EMERGY-BASED ANALYSIS ON LAND SUSTAINABILITY
基于能值分析理论，构建了多个能值指标（如总能值投入产出比、工业能值投入产出比、土地环境负荷指数和能值可持续指数），并用于评估中国1978-1999年农田生态系统的可持续性，发现环境压力巨大且生态影响负面。
In recent years, many approaches have been used to quantitative evaluate the sustainability of regional land ecosystem, but most of them failed to explore the intrinsic characteristics of land sustainability due to imperfect evaluation paradigms. Emergy analysis (EMA), which was developed by H.T.Odum, is bold and broad-reaching approach to quantify the role of the environment in land use activities. According to the emergy analysis theory, the emergy flows that input the land ecosystem control the performance and behaviors of the system. So, the indices and ratios based on emergy flows can be calculated and employed to evaluate the sustainability of land ecosystem. In this paper, by transforming original statistic data into solar emergy we develop some emergy-based indices and ratios such as total emergy input-output ratio, industrial emergy input-output ratio, land environmental loading index, and emergy-based sustainable index of land use. As an empirical study, the indices and ratios are used to evaluate the cropland sustainability of China from 1978 to 1999. The results indicate that emergy analysis is an alternative approach for assessing the dynamic behaviors of land ecosystem. Each indices and ratios of cropland ecosystem in China exhibit different dynamic trends through the selected period (1978-1999). The total emergy input-output ratio shows a smooth transition while industrial emergy input-output ratio presents sharp decline. The stable increase of land environmental loading index and gentle decrease of emergy-based sustainable index suggest that there are huge environmental pressures and negative ecological impacts on cropland ecosystem in China.