New research out of the University of Waterloo illuminates the importance of small, stand-alone wetlands.
These are wetlands that are geographically isolated, meaning that they may sometimes be connected to a downstream waterbody, and oftentimes are not.
“The main point that we were trying to make is that a lot of times when you have these smaller upland wetlands that are not near a coastal area, we don’t always think that they are connected to downstream waters, and we sometimes think that they are not really that important, because they are a small puddle of water someplace and maybe they don’t even have water all throughout the year, they have water part of the year,” said Nandita Basu, a tier-one Canada Research Chair in Global Water Sustainability and Ecohydrology and a professor of water sustainability and ecohydrology at the University of Waterloo.
“I’m not saying that they’re never connected, I’m saying their connections are less apparent than the more riverine wetlands or coastal wetlands. And because their connections are less apparent, a lot of times when you’re trying to pave over land, they don’t have as much protection.”
Basu and her team found these isolated wetlands actually outperform connected wetlands when it comes to filtering and cleaning pollutants.
When nutrients like nitrogen and phosphorus make their way through the watershed to wetlands, one of the main ways they clean these pollutants is through micro-bacteria that live in them. The micro-bacteria can break nitrogen down quickly, but need the time to be in contact with the nutrient, says Frederick Cheng, a postdoctoral researcher now at Colorado State University who worked with Basu on the research.
He said whereas more connected wetlands tend to flush nutrient-laden water to continue to move it through the watershed, these less connected wetlands hold the water and give the bacteria time to digest it.
“In isolated wetlands, most of the water leaves through evaporation, so the water leaves and the nitrogen stays in the wetland, so that increases the time that the microbes can then transform the nitrogen,” he said.
Cheng notes the process is actually pretty fast. “It’s just a matter of letting the nitrogen come into contact with the micro-bacteria which tend to live in the soil portion of the wetlands, so it can happen in a matter of hours or days. As long as there’s that contact.”
They studied 30 years of satellite imagery measuring water levels in 3,700 wetlands across the United States, and compared this with pre-established measurements of how much pollution wetlands at these water levels can filter to establish a model comparing connected and isolated wetlands.
Basu said that when a small wetland is connected continuously to a downstream water body, it removes about 40 per cent of the nitrogen that comes in. But when the same wetland is disconnected, it removes about 84 per cent.
The wetlands in question don’t need to be large. In fact, many of the wetlands studied for this research were less than 0.5 hectares, and some smaller than 0.1.
Excess nutrients like nitrogen and phosphorous cause algal blooms in the Great Lakes by providing more food for algae. These blooms can be potentially toxic and cause the closure of beaches. In 2014, the water supply for Toledo, Ohio on the coast of Lake Erie was shut off due to toxic algal bloom.
Recently, protection for wetlands in Ontario has been reduced, which Basu sees as disconnected from the research showing their importance.
“I’ve been thinking about it quite a lot. And this is true in southern Ontario, where we’ve already lost over 70 per cent of our wetlands and now we are at risk of losing more. And we argue that we need to do this because we need to build more houses. But the challenge of that is, if you add more people to our landscape, you create more pollution. And so you will need these wetlands even more. We will be taking them away at a time when we need them even more. And that’s the dissonance that is really striking.”
