Fertilizer Runoff: A Water Pollutant?

Fertilizers are a major source of water pollution, with agriculture being the leading cause of impairment of rivers and lakes. Excessive use of fertilizers can cause nutrient pollution, specifically an overload of nitrogen and phosphorus, which leads to eutrophication, or uncontrolled algae blooms, in water bodies. This depletes the water of oxygen, creating 'dead zones' where aquatic life cannot survive. The runoff of agro-chemicals during storms and irrigation contaminates surface water, and the volatilization of ammonia from manure storage adds to the acidification of land and water. While some fertilizers are water-insoluble, over-fertilization and improper management of nutrients can lead to negative impacts on plant and animal life, including humans.

Phosphorus and nitrogen runoff from fertilizers

Fertilizers are a source of nutrients for plants, providing them with nitrogen, phosphorus, and potassium. However, when fertilizers are over-applied or poorly managed, they can cause nutrient pollution in water bodies, leading to negative environmental impacts. This is particularly true for phosphorus and nitrogen runoff from fertilizers.

Phosphorus and nitrogen are essential nutrients for plant growth, but when they are not fully utilized by plants, they can be washed away from farm fields and into nearby waterways during rain or snowmelt events. This excess phosphorus and nitrogen can also leach through the soil and into groundwater over time. High levels of these nutrients in water bodies can lead to a process called eutrophication, which is characterized by uncontrolled algae growth.

The algae bloom blocks light, preventing the growth of other plants such as seagrasses. As the algae and seagrass die, they decay, using up the oxygen in the water and leading to hypoxic ("dead zone") conditions where aquatic life cannot survive. This has been observed in several water bodies, including the Chesapeake Bay and an 8,500-square-mile area in the Gulf of Mexico near where the Mississippi River drains.

To address this issue, farmers can adopt improved nutrient management practices. This includes applying the right amount of fertilizer at the appropriate time of year and using the correct method and placement. Implementing conservation tillage practices, such as reducing the frequency and intensity of tilling, can also help improve soil health, reduce erosion, and decrease the chance of nutrient runoff into waterways.

Additionally, using water-insoluble fertilizers, such as organic fertilizers, can prevent phosphorus from leaching into the water table and traveling into waterways. Cover crops and perennial species can be planted to prevent soil erosion and nutrient loss during periods of bare ground on farm fields. These practices are essential for maintaining water quality and preserving aquatic ecosystems.

Eutrophication and algal blooms

Eutrophication is a type of pollution that occurs when excess nutrients, primarily nitrogen and phosphorus, enter a body of water. This overload of nutrients causes algae to grow uncontrollably, depleting the water of oxygen as they die. This depletion of oxygen in water is known as hypoxia, which can stress aquatic life. When there is no oxygen in the water, it is called an anoxic condition, and no aquatic life can survive. Eutrophication is caused by agricultural, urban, and industrial activities that increase nitrogen and phosphorus pollution.

Fertilizers are a significant source of nutrient pollution in water. They supply plants with easily accessible nutrients, primarily nitrogen, phosphorus, and potassium. When fertilizers are overapplied or improperly managed, they can runoff into nearby water bodies, contributing to eutrophication. This is especially true for heavily fertilized crops like maize, which can have large nutrient losses. Additionally, animal wastes, manures, and sludges can also contribute to phosphorus and nitrogen pollution in water.

The problem of eutrophication and algal blooms is not limited to a specific type of fertilizer. Whether it is organic or inorganic, manure or bone meal, any fertilizer can cause an algal bloom if applied in excess. The uncontrolled growth of algae due to nutrient pollution leads to algal blooms, which can create taste and odor problems and threaten the safety of drinking water and aquatic food supplies. Algal blooms can also have economic impacts, with conservative estimates indicating losses of $1 billion for European coastal waters and $2.4 billion for lakes and streams in the United States.

While there have been improvements in controlling eutrophication in rivers, lakes, and coastal areas, it remains a global environmental challenge. The complex flow of water and nutrients through different ecosystems, such as streams, rivers, lakes, and estuaries, makes it difficult to manage eutrophication effectively. Reducing only one nutrient upstream may not be sufficient, as other nutrients can stimulate algal production downstream.

To address eutrophication and algal blooms, it is essential to adopt better land and fertilizer management practices. This includes applying fertilizers only when needed, during the proper season, and in the correct amounts. Using water-insoluble fertilizers, such as those with slow-release mechanisms, can also help prevent nutrient runoff into waterways. Additionally, leaving lawn clippings to decompose and returning valuable nutrients to the soil can reduce the need for fertilization.

Agriculture as a leading cause of water pollution

Agriculture is the single-largest consumer of water worldwide, accounting for 70% of total water consumption. It is also the most significant contributor to non-point-source pollution in surface water and groundwater. The intensification of agriculture often leads to increased soil erosion, salinity, and sediment loads in water, as well as the excessive or improper use of agricultural inputs like fertilizers to boost productivity.

Fertilizers, for instance, are a significant source of nutrient pollution in water. Excess nitrogen and phosphorus from fertilizers can cause eutrophication in lakes and coastal waters, impacting biodiversity and fisheries. This process, known as eutrophication, occurs when an overload of nutrients causes algae to grow uncontrollably, depleting the water of oxygen as they die. These "'dead zones'" are harmful to aquatic life and even people and their pets. In the United States, the Gulf of Mexico has a notorious 8,500-square-mile "dead zone" near where the nutrient-laden Mississippi River drains.

Agricultural activities also contribute to water pollution through the use of veterinary medicines (antibiotics, vaccines, and growth promoters). These substances move from farms into water ecosystems and drinking water sources, posing risks to human health and the environment. In addition, the agrofood-processing industry associated with agriculture is a significant source of organic pollution in most countries.

Furthermore, agriculture is a leading cause of groundwater pollution. In the United States, for example, 49 out of 50 states identified nitrate as the primary groundwater contaminant, closely followed by pesticides. The European Community has recognized this issue and implemented Directive 91/676/EEC to protect waters against pollution by nitrates from agricultural sources.

While agriculture is a significant contributor to water pollution, it is also a victim. With increasing food demand, farmers are turning to non-conventional water sources, including untreated wastewater, which can contain high levels of nutrients and pollutants. This unsustainable practice further exacerbates the problem of water pollution. However, it is important to note that simple off-farm techniques, such as riparian buffer strips or constructed wetlands, can cost-effectively reduce pollutants entering surface water bodies.

Manure and sludge as hazardous products

Fertilizers are a significant source of nutrient pollution in water bodies. Excessive use of fertilizers and subsequent nutrient runoff impact water quality. Phosphorus and nitrogen runoff from agricultural fields are some of the largest sources of pollution to coastal "dead zones".

Manure is a natural product of animal digestion and can be used as a fertilizer. However, it can also be hazardous due to the production of gases by microorganisms that live within the manure. These gases include ammonia (NH3), carbon dioxide (CO2), methane (CH4), and hydrogen sulfide (H2S). While typically not deadly, ammonia can cause eye irritation and respiratory issues. As the concentration of carbon dioxide increases, it displaces the oxygen in the air and can lead to shortness of breath, dizziness, and even asphyxiation at high levels. Methane can build up in non-ventilated or confined spaces and has a flammable and explosive potential under certain conditions. Hydrogen sulfide is the most dangerous of these gases, causing rapid loss of consciousness and death within minutes at high concentrations. Prolonged exposure to low levels of hydrogen sulfide can also have delayed effects, including long-term neurological damage.

Sludge, as defined by the EPA, refers to any solid, semi-solid, or liquid waste generated from a municipal, commercial, or industrial wastewater treatment plant. Sewage sludge, in particular, is a hazardous waste that contains thousands of toxic substances and chemical compounds. These contaminants include dioxins, flame retardants, metals, pesticides, and more. The full extent of radioactive contamination in sewage sludge is unknown, and it has been found to contaminate sewage treatment plants. The disposal of sewage sludge is challenging, as methods such as incineration, dumping into landfills, and ocean dumping can lead to air pollution, groundwater contamination, and the creation of underwater dead zones. While gasification is considered the most environmentally friendly method, it is also the most expensive.

Nitrate pollution of ground and surface water

Nitrogen is an essential nutrient for plants, and it is typically supplied to plants in the form of fertilizer. However, the increasing use of fertilizers has led to nitrate pollution of ground and surface water bodies, which has become a pervasive global problem. Nitrate pollution of water sources is primarily attributed to the application of fertilizers in agricultural settings and, to a lesser extent, residential usage.

Nitrate is highly soluble in water and can easily pass through the soil to reach the groundwater table. Once in the groundwater, nitrate can persist for decades and accumulate to high levels, especially in areas with high nitrogen input and vulnerable aquifers. The vulnerability of an aquifer refers to the likelihood of nitrate from a nitrogen source on the land surface reaching the water table. Factors that influence aquifer vulnerability include well-drained soils and a higher proportion of cropland relative to woodland.

The contamination of groundwater by nitrate poses health risks, particularly for infants. High levels of nitrate ingestion from drinking water can cause low oxygen levels in the blood, a potentially fatal condition. As a result, organizations like the U.S. Environmental Protection Agency (EPA) have established drinking water standards to safeguard against excessive nitrate concentrations.

The impact of nitrate pollution extends beyond groundwater, as it also affects surface waters. In surface waters limited by nitrogen, nitrate stimulation of phytoplankton productivity can lead to eutrophication, hypoxia, loss of biodiversity, and harmful algal blooms. These blooms can have detrimental effects on fisheries and sensitive marine environments such as coral reefs.

Addressing nitrate pollution requires a comprehensive approach. This includes improved water and fertilizer management in agroecosystems, the adoption of water-insoluble fertilizers, and the implementation of agricultural stewardship measures. By managing fertilizer application rates, reducing nutrient runoff, and considering the vulnerability of specific water bodies, it is possible to mitigate the contribution of fertilizers to nitrate pollution in both ground and surface waters.

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