Agricultural operations can be the source of non-point pollution in surface water. The major causes of surface water pollution associated with farming and ranching are sediment and nutrients.

Sediment

Soil erosion and resulting sedimentation is the leading cause of surface water pollution. Siltation is the leading cause of water quality problems in rivers and is the fourth leading cause in lakes and estuaries (1992 EPA 305[b] report). Although soil erosion is a natural process, it can be greatly accelerated by human activities such as farming.

Soil erosion is not only detrimental to agricultural production, but it also:

Major sources of sediment include runoff from agriculture (cropland), forestry and urban/suburban development.

Nutrients

Nutrients, especially nitrates and phosphates, can create significant water quality problems in both surface and ground water.

Surface Water

About 37% of the assessed river miles in the U.S. are impaired by nutrients (1992 EPA 305(b) report). Phosphates, and to a lesser extent nitrogen, can cause excessive growth of aquatic plants (eutrophication) in rivers and lakes. Eutrophication can be natural or human-induced. Agricultural sources of nutrients come from either fertilizer runoff or nutrients attached to eroded sediments. In most instances, the rate of human-induced eutrophication is many times faster than the natural process. For example, in a span of about 25 years (1950-1975), Lake Erie aged to about the same degree under human influences as would have occurred in 15,000 years naturally. Eutrophication can result in:

Non-point source runoff diagram

Major sources of nutrients in surface water include municipal wastewater, agriculture (crop and livestock production), forestry, urban/suburban development including landscapes, and recreation.

Ground Water

The most serious nutrient adversely impacting ground water supplies in the U.S is nitrates. Nitrates have been found above 2.0 parts per million (ppm) in 57% of rural domestic wells, although, only 2.4% of the wells had nitrates above the drinking water standard of 10 ppm NO3-N (1990 EPA National Pesticide Survey). Nitrates are naturally occurring in ground water, but concentrations can be greatly increased by human activities. High levels of nitrates can cause:

Major sources of nutrients in ground water include agriculture (crop and livestock production), urban/suburban landscapes, rural septic systems and land applications of waste.