四川盆地西缘浅层地下水铁、锰含量的空间变异特征

Spatial variability of iron and manganese contents in shallow groundwater in the west of Sichuan Basin

以四川盆地西缘低山丘陵区典型县——名山县为例,采用地统计分析方法,研究了四川盆地西缘低山丘陵区浅层地下水铁、锰含量的空间变异特征。结果表明,研究区浅层地下水铁含量变异较大,局部区域超标现象较为严重,42.86%的样点未达到欧盟生活饮用水水质标准(<0.2mg/L),25%的样点未达到我国和美国生活饮用水水质标准(<0.3mg/L);锰含量总体水平较低,其中94.64%的样点达到我国的生活饮用水水质标准(<0.1mg/L),所有样点均达到世界卫生组织规定的生活饮用水水质标准(<0.4mg/L)。研究区浅层地下水中铁、锰含量空间分布特征基本一致,均呈现出从东北向西南逐渐降低,至名山县城附近又有所上升的趋势,高值区主要出现在东北部一带,低值区主要出现在中南部一带。研究区地下水中铁、锰含量分布特征与区域土壤母质、土壤类型、人为活动等因素密切相关,其中受土壤母质和土壤类型的影响尤为明显。统计结果表明,第四系更新统冰碛物及冰水沉积物(Q2fgL)分布区域地下水铁、锰含量显著高于白垩系夹关组(K2j)、灌口组(K2g),第三系名山群(K1～2mn)等紫色岩分布区域;黄壤下浅层地下水铁、锰含量显著高于紫色土。

Iron and manganese are necessary elements for human health, but too much iron or manganese will be harmful to human＇s health. It is well known that groundwater was the main source of rural drinking water in china, and iron and manganese contents in groundwater have important effect on drinking water quality. Studies of spatial variability of iron and manganese in groundwater are helpful for the Rural Drinking Water Safety. Mingshan county, between Sichuan Basin and Western Plateau in Sichuan, China, is a typical low mountain and hill region. In this region, the Rural Drinking Water Safety was still serious because of dispersed population, inconvenient traffic and information, undeveloped economy, lack of infrastructure and so on. So that, spatial variability of iron and manganese contents in shallow groundwater in Mingshan county were studied by methods of traditional statistics and geostatistics. Using random sampling method, 56 sample points were selected in research area. Iron and manganese contents in shallow groundwater were analyzed by atomic absorption spectrometry method. The geostatistical characteristics, spatial trend and azimuth of anisotropic axle of iron and manganese contents were analyzed using the Geostatistical Analyst, ArcGIS 9.0. We created contour maps of iron and manganese contents for the study area using Kriging interpolation. Traditional statistical analysis （descriptive statistics） showed that the average contents of iron and manganese were 0. 27 mg/L and 0.10 mg/L. The coefficient of variation （CV） of iron and manganese contents were 52.12% and 30.34%.The iron criterion content in groundwater was high in general,42.86% of （less than 0.2 mg/L） prescribed by EU,25% of sample sample points did not reach the drinking water quality points did not reach the drinking water quality criterion （ less than 0.3 mg/L） prescribed by the Chinese Government and American Government. The highest value of iron content was 3.34 mg/L, which was exceed the national standard to a large extent. In generally, manganese content in groundwater was low,94.64% of sample points reached the drinking water quality criterion （less than 0.1 mg/L） prescribed by the Chinese Government, and 100% of sample points reached the drinking water quality criterion （less than 0.4 mg/L） prescribed by WHO. The geostatistics analysis showed that the trends of iron and manganese contents in groundwater were second order in the east--west and north--south direction, the structure variability of iron and manganese contents was all larger than the random variability, the spatial variability was obvious in northeast--southwest.. Spatial distribution characteristics of iron and manganese contents in shallow groundwater in the research area were similar, it decreased gradually from northeast to southwest, but increased near the town of Mingshan county. The highest value region mainly existed in the northeastern. The lowest value region mainly existed in the middle and south. The spatial distribution characteristics of iron and manganese contents in groundwater were closely related to hypsography, parent materials of soil, soil types and human activities. The iron and manganese contents in groundwater in regions of glacial till and fluvioglacial sediments of Quaternary System Pleistocene （ Q2fgL ） were significantly higher than in regions of purple rock of Cretaceous Jiaguan formation（ K2j ）, Cretaceous Guankou formation （K2g） and Tertiary Mingshan formation （ K1-2mn ）. The iron and manganese contents in groundwater in regions of yellow soil significantly higher than in regions of purple soil.