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Protecting Our Water Quality From Agricultural Runoff
The Environmental Protection Agency
The United States has more than 330 million acres of agricultural land that produce an abundant supply
of food and other products. American agriculture is noted worldwide for its high productivity, quality,
and efficiency in delivering goods to the consumer. When improperly managed however, agricultural activities
can affect water quality.
In the 2000 National Water Quality Inventory, states reported that agricultural nonpoint source (NPS)
pollution is the leading source of water quality impacts on surveyed rivers and lakes, the second largest
source of impairments to wetlands, and a major contributor to contamination of surveyed estuaries and ground
water. Agricultural activities that cause NPS pollution include poorly located or managed animal feeding
operations; overgrazing; plowing too often or at the wrong time; and improper, excessive, or poorly timed
application of pesticides, irrigation water, and fertilizer.
Agricultural pollutants that result from these activities are sediment, nutrients, pathogens, pesticides,
metals, and salts. Agricultural impacts on surface water and ground water can be minimized by using management
practices that are customized for local conditions. Many practices designed to reduce pollution also save
producers money in the long run.
The most prevalent source of water pollution caused by farming activities is soil that is washed off fields.
Rainwater carries soil particles (sediment) and dumps them into nearby lakes or streams. Too much sediment
can cloud the water, reducing the amount of sunlight that reaches aquatic plants. It can also clog the gills
of fish or smother fish larvae.
In addition, other pollutants like fertilizers, pesticides, and heavy metals are often attached to the
soil particles and wash into the water bodies, causing algal blooms and
depleted oxygen, which is deadly to much aquatic life. Farmers and ranchers can reduce erosion and sedimentation
by 20 to 90 percent by applying management practices that
control the volume and flow rate of runoff water, keep the soil in place, and reduce soil transport.
Producers apply nutrients like phosphorus, nitrogen, and potassium in the form of chemical fertilizers,
manure, and sludge. They may also grow legumes and leave crop residues to enhance production. When these
sources exceed plant needs, nutrients can wash into aquatic ecosystems. There they can cause algae blooms,
which reduce swimming and boating opportunities, create foul taste and odor in drinking water, and
kill fish by removing oxygen from the water. High concentrations of nitrate in drinking water can cause
methemoglobinemia, a potentially fatal disease in infants, also
known as blue baby syndrome. To combat nutrient losses, farmers can implement nutrient management plans that
help maintain high yields and save money on fertilizers.
Clean Water Is Everybody's Business
Did you know that runoff from farms is the leading source of impairments to surveyed rivers and lakes?
Animal Feeding Operations (AFOs) By confining animals in small areas or lots, farmers and ranchers can
efficiently feed and maintain livestock. But these confined areas become major sources of animal waste.
An estimated 238,000 farms and ranches in the United States are considered animal
feeding operations, generating about 500 million tons of manure each year. Runoff
from poorly managed facilities can carry pathogens (bacteria and viruses), nutrients,
and oxygen-demanding organics and solids that contaminate shellfishing areas and
cause other water quality problems. Groundwater can also be contaminated by waste
seepage. An operator can limit discharges by storing and managing facility wastewater
and runoff with an appropriate waste management system.
Overgrazing exposes soils, increases erosion, encourages invasion by undesirable plants, destroys
fish habitat, and may destroy streambanks and floodplain vegetation necessary for habitat and water quality
filtration. To reduce the impacts of grazing on water quality, farmers and ranchers can adjust grazing
intensity, keep livestock out of sensitive areas, provide alternative sources of water and shade, and promote
revegetation of ranges, pastures, and riparian zones.
Irrigation water is applied to supplement natural precipitation or to protect crops against freezing or
wilting. Inefficient irrigation can cause water quality problems. In arid areas, for example, where rainwater
does not carry minerals deep into the soil, evaporation of irrigation water can concentrate salts.
Excessive irrigation can affect water quality by causing erosion, transporting nutrients, pesticides,
and heavy metals, or decreasing the amount of water that flows naturally in streams and rivers. It can
also cause a buildup of selenium, a toxic metal that can harm waterfowl reproduction. Farmers can reduce NPS
pollution from irrigation by improving water use efficiency. They can measure actual crop needs and apply
only the amount of water required. Farmers may also choose to convert irrigation systems to higher efficiency
Insecticides, herbicides, and fungicides are used to kill agricultural pests. These chemicals can enter
and contaminate water through direct application, runoff, and
atmospheric deposition. They can poison fish and wildlife, contaminate food sources, and destroy the habitat
that animals use for protective cover. To reduce contamination from pesticides, producers should use
Integrated Pest Management (IPM) techniques based on the specific soils, climate, pest history, and crop
conditions for a particular field. IPM encourages natural barriers and limits pesticide use and manages
necessary applications to minimize pesticide movement from the field.