Ecological Risk Assessment In The Bailongjiang Watershed In Southern Gansu

Bailongjiang watershed, located in the southeast of Gansu province and the transitional zone among the Loess Plateau, Qinba Mountains, and Tibet Plateau, is well-known for its fragile environmental system and the importance of the ecological barrier of Yangtze River. The healthy and harmonious development of the local environment and human activity is very important for the water supply and ecological security of the upstream of the Yangtze River. Gansu section of Bailongjiang watershed is famous for it high occurance and huge damage due to the local geological disasters, such as landslide, debris flow, seismic, fallen stone and so on. With the development of local economic and industry, more interference of human activities had been gave to the local and mountainous environment, the original ecological structure and function of the natural system had been broken greatly, and resulted as the happening of environment problems, such as soil and water erosion, poor vegetation, lose of ecological function and service, and pose a serious threat to the security and health of local ecosystem. Regional ecological risk assessment aims to forecast the probable negative impact in the future of all sorts of disasters or accidents to the natural environment and ecosystems at the regional scale, and to provide certain theoretical guidance for the healthy and sustainable development of the local environment and ecological risk management.In this paper, the Gansu section of Bailongjiang watershed, a typical area with fragile natural environment and transitional ecotone, was took as a case to study the ecological risk at watershed scale. The human activities, geohazards including landslide and debris, and water and soil erosion were selected as risk sources, the landscape pattern index were selected as the measurement factors of risk source of adverse effects on the natural environment system, and an ecological risk evaluation model was set up finally. The paper evaluated firstly the ecological risk caused by the three single risk sources of human activities, geohazards and water and soil erosion respectively. And then, we assessed the integrated ecological risk of Bailongjiang watershed with the comprehensive consideration of all the risk sources witn single factor analysis which integrated with. The research results showed as the following:(1)The ecological risk map of human activities of Bailongjiang watershed indicated that whole ecological risk level in the both sides of the Bailong river and Mingjiang river and northern part of Bailong river is higher than that of the southern part.During the period of1990to2010, the area of moderate risk and the medium risk levels are both increased, and the area of the other risk level are decreased. In the period of1990to2002, most of the area of high risk level has changed into low risk level. From2002to2010, the area of all the risk level has changed into the medium risk level. Among all the landscape types, the ecological risk level of residential and industrial land, farmland land and unused land is the highest one, but the ecological risk level of the forestland is the lowestone. As to spatial distribution of the ecological risk level of Bailongjiang watershed, the risk level of Wudu and Tanchang is higher than other counties, and the risk level of Diebu is the lowest one.(2)The map of the ecological risk level of geological disaster in Bailongjiang watershed showed that the the highest risk area are mainly distributed in both the bank area of Bailongjiang river from Zhouqu to Wudu and the northern part of Zhouqu to Wudu, and the lower risk areas are mainly distributed in Diebu, southern part of Zhouqu, most area of Tangchang, southern part of Wenxian and a few township in the southwestern part of Wudu. Among all the landscape types of Bailongjiang watershed, the highest risk types is farmland, the lowest one is forestland and unused land. Among the five counties in the watershed, Wudu has the highest ecological risk level of the geological disaster, and the lowest risk area of geological disasters located in Diebu.(3) The spatial distribution of ecological risk level of water and soil erosion showed that the high risk area mostly located along the Bailongjiang river and its tributaries, Minjiang River, north and northwest part of Diebu. Among all the landscape types, the higher risk types are farmland and unused land, and the lower risk type is the forestland. As to five counties in the whole watershed, the highest ecological risk county of water and soil erosion is Wudu, but the lowest one is Zhouqu.(4) The integrated assessment of the ecological risk of Bailongjiang watershed showed that lager proportion of the watershed belonged to the higher and medium risk level in the study area. And also the high risk area mostly located both sides of the Bailongjiang river from Zhouqu to Wudu, the northern part of Zhouqu to Wudu and northwest part of Tanchang.The landscape with higher ecological risk level is the farmland, residential and industrial land, but the forestland is the lowest risk one. Among the five counties, the highest ecological risk area is Wudu, and the lowest one is Diebu.Finally, based on the analysis of different risk levels and risk sources, some management suggestions on hazards management, urban construction, water and soil conservation, ecological restoration, agricultural production and education of environmental awareness had been put forward for the ecological risk management of Bailongjiang watershed. This study has the practical and guiding significance for the effective environmental management, the maintenance of ecosystem function and regional ecological security for the mountainous area in China.