Sources of nitrogen in Puget Sound (infographic)

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What is nitrogen and why does it matter?

Nitrogen is a chemical element that is essential for the growth of all life on earth.

Known as a nutrient, it is a basic building block of the food web starting with algae (phytoplankton). 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.

The addition of nitrogen from human activities can influence the timing, location, and size of algae blooms and by extension organisms’ exposure to their effects.

As climate change warms the ocean, nitrogen is expected to increase and dissolved oxygen to decrease. At the same time, nitrogen from wastewater and agriculture may intensify as human populations grow.   

Where does nitrogen in Puget Sound come from?

• 77% of the nitrogen in Puget Sound comes from natural sources – mainly the ocean, with a small amount carried in from surrounding watersheds via surface runoff and rivers.
• 23% of nitrogen in Puget Sound is attributed to human activity in Washington State, primarily from wastewater treatment plants, agriculture, and urban runoff. 
• A little nitrogen (< 1%) comes from the atmosphere and groundwater.

Algae (e.g., phytoplankton) isn’t all bad! In fact, it’s the base of the food web that feeds many sea creatures. But an excess can cause problems.

Too much nitrogen can lead to low oxygen which can harm aquatic life

In the top 30-meters of Puget Sound, the euphotic zone, enough sunlight plus nitrogen can trigger large algal blooms. Mixing and stratification influence the availability of nitrogen to algae.

As algae die and sink, bacteria use up oxygen to break down the decaying algae.

If oxygen is too low, aquatic organisms may move away, acclimate to the conditions, or adapt over generations. Or they may die, especially if the change happens too quickly.

Data source: Mohamedali et al. 2011