As the climate warms, so do our waters. But to what extent and what can we do about it locally? Our work at the Spokane Riverkeeper aims to answer both of those questions. We monitor water temperature in Hangman Creek and the Spokane River. In previous years we have found alarmingly high water temperatures; water that could kill our native redband trout and is above state standards. Our surveys of the Hangman Creek watershed point to clear sources of this thermal pollution. Lack of riparian buffers on much of the mainstem and tributaries allow sunlight to warm surface waters. However, this year we found solutions to the water quality problems that plague our creeks as well. We also got serious about reporting our findings. We created Quality Assurance Plans and entered our data in the Electronic Information Monitoring (EIM) database, ensuring state regulators would use our data to evaluate pollution loading in the watershed.
Figure 1. We placed temperature loggers in Hangman Creek throughout the watershed. Many locations had only reed canary grass as a riparian buffer, such as here at Waverly, WA.
First the bad news. In 2019 water in all sites (see Map below) in Hangman Creek exceed water temperature standards. The seven day average daily maximum temperature (7DADMax) ranged from 19.7 (67.4 F) in California Creek to 25.4 (77.7 F) in Hangman Creek at Waverly (the Marshall Creek site was excluded due to outliers that most likely resulted from air exposure). The water quality standard in Washington State is 18 C (64.4 F). Unless trout can find a thermal refuge, such as cold spring or deep pool, they’re toast in much of the Hangman watershed.
Figure 2. Seven day average daily temperature maxima in the Hangman Watershed. These data summaries are what state regulators use to evaluate whether a water body meets water quality standards.
Interestingly, there may be some thermal refuges in the Hangman watershed (Figure 2). Looking at average temperatures locations like California Creek, Rock Creek, and Little Hangman have average temperatures well below the standard for much of the year. This is most likely due to groundwater influence in the area. With a high water table, cool water can flow into some of these creeks, creating thermal refuges, at least for some of the year. In June, Rock Creek has some of the warmest water temperatures, most likely due to high surface water flows.
Figure 3. Average daily water temperatures for sites in the Hangman Watershed.
Much of the reason for these high temperature are due to lack of riparian buffer, or streamside vegetation. The Hangman Watershed is notorious for denuded shoreline and the resulting pollution. However, many groups are solving this problem, with great effect. The Coeur d’Alene Tribe, has restored the upper reaches of Hangman Creek to its native condition (Figure 3). The result is cooler water temperatures, a higher water table, and a flourishing native ecosystem, complete with beaver and elk.
Figure 4. Hangman Creek previously flowed through a 15 foot incised channel, which was filled in (left). The creek now flows through it's native channel, which was replanted by the Coeur d'Alene Tribe and volunteers from Trouth Unlimited.
Figure 5. Maya Newman, Spokane Riverkeeper science intern, downloads water temperature data from the Spokane River at Harvard Road.
The Spokane River is a different story. As you probably know by now, the Spokane Valley Rathdrum Prairie Aquifer flows into the Spokane River at Sullivan Road. Downstream of Sullivan Road (the Upriver, Division St., and TJ Meenach sites in the graph) aquifer water makes up most of the surface water in the Spokane River. Upstream of Sullivan Road (the Harvard and Barker Road sites), the entirety of the River is surface water from Lake Coeur d’Alene. Not surprisingly these upstream sites are hot! In fact, their 7DADMax’s are around 25 C (77 F) (Figure 6). At the aquifer influenced sites, temperatures are much lower, hovering near the WQ standard. Not surprisingly, during the hot summer months, trout anglers focus on the cooler, aquifer influenced waters of the Spokane River.
Figure 6. Seven day average daily maximum water temperature for sites in the Spokane River.
Figure 7. Average daily water temperatures in the Spokane River.
The cause of much of these issues in the losing reach of the Spokane River are not lack of riparian vegetation, but climate change. Earlier spring melt offs, lower flows, and hotter summer nights all contribute to a warmer river. What once was a prized trout fishery is now more suitable for bass and other invasive fish in the summer months. Our research shows a warming climate in this portion of the Spokane River, due to mostly air temperature increases, but also river flow decreases. Using 11 years’ worth of river water temperature, air temperature, and river flow data, we created a formula to predict future water temperature (Figure 8). We then entered predicted future air temperatures and river flow, taken from the Spokane Community Adaptation Project (https://pnwcirc.org/spokane-community-adaptation-project) to predict average river temperature. Although there are some big dips, mostly due to past river flow, the prediction is grim. Average temperatures in the Spokane River will rise almost 2 C by 2100. Without drastic global action, the losing reach of the river will not have suitable habitat for redband trout.
Figure 8. Predicted river temperature increases to 2100.