Nitrogen

Nitrogen is a type of nutrient contributing to the Bay's poor water quality. While nitrogen is needed for plant growth, human activities—from driving cars to applying fertilizers—contribute more nitrogen than the Bay's waters can handle. Elevated nitrogen levels cause more algae to grow, blocking out sunlight and reducing oxygen for fish, blue crabs and other Bay life.

Where does nitrogen come from?

Most of the nitrogen delivered to the Bay comes from:

• Emissions from vehicles, industries, agriculture, electric utilities and other sources (33 percent)
• Chemical fertilizers applied to agricultural and urban and suburban lands, such as lawns and golf courses (26 percent)
• Treated wastewater discharged from industrial facilities and municipal wastewater treatment plants (19 percent)
• Manure from agricultural lands (18 percent)
• Septic systems that treat household wastewater and discharge nutrients into groundwater (4 percent)

Nitrogen also occurs naturally in soil, animal waste, plant material and the atmosphere.

How is excess nitrogen a pressure on the Bay?

Excess nitrogen fuels the growth of algae, creating dense algae blooms that rob the Bay's aquatic life of sunlight and dissolved oxygen.

• Algae blooms on the surface of the water block the sun's rays from reaching underwater bay grasses growing at the bottom. Algae can also grow directly on the grasses' leaves, further reducing the amount of sunlight they receive. Without sunlight, bay grasses cannot grow and provide critical food and habitat for blue crabs, waterfowl and juvenile fish.

• “Leftover” algae that are not consumed by the Bay's algae-eating organisms eventually die and sink to the bottom. There, they are decomposed by bacteria in a process that leaves bottom waters with little or no dissolved oxygen for crabs, oysters and other bottom-dwelling species. Just like humans and animals on earth, all aquatic species need oxygen to survive.