Losing small wetlands linked to algal blooms in lakes, research says

The algal blooms ruining your weekend plans at the lake might be due to disappearing wetlands, according to new research from the University of Waterloo by Nandita Basu and her Ph.D. student Frederick Cheng.

Blue-green algae that live in water feed on nitrogen and phosphorus, found in farm runoff and water from waste treatment plants. When excessive amounts of nutrient-rich water desposit into the lake, blue-green algae grow to very high concentrations, resulting in "blooms."

On Friday, the Grand River Conservation Authority announced Conestogo Lake would be closed to swimming and fishing until futher notice. The reservoir tested positive for blue-green algae over the weekend. 

But according to research by Basu and Cheng, small wetlands can help prevent those blooms.

Small wetlands are disappearing in Ontario, often converted into farmland or housing, even though they are most effective at filtering water by area.

"When we compare small versus large, we always compare on an equal area-basis," Basu told CBC News, "So what I mean by that is that 10 one-hectare [wetlands] is better than one 10-hectare [wetland]."

Basu said they are more effective because there is less existing water in smaller wetlands and when farm runoff makes its way to the wetland, more water is able to make contact with the soil — where the nutrient filtration happens.

• Ottawa construction company fined $275K for dumping into wetland
• Don't drain the swamp: report says wetlands help avert flood damage

Wetlands in action

When nutrient-filled water headed for the lake hits a wetland, the water slows down and nutrients either get absorbed into the wetland soil or get converted into gas.

The water leaving the wetlands is much lighter in nutrient-content — meaning less nitrogen and phosphorus for algae to feed on in the lakes and reservoirs. Nutrients that are left behind feed the wetland plants.

"Wetlands are very rich in fauna, so there's a lot of plants in them that need those nutrients,"  she said.

Losing wetlands means there is no buffer zone for farm runoff or water from waste treatment plants that are packed with nutrients. Algal blooms are much more likely to happen, especially with heavy rainfall.

If a bloom is made of blue-green algae, it can contain toxins because when the algae die, they release a toxin called mycrocystin. The decomposition process of the algae also uses up a lot of oxygen in the water, leaving little for existing wildlife.

• Charlottetown Duck Day will highlight urban wetland habitat
• Conservation authority pulls out of maligned Navan wetland project

Humans in action

Basu said part of the problem is that conservation efforts tend to focus on larger wetlands.

"A lot of the wetland protection comes from the idea of protecting the habitat," said Basu, but  she says communities need to do a better job at conserving wetlands of all sizes. 

Some may be better for flood-prevention, others for waterfowl habitat and in this case for nutrient filtration.

"Wetland restoration should then try to preserve a range of sizes, and that's not currently done. Currently it's done more on an ad hoc basis," she said, " If you protect small, medium, large, then you protect the different functions of the landscape."