Expert: Dana Krempels, Ph.D. - 5/18/2010

Question
Hi, I've been studying mangroves and must complete some questions about them. I am, however, very stuck on one question, and that is why mangrove mud has such an unpleasant smell.

I hope you can help,
thank you.

Answer
Dear Zoe,

Mud in many ecosystems where there's a lot of rotting organic matter are pretty much devoid of oxygen, and that means that the bacteria living in them and decomposing the organic matter are usually anaerobes.  Some species of anaerobic bacteria use sulfates (instead of oxygen) to help them break down organic matter, and the waste product of this process is hydrogen sulfide (H2S) instead of H2O (water), as it would be in aerobic bacteria.  

Hydrogen sulfide has a nasty "rotten egg" smell, and there's lots of that compound in mangrove mud.  You can read more about sulfate-reducing bacteria here:

http://en.wikipedia.org/wiki/Sulfate-reducing_bacteria

Hope that helps.  Good luck on your project!

Dana