Minnesota Republicans and Gov. Mark Dayton are approaching a showdown over who has the power to protect — or pollute — the state's waters.

One of two contentious bills looming at the Legislature would give lawmakers authority over the state's first attempt to protect drinking water from fertilizer. The second would halt the state Pollution Control Agency's faltering effort to rewrite protections for wild rice. Together, they reflect intensifying political frustrations over some of the biggest threats to Minnesota waters and the potential impact of protecting them on some of the state's most powerful industries.

"Too often, your state agencies have employed a 'ready-fire-aim' approach that leaves farmers and legislators feeling blindsided," 41 GOP legislators said in a letter to Dayton last week explaining their support of the fertilizer bill, which passed the House on Monday.

"I am troubled by your accusations," Dayton said in a response. His administration "has employed an open and transparent process" on the fertilizer rule, he said. He vowed to veto the bill if it passes.

The fertilizer rule has been years in the making. It's tied to a 1989 state law that requires the state Department of Agriculture to protect groundwater from farm pollutants, and its implementation would mark the first time the state regulated farmers' use of fertilizer. In some areas, up to 40 percent of private wells are contaminated with the nitrates that come primarily from fertilizers, and many cities face astronomical costs to remove nitrates from community systems.

"I worry that we are breaking the state with these drinking water costs," said Rep. Rick Hansen, DFL-South St. Paul.

The rule calls for local advisory groups to encourage voluntary measures by farmers to protect aquifers. Mandatory measures would kick in several years down the road if most farmers don't do as much as they can on their own.

Environmental groups say the rule wouldn't do enough, because even at the lowest recommended application rates, groundwater is still contaminated by fertilizer. And they point out that the agency did change the proposed rules in response to feedback from farmers.

Farm groups and Republican legislators have fought the rule every step of the way.

Sen. Bill Weber, R-Luverne, chairman of the Committee on Agriculture, Rural Development and Housing Policy, said he doubts that the Agriculture Department has considered all the factors that relate to how farmers use fertilizer.

GOP lawmakers now aim to take control by prohibiting adoption of a rule — or any other groundwater protections tied to fertilizer use — unless they are approved by the Legislature.

Source of nitrates

Bill sponsor Rep. Jeff Backer, R-Browns Valley, said it's necessary because of the "mistrust [of state government] that has developed" among farmers, and because the Agriculture Department is using faulty data. For example, he said, it has "not quantified the massive contribution of nitrates from feces like birds and wildlife."

Scientists and state environmental officials say agriculture, not wildlife, is the source of rising nitrate levels in water.

The wild rice legislation has roots in an equally contentious history. The state began the process of rewriting it in 2015 and has spent millions of dollars researching how sulfate, a mineral salt produced by taconite mines and wastewater treatment plants, affects wild rice.

Scientists say sulfate is just as harmful to other plants and plays a key role in how mercury gets into the aquatic food chain, where it contaminates game fish like walleye.

"If you knock out wild rice, you knock out a lot of other stuff too," said Daniel Engstrom, a senior scientist with the St. Croix Watershed Research Station who's studied the aquatic chemistry of sulfate and mercury.

The state-proposed plan relies on a chemical formula that would be applied to each body of water that contains wild rice, but it was largely thrown out earlier this year by an administrative law judge as too complicated and impossible to enforce.

Engstrom and state environmental officials say that the science underlying the rule is sound, and the biological processes on how sulfate harms wild rice is well understood. It should form the basis for a rule to protect wild rice, they say. Legislators, however, say it's time for the agency to start over and to consider other steps that might improve the fate of Minnesota's state grain.

In the meantime, the proposed bill would prevent the state from adopting or enforcing any standard until the completion of a new rule-making process.

"Everyone agrees we need to protect wild rice," said bill sponsor Rep. Bill Lueck, R-Aitkin. "But go back to the beginning. Let's get this right."

Josephine Marcotty • 612-673-7394