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481.
Loess Plateau,an arid and semi-arid region in Northwest China,is well-known for its most serious soil erosion in terms of sediment yield each year.Soil erosion,which is intensified by agricultural activities,is the major factor influencing sustainable agriculture development in this region.It reduces productivity by removing nutrients and especially reducing water availability that is essential for crop production in the area.It also brings about off-site costs by demanding more efforts for maintenance of banks and dame along Yellow River through raising the riverbed with sediment.Climate is capricious and extreme weather conditions occur frequently,which impairs normal agricultural production with erosion and also decrease of water availability.Extensive way of farming still dominates on the Loess Plateau,which canot produce satisfying economic results and needs to be improved or altered.Conventional agricultural production pattern needs to be reconsidered for husbandry has not been granted its due position.Agriculture is the backbone of economy.Poor agricultural production impedes economic development and vice versa,backward economy also influences the advancement of agriculture.Besides a large population,education status of farmers is another threshold that requires being resolved for a sustainable agriculture.Although conventional agriculture has been practiced there for more than 5000years,now it cannot meet the demand for food and fiber by the increasing population and some of its farming practices are contributing to environmental degradation directly or indirectly and can sustain no longer.Agriculture on Loess Plateau needs to find its own way of sustainability.To work toward a sustainable agriculture,chances and challenges both indwell on Loess Plateau. 相似文献
482.
通过室内试验探讨中华圆田螺营养盐释放的温度影响因子对氮磷营养盐循环、水体悬浮物以及摄入量和排泄量的影响等生态特性。研究发现,温度对中华圆田螺营养盐的释放有显著影响。TN和TDN随温度升高呈小幅度增加,TP和TDP则随温度升高呈明显增高,当温度分别由8℃升高至15℃和35℃时,TN则分别增加了5.71%和23.43%,TDN增加6.76%和17.57%;TP则增加92.60%和208.35%,TDP增加2.25%和110.17%。当温度分别由8℃升高至15℃和35℃时,NH4+-N分别增加了1.89%和26.55%,PO4--P增加了14.27%和225.96%,NO3--N则不受温度影响。另外,温度对SS的影响不明显(p>0.05),即使在8℃条件下仍有较高的去除率,为69.50%;试验各个温度下,螺对SS摄食量都大于排泄量,随着时间延长,螺对SS的摄入量有所降低,但仍高于其排泄量。由此可见,底栖软体动物对富营养化水体具有明显的净化作用,为湖泊富营养化控制提供了可供参考的依据。 相似文献
483.
综述了物理修复、化学修复、微生物修复及联合修复等几种主要的1,2,4-三氯苯(1,2,4-TCB)环境污染修复技术的研究进展。阐述了各种修复方法的反应原理、修复条件和效果,对比了各种修复方法的优缺点。提出今后的研究方向:解决物理吸附法修复1,2,4-TCB污染后的吸附剂的后续处理问题;优化化学降解1,2,4-TCB的工艺条件,避免二次污染,进行现场试验,实现工程应用;分离、培育1,2,4-TCB的优势降解菌种;深入研究联合修复技术的降解机理,实现1,2,4-TCB的高效、彻底降解。 相似文献
484.
Determination of hydroxyl radicals with salicylic acid in aqueous nitrate and nitrite solutions 总被引:1,自引:0,他引:1
The qualitative and quantitative analyses of reactive oxygen species are essential to determine their steady-state concentration and related reaction mechanisms in environmental aquatic systems. In this study, salicylic acid was employed as an innovative molecular probe of hydroxyl radical(OH) generated in aqueous nitrate and nitrite solutions through photochemical reactions. Kinetic studies showed that the steady-state concentrations of OH in aqueous NO3^-(10 mmol/L, pH=5) and NO2^ (10 mmol/L, pH=5) solutions under ultraviolet irradiation were at a same magnitude, 10v-15 mol/L. Apparent quantum yields of OH at 313 nm were measured as 0.011 and 0.07 for NO3^- and NO2^ respectively, all comparable to the results of previous studies. 相似文献
485.
486.
487.
滇池流域城市面源污染控制区划研究 总被引:1,自引:0,他引:1
滇池流域点源污染已逐步得到控制,面源污染成为水污染治理的重点。随着流域内城市迅速发展,城市面源污染控制将成为水环境改善的重要瓶颈。结合滇池流域城市发展规划,依据城市下垫面特征,降雨径流污染程度和距离入滇河道远近,将流域内城区划分为重点防控区、中等防控区和一般防控区,其面积百分比分别是17.9%、39.1%和43.0%;重点控制区为昆明市主城区,其次是呈贡新区,并在此基础上提出相应的防治措施。城市面源污染控制区划,对滇池流域面源污染治理具有重要意义。 相似文献
488.
生态修复水生植物根际氨氧化细菌的研究 总被引:8,自引:4,他引:4
为研究水生植被恢复对底泥氨氧化细菌(ammonia-oxidizing bacteria,AOB)种群的影响,选取在生态修复中广泛使用的4种水生植物,芦苇(Phragmites communis)、窄叶香蒲(Typha angustifolia L.)、菹草(Potamogeton crispus L.)和荇菜(Limnanthemun nymphoides),采用最大可能数法(most pmbable number,MPN)计数AOB的数量,巢式聚合酶链式反应-变性梯度凝胶电泳(nested polymerase chain reaction-denaturing gradienl gel electmphoresis,nested PCR-DGGE)及条带回收测序的方法分析AOB的主要种类.结果显示,水生植物根际AOB密度显著高于无水生植物的表层底泥,而芦苇(2.8×105cells/g)和菖蒲(4.3×10'celts/g)又明显高于菹草(9.3 x 104cells/g)和荇菜(7.7×104 cells/g).水生植物根际呈氧化环境,而NH 4的浓度低于无水生植物的对照区.DNA测序结果显示尽管不同植物根际AOB主要种类有所区别,但基本属于亚硝化单胞菌属(Nitrosomonas).此类微生物群落在水生植物根际的聚集对促进生态修复中N元素的循环具有重要作用. 相似文献
489.
针对受低浓度氨氮污染的地下水,实验筛选组合了不同的反应介质,利用串联的多介质填充柱模拟渗透反应格栅,通过物理吸附及生物硝化-反硝化作用来实现氮的去除。结果表明,在进水氨氮浓度为10 mg/L、流速为0.5 m/d的条件下,模拟柱对氨氮的去除率达到98%以上,且不会出现亚硝酸盐及硝酸盐浓度的升高。水体经过释氧柱后溶解氧由2mg/L升高至10 mg/L以上,表明释氧材料可提供硝化细菌所需的好氧环境。好氧柱中填充易于生物挂膜的生物陶粒及对氨氮有较强吸附能力的沸石,二者联用通过生物硝化-物理吸附协同作用实现对氨氮的去除,其中生物作用实现的氨氮去除量占总去除量的50%左右。后续厌氧反应柱填充海绵铁除氧并利用松树皮颗粒作为碳源,创造反硝化菌生长条件,硝酸盐氮浓度可由10 mg/L降低至5 mg/L以下,实现对好氧反应阶段所产生的硝酸盐的去除,避免了地下水的二次污染。 相似文献
490.
Photosensitized degradation of bisphenol A involving reactive oxygen species in the presence of humic substances 总被引:10,自引:0,他引:10
The photodegradation of endocrine disrupter bisphenol A (BPA) in the presence of natural humic substances (HS) under simulated solar irradiation was studied. BPA underwent slow direct photolysis in neutral pure water, but rapid photosensitized degradation in four kinds of HS, following pseudo-first-order reaction. Reactive oxygen species (ROS) formed from HS were determined, including OH, (1)O(2) and H(2)O(2). The enhancement of BPA degradation by adding Fe(III) was primarily attributed to the oxidation of OH produced from photo-Fenton-like reaction. And the joint effects of HS and nitrate ions coexisting on BPA degradation appeared to depend on respective concentration levels. The effects of dissolved oxygen suggested that the energy transfer between excited state of SRFA and NOFA likely occurred, while the abstraction of phenolic hydrogen atom to reactive triplet state of NOHA possibly took place. Based on the structural analyses of main intermediates and degradation products of BPA detected by GC-MS, the possible photodegradation pathways were proposed, involving the alky cleavage, alkyl oxidation and OH addition. This study gave a better understanding for the photochemical transformation of BPA induced by ROS generated from natural water composition under sunlight irradiation. 相似文献