Some organic matter not already in the soil comes from groundwater. When the groundwater saturates the soil or sediment around it, organic matter can freely move between the phases. Groundwater has its own sources of natural organic matter including:
* organic matter deposits, such as kerogen and coal.
* soil and sediment organic matter.
* organic matter infiltrating into the subsurface from rivers, lakes, and marine systems."
Organisms decompose into organic matter, which is then transported and recycled. Not all biomass migrates, some is rather stationary, turning only over the course of millions of years.