A letter in response to Wild River Audubon letter of March 7

Using a new approach often raises questions and we thank the Wild River Audubon Society for expressing concerns about protecting valuable water resources; a concept that is very important to the Rush Lake Improvement Association (RLIA).

Rush Lake is on the state Impaired Waters List due to excess levels of nutrients, especially phosphorus.

There are two primary sources of phosphorus: (1) external sources such as runoff from lawns, farm fields, and streets which is carried by rain or snow melt into Rush Lake and (2) internal loading which is the accumulation of decades of phosphorus runoff and is continuously cycled from the sediment into the water column. This latter category is the largest component of the phosphorus entering the water column of Rush Lake.

Adding iron particles to Rush Lake could dramatically improve water quality, but incremental steps should be taken first before a large-lake treatment occurs.

The RLIA is proposing small-scale field experiments because adding small amounts of iron mimics what has been observed in other lakes:  specifically; lakes with levels of iron above a certain value have good water quality.  However, lake sediment testing over the past few years shows that Rush Lake is low in iron.

If we add small amounts of iron to Rush Lake, shouldn’t it improve the lake as it does in lakes around the world that have natural iron above a certain value?

Currently, existing technology to control internal loading of phosphorus is weak and the primary method today is to apply aluminum sulfate to the lake bottom. However, this method has serious practical limitations and is very expensive to use.

The RLIA has received approval from the MPCA to conduct small-scale experiments using iron particles to sequester (bind) phosphorus in the lake sediment.  Importantly, in related research, iron has been shown to effectively remove phosphorus from storm water when passed through a berm containing iron particles.

This significant research project was performed, under MPCA sponsorship, at the University of Minnesota under the direction of Prof. John Gulliver who is also interested in extending his storm-water research to lake and stream environments.

In the spring of 2009 & 2011, the RLIA conducted experiments to test the effectiveness of iron particles on 6 acres of Rush Lake and the results of these experiments have been very positive.

This year, the RLIA is planning on conducting additional in-lake experiments to test the effectiveness of iron in binding phosphorus in lake sediment by using an “open water” dispersing technique to insure more uniform coverage. These experiments will cover 9 acres of our 2,800+ acre lake.

Prior to any deposition of iron particles, extensive chemical analysis of the particles is performed by two independent Labs according to EPA method 6020. This chemical analysis tests for Arsenic, Cadmium, Chromium, Copper, Iron, Lead, Mercury, Nickel, Zinc and the iron particles we use are always below the standards for EPA method 6020 for low levels of contamination.

All research being conducted on Rush Lake has been approved by the Minnesota Pollution Control Agency and the Chisago County Water Plan Policy Team and the Chisago County Board of Commissioners passed motions of support for these experiments.

We agree with on one point made in your letter:  that it is important to extend John Gulliver’s research on sequestration of phosphorus from stormwater to the lake environment and to coordinate the lab research with well-designed experiments performed in situ in lakes and streams.  That is a very important step that should be taken and the RLIA is doing its best to help make that happen.

Iron compounds have been used around the world for decades to improve water quality and  a variety of iron compounds have been used for more than 15 years in various lakes in the Twin City region.

For example, iron is routinely added to a St. Paul drinking-water supply lake (Vadnais) with no known negative impact on native vegetation, fish, or humans. Scientists from the DNR and MPCA have monitored our experiments in Rush Lake for the past 3 years and are interested in what we learn from our small-scale field trials because of the great potential for iron particles to decrease the negative impact associated with phosphorus contamination.

The RLIA welcomes dialogue with the Wild River Audubon Society which would then enable us to provide documentation as to why adding small amounts of iron to lakes naturally deficient in iron will likely improve the water quality of the lake.

David Cartwright 

President, RLIA 

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