What is agricultural runoff?
Runoff is water from rain or melted snow which is not absorbed and held by the soil, but runs over the ground and through loose soil. Agricultural runoff is water leaving farm fields because of rain, melted snow, or irrigation. As runoff moves, it picks up and carries pollution, which it can deposit into ponds, lakes, coastal waters, and underground sources of drinking water.
Agricultural runoff can include pollution from soil erosion, feeding operations, grazing, plowing, animal waste, application of pesticides, irrigation water, and fertilizer. Pollutants from farming include soil particles, pesticides, herbicides, heavy metals, salts, and nutrients such as nitrogen and phosphorus. High levels of nitrates from fertilizers in runoff can contaminate drinking water and cause potentially fatal “blue baby” syndrome in very young infants by disrupting oxygen flow in the blood.
Agricultural wastewater generated from a variety of farm activities including animal feeding operations and the processing of agricultural products, can pollute surface and ground water if not properly managed. Examples of agricultural wastewater include but are not limited to manure, milking center wash water, barnyard and feedlot runoff, egg washing and processing, slaughterhouse wastewaters, horse washing waters and runoff associated with composting. Additionally, runoff from croplands can contribute sediment, fertilizers and pesticides into surface waters.
Polluted agricultural runoff is the leading source of water pollution in rivers and lakes, according to a federal report. It can also trigger algae blooms in coastal waters, and produce “dead zones” in the ocean where there is no oxygen and few fish or wildlife can survive. In cities and suburbs, urban and industrial runoff is also a major source of water pollution.
Agricultural runoff can create a bad taste and odor in drinking water and contaminate drinking water, well water, and food sources. The pesticides in runoff can accumulate in fish, which can expose people who eat the fish to high levels of these chemicals.
Runoff occurs when there is more water than land can absorb. The excess liquid flows across the surface of the land and into nearby creeks, streams, or ponds. Runoff can come from both natural processes and human activity.
The most familiar type of natural runoff is snowmelt. Mountains that cannot absorb water from heavy snowfalls produce runoff that turns into streams, rivers, and lakes. Glaciers, snow, and rain all contribute to this natural runoff.
Runoff also occurs naturally as soil is eroded and carried to various bodies of water. Even toxic chemicals enter waterways through natural processes, such as volcanic eruptions. Toxic gases released by volcanoes eventually return to the water or soil as precipitation.
Runoff from human activity comes from two places: point sources and nonpoint sources.
Point source pollution is any source that empties directly into a waterway. This might include a pipe from specific sewage treatment plant, factory, or even a home. Regulations determine what type of runoff, and how much, industries are allowed to release. These regulations vary by region, state, and nation.
Nonpoint source pollution is any source where runoff does not go directly into a waterway. Nonpoint sources of runoff can be large urban, suburban, or rural areas. In these areas, rainwater and irrigation wash chemicals into local streams. Runoff from nonpoint sources includes lawn fertilizer, car exhaust, and even spilled gasoline from a car. Farms are a huge nonpoint source of runoff, as rainwater and irrigation drain fertilizers and pesticides into bodies of water.
Impervious surfaces, or surfaces that can’t absorb water, increase runoff.
Roads, sidewalks, and parking lots are impervious surfaces. Materials as diverse as car-washing soaps, litter, and spilled gas from a gas station all become runoff.
California Farm Run off into Seas
Irrigation practices that transformed California’s scorched desert into one of the nation’s most productive farming regions are the chief cause of pollution ruining the Salton Sea.
Growers who put food on the table dump waste water into the sea on a scale that would make big industries blush. Since the first drop of Colorado River water was diverted to make the desert bloom nearly a century ago, irrigated crop land spanning 600,000 acres in the Imperial and Coachella valleys has flushed a steady stream of salts, pesticides, fertilizers and selenium into the sea.
In the eyes of local farmers, the sea is first and foremost a waste dump. It is as vital to their fortunes as good markets and sunshine because its expansive shores swallow tainted water that if left on the fields would eventually saturate the soil with crop-killing minerals.
“The purpose of the sea is to receive agricultural drainage. That’s what it’s there for,” said John Benson, a second-generation farmer who grows lettuce, cotton and cauliflower on 4,000 acres near Brawley.
Salton Sea area farms pour about 3 million tons of salt into the sea annually — enough to fill about 40,000 railroad boxcars. The sea gets saltier each day, slowly killing fish and reducing the number of birds, fishermen and tourists that once flocked to it.
Farm wastewater pumps 50 pounds of selenium into the sea a year. Hazardous amount of the natural toxicant have been detected in silt, plants, insects, fish, birds and many living creatures in the sea and the maze of reedy canals that surrounds it.
Hundreds of miles of drains that funnel water from the farms to the sea contain elevated concentrations of pesticides washed from fields during irrigation. Fish kills in the drains are not uncommon. DDT has been linked to eggshell thinning in Salton Sea birds.
Yet, agricultural pollution goes largely unregulated in California and much of the nation. Clean Water Act requirements have cracked down on industries, sewer plants and other “point source” polluters for 20 years, but ignored farms until very recently.
“Agriculture is the number one non-point source pollution problem in this country,” said Jovita Pajarillo of the U.S. Environmental Protection Agency’s California office. “The agricultural industry has a very strong lobby. They are able to stave off a lot of regulations.”
California agricultural interests last year successfully opposed a plan to require farms to pay fees to support a statewide pollution-tracking program for agricultural drains.
FARMS WASTE MUCH OF WORLD’S WATER
Farms and their wasteful irrigation systems are major contributors to water scarcity on the globe.
Farming accounts for 70 percent of the water consumed and most of its wasteful use.
One-fifth of the world’s population lacks safe drinking water, the United Nations said in a report last week that laid much of the blame on mismanagement of resources.
With 525 million small farms in the world – and 2.5 billion people living off the land – farmers suffer the most from the problems discussed at the forum: poverty, disease, and the lack of sanitation and clean water.
Drought-parched fields, withered corn stalks and skinny cattle make up the face of the crisis in the developing world.
Getting farmers to use water less extensively is daunting, speakers said.
“There are great problems with irrigation,” said Michel Rocard, former prime minister of France. We must persuade our farmers to go to less extensive crops. It’s a question of changing the whole agricultural method.”
Traditionally governments have responded to the problems of small farmers – defined as those with plots of 5 acres or less – with big dam projects. But most small farms are so high up in the hills or removed from rivers that they cannot benefit from them, said McCully.
The answer is more efficient irrigation systems, said Ute Collier, of the World Wildlife Fund. “We can’t afford to waste water in irrigation systems that are 30 to 40 percent efficient,” he said. “If we could get that part of the equation done, we could probably cut down the number of dams we’re building by half, at least.”
Greater efficiency would free up money to help provide clean drinking water and food to small farmers who, despite raising food, constitute most of the 842 million people in the world who go hungry.
Many of the world’s poor live on less than 2.5 gallons of water per day – one-thirtieth of the daily usage in developed nations.
Collier’s work has focused on improving irrigation for notoriously thirsty cash crops, like cotton and sugarcane, although they are seldom grown on the smallest farms. Agriculture based on fields that temporarily flood is also a major problem because most of that water is wasted through evaporation, the forum was told.
Other problems include pesticide and herbicide runoff from farm fields that pollute rivers and lakes, as well as soil erosion and salt buildup from irrigation.
In Mexico, host of the international forum, farm water disputes are among the most sensitive issues in its relations with the United States. In 2004, farmers in Texas were outraged when Mexico failed to let billions of gallons of water flow into a border river under a 1944 treaty.
Texans also accused Mexico of growing alfalfa – a water-hungry feed crop – in desert areas. One state politician suggested that the United States retaliate by reducing its flow into another border river, the Colorado.
Mexico went to court last year to stop the United States from lining one of its irrigation canals with concrete. Mexico claims its farmers had become dependent on water seeping out of the earthen canal, located near the two countries’ border. The case has not been resolved.
Europe also has its conflicts. Spain would like France to share some of its water, but Rocard, France’s former prime minister, said the French are reluctant to do so until the Spaniards improve their water management.