"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.