Puget Sound Models

Why do we need water quality models and why do we need more than one model for Puget Sound?

We need a suite of models to diagnose Puget Sound for the same reason we need more than one medical doctor to diagnose our health problems. Some doctors are specialists and some are general practitioners, just like some models are specialists and others are general. Several doctors may work on the same body part depending on what the problem is, but they approach it from different perspectives. Sometimes you don’t need to see a doctor, you just need to quit smoking!

Human health problems may be acute: a broken leg or a dislocated shoulder. Other times the problem is less obvious: the patient has a sore abdomen. This could be indigestion or an appendix about to rupture. For this reason, we may seek some combination of general practitioners and specialists to diagnose the problem and recommend a course of action, and those actions are very different depending on what’s contributing to the symptom of the sore abdomen.

Similarly, Puget Sound health problems may be acute: fish kills in Hood Canal. Other times the problem is less obvious: fewer herring or salmon return to spawn. Fish counts are influenced by multiple factors that include food resources, ability to reproduce, oxygen to breathe, shelter from predators, and disease. Models are tools that help us understand which of these factors may be responsible and help us plan a course of action to fix the problems.

First we need information—what are the symptoms and underlying problems?

Models complement our monitoring programs. Monitoring programs are like taking the pulse of Puget Sound. But you can’t just take your pulse once and call it good. Instead, you need to understand the patterns that produce particular pulse rates. We use models to understand patterns in monitoring data. Models can be used to optimize monitoring plans for Puget Sound to help spend money wisely. Monitoring programs are a necessary complement to models because they help us identify the symptoms and isolate the factors contributing to the problem.

What do we do to improve the health of Puget Sound?

We know some actions make sense in general, regardless of the specific problems. But unless we really understand the problem, we have no guarantee that particular actions are enough. We have models under development to diagnose Puget Sound health problems and recommend courses of action. Rather than waiting years to see if a change in pollution control will improve water quality, we can use models to help us understand the effectiveness of various management actions. Models can be used to prioritize which actions are necessary to improve the health of Puget Sound.

 What models address the health of Puget Sound?


The generalist models predict how water moves around. Circulation modeling can be used to address a wide variety of questions about the health of Puget Sound. If a pollutant spill or shellfish larvae are released in one location, we can use a circulation model to identify where they might go under different tide or wind conditions. In the case of a pollutant spill, we need to know quickly and in which direction it might move under the tide patterns, so an intermediate or fine-scale model that can be applied quickly is most beneficial.


Specialist models include a variety of water quality and food web models. These answer questions like: Is nitrogen loading from point sources or non-point sources a major contributor to low dissolved oxygen levels? If discharges of polychlorinated biphenyls (PCBs) are reduced, what levels of PCBs will be in marine mammals in Puget Sound? Specialty model areas cannot be used interchangeably, just like you would not want your eye doctor to take over your family’s cancer care. However, medical specialists may consider some of the same information, as do various water quality and food web models. 

Domain and scale 

Generalist and specialist models are further complicated by domain and scale. “Domain” is the total area of interest, such as all of Puget Sound, or maybe only South Puget Sound. “Scale” is the smallest critical size within the domain, like the bottom water of inner Budd Inlet, or a particular shellfish growing area. We use a range of models from coarse to fine. Coarse models can be used to assess region-wide factors, like food web bioaccumulation of toxics in marine mammals or birds. However, other questions may need much more spatially-detailed models. For example, during what times of the year does a shellfish bed in Oakland Bay meet bacteria standards for harvesting? A coarse-scale model will not help, but the domain of the model does not need to include all of Puget Sound. Coarse, fine, and intermediate scale models with different domains all address specific questions.


Generalist and specialist models, which may cover all of Puget Sound or a management area or a specific bay, complement each other and are necessary to diagnose the problems affecting Puget Sound’s health. Just as “health” is a very broad term for humans, “Puget Sound health” is equally complex. Diagnosing problems and determining a course of action requires generalists and specialists working on different scales.



See: Focus on Modeling in Puget Sound: Water Quality Modeling in Puget Sound.

For more information on Puget Sound visit: Protecting Puget Sound