Numeric Nutrient Criteria for Water Quality

States and tribal agencies have had the responsibility in the USA to establish nutrient criteria for water quality protection, based on the Clean Water Act. According to the U.S. Environmental Protection Agency, over 10,000 nutrient and nutrient-related water quality impairments have been listed across 49 states. Some states and tribes have made progress in moving from “narrative” nutrient criteria to “numeric” criteria for protecting surface water resources, while others have faced more challenges.

Because of well-recognized regional water quality issues such as those in the Chesapeake Bay and the northern Gulf of Mexico, and prominent coastal issues as in Florida and California, pressures are growing to establish numeric criteria for nutrient impairment of surface waters. Numeric nutrient criteria may be used to establish standards that will enable determination of Total Maximum Daily Loads (TMDLs).

The EPA has initiated the formation of an ad hoc technical committee to advise the Ecological Processes and Effects Committee (EPEC) of its Science Advisory Board. This new ad hoc nutrient criteria committee is being asked “To augment the expertise of the EPEC … with specialized knowledge in the use of empirically-derived stressor-response relationships as the basis for developing nutrient assessment endpoints and criteria for the protection of aquatic life.”

In the absence of state and tribal numeric water quality nutrient criteria, the EPA has advocated since 2001 ecoregional criteria for nitrogen (N) and phosphorus (P). The criteria are largely based on a simple statistical approach using overlapping data from monitored vs. selected “reference” waters. This newly formed EPA science committee may establish new numeric nutrient (N and P, for example) criteria for lakes, reservoirs, rivers, streams and wetlands in 14 ecoregions based on the risk of biological impacts of nutrients. Unless states and tribes establish numeric criteria, or sufficiently address development of numeric criteria, the EPA’s ecoregional nutrient criteria may be imposed.

In addition to taking these actions, the EPA will soon release a report of its Integrated Nitrogen Committee, which calls for more control of the human-induced releases of reactive N (basically, all N forms other than atmospheric N₂, which makes up 78 percent of the air we breathe) into the environment. Taken collectively, these water quality actions by EPA underscore the need for intensified efforts by farmers, as well as the urban public (homeowners, turf managers, and others) to embrace and implement fertilizer best management practices based on 4R nutrient stewardship principles encouraged by the fertilizer industry. If you aren’t familiar with the practices that support the 4R principles (right source, right rate, at the right time and right place), talk with your certified crop adviser, ag consultant, extension educator or fertilizer industry representative to learn more.

Expanded implementation of 4R nutrient stewardship to protect water quality, while enhancing crop production and efficient nutrient recovery, may help prevent the risk of undesirable regulatory actions.

Learn more about the EPA’s role in regulation, protection and improvement on surface and groundwater here.

Source: Dr. Clifford S. Snyder, Nitrogen Program Director, International Plant Nutrition Institute

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