关键词: 生态风险, 风险重心, 米脂县, 时空分异, 风险分区, 黄土丘陵沟壑区

Abstract: Ecologically fragile regions such as loess hilly-gully region are highly responsive to global change. Regional development is on an unsustainable track under the background of fragile ecological environment and agricultural activities. The study of ecological risk in this region has become one of the hot spots of geographical and ecological response to ecosystem management. Taking Mizhi county for the study of loess hilly-gully region, land-use maps of this county in 2009 and 2015, a digital elevation model (DEM) and social and economic statistical yearbook of Mizhi county were needed and 253 small watersheds were identified as the auxiliary evaluation units by using ESRI's Hydrological Analysis Tools for ArcGIS 10.2. A comprehensive ecological risk assessment framework for identifying risk probability, habitat sensitivity, and system impairment was established, and multi-source data were integrated through range standardization and entropy weight method at watershed level. The spatio-temporal differentiation of criteria layers and comprehensive ecological risk were analyzed, at the same time, the evolution trend of comprehensive ecological risk was explored through the Standard Deviation Ellipse (SDE) and risk gravity. The risk precaution partitions were simultaneously delineated based on the risk dominant factor and the risk management strategies were formulated. The results were as follows: (1) The spatial distribution pattern of risk probability in Mizhi county was generally high in the middle and east and low in the northwest. The value of risk probability increased from 49.93% to 52.92% during 2009-2015. The habitat sensitivity index was 0.61 in 2009 and 0.60 and 2015, respectively, which was a decrease of 1.6% based on the InVEST model, and the habitat quality improved. The system impairment index was generally higher in the central and western regions while lower in the eastern region (southeast and northeast). The impairment index increased from 0.42 to 0.46 during 2009-2015, which indicated that the degree of impairment caused by ecological risk increased. (2) The spatial distribution pattern of comprehensive ecological risk was high in the middle, while low in the south and north. Between 2009 and 2015, the ecological risk index increased from 0.14 to 0.15, with an increase of 7.14%. The risk gravity of Mizhi county was distributed in Gaoqu township in 2009, and jumped into Yinzhou township in 2015. The main ecological risk evolution was northwest-southeast trending, and kept stable basically. (3) The study area was divided into four types of risk precaution partitions. Risk monitoring zones, ecological recovery zones, monitoring and recovery zones, and natural regulation zones encompassed 7.53%, 6.57%, 23.86% and 62.04% of the study area, respectively. Risk precaution partitions based on risk dominant factors can effectively eliminate risks and promote the sustainable development of regional habitats.

Key words: ecological risk, Mizhi county, risk gravity, spatio-temporal differentiation, loess hilly-gully region, risk precaution partitions