Harvesting wetlands to improve water quality


Photo courtesy Water Innovation Centre

Manitoba is trying a new approach to reducing phosphorus in Lake Winnipeg. The lake is in jeopardy because of too much phosphorus.

As I reported earlier this year, a significant share of that phosphorus comes from the Red River, which flows north draining a big chunk of northern Minnesota and eastern North Dakota.

There’s a very large marsh on the south end of Lake Winnipeg which filters much of the water flowing in from the Red River. Manitoba plans to harvest about 200 hectares (about 300 acres) of marsh grass and use it for biomass fuel.

Here’s the logic: Plants in a wetland take up phosphorus from the water while they are growing. That’s what makes wetlands good filters for pollution like phosphorus and nitrogen.

The problem is, when all that vegetation dies at the end of the growing season, the stored phosphorus in the plant is turned loose again as the vegetation decays. So in the spring when wetlands are usually flushed by high water, there’s a big spike in phosphorus flowing out of the wetland.

The idea here is to harvest the marsh grasses at the end of the growing season. That takes the stored phosphorus and nitrogen off the landscape.

Manitoba officials plan to turn the grass into biomass fuel to be burned in an electric generation plant, and they say they expect harvesting 300 acres of marsh grass will remove as much phosphorus and nitrogen as is produced annually in the waste water of a town of 20,000 people

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