Nitrogen

Excess nitrogen in the Bay is the primary cause of the excessive algae blooms we’ve seen in recent decades and, thus, of the dead zones so threatening to life in the Bay.

We have reduced the amount of nitrogen entering the Bay by 75.6 million pounds annually since 1985 through wastewater treatment upgrades, improved runoff controls at farms and other actions.  Unfortunately, we are still only 46.5% of the way to meeting the 175 million pound annual target by 2010.

Where is the Nitrogen Coming From?

Over one-third of the nitrogen contaminating the Bay is coming from agricultural sources. Of this, 48% is caused by manure, 42% comes from fertilizers, and the remainder results from air pollution that contaminates agricultural lands.

The second largest nitrogen pollution source is air pollution from cars, trucks, electricity-generating plants, boats, lawn mowers and other sources that either directly contaminates the Bay or falls on forests and non-tidal waters prior to running into the Bay.

Municipal and industrial wastewater facilities are the source of 19% of nitrogen contamination in the Bay. A large percentage of the progress made since 1985 in limiting nitrogen pollution has been made by improved treatment programs at wastewater treatment facilities.

Nitrogen that runs off urban and suburban lands is the source of 17% of the nitrogen load.  Almost 60% of this nitrogen is from fertilizer that is over-applied to lawns and then washes into the Bay. The remainder is primarily due to air pollution residues that pollute urban and suburban lands. This has proven to be one of the most difficult areas in which to make progress.

Poorly-functioning septic systems account for 4% of the nitrogen load entering the Bay.