MPCA releases draft recommendations for protecting wild rice from excess sulfate

Contact: Dave Verhasselt, 651-757-2278

St. Paul, Minn. — The Minnesota Pollution Control Agency is releasing its proposal for protecting wild rice from excess sulfate. Rather than relying on a single sulfate level for all wild rice waters in the state, the agency proposes to calculate a sulfate level for each wild rice water, based on location-specific factors.

The MPCA’s study of how sulfate affects wild rice, which began in 2012, finds:

  • 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.

The MPCA will be scheduling meetings with interested stakeholders to further describe and get input on its proposal. The agency will continue to refine the proposal based on feedback and any new data. At the same time, the MPCA will consider how the study’s findings will inform regulatory decisions and develop the data collection protocol needed to implement the proposal. The MPCA plans to go through formal rulemaking to change the existing standard later this year. The rulemaking will also include listing specific wild rice waters that are subject to the standard.

The MPCA has compiled a draft list of wild rice waters, along with a process to add waters to the list over time. The list and process are available on the MPCA's Draft proposal for protecting wild rice from excess sulfate webpage. The MPCA also proposes that a sulfate standard is not needed to protect commercial wild rice paddies.

About the study: In 2012, the MPCA contracted with scientists at the University of Minnesota’s Duluth and Twin Cities campuses to study the relationship between sulfate, sulfide and wild rice with field surveys and laboratory and outdoor container experiments. The agency integrated and analyzed the data with input from the study’s advisory committee, and developed a draft analysis that was subject to scientific peer review in summer 2014. The analysis was then refined based on the peer reviewers’ recommendations.

A report on the study’s findings is available on the MPCA's Draft proposal for protecting wild rice from excess sulfate webpage.