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Development of Nutrient Criteria for Water Quality

In 2001, the U.S. Environmental Protection Agency published water quality criteria for nutrients (nitrogen and phosphorus) as called for in section 304(a) of the Clean Water Act. These criteria were developed as a starting point for states, authorized tribes, interstate commissions, et al., to develop criteria that would be appropriate for their own jurisdictions. This approach was due to the recognition that the determination of suitable limits for nutrients for water bodies is a highly complicated issue. It is governed by wide variation in local ecological conditions, as well as the uses placed upon the waters. Too much nutrient loading to a water body can cause rapid growth of algal blooms, organic enrichment and depletion of dissolved oxygen. Too little may result in insufficient enrichment of the aquatic food chain, which would be detrimental to a healthy aquatic biological community.

Developing the nutrient criteria that will protect the waters of the state requires significant analysis of water quality data. It also requires input from citizens concerned with the impact of implementation of nutrient criteria. With this in mind, a plan for developing nutrient criteria in Missouri was developed in 2005 and is presented here.  There is also an update of the proposed schedule for development.


Nutrient criteria for lakes and reservoirs were adopted as part of the water quality standards rule in October 2009.  The part of the rule applicable to nutrients is at 10CSR 20-7.031(4)(N), on page 16.  The department has drafted a policy for implementation of the rule. In August, 2011, EPA denied approval of a substantial part of this rule, expressing some technical issues with the criteria that were introduced.  The department is in the process of addressing these concerns, with the goal of including them as part of ongoing revisions to the water quality standards. The department is currently amending 10 CSR 20-7.031 to include numeric nutrient criteria for lakes and reservoirs. Documents associated with this rulemaking can be found on the Water Protection Program's Rules in Development webpage.

Nutrient Criteria Analysis

Rivers and Streams

Stakeholders began meeting in 2009 for briefings on how criteria development for streams will proceed.  These meetings were suspended so a technical workgroup could take the time necessary to make recommendations for criteria that will be scientifically defendable and sufficiently protective of the state's streams and rivers.  Criteria will be based on a compilation of several lines of evidence, including a statistical review of available data, a USGS study of algae response to nutrients in the Ozarks, and analyses of macro-invertebrates and chlorophyll-a as response variables.  When all analyses are complete, stakeholder meetings will be reconvened for consideration of the recommendations.