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Nutrient Pollution and Animal Ag Overview

Industrialized animal agriculture is undoubtedly the largest factor in the pollution of U.S. waterways.[1] The key points, as detailed in the following pages:

Nutrient pollution (excess nitrogen and phosphorus in the environment) is the primary cause of pollution in U.S. waterways.
 Nutrient pollution causes eutrophication which leads to biological degradation and eventually the loss of functioning aquatic ecosystems.
Agriculture is likely the driver of about three-fourths of nutrient pollution.
Animal ag is by far the greatest share of agriculture’s contributions.
The sources of animal ag’s excess N and P are manure along with the chemical fertilizers used on feed crops.
Government regulations and incentives have failed to manage nutrient pollution; the nation’s waterways have received failing grades for decades.
 Federal agencies are unwilling to identify agriculture (and of course unwilling to highlight animal agriculture) as the primary driver.
Nutrient pollution from animal ag is more than a driver of water pollution; it is a key source of air pollution, GHG emissions, and biodiversity loss.
Of the earth’s planetary boundaries, nutrient pollution is the most severely transgressed.
 Its impacts may be as great as climate change or biodiversity loss, while it also contributes in large measure to both problems.

 

  1. We are not aware of any reports that methodically make this claim based on data. It would require the work of federal agencies, nationwide studies, and most importantly, a willingness to explore the decades-long failure to significantly reduce nutrient pollution along with an acknowledgment of the insurmountable design flaws of the factory farming system. We think these following points are self-evident from existing data; all the points on this page are documented in more detail on this and succeeding pages. We believe this subject is worthy of deep analysis as a central environmental issue of animal ag, and possibly the primary driver of U.S. environmental harms. Naturally, we welcome other assessments.

Nutrient pollution – The EPA defines nutrient pollution as “excess amounts of nitrogen and phosphorus in aquatic systems.”[1] Nutrient pollution leads to eutrophication.[2]

 

  1. U.S. EPA (2015) A Compilation of Cost Data Associated with the Impacts and Control of Nutrient Pollution, EPA 820-F-15-096, p. ES-1.
  2.  U.S. EPA (2021) Ambient Water Quality Criteria to Address Nutrient Pollution in Lakes and Reservoirs, EPA-822-R-21-005, p. 1. [“One visible consequence of nutrient pollution in lakes and reservoirs … is cultural (anthropogenic) eutrophication, an increase in primary productivity and algal abundance that increases the amount of organic matter in a water body.”]

Eutrophication – is the process by which water accumulates excess nutrients, primarily nitrogen (N) and phosphorus (P), leading to accelerated growth of algae and aquatic plants. This results in depletion of dissolved oxygen, reduced transparency, and changes in species compositions and loss of biodiversity.[1-3]

 

  1. U.S. EPA (2015) Preventing Eutrophication: Scientific Support for Dual Nutrient Criteria, EPA – 820-S-15-001, p. 1. [“Excess N and P in aquatic systems can stimulate production of plant (including algae and vascular plants) and microbial biomass, which leads to depletion of dissolved oxygen, reduced transparency, and changes in biotic community composition – this is called eutrophication.”]
  2. USDA NALT Concept Space. Eutrophication. [“Process by which bodies of water become enriched in dissolved nutrients, e.g. phosphates, nitrates, nitrogenous compounds. The nutrients deplete the dissolved oxygen of the water by stimulating the growth of algae and other aquatic plant life.”]
  3. U.S. National Oceanic and Atmospheric Administration (n.d.) What is eutrophication? [“Harmful algal blooms, dead zones, and fish kills are the results of a process called eutrophication—which begins with the increased load of nutrients to estuaries and coastal waters.”]

Globally, it is estimated that ~85% of all anthropogenic nitrogen usage is for agriculture along with more than 90% of all phosphorus usage.[1,2]

Agriculture is understood to be the most important driver of nutrient pollution.[3] Nitrogen losses from agriculture are estimated at ~67% of total anthropogenic losses. Phosphorus losses from agriculture are estimated at ~73% of total anthropogenic losses.[4]

Food production is estimated to create more than 75% of eutrophication worldwide.[5]

 

  1. Campbell, B. M., et al., (2017). Agriculture production as a major driver of the Earth system exceeding planetary boundaries. Ecology and Society, 22(4), 8, p. 3. [Agricultures’ share of total global anthropogenic N use has been estimated at 86.1%, and so we use ~85% as the level…” “…as much as 96% of mined P is used for fertilizer production.”]
  2. W.J. Brownlie, et al., (eds.), (2022) Our Phosphorus Future. UK Centre for Ecology & Hydrology, Edinburgh, p. 24. [“Globally, around 85% of phosphates produced for market are processed to make mineral P fertilisers, and 10% are used to make animal feed supplements.”]
  3. Kanter et al., (2022) Secretariat of the Convention on Biological Diversity. Science briefs on targets, goals and monitoring In support of the post-2020 global biodiversity framework negotiations. [“Agriculture is the primary source of nutrient and pesticide pollution.”]
  4. Kanter, D. R. & Brownlie, W. J. (2019). Joint nitrogen and phosphorus management for sustainable development and climate goals. Environmental Science & Policy, 92, 1-8. [See Figure 1, Page 2. N = 155/232.5 = 66.7%. P = 18/23.8 = 72.6%]
  5. Poore, J. & Nemecek, T. (2018). Reducing food’s environmental impacts through producers and consumers. Science (American Association for the Advancement of Science), 360(6392), 987–992, p. 1. [“Food production creates ~32% of global terrestrial acidification and ~78% of eutrophication.”]

Yes. We broadly estimate that most nitrogen and phosphorus pollution – about 75% – is generated by chemical fertilizers, crop fixation, and manure.[1-3]

Nitrogen – Newly created nitrogen (Nr or reactive nitrogen) is mostly produced for fertilizer and through crop fixation, though some is created from fossil fuel usage. Broadly estimated, crops receive about two-thirds of newly created anthropogenic reactive nitrogen and account for ~60% of total N losses (not including losses from manure).[4-6]

Phosphorus – Anthropogenic (mined) phosphorus is almost exclusively used for fertilizer, with livestock feed supplements as a minor secondary use. Combining both uses, agriculture is the source of ~95% of phosphorus usage.[7-10]

Manure – Manure adds another large component to both nitrogen (~15%) and phosphorus pollution, essentially the second generation of pollution after the animals consume and excrete large amounts of nutrients from feed crops and supplements.[11]

While most federal agencies are unwilling to identify agriculture as the primary source of nutrient pollution, one USGS site implies as much, noting that “Agriculture is the leading source of impairments in the Nation’s rivers and lakes. About a half million tons of pesticides, 12 million tons of nitrogen, and 4 million tons of phosphorus fertilizer are applied annually to crops in the continental United States.”[12]

 

  1. Falcone, J.A., (2021). Estimates of county-level nitrogen and phosphorus from fertilizer and manure from 1950 through 2017 in the conterminous United States: U.S. Geological Survey Open-File Report 2020–1153, 20 p. 1. [“The input of nutrients to the environment comes in large part from the (a) use of commercial fertilizer, primarily for agricultural purposes, and the (b) use of manure from livestock.”]
  2. Ribaudo, M. & Shortle, J. (2019). Reflections on 40 years of applied economics research on agriculture and water quality. Agricultural and Resource Economics Review, 48(3), 519-530, p. 521. [This presentation was co-written by a USDA researcher who spent 35 years at the agency trying to address nutrient pollution from agriculture. “The nation’s nutrient pollution problems are to a very large degree the result of the large scale direct (fertilizer) and indirect (animal feed) use of nitrogen and phosphorous in agricultural production.”]
  3. Ribaudo, M., et al., (2011). Nitrogen in agricultural systems: Implications for conservation policy. USDA-ERS Economic Research Report, Report 127, p. 2. [“Agriculture is the predominant source of reactive nitrogen emissions into the environment. In the United States, agriculture contributes 73 percent of nitrous oxide emissions, 84 percent of ammonia emissions, and 54 percent of nitrate emissions.” Current agricultural contributions: nitrous oxide ~79% of total, and ammonia emissions ~85%.]
  4. Davidson, E. A., et al., (2011). Excess nitrogen in the US environment: trends, risks, and solutions. Issues in ecology, (15), Table 1. [19.7 MMT N/ 28.8 MMT = 69% agricultural]
  5. Sobota, D. J., et al., (2013). Reactive nitrogen inputs to US lands and waterways: how certain are we about sources and fluxes? Frontiers in Ecology and the Environment, 11(2), 82-90, Table 2. [18.6 MMT N/ 26.9 MMT= 69% agricultural]
  6. U.S. EPA (2011) Reactive Nitrogen in the United States: An Analysis of Inputs, Flows, Consequences, and Management Options, EPA-SAB-11-013, p. ES-5. [“Crop agriculture receives 60% of U.S. annual new Nr inputs from anthropogenic sources (9.8 Tg from N fertilizer, 7.7 Tg from crop BNF versus 29 Tg total) and accounts for 58% (7.6 Tg) of total U.S. Nr losses from terrestrial systems to air and aquatic ecosystems.” at p. 17. (BNF = biological nitrogen fixation, mostly from soybeans and hay.) Manure totals about 6.0 Tg, compared to 5.7 Tg for fossil fuel combustion. at pp. 11-12, Figure 2 and Table 1]
  7. Brownlie, W. J., et al., (2022) Our Phosphorus Future. UK Centre for Ecology & Hydrology, Edinburgh, p. 24. [“Globally, around 85% of phosphates produced for market are processed to make mineral P fertilisers, and 10% are used to make animal feed supplements.” The remaining 5% is used in detergents, cleaning products, and other industrial uses.]
  8. U.S. Geological Survey, Mineral commodity summaries 2025: U.S. Geological Survey, p. 134. https://doi.org/10.3133/mcs2025. [“More than 95% of the phosphate rock mined in the United States was used to manufacture wet-process phosphoric acid and superphosphoric acid, which were used as intermediate feedstocks in the manufacture of granular and liquid ammonium phosphate fertilizers and animal feed supplements.” Presumably imported phosphate rock is similarly used.]
  9. Keiser, D. A. (2020). Policy Brief—The Effectiveness of Phosphate Bans in the United States. Review of Environmental Economics and Policy, p. 337. [“…recent regulations that focus almost exclusively on industrial use of phosphates will likely be limited in their ability to reduce overall nutrient loads. This is because agriculture continues to account for more than 95 percent of total phosphate use in the United States.” We are not aware of estimates of the total share of P pollution attributed to agriculture. Since almost all usage is for agriculture, we assume that the great majority of dispersal is due to crops and manure.] 
  10. MacDonald, et al., (2012). Embodied phosphorus and the global connections of United States agriculture. Environmental Research Letters, 7(4), 044024. [Gives total mineral P inputs to US domestic agriculture in 2007 as 1905 Gg and livestock supplements (fed directly to animals) as 193 Gg or ~10% of agricultural inputs.]
  11. U.S. EPA (2011) Reactive Nitrogen in the United States, pp. 11-12, Figure 2 and Table 1 [Manure nitrogen totals about 6.0 Tg, compared, for example, to 5.7 Tg for fossil fuel combustion (the largest non-agricultural source). Human waste is a much smaller component of nutrient pollution (1.3 Tg) and is also, unlike manure, commonly treated before release into the environment. 6.0/43.5 = 13.8% from manure, plus some share of atmospheric deposition also due to crops and manure.] 
  12. U.S. Geological Survey (2019) Agricultural Contaminants in Water Resources
    https://www.usgs.gov/mission-areas/water-resources/science/agricultural-contaminants (Accessed 9/6/24) [For updated figures on agricultural usage of nitrogen and phosphorous, see:  Chemical Fertilizer Use on Feed Crops

Yes, without doubt. Adding up the 3 sources shows that animal agriculture is the greatest share of agriculture’s contributions.[1] The sources include:

Close to half of the nitrogen and more than half of the phosphorus in chemical fertilizers is attributed specifically to animal feed.
 Almost all crop fixation of nitrogen (about 80%) is attributed to animal feed.
All the nitrogen and phosphorus in manure is of course due to animal ag.

There are many reports that document the high nutrient pollution “footprint” of animal-sourced foods. These fully support the conclusion that animal ag is the source of most of the nutrient pollution from agriculture.[2-4]

Creation or usage of nutrients does not necessarily mean that the nutrients are eventually released into the environment. However, in practice, the great majority of nutrients in animal agriculture are indeed released into the environment, either from chemical fertilizers and crop fixation in stage one, or from manure in stage two. It is well understood that the animal ag cycle is particularly inefficient in its nutrient usage.[5,6]

 

  1. For more information on these calculations of animal ag contributions to nutrient pollution, see,
    Animal Ag’s Contributions to Water Pollution
  2. Metson, G. S., et al., (2020). The US consumer phosphorus footprint: where do nitrogen and phosphorus diverge? Environmental Research Letters, 15(10), 105022. [“Animal products comprise 78% of the average per capita P footprint and 72% for N.” at p. 7. “Nutrient footprint tools estimate the amount of nutrients embodied in a product or an entity’s consumption activities.” at p. 2]
  3. Scarborough, P., et al., (2023). Vegans, vegetarians, fish-eaters and meat-eaters in the UK show discrepant environmental impacts. Nature Food, 4(7), 565-574, p. 569. [In the UK, the eutrophication impact of “medium meat-eaters” is estimated at almost triple that of vegans.]
  4. Poore, J. & Nemecek, T. (2018). Reducing food’s environmental impacts through producers and consumers. Science (American Association for the Advancement of Science), 360(6392), 987–992, p. 1. [See Figure 1 for eutrophication impacts by food, with many animal-sourced foods having more than 10 times the impact of various grains and vegetables.]
  5. Bouwman, L., et al., (2013). Exploring global changes in nitrogen and phosphorus cycles in agriculture induced by livestock production over the 1900–2050 period. PNAS, 110(52), 20882-20887, p. 20882. [“The rapidly increasing livestock production with its low nutrient recovery dominates the nutrient budget of the total agricultural system.” at p. 20885]
  6. M. A. Sutton (2013) Centre for Ecology and Hydrology, p 19. [“The inclusion of livestock in the food chain substantially reduces overall nutrient use efficiency, leading to large pollution releases to the environment and requiring more N and P to sustain the human population than would be required by plant-based foods. Globally, the 80% of N and P in crop and grass harvests that feeds livestock ends up providing only around 20% (15-35%) of the N and P in human diets, which emphasizes these inefficiencies.”]

The EPA is the key agency tasked with monitoring the health of U.S. waterways and enforcing regulations to maintain water quality. Nutrient pollution is a central factor in these assessments and in their regulatory efforts. Other agencies play a smaller role.

EPA Assessment – The EPA monitors the status and trends of the nation’s waterways, choosing metrics or “indicators” that reflect the physical, chemical, and biological conditions along with characteristics that pose risks to human health.[1] The agency generates reports approximately every 5 years assessing each of 4 categories of waterways: Rivers & Streams, Lakes, Wetlands, and Coastal Zones including near-shore areas of the Great Lakes. Together the reports are known as the National Aquatic Resource Surveys (NARS). “The purpose of these surveys is to generate statistically-valid reports on the condition of our nation’s water resources and identify key stressors to these systems.”[2]

EPA Regulation – The EPA is tasked, via the Clean Water Act, with regulating discharges of pollutants into waters of the United States and regulating quality standards for surface waters.[3] Despite the original mandate for the “control of both point and nonpoint sources of pollution,” in practice, the EPA has had limited ability and very little effectiveness in reducing nutrient pollution from crops and factory farms.[4]

USGS – The USGS (U.S. Geological Surveys) is “the Federal source for science about the Earth, its natural and living resources, natural hazards, and the environment.”[5] The USGS is an independent fact-finding agency with no regulatory or management authority.[6] Through the National Water Quality Assessment Program (NAWQA) the agency generates many reports evaluating specific locations and indicators of water quality, with several key reports addressing regional nutrient pollution.[7]

USDA – The USDA offers programs and guidelines through its Natural Resources Conservation Service (NRCS) to encourage farming conservation strategies to “conserve water and keep valuable nutrients on the field and out of local waterways.” Participation in NRCS programs is voluntary.[8] Despite decades of spending, research, and incentives to farmers, the USDA has had limited impact on agriculture’s overall contributions to nutrient pollution.[9]

 

  1. EPA (2024). National water quality inventory: report to Congress. [This report to Congress aggregates the results of the 4 separate water category reports. See p. 4 for an overview and a listing of those 4 reports] For more info on those reports, see, Water Pollution of Lakes, Rivers, & Streams
  2. US EPA. National Lakes Assessment 2022. Field Operations Manual. Version 1.2. EPA 841-B-16-011, p. 1.
  3. 33 U.S. Code § 1251 Clean Water Act, Congressional declaration of goals and policy. [“It is the national policy that programs for the control of nonpoint sources of pollution be developed and implemented in an expeditious manner so as to enable the goals of this chapter to be met through the control of both point and nonpoint sources of pollution.”]
  4. See, Clean Water Act Animal Ag Regulations and NPDES for CAFOs
  5. Robertson, D.M., and Saad, D.A. (2019) Spatially referenced models of streamflow and nitrogen, phosphorus, and suspended-sediment loads in streams of the Midwestern United States, U.S. Geological Survey Scientific Investigations Report 2019–5114, 74, p. ii. [This identifying “tagline” is used in many other USGS publications.]
  6. U.S. Geological Survey. Information Policies and Instructions. https://www.usgs.gov/information-policies-and-instructions (Accessed 2/18/25)
  7. U.S. Geological Survey. National Water Quality Program. [“The National Water Quality Program provides an understanding of water-quality conditions; whether conditions are getting better or worse over time; and how natural features and human activities affect those conditions.”]
  8. USDA, Natural Resources Conservation Service, Supporting America’s Working Lands (n.d.)
  9. Ribaudo, M. & Shortle, J. (2019). Reflections on 40 years of applied economics research on agriculture and water quality. Agricultural and Resource Economics Review, 48(3), 519-530, p.522. [This presentation was co-written by a USDA researcher who spent 35 years at the agency trying to address nutrient pollution from agriculture. “The voluntary approach has generally not led to sufficient aggregation of conservation efforts in impaired watersheds to produce needed improvements in water quality.”]

Water Pollution