Recycling wood ash could help calcium-starved Canadian lakes

Published: February 4, 2019

ash-from-wood-stove-debris Photo by Vladyslav Trenikhin/Shutterstock

Osteoporosis isn’t just a problem for people—calcium-starved lakes and forests suffer from weak and brittle “bones,” too. Aquatic species, including crayfish and tiny Daphnia plankton disappear when they lack calcium to build shells. In the bush, calcium-deprived maples are more likely to snap in windstorms.

Now Muskoka-based researchers say the ash from your cottage wood stove could reverse these shortfalls—think of wood ash as yogurt, or maybe canned salmon for suffering lakes and forests. “If your cottage is on the Canadian Shield and you’re burning firewood, you might not want to throw the ash out, but spread it in around hardwoods in the forest instead. Or share it with us,” says Norman Yan, chair of Friends of the Muskoka Watershed.

The Friends have won a three-year, $733,000 grant from Ontario’s Trillium Foundation to build what Yan calls Canada’s first recycling program for residential wood ash. The idea is to take the ash—which is about 30 per cent calcium, along with other nutrients including potassium and phosphorus—and begin sprinkling it in test plots in the region’s maple sugar bushes.

If the plan works, it has the potential to boost maple health (possibly leading to more sap, and more, yum, maple syrup) and hike calcium levels in lakes. “If we have enough wood ash to satisfy the needs of the trees, the groundwater calcium levels go up, and streams and groundwater will convey some of that calcium to the lakes,” Yan says. “Half the lakes in Muskoka currently have calcium levels that are problematic for the life of the lakes.”

The calcium deficit has been more than a century in the making. The Canadian Shield’s thin, acidic soils never had much calcium to begin with, but stores have been further depleted by acid rain. Logging, too, removes calcium when wood is carted off for lumber, and new trees suck up the soil’s remaining calcium.

As the recycling system grows during the next few years, Yan hopes to spread the ash from up to 1,000 homes in 10-15 hectares of forest. Researchers will track nutrient levels in the ash and soil and determine application rates that will build calcium without adding too many toxic heavy metals. Eventually, Yan hopes to expand the program to Parry Sound and Haliburton.

Cottagers can contribute by lightly sprinkling their own ash around maples or other hardwoods in forested areas away from the water. When you’re cutting a tree or splitting firewood, “if it’s possible to leave the bark in the watershed, that’s good for the watershed,” Yan says. Bark is about three per cent calcium.

For cottagers willing to haul ash to save local lakes, Yan says the Friends of the Muskoka Watershed are in talks with the District of Muskoka to have ash accepted at some waste transfer stations. Another option is“ to gather ash from participating wood burners in local “ash drives.” For information, contact the Friends’ Environmental Project Lead, Shakira Azan at: shakira@fotmw.org.

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