Low water, high stakes

How wetlands help mitigate water stress during droughts

Drought and heat stress, Badiou explains, go hand in hand and both are tough on fish.

Thanks to their aquatic vegetation (which provides shade and relief for fish in hot weather), the underlying waters of wetlands “can be up to 10 degrees cooler,” Badiou says. Cooler water, he adds, also retains more oxygen than warm surface waters—and that difference matters. Low dissolved oxygen is one of the most common causes of , where large numbers of fish die because there isn’t enough oxygen in the water. Add in oxygen produced by the aquatic vegetation itself and wetlands become a genuine summer refuge.

But perhaps the most significant component, Badiou says, is that wetlands help keep water flowing in small streams, rivers and creeks during droughts.

“In times of drought, if you have a watershed where your wetlands have been depleted, it is more likely that those creeks, streams and rivers are going to go dry and not be able to support fish,” he says.

However, where healthy wetlands remain intact, “you will still have lower water levels, but you will likely still have enough water flowing to sustain at least some of the biological productivity for the various fish species that use those systems.”

Wetlands also support the broader landscape in dry years, Badiou adds, by helping recharge shallow groundwater—something that’s important for anyone in a rural area who’s ever experienced their well running low during an exceptionally dry summer.

Additionally, wetlands moderate the local climate. If you’ve ever stood beside a large lake on a hot summer’s day, you might’ve noticed it’s cooler and more humid. “Wetlands offer the same function,” Badiou says, by cooling and humidifying the local atmosphere—a benefit that anglers likely notice too.

Why some fish cope better than others

Nature is resilient, and that includes fish, with some species being able to survive less-than-ideal conditions better than others.

“In prairie wetlands, often the only fish species you’ll find there are brook stickleback and fathead minnows, and that’s because they’re well adapted to low oxygen environments,” Badiou says.

Carp, he adds, can also tolerate low oxygen conditions quite well, which spells trouble for other species that anglers are trying to reel in, like walleye, pike and perch.

“That’s why [carp] have been a nuisance in many freshwater coastal wetlands; they can get into a system like that and essentially make it unusable for other recreationally important fish species.” (Learn how invasive species, like carp and Phragmites, affect fish habitats.)

The wetland buffer effect: Why some lakes and rivers “hold on” better

Whether it’s water quality or stress from dry spells, having wetlands on the landscape is the best defence against the worst impacts.

“If you have a lake or a river system that has a healthy population of wetlands in its catchment, you’re going to buffer against water quality impacts and drought impacts better than in the absence of those systems,” Badiou says.

“Under a changing climate, where things are potentially going to get hotter and drier, wetlands can help offset some of those impacts.”

Hot weather and drought will keep testing Canada’s fisheries. Healthy, intact wetlands are one of the best tools we have to keep water on the landscape longer, keep it cooler and keep fish populations resilient through the driest summers.