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1.
水稻子实对不同形态重金属的累积差异及其影响因素分析   总被引：3，自引：0，他引：3  
在分析成都平原核心区土壤重金属(Cd、Cr、Pb、Cu、Zn)全量、各形态含量及相应点位种植的水稻子实重金属含量的基础上,通过统计分析、空间插值及线性回归方程的模拟,研究了土壤Cd、Cr、Pb、Cu、Zn全量的空间分布状况、各形态重金属含量统计特征,以及水稻子实对重金属各形态的累积差异及其影响因素。结果表明,成都平原水稻土重金属污染较轻,除Cd外,均低于国家土壤环境质量二级标准。土壤中重金属的可交换态含量均较低,Cd主要以铁锰氧化态存在,Cr、Cu、Zn、Pb主要以残渣态存在。水稻子实对5种重金属的累积效应顺序为:Cd>Zn>Cu>Pb>Cr。与水稻重金属累积关系密切的重金属活性形态(可交换态、碳酸盐结合态、铁锰氧化物结合态和有机物结合态)主要有:Cd的碳酸盐结合态、Cr的可交换态、Pb的有机物结合态和Cu的碳酸盐结合态含量;Zn各活性形态对水稻子实含量的影响不明显。土壤理化性质对不同活性形态重金属元素的影响效应各不相同。活性态Cd主要受有机质、pH和容重的影响;活性态Cr与pH、有机质、CEC和容重密切相关;活性态Pb与有机质、容重、中细粉粒、砂粒等均有密切的关系;Cu的活性主要受粘粒、有机质含量的影响;Zn的有效性主要受pH、有机质、砂粒、容重的影响。总的看来,对土壤Cd、Cr、Pb、Cu、Zn各活性形态含量影响效应较强的是有机质、pH、容重,而与土壤吸附性能密切相关的颗粒组成、CEC的影响不甚明显。  相似文献   

2.
泉州走马埭典型土壤重金属的赋存形态分析   总被引：5，自引：3，他引：2  
何园  王宪  陈丽丹  郑盛华  蔡真珍 《土壤》2007,39(2):257-262
采用改进的Tessier连续萃取方法研究了泉州走马埭国家农田示范保护区典型土壤中重金属(Cr、Ni、Cu、Zn、Cd、Pb)的化学形态分布,通过土壤重金属的赋存形态分析比较了6种重金属的生物可利用性。研究结果表明,土壤中不同重金属元素化学形态分布具有不同的特点:Cr和Ni主要以残渣态存在,其余形态所占的比例很小;Cu以残渣态含量最高,碳酸盐结合态含量最低;Zn以残渣态为主,可交换态含量最低;Cd以可交换态和碳酸盐结合态为主,水溶态含量最低;Pb以残渣态和铁锰氧化物结合态为主,水溶态含量最低。土壤中除Cd外,Zn、Cu、Cr、Pb、Ni在正常自然条件下相对比较稳定。  相似文献   

3.
研究了江苏省昆山市农田土壤有效态Cu、Ni、Pb、Zn各形态含量及其有效性。结果表明,土壤重金属Cu、Ni、Pb、Zn各形态含量以残渣态有机质结合态铁锰氧化物结合态碳酸盐结合态、可交换态,残渣态含量明显高于其他形态。Cu和Pb有机质结合态所占比例相对也较高,分别达36.09%和28.30%。土壤可交换态含量、碳酸盐结合态含量、Fe-Mn氧化物结合态含量及残渣态含量均以Zn最高;土壤有机质结合态含量以Cu最高;土壤可交换态含量变异系数、土壤碳酸盐结合态含量变异系数及土壤Fe-Mn氧化物结合态含量变异系数以Ni为最大;土壤有机质结合态含量变异系数以Zn最大;土壤残渣态含量变异系数以Pb最大。土壤铁锰氧化物结合态铜和可交换态铜对土壤有效态铜含量影响最大;土壤可交换态镍含量对土壤有效态镍含量最大;土壤铁锰氧化物结合态铅和有机质结合态铅对土壤有效态铅含量影响最大;土壤可交换态锌和碳酸盐结合态锌对土壤有效态锌含量影响最大。  相似文献   

4.
长春市城区土壤中Pb、Cu、Zn、Cd及Cr化学形态特征   总被引：4，自引：1，他引：3  
为弄清长春市城市土壤中Pb、Cu、Zn、Cr及Cd的化学形态分布特征,系统采集了26件城市表层(0~20 cm)土壤样品,采用连续提取法对重金属各化学形态含量进行了测定。结果表明:Pb、Zn、Cu及Cr主要以残渣态存在,其次是铁锰氧化物结合态、腐殖酸结合态和强有机结合态占有次要地位,离子交换态和水溶态所占比例均较低;Cd则主要以碳酸盐结合态存在,同时,水溶态和离子交换态所占比例较高。残渣态Pb和Zn在城区表层土壤中所占比例较近郊土壤中略有下降,但幅度不大,除Cu外,其余各元素易迁移、高生物有效性的水溶态在城区表层土壤中所占比例略有上升。Pearson相关分析结果表明,各元素残渣态与全量均呈极显著正相关,其它各活性态与全量间的相关程度与重金属种类有关。土壤pH值和Fe、Mn含量对重金属的化学形态的影响也与重金属种类有关,而且,同一重金属的不同存在形态受土壤pH值和Fe、Mn含量的影响程度也不同。  相似文献   

5.
采用田间试验研究了施加不同用量(2、4、8、16 t·hm~(-2))的脱硫石膏对紫色水稻土重金属(Cd、Pb、Zn、Cu)全量、形态分布和水稻重金属吸收及分配的影响,为脱硫石膏农用的安全性提供科学依据。结果表明:施加脱硫石膏后,土壤Pb全量较对照显著增加14.00%~68.77%(P0.05),脱硫石膏用量低于4 t·hm~(-2)时土壤Cd全量与对照差异不显著,超过该用量时Cd全量较对照显著增加16.28%~19.94%,而土壤Zn、Cu全量与对照无显著差异,且土壤重金属全量均符合《土壤环境质量标准》(GB 15618—1995);同时施加脱硫石膏后,土壤中Cd可交换态占比降低,残渣态占比增高,并促进Pb的可交换态向有机结合态和铁锰氧化态转化,Zn铁锰氧化态占比增高,对Cu的赋存形态无明显影响;脱硫石膏处理组水稻根、茎叶和籽粒中重金属含量有不同程度的降低,水稻根、茎叶及籽粒对Cd、Pb的富集系数下降,且籽粒中Cd、Pb、Zn、Cu含量均符合我国《食品安全国家标准食品中污染物限量》(GB 2762—2012)。水稻各部分对Cd、Pb的积累与其可交换态、碳酸盐结合态、铁锰氧化态和有机结合态含量均呈正相关,其中籽粒Cd含量与可交换态Cd含量呈极显著正相关(P0.01)。在脱硫石膏2～16 t·hm~(-2)用量范围内,稻田土壤Cd、Pb全量有所增加,Zn、Cu全量无变化,Cd、Pb赋存形态向稳定态转化,水稻各部分Cd、Pb、Zn、Cu含量有不同程度降低,脱硫石膏可在水稻田安全利用。  相似文献   

6.
新乡市环宇大道工业区周边土壤重金属的污染特征和评价   总被引：2，自引：0，他引：2  
通过实地采样及室内化学分析的方法,研究了新乡市环宇大道工业区周边土壤Pb、Cd、Ni、Zn、Cu和Cr 6种重金属污染特征和风险评价,并应用Tessier五步连续萃取的方法对土壤中超标的Cd,Ni和Zn进行形态分析。结果表明:(1)土壤中Pb、Cd、Ni、Zn、Cu和Cr的平均含量分别是63.08 mg kg-1、176.85 mg kg-1、307.2 mg kg-1、485.6 mg kg-1,38.7 mg kg-1和47.9 mg kg-1,Pb、Cu、Cr平均含量达标,Cd、Ni、Zn平均含量均超标,分别是国家土壤环境质量二级标准的176.85、5.12、1.62倍。(2)Ni和Zn主要以铁锰氧化物结合态和残渣态存在,Cd主要以铁锰氧化物结合态存在,其次为碳酸盐结合态,3种重金属的迁移能力依次为:Cd>Zn>Ni。(3)每种重金属都存在不同程度的潜在生态风险,Cd的潜在生态风险最大并构成了很强的危害。  相似文献   

7.
长期施用畜禽养殖废弃物下潮土重金属的累积特征   总被引：1，自引：0，他引：1  
通过田间试验研究了畜禽养殖废弃物长期施用(2001—2013年)对重金属(Cr、Cu、Zn、Pb、Cd、As)在潮土中累积、形态转化及迁移行为的影响。试验设置畜禽养殖废弃物(猪粪,OM)和化肥氮磷钾(NPK)两个处理,每处理设置3个重复。结果显示,畜禽养殖废弃物的长期施用造成Cu、Zn在OM处理土壤中的含量明显高于NPK处理,并主要累积于耕层土壤(0~20 cm),但总体含量(Cu:38.71 mg/kg;Zn:83.26 mg/kg)较低,对农田生态安全的影响较小。形态分析结果显示,OM处理土壤中DTPA络合态、弱酸结合态和铁锰结合态Cu、Zn、As的含量均显著高于NPK处理,但不同形态Cr、Pb、Cd在两种处理土壤中的差异相对较小。其中,Cr主要以非提取态的形式存在(Cr95%)。外源性Cu易累积于非提取态(52%),而Zn则以弱酸溶解态(40%)和铁锰结合态(60%)为主。畜禽养殖废弃物的农田施用不仅是土壤重金属的重要来源,也是土壤重金属活性提高的重要原因,并造成部分重金属在剖面土壤中发生明显迁移行为,累积于更深层土壤中。  相似文献   

8.
海南岛砖红壤中铅、镉的化学形态与转化   总被引：2，自引：1，他引：1  
采用土培实验和连续提取.原子吸收分光光度法,研究了重金属Pb、Cd在海南岛花岗岩砖红壤中的形态组成、外源Pb、Cd污染及化学修复剂磷、钙、硫对土壤重金属形态的影响.结果表明:在供试原土壤中,重金属Pb的化学形态以结合态和残余态为主,土壤有效态Pb含量较低,其中残余态Pb>有机质结合态Pb>铁锰氧化物结合态Pb>碳酸盐结合态Pb>交换态Pb>水溶态Pb,说明土壤Pb的环境风险较低;重金属Cd的化学形态以铁锰氧化物结合态和碳酸盐结合态为主,土壤中交换态Cd含量较高,其中铁锰氧化物结合态Cd>碳酸盐结合态Cd>交换态Cd>有机结合态Cd>残余态Cd>水溶态Cd,说明土壤Cd的环境风险较高.当外源Pb、Cd污染土壤时,有铁锰结合态Pb>残余态Pb>有机态Pb>碳酸盐结合态Pb>交换态Pb>水溶态Pb,交换态Cd>铁锰氧化物结合态Cd>碳酸盐结合态Cd>残余态Cd>有机态Cd>水溶态Cd的趋势.向污染土壤施加化学改良剂过磷酸钙、硫化钠和石灰,能显著降低水溶态Pb、Cd和交换态Pb、Cd的含量,并使有机结合态Pb、碳酸盐结合态Pb和铁锰氧化物结合态Pb含量下降,但残余态Pb、碳酸盐结合态Cd、铁锰氧化物结合态Cd和有机态Cd有增加的趋势,残余态Cd的含量基本稳定.  相似文献   

9.
砂姜黑土中重金属Cu、Cd、Zn形态分布与土壤酶活性研究   总被引：2，自引：0，他引：2  
采用小麦农田取样,对土壤中的重金属运用连续提取方法,研究了皖北砂姜黑土中Cu、Cd、Zn的化学形态特征及其与四种土壤酶(过氧化氢酶、脲酶、蔗糖酶、中性磷酸酶)活性间的关系。结果表明:在砂姜黑土中,残留态Cu、Cd、Zn在总量中所占比例很高,交换态、有机态、碳酸盐结合态含量明显低于残留态。在三种元素中,Zn的化学形态变化趋势最为一致,表现为残留态>碳酸盐结合态>铁锰结合态>有机态>交换态;砂姜黑土中交换态Cu、Cd、Zn对脲酶活性有显著抑制作用,有机态Cu、Cd、Zn对过氧化氢酶表现为一定程度的促进作用。因此,在砂姜黑土壤中,把交换态Cu、Cd、Zn和脲酶以及中性磷酸酶的活性共同作为评价土壤Cu、Cd、Zn污染程度的主要生化指标是可行的。  相似文献   

10.
长三角和珠三角农业土壤中铅、铜、镉的化学形态与转化   总被引：9，自引：1，他引：9  
研究了重金属Pb、Cu、Cd在长江三角洲和珠江三角洲土壤中的转化及不同Pb、Cu、Cd负荷水平对土壤重金属形态的影响。结果表明:未明显污染土壤中重金属主要以残余态为主,可提取态组分的比例Cd>Cu>Pb,但不同土壤之间有较大变化;随着土壤重金属负荷的提高,土壤中交换态重金属的比例增大,残余态比例下降,有效性提高,对环境威胁增大;当重金属加入量较低时,重金属优先向氧化物结合态、有机质结合态转化,而当加入量较高时,向交换态和碳酸盐结合态转化的比例明显增加;pH和土壤组分对重金属在土壤中的转化有显著影响,土壤pH下降可使交换态Cd、Cu、Pb的比例递增。  相似文献   

11.
低氮和干旱胁迫对富士和秦冠生长及氮素利用的影响   总被引：2，自引：2，他引：0  
【目的】以富士（Fuji）、 秦冠（Qinguan）嫁接在平邑甜茶（Malus hupehensis Rehd.）上的当年生盆栽苗为试验材料,采用砂培方法,研究了缺氮胁迫和干旱对富士和秦冠生长情况、 光合参数、 植株各部位氮磷钾含量及氮素利用效率的影响,分析比较了低氮干旱条件下富士和秦冠生长及氮素利用的差异,以期为果树生产高效肥水利用提供理论指导。【方法】试验共设四个处理: 正常氮正常水（ZZ）、 低氮正常水（DZ）、 正常氮干旱（ZG）、 低氮干旱（DG）。氮素和水分均设置两个水平,分别为正常氮（6 mmol/L NO-3-N）、 低氮（0.3 mmol/LNO-3-N）、 正常供水（保持盆中砂子相对含水量为饱和含水量的80%~85%）、 干旱处理（保持盆中砂子相对含水量为饱和含水量的60%~65%）。【结果】富士和秦冠的生物量（茎和叶）、 株高茎粗等生长指标以及光合速率、 气孔导度、 蒸腾速率均为正常氮正常水（ZZ）＞低氮正常水（DZ）＞正常氮干旱（ZG）＞低氮干旱（DG）,并且相对应处理下秦冠的以上指标均高于富士;正常供水下,缺氮处理使富士、 秦冠的根冠比比正常氮处理均有所增加,富士提高了2.05%,秦冠提高了22.40%。富士和秦冠的氮、 磷、 钾含量均表现出正常氮正常水（ZZ）＞低氮正常水（DZ）＞正常氮干旱（ZG）＞低氮干旱（DG）; 氮、 钾元素含量在植株各部位的分布顺序依次是叶＞根＞茎,磷元素则是根＞叶＞茎;光合氮素利用效率（PNUE）和氮素利用效率表现为秦冠处理之间差异极显著,富士处理之间差异不显著;秦冠的PNUE和NUE明显高于富士,在低氮正常水（DZ）处理下,秦冠氮肥利用率比富士高42.07%,在低氮干旱（DG）处理下高64.14%;低氮胁迫下富士和秦冠的NUE显著提高,并且秦冠提高的幅度高于富士。【结论】施用氮肥能够显著提高富士与秦冠的干物质量,同等水肥条件下,秦冠生长优于富士;水分亏缺会减少叶片对氮的吸收,干旱条件下适度增施氮肥,可提高果树的抗旱能力;低氮干旱胁迫下秦冠的生长指标、 光合指标及氮素利用效率指标均优于富士,表现出较强的抗低氮干旱胁迫的能力。  相似文献   

12.
Laser-induced breakdown spectroscopy (LIBS) is a new technique for the analysis of plant material. This study investigates the application of LIBS to pasture-based plant samples. The LIBS measurements were obtained from pelletized pasture samples (100 samples) that had been also analyzed by inductively coupled plasma–optical emission spectroscopy (ICP-OES) following microwave digestion for calibration and comparison purposes. Comparisons for elements sodium (Na), potassium (K), magnesium (Mg), calcium (Ca), manganese (Mn), iron (Fe), copper (Cu), zinc (Zn), boron (B), phosphorus (P), and sulfur (S) showed that LIBS could be used for almost all the standard profile total elements with concentrations down to low mg/kg levels (observed error of Na: 0.024 percent, K: 0.18 percent, Mg: 0.016 percent, Ca: 0.073 percent, P: 0.017 percent, Mn: 31 mg/kg, Fe: 150 mg/kg, Zn: 6.6 mg/kg, and B: 1.1 mg/kg). Elemental analysis at less than mg/kg levels was not possible using LIBS. The elements S and Cu were particularly difficult to analyze with reliability using LIBS at the concentration levels found in the plant samples. Replacing microwave digestion and subsequent ICP analysis with a direct analysis of dried plant samples using LIBS has the potential to improve the productivity and reduce the cost of testing.  相似文献   

13.
正The Center for Agricultural Resources Research(CARR),the Institute of Genetics and Developmental Biology(IGDB),Chinese Academy of Sciences,invites applicants for several research group leader positions.CARR is one of the research organizations in Chinese Academy of Sciences(CAS).We seek nominations and applications from individuals who have expertise and a record of accomplishment in research areas related to ecology,agro-hydrology,  相似文献   

14.
The responses of tallgrass prairie plant communities and ecosystem processes to fire and grazing are well characterized. However, responses of invertebrate consumer groups, and particularly soil-dwelling organisms, to these disturbances are not well known. At Konza Prairie Biological Station, we sampled soil macroinvertebrates in 1994 and 1999 as part of a long-term experiment designed to examine the effects and interactions of annual fire, mowing, and fertilization (N and P) on prairie soil communities and processes. For nearly all taxa, in both years, responses were characterized by significant treatment interactions, but some general patterns were evident. Introduced European earthworms (Aporrectodea spp. and Octolasion spp.) were most abundant in plots where fire was excluded, and the proportion of the total earthworm community consisting of introduced earthworms was greater in unburned, unmowed, and fertilized plots. Nymphs of two Cicada genera were collected (Cicadetta spp. and Tibicen spp.). Cicadetta nymphs were more abundant in burned plots, but mowing reduced their abundance. Tibicen nymphs were collected almost exclusively from unburned plots. Treatment effects on herbivorous beetle larvae (Scarabaeidae, Elateridae, and Curculionidae) were variable, but nutrient additions (N or P) usually resulted in greater densities, whereas mowing usually resulted in lower densities. Our results suggest that departures from historical disturbance regimes (i.e. frequent fire and grazing) may render soils more susceptible to increased numbers of European earthworms, and that interactions between fire, aboveground biomass removal, and vegetation responses affect the structure and composition of invertebrate communities in tallgrass prairie soils.  相似文献   

15.
“Wicked” problems are those that are complex and that change when solutions are applied. Many conflicts in conservation fall into this category. The study approached the problem of how to constrain the apparent wickedness of a problem in the conservation management of a species by using simple empirical indicators to carry out iterative assessment of the risk to a population and to document how this risk evolves in relation to the addition of new data and the implementation of management actions. Effects of high levels of uncertainty within data and also concerning population structure were examined through stochastic simulation and by exploration of scenarios. Historical trends in the example used, the Steller sea lion, showed rapid declines in abundance in some regions during the 1980s. The current total population is 130,000-150,000 Steller sea lions through Alaska and British Columbia and this number has been stable since about 1990 in spite of regional differences in population dynamics. Regional differences in the sequence of changes in the number of pups and non-pups, suggested that an internal re-distribution of juveniles could have happened between 1980 and 1990. Current productivity also appears close to the long-term mean. Stochastic population projection using various scenarios showed that, based upon this history, the risk of extinction for the population has declined and is below reasonable thresholds for considering the population to be endangered. The trends in risk suggest that management actions taken since 1990 have probably been effective. Consequently, the conservation management objectives for the Steller sea lion are probably being met. The approach provides a mechanism, based upon experience and scenario analysis, for exploring future policy options and may help to constrain the debate amongst stakeholders about the cost-benefit trade-offs associated with different options.  相似文献   

16.
Nutrient distributions under no tillage (NT) compared with conventional disk-and-bed tillage (CT) management in the warm, humid region of the southeastern USA need to be assessed so that future placement, quantity, and type of fertilizers can be altered, if necessary, to efficiently match crop demands. We determined soil-profile distributions of pH, N, P, S, K, Ca, Mg, Na, Zn, Fe, Mn, and Cu to a depth of 0.9 m at the end of 8.5 years of continuous CT and NT management on a Weswood silty clay loam (fine, mixed, thermic Fluventic Ustochrept) in southcentral Texas. Most dramatic changes occurred within the 0–0.05 m depth, where soil under NT had lower pH, Fe, and Cu than under CT, but greater P, K, Zn, and Mn. Greater P and K under NT than under CT also occurred below the till-zone (0.15–0.3 m). At a depth of 0–0.3 m, soil under NT contained greater amounts of extractable P, K, Zn, Fe, Mn, and Cu than under CT. Nitrogen fertilization had little effect on nutrient distributions, except resulting in greater extractable K at 0–0.05 m and greater nitrate at 0–0.15 m. Few changes in soil-profile distributions were observed for extractable S, Ca, Mg, and Na. Long-term continuous use of NT on this fine-textured, high-fertility (except for N) soil had no apparent adverse effects on nutrient distributions relative to CT, but enhanced conservation and availability of P, K, Zn, Fe, Mn, and Cu near the soil surface where crop roots proliferate.  相似文献   

17.
Abstract

A 3-year study was carried out to investigate quality parameters in 14 tree fruit and berry species grown in southern Norway. The species were blueberry, apple, aronia, sour cherry, sweet cherry, red raspberry, strawberry, blackcurrant, gooseberry, red currant and elderberry, harvested along with wild bilberry, cloudberry and lingonberry. Significant differences between species were identified for all quality parameters. The coefficient of variation between species was lowest for pH (12.5%), dry matter (18.9%) and soluble solids (25.3%), followed by titratable acids (59.3%), total phenolics (83.8%), antioxidant capacity FRAP (85.7%) and antiradical power by the DPPH-assay (97.8%), total monomeric anthocyanins (132%) and ascorbic acid (137%). Average coefficient of variation within species were lower and ranged from 4 (pH) to 62% (ascorbic acid). Only the FRAP values were significantly affected by harvesting year with lower levels in 2004 than in 2005 and 2006. There were significant interactions between species and harvesting year for dry matter, soluble solids, pH, ascorbic acid and FRAP. The results indicate generic ranges in composition within species independent upon growing location and climate, and the composition of the tree fruits and berries is not likely to deviate from these ranges. It is concluded that desirable composition of tree fruits and berries and their products should primarily be achieved by selection among species rather than searching fors broadened variation within individual species.  相似文献   

18.
Potassium (K) fixation and release in soil are important factors in the long-term sustainability of a cropping system. Changes in K concentration and characteristics of K fixation and release in rhizosphere and nonrhizosphere soils in the rapeseed (Brassica napus L.)–rice (Oryza sativa L.) rotation were investigated using a rhizobox system. The concentrations of different forms of K in both rhizosphere and nonrhizosphere soils decreased with plants compared to without plants, regardless of K fertilizer application. Potassium uptake by crops mainly came from the rhizosphere soil. In the treatment without K fertilizer (–K), the main form of K supplied by the soil to the crops was 1.0 mol L?1 nitric acid (HNO3) nonextractable K, followed by nonexchangeable K, and then exchangeable K. In the treatment with K fertilizer (+K), the main K forms supplied by the soil to the crops were exchangeable K and nonexchangeable K. The amount and rate of K fixation after one cycle of the rapeseed–rice rotation was greater in rhizosphere soil than in nonrhizosphere soil. The amount and rate of K fixation of soil in the +K treatment were significantly less than in the –K treatment. The cumulative amounts of K released with 1.0 mol L?1 ammonium acetate (NH4OAc) and 1.0 mol L?1 HNO3 extraction increased with the increasing numbers of extractions, but the K-releasing power of soil by successive extraction decreased gradually and finally became almost constant. The release of K was less in rhizosphere soil than in nonrhizosphere soil. The release of K in the +K treatment was similar to that in the –K treatment in rhizosphere soil, but the K release in nonrhizosphere soil was greater with the +K than the –K treatment. Overall, the information obtained in this study will be helpful in formulating more precise K fertilizer recommendations for certain soils.  相似文献   

19.
Biologically enhanced dissolution offers a method to speed removal of chlorinated solvent dense non-aqueous-phase liquid (DNAPL) sources such as tetrachloroethene (PCE) and trichoroethene (TCE) from aquifers. Bioremediation is accomplished by adding an electron donor to the source zone where fermentation to intermediates leading to acetic acid and hydrogen results. The hydrogen and possibly acetic acid are used by dehalogenating bacteria to convert PCE and TCE to ethene and hydrochloric acid. Reductive dehalogenation is thus an acid forming process, and sufficient alkalinity must be present to maintain a near neutral pH. The bicarbonate alkalinity required to maintain pH above 6.5 is a function of the electron donor: 800 mg/L of bicarbonate alkalinity is sufficient to achieve about 1.2 mM TCE dechlorination with glucose, 1.7 mM with lactate, and a much higher 3.3 mM with formate. Laboratory studies indicate that in mixed culture, formate can be used as an electron donor for complete conversion to ethene, contrary to pure cultures studies indicating it cannot. Various strategies can be used to add electron donor to an aquifer for DNAPL dehalogenation while minimizing pH problems and excessive electron donor usage, including use of injection-extraction wells, dual recirculation wells, and nested injection-extraction wells.  相似文献   

20.
To evaluate the feasibility of long-term desert reforestation technology of mixed vegetation, cardon cactus (Pachycereus pringlei) seedlings from indoor and outdoor nurseries were planted in the field adjacent to one seedling of potential legume nurse trees: mesquite amargo (Prosopis articulata), yellow palo verde (Parkinsonia microphylla), and blue palo verde (Parkinsonia florida). Some of the planting holes were also supplemented with common dairy compost. Additionally, the combinations of legume tree–cactus were inoculated with either a consortium of desert arbuscular mycorrhizal (AM) fungi, plant growth promoting bacteria (PGPB; the diazotroph Azospirillum brasilense Cd, and the phosphate solubilizer Paenibacillus sp.), or a mixture of all. The field experiments were evaluated periodically during 30 months for survival and growth. Cardons reared in an outdoor screen house survived better in the field than those reared in a controlled growth chamber and hardened later outdoors. Association with any legume nurse tree increased survival and enhanced growth of untreated cardons. For cardons growing alone, application of either compost, AM fungi, and all the treatments combined increased survival. For these plants, no treatment affected plant growth during the first 3 months after transplanting. Later, all treatments, except for AM fungi, enhanced plant growth. However, only 2 years after transplanting the enhanced growth effect of AM fungi was also significant. In the presence of the legume nurse trees, transient positive effects on cardon growth were recorded. General evaluation after 30 months of cultivation showed that the treatments positively affected cardon growth when growing alone or in combination only with mesquite amargo but not with the other two legume trees. This study proposes that young legume trees have the capacity to enhance survival and growth of cardon cactus, depending on the legume cactus combination. Additional treatments such as compost or PGPB can either amplify the effect or else attenuate it.  相似文献   

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