoir. With the exception of Shasta Dam, no other regulated river in recent study has shown the natural temperature patterns that coldwater and coldwater ecosystems require.
George Rose/Getty Images
In order to protect habitat, water managers supply cold water to streams from reservoirs. But according to Ann Willis, lead author and researcher at UC Davis, no amount of temperature can guarantee the health of an ecosystem. For example, the temperatures required for the incubation of salmon eggs are different from those required for the juvenile growth of fish. “Rivers have the temperature they have due to interactions between water, trees, snowmelt and groundwater, creating unique temperature patterns,” she said. “Water temperature is more than just a number.”
Willis’ research highlights a difficult reality for conservationists: of 27 dams, only one has successfully duplicated the crucial temperature patterns on which cold-water ecosystems depend. “In science, when we have results like that, we call it an outlier, which means it’s the exception that proves the rule,” Willis said. Dams — even those designed to manage cold water ecosystems downstream — were extremely unable to mimic fluctuating temperature patterns.
Historically, water management has focused on releasing water from dams with a temperature target of one degree, or a seven-day average, to maintain cold-water ecosystems. But it simplifies temperature dynamics, smooths out an otherwise dynamic process, and disrupts seasonal patterns important to ecosystems. In other words, the right temperature is not always released at the right time.
Scientists and policymakers must carefully consider thermal regimes when assessing the future of California’s water infrastructure and imperiled cold-water ecosystems, said State University hydrologist Belize Lane. from Utah who did not participate in the study. “They make a good point: we have oversimplified environmental management goals.” But more study of complex stream-level dynamics is needed, Lane said, particularly the potential role the state’s existing dams play in meeting the temperature needs of ecosystems.
“They make a good point: we have oversimplified environmental management goals.”
Restoring a dynamic annual temperature pattern is crucial, both to preserve California’s salmon and trout — three-quarters of which are threatened with extinction — and to protect the broader ecosystems on which many Californians depend. Whether it comes with or without dams is another question.
Some argue that dams can help manage cold-water ecosystems in a changing climate by storing and releasing cool water. But Willis said the science is clear: environmental management must move away from oversimplified temperature goals.
Watershed management as a field has already seen its operational strategies challenged. After scientists noticed the importance of a varying amount of water flow, managers adjusted the timing and volume of water discharges. The same goes for temperature, Willis said: Adjustments need to be made to account for cold-stream patterns and the species that depend on them.
Willis said she is not advocating the removal of all dams. She simply believes that we need to be more deliberate about what our water infrastructure seeks to accomplish. As she said, we need to identify “inappropriate dams” – and remove them if necessary – while improving existing infrastructure if necessary. If we want to improve the ecosystems on which so many species depend, Willis said, we need to focus more clearly on how science informs our goals.
Increasing water storage is on the list as federal infrastructure spending heads to California. Willis hopes his research will give pause to anyone recommending expansion of the state’s already staggering dam footprint. She also cautions against using the existing approach to support cold-water ecosystems“Science doesn’t support that,” she said.
Theo Whitcomb is a writing intern at High Country News. We welcome letters from readers. Email him at [email protected] or submit a letter to the editor. See our letters to editor policy.
