莫索湾灌区棉田土壤重金属分布特征和评价及Cr污染修复效果研究

发布时间：2018-09-05 20:31

【摘要】：本文以新疆玛纳斯河流域莫索湾灌区为研究区域,通过区域调查分析和田间定位试验选取5a、10a、20a、30a棉田土壤与荒地土壤对比等方法,分析棉田耕作过程中土壤重金属的剖面分布特征和累积状况;利用地统计插值方法估测出研究区表层土壤重金属含量的空间分布规律,为该灌区的棉田土壤环境质量保护提供基础数据;选取灌区污染较重的Cr元素为改良对象,通过室内培养试验,揭示了几种化学改良剂对土壤中Cr的形态分布及转化的影响,得到以下主要结论:(1)棉田土壤(0~100 cm)重金属Cr、Ni、Cu、As、Pb含量分别为90.65、32.22、52.64、10.90、13.86 mg/kg,荒地土壤分别为78.21、32.34、44.16、9.48、13.91 mg/kg,Cr、Ni、Cu、As在棉田土壤中的含量显著大于荒地,且均高于新疆土壤背景值,Pb含量两者相差不大,均低于背景值。棉田土壤中5种重金属元素的变异系数均大于荒地土壤,属于中等变异。(2)对5a、10a、20a、30a棉田土壤不同剖面分布特征发现,随着连作年限的增加,Cr、Ni、Cu、As、Pb五种重金属在1 m土层均有所增加,且不同连作年限间差异显著;表层土壤的重金属含量显著高于底层,连作30年的棉田土壤垂直分布趋势更为明显。通过土壤元素相关性分析发现,棉田土壤中Cr、Cu、As和Ni重金属元素的累积主要由磷肥的施入造成的,而荒地土壤中重金属元素与N、P、K、pH之间的相关性不显著,进一步说明了棉田连作过程化肥的长期大量施入会对土壤重金属产生累积。(3)对便携式X射线荧光光谱仪的实用性进行了建模探究和模型验证,验证模型R2分别为0.9124、0.8979、0.7723、0.8729 mg/kg,斜率与截距得到优化,较接近理想模型,校准后的检测结果与传统实验室ICP-AES检测结果呈极显著正相关关系。通过二次采样的36~50号土壤样品组建的验证模型可以充分证明PXRF异位法的实用性和校准曲线的高准确性。(4)通过使用便携式X射线荧光光谱仪对灌区表层土壤重金属含量进行速效测定,土壤重金属含量变异函数和模型拟合发现:Cr、As以指数模型最佳,Ni、Pb以高斯模型最佳,Cu以球型模型最佳,Cr、Cu的块金效应分别为0.86、0.92,空间自相关性较弱,受人为随机因素影响较大,Ni、As、Pb的块金效应分别为0.57、0.41和0.46,空间相关性中等,受人为随机因素和空间结构因素的共同作用影响;研究区当前整体污染评价结果为Cr、As两种元素趋近轻微污染水平,Ni对土壤环境造成轻度污染。(5)利用盆栽试验研究不同改良剂对土壤重金属Cr的修复效果研究发现:改良剂的施入可以抑制Cr的可交换态含量,同时在一定程度上会增加土壤pH值,随着污染浓度的增加,对pH值影响力逐渐下降,但始终高于CK。4种改良剂中,以钙镁磷肥的改良效果最佳,土壤中可交换态含量先降低后升高,残渣态含量先升高后降低,最终表现为可交换态含量降低。石灰的改良效果仅次于钙镁磷肥,它主要使Cr的可交换态转化为铁锰氧化物结合态。两种改良剂效果显著高于活性炭与秸秆,但其对Cr可交换态含量降低的影响时间较短,在第42天后可交换态含量出现回升。活性炭主要将可交换态转化为有机物结合态,且在第56天后其含量出现升高趋势的现象,但改良效果低于钙镁磷肥和石灰。而秸秆施入对土壤pH值和Cr可交换态含量影响均不显著,这与改良的施入量和培养时间有关。综上所述,棉田长年连作的种植措施会导致土壤重金属累积加重,且主要富集在表层土壤。整个灌区棉田土壤环境尚属于无污染,但接近轻度污染水平,应在以后的种植过程中做好对重金属污染的防控工作。向Cr污染土壤中施入改良剂,会造成土壤pH有一定程度的升高,Cr的可交换态含量随着时间的变化最终含量有所下降,从而降低了土壤中Cr的生物有效性,达到了修复Cr污染土壤的目的。
[Abstract]:In this paper, the distribution characteristics and accumulation of heavy metals in soils under cotton cultivation in Mosuowan Irrigation Area of Manas River Basin in Xinjiang were analyzed by means of regional investigation and field location test. The table of the study area was estimated by geostatistical interpolation method. The spatial distribution of heavy metals in soil layers provides basic data for the protection of soil environmental quality in cotton field of the irrigation area. The Cr element which is heavily polluted in the irrigation area is selected as the improvement object. Through indoor culture experiment, the effects of several chemical amendments on the distribution and transformation of Cr in soil are revealed. The main conclusions are as follows: (1) Cotton field The contents of heavy metals Cr, Ni, Cu, As and Pb in soils (0-100 cm) were 90.65, 32.22, 52.64, 10.90, 13.86 mg/kg, respectively, and those in wasteland soils were 78.21, 32.34, 44.16, 9.48, 13.91 mg/kg, respectively. The contents of Cr, Ni, Cu and As in cotton soils were significantly higher than those in wasteland, and higher than those in Xinjiang soils. The differences of Pb contents between the two soils were not significant, but lower than those in cotton soils. The variation coefficients of heavy metals in cotton soils were higher than those in wasteland soils, which belonged to moderate variation. The results showed that the accumulation of Cr, Cu, As and Ni in cotton field soil was mainly caused by the application of phosphorus fertilizer, but the correlation between heavy metal elements and N, P, K, pH in wasteland soil was not significant, which further explained the continuous cropping of cotton field. (3) The practicability of portable X-ray fluorescence spectrometer was studied and validated. The validation models R2 were 0.9124, 0.8979, 0.7723, 0.8729 mg/kg, respectively. The slope and intercept were optimized, which were close to the ideal model. The calibration results were compared with the traditional laboratory. The results of ICP-AES test showed a very significant positive correlation. The practicability of PXRF heterotopic method and the high accuracy of calibration curve can be fully proved by the validation model of secondary sampling of 36-50 soil samples. (4) Using portable X-ray fluorescence spectrometer to determine the heavy metal content in surface soil of irrigation area, the heavy metal content in soil can be determined quickly. Content variation function and model fitting showed that Cr, As were the best in exponential model, Ni, Pb were the best in Gaussian model, Cu was the best in spherical model, Cr and Cu were 0.86, 0.92 respectively, and the spatial autocorrelation was weak, which was influenced by human random factors. The spatial correlation of Ni, As and Pb were 0.57, 0.41 and 0.46, respectively, with moderate spatial correlation, which was followed by human activities. The results showed that Cr and As were slightly polluted and Ni were slightly polluted. (5) Pot experiment was used to study the remediation effect of different amendments on heavy metal Cr in soil. Exchangeable state content and soil pH value increase to a certain extent. With the increase of pollution concentration, the influence on pH value decreases gradually, but the effect of calcium magnesium phosphate fertilizer is better than CK.4. Exchangeable state content of soil first decreases and then increases, residual state content first increases and then decreases, and finally shows exchangeable state. The effect of the two modifiers was significantly higher than that of the activated carbon and straw, but their effect on the reduction of the exchangeable state content of Cr was shorter. The exchangeable state content of Cr increased after 42 days. The effect of straw application on soil pH and Cr exchangeable state content was not significant, which was related to the amount of improved application and cultivation time. The soil environment of cotton field in the whole irrigation area is not polluted, but it is close to the level of slight pollution. It is necessary to do a good job in the prevention and control of heavy metal pollution in the future planting process. Exchangeable state content decreased with time, which reduced the bioavailability of Cr in soil and achieved the purpose of remediation of Cr contaminated soil.
【学位授予单位】：石河子大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：X53;X825

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