Too Much of a Good Thing: Increasing Nitrogen Deposition in Lakes
Increasing nitrogen emissions from motor vehicles, energy production, and agriculture are being deposited in lakes throughout the world, directly affecting lake biology and associated food webs. Alpine lake ecosystems are especially vulnerable to this deposition. USGS scientist Jill Baron, co-author of two new studies on how increased nitrogen pollution can affect lake ecosystems and water quality, discusses the issue.
Marisa Lubeck: Increasing nitrogen emissions from motor vehicles, energy production, and agriculture are being deposited in lakes throughout the world, directly affecting lake biology and associated food webs. I’m here today with USGS scientist Jill Baron, co-author of two new studies on how increased nitrogen pollution can affect lake ecosystems and water quality. Welcome Jill.
Jill Baron: Thank you. I’m glad to be here.
Marisa Lubeck: Your research suggests that nitrogen concentrations in lakes impact the animals and plants within this lake communities or ecosystems potentially moving their way to food chain.
Jill Baron: Yes. Although, we haven’t actually finished the research that says that we’re moving these effects of the food chain. We’ve done many years of research looking at how lake plants had been affected, plants being algae. What we have found is that in many alpine lakes, and actually in our new research in many lakes that are essentially pristine, they are deficient in nitrogen.
So you have a certain algae community, plant community that can live with very low nitrogen in their waters that they can take advantage of. When you start adding nitrogen to it, which is what happened to the atmosphere nitrogen deposition, you quickly allow them to pick up nitrogen almost a luxury and they take up so much nitrogen that they then become deficient in another important nutrient, which is phosphorus.
And that’s what could affect zooplankton, small swimming animals that eat algae. The analogy has been made by my colleague Jim Elzer who’s in Arizona State. He said having algae like that that can be eaten by zooplankton is a lot like feeding marshmallows to a teenager.
You can get a lot of free out of it, you can still use self up but you certainly don’t get the nutritional value that you get with more balanced diet. But what we seen so far with the added nitrogen is that a little bit of nitrogen allows some things to get a competitive advantage over others and that allows them to become more dominant and totally shift the assemblages of algae that live in these lakes.
Marisa Lubeck: What is your research on alpine lakes in places such as Colorado and Norway and Sweden suggest about the overall global nitrogen issue?
Jill Baron: Well, this is very interesting because for years people who study water quality have said the major pollutant that increases productivity in waters around the world is phosphorous. And it’s true that phosphorous is often nutrient limiting and to limiting nutrients for further algal growth, and when you add it in you get huge algal blooms in nitrification. But what we found in these lakes that had never been exposed to much human influence at all is that they started out nitrogen monitored not phosphorous limited.
So you add a little bit of nitrogen or a lot of nitrogen and you get the same kind of response you got in other more fertile lakes with additional phosphorous. And what the implication is that many lakes around the world before say the industrial revolution will probably nutrient deficient specifically for nitrogen.
And that has been masked in many other water bodies where we’ve had a long history of adding nutrients to them. So nitrogen with sort of forgotten as a limiting nutrient. So we see this in Colorado in our alpine lakes and our colleagues in Sweden and Norway also found it in very low nitrogen available lakes in nutrient four parts of those countries as well. In other words, it’s just to assess this is a global phenomenon and that some time in it is the past maybe many, many more waters were nitrogen deficient and now they’re not.
Marisa Lubeck: Are alpine lakes specifically more vulnerable to nitrogen pollution than others and which regions of the world should be most concerned about this?
Jill Baron: I think alpine lakes might be more vulnerable because they have up above and very little soil or terrestrial vegetation to take up the nitrogen that comes in from atmosphere deposition. Prehistorically, there was a very limited amount of nitrogen on earth and anytime we added nitrogen to plants’ natural vegetation grew better, it grew faster.
Alpine lakes historically would not have gotten much nitrogen at all out of the atmosphere or from nitrogen bearing organisms because it’s energetically expensive for them to fix nitrogen and then make it available for other plants. So they would have been historically deficient and when you then add a little bit from atmosphere deposition, there go in, “Woohoo! This is a good stuff for getting more food and then making grow better.”
But because there are harsh environments, low vegetation, thin soils, steep bedrock, probably snow dominated in many places so that a large part of the annual water runs out all at once. Because they are living in that kind of environment, it probably makes them much more responsive to small changes from outside. Then other more heavily vegetated water sheds where lot of things could dampen in coming nitrogen.
Marisa Lubeck: So you’re talking about incoming nitrogen from urban and agricultural areas. How does this pollution end up in what is often considered pristine lakes or ecosystems?
Jill Baron: Since the industrial revolution and especially since the 1960s, humanity has now added 100% additional reactive nitrogen to the globe through a combination of activities like you said one is agriculture. That is probably our largest source where we now fix nitrogen out of the atmosphere using fossil fuels to create synthetic nitrogen fertilizer ammonia, which then gets applied to agricultural crops.
We also have increased the numbers of livestock particularly here in Colorado that lives in confined animals feeding operations before they go to slaughter. And all of these agricultural sources give us nitrogen that either leaks up the bottom in terms of ground water or surface water and it affects water quality all the way down water sheds into the earth’s sanctuaries or is all volatilizes up into the atmosphere as ammonia or as nitrogen oxide.
And that travels long distances sometimes, and comes down in precipitation as nitrogen oxide or ammonium, which adds nitrogen to ecosystem. Now, I’ve only spoken about agriculture but in other large source of combustion that produces nitrogen oxide is internal combustion engine where every day may be so coal fire power plants any kind of energy production or industrial production and automobiles, any kind of motor vehicle or transport vehicle like trains where you have a large amount of energy at once coming together in one place.
You can take again atmospheric nitrogen and turn it from its inert nitrogen gas into reactive nitrogen oxide. And again those can get up into the atmosphere, travel distances, and come down as either rain or snow in places where it has not been at.
Marisa Lubeck: Is this nitrogen deposition entirely a negative force or are there any positive effects?
Jill Baron: Oh, sure there are positive effects where nitrogen is welcome as a fertilizer because that’s what it is. You add nitrogen to your plants when you want them to be greener because nitrogen is the stuff of DNA. It’s the stuff of protein and amino acid. So where nitrogen is needed, especially in agriculture it’s been a very positive thing.
The whole green revolution is as much a story about the application of nitrogen fertilizers as it is about irrigation and genetics and better craft. We in fact are approximately three billion people on earth today with synthetic nitrogen fertilizers. But there are places where nitrogen is not welcome. And those are natural ecosystems are protected in order to give us examples of an impacted natural environment.
So national parks or wilderness areas or clean air class I areas or areas that are supposed to be protected from air pollutants and not allow changes from human activities to occur. We have too much of a good thing and it changes ecosystems in ways that are not intended.
Marisa Lubeck: Is nitrogen pollution continues at the present rate or increases even more through out the years? What is your outlook on the status of lake communities through out the world?
Jill Baron: Nitrogen is a fertilizer and our work in alpine lakes and in many other lakes all over the world shows that when you add it, you increase productivity. You help to enhance nitrification. So, some of the really negative effects that come from nitrification can be production of toxic algal blooms. These are organisms that give out chemical toxins. They are harmful to other types of life including humans. When you add too much nitrogen such as the green of Gulf of Mexico right now, you enhance productivity of algae.
But as they die, they fall to the bottom and decompose. And that consumes oxygen nutrient the world of dead zones. So those are the kinds of changes that we can expect worldwide if nitrogen emissions continue to increase. Certainly alpine lakes are not immune from that so as zooplankton. We are trying to finish up that work right now. The zooplankton suffer because they’re getting nitrogen rich phosphorous for food.
That’s the hypothesis and it’s so do you create zooplankton that are then unbalanced. And that creates a problem perhaps even further up the food chain for fish that eats zooplankton.
Marisa Lubeck: Where can concerned citizens turn for more information?
Jill Baron: There is a wonderful website run by the United Nations International Nitrogen Initiative, INI in order to increase the awareness of the global scope of changing the nitrogen cycle on earth. There is also a website in the US Geological Survey run out of the Fort Collin’s Science Center that describes some of the work we’ve done on alpine lakes. And you can also look on the National Park Service Air Resources Division website where they have done a really nice job of summarizing the kinds of problems those nitrogen posses the national park.
Marisa Lubeck: All right. Thank you for speaking to me today.
Jill Baron: Thank you very much.
Marisa Lubeck: Jill’s research has featured in the November 2009 issues of the Journal Science and Ecology. This CoreCast is a product of the US Geological Survey Department of the Interior.
I’m Marisa Lubeck. Thanks for tuning in.