【作者】 杨胜香；

【导师】 束文圣；

【作者基本信息】 中山大学 ， 环境科学， 2010， 博士

【摘要】 矿业废弃地酸化和重金属污染是一个全球范围内严重的环境问题。在强酸环境下重金属溶解性增加,土壤板结严重,熟化受阻,致使氮、磷、钾等营养元素供应不足,植物无法生长。这种裸露的矿业废弃地常常因缺乏植被覆盖成为持久的污染源,对下游及周边地区造成严重的环境影响,并通过食物链危及人类健康。植被恢复能够增加地表稳定性,控制重金属和水土流失,改善土壤的营养状况,改善矿区景观。然而,在极端酸性重金属矿业废弃地上建立一个安全、稳定、自维持的植被是一个巨大的挑战。本研究通过对一个极端酸化的重金属矿业废弃地-大宝山多金属矿排土场进行详尽的野外调查、理化分析和净产酸潜力(NAG)实验,确定了该废弃地生态恢复的限制因素。采取原位基质改良模式,在废弃地上直接改土,添加石灰和鸡粪作为改良剂,采用营养袋育苗并引入土壤种子库,进行合理的生态配置,在排土场废弃地上建立起新的植被。新的土壤-植物系统形成后,从植被参数、土壤理化性质、重金属分布特征等方面对土壤的熟化过程、植被的恢复效果、环境生态效益进行了跟踪调查,并借助室内盆栽实验深入分析影响土壤理化性质变化的关键因子及各种生态因子间的相互关系。主要研究结果如下:1.基质改良与植被恢复有效地抑制了排土场土壤基质中金属硫化物的氧化产酸过程。土壤pH值显著性提高,净产酸潜力(NAG)逐渐降低,酸中和能力(ANC)逐渐升高。但植被恢复的两年间,土壤的NAG > 0,ANC < 0,表明排土场土壤还具有产酸潜力和再产酸的风险。室内盆栽实验进一步揭示,在只添加石灰或石灰+ NPK的情况下,土壤会重新恢复产酸能力,但联合添加石灰+ P肥或底泥时,能够有效地阻止土壤再产酸,说明磷肥和底泥抑制土壤硫化物的进一步氧化和新酸性物质的产生有特别的功效。2.重金属全量在植被恢复过程中没有显著性变化,说明重金属被固定在土壤系统中,植被建立和发展有效地降低了重金属移动性。但DTPA-Zn、DTPA-Pb含量却呈现增长的趋势,这可能与改土时对土壤的扰动有关。室内验证试验发现,不同的改良处理能降低DTPA-浸提态重金属的含量,其中添加底泥的处理(L1/L2+RS, L1/L2+NPK+RS)降低幅度最大,这主要与底泥的特殊性质有关。3.植被恢复有效地改善了土壤的营养状况,促进了营养元素的累积,有机质(OM)、全氮(TN)、氨态氮(NH4-N)、有效磷(AP)和有效钾(AK)的含量随着恢复时间的增加显著性增加。这种趋势在室内试验中也得到了很好地验证。4.大多数植物地上部分重金属含量(Zn、Pb、Cu)较低,但随着恢复时间的增加,不同的植物对同一重金属或同一种植物对不同的重金属的迁移-累积规律表现是不同的,Zn在所有的植物均表现出增加的趋势,Pb在类芦和铺地黍中呈显著增加趋势,在狗牙根、桉树和象草中基本保持恒定,Cu除了在铺地黍中呈增长趋势外,在其它植物中均保持恒定或略微下降趋势。总体来看,桉树和象草体内重金属(Zn、Pb、Cu)含量相对较低,且随着恢复时间的增加呈现稳定或略微下降的趋势。5.五种不同的植物及植物组合建立的植被恢复小区生态恢复效果均较好。这些植物半年内在排土场废弃地上迅速定居,形成了良好的植被覆盖,植被盖度达到30-80%,对重金属、水土流失控制率达到60-90%,对矿区粉尘污染的控制率为30-60%。其中Plot V (桉树+类芦+狗牙根)恢复效果最好,在植被建立2年后植被盖度达到100%,重金属、水土流失控制率超过90%,对粉尘污染的控制率达到60%以上。6.对添加不同改良剂处理的土壤微生物群落多样性、微生物量、微生物活性及土壤酶活性进行了测试分析,结果表明pH、NAG-pH和NAG等酸化因子直接影响着土壤微生物的群落结构和功能,重金属全量和有效态含量对土壤微生物具有显著性抑制作用,土壤营养状况促进了微生物的生长及活性。总而言之,基于二年研究,我们建立了一个经济、有效的极端酸性重金属矿业废弃地植被恢复技术体系。植被恢复显著性抑制了矿业废弃地酸化过程,有效地固定了重金属,改善了土壤的营养状况,提高了土壤微生物活性。植被的建立和发展增加了地表稳定性,有效地控制了重金属和水土流失,降低了风蚀带来的粉尘污染,改善了矿区景观,重建的植被正朝着顺行演替方向发展。但由于监测时段相对较短,对土壤酸化,重金属在土壤-植物系统中的迁移、累积继续进行更长期的监测是十分必要的。更多还原

【Abstract】 The extreme acidity and heavy metal pollution are two of major environmental problems associtated with mine wastelands around the world. The excess acidity tends to deteriorate soil properties (substrate structure, nutrient deficiency and so on), and enhance heavy metal toxicity, which greatly inhibit plant establishment, growth and colonization. These wastelands are therefore often absence of vegetation cover and readily become a source of pollution posing potential hazards to waters, soils and human health of the surrounding areas. A good vegetation cover can fulfill the objectives of stabilization, pollution control, visual improvement and removal of threats to human beings. However, establishing a healthy, long-standing and self-sustainable vegetation cover on those mine soils with extreme acidity and high heavy metal toxicity remains a great challenge.In the present study, a full ecological survey was conducted at an extremely acid mine wastelands_Dabaoshan mine overburden, in Guangdong Province. Physico- chemical analysis and net acid generation (NAG) test were employed to identify the major limiting factors to re-vegetation. The results showed that the extreme acidity and high heavy metal toxicity were the two major constraints to ecological restoration of the mine soils. Then, we established vegetations on the mine spoils according to the following procedures: (i) planting strips on the surface of the abandoned mine lands were constructed by digging ditches of 30×30 cm (50-cm intervals) and holes of 50×50×50 cm (2-m intervals); (ii) lime and chicken manure were added to the ditches at the rate of 15 t ha-1 (dry weight), respectively; (iii) the ditches were filled back with mine soil and allowed to equilibrate for one month prior to planting during the rainy season; (iv) The seedlings of different plants, having grown for five months in plastic containers, were planted in planting strips; (v) Five different vegetation composition patterns were built as follows: Cynodon dactylon (Plot I), Pennisetum purpureum (Plot II), Eucalyptus robusta (Plot III), Neyraudia reynaudiana + Panicum repens (Plot IV) and E. robusta + N. reynaudiana + C. dactylon (Plot V). During the follwing two years, the vegetation development on the mine spoils were investigated, meanwhile, the soil characteristics including acidification, fertility parameters, and the accumulation of heavy metals in the soil-plant systems were monitored Furthemore, a greenhouse experiment was conducted to reveal the interactions among soil acidification, vegetation, and heaby metal mobility, etc. The main findings were as follows:1. The mine soil pH values and acid neutralization capacity (ANC) increased gradually with time after the establishment of vegetation. The net acid generation (NAG) significantly decreased as the remediation time progressed. All the NAG values were above zero despite a general reduction trend, indicating that the mine soils still had acid-forming and re-acidification potential. The results of the greenhouse experiment suggested that there were high re-acidification risks in the mine soils of L1, L1+NPK treatments. However, the further additions of phosphate or river sediment (L1+P, L1+RS, and L1+NPK+RS) could prevent re-acidification effectively, which indicated that phosphate and river sediment played a quite specific role in preventing the re-acidification in the mine soils.2. The total heavy metal concentrations in the mine soil remained stable with the remediation time indicating the decreasing metal mobility. However, both DTPA-extractable Zn and Pb increased significantly as the remediation time progressed, which might be due to soil disturbance during the remedial works. The greenhouse experiment showed that the application of amendments and plant growth effectively reduced DTPA-extractable heavy metal concentrations. The strongest decrease was achieved in the treatments containing both lime and river sediment (L1/L2+RS and L1/L2+NPK+RS) which indicating that the river sediment maight played a specific role in reducing the availability of heavy metals in the mine soils.3. The vegetation development enhanced the nutrient accumulation in the mine soil. The organic matter (OM), total nitrogen (TN), ammoniacal nitrogen (NH4-N), available phosphorus (AP) and available potassium (AK) showed rapid increasing trends with the remediation time. Similar results were found in the greenhouse experiment. Re-vegetation plays an essential role in nutrient accumulation, organic matter turnover, thereby facilitating soil forming processes and accelerating ecological succession of the man-made habitats.4. Another particular concern associated with re-vegetation of mine soils is the accumulation of heavy metals in the shoots of plants. From the viewpoint of stabilizing metal-contaminated sites, a lower metal concentration in the above-ground parts of plants is desirable to prevent metal potentially entering the ecosystem through the food chain. In the present study, most plants accumulated lower levels of Zn, Pb and Cu in the shoots rather than the roots. However, there were great variations of metal accumulation among different metals and within the same metal at different species. For example, a significant increasing trend of Zn was observed in all the species; Pb exhibited an increasing trend in N. reynaudiana and P. repens, while remained constant in E. robusta, C. dactylon and P. purpureum; Cu showed a slight decreasing trend in most species except P. repens. Taken as a whole, among the tested plants in the present study, E. robusta and P. purpureum accumulated the lowest concentrations of Cu, Pb and Zn, and the both species could be a good candidate for re-vegetation of metalliferous mine wastelands.5. All the plant species used in the present study could well establish on the acid metal-contaminated soils and developed a good cover within a relatively short time. Vegetation cover varied from 30% to 80%, the prevention rates of wind and water erosion were between 60-90% and 30-60%, respectively. Among five vegetation plots, Plot V was the best for its plant cover (100% within two years), and its prevention rate of wind and water erosion were above 90% and 60%, respectively.6. The microbial diversity, biomass, activity and soil enzyme activities were determined in mine soils applied the different amendments. The results showed that pH, NAG-pH and NAG were the key factors influencing structure and function of soil microbial community. The total and available heavy metal had significant negative effects to soil microrganism while soil nutrients accelerated microbial diversity and activity.In conclusion, a cost effective revegetation model is established here for remediation of extremely acid metalliferous wastelands. Results presented in present study demonstrate that revegetation is an effective remediation option for soil stabilization, preventing acidification, enhancing nutrient accumulation and the subsequent soil forming processes. Acidification of the mine soils can be controlled effectively in the first two years after plant growth. Vegetation cover and nutrient accumulation are gradually enhanced with the remediation time. However, metal mobility increasing with time is also observed in present experiment, which may result in metal accumulation in the above-ground parts of plants. Therefore, increased metal uptake in the above-ground parts of plants. Therefore, metal accumulation in the soil-plant system should be of a great concern, and long-term monitoring of ecological risk should be further carried out.更多还原