The Minnesota Pollution Control Agency is claiming a victory in the fight to reduce pollution in the Minnesota River, one of the state's dirtiest waterways.
A study done last summer shows that efforts to limit phosphorous runoff into the river have significantly improved conditions in the waterway, as oxygen levels are stable enough to support fish and other life.
Agency officials and advocates for the river say much more remains to be done, particularly as recent years of drought can be hazardous to a river's health. During periods of low water flows, algae can suck up what little oxygen there is in the water, often resulting in massive fish kills.
But last summer, even as the level of the Minnesota River dropped steadily, researchers did not see large numbers of dead fish.
"The fact that we didn't have a fish kill this time, that's definitely a good thing," said Glenn Skuta, water monitoring manager for the MPCA.
Skuta attributes the good conditions in the river to sharply reduced levels of phosphorus, which acts like a fertilizer and promotes algae growth. Algae consume the oxygen fish need to live. "We saw phosphorus levels in the river this August at about less than half of what we had seen in the past when we've done previous surveys," Skuta said. "So, a big drop in the phosphorus level in the river."
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The lower phosphorus levels largely result from a decade-long, $250 million effort to clean up wastewater treatment plant discharges into the Minnesota River.
In 12 years, sewage treatment plants have reduced the amount of phosphorus they discharge into the river from 1,300 pounds a day to 460 pounds a day, Skuta said.
New Ulm spent nearly $2 million to reduce the levels of phosphorus emitted by its wastewater treatment plant by installing phosphorus removing tanks and equipment, wastewater supervisor Dan O'Connor said.
As a result, the amount of phosphorus the city discharges only 2,500 pounds of phosphorus into the Minnesota River, far below the 25,000 pounds it discharged before the upgrade, O'Connor said.
The plant inn New Ulm has some big phosphorus contributors in the four major food processing plants that together contribute roughly a third of the city's phosphorus load. But when the pollution reaches the plant, it's vanquished by a tiny foe: bacteria.
O'Connor said "phosphorus accumulating organisms," absorb phosphorus from wastewater in large tanks at the treatment plant.
Even though they receive a steady diet, weather can cause major disruptions, as a rainstorm did two years ago when it flushed far too much relatively clean runoff into the holding tanks. As the runoff water was basically phosphorus free, it drastically reduced the food available to the bacteria.
It took nearly three months to re-establish stable bacteria populations in the city's wastewater treatment system, O'Connor said.
But even with the success reducing phosphorus, the river still needs more work.
"Sediment levels, although they have dropped, are not acceptable," said Scott Sparlin, executive director of Coalition for a Clean Minnesota River.
The Minnesota River carries so much sediment that it threatens other waterways. Lake Pepin, on the Mississippi River, could start to fill in with mostly Minnesota River sediment yet this century.
Sparlin said ongoing efforts to reduce sediment include paying farmers to turn cropland near the river into protective grasslands. But he said more needs to be done for the land of the Minnesota River watershed that covers roughly 17 percent of the state.
"It all starts with how we manage the water flowing over the surface of this piece of ground," Sparlin said. "It's that simple and it's that complex."
But tackling sediment may be trickier than reducing phosphorous.
Because any solution likely involves planting fewer acres near rivers, preventing sediment may come at the cost of farm income.
There's also still a major disagreement between farmers and environmentalists over what causes the erosion that deposits sediment in the Minnesota — farm runoff, or increased precipitation.