Decomposition of dead Organisms is also an Autochthonous energy Source.

http://en.wikipedia.org/wiki/Lotic_system_ecology

Another form of autochthonous energy comes from the decomposition of dead organisms and feces that originate within the lotic system. In this case, bacteria decompose the detritus or coarse particulate organic material (CPOM; >1 mm pieces) into fine particulate organic matter (FPOM; <1 mm pieces) and then further into inorganic compounds that are required for photosynthesis.This process is discussed in more detail below.