The quest continues for a nutrient reduction plan


The quest continues for a large-scale plan to reduce human sources of nitrogen and improve the health of Puget Sound. This article is part of the Puget Sound Institute’s effort to explore the technical uncertainties related to the science of Puget Sound water quality. The project, jointly funded by King County and PSI, includes online workshops and discussions, along with informational blogs and articles.

By Christopher Dunagan

Human sources of nitrogen in Puget Sound have been blamed for increasing the intensity of algae blooms, lowering oxygen to critical levels, and impairing sea life. In response, officials with the Washington Department of Ecology are developing a Puget Sound Nutrient Reduction Plan to strategically reduce nitrogen in various places.

Ecology experts recognize that the Pacific Ocean is the greatest source of nitrogen to Puget Sound, but how much of that nitrogen contributes to low-oxygen conditions depends on many factors. Because oceanic nitrogen is practically beyond human control, much of the current focus is on the ever-increasing levels of nitrogen from human sources. See Ecology’s Oxygen and Nutrients in Puget Sound.

According to Ecology estimates, about two-thirds of the human-induced nitrogen is coming from sewage-treatment plants perched along the shoreline. The rest comes from diverse sources such as septic systems, fertilizers from farms and urban landscapes, animal waste from livestock and pets, and atmospheric deposition from the burning of fossil fuels and organic materials. For planning purposes, these diverse sources of nitrogen are grouped as “watershed” sources, and they enter Puget Sound mostly via streams and stormwater outfalls.

Ecology has begun to address the discharges from sewage-treatment plants with the issuance of a “nutrient general permit” that requires operators to conduct studies, curb nitrogen releases at basically current levels, and eventually cut back on the amount of nitrogen going into Puget Sound.

In response, eight cities, counties, and other sewer operators (listed below) filed appeals to the state’s Pollution Control Hearings Board. [Editor’s note: King County, which is appealing the permit, is one of the Puget Sound Institute’s funders.] A temporary out-of-court agreement has placed some of the permit requirements on hold until the board can decide whether the general permit is legal and necessary.

While stated reasons for the appeals vary among jurisdictions, the sewer operators broadly contend that the new general permit conflicts with federal permits already required of every sewage-treatment plant. Many argue that Ecology has failed to show how their individual operations contribute to the low-oxygen conditions, often mentioning the costs of planning and upgrades to their sewage-treatment plants without clear benefits.

As the eight sewer operators seek to overturn the nutrient general permit, two environmental groups and one tribal government contend that the permit does not go far enough to quickly accomplish corrective actions, considering that many areas of Puget Sound already fail to meet water-quality regulations.

In a joint appeal, the Washington Environmental Council and the Suquamish Tribe argue that loose timelines and other flaws in the permit will allow some treatment plant operators to increase, rather than decrease, nitrogen discharges over the next five years.  Similarly, Puget Soundkeeper Alliance is pressing Ecology to establish enforceable limits on nitrogen discharges and to declare that nitrogen reductions can be accomplished with available treatment technology.

Meanwhile, Ecology continues to work on the overall plan to reduce nitrogen loads from all human sources, with a current focus on so-called watershed sources, including stormwater. Solutions involving upland areas may vary for different parts of Puget Sound, according to Dustin Bilhimer, who heads up Ecology’s Nutrient Reduction Project. Some areas are more affected by agricultural runoff, while others have extensive discharges of urban stormwater.

Besides improving the ecological health of Puget Sound, the goal is to decrease the number of regulatory water-quality violations, which occur when the level of dissolved oxygen falls below a specific state standard. That standard  varies for defined areas of Puget Sound — generally between 4 and 7 milligrams of oxygen per liter in saltwater, depending on the designated use and water-quality classification. Basic concepts are explained further in an Ecology fact sheet (PDF 110 kb) addressing freshwater issues.

Violations of dissolved-oxygen standards have been found so far in 194 designated areas within 46 bays, inlets and open-water sectors in Puget Sound, according to Ecology’s Water Quality Assessment, sometimes called the 303(d) list of impaired waters. Another 290 areas in 45 inlets are on the list for low-oxygen problems, but more study is needed to determine regulatory violations.

These lists, prescribed by the Clean Water Act, may include some areas where low-oxygen conditions prevail because of natural conditions — where humans are not primarily to blame for oxygen levels below the numerical standard. Such areas would not be considered a violation and could be removed from the list if they meet so-called natural conditions criteria. At the moment, Ecology is rewriting its natural-conditions criteria for both oxygen and temperature in a formal rule-making process. The rewrite comes at the direction of the Environmental Protection Agency  which has temporarily suspended the state’s previous natural conditions criteria following a legal challenge.

Excess nitrogen is getting so much attention because nitrogen compounds are a key ingredient — along with sunlight — in the production of excess plankton. Large colonies of plankton eventually die and sink to the bottom, consuming available oxygen as they decay. See related stories: Understanding the causes of low oxygen in Puget Sound” and “Tiny plankton play a mighty role in the health of Puget Sound.”

As planning continues, the Puget Sound Nutrient Reduction Project is trying to identify the most significant sources of nitrogen resulting from human activities. The explicit goal is to identify actions that can lead to the highest level of compliance with the state’s dissolved-oxygen standards.

Using the Salish Sea Model, experts are studying various scenarios that consider the combined effects of reducing nitrogen from sewage treatment plants and from various watershed sources. Key questions revolve around the locations where nitrogen comes into Puget Sound as well as areas most affected by low-oxygen problems. For example, does it make more sense to reduce smaller inputs of nitrogen close to problem areas or cut back on larger sources farther away?

Considering the multitude of problem areas and nitrogen sources, examining the various options becomes a major challenge, even with the help of computer modeling, according to Ecology’s Bilhimer.

From work done so far, it appears that nitrogen-bearing waters readily move from one area of Puget Sound to another, undergoing changes along the way. These enriched waters may contribute to low-oxygen problems a fair distance from the original sources.

Bilhimer says one thing has become abundantly clear from model runs conducted last year: To meet the state’s dissolved-oxygen standards in Puget Sound, large reductions of nitrogen are needed from both sewage treatment plants and human watershed sources. Looking to the future, increasing inputs of nitrogen caused by population growth may exacerbate the low-oxygen problems in some areas if actions are not taken, he said.

To improve estimates of nitrogen from watershed sources, new automated monitoring equipment is being installed to gather data on nitrogen levels at 15-minute intervals in eight rivers, rather than the 30-day intervals used for data collected in the past. The result should be better estimates of nitrogen coming from the rivers under various conditions.

This network of monitoring equipment is expected to be in operation by late spring next year. The first device is currently being installed in the Cedar River. Others will go into the Duwamish, Deschutes, Nisqually, Puyallup, Stillaguamish, Nooksack and Skagit rivers.

At the same time, surveys looking upriver in the watersheds will help determine actual sources of nitrogen and their relative contributions to the overall problem, as well as finding ways to address the sources.

To gain a better understanding of upstream sources of nitrogen, Ecology plans to employ a watershed model developed by the U.S. Geological Survey. The model provides a more sophisticated analysis of sources, from urban runoff to agricultural fertilizers to atmospheric deposition. Specifics about the timing and locations of nitrogen flowing into Puget Sound is then incorporated as inputs into the Salish Sea Model. The statistics-based watershed model is called Spatially Referenced Regression On Watershed Attributes, or SPARROW.

An entirely separate modeling project, announced last week, is expected to play a role in the discussion about the effects of nitrogen on the water quality of Puget Sound. In fact, those involved in this new project envision a scope well beyond nitrogen as part of the Puget Sound Integrated Modeling Framework, a new project led by PSI. The work involves coupling together at least five separate models that link data across the watershed. The project will incorporate physical conditions, biological changes and even human interactions within the Puget Sound ecosystem.

In the new project, watershed inputs to Puget Sound will be described using a model developed by the EPA called VELMA, which stands for Visualizing Ecosystem Land Management Assessments. Like SPARROW but with an analytical framework that divides the landscape into discrete segments, VELMA will provide its own estimates of nitrogen going into Puget Sound, estimates that can be used to run the Salish Sea model.

While two or more watershed models might sound like an added complication, being able to compare their outputs will only improve the modeling process and boost confidence in the results, according to Stefano Mazzilli, senior research scientist at PSI. If the separate models produce similar results, it is likely that the modelers are on the right track, he explained. If the results are very different, then modelers will need to figure out what may be wrong with one or more models.

“Having multiple models for estuarine or watershed processes is always beneficial,” Mazzilli said. “Models are built with different purposes, and it is important to recognize that some are better at providing information for particular decisions.”

For example, some models may be better at dealing with rural versus urban areas, or addressing a multitude of environmental stressors, as in studies of toxic chemicals, he noted.

In any case, for a model to be useful to those making decisions about nitrogen, the model must accurately predict the results of actions that could be taken, Mazzilli said. Otherwise, decision-makers won’t know which options will produce the best results. Understanding and reducing uncertainties surrounding the effects of nitrogen and the results of potential actions is the goal a PSI project titled The Science of Puget Sound Water Quality.

As for Ecology’s Puget Sound Nutrient Reduction Project, the effort is edging closer to a formal plan after five years of study. The plan will include recommendations for reducing nitrogen to improve the low-oxygen conditions in Puget Sound.  

It is worth mentioning, said Bilhimer, that unrelated ecosystem-restoration projects are having their own beneficial effects. For example, efforts to reduce bacterial pollution and reopen shellfish beds — such as in Samish Bay in northern Puget Sound — have also reduced nitrogen levels in the area. Likewise, shoreline restoration projects — such as in Nisqually Estuary in South Puget Sound — have improved natural functions, helping to reduce nitrogen loads, he added.

Further studies of nitrogen sources are planned through next year, according to the latest schedule released Dec. 7 during a meeting of advisers — the so-called Puget Sound Nutrient Forum. Discussions about problem areas and potential solutions will be taken up in 2024, with a special focus on a draft plan to reduce nitrogen from various sources. Formal adoption of the plan could come in 2025.

Parties filing appeals of the Washington Department of Ecology’s new nutrient general permit: Puget Soundkeeper Alliance, King County, City of Tacoma, Washington Environmental Council, Suquamish Tribe, City of Everett, City of Bremerton, Birch Bay Water and Sewer District, Alderwood Water and Wastewater District, Pierce County, and City of Edmonds.