龙口市北部平原区不同土地利用类型对土壤重金属污染距离的影响

为探究不同土地利用类型及其组成对土壤重金属污染距离的影响，以龙口市北部平原作为典型研究区域，系统采集55个表层土壤样品并对w（Pb）、w（Cd）进行了测定；通过建立基于土壤样区的梯度缓冲区，利用Pearson相关性分析，研究不同土地利用类型及其组成对土壤重金属污染距离的影响；通过热点分析和空间插值方法，探究研究区内对Pb、Cd富集贡献较大的土地利用类型.结果表明:①龙口市北部平原土壤中Pb、Cd受人类活动影响的区域差异明显，w（Pb）、w（Cd）平均值均超过了山东省土壤相应背景值，其中，w（Pb）超过背景值的样品比例达到96.36%，研究区西部富集现象明显.②土地利用类型面积占比对Pb、Cd的污染距离各异.其中，交通用地面积占比对Pb、Cd的污染距离大约在2 000、500 m处，建设用地面积占比对二者的污染距离分别在1 000、200 m处左右，而耕地及园地面积占比对二者的污染距离较小，均在50 m处左右.③w（Pb）、w（Cd）的空间分布差异明显，整体表现为西高东低.④研究区内对Pb、Cd富集贡献最大的土地利用类型是耕地，其次是交通和建设用地.研究显示，不同土地利用类型对重金属污染距离的差异性是实际存在的，因此在进行重金属污染治理时，对不同的土地利用类型要根据其对重金属污染距离的差异加以区别. 

Effects of Different Land Use Types on Pollution Distance of Heavy Metals in North Plain of Longkou City

In order to explore the effects of difference of land use type and its composition on soil heavy metal pollution distance, the northern plain of Longkou City was taken as a study area.Fifty-five surface soil samples were collected and Pb and Cd contents were determined. By establishing gradient buffer zone based on soil sample area, the influence of land use type and its composition on soil heavy metal pollution under different gradients was analyzed. Through the hot spot analysis and spatial interpolation method, the land use types in the study area that contribute greatly to Pb and Cd enrichment was explored. The results showed that:(1) Pb and Cd in the soil of the study area were significantly affected by human activities, and the average value exceeded the background value of soil in Shandong Province. The proportion of Pb exceeding the background value reached 96.36%, and the western enrichment phenomenon is obvious. (2) In different gradients, the percentage of land use types had different correlations with Pb and Cd. The maximum correlation coefficient of traffic land with Pb and Cd reached 2000 and 500 m respectively, and the construction land was 1000 and 200 m. The correlation coefficient of cultivated land and garden land was the largest at the gradient of about 50 m. (3) The spatial distribution difference of Pb and Cd was obvious, and the overall performance was high in the west and low in the east. (4) The cultivated land in the study area contributed the most to Pb and Cd enrichment, followed by traffic and construction land. The study shows that different land use types have different heavy metal pollution distances. In the treatment of heavy metal pollution, different types of land use should be distinguished according to the difference of the pollution distance.