Nutrient Runoff

Overview

Plants and animals need nutrients to survive. But when too many nutrients enter rivers, streams and the Chesapeake Bay, they fuel the growth of algae blooms and create conditions that are harmful for fish, shellfish and other underwater life. In fact, excess nutrients are the main cause of the Bay’s poor health.

Why are excess nutrients a problem for the Chesapeake Bay?

Excess nutrients fuel the growth of harmful algae blooms, which:

block sunlight from reaching underwater grasses, and
during decomposition, create low-oxygen “dead zones” that rob the water of oxygen and suffocate marine life.

How do excess nutrients enter the Chesapeake Bay?

While nutrients are a natural part of the Chesapeake Bay ecosystem, nutrients have never been so abundant in the environment. Before humans built roads, homes and farm fields, most nutrients were trapped and absorbed by forest and wetland plants. As these habitats were removed to accommodate a growing population, nutrient pollution to the Bay increased.

Almost all people and industries in the watershed—and even some outside of the watershed—send nutrients into the Bay and its tributaries. Nitrogen and phosphorous are the two nutrients of concern in the area. In general, these nutrients reach the Bay from three sources: wastewater treatment plants; urban, suburban and agricultural runoff; and air pollution.

There are hundreds of wastewater treatment plants in the watershed. In 2005, watershed jurisdictions put a new permit process in place to limit the amount of nutrients these plants could send into rivers and streams. Computer simulations of pollution controls put in place between 2009 and 2015 indicate that nitrogen loads to the Bay from wastewater treatment plants and combined sewer overflows have declined 57 percent since 1985, while phosphorous loads from the same sources have declined 75 percent.
Nutrients that run off of the land and into the water through urban, suburban and agricultural runoff come from a range of sources, including lawn fertilizers, septic systems and livestock manure.
Air pollution emitted by cars and trucks, industries, gas-powered lawn tools and other sources contributes about one-third of the total nitrogen load entering Chesapeake waterways. This air pollution can come from any location within the Bay’s “airshed,” which measures about 570,000 square miles and stretches to Canada, Ohio and South Carolina.
Nutrients can also come from natural sources, like soil, plant material and wild animal waste.

How much nitrogen and phosphorus enters the Chesapeake Bay?

During 2021, average river flow to the Bay measured 54.8 billion gallons per day, a 4.5 billion gallon per day increase from 2020, and a 9% increase from the 1985-2021 mean. The corresponding pollutant loads entering the Bay in 2021 were approximately 286 million pounds of nitrogen and 19.9 million pounds of phosphorus. While all of these are below the 1985-2021 mean, they are increases from 2020 (up 16%, 38%, and 19% respectively).

Nitrogen Pollution

A line graph of nitrogen loads over time, with peaks in 2004, 2011 and 2019. The graph is on an image of a body of water with a pipe channeling the flow of water into it. — The amount of nitrogen the enters the Bay fluctuates from year to year and is strongly correlated to the amount of rainfall. Spikes in nutrient runoff in the above graph from 2011 and 2019 are mostly due to above average rainfall from that year. (Data provided by the U.S. Geological Survey.)

Phosphorus Pollution

A line graph of phosphorus loads over time, with the highest peak in 2011 and smaller peaks in 2004 and 2018. The graph is on an image of a body of water with a pipe channeling the flow of water into it. — The amount of phosphorus the enters the Bay fluctuates from year to year and is strongly correlated to the amount of rainfall. Spikes in phosphorus runoff in the above graph from 2011 and 2019 are mostly due to above average rainfall from that year. (Data provided by the U.S. Geological Survey.)

What you can do

To lower nutrient pollution in the Bay watershed, consider reducing the amount of pollution that can run off your property: install a green roof, rain garden or rain barrel to capture and absorb rainfall; use porous surfaces like gravel or pavers in place of asphalt or concrete; and redirect home downspouts onto grass or gravel rather than paved driveways or sidewalks. If you have a lawn to take care of, use fertilizers properly: do not use more than needed, and do not apply to dormant lawns or frozen ground. You can also reduce air pollution by walking, biking or taking public transportation, or using electric or manual lawn mowers and yard tools instead of gas-powered machines.

FAQ

Where do nutrients come from?

In general, nutrients like nitrogen and phosphorous reach the Chesapeake Bay from three sources: wastewater treatment plants; urban, suburban and agricultural runoff; and air pollution. Nutrients can also come from natural sources, like soil, plant material and wild animal waste.

What affects the amount of dissolved oxygen in the water?

Temperature, nutrient pollution, the way water flows in the Bay, and the shape of the Bay’s bottom all interact with each other to affect the amount of oxygen in the water.

What pollutants are found in wastewater?

Depending on the source, some wastewater can contain nutrient or sediment pollution, or dissolved chemical contaminants.

What are best management practices?

Best management practices (or BMPs) are conservation practices that can reduce a farm’s nutrient and sediment pollution while maintaining a productive farming operation. Some common agricultural BMPs include conservation tillage, cover crops, forest buffers, streamside fencing and manure storage areas.

How does farming affect the Chesapeake Bay?

Agriculture is the single largest source of nutrient and sediment pollution entering the Chesapeake Bay. But well-managed agricultural lands can offer the Bay watershed a number of benefits and services, including restored rivers and streams and valuable insect, bird and animal habitat.

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Terms

Nutrients

Chemicals that plants and animals need to grow and survive but, in excess amounts, can harm aquatic environments. Elevated levels of the nutrients nitrogen and phosphorous are the main cause of poor water quality in the Chesapeake Bay.

Eutrophication

The process of excess nutrients accelerating the growth of algae, ultimately depleting the water of dissolved oxygen.

Algae bloom

A dense population of algae whose growth is fueled by excess nutrients. Algae blooms can block sunlight from reaching underwater grasses, and their decomposition can rob the water of dissolved oxygen and suffocate marine life.

Point source

A source of pollution that can be attributed to a specific physical location - an identifiable, end-of-pipe "point." The vast majority of point source discharges of nutrients are from wastewater treatment plants, although some come from industries.

Phosphorus

A type of nutrient contributing to the Bay's poor water quality. While phosphorus is vital to plant life, human activities--like applying fertilizers or using household cleaners--contribute more phosphorus than the Bay's waters can handle. Elevated phosphorus levels cause more algae to grow, blocking out sunlight and reducing oxygen for fish, crabs and other Bay life.

Nitrogen

A type of nutrient that contributes to the Bay's poor water quality. While nitrogen is needed for plant growth, human activities--like driving cars or 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, crabs and other Bay life.

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