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991.
大口鲇幼鱼摄食、生长及驯化的初步研究 总被引:19,自引:4,他引:15
根据1991年1~12月的调查,陆水水库的浮游植物共8门118属,以绿藻、硅藻、蓝藻门的种类为主,占总属数的86.44%;浮游动物198种,其中原生动物38种、轮虫68种、枝角类61种、桡足类31种。浮游植物年平均数量和生物量分别为3.1449×10~6cell/L和1.937mg/L,数量以蓝藻、隐藻、硅藻最多,占总数量的91.33%,生物量以隐藻、硅藻、绿藻最大,占总生物量的85.03%,浮游植物初级毛产量为3.4gO_2/m~2·d。浮游动物年平均数量和生物量分别为2323.8ind/L和1.4837mg/L,数量以原生动物和轮虫最多,占96.89%,生物量以枝角类和桡足类为主,占79.94%.陆水水库浮游生物种类组成和现存量在不同的水域差异较大,季节变化明显。按水化学分析结果及浮游生物特征判定,陆水水库的营养类型为中营养型。还讨论了环境因子对水库浮游生物的影响。 相似文献
992.
Dedi?LiuEmail author Shenglian?Guo Zhaoli?Wang Pan?Liu Xixuan?Yu Qin?Zhao Hui?Zou 《Stochastic Environmental Research and Risk Assessment (SERRA)》2018,32(11):3099-3116
Hydrological models have been widely applied in flood forecasting, water resource management and other environmental sciences. Most hydrological models calibrate and validate parameters with available records. However, the first step of hydrological simulation is always to quantitatively and objectively split samples for use in calibration and validation. In this paper, we have proposed a framework to address this issue through a combination of a hierarchical scheme through trial and error method, for systematic testing of hydrological models, and hypothesis testing to check the statistical significance of goodness-of-fit indices. That is, the framework evaluates the performance of a hydrological model using sample splitting for calibration and validation, and assesses the statistical significance of the Nash–Sutcliffe efficiency index (Ef), which is commonly used to assess the performance of hydrological models. The sample splitting scheme used is judged as acceptable if the Ef values exceed the threshold of hypothesis testing. According to the requirements of the hierarchical scheme for systematic testing of hydrological models, cross calibration and validation will help to increase the reliability of the splitting scheme, and reduce the effective range of sample sizes for both calibration and validation. It is illustrated that the threshold of Ef is dependent on the significance level, evaluation criteria (both regarded as the population), distribution type, and sample size. The performance rating of Ef is largely dependent on the evaluation criteria. Three types of distributions, which are based on an approximately standard normal distribution, a Chi square distribution, and a bootstrap method, are used to investigate their effects on the thresholds, with two commonly used significance levels. The highest threshold is from the bootstrap method, the middle one is from the approximately standard normal distribution, and the lowest is from the Chi square distribution. It was found that the smaller the sample size, the higher the threshold values are. Sample splitting was improved by providing more records. In addition, outliers with a large bias between the simulation and the observation can affect the sample values of Ef, and hence the output of the sample splitting scheme. Physical hydrology processes and the purpose of the model should be carefully considered when assessing outliers. The proposed framework in this paper cannot guarantee the best splitting scheme, but the results show the necessary conditions for splitting schemes to calibrate and validate hydrological models from a statistical point of view. 相似文献
993.
994.
The three-dimensional hydrodynamic and eutrophication model was implemented based on EFDC to help eutrophication control decision making of Shenzhen Reservoir. Model calibration and validation were conducted with two set of independent observed data in 2009 and 2010–2011. The model represented the hydrodynamic process and the spatial and temporal distribution of water quality well. Subsequently, three eutrophication control scenarios were configured, included removing 100% nutrients from all tributaries, increasing by 50% of water flows, and removing 50% nutrients from Dongjiang. As results shown, the maximum chlorophyll-a concentrations were decreased by 1, 16.4 and 46.3%, the average chlorophyll-a concentrations were decreased by 1.3, 29.8 and 29.9%. Increasing water flows and removing nutrients from Dongjiang can significantly improve water quality and effectively reduce risk of water bloom. 相似文献
995.
Xuesong Wang Chunlai Zhang Xiaoqi Huang Yaping Shen Xueyong Zou Jiao Li Songbo Cen 《地球表面变化过程与地形》2019,44(2):614-623
Aeolian sand transport is a complicated process that is affected by many factors (e.g. wind velocity, sand particle size, surface microtopography). Under different experimental conditions, erosion processes will therefore produce different results. In this study, we conducted a series of wind tunnel experiments across a range of wind velocities capable of entraining sand particles (8.0, 10.0, 12.0, and 14.0 m s-1) to study the dynamic changes of the shear velocity, aerodynamic roughness length, and sand transport. We found that the shear velocity and aerodynamic roughness length are not constant; rather, they change dynamically over time, and the rules that describe their changes depend on the free-stream air velocity. For wind tunnel experiments without feeding sand into the airflow, the sand bed elevation decreases with increasing erosion time, and this change significantly affected the values of shear velocity and aerodynamic roughness length. A Gaussian distribution function described the relationships between the sand transport rate (qT) and the duration of wind erosion (T). It is therefore necessary for modelers to consider both deflation of the bed and the time scale used when calculating sand transport or erosion rates. © 2018 John Wiley & Sons, Ltd. 相似文献
996.
Lin Zou Lin Dong Meng Ning Kangjun Huang Yongbo Peng Shujian Qin Honglin Yuan Bing Shen 《Acta Geochimica》2019,(4):481-496
The continent is the second largest carbon sink on Earth’s surface.With the diversification of vascular land plants in the late Paleozoic,terrestrial organic carbon burial is represented by massive coal formation,while the development of soil profiles would account for both organic and inorganic carbon burial.As compared with soil organic carbon,inorganic carbon burial,collectively known as the soil carbonate,would have a greater impact on the long-term carbon cycle.Soil carbonate would have multiple carbon sources,including dissolution of host calcareous rocks,dissolved inorganic carbon from freshwater,and oxidation of organic matter,but the host calcareous rock dissolution would not cause atmospheric CO2drawdown.Thus,to evaluate the potential effect of soil carbonate formation on the atmospheric p CO2level,different carbon sources of soil carbonate should be quantitatively differentiated.In this study,we analyzed the carbon and magnesium isotopes of pedogenic calcite veins developed in a heavily weathered outcrop,consisting of limestone of the early Paleogene Guanzhuang Group in North China.Based on the C and Mg isotope data,we developed a numerical model to quantify the carbon source of calcite veins.The modeling results indicate that4–37 wt%of carbon in these calcite veins was derived from atmospheric CO2.The low contribution from atmospheric CO2might be attributed to the host limestone that might have diluted the atmospheric CO2sink.Nevertheless,taking this value into consideration,it is estimated that soil carbonate formation would lower 1 ppm atmospheric CO2within 2000 years,i.e.,soil carbonate alone would sequester all atmospheric CO2within 1 million years.Finally,our study suggests the C–Mg isotope system might be a better tool in quantifying the carbon source of soil carbonate. 相似文献
997.
Journal of Oceanology and Limnology - The relatively conserved 18S is often used in the phylogenetic analysis of microalgae. However, whether it can really help in barcoding microalgae needs to be... 相似文献
998.
基于SAR图像雨团足印的海面风向提取方法 总被引:1,自引:1,他引:0
利用地球物理模式函数进行SAR海面风速反演时,需以风向作为地球物理模式函数的输入。本文应用了一种利用SAR图像上雨团足印顺风一侧比逆风一侧明亮的图像特征的海面风向提取方法,以进行海面风速反演。4景RADARSAT-2卫星SAR示例数据风向提取结果相对于ASCAT散射计的风向均方根误差满足不大于16°。分别以本文方法提取的风向和ASCAT散射计风向作为输入,利用地球物理模式函数CMOD5进行海面风速的SAR反演,两者的风速反演结果基本一致,其均方根误差差值不超过0.3 m/s。本文利用SAR图像雨团足印信息的风向提取方法准确可靠,可应用于SAR海面风速反演。 相似文献
999.
A three-dimensional (3D) soil–structure interface model is proposed within the two-mechanism constitutive theory and bounding surface theory originally established for soils. The proposed model has two main characteristics: first, the model is formulated based on two different and superposed deformation mechanisms. The first mechanism is due to the stress ratio increment, and the second is due to the normal stress increment. Each mechanism induces a shear strain component and a normal strain component. The proposed model can be reduced to the conventional single-mechanism interface model. Second, the plastic modulus and stress dilatancy are defined using the bounding surface theory. The plastic flow rule under cyclic loading is modified and assumed to be dependent on both the stress state of the mapping point and the stress reversal loading direction. The proposed model was validated against the available 3D interface tests and was found to satisfactorily reflect the salient features of the interfaces under monotonic and cyclic loading paths with different normal boundaries. The problem in which the elastic normal stiffness in conventional single-mechanism interface models is often underestimated to enhance the simulation performance under varying normal stress conditions is solved by incorporating the second mechanism. And the effect of the second mechanism on the modeling behavior is discussed. The modified plastic flow direction accurately simulates the 3D cyclic shear response, and the difference between the model simulation and test result increases with the number of cycles by use of the plastic flow direction defined in conventional bounding surface theory. 相似文献
1000.
海底表层沉积物具有多相、多颗粒、多形态的组成结构,导致其声学特性复杂多样。通过分析压缩波速度和切变波速度特性的研究现状,指出有待于解决的科学问题和关键技术问题。在分析国内外有关海底沉积层声速特性研究基础上,提出采取系统、可控的实验测量手段解决当前测量存在的4点问题。综合分析了压缩波速度和切变波速度存在的统计回归关系和理论分析关系,探讨了当前地声反演、采样样品声学测量、原位声学测量3种方法存在的测量尺度、测量频率、测量状态等的差异,探讨建立不同测量方法和测量技术对测量结果进行统一性解释的方法,从而获得不同类型、不同区域的海底表层沉积物真实的声速特性。最后,从实验室声学测量、物理力学参数测量、流固耦合特性分析、原位测量及海底监测、采样测量与原位测量的误差分析及校正、海底大纵深声学测量6个方面提出技术需求,为提高声学探测海洋和海底的精度服务,推动海洋声学探测和海洋工程发展。 相似文献