Floating islands good fit for Iowa

Published: Nov. 1, 2016 at 7:40 AM CDT
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Farm lakes across the U.S. have problems with nutrients. With all the agricultural land around them, it's pretty normal to have surface and ground water push phosphorus or nitrogen from the soil into the lake.

At Iowa State University, vegetated floating islands are a part of a project designed to clean up the water.

In Spring of 2015, researchers planted flowers and perennials into a wire mesh designed to let roots grow through then set plant islands off floating into Lake LaVerne.

The idea is those roots will dredge the lake for excess nutrients.

Then in Fall of 2015, researchers pulled them out and harvested the plant matter. In total, three islands had about 11 pounds of dry weight.

They took the harvest to a limnologist who identified all the elements.

In Fall of 2016, the results are in, according to Associate Professor at ISU, Mimi Wagner, "The floating islands removed the amount of nutrients that we would expect them to remove based on the types of plants that we used and the sizes of them. And what that tells us is this particular best management practice is a really good fit for Iowa ponds and small lakes."

This project is a proof of concept, to see how these islands perform in the state.

Around the islands, there was an 80 percent reduction in phosphorus and a 70 percent reduction in nitrogen.

Data-wise the islands were mostly the same but according to Assistant Professor at ISU Austin Stewart, they grew better than research claimed, "Based on other peoples data, the root systems of these plants were only supposed to grow like the first year you're only supposed to get about a foot of depth below the islands. And we had massive root growth. There were two or three feet hanging below the islands when we pulled them out."

Wagner says another difference is normally the plants need two years to become fully effective, this project only had about 5 months on the lake, "So the fact that we had to remove them was a problem in terms of their long term status and their actual performance so that would be the next logical step is to find a location to test these where we can leave them permanently or semi-permanently."

That next step also includes a look at what plants would be best. Iowa State limited the project to good looking plants, rather than ones that are most effective like cattails.

Stewart says they wanted to use Iowa native plants and found 18 varieties, but there's not enough research on plants that are good at getting rid of nutrients and they had to risk it on six Iowa varieties.

Stewart says the results were surprising, "We still got, the same. Our data was basically exactly the same for how many nutrients they were able to pull out en mass as to other studies that had used plants that had specifically known uptake rates. So even though we used plants that didn't have precedent, we saw the same results, which is very promising."

The ISU team drafted a technical guideline of the project for the National Resource Conservation Service.

Stewart says that's also promising, "It's going through the process, so that farmers will be able to use this and get rebates or paid in order to implement these on their land, which is a fantastic outcome."

In the report and technical guidelines there are instructions that show how to make an island, each one costs about $1,500. Stewart says they tried to make it accessible to everyone. Wagner adds you could make one on you own.

In the future, Wagner would like to see these islands tested in Iowa drainage ditches. Even though there are challenges with water flow and anchoring, she says there have been positive results in other studies.

The vegetative floating islands was a part of a $40,000 grant by the Watershed Improvement Review Board and partly matched by Iowa State University.