三江平原耕地土壤重金属元素分布特征及影响因素的多元统计分析
A multivariate statistical analysis of the distribution and influencing factors of heavy metal elements in the cultivated land of the Sanjiang Plain
通讯作者: 杨凤超(1982-),男,2018年毕业于吉林大学,博士,高级工程师,岩石学、矿物学、矿床学专业,主要从事土地督察及地质矿产调查研究工作。Email:yangfc123@163.com
责任编辑: 蒋实
收稿日期: 2022-01-27 修回日期: 2022-06-7
基金资助: |
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Received: 2022-01-27 Revised: 2022-06-7
作者简介 About authors
宋运红(1983-),女,2009年毕业于吉林大学,硕士,高级工程师,地球化学专业,主要从事黑土地形成与演化研究工作。Email:
地统计学和多元数据分析是讨论土壤中重金属元素来源的有效方法。对比不同地质背景区表层和深层土壤中重金属元素的含量和分布情况,可以为研究土壤中重金属元素的来源提供依据。三江平原是我国沼泽湿地分布相对集中的地区之一,属于温带湿润、半湿润大陆性季风气候,是我国重要的粮食生产基地,以农业生产为主。本次以三江平原为典型地区,从区域尺度上研究影响耕地土壤中的重金属元素分布的主要因素,分别对表层和深层土壤进行取样,计算As、Cr、Cu、Hg、Ni、Cd、Pb和Zn共8种重金属元素的最小值、最大值、中值、平均值、变异系数及富集系数。结果表明,三江平原土壤环境质量优越,表层土壤中重金属元素(除Cd外)As、Cr、Cu、Hg、Ni、Pb和Zn含量均略低于深层土壤;元素富集系数均小于2,仅有个别点位的表层Cd、Hg、As富集系数存在较大的值;通过地统计学和Pearson相关性分析,在5种成土母质区域,确定了表层和深层土壤中重金属元素的主要影响因子,综合分析表明, Cr、Cu、Ni和Zn的主要物质来源于成土母质,Cd、Hg、As在部分地区可能受到人类活动的叠加影响。
关键词:
Geostatistical and multivariate analyses are effective methods to determine the source of heavy metal elements in the soil. The comparison of the contents and distribution of heavy metal elements in the topsoil and subsoil in different geological setting areas can provide a basis for studying the sources of heavy metal elements in the soil. As one of the areas with concentrated marsh wetlands in China, the Sanjiang Plain has a temperate humid and subhumid continental monsoon climate, is an important grain production base, and has a low degree of industrial activities. This study investigated the main factors affecting the distribution of heavy metal elements in the soil of cultivated land of the Sanjiang Plain on a regional scale. Samples were collected from the topsoil and subsoil of the Sanjiang Plain. The minimum, maximum, median, and average contents, coefficient of variation, and concentration coefficient of eight heavy metal elements (i.e., As, Cr, Cu, Hg, Ni, Cd, Pb, and Zn) in the samples were calculated. The results are as follows. The Sanjiang Plain has superior soil environmental quality. The topsoil samples had slightly lower contents of heavy metal elements except for Cd (e.g., As, Cr, Cu, Hg, Ni, Pb, and Zn) than the subsoil samples. All these elements in the topsoil samples had concentration coefficients less than 2, except for those in the topsoil samples collected at certain points, which had high concentration coefficients of Cd, Hg, and As elements. The main factors influencing heavy metal elements in the topsoil and subsoil in five soil parent material regions were determined through geostatistical and Pearson correlation analyses. The comprehensive analysis results show that elements Cr, Cu, Ni, and Zn mainly originate from the soil parent materials, and Cd, Hg, and As may also be affected by human activities in some areas.
Keywords:
本文引用格式
宋运红, 杨凤超, 刘凯, 戴慧敏, 许江, 杨泽.
SONG Yun-Hong, YANG Feng-Chao, LIU Kai, DAI Hui-Min, XU Jiang, YANG Ze.
0 引言
东北黑土区是中国最大的商品粮基地,黑土区的土壤环境质量问题已经引起了许多科学工作者的普遍关注[1⇓⇓⇓⇓⇓⇓-8]。土壤中重金属元素的迁移转化是地球关键带物质循环的重要组成,元素通过生物地球化学过程迁移到水圈、生物圈和食物链,最终对人类健康产生影响[9⇓-11]。经典的道库恰耶夫学说认为,土壤是由母质、气候、生物、地形和时间五大自然因素综合作用的产物,在很大程度上,土壤中的元素分布与成土母质具有明显的继承关系[12-13],同时也不同程度的受到人类活动的影响[14-15]。因此,研究土壤中重金属元素的来源首先应该弄清土壤中元素和成土母质间的关系,在此基础上,确定人为因素对重金属元素分布的影响程度。
三江平原在保障国家粮食安全中具有举足轻重的地位。但是人类快速增长的农业及工业活动,都可能会引起某些重金属元素在耕地土壤中的积累。由于主要人类活动是农业,这里的土壤受到现代工业的污染较少,所以分析深层土壤中的微量含量对于表层土壤的研究非常重要。目前对三江平原耕地土壤重金属元素的特征研究较少,重金属元素的种类研究也不全,利用表层和深层土壤对比研究更是鲜有报道。本研究利用2018年最新获得的1:25万表层和深层土壤重金属元素数据,运用地统计学和多元数据分析的方法[20-21],对比研究三江平原表层和深层土壤中As、Cd、Cr、Cu、Hg、Ni、Pb、Zn的特征及相关性,分析8种重金属元素的来源,对于摸清东北黑土地家底,保护东北大粮仓,实现黑土资源的可持续利用具有重要意义。
1 研究区概况
三江平原,又称三江低地,位于东北平原东北部,是我国最大的淡水沼泽分布区。三江平原的“三江”即黑龙江、乌苏里江和松花江,3条大江浩浩荡荡,汇流、冲积而成了这块低平的沃土。区内水资源丰富,气候属温带湿润、半湿润大陆性季风气候,土壤类型主要有黑土、白浆土、草甸土、沼泽土等,而以草甸土和沼泽土分布最广。这里是我国重要的商品粮生产基地,粮食商品化程度和农业机械化程度全国第一,在保障国家粮食安全中具有举足轻重的地位。
2 材料与方法
2.1 样品采集和分析方法
研究区样品来源于中国地质调查局实施的“东北黑土地1:25万土地质量调查”项目,在研究区网格化部署采样点,表层土壤样品采样密度为1个点/km2,主要采集耕层土,采样深度为0~20 cm,4 km2组合成一个样品进行分析测试;深层土壤样品采样密度为1个点/4 km2,深度为150~200 cm,16 km2组合成一个样品分析。三江平原共取得9 873件表层和2 697件深层土壤地球化学样品(图1)。样品分析测试由吉林省地质科学研究所和黑龙江省地质矿产测试应用研究所完成,其中Cd、Ni采用等离子体质谱法,As、Hg采用原子荧光光度法,Cr、Cu、Pb、Zn采用X射线荧光光谱法测定。采用国家标准物质监控分析测试准确度,采用密码样监控分析测试的精密度,所有监控样元素分析准确度和精密度均在允许监控限内,数据可靠。
图1
2.2 数据处理及评价方法
表层和深层土壤样品的描述性统计分析及Pearson相关性分析均在SPSS 21.0软件中完成,采用Arcgis 10.2软件绘制克里格元素空间分布图。
式中:q为富集系数;Ci表、Ci深分别为表层和深层土壤中重金属元素的含量;CSc表、CSc深分别为表层和深层土壤中Sc元素的含量。
表1 三江平原耕地表层和深层土壤重金属元素含量统计
Table 1
参数 | As | Cd | Cr | Cu | Hg | Ni | Pb | Zn | Sc | |||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
全部表层土壤,N=9873 | ||||||||||||||||
平均值/10-6 | 8.85 | 0.083 | 65.09 | 21.76 | 0.034 | 25.69 | 25.62 | 63.52 | 11.75 | |||||||
中位数/10-6 | 8.40 | 0.075 | 65.30 | 21.90 | 0.031 | 24.90 | 25.5 | 62 | 11.9 | |||||||
变异系数/% | 37.26 | 50.83 | 18.78 | 22.16 | 54.73 | 22.73 | 10.70 | 20.87 | 15.51 | |||||||
数据范围/10-6 | 1.80~116.8 | 0.009~1.740 | 16.5~281 | 4~74 | 0.013~1.25 | 5.8~147 | 2.3~68.3 | 24.4~225.1 | 2.3~21.9 | |||||||
(平均值±标准离差)/10-6 | 8.41±1.30 | 0.076±1.39 | 64.27±1.18 | 21.38±1.24 | 0.032±1.282 | 25.06±1.22 | 25.53±1.10 | 62.09±1.21 | 11.72±1.16 | |||||||
黑龙江省A层背景值[24]/10-6 | 7.3 | 0.086 | 58.6 | 20 | 0.037 | 22.8 | 24.2 | 70.7 | 10.79 | |||||||
全部深层土壤,N=2697 | ||||||||||||||||
平均值/10-6 | 11.16 | 0.075 | 71.40 | 21.98 | 0.036 | 28.42 | 25.97 | 71.33 | 12.17 | |||||||
中位数/10-6 | 10.80 | 0.072 | 75.30 | 23.6 | 0.035 | 29.50 | 26.3 | 73.6 | 13.1 | |||||||
变异系数/% | 51.07 | 36.60 | 29.75 | 30.27 | 34.43 | 38.45 | 12.84 | 20.67 | 24.11 | |||||||
数据范围/10-6 | 1.82~225 | 0.013~0.36 | 9.6~371.6 | 2.5~98.25 | 0.006~0.274 | 3.4~294.4 | 10.75~49.6 | 13.8~142.5 | 1.6~24.6 | |||||||
(平均值±标准离差)/10-6 | 10.50±1.34 | 0.071±1.40 | 73.11±1.19 | 21.78±1.32 | 0.034±1.34 | 27.48±1.31 | 25.82±1.13 | 72.44±1.19 | 12.42±1.22 | |||||||
黑龙江省C层背景值[24]/10-6 | 11.4 | 0.078 | 59.5 | 21 | 0.040 | 24.3 | 24.4 | 69.9 | 无 | |||||||
第四系表层,N=8383 | ||||||||||||||||
平均值/10-6 | 8.21 | 0.079 | 65.50 | 21.88 | 0.032 | 25.43 | 25.18 | 60.47 | 11.65 | |||||||
中位数/10-6 | 8.00 | 0.072 | 65.70 | 22.40 | 0.031 | 24.80 | 25.10 | 58.00 | 11.80 | |||||||
变异系数/% | 27.55 | 44.36 | 18.15 | 21.39 | 47.43 | 19.61 | 9.16 | 20.45 | 15.93 | |||||||
数据范围/10-6 | 1.80~43.45 | 0.009~1.167 | 16.5~121.6 | 4~49.4 | 0.013~0.986 | 8.08~47.9 | 9.2~61.75 | 27.4~212.1 | 2.9~19.1 | |||||||
(平均值±标准离差)/10-6 | 7.96±1.26 | 0.074±1.42 | 64.86±1.19 | 21.52±1.24 | 0.031±1.253 | 25.00±1.21 | 25.12±1.08 | 59.16±1.21 | 11.61±1.16 | |||||||
变质岩表层,N=454 | ||||||||||||||||
平均值/10-6 | 10.32 | 0.093 | 69.98 | 21.64 | 0.034 | 27.11 | 27.90 | 72.45 | 12.29 | |||||||
中位数/10-6 | 9.98 | 0.083 | 70.00 | 21.45 | 0.030 | 26.50 | 27.40 | 71.05 | 12.40 | |||||||
变异系数/% | 41.44 | 59.11 | 20.61 | 24.02 | 50.82 | 23.00 | 12.39 | 21.32 | 13.01 | |||||||
数据范围/10-6 | 1.84~59.70 | 0.023~0.790 | 31.40~197.8 | 9.15~55.15 | 0.015~0.258 | 10.40~62.10 | 19.40~53.20 | 42.00~213.4 | 6.76~17.2 | |||||||
(平均值±标准离差)/10-6 | 9.71±1.32 | 0.083±1.30 | 68.39±1.17 | 20.94±1.23 | 0.031±1.303 | 26.61±1.23 | 27.67±1.11 | 70.47±1.18 | 12.27±1.14 | |||||||
沉积岩表层,N=481 | ||||||||||||||||
平均值/10-6 | 10.15 | 0.085 | 68.78 | 21.52 | 0.035 | 25.71 | 27.29 | 66.42 | 12.32 | |||||||
中位数/10-6 | 10.40 | 0.077 | 68.80 | 21.30 | 0.032 | 24.60 | 27.10 | 63.90 | 12.40 | |||||||
变异系数/% | 24.45 | 44.98 | 18.45 | 18.35 | 37.57 | 24.55 | 11.78 | 18.10 | 13.10 | |||||||
数据范围/10-6 | 4.32~19.4 | 0.032~0.445 | 29.85~167.7 | 9~39 | 0.018~0.180 | 9.3~67.2 | 19.9~46.6 | 44~119.7 | 6.58~18 | |||||||
(平均值±标准离差)/10-6 | 9.89±1.29 | 0.077±1.34 | 67.45±1.15 | 21.23±1.18 | 0.032±1.265 | 24.94±1.22 | 27.04±1.12 | 65.16±1.18 | 12.25±1.13 | |||||||
花岗岩表层,N=251 | ||||||||||||||||
平均值/10-6 | 10.03 | 0.085 | 69.16 | 20.40 | 0.039 | 26.73 | 28.03 | 71.55 | 12.06 | |||||||
中位数/10-6 | 9.70 | 0.081 | 68.10 | 20.10 | 0.032 | 25.60 | 27.80 | 69.90 | 12.20 | |||||||
变异系数/% | 38.19 | 30.83 | 21.65 | 20.20 | 198.07 | 22.73 | 14.36 | 15.21 | 12.20 | |||||||
数据范围/10-6 | 3.80~33.05 | 0.030~0.255 | 36.9~170 | 11.5~33.8 | 0.016~1.25 | 13.1~56.2 | 20.2~46 | 46.7~108.7 | 8.26~15.4 | |||||||
(平均值±标准离差)/10-6 | 9.31±1.37 | 0.081±1.27 | 66.99±1.17 | 20.0±1.23 | 0.032±1.309 | 25.88±1.21 | 27.67±1.14 | 70.80±1.16 | 11.97±1.14 | |||||||
参数 | As | Cd | Cr | Cu | Hg | Ni | Pb | Zn | Sc | |||||||
火山岩表层,N=304 | ||||||||||||||||
平均值/10-6 | 10.85 | 0.083 | 73.79 | 23.18 | 0.033 | 28.20 | 26.69 | 67.84 | 12.86 | |||||||
中位数/10-6 | 9.99 | 0.080 | 69.85 | 22.90 | 0.031 | 26.15 | 26.40 | 67.05 | 12.70 | |||||||
变异系数/% | 50.85 | 28.56 | 25.29 | 21.77 | 29.46 | 31.06 | 11.73 | 16.48 | 14.02 | |||||||
数据范围/10-6 | 4.76~63.80 | 0.041~0.20 | 45~163.3 | 13.05~43.2 | 0.019~0.095 | 15.8~65.50 | 17.3~37.60 | 43.35~105.3 | 7.51~21.8 | |||||||
(平均值±标准离差)/10-6 | 9.84±1.30 | 0.079±1.31 | 71.45±1.25 | 22.65±1.23 | 0.032±1.276 | 26.92±1.31 | 26.49±1.12 | 66.99±1.18 | 12.74±1.13 | |||||||
第四系深层,N=2214 | ||||||||||||||||
平均值/10-6 | 10.98 | 0.074 | 69.61 | 21.88 | 0.036 | 27.99 | 26.09 | 70.11 | 12.02 | |||||||
中位数/10-6 | 10.65 | 0.070 | 76.30 | 24.30 | 0.036 | 30.30 | 26.60 | 72.60 | 13.20 | |||||||
变异系数/% | 45.32 | 37.47 | 25.88 | 29.19 | 27.86 | 27.32 | 12.53 | 21.29 | 25.19 | |||||||
数据范围/10-6 | 2.35~225 | 0.013~0.22 | 9.6~262 | 2.5~38.9 | 0.006~0.095 | 3.4~146.9 | 14~49.6 | 13.8~120.8 | 1.6~24.6 | |||||||
(平均值±标准离差)/10-6 | 10.30±1.31 | 0.070±1.45 | 71.78±1.22 | 21.63±1.35 | 0.034±1.33 | 27.42±1.32 | 26.00±1.13 | 70.80±1.21 | 12.05±1.28 | |||||||
变质岩深层,N=115 | ||||||||||||||||
平均值/10-6 | 12.58 | 0.075 | 84.87 | 23.53 | 0.037 | 30.04 | 28.17 | 77.15 | 12.84 | |||||||
中位数/10-6 | 11.20 | 0.073 | 83.50 | 23.4 | 0.032 | 30.50 | 28 | 78.70 | 13.40 | |||||||
变异系数/% | 140.56 | 31.04 | 33.76 | 40.02 | 41.26 | 45.93 | 12.75 | 16.17 | 19.40 | |||||||
数据范围/10-6 | 2.27~225 | 0.028~0.18 | 12.9~301.3 | 3.5~98.25 | 0.011~0.128 | 5.2~154.4 | 10.75~40.3 | 21~117.5 | 2.96~24.6 | |||||||
(平均值±标准离差)/10-6 | 10.94±1.28 | 0.071±1.32 | 82.04±1.16 | 22.18±1.29 | 0.034±1.38 | 28.91±1.23 | 28.18±1.11 | 76.56±1.18 | 12.91±1.16 | |||||||
沉积岩深层,N=131 | ||||||||||||||||
平均值/10-6 | 11.32 | 0.073 | 80.62 | 23.03 | 0.038 | 29.63 | 27.32 | 74.15 | 12.91 | |||||||
中位数/10-6 | 11.30 | 0.071 | 79.80 | 23.6 | 0.037 | 29.20 | 27.3 | 75.00 | 13.20 | |||||||
变异系数/% | 28.61 | 30.57 | 20.99 | 22.93 | 32.25 | 26.65 | 11.71 | 14.90 | 17.76 | |||||||
数据范围/10-6 | 2.66~28.4 | 0.017~0.20 | 15.75~180.7 | 4.7~40.6 | 0.013~0.115 | 6.9~68.00 | 17.80~40.3 | 39.5~108.3 | 3.96~19.2 | |||||||
(平均值±标准离差)/10-6 | 10.99±1.24 | 0.070±1.30 | 79.62±1.16 | 22.86±1.24 | 0.036±1.32 | 28.45±1.27 | 27.23±1.11 | 73.45±1.17 | 12.97±1.17 | |||||||
花岗岩深层,N=134 | ||||||||||||||||
平均值/10-6 | 10.43 | 0.072 | 83.90 | 22.62 | 0.038 | 32.09 | 27.50 | 77.39 | 12.96 | |||||||
中位数/10-6 | 11.0 | 0.071 | 80.60 | 21.60 | 0.035 | 29.40 | 27.7 | 78.6 | 13.1 | |||||||
变异系数/% | 27.39 | 26.53 | 32.29 | 34.66 | 37.41 | 68.26 | 11.76 | 15.79 | 17.73 | |||||||
数据范围/10-6 | 3.72~21.3 | 0.041~0.16 | 24.9~251.1 | 8.1~76.1 | 0.015~0.128 | 9.9~202.9 | 14.2~35.1 | 48.4~117.7 | 7.28~24.3 | |||||||
(平均值±标准离差)/10-6 | 10.26±1.32 | 0.070±1.29 | 78.52±1.16 | 21.33±1.27 | 0.035±1.32 | 28.84±1.23 | 27.48±1.12 | 76.38±1.17 | 12.79±1.16 | |||||||
火山岩深层,N=105 | ||||||||||||||||
平均值/10-6 | 11.47 | 0.081 | 93.37 | 26.93 | 0.037 | 41.64 | 25.72 | 80.67 | 14.30 | |||||||
中位数/10-6 | 10.95 | 0.079 | 81.20 | 24.80 | 0.036 | 32.60 | 26.1 | 80.6 | 14.2 | |||||||
变异系数/% | 31.55 | 36.26 | 41.49 | 36.68 | 29.78 | 88.93 | 12.25 | 17.21 | 19.78 | |||||||
数据范围/10-6 | 2.39~28.4 | 0.032~0.33 | 45.4~262.6 | 10.2~76.1 | 0.013~0.115 | 15.5~294.4 | 14.2~40.5 | 42.8~142.5 | 6.15~24.3 | |||||||
(平均值±标准离差)/10-6 | 11.09±1.23 | 0.076±1.34 | 82.99±1.27 | 24.83±1.21 | 0.036±1.27 | 33.19±1.37 | 25.88±1.10 | 80.17±1.15 | 14.19±1.15 |
3 结果与讨论
3.1 统计分析和地球化学特征
3.2 表层土壤重金属元素含量分布
表层土壤中元素的含量特征一般反映人类活动及自然因素双重影响下土壤中元素的分布状态,受人类活动因素的影响较明显。本次统计三江平原8种重金属元素平均值、变异系数以及黑龙江省背景值列于表1,为了进一步描述重金属元素的分布特征,利用SPSS 21.0软件分别绘制了表层8种重金属元素的直方图和箱形图(图2、图3)。三江平原表层土壤中As、Ni、Cr、Cu、Pb、Zn、Cd和Hg的平均含量分别为8.85×10-6、25.69×10-6、65.09×10-6、21.76×10-6、25.62×10-6、63.52×10-6、0.083×10-6和0.034 ×10-6,与黑龙江省土壤A层背景值相比, Cd、Hg、Zn的平均值较黑龙江省略低,而As、Cr、Cu、Ni、Pb平均值大于黑龙江省背景值。在对数转换后,基本均显示服从正态分布。
图2
图2
表层土壤元素含量分布直方图
Fig.2
Histograms for heavy metal elements in topsoils from Sanjiang Plain
图3
图3
表层土壤元素含量分布箱型图
Fig.3
Box-plot diagram for heavy metal elements in topsoils from Sanjiang Plain
按照不同母质类型分别对表层土壤中8种元素进行描述性统计。如表1所示,母质为变质岩的土壤中As、Cd、Zn含量分别为10.32×10-6、0.093×10-6、72.45 ×10-6,较其他母质土壤含量高;母质为花岗岩的土壤中Pb含量为28.03×10-6,远高于其他母质土壤;母质为火山岩的土壤中Cr、Cu、Ni含量分别为73.79×10-6,、23.18×10-6、28.20×10-6,也较其他母质土壤较高;表明成土母质的岩性对土壤中重金属元素的含量有明显影响。
3.3 深层土壤重金属元素含量分布
深层土壤由于受人类活动的影响较小,更能代表成土母质中元素的含量特征。深层土壤中8种重金属元素的含量分布特征如图4所示。从箱型图中可以看出,研究区内,Cr平均含量最高(71.40 ×10-6),其次是Zn(71.33×10-6)、Ni(28.42×10-6)、Pb(25.97×10-6)、Cu(21.98 ×10-6) 、 As(11.16×10-6)、Cd(0.075×10-6)和Hg(0.036×10-6)。变质岩母质的土壤中As、Cr、Pb含量分别为12.58×10-6、84.87×10-6,28.17×10-6,较其他母质土壤高;火山岩母质的土壤中Cr、Ni、Zn含量分别为93.37×10-6、41.64×10-6、80.67×10-6,明显高于其他母质土壤。深层土壤除Cd外,其他7种元素均表现为表层土壤含量低于深层土壤含量。与表层土壤中的分布相似,深层土壤中8 种元素在对数转换后,基本均显示服从正态分布(图5)。
图4
图4
深层土壤元素含量分布箱型图
Fig.4
Box-plot diagram for heavy metal elements insubsoils from Sanjiang Plain
图5
图5
深层土壤元素含量分布直方图
Fig.5
Histograms for heavy metal elements in subsoils from Sanjiang Plain
3.4 深层土壤重金属元素空间分布
表层土壤反映了地球关键带中物质的相互作用及循环过程,而深层土壤则反映成土母质的地质背景。表层和深层土壤的重金属元素空间分布显示见图6、图7,总体上,表层和深层土壤重金属元素高值区分布较一致,以松花江为界,左侧低、右侧高,形成明显的分界线,与深层元素分布比较,总体上表层土壤均未受到明显的重金属元素污染,说明三江平原土壤环境质量依然优越,仅发现同江市东北部土壤As、Cd、Cu、Ni表层较深层稍偏高,有轻微富集的趋势,佳木斯市表层土壤Hg较深层有富集的趋势,推测可能受到了人为活动的影响,这可能与城市化发展密切相关[25⇓-27]。表层土壤中变质岩区Cd、Zn均值含量高,火山岩区As、Cr、Cu、Ni含量高,花岗岩区Pb含量高;深层土壤在火山岩区中As、Cr、Cu、Ni、Zn含量高,变质岩区Cd、Pb含量高,这与表层分布相似,可以推断三江平原土壤中重金属元素主要来源主要是成土母质。
图6
图6
三江平原表层土壤重金属元素空间分布
Fig.6
Spatial distribution of heavy metal elements concentrations in the top soil from Sanjiang Plain
图7
图7
三江平原深层土壤重金属元素空间分布
Fig.7
Spatial distribution of heavy elements concentrations in the deep soil from Sanjiang Plain
区域上,影响三江平原表层土壤中重金属元素分布的主要因素是成土母质和少量的人类活动。8种重金属元素富集系数均小于2(表1),表明三江平原表层土壤中8种重金属元素均无潜在污染风险,仅有某些点位的表层土壤中Cd、Hg、As元素的富集系数存在较大的值,说明在部分地区可能受到人类活动的影响稍大。
岩石风化是土壤中重金属元素的主要自然来源,土壤中的元素分布与成土母质具有明显的继承关系。本次利用Pearson相关性分析分别计算了三江平原所有类型的成土母质区域内,表层和深层土壤中重金属元素之间的相关系数(表2),结果显示Cr、Cu、Ni和Zn分别呈显著正相关(相关系数0.3~0.6,P<0.01),说明表层土壤中这些重金属元素主要来源于深层土壤(成土母质),较少受到人类活动的干扰。但是,As、Cd、Hg和Pb在不同的母岩区均显示相关性较弱,表明三江平原表层土壤中的As、Cd、Hg和Pb可能受到人类活动的影响,如农业生产中的农药和化肥的施用等。
表2 三江平原表层及深层土壤中重金属元素间相关系数
Table 2
元素 | Pearson相关系数 | ||||
---|---|---|---|---|---|
第四系 | 变质岩 | 沉积岩 | 花岗岩 | 火山岩 | |
As | 0.018 | 0.009 | 0.380** | 0.266** | 0.216** |
Cd | 0.332** | 0.178** | 0.176** | 0.091 | 0.140* |
Cr | 0.602** | 0.185** | 0.480** | 0.395** | 0.625** |
Cu | 0.584** | 0.308** | 0.440** | 0.512** | 0.414** |
Hg | 0.137** | 0.250** | 0.218** | 0.100 | 0.249** |
Ni | 0.500** | 0.252** | 0.527** | 0.488** | 0.449** |
Pb | 0.264** | 0.206** | 0.268** | 0.367** | 0.045 |
Zn | 0.314** | 0.333** | 0.299** | 0.203** | 0.470** |
注:“**”表示在0.01级别相关性显著,“*”表示在0.05级别上相关性显著。
4 结论
1)三江平原土壤总体上表现为环境质量依然优越,除Cd外,表层土壤中重金属元素As、Cr、Cu、Hg、Ni、Pb和Zn含量(8.85×10-6、65.09×10-6、21.76×10-6、0.034×10-6、25.69×10-6、25.62×10-6、63.52×10-6)均略低于深层土壤。
2)表层和深层土壤的重金属元素Cd、Cr、Cu、Ni、Pb和Zn空间分布较一致,表现为以松花江为界,左侧低、右侧高,形成明显的分界线。
3)表层相对于深层土壤的重金属元素富集系数均小于2,仅个别点位的表层Cd、Hg、As富集系数存在相对较高的值,在部分地区可能受到人类活动的叠加影响。
4)在不同成土母质区域,表层和深层土壤中重金属元素Cr、Cu、Ni和Zn均呈显著正相关(相关系数0.3~0.6,P<0.01),表明表层土壤中这些重金属元素主要物质来源于成土母质。
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