新疆喀纳斯景区道路沿线表土环境磁学特征

Magnetic Properties of the Roadside Topsoils in Kanas Scenic Spots,Xinjiang Uygur Autonomous Region,China

为验证环境磁学方法监测旅游景区道路沿线土壤污染的可行性,分别采集新疆喀纳斯旅游景区道路沿线区(距离道路<0. 5 m)、远离道路区(距离道路>30 m)以及远离旅游活动区(作为对照区)的表土样品,利用磁测、扫描电子显微镜和能谱仪方法对其磁学性质、空间分布及其成因进行研究.结果表明:①道路沿线区表土样品χLF(低频磁化率)、SIRM(饱和等温剩磁)平均值分别为194. 24×10-8m3/kg和2 288. 62×10-5Am2/kg,显著高于远离道路区和对照区.②道路沿线表土样品SOFT(软剩磁)、HIRM(硬剩磁)及S-ratio(300 m T反向磁场测试的等温剩磁与SIRM比值的相反数)平均值分别是对照区的4. 35、3. 66、0. 99倍,S-ratio平均值接近于1,SIRM/χLF平均值小于20 k A/m,χFD(百分频率磁化率)平均值为2. 04%,IRM(等温剩磁)获得曲线呈先快后慢的上升趋势.③道路沿线区表土样品的χLF、IRM20 mT(20 m T正向磁场测试的等温剩磁)、SIRM相互之间以及三者与SOFT之间均呈显著正相关.χLF与χFD、SIRM/χLF均呈显著负相关,χFD与SIRM/χLF呈显著正相关,S-ratio与SOFT呈显著正相关、与HIRM呈显著负相关.④道路沿线区和远离道路区表土样品的磁性矿物均存在光滑完整的球粒状、不规则或片状颗粒,其元素组成主要是C、O、Si、Al、Fe等,并含有微量的Ni、Cr、Mn等重金属元素.研究显示,新疆喀纳斯旅游景区道路沿线表土样品磁性矿物含量较高,载磁矿物以多畴、假单畴粗颗粒的亚铁磁性矿物为主导,χLF、SIRM、SOFT的空间变化趋势类似,均在通往湖口的道路处出现高值区,并且磁性颗粒较粗,形成潜在土壤污染区.道路沿线区表土样品磁性增强可能与旅游交通活动产生的磁性颗粒外源输入有关.因此,环境磁学方法具有大范围监测景区土壤环境、判别污染物来源和圈定旅游交通土壤污染范围的能力.

In order to verify the feasibility of monitoring soil pollution along roads in scenic spots by the method of environmental magnetism,the topsoil samples were collected from the roadside areas( distance from roads <0. 5 m),far from roads( distance from roads >30 m) and the area far away from the tourist activity( as the control area) in the Kanas scenic spots. Their magnetic properties,spatial distribution and causes were investigated by magnetic measurement,scanning electron microscopy and energy dispersive spectrometer. The results showed that:( 1) The average values of χLF( low frequency magnetic susceptibility) and SIRM( saturated isothermal remanence) of roadside topsoil samples were 194. 24×10^-8 m^3/kg,2288. 62× 10^-5 Am^2/kg,respectively,which were significantly higher than those far away from the road and the control area.( 2) The average values of SOFT( soft remanence),HIRM( hard remanence) and S-ratio( the opposite number of the ratio of SIRM to isothermal remanence for 300 m T reverse magnetic field measurement) of topsoil samples along the road were 4. 35,3. 66,0. 99 times higher than those of the control area,respectively. The average value of SIRM/χLFwas less than 20 k A/m,and the average value of χFDwas 2. 04%. The curve of IRM( isothermal remanence) showed a fast and then slow upward trend.( 3) The parameters of χLF,IRM20 mTand SIRM from topsoil samples along the road correlated positively with each other and with SOFT.χLFcorrelated negatively with χFDand SIRM/χLF. There was a positive correlation between χFDand SIRM/χLF. S-ratiocorrelated positively with SOFT and correlated negatively with HIRM.( 4) The magnetic minerals of typical samples had smooth and intact spherical,irregular or flaky particles. The elements mainly included C,O,Si,Al,Fe,etc.,and contained trace heavy metal elements,such as Ni,Cr,Mn.The results indicated that the content of magnetic minerals in the roadside topsoil samples was high. The bearing magnetic minerals were mainly ferromagnetic minerals. The magnetic particles were mainly multidomain and pseudo-single domain coarse particles. The spatial variation trends of χLF,SIRM and SOFT were similar to each other,and the high value areas appeared on the roads leading to lake outlet,and the magnetic particles were thicker. The high value areas formed potential soil pollution areas. The magnetic enhancement of roadside topsoil samples might be related to the exogenous input of magnetic particles produced by tourism traffic activities. Therefore,the environmental magnetism method had the ability to monitor the soil environment of scenic spots,and it could be used to identify the sources of pollutants and screen the scope of tourist traffic soil pollution in scenic spots.