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231.
东北过伐林灌木层物种多样性与林分因子的典型相关分析 总被引:8,自引:0,他引:8
研究林分特征尤其是经营上可以控制的因子对生物多样性的影响,将有助于制定合理的经营措施来维持和保护生物多样性,本文作者以我国东北过伐林区3种典型天然林类型为对象,采用典型相关分析方法,研究影响灌木层物种多样性的主要因子。结果表明:影响灌木层物种多样性的主要因子包括土壤含水率,树种多样性和林分密度;灌木层多样性组的变异被林分组第一典型变量解释的比例为68.32%,仍有31.68%的变异不能得到解释。 相似文献
232.
Tomás Landete-Castillejos Andrés García Francisco R. López-Serrano Laureano Gallego 《Behavioral ecology and sociobiology》2005,57(3):267-274
Several theories predict a sex-biased investment either through unbalanced sex ratios in offspring or through differences in provisioning. According to them, one would expect an optimisation in indirect fitness, or else a compensation for increased mortality of one sex. In addition, biases in provisioning may also arise as a consequence of weight-dependent non-adaptive nutrient demands by offspring. This study examines milk provisioning and sex biases in offspring sex ratio together with maternal quality variables. Mothers of higher quality (weight and age) showed greater milk provisioning ability (in terms of production) resulting in greater calf weight gain. Mothers of sons produced greater yields of milk, milk protein, fat and lactose than mothers of daughters, and increased percentage of protein after controlling for higher male birth weight. In contrast, mothers of males did not differ from mothers of females in age or any body weight variables related to maternal quality. These results suggest that differences in milk production and composition for sons and daughters are rather a mechanism to optimise indirect fitness than a mechanism to compensate for increased mortality in male calves, or a consequence of greater weight-dependent nutrient demands by heavier male calves. Results also suggest that biases in milk provisioning may occur without biases in offspring sex ratio, and furthermore, in contrast to the prediction that biases should be relative to the mean investment of the population, that milk provisioning biases might not be relative.Communicated by F. Trillmich 相似文献
233.
铁改性赤泥吸附剂的制备及其除砷性能研究 总被引:5,自引:0,他引:5
以氧化铝生产废渣--赤泥为原料,采用铁盐改性处理制备了新型羟基铁包覆型赤泥除砷吸附剂.研究考察了吸附剂吸附砷效能、投加量、吸附时间和pH值对吸附除砷效果的影响;采用扫描电镜(SEM)、红外光谱(IR)、比表面积(BET)等仪器对吸附剂进行了表征,并探讨了吸附机制.结果表明,铁盐改性赤泥吸附剂对As(V)具有显著吸附效能,在pH为7,初始砷浓度为1 mg·L-1,铁盐改性赤泥吸附剂饱和吸附容量为50.6mg·g-1时,除砷率高达99.9%,吸附后出水砷含量可达到0.01 mg·L-1以下,吸附规律符合Langmuir等温方程式;溶液pH值显著影响砷去除效果,吸附机制主要为羟基铁的表面吸附机制;吸附后的吸附剂可通过NaOH溶液再生,脱附率达到92.1%. 相似文献
235.
食品生产废水属于高浓度有机废水,具有排水量大、污染物浓度、水质水量变化大的特点,如不处理就直接排放,将会对水环境造成严重的污染.本工程中废水原水水质参数为:CODCr<5000mg/L,BOD5<3000mg/L,SS<500mg/L,pH5.0~7.5,水温20~30℃.针对该废水水质特点,采用气浮-生化-砂滤工艺处理食品生产废水.运行结果表明,该处理工艺具有处理效率高、操作管理简便、抗冲击负荷、污泥量小、出水水质稳定、运行成本低等优点,处理后出水CODCr85mg/L,BOD524.3mg/L,SS56.2mg/L,pH6~8,达到<污水综合排放标准>(GB8978-1996)中的一级标准. 相似文献
236.
237.
Large amounts of 137Cs have been accidentally released to the subsurface from the Hanford nuclear site in the state of Washington, USA. The cesium-containing liquids varied in ionic strengths, and often had high electrolyte contents, mainly in the form of NaNO3 and NaOH, reaching concentrations up to several moles per liter. In this study, we investigated the effect of ionic strengths on Cs migration through two types of porous media: silica sand and Hanford sediments. Cesium sorption and transport was studied in 1, 10, 100, and 1000 mM NaCl electrolyte solutions at pH 10. Sorption isotherms were constructed from batch equilibrium experiments and the batch-derived sorption parameters were compared with column breakthrough curves. Column transport experiments were analyzed with a two-site equilibrium-nonequilibrium model. Cesium sorption to the silica sand in batch experiments showed a linear sorption isotherm for all ionic strengths, which matched well with the results from the column experiments at 100 and 1000 mM ionic strength; however, the column experiments at 1 and 10 mM ionic strength indicated a nonlinear sorption behavior of Cs to the silica sand. Transport through silica sand occurred under one-site sorption and equilibrium conditions. Cesium sorption to Hanford sediments in both batch and column experiments was best described with a nonlinear Freundlich isotherm. The column experiments indicated that Cs transport in Hanford sediments occurred under two-site equilibrium and nonequilibrium sorption. The effect of ionic strength on Cs transport was much more pronounced in Hanford sediments than in silica sands. Effective retardation factors of Cs during transport through Hanford sediments were reduced by a factor of 10 when the ionic strength increased from 100 to 1000 mM; for silica sand, the effective retardation was reduced by a factor of 10 when ionic strength increased from 1 to 1000 mM. A two order of magnitude change in ionic strength was needed in the silica sand to observe the same change in Cs retardation as in Hanford sediments. 相似文献
238.
Dahe Jiang Yang Zhang Xiang Hu Yun Zeng Jianguo Tan Demin Shao 《Atmospheric environment (Oxford, England : 1994)》2004,38(40):7055
An air pollution index (API) reporting system is introduced to selected cities of China for public communication on air quality data. Shanghai is the first city in China providing daily average API reports and forecasts. This paper describes the development of an artificial neural network (ANN) model for the API forecasting in Shanghai. It is a multiple layer perceptron (MLP) network, with meteorological forecasting data as the main input, to output the next day average API values. However, the initial version of the MLP model did not work well. To improve the model, a series of tests were conducted with respect to the training method and structure optimization. Based on the test results, the training algorithm was modified and a new model was built. The new model is now being used in Shanghai for API forecasting. Its performance is shown reasonably well in comparison with observation. The application of the old model was only weakly correlated with observation. In 1-year application, the correlation coefficients were 0.2314, 0.1022 and 0.1710 for TSP, SO2 and NOx, respectively. But for the new model, for over 8 months application, the correlation coefficients are raised to 0.6056, 0.6993 and 0.6300 for PM10, SO2, and NO2. Further, the new algorithm does not rely on manpower intervention so that it is now being applied in several other Chinese cities with quite different meteorological conditions. The structure of the model and the application results are presented in this paper and also the problems to be further studied. 相似文献
239.
240.
The current approach for modelling ion adsorption onto binary (hydr)oxides using homogeneous surface complexation models involves the assumption of either an ideal mixture of the two surfaces (i.e. two surface sites on one surface) or a patchwise surface (i.e. two surfaces with one surface site on each surface). As the physical truth should be between these two limiting cases, a model which assumes a patchwise surface constituted of three patches is proposed. Two patches represent the distinct (hydr)oxides, and the third one a mixture of these distinct (hydr)oxides. Using the diffuse layer model, the three approaches are applied to literature data for Cd adsorption onto binary mixtures of alumina-coated silica at total constant Cd concentration and varying amounts of alumina coatings. For Cd adsorption onto these binary (hydr)oxide systems, the new approach explains the observed potential effects. The proposed model, which contains two additional adjustable parameters in terms of site concentrations or one adjustable parameter in terms of specific surface area, is more successful than the two limiting cases. The new model is then validated by predicting Ca and Zn behaviour on the same binary (hydr)oxide system. 相似文献