Integrated emergy and economic evaluation of an ecological engineering system for the utilization of Spartina alterniflora

An integrated emergy and economic evaluation of a 7-step ecological engineering system (7-step EES) located in Jiangsu Province, China was carried out. This 7-step EES was constructed to fully utilize existing S. alterniflora production through a low waste, clean production process and to help control the expansion of this invasive grass. First, the above ground S. alterniflora biomass removed for invasion control is used as the feedstock for the extraction of a bio-mineral liquid and its encapsulation, both of which provide a health supplement to treat gout and angiocardiopathy patients. Next, the residues left after extraction are used as a medium for mushroom cultivation, and then for raising earthworms. Finally, the remaining residues become the main component of a microbe enriched organic fertilizer, which is then returned to the soil. A suite of emergy indices were constructed on multiple temporal and spatial scales to examine the operation of the whole system and its subsystems. The results showed that the temporal sustainability of the 7-step EES was relatively high at different spatial scales, especially at the local scale as indicated by its EISD_LS (1.55E+03). Full implementation of the 7-step EES for S. alterniflora currently residing on the coast of China can result in a potential economic output that is greater than 2% of the national GDP, with an economic output/input ratio over 29. In addition, the 7-step EES had an environmental loading ratio lower than that of the regional system. Sensitivity analysis showed that decreasing the cost of the purchased inputs needed to make the capsules is the key problem that needs to be solved to optimize the system, both for its sustainability and economic viability, on all spatial and temporal scales.