Rush Lake iron filing project needs closer scrutiny

The Executive Board of Wild River Audubon thinks the Rush Lake Improvement Association’s (RLIA) plan to deposit 13½ tons of iron concentrate into Rush Lake in the coming months deserves closer scrutiny.

The project, begun in 2009, is an attempt to control the level of phosphorus in the lake—phosphorus that originates from feedlots, farm run-off, and lawn fertilizer. Excess phosphorus has encouraged the growth of the invasive Curly Leaf Pondweed. This is a problem for the popular fishing lake.

But the lake is a complex ecosystem and the RLIA admits in its own plan, submitted to Chisago County, that “a thorough laboratory study of iron by a qualified research team is urgently needed”—that they are performing this “experiment” on Rush Lake without the backing of lab studies. Isn’t it better to run studies in a lab first, where variables can be controlled, and not in a living lake, where myriad unforeseen factors could jeopardize the plant s and animals that live in it?

The RLIA also admits in its plan that impact to the biota (plants and animals) of adding iron filings to lake sediments has not yet been systematically investigated. It then adds, “no negative impacts have been observed.” This amounts only to hearsay until a study has been published and peer-reviewed.

There are other questions: what is the source of the iron concentrate?  Newspapers articles refer to “filings” “from foundries” that are “100% iron”. But the iron concentrate that the RLIA put into Rush Lake in 2010 was the precursor to taconite pellets, not pure. In fact, one sample tested contained less than 50% iron.

There were trace amounts of heavy metals in these samples: cadmium, chromium, lead, mercury. There is not much, but they don’t have to be present in large amounts in order to bio accumulate and make their way up the food chain. What is the potential for this?

How big are the iron particles? The particles in the sample were powder fine.  County staff told me that iron is heavy, it will settle out. But the science is not so simple. Very fine particles may not settle out, or remain settled, if the pull of gravity on them is counteracted by buoyancy. Will bottom feeding fish rile up the particles that have settled out? How will fine particles act when the lake turns over every spring and fall?

How will fine particles affect fish gills? Filter-feeders like freshwater mussels? bottom-dwelling invertebrates like midge and dragonfly larvae?  Zooplankton? These are crucial in the food chain.

A member of the RLIA was quoted as saying that the pH of the lake bottom would be changed, inhibiting the growth of weeds. How does a changed pH affect the growth of native plants? They are the base of the food chain.

Crane Island, a Scientific and Natural Area, one of the “crown jewels” in the public lands of Minnesota, sits in the middle of Rush Lake, harboring a heron rookery.  The birds rely on fish and invertebrates from the lake. What if this “experiment” destroys their food supply? How do we know that it won’t?

This is a complex undertaking, far more complex than either the lake association and Chisago County seems to believe.  Wild River Audubon with the state office, Minnesota Audubon, is setting up a petition to the Environmental Quality Board to require an Environmental Assessment worksheet be completed before the project proceeds.

Sue Leaf, President

Wild River Audubon