Brain Food: Pollution In The Pines At The Grand Canyon

Dec 8, 2016

Auto exhaust at the Grand Canyon may be ruining more than just the view; it might be harming native plants, in particular. The National Park Service wants to know just how harmful excess nitrogen is to the ecosystem, so they offered a grant to soil ecologist Nancy Johnson at Northern Arizona University. Her study involved taking samples of soil, air and pinyon pine needles at the heavily trafficked South Rim. 

Long lines of cars are a regular site at the South Rim entrance of Grand Canyon National Park
Credit National Park Service

"The thing is," Johnson says, "nitrogen is an essential nutrient, so plants can't grow without nitrogen. It should be a good thing, right? Well, it turns out in native plants that have evolved to live in very nutrient poor environments that it can be detrimental to the native vegetation, and it enhances some non-native vegetation oftentimes."

Johnson's study revealed vehicle exhaust close to the main road was more than 50% higher than just 100 feet away. That could mean native plants will become stunted over time, while some non-native, nitrogen-loving plants thrive. Johnson says that dynamic could change the entire ecosystem. 

"So, there's a concern with the change in natural communities that occurs because of nitrogen deposition. And, if it gets high enough, it can work like an acid rain and actually have some of the same detrimental impacts as acid rain." Johnson adds, "Just at low levels, it can have these subtle effects on the composition of biotic communities; not just plants, but also microorganisms in the soil."

The NAU study will provide baseline data for park managers to assess traffic flow, and possibly reduction at the Canyon.