Greta Jimenez
Agriculture is the single largest user of freshwater on a global basis, accounting for 70% of total water consumption worldwide. It is also a major cause of degradation of surface and groundwater resources through erosion and chemical runoff. The effects of agricultural runoff vary widely depending on the type of operation, landscape conditions, soils, climate, and farm management practices. However, increased levels of nitrogen and phosphorus from fertilizer and manure can stimulate algal blooms in lakes and rivers, leading to the development of hypoxic (low oxygen) conditions that are harmful to aquatic life. Pesticides are also widespread in surface water and groundwater, with at least one pesticide found in about 94% of water samples and more than 90% of fish samples taken from streams across the United States. In addition, the unsafe use of non-conventional water sources, especially wastewater, in agriculture can lead to the accumulation of microbiological and chemical pollutants in crops, livestock products, and soil and water resources, ultimately posing severe health risks to exposed food consumers and farm workers.
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What You'll Learn
Pesticides, fertilizers, and manure
Agriculture is the single largest contributor to non-point-source pollution of surface water and groundwater. Globally, agriculture accounts for 70% of total water consumption. The unsustainable intensification of agriculture, driven by the increasing demand for food, is a significant contributor to water quality degradation.
Pesticides
Pesticides are widely used in agriculture to control pests and diseases. However, they can contaminate water bodies through runoff, infiltration, and irrigation return flows. In the US alone, about half a million tons of pesticides are applied to crops annually. When pesticides enter water bodies, they pose risks to aquatic life, fish-eating wildlife, and drinking water supplies.
Fertilizers
The excessive use or misuse of fertilizers in agriculture can lead to increased soil erosion and nutrient loss, impacting water quality. Fertilizers contain high levels of nitrogen and phosphorus, which can stimulate algal blooms in lakes and rivers when they enter water bodies through runoff and soil erosion. These algal blooms can lead to hypoxic (low oxygen) conditions that are harmful to aquatic life and can also affect recreational uses of water bodies.
Manure
Livestock manure contains nutrients such as nitrogen and phosphorus, which can enter water bodies through runoff and soil erosion. Manure also contains bacteria, viruses, parasites, and fungi, including disease-causing pathogens. When manure is not managed properly, it can contaminate groundwater and surface water, leading to negative impacts on plant, animal, and human life.
To mitigate the water pollution caused by pesticides, fertilizers, and manure, it is essential to implement nutrient management practices. This includes targeting fertilizer and manure application through soil testing, crop-specific calibration, and timing applications to maximize uptake and minimize runoff. Storing livestock manure in lagoons or covered stockpiles can also help minimize runoff risks. Additionally, using drip irrigation instead of furrow irrigation allows for better control of the amounts of pesticides and nutrients added to irrigation water.
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Aquaculture and ecosystems
Agriculture is a major cause of water pollution, contributing to the degradation of water quality and posing risks to aquatic ecosystems, human health, and economic activities. Aquaculture, in particular, has seen significant growth, especially in Asia, and has become a significant factor in the pollution of inland and coastal waters.
Aquaculture ecosystems refer to the integration of aquatic plant, agronomic, algal, and animal subunits into a sophisticated, knowledge-based designed farming ecosystem. These subunits are embedded within the broader context of human social systems, aiming to deliver economic and social profits. Ecological aquaculture is an alternative model that applies ecological principles to the development of aquaculture. It involves planning, designing, monitoring, and evaluating aquatic farming ecosystems to preserve and enhance the natural and social environments in which they are situated.
Aquaculture ecosystems aim to be resilient, capable of withstanding physical and economic shocks and rebuilding themselves. They also aim to prevent environmental degradation and facilitate recovery, prioritizing long-term sustainability. This includes the responsible use of resources and the prevention of pollution.
However, aquaculture can contribute to water pollution through fish excreta, uneaten feeds, antibiotics, fungicides, and anti-fouling agents. These pollutants can contaminate downstream ecosystems, affecting biodiversity and fisheries. The increased use of antibiotics and chemicals in aquaculture can also contribute to polluting downstream ecosystems and may have unintended effects on the environment.
To mitigate the harmful impacts of aquaculture on water resources, proper diagnosis, prediction, and monitoring are essential. Implementing conservation practices, such as nutrient management, manure storage, and drip irrigation, can help minimize pollution and improve soil health. By adopting ecological aquaculture practices and improving sustainability, it is possible to reduce the environmental footprint of the aquaculture industry and protect aquatic ecosystems.
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Water consumption and waste
Agricultural practices contribute to water pollution through the discharge of pollutants and sediments into surface and groundwater. Fertilizers, pesticides, and manure are major sources of pollution, leading to increased nutrient levels, particularly nitrogen and phosphorus, in water bodies. These nutrients can stimulate algal blooms, creating hypoxic conditions harmful to aquatic life and impacting recreational activities. Additionally, the misuse of agricultural inputs, such as excessive fertilizer application, contributes to increased soil erosion, salinity, and sediment loads in water.
The impact of agricultural pollution on water quality varies depending on factors such as the type of operation, landscape conditions, soils, climate, and farm management practices. For example, improper grazing and manure management can lead to bacteria and pathogens entering streams and groundwater. Pollutants from agricultural operations can also enter groundwater, degrading sources of drinking water and posing risks to human health.
To address these issues, management practices play a crucial role. Techniques such as drip irrigation can help reduce water loss and improve pesticide and nutrient control. Proper storage of livestock manure and targeted fertilizer application based on soil testing can minimize runoff risks. Additionally, a multidimensional approach that considers socio-economic, health, environmental, and food safety factors is essential for effective pollution control.
Furthermore, agriculture is both a contributor to and a victim of water pollution. The use of untreated wastewater in agriculture can lead to the accumulation of microbiological and chemical pollutants in crops, affecting human health. However, if adequately treated and safely applied, wastewater can be a valuable water and nutrient source, contributing to food security and livelihood improvement.
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Soil erosion and sediment
Soil erosion is a significant contributor to water pollution, and it is a complex process influenced by various natural and human-induced factors. Natural factors include rainfall, runoff, wind, soil structure, and vegetation, while human activities such as deforestation, agricultural practices, construction, mining, urbanisation, and climate change also play a role. Soil erosion has been recognised as a threat to agriculture and the environment since 1935, when the US Congress declared it a "national menace".
When soil erosion occurs, it can lead to the loss of nutrient-rich topsoil, which is essential for plant growth and agricultural productivity. The topsoil is washed away into nearby streams, rivers, and lakes, leading to increased sedimentation in these water bodies. This sedimentation can disrupt the natural flow of water, clogging waterways and causing flooding. It also reduces water clarity and negatively impacts aquatic habitats and biodiversity. Soil often contains nutrients like nitrogen and phosphorus, which, when washed into water bodies in large amounts, can lead to nutrient pollution and eutrophication. Eutrophication is the significant growth of algae and other aquatic plants in nutrient-enriched waters, which lowers dissolved oxygen levels, leading to fish kills, increased turbidity, and shifts in aquatic flora and fauna populations.
The impact of soil erosion on water quality is evident in Iowa's surface water bodies, where sediment from soil erosion is a major pollutant. Additionally, increased levels of nitrogen and phosphorus in surface waters contribute to reduced water quality. Agricultural practices, such as the use of pesticides and fertilisers, further exacerbate the problem, as these chemicals can be washed into waterways, damaging freshwater and marine habitats and the communities that depend on them.
Controlling soil erosion and managing nutrients are crucial for improving surface water quality and preserving soil fertility and agricultural productivity. Conservation practices such as conservation tillage, no-till farming, buffer strips, and terracing, and effective residue management can help reduce soil erosion. Implementing best management practices for nutrient management, including manure and commercial fertiliser use, is also essential. By adopting these practices, producers can help protect water quality and mitigate the environmental and economic impacts of soil erosion.
Soil erosion is a global issue, with severe challenges in regions like China and Indonesia due to long-term human activities and erosion-prone landforms. It is a significant environmental threat to sustainability and productivity, affecting food security and contributing to the climate crisis. Soil erosion also carries economic costs, with the US agricultural sector losing about $44 billion per year due to erosion and reduced productivity. Therefore, addressing soil erosion through sustainable land management practices is essential for preserving natural resources, the environment, and agricultural livelihoods worldwide.
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Health and environmental impacts
Agriculture is the leading cause of water quality degradation in rivers and streams, the third leading source for lakes, and the second-largest source of impairments to wetlands. It is also the single-largest contributor of non-point-source pollution to surface water and groundwater.
The health and environmental impacts of agricultural water pollution are far-reaching and interconnected.
Eutrophication and Aquatic Ecosystems
Agricultural pollution causes eutrophication, the accumulation of nutrients in lakes and coastal waters, which impacts biodiversity and fisheries. Eutrophication has been identified in 415 coastal areas, and 38% of water bodies in the European Union are under pressure from agricultural pollution. This pollution affects aquatic ecosystems, with about a quarter of produced food being lost along the food supply chain, accounting for 24% of freshwater resources used in food crop production, 23% of global cropland, and 23% of global fertilizer use.
Groundwater Contamination
Agricultural pollutants such as pesticides, fertilizers, and livestock manure can contaminate groundwater, impacting drinking water sources and human health. Over 13 million households in the US obtain drinking water from private wells, which are vulnerable to agricultural pollution.
Veterinary Medicines
A new class of agricultural pollutants, including antibiotics, vaccines, and growth promoters, has emerged in the last 20 years. These contaminants move from farms through water to ecosystems and drinking water sources, potentially exacerbating antimicrobial resistance.
Soil Erosion and Nutrient Loss
Soil erosion, caused by agricultural practices and heavy rainfall, contributes to nutrient loss and the runoff of pesticides and other contaminants. This impacts water quality and can lead to eutrophication and oxygen depletion in aquatic ecosystems, decimating fish and shellfish populations.
Climate Change
Agricultural water pollution contributes to climate change. Livestock production, which accounts for 70% of agricultural land, is resource-intensive and polluting. Clearing land for livestock releases stored carbon and destroys diverse ecosystems. Additionally, meat diets produce 59% more greenhouse gases than vegetarian ones, with beef being 34 times more damaging to the climate than legumes.
Human Health
Agricultural pollution can lead to severe health impacts among exposed food consumers and farm workers. The unsafe use of wastewater in agriculture can result in the accumulation of microbiological and chemical pollutants in crops, livestock products, and soil, posing risks to human health.
Addressing these health and environmental impacts requires a combination of approaches, including regulations, economic incentives, and information dissemination, to encourage sustainable practices and reduce agricultural water pollution.
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Frequently asked questions
Agriculture is the single largest user of freshwater on a global basis and is the main cause of degradation of surface and groundwater resources through erosion and chemical runoff. It accounts for 70% of total water consumption worldwide and is the largest contributor of non-point-source pollution to surface water and groundwater.
The sources of water pollution in agriculture can be both point-source and non-point-source. Point-source pollution comes from a single discharge point, while non-point-source pollution comes from more diffuse, landscape-level causes. Examples of these sources include pesticides, fertilizers, and animal manure, which can enter groundwater depending on local land use and geologic conditions.
Water pollution from agriculture can have both direct and downstream effects on surrounding ecosystems. It can kill local wildlife, contaminate drinking water, and create dead zones in large water bodies. It can also lead to eutrophication and ecosystem damage, as well as limit the amount of light penetrating the water, affecting aquatic biota.
