The Theory And Method Of Island Ecological Risk Assessment

Compared with the mainland, an island is easily affected by water around it, especially by sea or ocean. Natural disasters in an island happen more frequently than those in the mainland, and its ecosystem is more vulnerable, and highly sensitive to disturbance from nature and human activities. Otherwise, due to long distances from the mainland and restricted resources, most islands are relatively undeveloped in the world. In the last ten years, many countries have paid more attention to develop economy of an island. With the fast development of an island, the degradation of environment and the decrease of biodiversity have taken place. The ecological security of an island is facing the threat from the natural and artificial risk. At present, assessments on ecological risk mainly focus on ecosystems of the mainland and there are few researches on an island. It is very important and necessary to develop a new theory and methods for island ecological risk assessment based on its character.Three islands of Chongming, meeting the Yangtze River on the west and facing the East China Sea on the east, are alluvial islands in the Yangtze estuary, located in the "T" junction of Yangtze River and eastern China Sea. Their location and environment are very special. The islands ecosystem is easily affected by sea, the Yangtze River and cities near them. Along with the construction of the Shanghai Chongming River crossing Project and the exploitation of the islands of Chongming, more economic development will come to Chongming, but new stressors will appear for resources and eco-safety. To analyze the ecological security of the islands of Chongming and study how to avoid the ecological risk in future development are very urgent and important tasks.The study of the dissertation used three islands of Chongming as the research area. The guideline, index system and models adapted for regional ecological risk assessment were constructed, the main eco-risk and risk sources of three islands of Chongming systematically analyzed, the present eco-risk assessed and the future eco-risk predicted. The result would perfect the theory and method of regional ecological risk assessment, contribute to the region programming and environment management of the three islands of Chongming and the construction of the region's ecological risk warning decision support system.The main conclusions are summarized as follows:(1) The ecological risk assessment of a complex ecosystem can be done by the guideline of Three Tiered Risk Assessment. In tier 1, the hazard index about the risk source to receptors was set, based on the formation and the probability of the risk source and the analysis of adverse ecological effects in situ. This step is elementary assessment. In tier 2, whether the risk source makes receptors damnous or not will be assessed based on the ecological vulnerability of receptors. This step issemi-quantified assessment. In tier 3, the loss of risk will be quantified, and the risk sub-area will be set based on the risk index and the risk loss. Not regional ecological risk assessment for all risk sources need to be assessed on the three tiers. The quantity of tiers is decided by the character of risk source, the aim of assessment, and the information.(2) Regional eco-risk was determined by the probability and the hazard index of risk sources, and the ecological vulnerability of receptors, expressed by the risk loss. The higher the risk index value and risk loss is, the larger the eco-risk is. Considering the above factors, the regional ecological risk assessment model was constructed. Four parts were included in the model.â‘  The hazard index setIn this part, the intensity of risk source to affect the receptors was analyzed. The value of the hazard index was set by the understanding for the process of risk source and the character of the receptors.â‘¡ The ecological vulnerability assessment sub-modelIn this part, ecological vulnerability includes ecosystem vulnerability and socio-economic vulnerability.â‘¢ The risk index assessment sub-modelIn this part, the risk index representing the probability of receptor damage was assessed by the hazard index multiplied the ecological vulnerability index.â‘£ The risk loss assessment sub-modelIn this part, the risk loss assessment sub-model was constructed to quantify the risk loss. In the sub-model the risk index in the risk index assessment sub-model was set as a parameter.(3) The ecosystems of the Chongming islands are exposed to many kinds of risk sources from the drainage basin, the sea and the human activities, so it became very unstable. The risk sources to affect the Chongming islands mainly include saltwater intrusion, storm tide, floods, typhoon, pollution and big projects in the drainage basin like the South-to-North Water Diversion Projects and the Three Gorges Project. The main eco-risks of the Chongming islands are decrease of wetland area, shortage of fresh water, decline of biodiversity, fragmentation of habitat and so on. Considering the probabilities and duration of risk sources and the quantity of its receptor and the loss, the reversibility of harm, rainstorm, storm tide, flooding, saltwater intrusion and inning were chosen as the main risk sources of the islands of Chongming in this study.(4) The order of ecological vulnerability of an ecosystem in the Chongming islands from highest to lowest is farm, wetland, pond, village, city, forest, river and lake. Based on their ecological vulnerability, the wetland and the farm land should be more protected for high biodiversity and better function of ecosystem. The safeguard of cities in the south Chongming Island, Hengsha Island and Changxing Island should be improved for the sustainable development of their economy and the safety of their inhabitants.(5) Dynamics of ecosystems in future Chongming islands were simulated by CLUE-S model. The result showed that the inhabitancy area would increase greatly from 2005 to 2020 in scenario 2 developed by historical trends. The increased area of it would be mainly transferred from the farmland distributing at the side of city. In scenario 1, developed by region programming, the constructed area showed high density spot distribution. The area of farm, wetland and forest would be higher in scenario 1 than that in scenario 2. The ecological vulnerability in scenario 2 would is bigger than that in scenario 1.(6) The risk indexes of the five risk sources and the integrated risk source would increase from 2005 to 2020. And the risk index in scenario 1 would be higher than that in scenario 2. In each class of eco-risk, risk loss per area would greatly increase, more in scenario 1 than in scenario 2. But the proportion between risk loss and the gross output value of industry and agriculture would decrease from 2005 to 2020, lower in scenario 1 than that in scenario 2. This indicates that the eco-risk in scenario 1 might be relatively lower than that in scenario 2 and the Three Tiered Risk Assessment method is superior to the past semi-quantified risk index risk assessment method(7) The result showed that the eco-risk of rainstorm was mainly distributed at Chengqiao Town, Bao Town, ponds in Dongtan and northern Chongming Island, Hengsha Town, the eco-risk of flood at Chengqiao Town, Dongtan, ponds in the northern Chongming Island, Hengsha Town, the eco-risk of storm tide at ponds in Dongtan and northern Chongming Island, Tuanjiesha, Xincun Town, Hengsha Town and Changxing Town., the eco-risk of saltwater intrusion at Chengqiao Town, Bao Town, Xinhe Town and the eco-risk of inning at the wetland to joins with other types of ecosystem, descending from the interior of island to the exterior.(8) Chengqiao Town, Hengsha Island and Tuanjiesha belong to the first class risk area. The main risk sources of Chengqiao Town are rainstorm and saltwater intrusion; while the ones of Hengsha Island and Tuanjiesha are rainstorm, storm tide, saltwater intrusion and inning. The northern and southern part of Changxing Island, Dongtan and the northern part of Chongming Island belong to the second class risk area. Their main risk sources are rainstorm, storm tide, saltwater intrusion and inning. Besides, the risk loss per area for each risk source is also given in each risk area. The result modeled by the model shows similar pattern with the above one.