Fertilizer Runoff: Which Country's Water Is At Risk?

Water pollution caused by fertilizers is a pervasive global problem. Nitrogen and phosphorus are the two main fertilizers that farmers add to their fields to grow crops. However, when these fertilizers are overapplied, they become pollutants. Research shows that nearly two-thirds of the nitrogen used on crops becomes a pollutant, and more than half of the applied phosphorus does as well. This leads to eutrophication of water bodies, causing dead zones that result in fish kills and a decrease in aquatic life. Furthermore, excess nutrients can cause harmful algal blooms, which produce toxins harmful to humans. While this is a global issue, specific instances of water pollution by fertilizers have been noted in Lithuania, Italy, Canada, and the United States, where fertilizer pollution disproportionately affects rural areas.

Nitrogen and phosphorus fertilisers

Nitrogen and phosphorus are the two primary fertilisers used by farmers to enhance crop yields. However, when overapplied, these nutrients can become pollutants, causing environmental damage and negatively impacting water quality. This issue is particularly prevalent in regions with large populations and extensive farmland, where surrounding water bodies are at high risk of contamination.

Nitrogen, in the form of nitrate, is a common pollutant in both surface and groundwater. The increasing global use of fertiliser nitrogen has led to rising nitrate levels in water supplies, affecting both developing and industrialised nations. Regions in East and South Asia, North America, and Europe are experiencing significant nitrate pollution due to intensive agriculture and substantial fertiliser consumption.

Phosphorus, often associated with the solid phase (sediment), also contributes to water pollution. While phosphorus losses are generally smaller compared to the more soluble nitrogen, certain agricultural practices, such as intensive pig farming, have been identified as major sources of phosphorus surface water pollution in Lithuania and Italy. Additionally, cattle feedlots and manure storage facilities in Canada have been found to contribute a significant amount of phosphorus to the Great Lakes.

The overapplication of fertilisers has led to excess nutrients entering water bodies through runoff and leaching processes. This can result in eutrophication, creating "dead zones" where fish and other aquatic life struggle to survive. Excess nutrients can also cause harmful algal blooms (HABs) in freshwater systems, producing toxins harmful to humans and wildlife.

To address this issue, farmers can implement improved water and fertiliser management practices, such as adopting nutrient management techniques, using conservation drainage practices, and ensuring year-round ground cover to prevent nutrient loss and erosion. By balancing crop needs with environmental considerations, farmers can help reduce the impact of nitrogen and phosphorus fertilisers on water pollution.

Eutrophication and hypoxia

Eutrophication occurs when there is an abundance of nutrients in water, often from agricultural runoff or manure, which can cause harmful algal blooms, dead zones, and fish kills. In the past 50 years, eutrophication has become one of the leading causes of water quality impairment, with global synthetic nitrogen fertilizer use increasing more than sevenfold, and phosphorus use more than tripling. This has resulted in excessive nutrient inputs to estuaries and coastal waters, leading to organic matter over-enrichment of sediments and seasonal hypoxia of bottom water, which can have significant deleterious effects on benthic community biodiversity, abundance, and biomass.

Hypoxia, or low oxygen levels, occurs when a water body has dissolved oxygen concentrations of less than 2-3 mg/L. This can be caused by excess nutrients and waterbody stratification due to saline or temperature gradients. Hypoxia can lead to the destruction of aquatic life, including fish kills and the death of marine mammals and shorebirds. It has escalated dramatically in the past 50 years, increasing from about 10 documented cases in 1960 to at least 169 in 2007.

The impacts of eutrophication and hypoxia are not limited to environmental damage but also have economic and social consequences. For example, a red tide event in Hong Kong in 1998, caused by eutrophication, wiped out 90% of the entire stock of the city's fish farms and resulted in an estimated economic loss of $40 million. Additionally, rural areas often bear the brunt of nitrate pollution, with residents facing higher costs for clean water.

To address these issues, it is crucial to reduce nutrient runoff from agricultural practices and improve manure management. Additionally, increasing public awareness and dialogue about eutrophication and hypoxia can help drive action to protect and restore affected water bodies.

Nitrate pollution

In the United States, nitrate pollution in drinking water is a significant concern, especially in rural areas. An Environmental Working Group analysis revealed that over 2,100 utilities across the Midwest, Southwest, Atlantic Coast, and California serve water with unsafe nitrate levels to nearly 21 million people. California, Illinois, Iowa, Kansas, Maryland, Nebraska, Oklahoma, Pennsylvania, Texas, and Wisconsin are among the states with the most widespread contamination. In Nebraska, researchers linked high birth defect rates to nitrate-contaminated water, while Wisconsin experts warn of increased colon cancer risks.

Minnesota is another state grappling with nitrate pollution, with the compound detected in groundwater, surface water, and drinking water sources. The Minnesota Pollution Control Agency found concerning levels of nitrate in 27% of surface water samples. The state's Department of Health recommends regular testing of well water, especially for households with infants, as nitrate consumption can lead to methemoglobinemia or "blue baby syndrome," a potentially fatal condition.

The issue of nitrate pollution extends beyond the US. In developing countries, point source control for nutrients is a primary concern, while agricultural control measures have been found to be lacking in developed nations. For instance, Lithuania's intensive pig farming industry has resulted in significant surface water pollution from pig waste. Similarly, Italy's Po River and Canada's Great Lakes have experienced pollution from manure and cattle feedlots.

The challenge of nitrate pollution in water demands urgent attention, with far-reaching consequences for human health and the environment. Addressing this issue requires a multifaceted approach, including improved agricultural practices, effective runoff control, and the development of affordable, accessible solutions for water treatment and management.

Manure and animal waste

Animal manure is a significant source of water pollution, particularly in countries with large-scale industrialised agriculture. Livestock rearing generates vast quantities of animal waste, which can be disposed of or used to produce manure. Unlike human waste, animal manure is often not treated before disposal, and when it is used as fertiliser, it can contaminate water sources if not properly managed.

In the United States, for example, livestock and poultry on concentrated animal feeding operations (CAFOs) or factory farms produced almost 13 times more waste than the entire US population in 2012. This waste is stored in open lagoons or pits and then applied untreated as fertiliser to farm fields. While the US Environmental Protection Agency (EPA) has the authority to regulate CAFO waste, it has largely shifted responsibility to individual states. The original EPA rule from 2003, which required all CAFOs to obtain a National Pollutant Discharge Elimination System (NPDES) permit, has been updated, and as of 2012, only large operations that discharge manure directly into waterways must obtain a federal NPDES permit.

The impact of manure on water pollution is not limited to the US. In Lithuania, for instance, the discharge of pig wastes from intensive pig-raising operations has been identified as a major source of surface water pollution. Similar issues have been reported in Italy's Po River and the Canadian portion of the Lower Great Lakes. In developing countries, point source control for nutrients has been challenging, and without major changes in land use to control fertiliser runoff, agriculture will likely contribute to increasing surface water pollution.

Manure can contain various pollutants, including nitrogen, phosphorus, antibiotics, hormones, and pathogens such as Salmonella, E. coli, and enteroviruses. These contaminants can enter and pollute groundwater through runoff after excessive land application of manure or leaching due to improper storage and application practices. The timing and method of manure application play a crucial role in minimising the risk of groundwater contamination. For instance, spreading manure in late spring or early summer allows growing crops to utilise the nutrients better, reducing the likelihood of runoff into water sources.

To address the issue of manure-related water pollution, proper manure management practices are essential. This includes optimised treatment techniques such as composting, which can inactivate pathogens in manure. Additionally, technologies like anaerobic manure digesters are being explored, which process waste using microbes, heat, water, and agitation to produce methane gas, liquid manure, and solid manure. While these digesters aim to create cleaner fertiliser products, there is growing scepticism about their effectiveness in mitigating pollution and greenhouse gas emissions.

Agricultural control measures

Nutrient Management Techniques

Farmers can adopt improved nutrient management practices by carefully considering the amount, timing, method, and placement of nutrient application. This involves applying the right amount of fertilizer at the appropriate time of year, using suitable methods, and ensuring proper placement to minimize nutrient loss and reduce the risk of excess nutrients reaching water bodies.

Watershed Efforts and Collaboration

Collaboration among various stakeholders, including farmers, state governments, farm organizations, conservation groups, educational institutions, and community groups, is vital. By working together across an entire watershed, these groups can effectively reduce nutrient pollution in water and air. Farmers, in particular, can play a leadership role in driving these collaborative efforts.

Ensuring Year-Round Ground Cover

Farmers can plant cover crops or perennial species to prevent bare ground on farm fields. This practice helps protect the soil and nutrients from erosion and loss into nearby waterways, reducing the risk of fertilizer pollution in water bodies.

Planting Field Buffers

The strategic planting of trees, shrubs, and grasses along the edges of fields, especially those bordering water bodies, can act as a natural buffer. These buffers absorb or filter out excess nutrients before they reach water bodies, providing a natural barrier that helps maintain water quality.

Implementing Conservation Tillage

Reducing the frequency and intensity of tilling fields can improve soil health and reduce erosion, runoff, and soil compaction. By minimizing soil disturbance, there is a lower chance of nutrients, including fertilizers, reaching waterways through runoff, thus mitigating water pollution.

Distancing Polluting Activities from Water Sources

Farmers should distance potentially polluting activities, such as the application of fertilizers or the storage of manure, from nearby water sources. Creating a buffer strip, such as a grass or woodland strip, between the field and a watercourse can help catch and filter potential pollutants before they reach the water body.

Compliance with Regulations

Farmers should adhere to statutory controls and regulations regarding the application of sewage sludge and organic wastes to agricultural land. This includes following guidelines for specific practices, such as those outlined in the Code of Good Agricultural Practice, to minimize pollution and protect water quality.

Frequently asked questions