Ecosystem models expand our understanding of the Salish Sea

Scientists are using computer models to address complex issues in the Salish Sea like the rise of harmful algal blooms and the movement of toxic PCBs. LiveOcean, Atlantis and the Salish Sea Model are three systems that are changing the game for ecologists and other researchers.

Locations of shellfish beds in the Salish Sea (left) compared to regions predicted by the Salish Sea Model to have high microplastic accumulation (right). Maps: PNNL
Locations of shellfish beds in the Salish Sea (left) compared to regions predicted by the Salish Sea Model to have high microplastic accumulation (right). Maps: PNNL

Engineers have known for some time that they could build models to simulate the movements of ocean currents in the Salish Sea. One of the most ingenious of these was created in the 1950s when scientists at the University of Washington built a scale version of Puget Sound out of concrete. It used saltwater and dye to track tidal flows and it was a standard for oceanographers for more than 30 years.  

Now, computer models can replace circulating dye and water pumps with just about any conceivable data. They can reveal how water temperature changes and moves, how fast Arctic melting will raise the tideline along the shore, where endangered killer whales go or when global carbon emissions will eventually turn the Salish Sea acidic. They can anticipate herring spawns or show the movements of toxic chemicals. The better the model, the more accurate the predictions.

The Salish Sea Model

The Salish Sea Model from the Pacific Northwest National Laboratory was initially developed with support from the Environmental Protection Agency to understand how nutrients from wastewater might be diminishing Puget Sound’s water quality. That work led to ongoing discussions about the future of the region’s wastewater treatment plants, and the model has been at the center of policy debates that could affect hundreds of millions of dollars in treatment plant retrofits.  

But the model has quickly become a tool for answering all sorts of scientific questions. Its open source software is designed to be used by anyone, and scientists from many different disciplines are now plugging in their data. Consider a species like eelgrass, says Tarang Khangaonkar, who led the model’s development. He hopes that the model will help to spur collaborations among researchers.

“An eelgrass expert probably has [much of] the data he needs on eelgrass, where it exists on the maps and so forth,” says Khangaonkar. “But when it comes to trying to predict what might happen in future scenarios, they don’t have currents, hydrodynamics, nutrient pollution and so on. So, here is a tool that allows a researcher to work in their area but not be impeded by the fact they are not a hydrodynamic expert. We can help with that."

Other research using the model includes the tracing of PCBs in shellfish, herring and other species, as well as far reaching analyses on ocean acidification and other questions critical to Salish Sea conservation.

For the Salish Sea Model, Khangaonkar says, the sky’s the limit. “We have done the hard part,” he says. “The hard part was getting it to work. Now we can look at all kinds of scenarios.”

LiveOcean

Another computer model that is helping scientists forecast ocean conditions is LiveOcean, developed by the University of Washington Ocean Modeling Group. It makes three-day forecasts of currents, temperature, salinity and many biogeochemical fields in Puget Sound and the Pacific Northwest including harmful algal blooms.

That model is also available for use by the public “to facilitate communication between resource users, managers, and scientists, and to improve the quality and utility of the forecasts,” according to the LiveOcean website.

Atlantis Ecosystem Model

Diagram of Atlantis model structure. Image: Atlantis NOAA is updating a model of the California Current that is being used to understand some scenarios in the Salish Sea. According to NOAA, “Atlantis is intended as a strategic management tool to evaluate hypotheses about ecosystem response, to understand cumulative impacts of human activities, and to rank broad categories of management options.”