【作者】 林文杰；

【导师】 马焕成； 肖唐付； 胡庭兴；

【作者基本信息】 四川农业大学 ， 森林培育学， 2007， 博士

【摘要】 黔西北土法炼锌具有300多a的冶炼历史，由于冶炼工艺简单，重金属回收率低，大量重金属累积废渣中，造成冶炼区环境严重污染。冶炼过程中产生了大量的烟尘，没有采取任何环境保护措施，烟尘中含有大量的重金属和二氧化硫等有毒有害物质，破坏了冶炼区附近植被，大量的重金属随烟尘向四周扩散，导致大面积大气、土壤、植物、水体的重金属污染。虽然土法炼锌目前已基本上取缔，但留下了2000万t废渣和1200hm~2的废弃地。因而对废弃地的植被重建与生态恢复、对污染环境的修复具有重要科学价值和实际意义。本研究充分调查了重金属在生态系统中的分布与扩散规律，分析了土壤和植被退化的过程。通过苗圃的模拟实验和田间植被重建实验，探讨了废弃地植被重建的主要限制因子，基质改良的有效手段及耐性植物的筛选。对废弃地自然形成的优势植物进行调查，筛选重金属的超富集植物，并研究其富集特性与机理。主要的研究结果如下：土法炼锌导致了Pb、Zn、Cd在土壤、水体和植物中大量积累，对整个生态系统构成了严重的威胁。在冶炼废渣中，Pb、Zn、Cd的含量分别为4632 mg／kg、8968 mg／kg、58 mg／kg；冶炼区周围的土壤Pb、Zn、Cd含量分别达到234 mg／kg、400 mg／kg、9.6mg／kg。废弃地的基质的地球化学形态分析表明，废渣中Pb、Zn、Cd具有很低的生物有效性和迁移性，交换态含量低于0.2％，但其交换态与碳酸盐态含量相当高，构成了潜在的环境风险。相对而言，冶炼区附近污染土壤的Pb、Zn、Cd可交换态含量较高，具有较大迁移性和生物有效性。冶炼区的小河受到严重的Pb、Zn、Cd污染，地下水受到轻微污染，未超出三类水体的质量标准。在小河水体中，可溶态的Pb、zn、Cd含量少，大部分的Pb、Zn、Cd以悬浮态的形式存在，表明了河流重金属污染主要因为废弃地的水土流失。为了有效地控制废弃地重金属向河流扩散，以致污染和破坏下游地区的生态系统，废弃地的植被重建是最有效的途径。冶炼残渣具有较高的pH值和EC值、低CEC，有机质极为缺乏，含N量低。冶炼区污染土壤明显酸化，导致P有效性降低。在冶炼时造成大面积的植被破坏，成为裸地，停止冶炼后，植被自然恢复极为缓慢，特别是废渣。为了控制水土流失和重金属扩散，需要人工措施以加速植被重建。在苗圃中，以土法炼锌废弃地的废渣、污染土壤和背景土壤为基质材料，并设计了基质的改良处理，分别种植黑麦草(Lolium perenne)、三叶草(Trifolium pretense)、刺槐(Robinia pseudoacacia)，进行植被恢复的模拟实验，以探讨废弃地植被重建的限制因子和基质改良的有效途径。土法炼锌新废渣上植被重建的主要限制因子包括盐碱胁迫、有机质含量低、养分缺乏(总N、碱解N、总K)。废弃了多年(20a以上)废渣经过了长期的淋溶过程，盐碱胁迫明显降低，养分状况有了明显的改善，植被重建的限制因子明显降低。所有冶炼废渣具有高的孔隙度，具有良好通气性，但持水保水能力差，田间持水量低于土壤，而凋萎系数高于土壤，有效水分含量范围明显低于土壤，干旱胁迫是植被恢复的重要限制因子。污染土壤的植被重建的胁迫因子包括重金属毒性、P有效性低。通过苗圃模拟实验与田间造林实验研究，可以获得植被重建有效方法：1)在新废渣上进行植被恢复，采用部分客土法能有效地降低盐碱胁迫、缓和营养缺乏的矛盾、提高基质的持水保水能力、促进植物生长，结合选择耐性植物，可以成功进行植被重建；2)废弃多年的废渣，采用部分客土或保水剂能提高基质的持水保水能力，可以大大促进植被恢复进程；3)在污染土壤上，通过碱石灰改良，提高了养分的有效性，降低重金属的毒性，促进了植物生长。通过对冶炼区优势植物的筛选，并且结合水培实验，筛选出一种Zn的超富集植物——南黄堇(Corydalis davidii)。南黄堇对Pb、Zn、Cd都具有很强耐性，并且为Pb、Cd的富集植物。Pb、Zn、Cd在南黄堇的各器官中均表现明显的区隔化分布特征，其中有70～90％累积在细胞壁中。在Pb、Cd的胁迫浓度处理下，抗氧化酶(SOD、POD、CAT)是重要的防护系统，随着浓度增强，酶活性明显增强，但在高浓度下表现出受到抑制现象。在Zn的不同浓度处理下，抗氧化酶活性变化很小。更多还原

【Abstract】 The widely spread indigenous zinc smelting sites in western Guizhou, China, with a history of 300 years, have caused serious pollution of heavy metals of lead (Pb), zinc (Zn) and cadmium (Cd) in slags due to low recovery rate. A large amount of fumes rich in heavy metals and sulfur dioxide, have destroyed vegetation around the smelting areas and have released heavy metals into soil, plant and water body. Although indigenous zinc smelting activities have been abolished due to heavy environmental pollution in 2004, 20 millions tons of open dumped slags and 1200 hectares of polluted land were environmental concerns at present with high risk to the local ecosystem. It is of importance to understand revegtation on smelting wasteland and remediation on heavy metals in the smelting areas. This study is conducted to: 1) analyze distribution and transfer of heavy metals and degradation of soil and vegetation in the polluted environments; 2) explore limited factors on revegetation, substrate amendment methods and strongly-tolerant plant; 3) screen hyperaccumulators for heavy metals and study their accumulation properties and mechanism. The main research results were as follows.Concentrations of Pb, Zn and Cd in slags averaged at 4632 mg/kg, 8968 mg/kg, and 58 mg/kg, respectively, whereas 234 mg/kg Pb, 400 mg/kg Zn and 9.6 mg/kg Cd occurred in soil around the smelting areas. The geochemical leaching test showed that Pb, Zn and Cd in slags have low mobility and bioavailability because their concentrations presented small percentages (all less than 2 %) in the exchangeable fraction, whereas the contaminated soils had higher mobility and bioavailability for the metals. The Pb, Zn and Cd concentrations in exchangeable and carbonate fractions in slags were high and posed potential environmental risks. Concentrations of Pb, Zn and Cd were high in the local stream water but low in groundwater. In the stream water, Pb, Zn and Cd were significantly concentrated in the suspended sediments, and indicated that metal-rich erosion process of slag and contaminated soil contributed to metal mobility into stream water. To remediate the local environment polluted by Zn smelting activity, revegetation is an effective approach to control dispersion of Pb, Zn and Cd in the indigenous zinc smelting areas.Compared to background soil, slags have higher pH values and EC values, lower CEC values, lower organic matter and nitrogen. The pH values and bioavailable P contents in contaminated soil decrease compared to background soil. The indigenous zinc smelting activities destroyed vegetation around the smelting areas. The natural restoration for vegetation is quite slow on smelting waste land, especially on slags. Therefore, it is important to accelerate revegetaion by artificial measures so as to control soil and water erosion and dispersion of heavy metals.Pot experiments were applied to understand the limited factors on revegetation and substrate amendment on smelting waste land by planting Lolium perenne, Trifolium pretense and Robinia pseudoacacia. The limited factors to revegetation on newly-produced slags were salt-alkali stress, low contents of organic matter and nutrients (total N, bioavailable N and total K). The salt-alkali stress in slags was remarkably mitigated, their soil nutrients were improved after long-term eluviation. Therefore, the constraints to revegetation in slag decreased remarkably after 20 years. The slag still has high porosity and aeration, however its capacity of water provision and retention were poor with low field capacity and wilting coefficient. Therefore, droughty stress was constraint to revegetation in slag. The constraints to revegetation in contaminated soil were toxicity of heavy metals and low bioavailable P.Through pot and field experiments, some findings were obtained: 1) alien soil amendment on slag could mitigate salt-alkali stress, improve nutrients in new smelting residue, and increase water provision and retention. Revegetation could be obtained in newly-produced slag by alien soil and stong-tolerant plants. 2) Alien soil or hydrogel applied in old slag could increase water provision and retention and accelerate revegetation. 3) Applying lime in contaminated soil could improve available nutrients and reduced toxicity of heavy metals, improving growth of plant.A new Zn-hyperaccumulator, Corydalis davidii, was found in the smelting areas through screening in fields and hydroponic solutions. Corydalis davidii has strong tolerance for Pb, Zn and Cd, even though high accumulation for Pb and Cd. 70～90 percent of Pb, Zn and Cd accumulated in cell wall. Antioxidant enzymes (SOD, POD, CAT) are important protection systems of Corydalis davidii. Activities of antioxidant enzymes increase with increase of Pb and Cd concentrations in lower concentrations, but decrease in higher metal concentrations. Activities of antioxidant enzymes slightly increase with increase of Zn concentration.更多还原