Wild riceWild rice is an important part of the ecosystem in many Minnesota lakes and streams. Wild rice is also a cultural resource to many Minnesotans, and is an important economic resource to those who harvest and market it.

In 1973, Minnesota adopted a sulfate standard to protect wild rice based on studies showing that wild rice was found primarily in low sulfate waters. The MPCA and many other organizations and individuals have been working on revising this standard. The 1973 standard was based on observations and water chemistry correlations made by Dr. John Moyle in the late 1930s and early 1940s, concluding that “no large stands of rice occur in water having sulfate content greater than 10 parts per million (mg/L), and rice is generally absent from waters with more than 50 ppm.” While these findings were based on sound scientific observation, Dr. Moyle’s study did not address the specific mechanism by which sulfate appears to impact wild rice growth.

The MPCA studied how sulfate affects wild rice and concluded sulfate levels should be calculated for each wild rice water, based on location-specific factors. The study, which began in 2012, found:

  • In the sediment in which wild rice is rooted, sulfate from the water above is converted to sulfide by bacteria.
  • Higher levels of sulfide in the sediment create an environment that is less hospitable to wild rice.

However, certain factors change the rate at which sulfate is converted to sulfide. Most significantly, higher levels of iron can lead to less sulfide, and higher levels of organic carbon can lead to more sulfide.

To take these variables into account, the MPCA developed an equation that can determine a sulfate level that will protect wild rice for a specific water body. The agency proposes collecting sediment samples in wild rice stands, measuring the iron and organic carbon concentrations in the sediment, and then plugging the data into the equation to calculate a protective sulfate concentration for that particular wild rice water.

Interactive tool for locations of proposed wild rice waters

PDF icon Sources and their abbreviations (wq-rule4-15k)

Wild Rice Sulfate Standard Study

In 2011, the Minnesota Legislature funded a study on the effects of sulfate and other substances on the growth of wild rice. The University of Minnesota was contracted to conduct several research projects as part of this study. Study background, final research reports and data can be found or accessed on the Wild Rice Sulfate Standard Study webpage.

Preliminary analysis and MPCA draft analysis for scientific peer review

The Wild Rice Sulfate Standard Study was completed in December 2013, and the MPCA analyzed the research: PDF icon Wild Rice Sulfate Standard Study Preliminary Analysis

Over the next several months, the MPCA met with Minnesota Tribes, its wild rice advisory committee, the U.S. EPA, and other stakeholders to hear their comments on the preliminary analysis. The MPCA refined the analysis based on comments, review of additional literature, and additional statistical analyses and released the result in June 2014: PDF icon Analysis of the Wild Rice Sulfate Standard Study — Draft for Scientific Peer Review

Scientific peer review

The MPCA sought input on its draft analysis from peer reviewers. See the Wild Rice Sulfate Standard Study webpage  (under “Scientific Peer Review” heading) for background documents and the final report on the peer review process. The accumulated research and peer input formed the basis for the agency’s draft proposal for protecting wild rice from excess sulfate (see above).

March 2015 draft proposal

December 2016 documents for preliminary review

2015 Request for Comments

Pre-rulemaking documents