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摘要
MilA i Canals et al. (Int J Life Cycle Ass 14(1):28-42, 2009) referred to as 'Part 1' in this paper) showed that impacts associated with use of freshwater must be treated more rigorously than is usual in life cycle assessment (LCA), going beyond the conventional consideration only of 'blue' water (i.e. irrigation and other abstractions), and suggested an operational method to include the impacts on freshwater ecosystems (freshwater ecosystem impact) and abiotic resource depletion (freshwater depletion). The inclusion of water-related impacts in LCA is of paramount importance, particularly for agricultural systems due to their large water consumption worldwide. A case study of UK consumption of broccoli grown in the UK and Spain is presented here to illustrate the method suggested in Part 1.
Water footprint (WF) and life cycle impact assessment (LCIA) methods presented in Part 1 are applied to six different and synchronic supply chains providing broccoli during the British colder months (November-April); four of these chains refer to broccoli produced in Spain and the other two are based on frozen British produce. In addition, four UK-based supply chains delivering fresh broccoli from April to November are studied to provide a year-round perspective.
Using WF accounting methods helps to provide a richer picture of the total water consumption associated with growing broccoli. Including the volumes of water consumed in the life cycle inventory (LCI), assessed following the WF approach (evaporative uses of irrigation water and soil moisture), shows that the total water consumption does not vary greatly between UK and Spanish broccoli production. However, when impact assessment indicators based on the water use per resource ratio are applied, water use in Spain is shown to be much more critical, with significantly higher impact for Spanish cultivation. While the largest component of water use in Spain is linked to irrigation, the study reveals other important uses in the life cycle of vegetables, namely direct use of water for cooking and sanitation, land use effects on the water cycle and electricity production.
The results highlight the importance of distinguishing between different water volumes and sources in the different LCA phases: LCI (with and without full WF consideration) and LCIA. Traditional LCI results may be misleading when comparing irrigated systems in regions with differing water scarcity. The WF estimates are more relevant for sourcing strategies, as they show the total water requirements of crops including both irrigation water use as well as the use of green water (effective rainfall stored as soil moisture). Finally, LCIA results show the potential impacts of water consumption on freshwater ecosystems and future freshwater availability.
This methodological framework improves the representation of impacts associated with water use in LCA. This helps in identifying the hotspots of the production system in terms of potential impacts to freshwater ecosystems, as well as in identifying where investments for water-saving may have the greatest benefit. In addition, this approach addresses a regional specific issue, water scarcity, which may often be closer to critical thresholds than other environmental impacts.
The method should be tested with further case studies in order to confirm the suitability and necessity of the LCI modelling requirements and LCIA characterisation factors such as the explicit inclusion of evaporative water losses. The WF approach can benefit from experience of systems analysis gained in LCA, while LCA may benefit from the detailed accounting framework embodied in the WF approach, as illustrated in this paper. Because the purposes of the two tools are different, they will continue to evolve separately, but complementarity in application should guide this development.
- 出版日期2010-7
