Emergy-based Health Assessment of Baiyangdian Watershed Ecosystem in Temporal and Spatial Scales

The shrinking Baiyangdian Lake and drying up rivers are widely observed in recent years. Due to the significant advantages in integrated analyses of natural and economic systems, emergy analysis is introduced in this paper to assess the health status of Baiyangdian Watershed. First, we establish a emergy based conceptual framework for the assessment, delineate an emergy flow diagram of Baiyangdian Watershed Ecosystem, and propose an emergy-based comprehensive assessment index system, which includes 11 indices categorized into 4 groups, i.e., ecosystem efficiency, ecosystem organization structure, ecosystem service function and ecosystem load. In the principle of ecosystem health assessment, six indicators from efficiency, organization structure, service function and load are integrated to construct an emergy-based ecosystem health index (EHI). In temporal scale, the health status of Baiyangdian Lake is evaluated from 1975 to 2009 which divided into five time periods. In spatial scale, Baiyangdian Watershed are divided into six sub-watershed based on DEM, the change of EHI in the six sub-watershed are compared. The results show that, in temporal scale, ecosystem service function has decreased sharply, while ecosystem load has been improved, self sufficiency of ecosystem, emergy yield and competitiveness have been damaged severely. The condition of ecosystem health of Baiyangdian Lake has deteriorated continuously especially after 1985. The results in spatial scale show that Fu River sub-watershed and Tang River sub-watershed have poorer health status, Juma River sub-watershed and Zhulong-Xiaoyi River sub-watershed has better health status. Shortage of instream flow, deterioration and sedimentation are the most dominated factors resulted in poor health status in Baiyangdian Watershed Ecosystem.