nutrient pollution

File:Nutrient sources Gulf-Mex & Chesbay - EPA 2010.png. In the Chesapeake Bay, agriculture is a major source, along with urban areas and atmospheric deposition.]]

{{Bar chart|title=Mean eutrophying emissions (measured as
phosphate equivalents) of different foods{{Cite journal |last1=Nemecek |first1=T. |last2=Poore |first2=J. |date=2018-06-01 |title=Reducing food's environmental impacts through producers and consumers |journal=Science |volume=360 |issue=6392 |pages=987–992 |doi=10.1126/science.aaq0216|issn=0036-8075|pmid=29853680|doi-access=free |bibcode=2018Sci...360..987P }}|label6=Pork|label13=|data12=|label12=|data11=6.2|label11=Tofu|data10=7.5|label10=Peas|data9=14.1|label9=Groundnuts|data8=21.8|label8=Eggs|data7=48.7|label7=Poultry|data6=76.4|data5=97.1|float=right|label5=Lamb and mutton|data4=98.4|label4=Cheese|data3=227.2|label3=Farmed crustaceans|data2=235.1|label2=Farmed fish|data1=365.3|label1=Beef|data_max=360|width_units=em|bar_width=12 |data_type=Eutrophying emissions
(g PO₄^3-eq per 100g protein)|label_type=Food types|data13=}}

File:NRCSTN83003_-_Tennessee_(6251)(NRCS_Photo_Gallery).jpgThe principal source(s) of nutrient pollution in an individual watershed depend on the prevailing land uses. The sources may be point sources, nonpoint sources, or both:

• Agriculture: animal production or crops
• Urban/suburban: stormwater runoff from roads and parking lots; excessive fertilizer use on lawns; municipal sewage treatment plants; motor vehicle emissions
• Industrial: air pollution emissions (e.g. electric power plants), wastewater discharges from various industries.{{cite web |author= |date=2021-08-31 |title=Sources and Solutions |url=https://www.epa.gov/nutrientpollution/sources-and-solutions |website=Nutrient Pollution |publisher=EPA}}

Nutrient pollution from some air pollution sources may occur independently of the local land uses, due to long-range transport of air pollutants from distant sources.{{cite web|author=|date=2021-03-01|title=The Effects: Environment|url=https://www.epa.gov/nutrientpollution/effects-environment|website=Nutrient Pollution|publisher=EPA}}

In order to gauge how to best prevent eutrophication from occurring, specific sources that contribute to nutrient loading must be identified. There are two common sources of nutrients and organic matter: point and nonpoint sources.

Use of synthetic fertilizers, burning of fossil fuels, and agricultural animal production, especially concentrated animal feeding operations (CAFO), have added large quantities of reactive nitrogen to the biosphere.{{cite journal |last1=Galloway |first1=J.N. |last2=Dentener |first2=F.J. |display-authors=1 |date=September 2004 |title=Nitrogen Cycles: Past, Present, and Future |journal=Biogeochemistry |volume=70 |issue=2 |pages=153–226 |doi=10.1007/s10533-004-0370-0 |bibcode=2004Biogc..70..153G |s2cid=98109580}} Globally, nitrogen balances are quite inefficiently distributed with some countries having surpluses and others deficits, causing especially a range of environmental issues in the former. For most countries around the world, the trade-off between closing yield gaps and mitigating nitrogen pollution is small or non-existent.{{Cite journal |last1=Wuepper |first1=David |last2=Le Clech |first2=Solen |last3=Zilberman |first3=David |last4=Mueller |first4=Nathaniel |last5=Finger |first5=Robert |date=November 2020 |title=Countries influence the trade-off between crop yields and nitrogen pollution |url=https://www.nature.com/articles/s43016-020-00185-6 |journal=Nature Food |volume=1 |issue=11 |pages=713–719 |doi=10.1038/s43016-020-00185-6|pmid=37128040 |issn=2662-1355 |hdl-access=free |hdl=20.500.11850/452561 |s2cid=228957302}}

Phosphorus pollution is caused by excessive use of fertilizers and manure, particularly when compounded by soil erosion. In the European Union, it is estimated that we may lose more than 100,000 tonnes of Phosphorus to water bodies and lakes due to water erosion.{{Cite journal |last1=Panagos |first1=Panos |last2=Köningner |first2=Julia |last3=Ballabio |first3=Cristiano |last4=Liakos |first4=Leonidas |last5=Muntwyler |first5=Anna |last6=Borrelli |first6=Pasquale |last7=Lugato |first7=Emanuele |date=2022-09-13 |title=Improving the phosphorus budget of European agricultural soils |journal=Science of the Total Environment |language=en |volume=853 |pages=158706 |doi=10.1016/j.scitotenv.2022.158706|pmid=36099959 |bibcode= 2022ScTEn.85358706P|s2cid=252219900 |doi-access=free }} Phosphorus is also discharged by municipal sewage treatment plants and some industries.{{cite web |author= |date=2018-03-13 |title=Phosphorus and Water |url=https://water.usgs.gov/edu/phosphorus.html |website=USGS Water Science School |publisher=U.S. Geological Survey (USGS) |location=Reston, VA}}

Point sources are directly attributable to one influence. In point sources the nutrient waste travels directly from source to water. Point sources are relatively easy to regulate.{{Cite web |url=https://oceanservice.noaa.gov/education/tutorial_pollution/03pointsource.html |title=Point Source; Pollution Tutorial |access-date=2022-06-10 |publisher=U.S. National Ocean Service |location=Silver Spring, MD}}

Nonpoint source pollution (also known as 'diffuse' or 'runoff' pollution) is that which comes from ill-defined and diffuse sources. Nonpoint sources are difficult to regulate and usually vary spatially and temporally (with season, precipitation, and other irregular events).{{Cite web |url=https://www.epa.gov/nps/basic-information-about-nonpoint-source-nps-pollution |title=Basic Information about Nonpoint Source Pollution |date=15 September 2015}}

It has been shown that nitrogen transport is correlated with various indices of human activity in watersheds,Cole J.J., B.L. Peierls, N.F. Caraco, and M.L. Pace. (1993) "Nitrogen loading of rivers as a human-driven process", pp. 141–157 in M. J. McDonnell and S.T.A. Pickett (eds.) Humans as components of ecosystems. Springer-Verlag, New York, New York, USA, {{ISBN|0-387-98243-4}}.{{cite journal |year=1996 |title= Regional nitrogen budgets and riverine inputs of N and P for the drainages to the North Atlantic Ocean: natural and human influences |journal=Biogeochemistry |volume=35 |pages=75–139 |url=http://www.public.iastate.edu/~downing/tier%202/jadpdfs/1996%20Biogeochemistry%2035.%2075-139.pdf|doi= 10.1007/BF02179825|last1= Howarth|first1= R. W.|last2= Billen|first2= G. |last3=Swaney |first3=D. |last4=Townsend |first4=A. |last5=Jaworski |first5=N. |last6=Lajtha |first6=K. |last7=Downing |first7=J. A .|last8= Elmgren|first8= R.|last9= Caraco|first9= N.|last10= Jordan|first10= T.|last11= Berendse|first11= F.|last12= Freney|first12= J. |last13=Kudeyarov |first13=V.| last14= Murdoch |first14=P. |last15=Zhao-Liang |first15=Zhu |s2cid= 134209808 |access-date=2013-03-31 |archive-url=https://web.archive.org/web/20130503205457/http://www.public.iastate.edu/~downing/tier%202/jadpdfs/1996%20Biogeochemistry%2035.%2075-139.pdf |archive-date=2013-05-03 |url-status=dead}} including the amount of development.{{cite journal |doi=10.1073/pnas.022447299 |pmc=122201 |jstor=3057772 |year=2002 |last1=Bertness |first1=M. D. |title=Anthropogenic modification of New England salt marsh landscapes |journal=Proceedings of the National Academy of Sciences of the United States of America |volume=99 |issue=3 |pages=1395–1398 |last2=Ewanchuk |first2=P. J. |last3=Silliman |first3=B. R. |pmid=11818525 |bibcode=2002PNAS...99.1395B |doi-access=free}} Ploughing in agriculture and development are among activities that contribute most to nutrient loading.

Nutrients from human activities tend to accumulate in soils and remain there for years. It has been shown{{cite journal |vauthors=Sharpley AN, Daniel TC, Sims JT, Pote DH |year=1996 |title=Determining environmentally sound soil phosphorus levels |journal=Journal of Soil and Water Conservation |volume=51 |pages=160–166 |url=http://naldc.nal.usda.gov/download/20713/PDF |access-date=2021-02-12 |archive-date=2023-03-30 |archive-url=https://web.archive.org/web/20230330040910/https://naldc.nal.usda.gov/download/20713/PDF |url-status=dead }} that the amount of phosphorus lost to surface waters increases linearly with the amount of phosphorus in the soil. Thus much of the nutrient loading in soil eventually makes its way to water. Nitrogen, similarly, has a turnover time of decades.

Nutrients from human activities tend to travel from land to either surface or ground water. Nitrogen in particular is removed through storm drains, sewage pipes, and other forms of surface runoff.

Nutrient losses in runoff and leachate are often associated with agriculture. Modern agriculture often involves the application of nutrients onto fields in order to maximize production. However, farmers frequently apply more nutrients than are needed by crops, resulting in the excess pollution running off into either surface or groundwater.{{Cite journal |last1=Buol |first1=S. W. |doi=10.1146/annurev.es.26.110195.000325 |title=Sustainability of Soil Use |journal=Annual Review of Ecology and Systematics |volume=26 | pages=25–44|year=1995}} or pastures. Regulations aimed at minimizing nutrient exports from agriculture are typically far less stringent than those placed on sewage treatment plants{{cite journal |last1=Carpenter |first1=S. R. |last2=Caraco |first2=N. F. |last3=Correll |first3=D. L. |last4=Howarth |first4=R. W. |last5=Sharpley |first5=A. N. |last6=Smith |first6=V. H. |title=Nonpoint Pollution of Surface Waters with Phosphorus and Nitrogen |journal=Ecological Applications |date=August 1998 |volume=8 |issue=3 |pages=559 |doi=10.2307/2641247 |jstor=2641247 |hdl=1813/60811 |hdl-access=free}} and other point source polluters. It should be also noted that lakes within forested land are also under surface runoff influences. Runoff can wash out the mineral nitrogen and phosphorus from detritus and in consequence supply the water bodies leading to slow, natural eutrophication.{{cite journal |last1=Xie |first1=Meixiang |last2=Zhang |first2=Zhanyu |last3=Zhang |first3=Pingcang |title=Evaluation of Mathematical Models in NitrogenTransfer to Overland Flow Subjectedto Simulated Rainfall |journal=Polish Journal of Environmental Studies |date=16 January 2020 |volume=29 |issue=2 |pages=1421–1434 |doi=10.15244/pjoes/106031 |doi-access=free }}

Nitrogen is released into the air because of ammonia volatilization and nitrous oxide production. The combustion of fossil fuels is a large human-initiated contributor to atmospheric nitrogen pollution. Atmospheric nitrogen reaches the ground by two different processes, the first being wet deposition such as rain or snow, and the second being dry deposition which is particles and gases found in the air.{{cite web|title=Critical Loads – Atmospheric Deposition|url=https://www.srs.fs.usda.gov/airqualityportal/critical_loads/atmospheric_deposition.php|website=U.S. Forest Service|publisher=United States Department of Agriculture|access-date=2 April 2018}} Atmospheric deposition (e.g., in the form of acid rain) can also affect nutrient concentration in water,{{cite journal |author=Paerl H. W. |year=1997 |title=Coastal Eutrophication and Harmful Algal Blooms: Importance of Atmospheric Deposition and Groundwater as "New" Nitrogen and Other Nutrient Sources |journal=Limnology and Oceanography |volume=42 |pages=1154–1165 |url=http://www.aslo.org/lo/pdf/vol_42/issue_5pt2/1154.pdf|doi=10.4319/lo.1997.42.5_part_2.1154 |issue=5_part_2 |bibcode=1997LimOc..42.1154P|s2cid=17321339 }}{{dead link|date=December 2017 |bot=InternetArchiveBot |fix-attempted=yes}} especially in highly industrialized regions.

{{Main|Eutrophication#Effects}}

File:Harmful Algal Bloom in Western Lake Erie, July 9, 2018 (41641076380).jpg

Excess nutrients have been summarized as potentially leading to:

• Excess growth of algae (harmful algal blooms);{{cite web|author=|date=2020-11-30|title=Harmful Algal Blooms|url=https://www.epa.gov/nutrientpollution/harmful-algal-blooms|website=Nutrient Pollution|publisher=EPA}} and biodiversity loss;{{Cite web |date=2021-08-18 |title=National Nutrient Strategy |url=https://www.epa.gov/nutrient-policy-data/national-nutrient-strategy |publisher=EPA}}
• Species composition shifts (dominant taxa);
• Food web changes, light limitation;
• Excess organic carbon (eutrophication); dissolved oxygen deficits (environmental hypoxia); toxin production;

Nutrient pollution can have economic impacts due to increasing water treatment costs, commercial fishing and shellfish losses, recreational fishing losses, and reduced tourism income.{{Cite web |title=The Effects: Economy |url=https://www.epa.gov/nutrientpollution/effects-economy |date=2022-04-19 |website=Nutrient Pollution |publisher=EPA}}

Human health effects include excess nitrate in drinking water (blue baby syndrome) and disinfection by-products in drinking water. Swimming in water affected by a harmful algal bloom can cause skin rashes and respiratory problems.{{cite web |title=The Effects: Human Health |url=https://www.epa.gov/nutrientpollution/effects-human-health |date=2022-04-19 |website=Nutrient Pollution |publisher=EPA}}

{{Further|Eutrophication#Prevention}}

Nutrient trading is a type of water quality trading, a market-based policy instrument used to improve or maintain water quality. The concept of water quality trading is based on the fact that different pollution sources in a watershed can face very different costs to control the same pollutant.{{cite web |title=Frequent Questions about Water Quality Trading |url=https://www.epa.gov/npdes/frequent-questions-about-water-quality-trading |website=NPDES |publisher=EPA |date=2022-02-25}} Water quality trading involves the voluntary exchange of pollution reduction credits from sources with low costs of pollution control to those with high costs of pollution control, and the same principles apply to nutrient water quality trading. The underlying principle is "polluter pays", usually linked with a regulatory requirement for participating in the trading program.{{cite web |author1=Genevieve Bennett |author2=Nathaniel Carroll |author3=Katherine Hamilton |title=Charting New Waters, State of Watershed Payments 2012 |url=http://www.forest-trends.org/documents/files/doc_3308.pdf |date=2013 |publisher=Forest Trends Association |location=Washington, DC}}

A 2013 Forest Trends report summarized water quality trading programs and found three main types of funders: beneficiaries of watershed protection, polluters compensating for their impacts and "public good payers" that may not directly benefit, but fund the pollution reduction credits on behalf of a government or NGO. As of 2013, payments were overwhelmingly initiated by public good payers like governments and NGOs.{{rp|11}}

Nutrient source apportionment is used to estimate the nutrient load from various sectors entering water bodies, following attenuation or treatment. Agriculture is typically the principal source of nitrogen in water bodies in Europe, whereas in many countries households and industries tend to be the dominant contributors of phosphorus.{{Cite book |title=Source apportionment of nitrogen and phosphorus inputs into the aquatic environment |date=2005 |publisher=European Environment Agency |others=European Environment Agency |isbn=978-9291677771 |location=Copenhagen |oclc=607736796}} Where water quality is impacted by excess nutrients, load source apportionment models can support the proportional and pragmatic management of water resources by identifying the pollution sources. There are two broad approaches to load apportionment modelling, (i) load-orientated approaches which apportion origin based on in-stream monitoring data{{Cite journal |last1=Greene |first1=S. |last2=Taylor |first2=D. |last3=McElarney |first3=Y.R. |last4=Foy |first4=R.H. |last5=Jordan |first5=P. |title=An evaluation of catchment-scale phosphorus mitigation using load apportionment modelling |journal=Science of the Total Environment |volume=409 |issue=11 |pages=2211–2221 |doi=10.1016/j.scitotenv.2011.02.016 |pmid=21429559 |year=2011 |bibcode=2011ScTEn.409.2211G}}{{Cite journal |last1=Grizzetti |first1=B. |last2=Bouraoui |first2=F. |last3=Marsily |first3=G. de |last4=Bidoglio |first4=G. |title=A statistical method for source apportionment of riverine nitrogen loads |journal=Journal of Hydrology |volume=304 |issue=1–4 |pages=302–315 |doi=10.1016/j.jhydrol.2004.07.036|year=2005 |bibcode=2005JHyd..304..302G}} and (ii) source-orientated approaches where amounts of diffuse, or nonpoint source pollution, emissions are calculated using models typically based on export coefficients from catchments with similar characteristics.{{Cite journal |last1=Mockler |first1=Eva M. |last2=Deakin |first2=Jenny |last3=Archbold |first3=Marie |last4=Daly |first4=Donal |last5=Bruen |first5=Michael |date=2016 |title=Nutrient load apportionment to support the identification of appropriate water framework directive measures |jstor=10.3318/bioe.2016.22 |journal=Biology and Environment: Proceedings of the Royal Irish Academy |volume=116B |issue=3 |pages=245–263 |doi=10.3318/bioe.2016.22 |s2cid=133231562 |hdl=10197/8444|hdl-access=free}}{{Cite journal |last1=Smith |first1=R.V. |last2=Jordan |first2=C. |last3=Annett |first3=J.A. |title=A phosphorus budget for Northern Ireland: inputs to inland and coastal waters |journal=Journal of Hydrology |volume=304 |issue=1–4 |pages=193–202 |doi=10.1016/j.jhydrol.2004.10.004 |year=2005 |bibcode=2005JHyd..304..193S}} For example, the Source Load Apportionment Model (SLAM) takes the latter approach, estimating the relative contribution of sources of nitrogen and phosphorus to surface waters in Irish catchments without in-stream monitoring data by integrating information on point discharges (urban wastewater, industry and septic tank systems), diffuse sources (pasture, arable, forestry, etc.), and catchment data, including hydrogeological characteristics.{{Cite journal |last1=Mockler |first1=Eva M. |last2=Deakin |first2=Jenny |last3=Archbold|first3=Marie |last4=Gill |first4=Laurence |last5=Daly |first5=Donal |last6=Bruen |first6=Michael |title=Sources of nitrogen and phosphorus emissions to Irish rivers and coastal waters: Estimates from a nutrient load apportionment framework |journal=Science of the Total Environment |volume=601-602 |pages=326–339 |doi=10.1016/j.scitotenv.2017.05.186 |pmid=28570968 |year=2017 |bibcode=2017ScTEn.601..326M |doi-access=free|hdl=10197/9071 |hdl-access=free }}

Various nature-based solutions exist to tackle nutrient solution. For instance, farms can create artificial wetlands, which help remove nutrient run-off. These can have also have a waterbody included. Farms can also create buffer zones, to capture nutrients in groundwater or run-off. Finally, by vegetating drainage ditches, there is another opportunity for excess nutrients to be captured.{{Cite journal |last=Rizzo |first=A. |last2=Sarti |first2=C. |last3=Nardini |first3=A. |last4=Conte |first4=G. |last5=Masi |first5=F. |last6=Pistocchi |first6=A. |date=2023-01-01 |title=Nature-based solutions for nutrient pollution control in European agricultural regions: A literature review |url=https://www.sciencedirect.com/science/article/pii/S0925857422002336#s0025 |journal=Ecological Engineering |volume=186 |pages=106772 |doi=10.1016/j.ecoleng.2022.106772 |issn=0925-8574|hdl=2158/1292219 |hdl-access=free }}

Based on surveys by state environmental agencies, agricultural nonpoint source (NPS) pollution is the largest source of water quality impairments throughout the U.S..{{cite report|url=https://www.epa.gov/nps/319-grant-reports-and-project-summaries |title=National Nonpoint Source Program: A catalyst for water quality improvements |date=October 2016 |publisher=EPA |id=EPA 841-R-16-009}}{{rp|10}} NPS pollution is not subject to discharge permits under the federal Clean Water Act (CWA).{{cite web |author= |date=2021-09-28 |title=NPDES Permit Basics |url=https://www.epa.gov/npdes/npdes-permit-basics |publisher=EPA}} EPA and states have used grants, partnerships and demonstration projects to create incentives for farmers to adjust their practices and reduce surface runoff.{{rp|10–11}}

The basic requirements for states to develop nutrient criteria and standards were mandated in the 1972 Clean Water Act. Implementing this water quality program has been a major scientific, technical and resource-intensive challenge for both EPA and the states, and development is continuing well into the 21st century.

EPA published a wastewater management regulation in 1978 to address the national nitrogen pollution problem, which had been increasing for decades.{{cite journal |last1=Kilian |first1=Chris |date=2010 |title=Cracking down on Nutrient Pollution: CLF Fights to Bring New England's Coastal Waters Back to Life |journal=Conservation Matters |volume=16 |issue=2}} In 1998, the agency published a National Nutrient Strategy with a focus on developing nutrient criteria.{{cite report |url=https://nepis.epa.gov/Exe/ZyPURL.cgi?Dockey=20003NOU.txt |title=National Strategy for the Development of Regional Nutrient Criteria |date=June 1998 |publisher=EPA |id=EPA 822-R-98-002}}

Between 2000 and 2010, the EPA published federal-level nutrient criteria for rivers/streams, lakes/reservoirs, estuaries, and wetlands; and related guidance. "Ecoregional" nutrient criteria for 14 ecoregions across the U.S. were included in these publications. While states may directly adopt the EPA-published criteria, the states need to modify the criteria to reflect site-specific conditions in many cases. In 2004, EPA stated its expectations for numeric criteria (as opposed to less-specific narrative criteria) for total nitrogen (TN), total phosphorus (TP), chlorophyll a(chl-a), and clarity, and established "mutually-agreed upon plans" for state criteria development. In 2007, the agency stated that progress among the states on developing nutrient criteria had been uneven. EPA reiterated its expectations for numeric criteria and promised support for state efforts to develop their criteria.{{cite web |last=Grumbles |first=Benjamin |date=2007-05-25 |title=Nutrient Pollution and Numeric Water Quality Standards|url=https://www.epa.gov/sites/production/files/2014-08/documents/nutrient-memo-may252007.pdf |publisher=EPA |id=Memorandum to State and Tribal Water Program Directors}}

After the EPA had introduced watershed-based NPDES permitting in 2007, interest in nutrient removal and achieving regional

Total Maximum Daily Load (TMDL) limitations led to the development of nutrient trading schemes.{{cite web |date=2021-10-11 |title=Permit Limits: Watershed-based Permitting |url=https://www.epa.gov/npdes/watershed-based-permitting |website=NPDES |publisher=EPA}}

In 2008, the EPA published a progress report on state efforts to develop nutrient standards. Most states had not developed numeric nutrient criteria for rivers and streams; lakes and reservoirs; wetlands and estuaries (for those states with estuaries).{{cite report |url=https://nepis.epa.gov/Exe/ZyPURL.cgi?Dockey=P1002TQ0.txt |title=State Adoption of Numeric Nutrient Standards (1998–2008) |date=December 2008 |publisher=EPA |id=EPA 821-F-08-007}} In the same year, EPA also established a Nutrient Innovations Task Group (NITG), composed of state and EPA experts, to monitor and evaluate the progress of reducing nutrient pollution.{{cite web |author=|date=2017-05-16 |title=Programmatic Information on Numeric Nutrient Water Quality Criteria |url=https://www.epa.gov/nutrient-policy-data/programmatic-information-numeric-nutrient-water-quality-criteria |publisher=EPA}} In 2009 the NTIG issued a report, "An Urgent Call to Action", expressing concern that water quality continued to deteriorate nationwide due to increasing nutrient pollution, and recommending more vigorous development of nutrient standards by the states.{{cite report |url=https://nepis.epa.gov/Exe/ZyPURL.cgi?Dockey=P100U1TD.txt |title=An Urgent Call to Action: Report of the State-EPA Nutrient Innovations Task Group |date=August 2009 |publisher=EPA |id=EPA 800-R-09-032}}

In 2011 EPA reiterated the need for states to fully develop their nutrient standards, noting that drinking water violations for nitrates had doubled in eight years, that half of all streams nationwide had medium to high levels of nitrogen and phosphorus, and harmful algal blooms were increasing. The agency set out a framework for states to develop priorities and watershed-level goals for reductions of nutrients.{{cite web |last=Stoner |first=Nancy K. |date=2011-03-16 |title=Working in Partnership with States to Address Phosphorus and Nitrogen Pollution through Use of a Framework for State Nutrient Reductions |url=https://www.epa.gov/sites/production/files/documents/memo_nitrogen_framework.pdf |publisher=EPA |id=Headquarters Memorandum to EPA Regional Administrators}}

Many point source dischargers in the U.S., while not necessarily the largest sources of nutrients in their respective watersheds, are required to comply with nutrient effluent limitations in their permits, which are issued through the National Pollutant Discharge Elimination System (NPDES), under the CWA.{{cite web |author= |date=2021-09-28 |title=Status of Nutrient Requirements for NPDES-Permitted Facilities |url=https://www.epa.gov/npdes/status-nutrient-requirements-npdes-permitted-facilities |website=NPDES |publisher=EPA}} Some large municipal sewage treatment plants, such as the Blue Plains Advanced Wastewater Treatment Plant in Washington, D.C. have installed biological nutrient removal (BNR) systems to comply with regulatory requirements.{{cite web |author= |title=Removing Nitrogen from Wastewater Protects our Waterways |url=https://www.dcwater.com/nitrogen-reduction |access-date=2018-01-15 |publisher=DC Water |location=Washington, D.C.}} Other municipalities have made adjustments to the operational practices of their existing secondary treatment systems to control nutrients.{{cite web |author= |date=2021-09-22 |title=National Study of Nutrient Removal and Secondary Technologies|url=https://www.epa.gov/eg/national-study-nutrient-removal-and-secondary-technologies |publisher=EPA}}

NPDES permits also regulate discharges from large livestock facilities (CAFO).{{cite web|author= |date=2021-07-23 |title=Animal Feeding Operations |url=https://www.epa.gov/npdes/animal-feeding-operations-afos |website=NPDES |publisher=EPA}} Surface runoff from farm fields, the principal source of nutrients in many watersheds,{{cite web |author= |title=Agriculture |url=https://www.chesapeakebay.net/issues/agriculture |access-date=2018-10-06 |website=Learn the Issues |publisher=Chesapeake Bay Program |location=Annapolis, Maryland |archive-date=2018-10-07 |archive-url=https://web.archive.org/web/20181007000354/https://www.chesapeakebay.net/issues/agriculture |url-status=dead }} is classified as NPS pollution and is not regulated by NPDES permits.

A Total Maximum Daily Load (TMDL) is a regulatory plan that prescribes the maximum amount of a pollutant (including nutrients) that a body of water can receive while still meeting CWA water quality standards.{{cite web |author= |date=2021-09-20 |title=Overview of Identifying and Restoring Impaired Waters under Section 303(d) of the CWA |url=https://www.epa.gov/tmdl/program-overview-impaired-waters-and-tmdls |website=Impaired Waters and TMDLs |publisher=EPA}} Specifically, Section 303 of the Act requires each state to generate a TMDL report for each body of water impaired by pollutants. TMDL reports identify pollutant levels and strategies to accomplish pollutant reduction goals. EPA has described TMDLs as establishing a "pollutant budget" with allocations to each pollutant source.{{cite web |title=TMDLs at Work: Long Island Sound |url=https://www.epa.gov/tmdl/tmdls-work-long-island-sound |date=2021-06-16 |publisher=EPA}} For many coastal water bodies, the main pollutant issue is excess nutrients, also termed nutrient over-enrichment.{{cite web |last=Golen |first=Richard F. |date=2007 |title=Incorporating Shellfish Bed Restoration into a Nitrogen TMDL Implementation Plan |url=http://www.coonamessettfarm.com/sitebuildercontent/sitebuilderfiles/Incorporating_Shellfish_Bed_Restoration_into_Nitrogen_TMDL_Implementation_Plan.pdf |publisher=University of Massachusetts, Dartmouth |location=Dartmouth, MA |access-date=2013-05-24 |archive-date=2016-11-16 |archive-url=https://web.archive.org/web/20161116101657/http://www.coonamessettfarm.com/sitebuildercontent/sitebuilderfiles/Incorporating_Shellfish_Bed_Restoration_into_Nitrogen_TMDL_Implementation_Plan.pdf |url-status=dead }}

A TMDL can prescribe the minimum level of dissolved oxygen (DO) available in a body of water, which is directly related to nutrient levels. (See Aquatic Hypoxia.) TMDLs addressing nutrient pollution are a major component of the U.S. National Nutrient Strategy.{{cite web |title=National Nutrient Strategy |url=https://www.epa.gov/nutrient-policy-data/national-nutrient-strategy |date=2007 |publisher=EPA}} TMDLs identify all point source and nonpoint source pollutants within a watershed. Wasteload allocations are incorporated into their NPDES permits to implement TMDLs with point sources.{{cite report |title=NPDES Permit Writers' Manual |date=September 2010 |publisher=EPA|id=EPA-833-K-10-001 |chapter-url=https://www.epa.gov/npdes/npdes-permit-writers-manual |chapter=Chapter 6. Water Quality-Based Effluent Limitations}} NPS discharges are generally in a voluntary compliance scenario.

EPA published a TMDL for the Chesapeake Bay in 2010, addressing nitrogen, phosphorus and sediment pollution for the entire watershed, covering an area of {{convert|64000|sqmi|km2}}. This regulatory plan covers the estuary and its tributaries—the largest, most complex TMDL document that EPA has issued.{{cite web |title=Chesapeake Bay Total Maximum Daily Load |url=https://www.epa.gov/chesapeake-bay-tmdl |date=2022-04-20 |publisher=EPA}}{{cite report |title=Chesapeake Bay TMDL Executive Summary |url=https://www.epa.gov/sites/production/files/2014-12/documents/bay_tmdl_executive_summary_final_12.29.10_final_1.pdf |date=2010-12-29 |publisher=EPA}}

In Long Island Sound, the TMDL development process enabled the Connecticut Department of Energy and Environmental Protection and the New York State Department of Environmental Conservation to incorporate a 58.5 percent nitrogen reduction target into a regulatory and legal framework.

Similar to the U.S., nutrient pollution is dominant in surface water pollution in China.{{Cite journal |last=Chen |first=Xi |last2=Strokal |first2=Maryna |last3=van Vliet |first3=Michelle T. H. |last4=Fu |first4=Xing |last5=Wang |first5=Mengru |last6=Ma |first6=Lin |last7=Kroeze |first7=Carolien |date=2022-02-01 |title=In-stream surface water quality in China: A spatially-explicit modelling approach for nutrients |url=https://www.sciencedirect.com/science/article/abs/pii/S0959652621043730 |journal=Journal of Cleaner Production |volume=334 |pages=130208 |doi=10.1016/j.jclepro.2021.130208 |issn=0959-6526}} Urbanization and agriculture have contributed to nutrient pollution most notably, the practice of discharging of manure where animal manure is treated as waste and is discharged into water. Surveys and models have also shown that Nitrogen and Phosphorus inputs to rivers are high in southern and eastern regions of China.{{Cite journal |last=Chen |first=Xi |last2=Strokal |first2=Maryna |last3=Van Vliet |first3=Michelle T.H. |last4=Stuiver |first4=John |last5=Wang |first5=Mengru |last6=Bai |first6=Zhaohai |last7=Ma |first7=Lin |last8=Kroeze |first8=Carolien |date=2019-08-20 |title=Multi-scale Modeling of Nutrient Pollution in the Rivers of China |url=https://pubs.acs.org/doi/10.1021/acs.est.8b07352 |journal=Environmental Science & Technology |volume=53 |issue=16 |pages=9614–9625 |doi=10.1021/acs.est.8b07352 |issn=0013-936X |pmc=6706797 |pmid=31321972}}{{Cite journal |last=Strokal |first=Maryna |last2=Ma |first2=Lin |last3=Bai |first3=Zhaohai |last4=Luan |first4=Shengji |last5=Kroeze |first5=Carolien |last6=Oenema |first6=Oene |last7=Velthof |first7=Gerard |last8=Zhang |first8=Fusuo |date=2016-02-01 |title=Alarming nutrient pollution of Chinese rivers as a result of agricultural transitions |url=https://iopscience.iop.org/article/10.1088/1748-9326/11/2/024014 |journal=Environmental Research Letters |volume=11 |issue=2 |pages=024014 |doi=10.1088/1748-9326/11/2/024014 |issn=1748-9326}}

• Agricultural wastewater treatment

{{Reflist|2}}

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• {{CRS|article = Report for Congress: Agriculture: A Glossary of Terms, Programs, and Laws, 2005 Edition |url = https://web.archive.org/web/20110810044532/http://ncseonline.org/nle/crsreports/05jun/97-905.pdf}}
• EPA. [https://19january2017snapshot.epa.gov/nps/nonpoint-source-fact-sheets_.html "Protecting Water Quality from Agricultural Runoff."] March 2005. Document No. EPA 841-F-05-001. Fact sheet.

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Category:Agricultural soil science

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Category:Nutrient pollution