Stories tagged nitrogen cycle

Mar
21
2013

Gulf of Mexico Dead Zone: Nitrates washed off of cropland and delivered to the ocean by the Mississippi River feed big algae blooms, seen as red in this false-color satellite image.  Bacterial decomposition of the dying algae consumes all oxygen in the water, producing a large area uninhabitable by fish and other sea creatures.
Gulf of Mexico Dead Zone: Nitrates washed off of cropland and delivered to the ocean by the Mississippi River feed big algae blooms, seen as red in this false-color satellite image. Bacterial decomposition of the dying algae consumes all oxygen in the water, producing a large area uninhabitable by fish and other sea creatures.Courtesy NOAA
Nitrogen is an essential nutrient for plants. So how can nitrogen limit plant growth, given that nitrogen comprises 79 percent of the atmosphere? But atmospheric nitrogen is composed of molecules consisting of two atoms of nitrogen and this form of nitrogen cannot be used by plants.

Farmers have for centuries spread animal manure on fields or plowed under leguminous crops (such as alfalfa which has microbial communities living on its roots that fix nitrogen) to add useful, reactive forms of nitrogen to soils. German ingenuity in the early 20th century invented an industrial process that made it possible for the first time to manufacture plant-usable forms of nitrogen, which made possible the artificial fertilizing of crops.

Manmade production of ammonia and nitrate fertilizers has exploded in recent decades and now vastly exceeds the amount of atmospheric nitrogen converted into reactive nitrogen by microbial organisms around the world. At the same time, the burning of ever-increasing quantities of coal, oil and natural gas converts some atmospheric nitrogen into oxides of nitrogen (NOx). NOx emissions can both increase crop growth and diminish it because NOx gases help catalyze the formation of ground-level ozone and this gas is toxic to plant life.

The huge increases of human-produced forms of nitrogen that are applied to croplands and that are released into the atmosphere and eventually settle out have many unintended consequences. In particular, excess nitrogen washes off of agricultural and urban landscapes and is accelerating the destructive growth of algae in lakes, rivers and coastal estuaries around the world.

The connections between manmade carbon dioxide emissions and climate change are quite worrying and receive much scientific and media attention. Nitrogen pollution receives much less notice but is a dramatic example of how human activities now dominate many of the chemical, physical and biological processes that make this plant so amenable to human life.

Oct
15
2010

Water issues are complex and interrelated, so it can be difficult to solve them. But because water is essential to our way of life, we gotta get to work!

Here's an example of how convoluted things can get:

A study at the University of California in Irvine found that freshwater runoff (from precipitation and ice sheet melting) into the oceans has increased significantly--18% more water flowed into the oceans in 2006 compared to 1994. The main problem with this is that the freshwater then becomes saltwater, and we have to wait for it to evaporate and rain onto the ground for it to become drinkable/cookable/agriculturable again. But with global warming, precipitation patterns have changed so that the areas that need water aren't getting as much as they used to.

Speaking of global warming, CO2 in the atmosphere does more than heat things up--it dissolves into the ocean, which makes the water more acidic. This change in pH, though subtle, could become sufficient to kill delicate creatures such as krill in the Southern Ocean within 100 years. Considering that many of the fish we like to eat dine on krill, this could pose a big problem in the future.

But it gets more complicated. The runoff from agricultural fields contains nitogren-based fertilizers, and rivers release tons of it into the ocean each year. The nitrogen fuels an overgrowth of algae, which die when the nitrogen is gone and fall to the seafloor. There, they are consumed by bacteria that thrive and gobble up all the oxygen, creating a "dead zone" where plants and animals cannot live. While human activities add double the natural amount of nitrogen into soils, about 60% of that fertilizer is never used by the plant and ends up in the ocean. Some of it also ends up in the atmosphere, where it becomes N2O--a more powerful greenhouse gas than CO2. This adds to global warming, bringing us back to increased freshwater runoff.

In short, more water is running into the ocean and that water is full of ick that kills stuff and makes more water run into the ocean. Ick.

Oct
13
2010

Happy as a whale in: ... in whatever.
Happy as a whale in: ... in whatever.Courtesy Ineuw
We love whale poop around here. Love it love it love it. Can’t get enough. It’s fortunate for us that whales poop so much—if you were to get the planet’s daily supply of whale poop in one place, and if you were also in that place, you would suffocate. It’d be awful.

The reason we love whale poop so much is because of its role in what Elton John and I like to call “the circle of life.”

We’ve already discussed how sperm whales have a net negative contribution to atmospheric CO2, because of all the iron in their poop. (The iron rich waste feeds tiny sea creatures, which, in turn, suck up CO2.)

It turns out that whales and their poop are also vital for the nitrogen cycle. Nitrogen is a vital nutrient for ocean life. While some parts of the ocean have too much nitrogen—extra nitrogen from fertilizers washes out through rivers, causing algae to grow out of control and create a dead zone—other areas contain a very small amount nitrogen, and local ecosystem productivity is limited by nitrogen availability.

So what brings more nitrogen to these nitrogen-poor areas? Microorganisms and fish bring it from other parts of the ocean, and release it by dying or going to the bathroom. But, also… whales bring it. Whales bring it by the crapload.

Whales, it turns out, probably play a very heavy role in the nitrogen cycle. And because the nitrogen feeds tiny ocean creatures, and those tiny ocean creatures feed larger ocean creatures, and on and on until we get to fish, more whales (and whale poop) means more fish. And we (humans) love fish.

Commercial whaling over the last several hundred years reduced global whale population to a small fraction of what it once was, but even at their current numbers whales contribute significantly to nitrogen levels in some areas. More whales, the authors of a recent whale poop study say, could help offset the damage humans have done to the oceans and ocean fisheries, while relaxing restrictions on whaling could have much further reaching ramifications than we might expect.

See? Whale poop is the best! (Whales too, I guess.)

We've talked about "planetary boundaries" on Science Buzz before—natural thresholds past which life gets tricky. There's a new study out on one of those boundary areas: the nitrogen cycle.

The article behind the link talks about why nitrogen is important, how it's dangerous, and what we can do to let natural self-correcting systems kick in for the nitrogen cycle.

Jul
22
2008

Eutrophication: Agricultural run-off rich in fertilizers stimulates rampant growth of algae.
Eutrophication: Agricultural run-off rich in fertilizers stimulates rampant growth of algae.Courtesy NASA

Human populations effect lakes

Human sewage and fertilizer runoff effects the health of lakes. It often causes huge algal blooms, kills fish, and creates other problems.

Long term study of "cultural eutrophication" released

For 37 years researchers have examined the best ways to control this "cultural eutrophication" process of lakes by varying the levels of phosphorous and nitrogen added to the lake.

After completing one of the longest running experiments ever done on a lake, researchers from the University of Alberta, University of Minnesota and the Freshwater Institute, contend that nitrogen control, in which the European Union and many other jurisdictions around the world are investing millions of dollars, is not effective and in fact, may actually increase the problem of cultural eutrophication.

Time to rethink current practices for healthy lakes

"David Schindler, professor of ecology at the University of Alberta, and one of the leading water researchers in the world, wants to change current practice in controlling nitrogen runoff by stating that

"Controlling nitrogen does not correct the polluted lakes, and in fact, may actually aggravate the problem and make it worse."

This study done by the University of Alberta, University of Minnesota and the Freshwater Institute appears in the journal, Proceedings of the National Academy of Sciences.

Source: PhysOrg.com

Feb
24
2008

Grand Challenges for Engineering in the 21st Century

Want to know what to do with your life. A diverse committee of experts from around the world, at the request of the U.S. National Science Foundation, identified 14 challenges that, if met, would improve how we live.

Here is their list in no particular order. You can learn more about each challenge by clicking on it.

You can vote for which is most important

The committee decided not to rank the challenges. NAE is offering the public an opportunity to vote on which one they think is most important and to provide comments at the Engineering Challenges website