Special Topic: Numeric Nutrient Criteria

  • Jun 30, 2010
  • Greg Blanchard and Scott Browning
Algae bloom in an agricultural drainage system caused by excess nutrients

The US Environmental Protection Agency (EPA) and the Florida Department of Environmental Protection (FDEP) have begun a multi-year process to update the Florida state water quality standards for nutrients and replace the current narrative standards with environmentally appropriate numeric standards. Well designed numeric standards simplify the process of evaluating water bodies for compliance with water quality standards. Regional variability in nutrient types and levels have complicated the process. It is clear, however, that excessive nutrient levels are a major cause of poor water quality throughout the state.

What's the Problem?


Nutrient pollution, especially from nitrogen and phosphorus, is one of the top causes of water quality degradation in many parts of the United States, with the waters of Manatee County no exception. Like the human body, water bodies require nutrients to be healthy, but too many nutrients can be harmful. The addition of excess nutrients, such as nitrogen and phosphorus, often associated with human alterations to watersheds, can negatively impact waterbody health and interfere with designated uses of waters by causing noxious tastes and odors in drinking water, producing algal blooms and excessive aquatic weeds in swimming and boating waters, and altering the natural community of flora and fauna.
Here are some things that contribute to nitrogen and phosphorus pollution:
  • Fertilizer over-application (both residential and agricultural usage)
  • Animal wastes in stormwater runoff
  • Stormwater runoff from urbanized areas (e.g., parking lots, lawns, rooftops, roads) without sufficient stormwater treatment
  • Wastewater treatment plant discharges
  • Leaking and/or poorly operating septic systems


What's Being Done About the Problem?


Florida currently uses a narrative nutrient standard for protection of its waters; Chapter 62-302.530 of the Florida Administrative Code (FAC) states that “in no case shall nutrient concentrations of a body of water be altered so as to cause an imbalance in natural populations of flora or fauna.” The narrative criteria also states that (for all waters of the state) "the discharge of nutrients shall continue to be limited as needed to prevent violations of other standards contained in this chapter [Chapter 62-302 FAC]." FDEP has relied on this narrative for many years because unlike any other “pollutant” regulated by the federal Clean Water Act (CWA), nutrients are not only present naturally in aquatic systems, they are absolutely necessary for the proper functioning of biological communities.
However, this narrative approach has not proven effective with all sources of pollution, nor in all aquatic systems. As a result, the Environmental Protection Agency (EPA), in cooperation with the State of Florida, has initiated rulemaking to adopt quantitative nutrient water quality standards for nutrients to facilitate the assessment of designated use attainment for its waters. Numeric criteria will be developed recognizing the hydrologic variability (waterbody type) and spatial variability (location within Florida) of the nutrient levels of the state’s waters.

How is Manatee County Involved?


The Manatee County Natural Resources Department is actively participating in the EPA’s and FDEP’s efforts to establish appropriate nutrient criteria for this region. Of particular importance is the standard for phosphorus, a nutrient that is naturally abundant in this region. In fact, because of its commercial significance (as a component of fertilizer, detergents, etc.), phosphorus is commercially extracted from a geologic formation underlying a large portion of the County. As a result of this natural abundance, phosphorus concentrations in surface waters of the region are naturally elevated in comparison to other parts of the state. 

The abundance of naturally occurring phosphorus in the region’s aquatic systems has resulted in the region being categorized as “nitrogen-limited,” i.e., water quality degradation typically occurs with the addition of excess nitrogen to the environment. Manatee County has actively participated in the nutrient criteria rulemaking process to ensure that the naturally occurring concentrations of phosphorus within this region are recognized. Otherwise, a nutrient standard for phosphorus might be adopted that would be expensive, if not impossible, to achieve in most of the County’s waterbodies.  Manatee County’s Natural Resources Department will continue to work with the EPA and the FDEP to develop appropriate criteria for its waterbodies, and if determined to be nutrient-impaired, to assist in improving water quality in those waterbodies.