Lecture 21 + 22 Flashcards
Which of the following is the biggest pool of nitrogen on earth?
Nitrogen in the atmosphere
Nitrogen fixation involves
A process where N2 is converted to a form usable by plants
In the amphibian disease example in your book… Amphibian disease may be related to fertilizer production because?
Fertilizer enhances an intermediate host of a frog parasite
Biodiversity and nitrogen cycle are
way past the tipping point
Less nitrous oxide (N2O) than CO2 or methane in atmosphere
- rate of increase is less
- but, nitrous oxide is even more potent as a ghg per mass (200-fold greater than CO2; 2-fold greater than methane)
- is the 3rd most important gas behind current greenhouse warming
- AND, holes in the ozone layer!
Remember: 99.9% or more of nitrogen on Earth is N2.
Prior to human intervention, only bacterial N fixation could make this nitrogen biologically available
Fritz Haber discovered a way to make synthetic nitrogen fertilizer from atmospheric N2 gas in 1909
Today, this literally feeds the world!
80% of the nitrogen that supports food production comes from this industrial process (and 80% of the nitrogen in your proteins, if you eat like an average person)
Fritz Haber –lessons to consider
- brilliant scientist
- changed world agriculture forever, hugely increasing productivity
- starvation and malnutrition decreased
- global population boom in response
- won Nobel Prize for his nitrogen work
- also a MAJOR player in developing and applying chemical gas weapons in WWI
- today, widely considered a war criminal (although never tried or convicted)
Greenhouse gas warming is not the major problem with human alteration of the nitrogen cycle
Rather, creation of reactive, biologically available forms of nitrogen that cause acidification and fertilization, with multiple ecological (and human health) ramifications
CO2 and methane are almost uniformly distributed on Earth, so alteration of their cycles is truly global
For nitrogen, alteration of cycle is not of N2 (too ubiquitous!), but rather of reactive, biologically available forms of N
Huge regional and local variation, since reactive nitrogen (nitrate, ammonium) tends to cycle at scales of 10s of metres to hundreds of kilometres
Regions of greatest nitrogen were once limited mainly to Europe and North America. But as new economies develop and agricultural trends shift, patterns in the distribution of nitrogen are changing rapidly.
Recent growth rates in nitrogen are changing rapidly. Recent growth rates in nitrogen use are now much higher in Asia and in Latin America, whereas other regions – including much of Africa –suffer from fertilizer shortages
Southern Brazil
Rapid population growth and industrialization around Sao Paulo, poor civic sewage treatment and vibrant sugar cane production all contribute to this new South American nitrogen hotspot
East and South Asia
More vigorous application of fertilizer has produced stunning increases in maize and wheat production, but China now has the highest fertilizer inputs in the world
So while humans have doubled the rate of creation of reactive nitrogen across the terrestrial biosphere
the increase has been 20-fold in some regions with almost no change in others
Environmental consequences of accelerated N cycle
- coastal eutrophication and “dead zones”
- loss of biodiversity in forests, wetlands, grasslands, etc.
- acid rain: damage to waters and soils
- damage to growth of forests and agriculture, due to ozone pollution (reactive N in atmosphere + methane or other organic molecules = ozone)
- global warming and stratosphere ozone holes from N2O
Nitrogen is the biggest pollution problem in coastal marine ecosystems
Phosphorus is a bigger problem in freshwater lakes
Step 1 of process of eutrophication
Farmers apply fertilizer or manure to their crops
Step 2 of process of eutrophication
N enters small waterways via runoff or leaching
Step 3 of process of eutrophication
N from entire watersheds enters estuaries and oceans
Step 4 of process of eutrophication
Because N is limiting for most photosynthesizers in oceans, their populations grow
Step 5 of process of eutrophication
There are large phytoplankton (algal) blooms
Step 6 of process of eutrophication
Many phytoplankton die and sink out of the surface waters into deeper waters
Step 7 of process of eutrophication
Dead phytoplankton are consumed by decomposers
Step 8 of process of eutrophication
The amount of oxygen in the bottom water declines