United States water quality criteria for nitrogen By Hua Xie (International Food Policy Research Institute) Abstract Water quality degradation caused by over-enrichment due to nitrogen is a widespread and pressing environmental issue. While quantitative water quality standards have been established for nitrogen compounds in drinking water, challenges remain in regulating the presence of nitrogen in the ambient water environment. In the United States, the USEPA initiated a strategy to develop region- specific numeric water quality criteria for nutrients to provide better protection to aquatic ecosystems from eutrophication. This U.S. effort exemplifies the complexity in establishing water quality standards to meet ecological goals in water quality management.
Context Nitrogen is essential for sustaining life. However, century, human activities have significantly excess nitrogen in water causes health and impacted the nitrogen cycle and have intensified environmental risks. Nitrogen may exist in water nitrogen flux into the water environment in several forms. Two nitrogen compounds are substantially. It is estimated during the 20th hazardous to human health: nitrate and nitrite century, nitrogen discharges from the global (Lennetech, 2015). Nitrite impairs blood oxygen agricultural production system rapidly increased transport by disrupting haemoglobin to from 6 Tg/yr to 57 Tg/yr (Bouwman et al., 2011). methemoglobin conversion. This may cause In the US., agriculture has been identified as the nausea and stomach aches for adults and “blue main culprit causing nitrogen pollution. The baby" syndrome in infants six months or estimated median percent contribution of younger, who are more susceptible to oxygen agriculture (fertilizer use plus animal agriculture) deprivation caused by nitrite. High nitrate intake to total nitrogen export from watersheds in is also suspected to be associated with gastric major water-resource regions in the US cancer, although there is no conclusive evidence (excluding Alaska and Hawaii) amounts to 36%, (WHO, 2003). Nitrate itself is not toxic, but it can exceeding contribution from any other single convert to nitrite in the human body. The main non-agriculture source (Smith and Alexander, environmental problem caused by over- 2000). enrichment of nitrogen and other nutrients in the ambient water environment is eutrophication. In eutrophied waters, the overabundance of nutrients stimulates growth of algae and aquatic plants. An explosion of these species is often associated with hypoxia, a lack of oxygen in water, which damages the diversity of aquatic ecosystems. Water quality degradation inducted by over- enriched nitrogen has become a widespread and pressing environmental issue in the world (UNEP, 2007). Nitrogen pollution is largely a consequence of human activities from sewage, fertilizers and animal agriculture. Over the past Analysis Water quality criteria describe chemical, turbidity) related to assessment and prevention physical, biological, and other conditions for a of eutrophication. In terms of these regulations, designated use of water. This is a vital part of the the concentrations of nitrogen-based pollutants regulations governing water quality are regulated by measuring total nitrogen (TN)1. management. In the US, under the Safe Drinking According to the strategy, the US EPA developed Water Act, the United States Environmental national recommendations on nutrient criteria. Protection Agency (USEPA) regulates Maximum In the national criteria development, a “region Contaminant Levels (MCLs) of nitrate and nitrite and waterbody approach” is taken, the country in drinking water to protect public health. The is divided into ecoregions, with four waterbody MCLs of nitrate and nitrite (measured as types defined as: (1) streams and rivers, (2) lakes nitrogen) are set to 10 mg/L (10 ppm) and 1 and reservoirs, (3) estuaries and marine coastal mg/L (1 ppm), respectively. This regulation took waters, and (4) wetlands. The nationally- effect in 1992, and following the USEPA’s Six- recommended nutrient criteria serve to provide Year Review has remained unchanged. The same guidance and a starting point for criteria for nitrate and nitrite in drinking water states/territories to develop a more locally- are recommended by the World Health specific numeric nutrient criteria. Organization (WHO, 2006). The US EPA publishes the status of numeric While numeric water quality criteria have been nutrient criteria development online set for nitrogen compounds in drinking water, (http://cfpub.epa.gov/wqsits/nnc- criteria to regulate the presence of nitrogen in development/). In terms of nitrogen/phosphorus the ambient water environment to protect the criteria, as of June 2015, four states/territories health of ecosystems are not well established. have completed nitrogen/phosphorus criteria for The ambient water quality in the US is regulated all water body types, five states/territories by the Clean Water Act. The Act requires the US developed nitrogen and/or phosphorus criteria EPA to develop criteria for ambient water quality for two or more water types, three which reflect state-of-the-art knowledge. states/territories have nitrogen and/or However, a study in 1994 commissioned by the phosphorous criteria for one water type, and the US EPA showed that many states/territories had remaining states/territories only have nitrogen no water quality criteria to regulate the levels of and/or phosphorus criteria for some waters or nutrients (including nitrogen) in ambient waters, no nitrogen and/or phosphorus criteria were set. and that the existing nutrient water quality criteria for ambient waters are mainly narrative (US EPA, 1998, Appendix A). In view of this situation and recognizing the importance of controlling nutrient pollution, the US EPA outlined a Numeric Nutrient Strategy in 1998 (US EPA, 1998) and started to work with states/territories to develop and promote the adoption of numeric nutrient criteria across the nation. The criteria are designed to accommodate water quality parameters including both causal (nitrogen and phosphorus) 1 and responsive variables (Chlorophyll-a and Total nitrogen consists of ammonia, nitrite, nitrate and organic nitrogen.
Figure 1 Status of numeric water quality criteria development for nitrogen (N) and/or phosphorus (P) in the U.S.A. as of June 2015 (Level I: No N and/or P criteria; Level II: N and/or P criteria for some waters; Level III: 1 water type with N and/or P criteria; Level IV: 2 or more water types with N and/or P criteria, and Level V: N and P criteria for all water types). Five US overseas territories: American Samoa (Level V), Guam (level V), Northern Marianas Islands (level V) Puerto Rico (level IV), and U.S. Virgin Islands (level III) are not displayed. Source of data: USEPA State Development of Numeric Criteria for Nitrogen and Phosphorus Pollution (http://cfpub.epa.gov/wqsits/nnc-development/; last access: June 25, 2015)
Lessons Learned The recent effort of the US to develop nitrogen- bodies by their intended functions, and the related water quality criteria focuses on standard is enforced nationally uniformly. The establishing limits on the amount of total US strategy sets out a framework for developing nitrogen in the ambient water environment. regional-specific nitrogen criteria. However, the These criteria are designed to project implementation of this strategy proves to be a ecosystems from the risks of eutrophication. process full of challenges, which are exemplified Compared to setting criteria to protect human by the large span of time since the launch of the health, which could be established on the basis effort and the slow progresses of nutrient of epidemiological evidence and adopted with criteria development/adoption in many states. less geographical differentiation, it is apparently Some reasons for these challenges (Bhattarai more complicated to develop numeric criteria to and Peña-Tijerina, 2013) include: (1) the meet varying water quality requirements for uncertainty in numerically determining diverse aquatic ecosystems. Due to this nutrient/nitrogen thresholds in water bodies – complexity, the variability is ignored in the water although the US EPA (2014) has published a quality criteria legislation in some collection of documentation to recommend countries/regions. For example, in China, the technical approaches for numeric nutrient environmental quality standard for surface criteria development, there is still considerable water (GB 3838-2002) provides that the scientific uncertainty associated with the results maximum allowable values of total nitrogen are obtained using these methods; (2) the high cost set under the classification system for water of nutrient/removal; and, (3) the inequitable distribution of responsibility, with, typically, reduction. Both the merits and challenges should point-source dischargers receiving more be recognised when other countries or regions stringent monitoring and regulation than non- look to the US experience to develop their own point source dischargers and, therefore bearing nutrient/nitrogen criteria to better address more of the burden for nutrient loading ecological water quality requirements.
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