Special Feature on the Environmentally （特殊的环境特性）.pdfVIP

International Review fo r Environmenta l Strategies JGES Vol. 5, No. 2, pp. 499 - 510, 2005 O 2005 by the Institute for Global Environmenlal Stmlegies AU nghts reserved Special Feature on the Environmentally Sustainable City Material Flows for a Sustainable City Frank Ackerman^ Materials flow through cities on a daily basis , entering as needed products and leaving as wastes . Management of municipal solid waste provides both sanitation and recovery of valuable materials . At low income levels, market forces lead to recycling with no need for planning . In developing countries today, as in developed countries in the past, the relationship between urban wages and material prices promotes recovery of many materials . However, as wages rise, people become less willing to engage in labor- intensive recycling . At the same time, the waste stream expands and changes in composition ; in particular, paper represents a greater fraction of urban waste at higher income levels . Although the market no longer compels recycling, people in high-income countries are willing to pay for municipal recycling programs , and often protest when recycling is cut back or eliminated . There is a need to plan for recycling in a high- income context, particularly for recovery and recycling of paper products, without reliance on the low