Sulfate may affect wild rice plants

U researchers are studying how sulfate levels in lakes can decrease seed populations.

Eliana Schreiber

Sulfate from acid rain, sewage treatment plants, mines and bacteria is creating a harmful byproduct affecting wild rice in Minnesota.
 
The Minnesota Pollution Control Agency and University of Minnesota scientists have been investigating the relationship between sulfate levels in water and the presence of rarely studied wild rice.
 
John Pastor, a professor of biology at the University of Minnesota-Duluth, has been growing wild rice in tanks to learn more about how sulfur affects the plant. He’s looking for patterns to see what is causing a decrease in seed populations, he said.
 
Data shows that sulfate is not toxic, but the sulfide it produces has harmed rice populations, he said.
 
“It doesn’t take much sulfate entering into the water to cause the production of enough sulfide to cause the population to go extinct,” Pastor said.
 
In the 1970s, Minnesota added language to its water quality legislation stating that water with sulfate levels greater than 10 milligrams per liter can’t be discharged to bodies of water that grow wild rice, said Amy Myrbo, a research associate in the Department of Earth Sciences and the director of outreach, diversity and education in her lab group.
 
Sulfate isn’t thought to be harmful on its own, she said, so scientists want to find out what is causing smaller seeds and lower populations of rice.
 
Myrbo and her lab group have gone to lakes and rivers around Minnesota to sample the density of wild rice, the surface water chemistry and the water in the sediment in areas where wild rice grows. She has been working with students and other researchers to test their hypothesis on over 100 different sites.
 
“By looking at several hundred different types of data over a couple hundred different sites, we could start to look at the correlations between the chemistry and the abundance and presence of wild rice,” she said.
 
Another concern, Pastor said, is the mines operating near the areas where rice grows, mainly in northern Minnesota.
 
“Sulfate is one of the forms of sulfur that is leaching from iron mines right now and could leach from the copper nickel mine,” he said. “There’s a concern about this for all mines.”
 
While the mines are part of the problem, there are other sources of sulfur, such as agricultural fields, sewage treatment plants and acid rain, Pastor said.
 
Most people are focused on the mines because the sulfur concentration levels nearby are at least 10 times the state standard, he said.
 
Ed Swain, a research scientist for the MPCA said the state Legislature gave the agency $1.5 million to cover the research in 2011. He said the large grant allowed the agency to collect a hefty amount of data. A proposal draft has also been devolped. 
 
Swain said the team is planning to figure out how much sulfate is too much for wild rice.
 
The research group is going to evaluate the existing 10 milligram standard and propose a way of calculating a unique number for every body of water that grows wild rice, he said. This is unusual because water quality standards are usually uniform for every body of water, he said.
 
“The chemistry is different in every system, and no individual number is appropriate,” Swain said.
 
Myrdo said the researchers plan to publish their findings in the near future.