With every gas-powered car and every traditional wastewater treatment plant, a little nitrogen pollution gets released into the atmosphere. But that doesn’t mean it stays there.
Nitrogen pollution in the atmosphere affects how forests grow. Photo: stpaulgirl (flickr)
“We were curious as to where all this nitrogen was going,” said Alan Talhelm, a researcher at the University of Idaho.
And scientists say the nitrogen that settles from the atmosphere into the soil is changing the ecosystems of sugar maple forests.
“The extra nitrogen we’ve been adding has slowed the decay of sugar maple leaf litter, and that’s caused the forest floor to build up and get thicker,” said Donald Zak, a professor at the University of Michigan.
A thicker forest floor can be a good and bad thing. It can store more carbon from the atmosphere, but can also lead to runoff, biodiversity loss and fewer tree seedlings.
Zak is working with other scientists from Michigan Technological University and the University of Idaho on a century-long study to see how increased nitrogen in soil will affect sugar maple forests. They add extra nitrogen to forests throughout Michigan to see how they will react to the pollution levels expected in 2100.
They found that sugar maple seedlings have a hard time stretching through the bulkier forest floor to reach soil and sunlight.
“In the experimental plots that receive extra nitrogen, there are fewer sugar maples regenerating,” Zak said.
But while young sugar maples fight to take root, older trees grow taller. Nitrogen is usually the first nutrient used up by plants in sugar maple forests, so when there’s more available, the trees grow faster.
That creates a carbon sink. When those trees grow taller and the leaf litter decays slowly, more carbon is stored in the forest and not in the atmosphere, a good thing for slowing global climate change.
And taller, faster growing trees could be good for the forest products industry, Talhelm said.
But despite the carbon storage benefit, which may be temporary if tree seedlings have trouble taking root, extra nitrogen raises other environmental concerns, like decreased biodiversity and runoff into lakes and streams.
“There are plants that are specialized to live in low-nitrogen environments, so when you have a lot of extra nitrogen floating around they can be out-competed,” Talhelm said.
When those low-nitrogen plants lose out, that leads to decreased biodiversity, or variation of life, in the forest.
And when plants don’t use up nitrogen in the soil, it eventually will find its way to surface water, said Dan Button, physical scientist at the U.S. Geological Survey Science Center in Ohio.
When nitrogen runoff mixes with phosphorus runoff, it can lead to algae growth that can create toxic algae blooms, Talhelm said.
Button said when all that algae dies off and decays, oxygen is removed from the water. The oxygen-deficient environment stresses aquatic life and can even lead to fish kills.
“It depends on concentrations,” Button said. “If you have higher concentrations of nitrogen in surface water and all other conditions are right, like temperature and light, you’re going to get algal growth.”
Most aquatic ecosystems are Phosphorus limited, not Nitrogen limited. P is the key nutrient pollutant for surface waters.
Surprised there was no discussion of the impacts of CAFOs on the nitrogen cycle, particularly the addition of toxic nitrates to groundwater. All in all a bad article….not up to the usual quality of the GL Echo.
This is the biggest crock of bull I’ve ever read on this site. Start with a pair of unproven hypotheses, then work them 2 different ways and come up with conclusions that could mean different things. Therefore, the researchers get to keep their jobs because, obviously, more studies are needed. Throw in a few worms here, some suppressed wildfires there and it’s a true calamity. Nitrogen is 78% of the atmosphere. We are just going to have to accept living with it in its various forms.
Don’t forget the impact of green rain on wildfires. Sadly we’ll have to live with wild fires, as long as we refuse to acknowledge that not only carbon dioxide and temperature stimulates plant growth, but more important the increase of reactive nitrogen in the atmosphere. Although the atmosphere consists out of 80% nitrogen gas, this form of nitrogen is not available, due to the strong bond between the two atoms. Other forms, like nitrogen oxides and ammonia, many caused by human activities, are ‘reactive’ and can be used as fertilizer for plant growth, which will not happen when still part of the air. However, this will change when it rains and this reactive nitrogen is dissolved in the water and this “green’ rain will fertilize the plant growth where it comes down.
So during wet weather conditions you will get excessive growth, while during dry weather this growth (grasses and brush) will become kindle wood for the hard to control wild and range fires. Now often so hot that also large trees will catch fires and root systems are destroyed that keep the soil together. When it rains again this will cause soil erosion and in some locations, mud slides. These large nitrogen molecules in the air also cause global warming, but since that does not exist, neither does ‘green’ rain.
The impact of the consumption of leaf litter by invasive earthworms is interesting. Most people think the worms are good for the environment. Few realize that they are an invasive species.
Echo reported on that issue here: http://greatlakesecho.org/2011/09/26/the-underground-master-of-invasive-species-%E2%80%93-earthworms/
In regard to leaf litter, isn’t consumption of leaf litter by nonnative earthworms a greater threat than minimally decreased decomposition due to increased nitrogen? The only thing that seems clear is that there are no clear answers about various cause/effect relationships. But…that’s the nature of science. Our understanding of this blue marble is always evolving.