基于Landset TM/ETM 和HJ 1A/B影像的丹江口水库水域变化监测研究

位于湖北和河南两省交界的丹江口水库是南水北调中线工程的水源地,水库的水域变化监测与评估,对保障水库调水能力具有重要意义。收集了2002~2011年47幅Landsat TM/ETM和HJ 1A/B卫星遥感影像,采用基于阈值分割的归一化水体指数法（NDWI）提取了过去10 a的水库水域动态信息。结果表明：水库各月份平均水域面积从12月至次年3月,呈现下降趋势,而从3月到12月,呈现波动上升的趋势,最小水域面积出现在3月份,最大水域面积出现在12月份;由于受上游明显季节性降雨及水库运行管理的影响,丹江口水库丰水期（7月~次年1月）水域面积较枯水期（2月~6月）波动更为明显。而四季之中,春夏季节水库水域面积相对稳定,秋冬季节水域面积波动较大。针对枯水季节水库水量少的情况,管理部门应该加强监测力度,合理调蓄,保证水库的供水能力。从过去10 a整体来看,水库水域面积基本维持在300 km2以上,通过分析水库水域面积波动较小、影像积累最多的5月份遥感影像,发现水库水域面积呈现增长趋势,并且在枯水期、丰水期和过去10 a整体上都呈现了不同程度的增长趋势;此外,水库蓄水新增的水域面积主要集中在水库东、北部地区,应加强对这部分地区的生态恢复和环境监测     

高铁扣件弹条疲劳断裂原因分析

通过对WJ-7型扣件中60Si2MnA弹条在拉伸-扭转试验过程发生断裂的原因进行分析和数值模拟研究,得出弹条断裂的原因.对60Si2MnA弹条承受的荷载进行分析可知,WJ-7型扣件在铁垫板与弹条后端接触区域内弯处应力集中最大,是造成弹条断裂破坏的主要原因之一,而弹条断裂的根本原因是弹条长期处于极限强度下工作,使弹条最终...     

Highly efficient conversion of sugarcane bagasse pretreated with liquid hot water into ethanol at high solid loading

Liquid hot water (LHW), an environmental-friendly physico-chemical treatment, was applied to pretreat the sugarcane bagasse (SCB). Tween80, a non-ionic surfactant, was used to enhance the enzymatic hydrolysis of the pretreated SCB. It found that 0.125 mL Tween80 /g dry matter could make the maximum increase (33.2%) of the glycan conversion of the LHW-pretreated SCB. A self-designed laboratory facility with a plate-and-frame impeller was applied to conduct batch hydrolysis, fed-batch hydrolysis, and the process of high-temperature (50°C) fed-batch hydrolysis following low-temperature (30°C) simultaneous saccharification and fermentation (SSF) which was adopted to overcome the incompatible optimum temperature of saccharification and fermentation in the SSF process. After hydrolyzing LHW-pretreated SCB for 120 h with commercial cellulase, the total sugar concentration and glycan conversion obtained from fed-batch hydrolysis were 91.6 g/L and 68.3%, respectively, which were 9.7 g/L and 7.3% higher than those obtained from batch hydrolysis. With Saccharomyces cerevisiae Y2034 fermenting under the non-sterile condition, the ethanol production and theoretical yield obtained from the process of SSF after fed-batch hydrolysis were 55.4 g/L and 88.3% for 72h, respectively, which were 15.5 g/L and 24.7% higher than those from separate fed-batch hydrolysis and fermentation. The result of this work was superior to the reported results obtained from the LHW-pretreated SCB.     

Current status and historical variations of phthalate ester (PAE) contamination in the sediments from a large Chinese lake (Lake Chaohu)

The residual levels of phthalate esters (PAEs) in the surface and two core sediments from Lake Chaohu were measured with a gas chromatograph–mass spectrometer (GC–MS). The temporal–spatial distributions, compositions of PAEs, and their effecting factors were investigated. The results indicated that di-n-butyl phthalate (DnBP), diisobutyl phthalate (DIBP), and di(2-ethylhexyl) phthalate (DEHP) were three dominant PAE components in both the surface and core sediments. The residual level of total detected PAEs (∑PAEs) in the surface sediments (2.146?±?2.255 μg/g dw) was lower than that in the western core sediments (10.615?±?9.733 μg/g) and in the eastern core sediments (5.109?±?4.741 μg/g). The average content of ∑PAEs in the surface sediments from the inflow rivers (4.128?±?1.738 μg/g dw) was an order of magnitude higher than those from the lake (0.323?±?0.093 μg/g dw), and there were similar PAE compositions between the lake and inflow rivers. This finding means that there were important effects of PAE input from the inflow rivers on the compositions and distributions of PAEs in the surface sediments. An increasing trend was found for the residual levels of ΣPAEs, DnBP, and DIBP from the bottom to the surface in both the western and eastern core sediments. Increasing PAE usage with the population growth, urbanization, and industrial and agricultural development in Lake Chaohu watershed would result in the increasing production of PAEs and their resulting presence in the sediments. The significant positive relationships were also found between the PAE contents and the percentage of sand particles, as well as TOC contents in the sediment cores.     

Effect of alginate on the aggregation kinetics of copper oxide nanoparticles (CuO NPs): bridging interaction and hetero-aggregation induced by Ca<Superscript>2+</Superscript>

The stability of CuO nanoparticles (NPs) is expected to play a key role in the environmental risk assessment of nanotoxicity in aquatic systems. In this study, the effect of alginate (model polysaccharides) on the stability of CuO NPs in various environmentally relevant ionic strength conditions was investigated by using time-resolved dynamic light scattering. Significant aggregation of CuO NPs was observed in the presence of both monovalent and divalent cations. The critical coagulation concentrations (CCC) were 54.5 and 2.9 mM for NaNO₃ and Ca(NO₃)₂, respectively. The presence of alginate slowed nano-CuO aggregation rates over the entire NaNO₃ concentration range due to the combined electrostatic and steric effect. High concentrations of Ca²⁺ (>6 mM) resulted in stronger adsorption of alginate onto CuO NPs; however, enhanced aggregation of CuO NPs occurred simultaneously under the same conditions. Spectroscopic analysis revealed that the bridging interaction of alginate with Ca²⁺ might be an important mechanism for the enhanced aggregation. Furthermore, significant coagulation of the alginate molecules was observed in solutions of high Ca²⁺ concentrations, indicating a hetero-aggregation mechanism between the alginate-covered CuO NPs and the unabsorbed alginate. These results suggested a different aggregation mechanism of NPs might co-exist in aqueous systems enriched with natural organic matter, which should be taken into consideration in future studies.

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Graphical abstract Hetero-aggregation mechanism of CuO nanoparticles and alginate under high concentration of Ca²⁺

     

In situ immobilization of cadmium in soil by stabilized biochar-supported iron phosphate nanoparticles

The potential for nanoscale phosphate amendments to remediate heavy metal contamination has been widely investigated, but the strong tendency of nanoparticles to form aggregates limits the application of this technique in soil. This study synthesized a composite of biochar-supported iron phosphate nanoparticle (BC@Fe₃(PO₄)₂) stabilized by a sodium carboxymethyl cellulose to improve the stability and mobility of the amendment in soil. The sedimentation test and column test demonstrated that BC@Fe₃(PO₄)₂ exhibited better stability and mobility than iron phosphate nanoparticles. After 28 days of simulated in situ remediation, the immobilization efficiency of Cd was 60.2 %, and the physiological-based extraction test bioaccessibility was reduced by 53.9 %. The results of sequential extraction procedures indicated that the transformation from exchangeable (EX) Cd to organic matter (OM) and residue (RS) was responsible for the decrease in Cd leachability in soil. Accordingly, the pot test indicated that Cd uptake by cabbage mustard was suppressed by 86.8 %. Compared to tests using iron phosphate nanoparticles, the addition of BC@Fe₃(PO₄)₂ to soil could reduce the Fe uptake of cabbage mustard. Overall, this study revealed that BC@Fe₃(PO₄)₂ could provide effective in situ remediation of Cd in soil.     

Influence of filtration velocity on DON variation in BAF for micropolluted surface water treatment

Biological aerated filters (BAFs) are widely used for the treatment of micropolluted surface water. However, the biological process produces dissolved organic nitrogen (DON), which, as precursors of nitrogenous disinfection by-products, pose potential threats to drinking water safety. Therefore, to control DON in BAF effluent, it is necessary to study the influence of BAF operation parameters on DON production. In this study, the influence of filtration velocity in a BAF on DON production was investigated. Under different filtration velocity (0.5, 2, and 4 m/h) conditions, profiles of DON concentrations along the media layer were measured. The profile at a filtration velocity of 0.5 m/h showed a decreasing trend, and the ones under filtration velocities of 2 and 4 m/h fluctuated in a small range (from 0.1 to 0.4 mg/L). Moreover, the relatively high filtration velocities of 2 and 4 m/h resulted in a lower level of DON concentration. Additionally, 3D excitation-emission matrix fluorescence spectroscopy was used to characterize DON. It is found that the patterns of DON at a relatively high filtration velocity condition (4 m/h) were obviously different from the ones under low filtration velocity conditions (0.5 and 2 m/h).     

贵州省三岔河流域水化学特征及其控制因素

对乌江源区三岔河流域枯水期和丰水期河水样品离子浓度及组成特征分析表明,河水主要的阴阳离子分别是HCO_3~–和Ca~(2+),分别占到总阴离子量的55%和总阳离子量的70%,与喀斯特地区流域相似。主要离子的时空分布的对比分析表明,Ca~(2+)、Mg~(2+)、Na~+、HCO_3~–、Cl~–枯水期浓度略高于丰水期,而K+、SO_4~(2–)、NO_3~–两期浓度变化相对较小;空间分布的多样化,反映了不同小流域在地质背景、生态环境、人为活动等方面的差异对河水离子的影响。通过Gibbs图分析表明,研究区河水水化学主要受到岩石风化的影响,通过阴阳离子三角图分析表明,研究区河水水化学主要受到碳酸岩盐的影响,并且硫酸广泛参与到岩石风化中,人为活动对流域水化学组成也有一定影响。     

2000~2014年武汉市城市扩展时空特征分析

基于不同时相的高分辨率遥感影像,采用面向对象的解译方法提取了武汉市2000、2005、2010和2014年的土地覆被信息,从城市扩展强度指数,城市中心坐标迁移和分形维数等方面分析了武汉市2000～2014年城市扩展时空特征。结果表明：2000～2014年间,武汉市城市扩展强度指数为1.41,各主城区城市扩展强度不一,洪山区建设用地的增加对主城区城市扩展的贡献最大;在扩展过程中,武汉市城市分形维数增加,城市空间形态变复杂;其扩展呈现核心-放射扩展模式,并逐渐转向圈层式;自然条件、经济、人口、交通、政策和城市规划是武汉市城市扩展的主要驱动力,但随着交通的发展,自然条件和经济对武汉市城市扩展的驱动作用正逐渐减弱。