【作者】 苏春田；

【导师】 单海平；

【作者基本信息】 广西师范大学 ， 生态学， 2008， 硕士

【摘要】 本文针对农田生态系统中土壤这一关键要素,围绕铁锰结核-土壤-旱地作物中元素含量关系以及土壤肥力、土壤环境质量、旱地作物食用部分质量等问题,以黎塘岩溶区为例,开展了取样调查、室内实验及理论分析,结果表明:1、研究区土壤以硅质土为主,其特点是高硅低钠锰。土壤多呈中性,A层土壤有机质、全氮、有效氮、全磷、有效磷、全钾、阳离子交换量的含量与肥力指标普遍高于B层,有效磷、全钾肥力指标整体表现为甚缺乏,其含量不能满足旱地作物的正常生长需要,已成为旱地作物生长的主要限制因子。2、研究区铁锰结核表面多呈黄棕色且表面光滑,形态上为球状、次球状或椭球状;A、B层铁锰结核氧化物含量均以SiO2、Al2O3、Fe2O3为主,以高Fe低Mn为主要特征,与土壤相比,铁锰结核对Fe2O3和MnO具有明显的富集效应,并且Fe2O3的富集程度大于MnO,垂向上,B层铁锰结核对Fe2O3、MnO的富集程度又高于A层。铁锰结核对Si、Mg、Ca、Na、K、Ti等元素具有成核减弱的效应,对P元素具有专性吸附的效应。A、B层铁锰结核重金属元素Pb、Co、Cr、Ni、Zn、Li含量均超过地壳元素克拉克值,各重金属平均含量顺序均为Cr(Ⅵ)>Zn>Pb>Ba>Co>Ni>Li>Hg,但同一重金属元素含量在深度上具有明显差异,B层元素含量普遍是A层元素含量的1.5倍。A、B层铁锰结核对重金属元素的富集系数具有一定差异,纵向上,B层铁锰结核的富集系数普遍高于A层,富集系数的大小顺序也有一定差异,但都以铁族元素(Cr、Co、Ni)和亲硫元素(Zn、Pb)占主导地位,造岩元素(Ba、Li)居次要地位。其中,Cr(Ⅵ)、Co和Zn表现为高度富集,Pb表现为高度或中度富集,Ni表现为中度富集,Ba表现为中度或轻微富集,Li表现为轻微富集。元素的相关矩阵表明重金属元素的富集主要与氧化铁有关,因子分析表明铁锰结核具有成核富集效应、专性吸附效应和成核易淋溶效应的特点。3、研究区A层土壤6种重金属的平均含量分别为Pb 53.55mg/kg、Co 15.47 mg/kg、Cr(Ⅵ) 243.30mg/kg、Ni 20.34mg/kg、Zn 116.14mg/kg、Cu 12.01mg/kg, B层土壤6种重金属的平均含量分别为Pb 51.95mg/kg、Co 24.94mg/kg、Cr(Ⅵ)208.28mg/kg、Ni 33.95mg/kg、Zn 159.86mg/kg、Cu 14.99mg/kg。与广西土壤元素背景值相比较,A层土壤Pb、Co、Cr(Ⅵ)和Zn的含量偏高,而Ni、Cu的含量偏少,B层土壤Pb、Co、Cr(Ⅵ)、Ni和Zn含量偏高,Cu含量偏低;与全国土壤元素背景值相比较,A层土壤Pb、Co、Cr(Ⅵ)、Zn和Cu含量偏高,而Ni含量偏少,B层土壤重金属元素Pb、Co、Cr(Ⅵ)、Ni、Zn和Cu的含量偏高;与绿色食品产地环境质量标准值相比较,A、B层土壤重金属元素Pb、Cr(Ⅵ)和Zn的平均含量超过其警戒值;按国家土壤环境质量二级标准来看,A、B层土壤重金属元素Cr(Ⅵ)的平均含量已超过其警戒值。本文使用单因子污染指数法、综合污染指数法、污染负荷指数法和潜在生态危害指数法对土壤重金属进行了污染评价。结果表明重金属元素Pb、Co、Cr、Ni、Zn对土壤造成了一定程度的污染,尤以Cr污染较为严重,各样地土壤污染程度为轻微或中等污染、甚至达到了重污染。土壤质量评价结果表明以国家土壤环境质量二级标准作为评价标准时,A、B层土壤Cr的质量级别为中等,1#样地A层土壤、3#样地A、B层土壤的综合质量级别为中等,其余为警戒级;以绿色食品产地土壤环境质量作为评价标准时,A层土壤Pb、Zn质量级别为中等,Cr为坏,各样地综合质量级别为中等,B层土壤Pb、Cr、Zn质量级别为中等,各样地综合质量级别为中等。4、研究区旱地作物食用部分重金属含量对比表明As、Cd和Pb含量最高的是白萝卜根,Cr、Cu和Zn含量最高的是黄瓜果实,玉米种子中Cd、Cr、Cu和Pb含量最低,甘蔗茎中As和Zn含量最低。4种旱地作物对Zn、Pb和Cu的富集系数较高,Cd、As和Cr的富集系数较小,但富集系数均小于1。旱地作物质量评价结果表明,玉米种子中6种重金属质量级别均为好,综合质量级别为安全,可放心食用;甘蔗茎、白萝卜根和黄瓜果实中Pb、Cd质量级别为很坏,Zn的质量级别为中等,综合质量级别为很坏;生态风险评价表明白萝卜根和黄瓜果实中Pb元素含量大大超过PTWI水平,As元素略高于PTWI,其健康风险指数也大于1,说明长期食用会对人体产生潜在的健康风险。更多还原

【Abstract】 Addressed to soil,a key element in the field ecosystem,to find out the relationship of elements contents in Fe-Mn nodules,soil and dryland crops,and solve the problems like soil fertility, soil environmental quality and the quality of edible parts of dryland crops,we carried out sample survey,indoor experiment and theoretical analysis(take the karst area in Litang for example).The results were as follows:Firstly,the characteristic of the soil in the study area was high silicon and low sodium and manganese.The soil was mostly neutral.The fertility indicators of the organic matter、total N、available N、total P、avaliable P、total K and CEC in A layer soil were higher than those in B layer.The fertility indicators of available P and total K were quite lack,its contents can not meet the normal growth of crops and it has become the mail limiting factors.Secondly,the surface of Fe-Mn nodules were mostly yellow brown and smooth,the shape was sphere、spherical or globular ellipsoid. SiO2、Al2O3 and Fe2O3 were still the main chemical elements in Fe-Mn nodules,compared with soils, the Fe-Mn nodules’enrichment effect on Fe2O3 and MnO was obvious and the degree of enrichment of Fe2O3 was higher than that of MnO, Vertical,the enrichment effect on Fe2O3 and MnO in B layer was higher than that in A layer. Elements of Si,Mg,Ca,Na,K,Ti were weaking and P was specific adsorption effect in Fe-Mn nodules.Heavy metal contents in A、B layer of Fe-Mn nodules such as Pb、Co、Cr、Ni、Zn、Li were higher than clark value,it’s order of average concents was Cr (Ⅵ)> Zn> Pb> Ba> Co> Ni> Li> Hg,However,the same heavy metal contents were obviously difference in depth,it’s contents in B layer were 1.5 times as much as in A layer.The enrichment coefficient of heavy metals in A、B layer of Fe-Mn nodules had some differences vertical, its coefficient of concentration is generally higher in B layer than that in A layer,and its order and magnitude was also different in some extent. But iron group elements (Cr、Co、Ni) and the pro-sulfur elements (Zn、Pb) were dominating status,rock-forming elements (Ba、Li) were following status. Among them,Cr (Ⅵ)、Co and Zn indicated high enrichment, Pb was high or moderate enrichment,Ni was moderate enrichment,Ba was moderate or slight enrichment,Li was slight enrichment.Correlation matrix analysis showed that enrichments of heavy meatal were related to Fe2O3,there existed nuclear enrichment,specific adsorption and leaching features by factor analysis.Thirdly,the average contents of the six kind of heavy metals in A layer soil were like this:Pb 53.55 mg / kg、Co 15.47 mg / kg、Cr (Ⅵ) 243.30mg/kg、Ni 20.34mg/kg、Zn 116.14mg/kg、Cu 12.01mg / kg,while B layer were like this:Pb 51.95mg/kg、Co 24.94mg/kg、Cr (Ⅵ) 208.28mg/kg、Ni 33.95mg/kg、Zn 159.86mg/kg、Cu 14.99mg/kg. Compared with background values of elements in Guangxi soil,Pb、Co、Cr (Ⅵ)、Ni were higher and Ni、Cu were lower in A layer soil, while Pb、Co、Cr (Ⅵ)、Ni、Zn were higher and Cu was lower in B layer soil; When compared with background values of elements in country soil,Pb、Co、Cr (Ⅵ)、Zn、Cu were higher and Ni was lower in A layer soil, while Pb、Co、Cr (Ⅵ)、Ni、Zn、Cu were higher;When compared with quality standard of gree food environment, heavy metals such as Pb、Cr (Ⅵ) and Zn in A、B layer were more than alert level;According to quanlity standards(Ⅱ) of country ,Cr (Ⅵ) in A、B layer soil had already exceeded warning level.Ways of single-factor pollution index、the comprehensive index pollution index、pollution load index and potential ecological risk index were used to evaluate heavy metal of the soil,the results showed that the soil were polluted by heavy metals such as Pb、Co、Cr、Ni、Zn, among them ,the pollution caused by element of Cr was particularly serious,pollution degree of every plots were slight、moderate , even heavy pollution. With environmental quality of national soil standards as evaluation criterion ,quality degree of Cr in A、B layer was medium,comprehensive quality degree was medium in A layer soil of 1# and A、B layer soil of 3#,others were alert level.With environment quality of green food as evaluation criterion ,Pb、Zn were medium and Cr was bad in A layer,Pb、Cr、Zn were medium in B layer, comprehensive quality degree in every plots are medium.Fourth,compared with heavy metal contents in the edible parts of dryland crops, contents of As、Cd、Pb were the highest in white radish ,contents of Cr、Cu、Zn were the highest in the cucumber ,contents of Cd、Cr、Cu、Pb were the minimum in the maize,contents of As and Zn were the minium in the sugar cane. Enchrichment coefficient was all less than 1,among them Zn、Pb、Cu were more high while Cd、As、Cr were low.Results of quality evaluation in dryland crop showed that the quanlity critieron of the six heavy metals in maize seed were good and comprehensive quality level was safe.The quality level of Pb、Cd were very very bad and Zn was medium in sugar cane、white radish and cucumber,it’s comprehensive quality critieron was very bad;Ecological risk assessment showed that Pb was greatly exceeding the PTWI level and As was slightly high than PTWI level in the carrot and cucumber, it would be harmful to human health if we ate them as food for a long time.更多还原