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Nitrogen, Dead Zones, and New York Harbor

By Heather Flanagan
March 6, 2017

The BOP Curriculum Team is hard at work creating restoration education curriculum for our BOP teachers- our full curriculum archive lives on the BOP Digital Platform here, and it’s growing every day!  Last month, they rolled out the Nitrogen Cycle Investigation, which uses a classroom oyster aquarium as a microcosm for examining the global nitrogen cycle and the impact of nitrogen on estuaries.  The nitrogen cycle has real and potentially deadly consequences for organisms living in the classroom tank, and this motivates students to learn about different nitrogen molecules and how to test for their presence, followed by daily testing and data collection, research, and a final analysis to answer the question, “Is our tank ready for animals?”  Throughout the unit, students consider the cycling of matter through ecosystems at the tank, neighborhood, city, national, and global scale.

“Nitrogen, Dead Zones, and New York Harbor” is a student-friendly text the Curriculum Team created for this unit.  It appears as a part of a topic library, “Nitrogen and Estuaries,” from the lesson “Nitrogen Pollution.”

The Hudson River Estuary is the most nitrogen-loaded estuary in the world.  More than half of that nitrogen is from wastewater.  “Wastewater” includes, among other things, everything you flush down the toilet and everything that goes down the drain from your sink and shower.  It’s also called “sewage.”

Why does this matter?
Too much nitrogen can set off a chain of events that creates “dead zones” in the water- areas of low oxygen- that can kill aquatic life.  Mobile animals, like fish, might be able to swim away.  But sessile organisms that can’t move, like oysters, are stuck with too little oxygen to survive.  It’s like a person not having any air to breathe!


Even though fish can swim, sometimes they still cannot escape a dead zone. Thousands of menhaden were killed in this Long Island dead zone caused by an algal bloom in 2015. Image via the New York Times.

How does New York Harbor end up with too much nitrogen?
When you put millions of people in one place- like the New York City metro area- they produce a lot of waste in the form of…well…poop.  And pee.  And that waste is full of nitrogen.  For a long time, when you flushed the toilet, everything in it went through the drain pipes, into the sewers, and straight into our waterways.  Now, on most days, this wastewater goes to a wastewater treatment plant (WWTP).

The Newtown Creek Wastewater Treatment Plant in Greenpoint, Brooklyn.  

A wastewater treatment plant is massive factory-like building designed to remove solids, garbage, and chemical pollutants from sewage before draining the treated water back into waterways.  (This treated water is called “effluent”- you may have noticed that word earlier in this topic library in the tables of nitrogen loads to the Hudson River Estuary.)  Traditional WWTP remove some nitrogen, but not a lot.  In the past ten years, six of NYC’s fourteen wastewater treatment plants have been re-designed to remove more nitrogen, but thousands of tons of nitrogen from WWTP still enter the Hudson River Estuary each year.

What exactly happens when there’s too much nitrogen?

Nitrogen is a
nutrient for plants and algae.  A nutrient is something living things take in to survive.  Humans get nutrients from eating food.  Oysters get nutrients by consuming a type of algae- microscopic organisms called “phytoplankton” that they filter out of the water.  Algae don’t need to eat other organisms, because like plants, they can photosynthesize- a way to get energy from the sun.  But they still need nutrients like carbon dioxide, iron, phosphorus, and nitrogen to carry out that photosynthesis.

When there’s lots of nitrogen in the harbor from sewage, that means there are a lot of nutrients available for the algae, and they reproduce rapidly, forming huge masses called
algal blooms.  

An algal bloom in Florida described as “vile-smelling and guacamole-thick.”

An algal bloom in Florida described as “vile-smelling and guacamole-thick.”  Via ABC News.


One resident said, “I live on the water and I can’t even go out my back door.  It smells vile.”  Via ABC News.

If oysters eat algae, then why are algal blooms a bad thing?
For oysters, an algal bloom is too much of a good thing.  Algae produce oxygen, but they also consume oxygen.  And when the nutrients run out and the phytoplankton die, bacteria use up oxygen to decompose them.  This means that the oxygen gets used up.  But oysters and other animals need that oxygen to live!  That’s why we call areas of low oxygen “dead zones”- because low oxygen can kill many organisms living in that area.  

Is New York Harbor a dead zone?
The Hudson River Estuary is unusually resilient because the Atlantic Ocean helps “flush” some of the polluted water out more quickly than most other estuaries get flushed.  So even though the Hudson River Estuary is the most nitrogen-loaded estuary in the world, it’s not even the biggest dead zone in the United States (that title goes to the Gulf of Mexico).  But many scientists argue there have still been significant consequences for New York Harbor, like soft shell clam die-offs and salt marsh destabilization.  Others are concerned that climate change may reduce the flow of the Hudson River.  If that happens, our harbor won’t be flushed so quickly every day, and we could end up with a smelly city of water that cannot support life.

What are some terms you might see when reading about dead zones?

Too much nitrogen in the water is a form of “nutrient pollution”- because certain nutrients, in excess, can have harmful effects on the environment, just like other forms of pollution.  Another word for nutrient pollution is “eutrophication.

Another word you might see is “hypoxia.”  Hypoxia is the state of having low oxygen.