Salt marshes are marshy because the soil is composed of deep mud and peat. Peat is made of decomposing plant matter that is often several feet thick.  The salt marsh life cycle may have been undisturbed for hundreds of years.

   
The soil of a salt marsh

Peat is waterlogged, root-filled, and very spongy. Because salt marshes are frequently submerged by the tides and contain a lot of decomposing plant material, oxygen levels in the peat can be extremely low. The growth of bacteria under condidions of low oxygen produce the wonderful aroma that is associated with marshes and mud flats.

                                          
Microorganisms of the salt marsh. Can you distinguish the bacteria form the fungi from the algae, protozoa?

Detritus
noun, de·tri·tus
1. any disintegrated material; debris.

In biology, detritus is dead particulate organic material.  Detritus is typically colonized by communities of microorganisms which act to decompose the material.

 
See the primary consumer?

What’s next in the food chain?