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Points North Wild Rice and Sulfates

As the annual wild rice crop ripens across the state, a scientific debate is occurring over whether the state has an appropriate water quality standard for sulfate emissions to protect wild rice. The Minnesota Pollution Control Agency recently completed a research project to determine if the current standard of 10 mg/liter is correct. The research is currently undergoing an independent scientific peer review.

While the current wild rice standard has been in place for decades, the state hasn’t enforced it. The lack of enforcement became an issue when opponents to proposed copper and iron mining projects on the Iron Range questioned why water released from mining operations didn’t meet the sulfate standard. Subsequently, the public learned municipal sewage treatment facilities, power utilities, and other industrial-scale water users may not meet the standard either.

A counter question is whether that current standard actually does protect wild rice. Perhaps the native plant can flourish waters with higher sulfate levels. Depending upon local geology, land use, and water chemistry, perhaps the amount of sulfates wild rice can tolerate may vary. If such is the case, maybe the current standard is too stringent.

Clearly, the outcome of the MPCA’s research will have significant consequences for industrial-scale water users.

“Because the outcome of the work is so important, we have to make sure we get the science right,” Kurt Anderson, manager of environmental and land management for Allete (commonly known as Minnesota Power), told an audience in Grand Marais last week when he gave a PowerPoint presentation for interested community members.

As a toxicologist and a gatherer of wild rice, he has both professional and personal expertise on the topic. He has worked on previous wild rice studies as a contractor for MPCA, Environmental Protection Agency, and other organizations. He gathers wild rice with his children near his home in Brookston.

Minnesota is the only state with a low sulfate standard that is based on wild rice. The current standard is derived from the work of Dr. John Moyle, who did lake and stream surveys throughout the state for the Minnesota Department of Conservation during the 1930s and 1940s. Moyle noted wild rice was most abundant in northern Minnesota, where the water had low natural levels of sulfates. It was largely nonexistent in southern and western Minnesota, where the water had higher sulfate levels. Anderson said Moyle’s wild rice maps closely match the state landscape types of forest, transition zone, and prairie.

At relatively low levels, sulfates are a plant nutrient. Sulfates can become harmful to wild rice when they are converted by bacteria to sulfide in the anoxic bottom sediment. Sulfide inhibits a plant’s ability to grow. However, sulfide binds easily with iron, rendering it inert. The presence of iron in bottom sediments may make the sulfate issue a moot point in some waters – or necessitate different sulfate standards for individual waterways.

The current research includes field work to look for correlations between wild rice abundance and sulfate and sulfide levels, as well as other factors. Other scientists grew wild rice in a laboratory with the goal of developing a close response curve for sulfate and sulfides. Wild rice was also grown outdoors in plastic tubs where sulfate levels are controlled, allowing researchers to introduce many other variables, such as salt content, temperature, and oxidation.

Anderson says the results show that wild rice seedlings can be unaffected by sulfate levels far greater than 10 mg/liter. However, he doesn’t agree with the MPCA’s conclusion that they have adequately measured the toxicity of elevated sulfide concentrations to wild rice seedlings. Sulfides occur naturally only in an environment that contains no or little oxygen. He believes that because plants take in carbon dioxide and give out oxygen, they may have evolved the ability to counter sulfide in the soil. The plants in the lab were kept in a tube that was purged of oxygen, which would negate that ability. He said the MPCA tests only observed sulfide toxicity in the shoots and leaves, parts of the plant unlikely to encounter sulfide in nature. The roots and seeds, which are much more likely to encounter sulfide in bottom sediment, were unaffected at the concentrations tested by MPCA.

He pointed out those lakes with high sulfide levels in the bottom sediment are outside of the natural range of wild rice and receive run-off from other land uses, including intensive agriculture and extensive shoreline development. Some parts of the state outside the wild rice range have more sulfur in the soil, too.

But the bottom line of the wild rice debate is the bottom line. Removing sulfates from the water isn’t easy. Anderson said the only viable method for doing so is via reverse osmosis, where water is pushed through a semi permeable membrane to remove impurities. PolyMet, the company that has proposed mining and processing ore on the eastern Iron Range for copper and other precious metals, is planning to use reverse osmosis for its water treatment. The company has said it can meet the 10 mg/liter sulfate standard.

Anderson said the cost of installing reverse osmosis treatment systems at taconite mines, power plants, municipal treatment facilities, and other industrial operations that do not meet the current sulfate standard may be prohibitively expensive. He said one study found that adding reverse osmosis to a sewage treatment plant would have an estimated additional cost of $140 per household per month. He warned cities and industries could go bankrupt attempting to meet the sulfate standard.

Since Anderson works for industry, you could say that he may have an incentive to overstate the cost of compliance with the sulfate standard. But no one seems to disagree that meeting the standard will be very expensive for industrial-scale water users in northern Minnesota. Where they disagree is whether complying with the standard will benefit wild rice.

With its multi-pronged approach to wild rice research, the MPCA is doing what it can to make sure the sulfate standard is based on the best available science. The independent peer review, which is due in September, should provide some clarity for those of us who are not scientists as to the strengths and potential weaknesses in the research effort. However, it will be up to bureaucrats and lawmakers to use the peer-reviewed research to do what is best for clean water, wild rice, and people.

Golden Eagle Lodge

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