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Abstract
Ecological footprint (EF) analysis is an effective tool to assess ecosystem appropriation, but weaknesses still exist. In order to estimate a city's ecosystem appropriation, we made two modifications to EF: 1) including different types of freshwater area in the calculating framework; and 2) re-adjusting all equivalent factors in terms of different types of freshwater. The modifications are mainly concerned with changes in the composition of freshwater areas in EF analysis; that is, the proportion of aquaculture freshwater and tap freshwater. An assumption of 25% of aquaculture freshwater was used to conduct a sensitivity test. It shows that variation of the proportion leads to different equivalent and yield factors for tap freshwater areas. The variations not only change the EF of freshwater but also the total EF. The modified EF calculation served to assess ecosystem appropriation in Jiangyin city in 1998. By comparing the original and the modified EF, it was found that the ecological deficit was larger (2.19 ha per capita) in the modified calculation than in the original (2.16 ha per capita). The original calculation is an underestimate because direct consumption of freshwater was not fully included in its calculating framework. From the modified calculation, the EF for different categories of ecosystems decreased, from fossil energy land, arable land and pasture to built-up areas, which together occupy about 97.58% of the total EF. Fossil energy land occupied 68.55% of the total, while freshwater areas took only 0.62%. The main ecological deficits were from fossil energy land, arable land, pasture and marine areas. Ecological supply is lacking within Jiangyin and relies on ecosystems outside the city to survive. Ecosystem management is indispensable to optimise the efficiency of ecosystem use and to expand the biological capacity of the city. The modified EF could provide a more reasonable instrument in policy-making and implementing sustainable management of freshwater ecosystems.