下辽河平原地下水脆弱性的时空演变

Spatial-temporal evolution of groundwater vulnerability in the lower reaches of the Liaohe River Plain

地下水脆弱性受相关因子变化的影响,在时空分布上具有动态变化性,因此分析地下水脆弱性的时空演变及结构变化规律对于地下水有针对性地污染防治具有重要意义。以下辽河平原为研究区,选取1991、2000和2010年的相关人为因子参数,结合DRASTIC模型计算这3个年份的地下水脆弱性综合指数,利用Arc GIS的地理统计工具分析地下水脆弱性的演变状况。在此基础上计算G指数得到地下水脆弱性的空间热冷点分布,结合重心和标准差椭圆对热点的变动情况进行定量分析。研究结果表明:(1)1991年地下水脆弱性以较低脆弱性和高脆弱性区为主,分别占研究区面积的36.5%和31.3%,到2000年以一般脆弱性和较高脆弱性区为主,面积比例分别达到31.6%和25.9%,发展到2010年主要以较高脆弱性为主,面积比例占41.71%;(2)1991—2010年下辽河平原地下水脆弱性总体上呈现先增后减的趋势,沈阳市及周边长期处于高值状况,南部沿海地区逐步演化为高值脆弱性区;(3)1991和2000年的热点集中区主要分布在新民市和辽中县的西部地带,期间变化较小,2010年的滨海地区也发展成热点集中区,各时期内冷点分布面积比较少,且零散;(4)1991年至2000年,热点重心向西南方向位移了2.264km,热点分布格局进一步趋于东—西方向;2000年到2010年,热点重心向西南方向位移了30.787km,标准差椭圆长轴旋转角逆时针转动了32.44°,整体热点分布格局为东北—西南方向。

A study was carried out to assess groundwater vulnerability in the lower reaches of the Liaohe River Plain over a number of years. Groundwater bodies with a relatively stable quantity of water,good water quality,and a high degree of resistance to pollution are widely distributed throughout the world,and they have many different roles,including as domestic water supply,in economic development,integrity maintenance of the geological environment,and ecological balance. The rapid development of the social economy and subsequent increased demand for natural resources has resulted in an increased pressure on groundwater and has led to its over use. Consequently,groundwater systems in many regions and countries all over the world are exposed to varying degrees of pollution and destruction,resulting in an increasingly pronounced contradiction between supply and demand for water resources. Due to changes in the parameters affecting ground water,the spatial-temporal distribution of groundwater vulnerability is dynamic; hence,the analysis of spatial-temporal evolution and its structural variation is important when attempting to prevent groundwater pollution. The parameters affecting ground water,combined with the DRASTIC model and human factors,were used to calculate groundwater vulnerability in the lower reaches of the Liaohe River Plain in 1991,2000,and 2010. We also analyzed the evolution of groundwatervulnerability using Arc GIS and the change in the proportion of different levels of groundwater vulnerability. The hot and cold spots for groundwater vulnerability were calculated using Getis-Ord G＊i,and the dynamic changes in hotspots were quantitatively analyzed using gravity and the standard deviational ellipse method. In 1991,the groundwater vulnerability was low in 36. 5% of the study area and high in 31. 3% of the study area. In 2000,the moderate and high groundwater vulnerability areas reached 31.6% and 25.9% of the study area,respectively,while in 2010,groundwater vulnerability was high in 41.71% of the study area. Groundwater vulnerability in the study area showed a decreasing trend from 1991 to 2010 High groundwater vulnerability areas were diffused from the center of Shenyang to South coast. Hotspots were mainly distributed in the western zone of Xinmin City and Liaozhong County in 1991 and 2000,and only small changes occurred during this period,whereas the coastal areas became hotspots in 2010. Cold spots were relatively small and fragmented from1991 to 2000. During the same period,the gravity center of hotspots shifted 2. 264 km southwest,and the hotspot distribution pattern had an east-west direction. From 2000 to 2010,the gravity center of hotspots shifted 30. 787 km southwest,the long axis of standard deviation ellipse was rotated counterclockwise by 32.44°,and the overall distribution pattern for hotspots had a northeast-southwest direction. In addition,the improved DRASTIC method that was used to investigate nitrogen concentration at the monitoring points and calculate the corresponding vulnerability ratio proved to be an important analysis tool. Spatial-temporal evolution of groundwater vulnerability,when investigated through the assessment of groundwater vulnerability and hot-spot distribution,may improve the utilization of groundwater and lead to the development of a protection plan for the study area.