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521.
Changes in soil organic matter composition after afforestation of arable farmland in northeast China
Since the 1970s, a substantial area of arable farmland in a semi-humid area of northeast China has been planted as deciduous forests (Populus tomentosa Carr.). This study investigates the effects of afforestation on soil organic carbon (SOC) content and the chemical composition of the soil. Soil samples (Calcic chernozem) were collected from the upper 10?cm of paired arable land and secondary forests established 5 and 25 years previously. Carbon isotope analysis and pyrolysis–gas chromatography/mass spectrometry were used to determine SOC composition. The results show that (i) compared to the arable land, five years of afforestation caused a decrease in SOC and N concentration, while 25 years of afforestation resulted in an increase in SOC content; (ii) stable isotope δ13C analyses of the forest soils show gradual loss of crop-derived C and an accumulation of forest-derived C; and (iii) afforestation increased lignin abundance and decreased decompositional activity in the 25-year-old forest topsoil. Higher amounts of short-/mid-chain aliphatic compounds were observed in the 5-year-old forest (5–10?cm); and (iv) the arable soil contained substantially higher amounts of decomposed plant material and microbially derived substances. The results obtained suggest that long-term afforestation increases the SOC concentration, and alters the chemical composition of SOC. 相似文献
522.
为研究3种典型有机氯农药(%-六六六、p,p'-DDT和七氯)低浓度暴露对锦鲤幼鱼的雌激素效应及其体内富集效应,将锦鲤幼鱼暴露于有机氯农药的6个浓度组中进行20 d慢性毒性试验,测量血清中游离钙和蛋白结合磷含量及体内各组织有机氯农药残留。结果表明,在低浓度暴露20 d后,锦鲤幼鱼血清中游离钙和蛋白结合磷含量均随暴露浓度增加而呈先增后减之势,产生了明显的雌激素效应。p,p'-DDT在鱼体各组织中的富集能力远高于%-六六六和七氯;p,p'-DDT主要在鱼油中富集,其次为鱼肝、鱼鳃和鱼皮;%-六六六和七氯主要在鱼肝中富集,其次为鱼皮、鱼鳃和鱼油;3种有机氯农药在鱼肉中的富集相对较少。 相似文献
523.
Natural disasters cause considerable property damage and loss of life as well as destruction of ecosystem and natural resources. In the context of global change, extreme events are expected to increase in both frequency and intensity. To prevent natural disasters and mitigate the loss, we need to act quickly and effectively. It would be conducive to achieve sustainable economic development, reduce disaster vulnerabilities and risks, and build resilience through implementing effective measures of disaster prevention, preparedness, response, and recovery. 相似文献
524.
Jing REN Nan LI Lin ZHAO Nanqi REN 《Frontiers of Environmental Science & Engineering》2014,8(4):531-538
Ferric oxyhydroxide loaded anion exchanger (FOAE) hybrid adsorbent was prepared by loading nanosized ferric oxyhydroxide (FO) on anion exchanger resin for the removal of phosphate from wastewater. TEM and XRD analysis confirmed the existence of FO on FOAE. After FO loading, the adsorption capacity of the hybrid adsorbent increased from 38.70 to 51.52mg.g-1. Adsorption processes for both FOAE and anion resin were better fit to the pseudo first order model. Batch adsorption experiments revealed that higher temperature (313K), higher initial phosphate concentration (50 mg.L-1) and lower solution pH (pH value of 2) would be more propitious to phosphate adsorption. Competition effect of coexisting anions on phosphate removal can be concluded as sulfate 〉 nitrate 〉 chloride. Freundlich isotherm model can describe the adsorption of phosphate on FOAE more accurately, which indicated the heterogeneous adsorption occurred on the inner-surface of FOAE. 相似文献
525.
Oxidative stress parameters and some antioxidant defense systems in the liver of Carassius auratus exposed to glyphosate and its formulation (Roundup®) have been studied. Fish were exposed to glyphosate and its formulation at concentrations of 0.032, 0.16, 0.8, and 4.0 mg L?1, all calculated on glyphosate basis, for 11 days. Hydroxyl radical generation as determined by electron spin resonance spectroscopy of its spin-adduct with α-phenyl-t-butyl nitrone increased with the concentration of Roundup®. Superoxide dismutase activities were decreased relative to control by 21%–46% when exposed to glyphosate and 45%–52% when exposed to Roundup®, suggesting that the formulation is more toxic than glyphosate alone. Catalase showed no difference between both groups. 相似文献
526.
PFOS及其4种替代品对两栖动物非洲爪蟾和黑斑蛙蝌蚪的急性毒性结果为:用调聚法合成的织物三防整理剂对非洲爪蟾蝌蚪和黑斑蛙蝌蚪的96h-LC50分别为8和21mg·L-1,而PFOS对两种蝌蚪的96h-LC50分别为92和81mg·L-1。此实验结果说明织物三防整理剂的急性毒性高于PFOS。用电解氟化法合成的C4、C6织物三防整理剂和50%的全氟丁基有机铵盐阳离子表面活性剂浓度在100mg·L-1时,对两种蝌蚪都没有毒性。这说明,从急性毒性的角度,C4、C6织物三防整理剂和表面活性剂可作为PFOS的替代品使用,但是织物三防整理剂的急性毒性比PFOS大,作为替代品使用应慎重考虑。另外,PFOS和织物三防整理剂对黑斑蛙蝌蚪的急性毒性与对非洲爪蟾蝌蚪的急性毒性存在差异。出于保护我国本土两栖动物的目的,使用黑斑蛙开展毒性评价比使用非洲爪蟾更有现实意义。 相似文献
527.
528.
Effect of nitrogen deposition on China's terrestrial carbon uptake in the context of multifactor environmental changes 总被引:7,自引:0,他引:7
The amount of atmospheric nitrogen (N) deposited on the land surface has increased globally and by nearly five times in China from 1901 to 2005. Little is known about how elevated reactive N input has affected the carbon (C) sequestration capability of China's terrestrial ecosystems, largely due to the lack of reliable data on N deposition. Here we have used a newly developed data set of historical N deposition at a spatial resolution of 10 km x 10 km in combination with other gridded historical information on climate, atmospheric composition, land use, and land management practices to drive a process-based ecosystem model, the dynamic land ecosystem model (DLEM) for examining how increasing N deposition and its interactions with other environmental changes have affected C fluxes and storage in China's terrestrial ecosystems during 1901-2005. Our model simulations indicate that increased N deposition has resulted in a net C sink of 62 Tg C/yr (1 Tg = 1012 g) in China's terrestrial ecosystems, totaling up to 6.51 Pg C (1 Pg = 10(15) g) in the past 105 years. During the study period, the N-induced C sequestration can compensate for more than 25% of fossil-fuel CO2 emission from China. The largest C sink was found in southeast China, a region that experienced the most significant increase of N deposition in the period 1901-2005. However, the net primary productivity induced by per-unit N deposition (referred to as ecosystem N use efficiency, ENUE, in this paper) has leveled off or declined since the 1980s. This indicates that part of the deposited N may not be invested to stimulate plant growth, but instead leave the ecosystem by various pathways. Except shrubland and northwest/southwest China, signs of N saturation are apparent in the rest major biome types and regions, with ENUE peaking in the 1980s and leveling off or declining thereafter. Therefore, to minimize the excessive N pollution while keeping the N-stimulated C uptake in China's terrestrial ecosystems, optimized management practices should be taken to increase N use efficiency rather than to keep raising N input level in the near future. 相似文献
529.
双光谱卫星云图的模糊推理云分类 总被引:3,自引:0,他引:3
基于观测事实和分类经验,在对卫星云图上云系形态特征定性分析的基础上,采用模糊推理方法,提取出云类识别的诊断判别因子和模糊推理规则。通过对判别因子的模糊化处理和隶属度函数的调制优化,建立了卫星云图定量化的模糊推理云分类模型。4种常见云系的模糊推理分类试验结果表明,模糊推理方法在定量性、客观性和自动化等方面优于传统卫星云图目视判读方法,在卫星遥感资料的分析处理和天气预报等领域有较好的实用意义。 相似文献
530.