Agricultural Contaminants

Featured: Nutrient yields in the Mississippi/Atchafalaya River Basin

Featured: Nutrient yields in the Mississippi/Atchafalaya River Basin

new USGS study estimates total nitrogen and phosphorus yields from catchments throughout the Mississippi/Atchafalaya River Basin, which drains about 41% of the conterminous U.S. Agricultural activities were the largest nutrient source.

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Nitrogen Fertilizer on Agriculture Contributing N to Chesapeake Bay

Nitrogen Fertilizer on Agriculture Contributing N to Chesapeake Bay

A new USGS study uses the SPARROW (SPAtially Referenced Regression On Watershed attributes) model to assess how nitrogen loading to the Chesapeake Bay might change in response to changing different sources of nitrogen inputs. 

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Science Center Objects

About 40 percent of the land in the United States is used for agriculture, and agriculture supplies a major part of the our food, feed, and fiber needs. Agricultural chemicals move into and through every component of the hydrologic system, including air, soil, soil water, streams, wetlands, and groundwater.


Over the last 100 years, agricultural expansion and intensification has led to changes in water quality and the health of stream ecosystems. Considerable increases in fertilizer and pesticide use began in the 1960s. In 2010, about 11 billion kilograms of nitrogen fertilizer and 300 million kilograms of pesticides were used annually to enhance crop production or control pests. Increased levels of nutrients from fertilizers draining into streams can stimulate algal blooms and affect stream health and recreational uses of local streams, downstream reservoirs, and estuaries, and increase treatment costs for drinking water. Pesticides that are transported to streams can pose risks for aquatic life and fish-eating wildlife and drinking-water supplies.

Find maps, graphs, and data for estimated agricultural use of hundreds of pesticides since 1992.


Tractor pulling fertilizer on a new crop

A farmer applies fertilizer on a new agricultural crop.


Agricultural contaminants commonly studied by the USGS include:

  • nutrients, such as nitrogen and phosphorus
  • pesticides, including herbides, insecticides, and fungicides

Agricultural contaminants can impair the quality of surface water and groundwater. Fertilizers and pesticides don't remain stationary on the landscape where they are applied; runoff and infiltration transport these contaminants into local streams, rives, and groundwater. Additionally, when land is converted to agricultural use, it is modified to be optimized for agricultural production. Oftentimes these modifications have unintended environmental impacts on receiving waters and their ecosystems, including changes in water quality and quantity. Read about the connections between agriculture and water quality.

Agriculture is the leading source of impairments in the Nation’s rivers and lakes. About a half million tons of pesticides, 12 million tons of nitrogen, and 4 million tons of phosphorus fertilizer are applied annually to crops in the continental United States.1

Pesticides are widespread in surface water and groundwater across the United States. For example, at least one pesticide was found in about 94 percent of water samples and in more than 90 percent of fish samples taken from streams across the Nation, and in nearly 60 percent of shallow wells sampled.2

Transport of excess nutrients is influenced by agricultural practices, such as methods of tillage and drainage, and the timing of application and runoff events like storms and snowmelt. Farmers may leave the soil surface undisturbed from harvest to planting (referred to as “no-till”), and may plant and maintain buffer strips around fields and streams. They may also time fertilizer and manure application to maximize uptake and avoid precipitation events. Use of drip irrigation in lieu of furrow irrigation decreases the amount of water lost to ditches or evaporation, and allows better control of the amounts of pesticides and nutrients added to irrigation water. The USGS studies the amount of nutrients transported off agricultural fields, the effects excess nutrients have on downstream receiving waters, and the effectiveness of on-farm conservations practices that try to reduce the amount of nutrient transport due to runoff. Read about the influence of nutrients on stream ecosystems in agricultural landscapes.


Cafo hogs

Concentrated animal feeding operations hog pen (Photo: Kent Becker)


Concentrated animal feeding operations (CAFOs) refer to a specific type of animal feeding operation where animals are kept and raised in confined situations for the duration of their lives. Rather than roaming and feeding in a pasture, food is brought to the animals in their pens. Given the cramped conditions, everything is condensed in these facilities, including both live and dead animals, feed, and animal waste. These operations create a significant amount of animal waste which, if released, can greatly affect the environmental. Runoff from these facilities can impair downstream waterways, kill fish, produce harmful algal blooms, and potentially transmit disease. Because of issues that may arise from CAFOs, the USGS works to monitor and quantify potential impacts of these operations to the environment. 


Activities associated with intensive agriculture, such as found in the Midwestern Corn Belt region of the U.S., can change both the water quality and the physical habitat of small streams.  In 2013, the USGS intensively monitored 100 small streams in this region, and evaluated the effects of stream "stressors"—including pesticides, nutrients, sedimentation, and riparian disturbance—on stream health. Learn more about the USGS Midwest Stream Quality Assessment and the health of small Midwestern streams here.





U.S. Environmental Protection Agency

U.S. Department of Agriculture