IEC releases new infographics outlining need for Numeric Nutrient Criteria

Nutrient pollution from fertilizer (excess nitrogen and phosphorus) is the state’s most severe water quality problem. The federal Clean Water Act requires states to set water quality standards limiting the amount of these types of pollutants and offers two approaches: narrative and numeric. The Iowa Department of Natural Resources (DNR) currently uses narrative criteria for fertilizer pollution control, which is inherently subjective and impossible to measure.

For example, the Iowa DNR standard for a lake says that it cannot have “nuisance aquatic life” like algae. But how much algae rises to the level of a nuisance for you? For your kids? For a community that relies in water-related tourism? 

The alternative is numeric nutrient criteria. With numeric nutrient criteria (NNC), the Iowa DNR would establish numeric nitrogen and phosphorus limits for specific water bodies. This data-based method would make it possible to measure how each waterbody compares to the standard. 

IEC and other groups have been calling for the DNR to adopt NNC, particularly in Iowa lakes, for years. IEC and the Environmental Law & Policy Center have twice petitioned the Environmental Protection Commission (EPC), a citizen board that oversees DNR, to direct DNR to begin developing numeric nutrient criteria. The EPC denied both petitions based on the DNR’s argument that the Iowa Nutrient Reduction Strategy (NRS) exists and should be given more time to work. However, guidance for developing the NRS itself included NNC as a tool for reaching 45% nutrient pollution reduction. 

Most recently, the EPA recommended new methods for states to develop state-specific numeric nutrient criteria. The EPA used actual water quality data from Iowa as a case study (see page 98) to show how to apply the methods here. The results of the case study provide a scientific basis for Iowa to adopt NNC. 

The NRS is not a water quality standard as defined by the Clean Water Act, and the NRS’s statewide nutrient reduction target is not a substitute for waterbody-specific standards. Establishing NNC would provide numeric limits to measure against, and under the Clean Water Act could trigger actions to address and mitigate excess pollution in individual waterbodies that exceed those limits. Currently, the nonpoint source NRS policy is completely voluntary and does not place any requirements on agricultural pollution sources, which account for roughly 80% of phosphorus and 92% of nitrogen pollution in the state.  

Most importantly, the DNR should develop and implement NNC because the NRS is not actually reducing nutrient pollution. Iowa DNR has an opportunity to consider NNC in its upcoming Triennial Review for 2024-26.  

Check out IEC’s new infographics to learn more about NNC

• A History of Failure to Adopt Numeric Nutrient Criteria for Iowa's Lakes - a timeline
• Numeric Nutrient Criteria for Iowa's Lakes: How water quality standards work

1. clean water
2. clean water act
3. dnr
4. nitrate pollution
5. nutrient reduction strategy
6. phosphorus pollution
7. water quality
8. water recreation