Nitrogen Cycle (II)

Nitrogen is used by living organisms to produce a number of complex organic molecules. (as mentioned by Cho Ling above) Major stores of nitrogen include the atmosphere, living organisms, and organic matter in soil and the oceans.

Figure 1: Yellow arrows indicate human sources of nitrogen. Red arrows indicate microbial conversions of nitrogen. Blue arrows indicate physical forces acting on nitrogen. While green arrows indicate natural processes affecting the form of nitrogen.

The five main processes of the Nitrogen Cycle (taught in class)

1. Nitrogen fixation

2. Nitrogen Uptake

3. Nitrogen mineralisation (decay)

4. Nitification

5. Denitrification

Interesting Facts about the Nitrogen Cycle (:

• Scientists estimate that biological fixation globally adds ~140 million metric tons of nitrogen to ecosystems yearly.
• Denitrification is the only process that removes nitrogen from ecosystems, and it somewhat balances the amount of nitrogen fixed.
• The five processes in the nitrogen cycle-- are all driven by microorganisms.
• Human activities increase nitrate levels in drinking water by at least 10 times. From 1mg/L to 10mg/L.

 

WHAT GOES AROUND COMES AROUND

Like the Nitrogen Cycle, man and the atmosphere are both part of a system. Should one aspect of the system be affected (Eg. Nitrogen Cycle), later stages of the cycle would be affected too. (Eg. Man)

• Excess/unabsorbed fertilizer is washed off by irrigation/rain into groundwater or water bodies. Unfortunately, groundwater is often used as a direct drinking source.
  Excess nitrogen can lead to cancer in humans and respiratory problems in infants.
• On surface waters, excessive nitrogen can lead to eutrophication, the over-nourishment of phytoplankton. Eutrophication causes increased frequencies of coastal fish-kill events, harmful algal blooms, and even causes species shifts.
  (Hence, reduces the supply of fish and other seafood.)
• Atmospheric nitrogen (like NO₃^- and NH₄⁺) can also change the acidity of acid rain causing many long-term changes.For example forests' death and decline.
  (Hence, reducing the amount of carbon dioxide absorbed.)

Reflections and Key Learning Points

After last week's lesson and today's blog post, I have come to greater understanding about the word "systems", having applied it in today's blog post. I have come to understand that the man and the atmosphere are both part of a larger system, where if one aspect is missing/changes, it will ultimately affect the entire system. (Eg, the addition of man-made fertilizers) Ultimately, it will affect the entire Nitrogen Cycle and come back to affect Man.

"What goes around, comes around."

Personally, like the Carbon Cycle, i feel that each stage is as important as the next. There is a kind of interdepence within the cycle, without one the other cannot take place.  Another thing that I learnt while posting this blog entry was that microorganisms. Just when we thought they weren't so important, they're actually the driving force behind the whole cycle. I also marvel the work of Nature, how the whole large system can be at equilibrium so that there's just enough of everything to balance the entire Nitrogen Cycle :)

*Click the cycle for a bigger picture*