What are nutrients?
Nutrients are substances that all living organisms need for growth
and reproduction. Two major nutrients, nitrogen and phosphorus, occur
naturally in water, soil, and air. Nutrients are present in animal and
human waste and chemical fertilizers. All organic material such as leaves
and grass clippings contains nutrients.
How do nutrients enter the Bay?
Nutrients can find their way to the Bay from anywhere within the
64,000 square mile watershed. All streams, rivers and storm drains in
this huge area eventually lead to the Chesapeake. The activities of over
13.6 million people in the watershed have overwhelmed the Bay with excess
nutrients. Nutrients come from a wide range of sources, which include
sewage treatment plants, industry, agricultural fields, lawns, and even
the atmosphere. Nutrient inputs are divided into two general categories,
point sources and nonpoint sources.
Sewage treatment plants, industries, and factories are the major
point sources. These facilities discharge wastewater containing nutrients
directly into a waterway. Although each facility is regulated for the
amount of nutrients that can be legally discharged, at times, violations
Nonpoint sources pose a greater threat to the Chesapeake ecosystem,
as they are much harder to control and regulate. Nonpoint source nutrients
are usually carried to a waterway by rainwater runoff. Rain picks up nutrients
from the land and travels either directly overland to a waterway or soaks
into groundwater, which eventually feeds into streams. Farm fertilizers
and animal manure comprise a large portion of nonpoint source nutrients.
Other nonpoint sources originate from the urban environment and include
lawn fertilizers, septic tanks, organic material, and discharge from boat
What are the problems?
Excess nutrients cause algae populations to grow rapidly, or "bloom."
An overabundance of algae contributes to two problems in the Bay: reduction
in sunlight and reduction in dissolved oxygen. Algae occur as tiny single-celled
plants called phytoplankton or as larger seaweeds which look like leafy
"slime"; growing on rocks and jetties. Phytoplankton blooms turn the water
brown or blue-green and prevent essential sunlight from reaching rooted
underwater plants known as submerged aquatic vegetation (SAV).
Excess nutrients also cause algae to grow directly on the leaves of SAV,
further limiting essential sunlight. Without this sunlight, the plants
die. Many shellfish, fish, and waterfowl depend on SAV as their primary
habitat and food source.
The second problem created by widespread algal blooms occurs when the
algae die, sink to the bottom, and decay. During the decay process, bacteria
consume large amounts of dissolved oxygen from the water. This causes
extremely low levels of dissolved oxygen in large areas of the Bay. Because
warm water holds less oxygen than cool water, this problem worsens in
the summer. With out oxygen, many organisms perish.
Impacts on fish and wildlife
The nutrient-related decline of submerged aquatic vegetation has eliminated
essential habitat for many fish, shellfish, and other aquatic life. SAV
is a rich nursery ground, providing food and habitat for juvenile fish.
Molting crabs hide from predators in the grass beds. Larger fish such
as sea trout, bluefish, perch, pickerel, and drum patrol the grass beds
in search of food. Many small and interesting creatures including pipefish,
seahorses, mud crabs, spider crabs, and several kinds of shrimp and minnows
inhabit the underwater grass beds.
>Loss of submerged aquatic vegetation has contributed to a substantial
reduction in the once massive flocks of waterfowl that darkened the skies
of Chesapeake winters. Populations of redhead ducks have declined markedly
with the loss of SAV. Other species, such as the Canada goose, American
widgeon, and canvasback, have had to change their feeding habits to include
other sources of food.
The low oxygen conditions created by excess nutrients have severely impacted
life in the Bay. Since 1960, there has been a substantial increase in
the amount of Bay bottom with dangerously low levels of dissolved oxygen.
Bottom-dwelling, or benthic, organisms including worms, clams, oysters,
crabs, and many smaller invertebrates are an essential link in the food
web. With the decline of these benthic organisms, the entire Chesapeake
ecosystem is altered.
Correcting the problem
Actions are being taken to reduce nutrient inputs to the Bay. Sewage
treatment plants and industries are installing nutrient removal equipment.
Many farmers are developing nutrient management plans for their farms.
Streamside forest buffers, manure pits, and proper fertilizer applications
are "best management practices" farmers can use to help reduce nutrient
runoff into waterways. Some counties require stormwater management ponds
in new construction projects. Primarily designed to trap sediment, the
ponds can provide some nutrient removal as well. As the population of
the Bay watershed grows, the challenge to reduce nutrients increases.
Signs of progress!
The 1987 Chesapeake Bay Agreement, a Federal/State/private partnership,
calls for a 40 percent reduction in nutrient inputs to the Bay by the
year 2000. Progress toward this goal is evident. Phosphorus inputs to
the Bay from point and nonpoint sources are declining. Upgrades at the
watershed's largest sewage treatment plant in Washington, D.C. have paid
off; more SAV, fish, and waterfowl now inhabit the upper Potomac River.
Yet, a continued effort from governments, businesses, citizen groups,
and individuals is necessary to reach the nutrient reduction goal.
What You Can Do
- Follow directions when applying fertilizers; don't apply before
- Plant streamside vegetation.
- Pump out septic tanks regularly.
- Pump boat waste to an onshore facility.