I’m sure you remember the exciting news that came a few years ago about beaver ponds removing nitrogen from soil, right? Well I’m not sure how I feel after comparing this recent article comparing it to Arthur Gold’s great study in 2017. I guess farmers will be more happy to make their own wetlands if they’re almost as effective as beaver ponds at removing nitrogen?
Small wetlands can have big impacts
In a new study, researchers have shown that wetlands built next to farmlands can dramatically reduce the amount of excess nutrients reaching aquatic environments.
“Even very small wetlands can be effective,” says Maria Lemke, lead researcher of the study at The Nature Conservancy.
The study was conducted over 12 years on a 272-acre farm in McLean County in central Illinois. Many farms in this part of the United States use tile drainage systems—a network of interconnected underground pipes that drain water from the farms.
“Our findings show that constructed wetlands can be very effective at reducing excess nitrogen losses from agricultural tile systems,” says Lemke. “We also show that these wetlands can capture dissolved phosphorus efficiently.”
Lemke and colleagues showed that wetlands as small as 3% of the tiled area draining into them can be effective. These wetlands catch excess nutrients draining from surrounding farmlands. This means less nutrients end up in streams and rivers, and ultimately, the ocean.
Really small. Say like “pond sized”. Like ohh say something a beaver might make. Though not an ACTUAL beaver because they’re icky.
Constructed wetlands can be a useful conservation practice that mitigates nutrient export from farms to aquatic ecosystems. Nitrogen runoff that enters wetlands comes in the form of dissolved compounds called nitrates. Microbes in wetlands can use these dissolved nitrates as energy sources.
These microbes convert the nitrates into harmless nitrogen gas, which is released into the atmosphere. Conversion from dissolved nitrate to nitrogen gas results in less nitrogen exiting the wetlands into aquatic ecosystems. “Wetlands provide the perfect habitats for microbes to perform this process,” says Lemke.
Phosphorus removal from farm drainage is a more complex process. Soil chemistry and clay content play important roles in removing dissolved phosphorus. “It’s important to analyze soils at potential wetland sites to characterize their long-term retention capacity for phosphorus,” says Lemke.
Even the smallest wetlands reduced nitrogen loss from farm tiles by 15 to 38%. As drainage water moved through a series of connected wetlands, nitrogen loss was increased up to 57%.
Sure beaver ponds do it BETTER and when the pond is damaged the beavers fix it for free but they’re so icky and unpredictable. No one wants them around. People just want beaver benefits without beavers. That’s possible right?
Beaver Ponds: Resurgent Nitrogen Sinks for Rural Watersheds in the Northeastern United States
Using the annual range of denitrification observed in our three ponds, we estimate that denitrification in beaver ponds that average 0.26 ha can annually remove 49 to 118 kg nitrate N km−2 of catchment area. In beaver ponds that average 1 ha, denitrification can account for 187 to 454 kg nitrate N km−2 of catchment area. Moore et al. (2004), using the SPARROW model, predicted total N catchment yields between 200 and 1000 kg km−2 for undeveloped land uses (i.e., rural) in southern New England. Based on the beaver pond/watershed area ratios (0.18–0.7%), and interpond variability in denitrification, we estimate that beaver ponds in southern New England can remove 5 to 45% of watershed nitrate loading from rural watersheds with high N loading (i.e., 1000 kg km−2). Thus, beaver ponds represent an important sink for watershed nitrate if current beaver populations persist.
Well, okay, beavers are better, but to refer to my previous point. they’re icky. And so unpredictable.It’s much easier to do it without them.
“The idea is that if we combine in-field practices with edge-of-field wetlands, we may be able to decrease further the wetland sizes needed for desired nutrient reductions,” says Lemke.
