The production of marine biomass in the ocean, even on the largest scale envisaged for energy applications, would require only a very small fraction of

the available ocean areas. For example, it is estimated that, depending on biomass yield, a square area about 320 to 540 km on each edge off the coast of California may be sufficient to produce enough giant brown kelp for conversion to methane to supply all U. S. natural gas needs (Bryce, 1978). This is a large area, but it is very small when compared with the total area of the Pacific Ocean. Also, the benefits to other marine life from large kelp plantations have been well documented. Any conflicts that might arise would be concerned primarily with ocean traffic. With the proper plantation design for marine biomass and precautionary measures to warn approaching ships, it is expected that marine biomass growth could be sustained over long periods.

Freshwater biomass could in theory be grown on the 20 million ha of fresh water in the United States. But there are several difficulties that mitigate against large-scale freshwater biomass energy systems. About 80% of the fresh water in the United States is located in the northern states, whereas several of the freshwater biomass species considered for energy applications require a warm climate such as that found in Gulf states. The freshwater areas suitable for biomass production in the southern states, however, are much smaller than those in the North, and the density of usage is higher in southern inland waters. Overall, these characteristics make small-scale aquatic biomass produc­tion systems more feasible for energy applications. In the future, it may be advisable to examine the possibility of constructing large man-made lakes for this purpose, but this does not seem practical at this time except possibly where an aquatic biomass species is used for wastewater treatment.