In limnology, allochthonous sources of carbon or nutrients come from outside the aquatic system (such as plant and soil material). Carbon sources from within the system, such as algae and the microbial breakdown of aquatic particulate organic carbon, are autochthonous. In aquatic food webs, the portion of biomass derived from allochthonous material is then named "allochthony".[2] In streams and small lakes, allochthonous sources of carbon are dominant while in large lakes and the ocean, autochthonous sources dominate.[3]