This discussion focuses on three main types of aquatic biomass; macroalgae, microalge, and floating plants. The difference between macroalgae and microalgae is that macroalge are big organisms like seaweed and kelp, but microalgae are single celled organisms like spirulina and chlorella. Floating plants are an interesting biomass to consider insomuch as they are invasive, they grow fast, and they are fairly easy to harvest. 

From a bioenergy perspective landfills are an excellent source of biomass and carbon, if you can engineer a way to deal with its unpredictable composition and level of contaminants. The only solution for trash for decades has been to landfill it or incinerate it, but this is changing. The size of the carbon reserve, the fact they are so consolidated, and their frequent presence near urban areas is making landfills the target for a variety of bioenergy companies.