Nutrients

Nutrients are chemicals that plants and animals need to grow and survive. When too many nutrients make their way into local rivers, streams and the Bay, they can create conditions that are harmful for blue crabs, bay grasses and other underwater life. Excess amounts of nitrogen and phosphorus, two types of nutrients, are the main cause of the Bay's poor health.

Where do excess nutrients come from?

Virtually all people and industries in the Bay's seven-jurisdiction watershed — and even some beyond the watershed — contribute nutrients to the Bay and its tributaries. In general, excess nutrients reach the Bay from three major sources: specific, identifiable entry pipes; runoff from the land; and air pollution.

• Wastewater treatment plants contribute the majority of nutrients that enter the Bay through specific, identifiable entry pipes. Wastewater plants release treated water — often still containing large amounts of nutrients — into local streams and rivers, which eventually flow to the Bay.
• Nutrients that run off the land — including farmland and urban and suburban areas — come from a number of sources, including fertilizers, septic systems, boat discharges and farm animal manure.
• Air pollution from vehicles, industries, gas-powered lawn tools and other emitting sources contribute nearly one-third of the total nitrogen load to the Chesapeake's waterways. Airborne nitrogen is contributed to the Bay region from an enormous 570,000-square-mile airshed that stretches north to Canada, west to Ohio and south to South Carolina.

Nutrients also come from a number of natural sources, including soil, plant material, wild animal waste and the atmosphere.

Nutrients have always been a part of the Bay ecosystem, but not at the excessive levels found today. Prior to significant human activity in the region, most nutrients were absorbed or held in place by natural forest and wetland vegetation. As forests and wetlands were replaced by farms, cities and suburbs to accommodate a growing population, nutrient pollution to the Bay has vastly increased.

How are excess nutrients a pressure on the Bay?

Excess nutrients fuel the growth of dense algae blooms that:

• Block sunlight that underwater bay grasses need to grow. Bay grasses provide food for waterfowl and shelter for blue crabs and juvenile fish
• Rob the water of oxygen, which crabs, oysters and other bottom-dwelling species need to survive.