西藏自治区拉萨河流域湿地脆弱性评价与成因分析

Assessment and Origin Analysis on Wetland Vulnerability in Lhasa River Basin of Tibet Autonomous Region

构建了基于"敏感性—人为脆弱性"的脆弱性评价指标体系,运用ArcGIS的空间叠加分析和脆弱性评价模型,开展拉萨河流域湿地脆弱性评价,并运用障碍度计算方法,分析了影响脆弱性的主要因素。研究结果表明,拉萨河流域湿地脆弱性范围为0.115 3~0.742 7,可分为轻度脆弱、中度脆弱和重度脆弱3个等级,其中,中度脆弱面积最大,占湿地总面积的59.59%,集中分布在河谷区和高山盆地区,主要类型为藏北嵩草(Kobresia lit?tledalei)沼泽化草甸、杂类草湿草甸和河流;其次是轻度脆弱湿地,占湿地总面积的38.25%,主要分布于河源区的嘉黎县;重度脆弱湿地仅占2.16%,分布在河源区的那曲县和河谷区的桑日县。轻度和重度脆弱湿地的类型都以藏北嵩草沼泽化草甸、河流和湖泊为主。影响湿地脆弱性的主要因素有9个,其重要性从高到低依次为年降水量、污染源、牲畜密度、人均牧业产值、植被盖度、人均耕地面积、污水排放量、猪的密度和高程,其中,年降水量、放牧和植被盖度是普遍存在的最重要的影响因素。降低湿地脆弱性的关键在于保障水源供给、控制污染和限制过度放牧。

In this paper, an index system based ecological sensitivity and artificial vulnerability had been con- structed for assessing wetland vulnerability in the Lhasa River basin by using spatial overlay analysis of Arc- GIS and vulnerability assessment model. The indices of wetland vulnerability were classified into 4 sequential levels through the method of analytic hierarchy process, and the importance of indices were marked in a range by 1-9 through pair wise comparison. The weight of each index reflects its influence on wetland vulnerability, and the weights of different levels are calculated by mean of the largest eigenvalue. In the index system of eco- logical sensitivity and artificial vulnerability, natural factors and artificial factors were dealt with separately, which is helpful to the management of human activities directly and biophysical factors indirectly. In this pa- per, a grid unit of 30 m^30 m was put into application. Analyzing the factors affecting vulnerability was con- ducted by using the method of calculating obstacle degrees of wetland vulnerability management. Spatial dis- tribution maps of obstacle degrees for each index were created by GIS. With the criteria （obstacle degress more than 0.1） determined, obstacle factors of wetlands in the Lhasa River basin and their contribution are quantified. The research results showed that the range of wetland vulnerability in the Lhasa River basin was between 0.115 3-0.742 7, which could be divided into 3 levels： slight vulnerability, moderate vulnerability and heavy vulnerability. The wetlands with moderate vulnerability account for 59.59% of total wetland area, which are mainly distributed in regions of valley and high mountain basin, and the typical wetland types are Kobresia littledalei swampy meadow, weedy wet meadow and river; wetlands with slight and heavy vulnerabil- ity respectively account for 38.25% and 2.16% of total wetland area, and the former is mainly located at Lhari county of the source region, and the latter at Nagqu county of the source region and Sangri county of valley re- gion. The typical types of the wetlands with slight and heavy vulnerability were Kobresia littledalei swampy meadow, river and lake. The main obstacle factors affecting wetland vulnerability management, in order of im- portance, were annual precipitation, pollution source, livestock density, per capita animal husbandry output value, vegetation cover, per capita cultivated land area, quantity of wastewater effluent and density of free-ranging pigs, of which annual precipitation, grazing and vegetation cover were common factors that exist in various wetlands, therefore, the key to reduce wetland vulnerability is security water supply, control pollu- tion, and limit overgrazing.