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模拟酸雨对典型紫色母岩风化特征的影响
Alternative TitleEffects of Simulated Acid Rain on Weathering Characteristics of Typical Purple Parent Rock
赵吉霞
Subtype博士
Thesis Advisor刘刚才
2018
Degree Grantor中国科学院大学
Place of Conferral北京
Degree Discipline土壤学
Keyword紫色母岩 模拟酸雨 崩解特征 离子释放
Abstract紫色母岩在环境酸化条下的风化作用的研究,不仅对于我们认识土壤生态系统酸沉降敏感性具有重要的意义,而且可以为精准确定紫色土的容许土壤流失量等提供科学依据。因此,为了分析典型紫色母岩在风化过程中对酸化环境的响应机理,以侏罗纪紫色岩层中的遂宁组(J3s)、沙溪庙组(J2s)和蓬莱镇组(J3p)为研究对象,通过室内模拟不同的酸化环境,采用浸泡循环试验和动态淋溶实验,研究不同pH值的酸溶液下的母岩崩解特征及风化过程中离子的释放规律,定量分析母岩风化速率与溶液pH值的相互关系,并探讨了母岩风化产物特征对酸溶液的响应机制,初步取得了以下一些结论和认识:(1)同组母岩在不同pH值酸溶液浸泡处理中的崩解方式基本一致,而且酸性越强,崩解程度越深。遂宁组和沙溪庙组母岩基本呈现溃散式崩解,且崩解前期遂宁组崩解能力大于沙溪庙组,而后期则相反;蓬莱镇组母岩则呈分离式崩解,且整个崩解过程中崩解能力明显小于遂宁组和沙溪庙组;浸泡液pH对母岩崩解影响显着,溶液酸度越大,崩解越迅速,崩解颗粒分维数的增长也越快。经24次崩解循环后,遂宁组和沙溪庙组母岩在不同pH酸溶液处理下的崩解分维数均趋近于3,崩解基本达稳定,且溶液酸性越强,崩解趋于稳定所需的循环次数越少。而此时,蓬莱镇组崩解颗粒分维数值介于2.586~2.759之间,母岩崩解未达稳定状态;(2)3组母岩浸泡处理后溶液的pH值从2.5~7.0上升为7.40~8.76,且基本呈现先增加后降低的趋势。浸泡液中的离子释放量以Ca2+最高,Mg2+、Na+ 次之,K+最小。基于每次浸泡过程中的盐基离子总量(K+、Na+、Ca2+、Mg2+)的释放速率及温度的变化情况,通过多元非线性回归建立了溶液酸度变化条件下的盐基离子释放速率的定量分析模型,表明同时考虑温度和溶液酸度影响下的双变量模型相关系数R2都在0.88以上,均呈极显着性相关(p﹤0.001),且相关系数均明显高于仅考虑温度或溶液酸度影响下的偏相关系数;3组母岩中盐基离子的累计释放量呈蓬莱镇组>遂宁组>沙溪庙组,且各离子累计释放量随pH值的增大呈指数递减趋势(p < 0.001),相关系数均大于0.97;(3)与淋溶前各径级的母岩颗粒组成相比,淋溶液酸性越强,3组母岩粒径小于5mm颗粒含量增幅越大,且遂宁组和沙溪庙组母岩粒径大于20mm颗粒含量减幅越大,而蓬莱镇组大颗粒减幅随淋溶液pH变化无统一的规律呈现;3组母岩在不同pH值降雨淋溶处理下的颗粒直径小于5mm组分含量变幅均为遂宁组>沙溪庙组>蓬莱镇组。遂宁组母岩覆土淋溶处理的各粒径变化幅度较裸岩淋溶处理低,但其规律基本一致,且各粒组含量的变幅随覆盖土层厚度的增加基本呈降低趋势。(4)模拟不同pH值降雨淋溶处理下的母岩风化成土速率表现为遂宁组>沙溪庙组>蓬莱镇组,酸性越强,母岩风化成土率越高,且其成土率随累计淋溶量增加的幅度也越大,经pH值为2.5、3.5、4.5、5.6和7.0的模拟降雨累计淋溶量达2a降雨量时,遂宁组、沙溪庙组和蓬莱镇组母岩的成土率较1a降雨量时分别提高了0.28~1.86倍、0.16~1.82倍和0.27~1.60倍,3组母岩年均成土率与pH均呈显着的(p<0.05)指数函数关系。与裸岩淋溶相比,对遂宁组母岩进行覆土淋溶显着降低了母岩的风化成土速率,覆盖土层厚度越深,母岩风化成土率越低;(5)模拟不同pH值降雨淋溶处理下的母岩淋出液pH随累计淋溶量的增加呈波动上升趋势,且相同淋溶条件下的遂宁组母岩经覆土处理后的淋出液pH值较裸岩淋溶高;3组母岩淋出液的电导率变化与淋出液pH均呈显着的负相关关系(p<0.05),均以遂宁组>蓬莱镇组>沙溪庙组 ,且淋溶液电导率值随处理液酸度的增加而增大;(6)模拟不同pH值酸雨淋溶处理下的3组母岩中盐基离子的释放量与浸泡处理的结果一致,均以Ca2+为最高,占各母岩盐基离子淋失总量的44%以上,Na+和Mg2+淋失量次之,K+的淋失量最低,不足盐基离子淋失总量的5%;累计模拟2a降雨量处理下的3组母岩盐基离子淋失总量为遂宁组>蓬莱镇>沙溪庙组,且盐基离子释放总量随淋溶液pH值增加呈指数递减,拟合系数R2都在0.99以上,呈极显着相关(p﹤0. 001)。模拟降雨淋溶比浸泡处理更有利于盐基离子的释放,基于相同的浸泡和淋溶次数,且水-岩比例一致的条件下,淋溶处理下的3组母岩盐基离子释放量较浸泡处理大都呈不同程度的增加,增幅介于3.98%~59.11%之间,平均增幅达25.09%;(7)不同pH值模拟降雨淋溶处理下的3组母岩盐基离子的释放量基本与淋溶前后粒径大于10mm颗粒含量的变化率呈负相关关系,且相关性基本不显着(p>0.05);而与小于5mm的颗粒组分含量的增幅基本都呈正相关关系,且相关性基本达显着(p<0.05)或极显着水平(p<0.01)。母岩的物理风化速率与化学风化速率间存在显着(p<0.01)的指数相关关系,且降雨pH值对盐基淋失作用的影响明显大于其对物理风化成土率的影响;(8)不同pH值酸浸泡处理后的母岩风化产物(粒径<2mm部分)中交换性盐基离子总量随处理pH值降低而减少,且与风化产物的酸缓冲容量均呈显着的正相关关系(p<0.05)。沙溪庙组母岩在不同酸处理下的风化产物酸缓冲容量差异较小,其值介于5.10~6.76 mmol/kg.pHunit间,且明显低于遂宁组(26.65~33.11mmol/kg.pHunit)和蓬莱镇组(18.83~23.86 mmol/kg.pHunit);(9)模拟降雨酸度和降雨量均对母岩风化产物中的交换性盐基离子含量有直接作用,适度的模拟酸雨淋溶(累计淋溶达1a降雨量),可以增加母岩中可交换盐基离子的活性,使风化产物中交换性盐基离子总量随处理pH的降低基本呈现增加趋势。但随着酸雨淋溶量的增加至达2a降雨量时,3组母岩风化产物中的交换性盐基总量均有不同程度的降低,且以pH2.5处理下的母岩风化产物中的交换性盐基离子总量降幅最大,超过20%,导致3组母岩风化产物中交换性盐基总量均随淋溶液pH值降低而降低。 
Other AbstractThe research on the weathering of the purple parent rock under acidification environment not only has important significance for us to understand the soil sensitivity to acid deposition, but also provide a scientific basis for accurately determing the soil loss tolerance of purple soil. Therefore, in order to study the response mechanism of typical purple parent rock to acidification environment during weathering, three types of purple rock were sampled and tested: from Suining Group (J3s), Shaximiao Group (J2s), and Penglaizhen Group (J3p), the paper simulates different acidizing environment in the laboratory, and immersion cycle test and dynamic leaching experiment were used. In this paper, the impacts of a solution’s pH on disintegration and cation release from the purple rock were studied to quantitative analyze the relationship between the weathering rate of parent rock and pH value of solution, and the response mechanism of weathering product characteristics of parent rock to acid solution is discussed. The following conclusions and understandings are preliminarily obtained:(1) The patterns of the each purple rock group disintegration were similar under treatment soaked at different pH values, but differed in the degrees of reaction. The purple rock of J3s and J2s disintegrated in a scattered way in solutions, and the disintegration ability of J3s was larger than that of J2s in the early stage of disintegration, whereas opposite in the late stage. The purple rock of J3p disintegrating separately, and the disintegrating ability was obviously less than that of J3s and J2s in the whole process of disintegration. The pH value played an important role in the disintegration of purple rock. The lower the pH value, the stronger the disintegration was. The fractal dimension of J3s and J2s under different pH values approached to 3 after 24 test cycles, and the lower the pH solution, the fewer cycles to obtain the stable fractal dimension, while the fractal dimension of J3p were 2.586-2.759 and didn’t reach the stable fractal dimension. (2) The pH value of the soaking solution increased from 2.5-7.0 to 7.40-8.76 to be alkalescency under various treatments, which increased first and then decreased, and all curves showed “sharp peaks” when measured between the cycles of the experiment. The amount of cations release in soaking was the highest in Ca2+, followed by Mg2+ and Na+, and K+ was the lowest. Based on the rate of total base cations and natural temperature under each soaking, the quantitative model of chemical weathering rate of base cations with varied acid conditions was obtained by nonlinear multivariate regression. The results showed that the models for cation release rates fit the observed data well when the two variables were introduced (i.e. H+ concentration and air temperature) with the correlation coefficients (R2) more than 0.88 (p﹤0.001), which were higher than the partial correlation coefficients. The release amount of base cations in 3 groups of parent rocks were J3p > J3s > J2s, and the amount of individual cations that were released appeared to significant exponentially decrease (p < 0.001) as pH increased, with correlation coefficients (R2) being above 0.97.(3) Compared with the parent rock particle composition of each diameter grade before leaching, the more acidic the leaching solution was, the higher change rate of the percentage of particle with diameter <5 mm and ≥20mm for J3s and J2s. However, there was no uniform rule of decreasing amplitude of large particles in group J3p with pH change of leaching solution. The change rate of particle diameter <5 mm component content of parent rock in three groups after treatment simulated rain at different pH values were J3s > J2s > J3p. Under the different depth of covering soil, the particle sizes variation of J3s showed the same changing rule, while the change rate of each particle size decreased with the increase of covering soil depth.(4) The soil-formation rates of parent rock after treatment simulated rain at different pH values were J3s > J2s > J3p. The stronger of acidity was, the higher of formation proportion of parent rock was, and the larger the soil-formation proportion increases with the leached amount increased. Compared with the amount of simulated rainfall at different pH values to 1a, the soil-forming proportion of purple rocks of group J3s , J2s , J3p increased by 0.28-1.86,0.16-1.82 and 0.27-1.60 times when the amount of simulated rainfall to 2a. The annual soil-forming rate appeared to significant exponentially decrease (p < 0.001) as pH increased. Under the different depth of covering soil, the soil formation proportion of J3s decreased with the increase of covering soil depth.(5) The pH values of the leachates from purple rocks had a fluctuate rising tendency with the leached amount increasing. Compared with leaching the exposed purple rock of J3s, the pH values of the leachates from J3s increased with the increase of covering soil depth, under the same treatment conditions. The electric conductivity of the leachates from purple rocks were J3s > J3p > J2s, which had markedly negative correlation (p<0.05) with the pH of the leachates. (6) The amount of cations released in the leachates from purple rocks after treatment with simulated rain at different pH values were the highest in Ca2+, accounting for more than 44% of the total amount of cations release of each parent rock, followed by Mg2+ and Na+, and released of K+ was the lowest, less than 5% of the total amount of cations released, and these results were in agreement with the immersion cycle test. The total amount of cations release from the 3 groups of purple rocks under the cumulative simulated 2a rainfall treatment were the same as that of the soil-formation proportion, and all were J3s > J3p > J2s, and the total released of cations significantly increased by exponentially with decreasing pH of simulated rain, the fitting coefficients R2 were more than 0.99. Compared with the immersion cycle test, the dynamic leaching experiment was more beneficial to the cations release. Based on the same treatment conditions, the amount of cations released from 3 groups of purple rocks by dynamic leaching experiment increases to varying degrees compared with that of immersion cycle test, with an increase of 3.98% to 59.11 % and an average increase of 25.09 %.(7) The total amounts of cations leaching from the purple rock after treatment with simulated rain at different pH values was negatively correlated (p > 0.05)with the decrease rate of particle diameter >10 mm component content, but there was a positive correlation (p < 0.05 or p < 0.01) with the increase rate particle diameter <5mm component content. We show that an exponential relationship exists between physical and chemical weathering rates, and the effect of the pH value of precipitation on cations released was obviously greater than its effect on physical weathering.(8) The contents of base exchangeable cations of weathering products (particle size < 2 mm) after treatment soaked decreased with the decrease of pH value, which had a significant positive correlation (p<0.05) with the acid buffer capacity of the weathered products. There were no significant differences in acid buffer capacity of the weathering product of J2s among the soaked treatment at different pH values, its varied from 5.10-6.76 mmol/kg.pHunit and was obviously lower than that of J2s(26.65-33.11mmol/kg.pHunit)and J3p (18.83~23.86 mmol/kg.pHunit).(9)Both the pH of simulated rain and the simulated rainfall amount had a direct effect on the contents of base exchangeable cations of weathering products, and the moderate simulated acid rain leaching (accumulative leaching amount to 1a rainfall) can increase the activity of base cations in the parent rock, which lead to the contents of base exchangeable cations of weathering products increased with the decrease of the pH of simulated acid rain. However, with the increase of the amount of acid rain leaching to 2a rainfall, the contents of base exchangeable cations of weathering products of the purple rock shown a decrease in different degrees, which decreased with the decrease of the pH of simulated acid rain, especially for the pH of simulated acid rain was 2.5, result in the contents of base exchangeable cations decreased more than 20%. 
Pages138
Language中文
Document Type学位论文
Identifierhttp://ir.imde.ac.cn/handle/131551/24772
Collection山地表生过程与生态调控重点实验室
Affiliation中国科学院成都山地灾害与环境研究所
First Author Affilication中国科学院水利部成都山地灾害与环境研究所
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赵吉霞. 模拟酸雨对典型紫色母岩风化特征的影响[D]. 北京. 中国科学院大学,2018.
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