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The “tomato soup” color in waters near Edmonds was produced by a dinoflagellate called Noctiluca scintillans, one of many types of algae that can grow rapidly in the presence of excess nitrogen and sunlight. // Photo (2013): Jeri Cusimano via Department of Ecology (CC BY-NC 2.0)

Low-oxygen problems to be scrutinized in talks about research, modeling efforts

By Christopher Dunagan

For decades, researchers have been advancing their understanding of what causes the harmful and sometimes deadly low-oxygen problems afflicting some areas of Puget Sound. Computer models have been developed to replicate conditions and point the way to possible solutions.

Experts generally agree that excess nitrogen flowing into Puget Sound contributes to the low-oxygen conditions. What is needed now, some argue, is a stronger regionwide consensus around solutions to the problem. That could mean coming to terms with research findings, understanding the strengths and weaknesses of the models, and figuring out the most effective ways of reducing nitrogen sources.

Expanding the discussion to all interested parties is the thinking behind a series of 10 workshops, coordinated by the Puget Sound Institute (PSI), that will begin on Tuesday and continue into next year. The workshops will build on previous discussions, such as the Washington Department of Ecology’s Nutrient Forum and a forthcoming Marine Water Quality Implementation Strategy that will help focus actions for Puget Sound restoration, said Stefano Mazzilli, senior scientist at PSI who is leading the discussions.

“We are focused on the scientific uncertainties that regional collaboration can advance in the next year,” Mazzilli said, adding that modeling may support immediate as well as long-term recovery actions, as the effort builds confidence in the environmental benefits of various options.

PSI, which also supports this blog, is an independent group within the University of Washington, providing analysis, research and communication about Puget Sound protection and restoration.

In general, open discussions among scientists, managers and those affected by plans and regulations help to build confidence in the scientific underpinnings and the models that support specific actions, according to Martha Sutula, head of the Biogeochemistry Department at the Southern California Coastal Water Research Project and a keynote speaker at Tuesday’s forum.

Martha Sutula

“Over the last 20 years of my career, I have played the role of a scientist who uses models for decision support to improve water-quality management of coastal habitats — from coastal rivers to coastal estuaries to the nearshore,” Sutula said in an interview.

The Southern California Coastal Water Research Project, or SCCWRP, is an intergovernmental public agency that conducts research and translates science for water-quality managers who deal with discharge permits, watershed planning, runoff requirements for development, water-quality standards and more.

SCCWRP’s 14-member commission reviews the research of its scientists, who strive to build a consensus around the best available information. Members are able to informally discuss the policy implications of the latest scientific findings. Among the agency members, some are involved in sewage treatment; some are responsible for stormwater; and some write the rules that govern the other two agency groups.

“Puget Sound is already famous for its collaborative science partnership,” Sutula said. “What I will bring to the discussion is our philosophical tenants about how we approach the issue of coastal water-quality management.”

Management decisions — including regulations — flow from scientific findings, she said. Answering questions and getting everyone up to speed on the current science as well as the limitations of the research leads to faith that decisions will protect the environment.

Computer models designed to represent ecological functions of a waterway must account for water flow, temperature, chemistry and a host of other physical and biological parameters, Sutula said. But the models must also accommodate the human communities — specifically how human actions influence natural systems.

Since models are only a representation of reality, it is essential for policymakers to understand the limitations and uncertainty that comes with a given model, she said.

Sutula has worked on a variety of models related to waterways large and small, including one highly complex coastal model addressing the Southern California Bight, a 430-mile stretch of coastline with ever-changing currents and other conditions.

“While I don’t have experience modeling in Puget Sound, for the size and complexity of the system, it would rival any project I’ve been involved in,” she noted.

The Salish Sea Model, under development for more than a decade, is a major tool used to predict the effects of increasing or decreasing nitrogen inputs at various places in Puget Sound. It can also be used for other purposes, such as addressing issues of climate change, including ocean acidification.

Since low-oxygen conditions can affect most living creatures, the model reflects how excess nitrogen can stimulate an excessive growth of plankton, which then dies and decays. The bacterial breakdown of the dead plankton consumes oxygen, and can, under certain conditions, lead to areas of low oxygen harmful to living things.

Using the model, the Department of Ecology ran simulations to better understand the effects on water quality of increasing and decreasing nitrogen input from sewage-treatment plants as well as incoming rivers, which are influenced by runoff from development, farms and natural sources. The results led to discussions by an advisory committee and eventually a proposal to begin monitoring for nitrogen at sewage-treatment plants and to look for ways to limit nitrogen releases with current equipment. Eventually, some plants would need to reduce their nitrogen discharges. The regulatory process involves a “nutrient general permit,” separate from the discharge permits already required under the federal Clean Water Act. (See Our Water Ways, Feb. 12, 2021.)

In response, a number of city and county sewer operators have filed appeals to the permit, challenging the scientific basis used by Ecology to limit nitrogen discharges. King County has stated that potential permit conditions would require a fourth regional plant, “a multi-billion project that would take more than a decade of planning and construction,” according King County’s webpage on the issue. King County contends that other steps can be taken to reduce nitrogen inputs into Puget Sound.

“We want to participate in a constructive conversation with stakeholders about what collective actions we can take to achieve shared goals,” states the webpage.

King County has provided a $500,000 grant to support the upcoming workshops and related communications, such as this blog; expand access to modeling tools; and help fund the Model Evaluation Group, a team of experts reviewing the Salish Sea Model and its capabilities. Others, including the city of Tacoma, are expected to participate in funding through the newly formed Puget Sound Clean Water Alliance.

Several environmental groups in the Puget Sound region have argued that Ecology’s new permit fails to reduce nitrogen quickly enough in the face of a growing population.

For its part, Ecology has responded to calls for delay by saying the problem of low oxygen has been studied since the 1990s, and the nutrient general permit is a necessary start toward a solution.

“Ecology is using the best available science to drive nutrient reduction decisions,” Ecology stated in a response to public comments (PDF 2.4 mb). “Model results show that nutrient loads from municipal wastewater treatments plants, especially the largest plants, have a significant ecological impact within the WA waters of the Salish Sea.

“Both point and nonpoint sources of nutrients must be reduced in order for the Salish Sea to meet DO standards,” Ecology’s response continues. “Permit requirements are geared towards understanding rate impacts from upgrade alternatives, so that they may address affordability concerns.”

Tuesday’s online workshop is scheduled from 8 to 10 a.m. as a Zoom meeting, with registration required.

In addition to a presentation by Sutula, Tuesday’s workshop will include discussions about the overall intent and content of the workshops, modeling issues, and parallel efforts addressing the low-oxygen problems of Puget Sound. Separate breakout discussions will focus on year-to-year variability of nitrogen sources; the effects of dissolved oxygen on key species and habitats; the growth of phytoplankton — the “primary producers” in the food web; and modeling at the watershed scale.

Future workshops will include more detailed discussions about how scientific findings influence decision-making in Puget Sound and other regions, how low oxygen levels affect important species, what is known about year-to-year changes in nitrogen versus climate change and human influences, and how modeling can be used to understand dynamic changes in Puget Sound. Other topics connect oxygen levels to phytoplankton growth, sediment exchange and human sources of nitrogen.

Information is available on PSI’s webpage, The Science of Puget Sound Water Quality.

Christopher Dunagan is a senior writer at the Puget Sound Institute.