The Salish Sea is a complex web of waterways that includes Puget Sound and the straits of Juan de Fuca and Georgia. It also has inflows from 64 rivers and 99 wastewater treatment plants in the U.S. and Canada. Getting a handle on water quality in this unique geography is challenging.
Washington’s Department of Ecology has collaborated with the Pacific Northwest National Laboratory to create the “Salish Sea Model.” It’s a mathematical tool to predict how human activity affects the health of the sea.
“If you go to the doctor, they measure your blood pressure and your pulse. And that’s kind of what we do when we monitor water quality in Puget Sound,” said Teizeen Mohamedali, an environmental engineer working on the model for the Department of Ecology.
I met Mohamedali on the shore of Padilla Bay, an estuary reserve near Mount Vernon. It's known for its massive 8,000-acre eelgrass meadow, the second largest one on the West Coast.
The Department of Ecology has four monitoring stations here. Scientists are looking at temperature, salinity, pH, dissolved oxygen and turbidity, which is how cloudy the water is.”
“When you do this for example over 20 years, you get to see how things are changing over time,” Mohamedali said.
That understanding amps up when they plug the data into their computer model.
“It simulates all the different processes in the Salish Sea that govern water quality,” she said. “So first you have circulation, how water moves around, Pacific Ocean water entering the Sound, all the rivers, all the wastewater treatment plants and their effluent.”
That information allows the model to predict how the water will move. Then researchers can learn about oxygen levels and algae blooms over a given period of time.The scientists calibrate the model by comparing its results with real data from their monitoring stations.
The goal is to predict and understand how human activity affects the health of the ecosystems. After about ten years of development, scientists have achieved a level of accuracy that is sufficient to shape local policy.
“The model is going to be used to develop the Puget Sound nutrient reduction strategy, which is to help us define what we need to do in terms of nutrient management in Puget Sound,” Mohamedali said.
Part of the model’s success came from recognizing that its scope needed to include the entire Salish Sea, not just Puget Sound, which was what they were using when the project started. At the time, the model was primarily aimed at analyzing the low oxygen levels in those areas.
”So we had a model of south and central Puget Sound,” Mohamedali said. “But we started to realize that all of these waterways are really connected.”
Northern Puget Sound, the Fraser River and the Pacific Ocean were all influencing their results. They were able to expand the model and change its name.
“And as we had more funds to improve the Salish Sea Model, it became a better tool,” she says.
Mohamedali has a youthful enthusiasm for the power of the model. She agrees it could simultaneously be compared to a crystal ball and a virtual reality video game.
It allows scientists to see into the future or look back into our past and try to predict consequences of choices we make. It allows them to run scenarios that represent experiments you couldn’t do in real life.
“We can go back in time and say, ‘What if we removed humans from the equation? What if there were no human nutrient sources and no wastewater facilities discharging into Puget Sound, what would water quality look like?’” she said.
The model scenarios can also spin forward with datasets based on future stressors such as projected population growth or urbanization. Another a big area of interest and collaboration is in predictions of climate change.
“So for example the University of Washington climate impacts group has estimates of what river flows will look like in a future climate and how the hydrology will change. And we have global climate models that can tell us how air temperature changes will be. And we have some idea, but not as much, of how the Pacific Ocean is going to change in the future,” Mohamedali said.
Let’s take the year 2015. Water quality in the Salish Sea suffered from a drought combined with a warm patch of water off the Pacific Coast, nicknamed “the blob.” Algae blooms thrived.
Mohamedali’s team has not yet modeled all the conditions for that year, but they expect it to shed light on what might become the new normal under climate change.
That insight can be a powerful motivator to shape policy and help people shape the future more proactively, rather than deliberating about why our problems are so large and out of control, Mohamedali says.
“What the model does is it actually helps us get down to the details of what it is locally that we can do or how much our local activities are having an impact,” she said.
Once people see that, they can be empowered. The key is clearing up uncertainty that can be overwhelming. What might seem overly technical or abstract is actually very meaningful.
“This is actually pretty cool that we're able to look at a window into the future and help us plan for that uncertainty by having, you know, math, essentially,” Mohamedali said.
Updated at 10:30 am, Nov. 20th, 2017 to correct that Padilla Bay’s eelgrass beds cover nearly 8,000 acres, not 800. We regret the error.