Scientific peers to review MPCA’s analysis of wild rice, sulfate research

DNR scientist John Moyle determined in the 1940s that wild rice tends to grow in low-sulfate water.

Minnesota’s approach to protecting wild rice from sulfate pollution faces a key test this week.  A group of scientists recruited from around the country will evaluate the state’s analysis of a series of research projects designed to determine whether Minnesota’s current sulfate standard for wild rice waters is right. Sulfate occurs naturally, but it’s also added to water by industry, including wastewater treatment plants and mining operations. The Minnesota Pollution Control Agency is bending over backward to make the process as transparent as possible. But members of its own advisory group are already picking apart the analysis.

The studies included hydroponic experiments in the lab, “mesocosm” experiments in stock tanks, and field surveys of more than 120 sites. The researchers are operating under the theory that sulfate itself does not harm rice, but that bacteria in lake sediments convert it to sulfide, which is known to harm plants rooted in saturated soils. 

MPCA’s preliminary analysis says the hydroponic experiments showed wild rice can tolerate very high levels of sulfate, but is likely to be harmed at sulfide levels far lower than the current standard. The agency’s analysis says the mesocosm experiments showed seed weight, seed viability, and seedlings emerging from the sediment each spring declined with increasing sulfate. Also, there was a positive correlation between sulfate in the surface water and sulfide in the porewater (water in the sediments). And it says the field survey confirms the findings of DNR scientist John Moyle back in the 1940s that wild rice tends to grow in low-sulfate water.  Moyle’s research was the basis for the standard, established in 1973, of 10 milligrams per liter of sulfate “in water used for production of wild rice during periods when the rice may be susceptible to damage by high sulfate levels.” 

Industry critics, such as the Minnesota Chamber of Commerce, point to the hydroponic experiments and say a sulfate standard is not needed at all, but if there is one, it should be 1,600 parts per million. That would be more than six times the federal guideline for drinking water.  The industry scientists also say the study does not demonstrate a correlation between sulfate in the surface water and sulfide in the porewater.

On the other hand, environmental advocates criticize a part of the analysis that steps outside the research design to theorize about how iron in the sediments might mitigate the toxic effects of sulfide. In the complicated chemical dance that goes on in lake sediments, iron can react with sulfide to produce a precipitate, a solid. In these studies, researchers discovered that the precipitate can form a crust that sticks to the plant’s roots. It’s possible that this crust might protect the roots from sulfide in the water. It’s also possible that it might prevent the roots from absorbing nitrogen, which would stunt the plant’s growth. This question was not part of the original research design, but in 10 paragraphs at the end of its analysis, the MPCA suggests it might be possible to predict the iron-mitigating potential for a given water body, and use that information to decide how much sulfate could be added to the water. This implies there could be different sulfate standards for different bodies of water.

Tribal and environmental groups protest a discussion of this possibility, saying the research was not designed to study the question, and there is far from enough evidence to draw any conclusions. The MPCA’s point person on the studies, Shannon Lotthammer, says the topic arose from data revealed by the studies, and the agency, still in the middle of data review, will do more analysis before deciding how to approach the standard.

Peer reviewers will meet Wednesday and Thursday in St. Paul; their deliberations will be conducted in public. Meetings will be held at the Embassy Suites Hotel, 175 East 10th St.  People interested in attended are encouraged to register in advance.  More information is on the MPCA’s website.

No comments yet

Leave a Reply