Water Pollution from Agricultural Runoff
According to a United States Environment Protection Agency (EPA) fact sheet “Protecting Water Quality from Agricultural Runoff” (2005), “runoff from farms is the leading source of impairments to surveyed rivers and lakes.” Due to water seepage into surface water sources, groundwater can also become polluted. This type of pollution is generally referred to as NPS – nonpoint source – as it may emanate from a variety of sources, unlike point sources such as specific industrial and/or sewage treatment plants where the precise pollution source can be readily identified. This paper assesses the issues involved, reviews instances of water pollution caused by agriculture, and proposes the ways that agricultural runoff can be minimized or eradicated to prevent NPS pollution contaminating water supplies.
The Major Causes of Pollution from Agricultural Runoff
According to the EPA fact sheet referenced above, typical agricultural activities that are major contributors to NPS pollution include badly-located or mismanaged animal feeding arrangements, excessive or badly timed plowing of the fields, and incorrectly timed or excessive application of pesticides or fertilizers and irrigation. The fact sheet claimed that pollutants entering the water supply system (both surface water and groundwater) as a consequence can include “sediment, nutrients, pathogens, pesticides, metals, and salts.” However, it also stated that the impact of those agricultural activities can be minimized by implementing management methods customized for the local conditions. Not only that, but those improved methods will also produce higher productivity and in the longer term reduce the costs for farmers and ranchers, partly through taking advantage of government programs and/or improved technology.
Sedimentation. The referenced EPA fact sheet described sediment – soil washed off fields by rainwater or irrigation – as “the most prevalent source of agricultural water pollution.” It explained the process as soil particles carried away by the water and dumped into any nearby streams, rivers and lakes. Excessive amounts of sediments not only cause the water to become cloudy, but reduce the light received by underwater plants and can clog the gills of fish or smother their larvae. On top of that, the sediment often carries with it some of the other polluting particles such as fertilizer, chemical pesticides and even heavy metals, which cause depletion of the oxygen levels in the water and algae growth that can kill aquatic life.
The fact sheet claimed that farmers or ranchers can reduce the erosion and the associated sedimentation by between 20 and 90 percent, simply by implementing management systems that control the amount and the flow of runoff, and therefore keep the soil from eroding.
Nutrients Pollution. To increase crop yields, farmers apply nutrients which may be in the form of fertilizer (containing chemicals such as phosphorus, nitrogen, and potassium), or animal manures, or sludge. Also, growing legumes (beans, lentils, or peas) helps add nitrogen into the soil. The fact sheet explained that if the amounts of nutrients in the soil exceed the needs of the planted crops, or if they are applied just prior to significant rainfall, the “free” nutrients can be washed away and into nearby surface water resources, polluting them and causing the negative effects mentioned above under “Sedimentation.” In addition, not only will the water taste foul and have a strong odor, drinking water containing high concentrations of nitrates can cause “methemoglobinemia, a potentially fatal disease in infants, also known as blue baby syndrome.”
The fact sheet stated that the solution in this case is for farmers to implement better management of nutrients application, so that crop yields are not reduced but fertilizer costs are.
Animal Feeding Systems Pollution. By keeping their livestock restricted to small areas, farmers find it easier / more efficient to feed them, but it does mean that those areas have high concentrations of animal waste. The referenced fact sheet estimated that across the United States as a whole, 500 million tons of manure is produced annually from some 238,000 operational farms and ranches. If those feeding areas are poorly managed, the consequent runoff can carry “bacteria and viruses, nutrients, and oxygen-demanding organics and solids that contaminate shellfishing areas and cause other water quality problems.” Not only that, but seepage of the waste can allow that runoff to contaminate groundwater sources.
The solution recommended in the fact sheet was to use suitable waste management systems to store the waste and limit discharges.
Effects of Livestock Overgrazing. If livestock are allowed to overgraze, the bare soil is exposed and invasive plants encouraged. Also, in waterside locations, banks may be damaged and fish habitat and vegetation important for filtering water destroyed.
Irrigation Control. Use of irrigation must be managed to be efficient. For example, irrigating in dry areas can concentrate salts in the soil surface when the water evaporates before it can penetrate deeper into the soil. Excessive amounts of irrigation can mean that much of the water applied causes runoff, polluting nearby streams, etc. Advice given in the fact sheet was to manage irrigation better, so that only the correct amounts of water are applied, and/or to use more efficient irrigation equipment.
Pollution from Pesticides. Farmers use pesticides (insecticides, herbicides and fungicides) to control agricultural pests and weed growth. All those chemicals used can contaminate the water, either through runoff or overspray, or even by deposit from the atmosphere. They may also poison wildlife and fish, contaminate their sources of food and damage or destroy their habitats.
In order to limit those negative and harmful side effects, the fact sheet advised farmers to implement an Integrated Pest Management (IPM) program. Techniques include tailoring the pest control to suit local soil and climate conditions, plus natural barriers to limit the possibility of pesticide being applied beyond the actual crop limits.
Agricultural Water Pollution Case Studies
Nonpoint Sources of Pollution in the Lower Bhavani River Basin, Tamilnadu, India. Mukherjee (2010) presented the results of his study to the 2010 World Water Week in Stockholm in September 2010. His main objective was to determine the willingness of the local farmers to prevent NPS pollution of the groundwater aquifers. However, our primary interest in that study is to consider the causes of the pollution levels found. Mukherjee reported that random sampling was used in the study during June and July 2006, and that the sample size was 395 households spread over 6 villages in the area. High levels of nitrogen were found in the groundwater. His results showed an estimated annual nitrogen load in the river basin studied to be between 9,000 and over 11,000 Kg. per square Km. (Note: That level is far above the nitrogen levels of below 500 Kg./Km.2 found by Clark, Mueller & Mast (2001) in undeveloped stream basins in the U.S.)
Of those high nitrogen levels found in the basin’s groundwater, Mukherjee attributed the causes as follows: Animal waste 43 to 44 percent; Fertilizers 29 to 37 percent; Others (including human waste) 20 percent. Actual percentages depended on the specific village locations tested.
In the results summary of the study, Mukherjee commented that:
a) Regularly monitoring groundwater contamination and informing the farmers of the risks of drinking it, could help them take steps to reduce levels of NPS pollution;
b) The farmers could be persuaded to take action to protect the groundwater if they were provided with educational and agricultural information and agricultural assistance.
Regarding the pollution of groundwater by nitrates in India as a whole, Mukherjee noted in his supporting data that at the time there was no national agency that provided systematic monitoring of NPS pollution, and little information available on groundwater quality.
Water Quality in the Rhine Basin. This case study was included as part of a European Commission paper by Strosser, Pau Vall, and Plötscher (1999), entitled “Water and agriculture: contribution to an analysis of a critical but difficult relationship.” Describing the Rhine basin as one of Europe’s largest, including its tributaries crossing nine countries in total, the paper noted that pollutants of all kinds collect in the river, and that it has limited ability to “self-purify” nitrogen and phosphates, so that the levels of those nutrients are greater downstream. It did report that average nitrate concentrations of between 1 and 2 milligrams per litre (mg/l) were safely below the drinking water limit of 25 mg/l, but that the phosphorus concentrations of circa 60 mg/l, meant that the water quality of the Rhine was not good. It was noted that as of 1995 the situation in the downstream basin had improved, with phosphate levels down to less than 1 mg/l, attributed to the following factors:
Phosphates in detergents being replaced by other softeners;
Phosphate eliminating equipment added to sewage treatment plants;
Reduced discharge of treated sewage and industrial wastes into rivers, etc.;
Since the 1980’s, less phosphate fertilizers used.
The study did note however that pesticides were still a problem, and that although the levels detected were below the World Health Organisation threshold, more needs to be done to reduce the use of pesticides. It also suggested that organic farming policies and practices should be expanded and recommended the following actions:
Implementation of the European Directive – at all levels – on the use of nitrates;
Participation by those involved in agriculture in planning and establishing water management of the catchment basins;
Economic incentives (e.g. taxes and subsidies) to encourage better use of water and minimizing pollutants.
The Lower Fraser Valley in British Columbia. The paper by Schreier et al (1999) entitled: “Agriculture: An Important Non-Point Source of Pollution” described the situation in the Lower Fraser Valley in British Columbia – an intensively farmed area comprising circa 5,500 farms each averaging 67 hectares. The paper suggested that because fertilizer represents a relatively minor cost of agricultural production, the tendency has been to use excessive amounts. Also, during the previous decade, increased numbers of animals had resulted in more manure being applied to the land, which in turn had caused an excess of nutrients in the soil. Further, because urban development in the area has affected water quality and habitats, some fish species including salmon are endangered, as are amphibians such as salamanders, frogs and toads.
Drinking water in the Lower Fraser Valley is sourced primarily from groundwater, which it was found had been contaminated by nitrates, mainly from agricultural sources. The research program undertaken was to identify the precise causes and extent of the contamination of surface water and groundwater resources, and to determine the impact on the health of the ecosystems. The major concerns in respect of the agriculture-originated pollution were:
Nitrate levels in drinking water and hence risk of the blue baby syndrome;
Excessive nutrients in surface water causing algae growth and reduced oxygen;
Pesticides entering both streams and the groundwater sources;
Health risk to humans and aquatic life from microbial issues.
A survey undertaken showed that generally far too much nitrogen, phosphorus and potassium had been applied to the land in the valley as a whole, although some areas had very low levels. It was also found – as might be expected – that areas concentrating on animal production had used fewer pesticides than the locations growing crops.
Another part of the study in the Lower Fraser Valley was in the area of the Sumas River watershed, an intensively farmed part of the valley. An analysis showed that between 1954 and 1995, on the same area farmed, the number of farms had increased by 59, from 224 to 283 (about 26 percent). In parallel with those changes, there had been a dramatic increase in the numbers of chickens and hogs produced. As a consequence, the applied quantity of manure per hectare had also shot up to excessive levels, thereby unavoidably affecting both surface and groundwater through runoff and seepage, especially in the late fall when farmers typically empty manure pits to make room for winter manure storage. Because there were few crops to take up those nutrients plus heavy seasonal rainfall, excess nutrients were washed away and into drainage ditches.
Nitrate levels in the Sumas River have quadrupled since the early 1970’s, matched by ammonia increases and decreased oxygen levels in surface water. Other pollutants detected included high levels of nickel and chromium, and exceptionally high levels of copper and zinc in the lower Sumas River resulting from hog feed supplements. The study also found reduced breeding success rates among amphibian species, attributed to the deterioration in water quality.
Another factor contributing to water quality deterioration due to pollution was the greatly increased numbers of human inhabitants, mostly living in homes having septic sewage systems.
In the Salmon watershed area, 13,000 people had a total of 4,000 septic systems. In checking groundwater quality, it was found that 13 percent of wells had nitrate levels exceeding Canadian drinking water guidelines, and a third of the samples had levels declared to have human impact. Shallow wells were more contaminated than deep wells. Overall, 49 percent of the excessive nitrogen levels were attributed to agriculture, 33 percent to the septic systems and 18 percent to hobby (horse) farms. A separate survey conducted found that one third of the septic systems were not working properly, and that most of the landowners there thought that fertilizers and other agrochemicals were more of a contamination risk than applying manure to the land.
In summary, the authors concluded that agriculture in the Lower Fraser Valley makes a significant contribution to water pollution. Continued application of fertilizers in conjunction with applying manure, and feeding livestock on concentrated feedstuffs that cause higher nitrogen levels in animal waste (especially poultry), means that nutrient levels applied to the soil are far in excess of what it can hold, so increasing pollution of surface and groundwater resources. To reverse this trend the authors stated that surplus nutrient input from fertilizers, manure, and septic systems must be reduced. Actions recommended included:
1. Reduce farm animal stocking densities (as in European countries);
2. Encourage farmers to calculate nitrogen and phosphorus budgets to reduce excess;
3. Enforce the Best Management Practices agricultural code;
4. Encourage manure exports to areas with nutrient deficits;
5. Mandatory septic system servicing every three years;
6. Educating the public about the effects of farming activities and how to avoid further deterioration of surface and groundwater resources, co-ordinating the efforts with local, provincial and government policies.
The Zai System in Mali. This is an unusual and interesting case related to agricultural runoff. Whereas runoff (and the sediment and nutrients, etc that it carries with it) is generally a negative factor in agriculture, in this agricultural technique utilized in Mali, it is the opposite. The study describing the technique is entitled “The Combat Against Desertification and the Conservation of Water: The Zai System of Water Harvesting in Mali”(p5-7). It is just one of 15 case studies included in “Good Practices in Agricultural Water Management: Case Studies from Farmers Worldwide” a United Nations Commission on Sustainable Development paper (2005).
Because Mali is a semi-desert country, where the only rainfall there is comes from June to August each year, the zai method is an ideal way to capture, conserve and use that precious water. It is a traditional technique, often used to recover poor or previously abandoned land. The farmers dig the zai pits to a depth of between 5 and 15 cm (2 to 6 inches) and spaced about 80 cm (30 inches) apart, then filled with organic matter to retain and hold water (and improve the soil), and planted with millet, sorghum, or other annual crops. Because the dry land is generally less permeable to water, rainwater in the form of runoff fills the pits and is trapped by the organic matter. Although the pits can be waterlogged in years which are more wet than usual, generally the system has been proved a great success. The paper reported a project in 1989-1990 in which some 1600 farmers participated. Crop yields were more than 1000 Kg per hectare better using the zai pit system, than yields from control plots cultivated in the normal manner. Also, according to the paper, recent studies showed that soil improvement and water conservation are the two key factors in reversing the desertification of the region, coupled with other techniques such as mulching, regenerating vegetation, and the construction of stone bunds along contour lines to slow / direct water runoff.
Having first described in summary form the principal causes of NPS pollution of water from agricultural activity – all primarily attributable to water runoff reaching both surface water and groundwater resources, this paper then considered four case studies where water pollution was to a major extent caused in that way. Other factors also contributed in specific instances, e.g. industrial pollution, but it was found that agricultural activities (e.g. excessive applications of fertilizers, pesticides, and manure, intense concentrations of livestock, over-irrigation) were the main causes. It was also found that the pollution levels were worse, either where the local populations were unaware of the consequences of their activities, and/or where regulation of their activities was absent or inadequate (e.g. in the Lower Bhavani Basin in India).
Because intensity of farming is generally increasing, along with population growth and urban and industrial development, the pressure on the world’s precious water resources is ever greater. It is therefore extremely important that water resources everywhere are constantly monitored to prevent serious pollution and the associated health risks. It is also important that the excessive use of agrochemicals is strictly curbed and that farmers everywhere are educated to raise awareness of the problems that can be caused, and perhaps given economic incentives to change their current potentially damaging practices and techniques.
Clark, Gregory, M., Mueller, David, K., and Mast, Alisa, M. “Nutrient Concentrations and Yields in Undeveloped Stream Basins of the United States.” (2001). Oklahoma Water Resources Board. Retrieved from http://www.owrb.ok.gov/quality/standards/pdf_standards/Nutrient%20Concentrations%20and%20Yields%20Clark%20etal.pdf
“Good Practices in Agricultural Water Management: Case Studies from Farmers Worldwide.” (2005). United Nations Commission on Sustainable Development. Retrieved from http://www.un.org/esa/sustdev/csd/csd13/documents/bground_3.pdf
Mukherjee, Sacchidananda. “Determinants of Farmers’ Willingness To Protect Groundwater From Nonpoint Sources of Pollution in the Lower Bhavani River Basin, Tamilnadu, India.” (2010). National Instititute of Public Finance and Policy, New Delhi, India. Retrieved from http://www.worldwaterweek.org/documents/WWW_PDF/2010/tuesday/K16-17/Mukherjee.pdf
Schreier, H., Hall, K. J., Brown, S. J., Werrnick, B., Berka, C., Belza, W., & Pettit, K. “Agriculture: An Important Non-Point Source of Pollution.” Simon Fraser University, Canada. Retrieved from http://research.rem.sfu.ca/downloads/frap/S_47.pdf
Strosser, P., Pau Vall, M., & Plötscher, E. (1999). “Water and agriculture: contribution to an analysis of a critical but difficult relationship.” European Commission. Retrieved from http://ec.europa.eu/agriculture/envir/report/en/eau_en/report.htm
“Protecting Water Quality from Agricultural Runoff.” (2005). Environment Protection Agency. Retrieved from http://www.epa.gov/owow/NPS/Ag_Runoff_Fact_Sheet.pdf