Emergy evaluations of three aquaculture systems on wetlands surrounding the Pearl River Estuary, China

Emergy and economic analysis, accompanied by sensitivity analysis, were used to evaluate the ecological economic characteristics of three fish aquaculture systems on wetlands surrounding the Pearl River Estuary in China. The sustainability of these systems was compared to two aquaculture systems and two wetland systems, to provide reference conditions for the best use of limited wetland areas. We found that the three systems studied had similar emergy characteristics, despite their very different economic characteristics. Counter intuitively, the high economic input and output mode did not have higher environmental impact or lower sustainability compared with low economic input and output mode. Apparently, the sustainability of an intensive aquaculture system is determined mainly by how many natural renewable resources are exploited. The large differences in economic benefit and environmental impacts between the mangrove reserve and the aquaculture systems demonstrated the important role of nature reserves on preserving the sustainability of an estuary. Transformity (TR) and Emergy Yield Ratio (EYR) are both indicators of system efficiency, but from different points of view, and they produced opposite results in assessing the efficiency of the same system in this study. The ratio of EYR to TR might be used in addition to the EYR and transformity as a discreet perspective on overall system production efficiency.