Eutrophication

Eutrophication of water bodies occurs when high levels of nutrients fuel high rates of primary production and accumulation of algal biomass, either as macroalgae or phytoplankton. Some ecosystems are naturally eutrophic, but in others human activity causes ecosystems to undergo transformations into a eutrophic state. This is termed cultural eutrophication, and is the primary concern in evaluating the status of marine waters of Puget Sound.

Source: Puget Sound Science Review

RELATED ARTICLES

Report cover
7/14/2023

Eyes Over Puget Sound: Surface Conditions Report - June 2023

In June we observed a widespread Noctiluca bloom in Central Puget Sound, evident by bright orange streaks in the water. Noctiluca blooms in Puget Sound have lasted much longer and occurred on a much larger scale than in previous years.

Infographic describing impacts of low oxygen on Puget Sound aquatic life
5/11/2023

Impacts of low oxygen on Puget Sound aquatic life (infographic)

Chronic stress from lack of oxygen can make aquatic organisms more vulnerable to disease, pollution, or predation. Low oxygen can also result in reduced habitat for some species. Aquatic species may escape, acclimate, adapt, or die with exposure.

Infographic describing sources of nitrogen in Puget Sound
5/5/2023

Sources of nitrogen in Puget Sound (infographic)

Nitrogen is a chemical element that is essential for the growth of all life on earth. But too much nitrogen can lead to low dissolved oxygen and other problems such as toxic algal blooms that can harm or kill aquatic organisms. 

A crab pot (circular mesh cage) with an oxygen sensor (a white tube inside the cage) is held off the side of a boat as it is about to be dropped into the water.
4/7/2023

When are waters considered hypoxic?

The search goes on for a set of definitions and thresholds to represent low-oxygen concentrations that threaten various aquatic creatures. Over the years, ecologists have relocated, reshaped and revised the word “hypoxia” to describe these conditions. In part four of our series "Oxygen for life" we look at how scientists determine whether oxygen levels are low enough to be considered harmful to sea life. 

A person holding a rope attached to a wire cage holding recently captured Dungeness crabs.
3/31/2023

How crabs respond to low oxygen in Hood Canal

As observed in Hood Canal, low-oxygen conditions can upend the lives of Dungeness crabs trying to stay alive. Levels of dissolved oxygen can alter predator-prey relationships for a multitude of species, affecting populations throughout the food web. Part two of our series "Oxygen for life" examines a crab case study.

View from underwater of bubbles rising to the surface of the ocean with sunlight above.
3/31/2023

Warmer waters will mean less oxygen for species

In time, lower dissolved oxygen worsened by climate change could increase the abundance of rare species in Puget Sound while putting populations of more common species into a tailspin. Part three of our series "Oxygen for life" looks at how warmer waters will gradually make it harder for many sea creatures to breathe. 

View of Puget Sound with red-orange water near the shoreline and blue sky with clouds above land in the distant background.
12/5/2022

Understanding the causes of low oxygen in Puget Sound

How do excess nutrients trigger low oxygen conditions in Puget Sound and what do those conditions mean for the species that live here?

Maps generated from the Salish Sea Model showing surface layer transport in the Northwest Straits (left) and sea surface salinity (right). Images: Pacific Northwest National Laboratory
5/18/2021

The Salish Sea Model

The Salish Sea Model is a computer model used to predict spatial and temporal patterns related to water circulation in the Salish Sea. It was developed at the United States Department of Energy's Pacific Northwest National Laboratory with funding from the Environmental Protection Agency. It is housed at the University of Washington Center for Urban Waters which is affiliated with the Encyclopedia of Puget Sound.  

Predicted annual average Δ in surface temperature and salinity over (a) the entire Salish Sea domain, as well as (b) in the nearshore intertidal regions of the Snohomish River estuary (see Khangaonkar et al. 2019 for details).  Image courtesy of Journal of Geophysical Research: Oceans.
7/15/2019

Salish Sea Model looks at climate impacts on the nearshore

A 2019 paper in the Journal of Geophysical Research: Oceans outlines how the Salish Sea Model describes the impacts of climate change, sea level rise and nutrient loads on the region's nearshore environment.

A milky, turquoise, phytoplankton bloom in Hood Canal visible from space. Natural color MODIS image from Landsat 8 acquired July 24, 2016. Photo: NASA Earth Observatory https://earthobservatory.nasa.gov/NaturalHazards/view.php?id=88454
3/6/2018

Does Puget Sound need a diet? Concerns grow over nutrients

As the region's population grows, scientists say we can expect to see increasing amounts of nitrogen and other elements flowing into Puget Sound. Known as “nutrients” these elements are naturally occurring and even necessary for life, but officials worry that nutrients from wastewater and other human sources are tipping the balance. That could mean big problems for fish and other marine life, gradually depleting the water of oxygen and altering the food web.

The Budd Inlet sewage treatment plant. Photo courtesy of LOTT Clean Water Alliance
3/6/2018

Sewage treatment plant in Olympia a leader in nitrogen removal

A regional sewage-treatment system in Thurston County has helped contain  low-oxygen problems in Budd Inlet as the population continues to grow. The system cleans up some of the effluent for replenishing groundwater supplies.

The rapid growth of a red-orange algae, Noctiluca scintillans, dramatically colors the waters of Puget Sound near Edmonds on May 16, 2013. Such algae blooms have been seen more frequently in recent years. Photo: Jeri Cusimano via WA Ecology (CC BY-NC 2.0) https://www.flickr.com/photos/ecologywa/8744775119
2/28/2018

Dead plankton leave clues to a food-web mystery

High amounts of elements such as nitrogen can cause blooms of phytoplankton that sometimes trigger perturbations throughout the food web. This occurs most often in the spring and summer after the long, dark, cloudy days of winter begin to fade.

A sharp boundary appears as sediment-laden freshwater is discharged from British Columbia's Fraser River into the Salish Sea. Fresh water, which is less dense than salt water, spreads in a shallow (approximately 1 m deep) plume at the sea surface. Photo: Ed McNichol, Ocean Networks Canada (CC BY-NC-SA 2.0) https://www.flickr.com/photos/oceannetworkscanada/8711686267
2/28/2018

Puget Sound circulation triggers low-oxygen conditions at different times and in different places

The amount of oxygen in the Salish Sea is dependent on water circulation which distributes chemical elements such as nitrogen through the system.

Image describing low oxygen "dead zones"; image courtesy of NOAA
2/26/2018

How the state assesses low oxygen in Puget Sound

Under the federal Clean Water Act, states are required to assess the quality of their surface waters and compile a list of polluted water bodies. The law mandates cleanup plans to address pollution and other water-quality problems. This article describes how this process works in Washington state for dissolved oxygen. 

Puget Sound Marine Waters 2015 report cover
9/27/2016

2015 Puget Sound Marine Waters Overview

The Puget Sound Ecosystem Monitoring Program released its fifth annual Marine Waters Overview this week. The report provides an assessment of marine conditions for the year 2015 and includes updates on water quality as well as status reports for select plankton, seabirds, fish and marine mammals.

Dead salmon. Photo: Boris Mann (CC BY-NC 2.0) https://www.flickr.com/photos/boris/3037705761
2/23/2016

Transfer of nutrients in the ecosystem

Decaying organic matter plays an important role in marine ecosystems. 

2003 Seattle Marathon - Seward Park Photo: J Brew (CC BY-SA 2.0) https://www.flickr.com/photos/brewbooks/1282527696
2/17/2016

Cleaning up Lake Washington

Lake Washington was heavily contaminated by untreated sewage until extensive pollution controls by the city of Seattle. 

8/7/2015

A study of the nutrients in the main basin of Puget Sound

This study compared recent and historical data to determine the presence of any significant changes in nutrient and oxygen concentrations subsequent to METRO discharge, examined seasonal cycles in water properties, and examined the flux of nutrients within the study area.

6/7/2015

Dissolved oxygen and hypoxia in Puget Sound

Hypoxia, defined as dissolved oxygen (DO) concentrations less than 2 mg / L, has become widespread throughout estuaries and semi-enclosed seas throughout the world (Diaz 2001). 

Map of the Hood Canal Action Area; courtesy Puget Sound Partnership
9/19/2012

Review finds minimal evidence for human impacts on Hood Canal hypoxia

An independent review conducted by the Puget Sound Institute (PSI) is featured in findings by the Environmental Protection Agency and the Washington State Department of Ecology that there is currently “no compelling evidence” that humans are the cause for recent trends in declines in dissolved oxygen in Hood Canal.