Every day I cross the Dumbarton Bridge from my home in Fremont to MSI in Redwood City, and almost always I’m greeted by the strong odor of the mudflats along the eastern shore of the Bay. It’s a pretty gross smell, and so strong that even with the windows up the car starts to smell like rotten eggs. But it doesn’t bother me too much, because I know the stench is evidence of essential organisms hard at work.
Marshes and mudflats are super-productive biomes, filled with plants and animals both aquatic and terrestrial. Eventually, all those living things must die. This is when the decomposers come in to play.
Decomposition doesn’t “just happen.” Take your Halloween decorations, for instance: in order to get disgusting and rotten, your jack-o-lantern needs a lot of help. You can try this at home if you want to! Leave your jack-o-lantern outside after Halloween for at least a week, and see what happens. As you watch it change, you’re actually seeing a whole community of microorganisms work together to dismantle that pumpkin at a molecular level. Fruit flies, mold and bacteria all want a piece of that sweet, rotting pie.
Essentially, the same thing is happening in a mudflat, but with some important differences. Tons of organic matter ends up buried in the mud, and the microorganisms go to town on it. But unlike your front porch, mud is a low-oxygen, or hypoxic, environment. The mold and bugs that take over your pumpkin can’t live in this habitat. But certain bacteria can!
These bacteria are called sulfate-reducing bacteria. Unlike most living things, they don’t use airborne oxygen (O2) for respiration. Instead, they use sulfate (SO4), which is a molecule made of sulfur bonded with oxygen. This makes them able to live where most bacteria can’t – in super low-oxygen environments like a mudflat – and break down matter in the absence of oxygen. Just like other organisms, these bacteria produce a waste product when they “breathe,” but it’s not carbon dioxide (CO2) – it’s hydrogen sulfide (H2S). This produces that funky rotten egg smell.
So the next time you find yourself wrinkling your nose in disgust at the smell of a mudflat, remember that you’re smelling the evidence of decomposers hard at work! Thanks, decomposers!