Animal Manure: Air Pollutants And Their Sources

Animal manure is a significant source of air pollution, with manure management alone accounting for 12% of all agricultural greenhouse gas emissions in the United States, according to the EPA. When large numbers of animals are concentrated in confined spaces, such as in industrialized animal agriculture, their manure can release harmful emissions into the air, including ammonia, methane, nitrous oxide, and particulate and gaseous emissions. These emissions contribute to climate change and can have negative impacts on both human health and the environment.

Manure management: Wet storage and spreading of manure produce emissions

Manure management is the process of capturing, storing, treating, and using animal excretion. While manure is a cost-efficient and valuable fertiliser, it can also pose environmental challenges, particularly regarding air pollution. Manure management accounts for about 10% of total global livestock greenhouse gas (GHG) emissions, with cattle and swine manure management producing the highest rates of emissions.

Wet storage and the spreading of manure are significant sources of emissions. Liquid management systems, such as lagoons, promote methane (CH4) production due to the decomposition of organic matter in the manure under anaerobic conditions. The climate in which manure is kept influences bacterial growth, with warm temperatures increasing both nitrous oxide (N2O) and CH4 production by enhancing microbial activity.

To mitigate emissions from wet storage, one effective strategy is to capture CH4 emissions generated under low-oxygen conditions and prevent their release into the atmosphere. Additionally, enhancing manure storage and handling practices can help reduce emissions. For example, manure stockpile aeration inhibits methanogens, leading to decreased CH4 emissions.

The spreading of manure on fields can also contribute to air pollution. When manure is spread on fields and not adequately utilised by crops, it can lead to excess phosphorus in the soil. This phosphorus can be washed away by erosion or runoff and accumulate in water bodies, leading to unwanted plant growth and water quality issues. Furthermore, the application of manure at rates exceeding crop requirements can result in excessive nitrogen levels, contributing to nitrate pollution of ground or surface waters.

To minimise pollution, it is crucial to implement efficient manure management and application systems. This includes matching manure application rates to the nutrient needs of crops and applying manure to fields with lower phosphorus levels to prevent excess phosphorus in the environment.

Nitrogen content: Excess nitrogen in manure leads to nitrate pollution of water and air

Animal manure is a significant source of nitrogen and phosphorus for surface and groundwater. When manure is mismanaged, it can lead to environmental pollution, including air pollution. Nitrogen content in manure is a critical aspect to consider in this context.

Excess nitrogen in manure can have detrimental effects on both water and air quality. When manure is applied to fields at rates exceeding crop requirements, it results in excessive levels of soil nitrogen. This, in turn, leads to nitrate pollution of ground and surface waters. The nitrogen that is not utilised by crops or plants can easily leach through the soil and reach the groundwater. This process is known as nitrate leaching, and it contributes to the contamination of water sources.

Moreover, the volatilisation of ammonia, which is a component of nitrogen in manure, can occur when manure is agitated, pumped, or applied to fields. This process releases ammonia gas into the atmosphere, impacting air quality. Improper manure management practices, such as applying too much manure or mishandling it, can exacerbate this issue.

The application of manure at rates higher than crop needs can also result in the application of phosphorus and other micronutrients above crop requirements. While phosphorus is not directly implicated as a groundwater contaminant, its loss in surface runoff can stimulate algae growth, negatively affecting water quality in streams, lakes, and ponds. This process is known as eutrophication and leads to undesirable conditions in water bodies.

To minimise the environmental impact of animal manure, it is crucial to implement comprehensive manure nutrient management plans. These plans should consider the nitrogen content of the manure and ensure that application rates meet, but do not exceed, the nutrient needs of the crops. By managing manure effectively, the benefits of manure as a nutrient source for farm crops can be maximised while reducing the risk of pollution and its associated effects on air and water quality.

Phosphorus content: Phosphorus stimulates algae growth, impacting water quality and air

Animal manure can pollute the air through the emission of gases and odours, which can be harmful to human and animal health. Manure is rich in nutrients such as nitrogen, phosphorus, and potassium, which are beneficial to crops. However, improper manure management can lead to excess phosphorus in water bodies, which in turn stimulates algae growth and negatively impacts water quality and the air.

Phosphorus, an essential element for all life, plays a critical role in algae growth. When excess phosphorus from manure enters water bodies through runoff or erosion, it can cause an overabundance of algae, known as algal blooms. These blooms have detrimental effects on the aquatic environment, leading to low dissolved oxygen levels, the production of harmful algal toxins, and the blockage of sunlight needed by other organisms and plants. The growth of algae also results in degraded habitat conditions for benthic macroinvertebrates and other aquatic life.

The excess phosphorus contributes to eutrophication, causing changes in the community structure of phytoplankton and zooplankton, as well as disrupting the food chain. This can have far-reaching ecological consequences, impacting the behaviour and reproductive strategies of consumers, such as rotifers, which feed on algae.

To minimise the impact of manure on the environment, it is crucial to implement proper manure management practices. This includes developing a comprehensive manure nutrient management plan that considers the nutrient needs of crops and applies manure accordingly. By minimising the excess phosphorus that reaches water bodies, the stimulation of unwanted algae growth can be reduced, improving both water and air quality.

By addressing the issue of phosphorus content in animal manure and its impact on algae growth, we can help mitigate the negative effects on water quality and air, creating a healthier and more sustainable environment for all.

Livestock emissions: Livestock generate methane and nitrous oxide, contributing to climate change

Livestock production is a significant contributor to global warming, with emissions of methane and nitrous oxide being the most important greenhouse gases from animal agriculture. These gases have a larger warming impact than carbon dioxide, as they trap more heat per molecule.

Enteric fermentation, a regular part of the digestive process for ruminants like cattle and sheep, produces methane. Over 90% of enteric methane from cattle is emitted through burping. This is the largest source of livestock emissions. Manure, on the other hand, is an emission source for both methane and nitrous oxide. The quantity of these emissions depends on environmental conditions, management type, and manure composition. For instance, methane emissions are typically highest when manure is stored in liquid systems such as manure lagoons.

Manure management practices can significantly influence the level of emissions. Methane production increases when liquid manure (slurry) is stored or treated in a lagoon or tank, creating an anaerobic environment that promotes the decomposition of organic matter by bacteria. On the contrary, nitrous oxide production increases when manure is handled as a solid (dung) or deposited on pastures, requiring a combination of aerobic and anaerobic conditions.

The livestock sector demands a significant amount of natural resources, and with the world population projected to reach 9.8 billion by 2050, the demand for livestock products will only increase. To meet future needs, animal productivity will need to rise, and greenhouse gas emission intensity per unit of product will have to decrease. Effective mitigation strategies are essential to achieving this balance.

In conclusion, livestock emissions, particularly of methane and nitrous oxide, contribute significantly to climate change. To reduce their environmental impact, it is crucial to implement comprehensive manure management plans and adopt effective mitigation strategies that consider the complex interactions within livestock production systems.

Industrial agriculture: Large-scale animal operations release pollutants into the air

Industrial agriculture and large-scale animal operations have become increasingly common, and with them, a host of environmental concerns. Concentrated animal feeding operations (CAFOs) are a significant source of air pollution, with the waste produced, including manure, being a key contributor.

The sheer number of animals in these facilities leads to an enormous amount of manure, which is often mismanaged, leading to air and water pollution. When manure is stored and spread, it produces emissions, particularly when wet storage and spreading methods are used, which is common in livestock facilities. This releases methane, ammonia, and nitrous oxide emissions, all of which contribute to climate change. Methane is produced when manure is left to decompose with oxygen on pastureland, and nitrous oxide is released when cow manure is composted.

The ammonia emitted from manure combines with other air pollutants, such as nitrogen oxides and sulfates, forming solid particles that are harmful to human health. These particles are associated with heart and lung diseases and are estimated to cause millions of deaths annually worldwide. The concentration of animals in CAFOs also leads to the release of other hazardous emissions, including microorganisms, endotoxins, and malodorous compounds, which can negatively impact the health of both workers and animals.

Furthermore, the application of manure on fields can result in nutrient mismanagement, particularly when it comes to nitrogen and phosphorus content. Excess nitrogen in manure can lead to nitrate pollution of ground and surface waters, while phosphorus runoff can stimulate unwanted plant growth, such as algae blooms, which have negative consequences for water quality and can produce toxins harmful to humans and wildlife.

The environmental impact of industrial agriculture is significant, and the pollution from large-scale animal operations extends beyond air quality to include water contamination and climate change. Proper manure management and nutrient planning are crucial to reducing these environmental and health risks.

Frequently asked questions