In a ruling with potential implications both on the health of Minnesota’s culturally vital wild rice and on mining and other industry critical to northern Minnesota’s economy, a state administrative law judge ruled Thursday that state regulators failed to justify a proposed change to a controversial water quality standard for protecting wild rice.

In her report, Administrative Law Judge LauraSue Schlatter said the Minnesota Pollution Control Agency failed to justify changing the current wild rice sulfate standard, which limits discharges of sulfates into waters where wild rice grows to 10 milligrams per liter.

The rule has its roots in the 1930s and 40s, when a University of Minnesota scientist found that wild rice didn’t grow well in water that contained a lot of sulfate, a pollutant released by industries like iron ore mines and paper mills, as well as wastewater treatment plants.

Based on that research, Minnesota adopted a standard in 1973 that limited how much sulfate could be discharged into wild rice waters.

After environmental groups and Indian tribes pressured regulators to start enforcing it, the state legislature in 2011 asked the MPCA to study the rule and see if it needed changes.

Last year the agency proposed a complex, flexible formula that would determine what standard would be appropriate for each specific lake or stream.

But Schlatter wrote that the agency failed to demonstrate that repealing and replacing the current standard would be equally or more protective of wild rice.

The agency also “failed to recognize the proposed rule’s burden on the Native American community in its discussion of classes of people who will be burdened by adoption of the proposed rule,” the judge wrote.

The ruling was cheered by both environmental groups and industry groups, although the two sides still disagree on the validity of the state’s current standard.