Diatom succession in an urban reservoir system

A 43 cm by 5 cm diameter sediment core sample was obtained from Ford Lake reservoir in Washtenaw County, Michigan, and sectioned at 1 cm intervals. The purpose of this study was to determine whether diatom communities in this reservoir have undergone quantifiable changes in abundance and composition since its creation. Thirty-one cm of this core appeared to represent material deposited since the creation of the reservoir based on changes in diatom abundance, the physical composition of the sediment and the change in biogenic SiO₂ concentration. Fortyseven species of diatoms were identified total concentrations of diatom remains varied from 1×10⁴ g^-1 to 1×10⁷ g^-1. Prior to the establishment of the reservoir, the diatom flora was dominated by benthic taxa. Benthic diatoms were numerous throughout the entire core, but eutrophic taxa (e.g., Aulacoseira italica, Aulacoseira granulata, Stephanodiscus niagarae, Fragilaria crotonensis) dominated much of the core after the reservoir's creation. Total diatom density increased about tenfold in the about the first 10–15 years after the reservoir's creation before declining markedly.     

DEM在丘陵地区土地整理项目中的应用研究

本文选取巴中市巴州区某镇土地整理项目作为研究对象,首先利用一个典型区域的数字化等高线插值生成规则格网DEM,然后利用DEM进行土地平整土方量的计算、道路和渠系的纵断面提取以及由DEM自动提取水系等。由DEM进行以上信息的提取时,主要利用MapGIS软件的DTM分析模块和ArcGIS水文分析工具。本文将DEM与土地整理项目有机结合,在计算精度和计算效率上比以前的方法均有所提高,但由于受原始地形图精度和软件的影响,DEM的精度尚需提高,计算方法尚需进一步的改进。     

INDUSTRIAL TOPOGRAPHY,GROUNDWATER, AND THE CONTOURS OF ENVIRONMENTAL KNOWLEDGE*

ABSTRACT. Civil engineers have played a central role in reshaping the physical environment during the past two centuries. Their accomplishments were made possible in no small measure by an ability to assess local hydrologic conditions and design structures to withstand the forces of water. Recent assertions that engineers had little comprehension of groundwater processes until the 1970s prompted an analysis of the engineering literature to reconstruct the state of knowledge up to the 1950s. Textbooks and manuals demonstrated that knowledge developed in constructing transportation lines, in draining cities and farms, in creating sewers, dams, canals, and lagoons, and in erecting manufacturing facilities contributed to design with groundwater in mind. In practice, this knowledge was available and drawn on, but the success of its application was inconsistent.     

Worth of secondary data compared to piezometric data for the probabilistic assessment of radionuclide migration

A common approach for the performance assessment of radionuclide migration from a nuclear waste repository is by means of Monte-Carlo techniques. Multiple realizations of the parameters controlling radionuclide transport are generated and each one of these realizations is used in a numerical model to provide a transport prediction. The statistical analysis of all transport predictions is then used in performance assessment. In order to reduce the uncertainty on the predictions is necessary to incorporate as much information as possible in the generation of the parameter fields. In this regard, this paper focuses in the impact that conditioning the transmissivity fields to geophysical data and/or piezometric head data has on convective transport predictions in a two-dimensional heterogeneous formation. The Walker Lake data based is used to produce a heterogeneous log-transmissivity field with distinct non-Gaussian characteristics and a secondary variable that represents some geophysical attribute. In addition, the piezometric head field resulting from the steady-state solution of the groundwater flow equation is computed. These three reference fields are sampled to mimic a sampling campaign. Then, a series of Monte-Carlo exercises using different combinations of sampled data shows the relative worth of secondary data with respect to piezometric head data for transport predictions. The analysis shows that secondary data allows to reproduce the main spatial patterns of the reference transmissivity field and improves the mass transport predictions with respect to the case in which only transmissivity data is used. However, a few piezometric head measurements could be equally effective for the characterization of transport predictions.     

汕尾电厂煤港工程泥沙问题研究

通过实测水文泥沙资料、岸滩冲瘀演变分析、泥沙计算、泥沙物理模型试验等手段对汕尾电厂煤港工程泥沙问题进行了研究。通过研究，了解了煤港工程海域--后江湾的水文泥沙基本特征、泥沙来源和泥沙运动规律，找出了煤港工程泥沙淤积成因，预报了煤港工程方案的泥沙淤积量，从泥沙淤积角度论证了煤港建设的可行性。     

Pore pressures in marine sediments: An overview of measurement techniques and some geological and engineering applications

Pore pressures in the seabed are extremely sensitive to any imposed stress because of the low permeabilities commonly exhibited by marine sediments. Consequently, the measurement of sediment pore pressures can be used to infer either the nature of the imposed stress (if the sediment properties are known) or the physical properties of the sediment (if the imposed stresses are known). Stresses of many different types may be exerted on the seabed either through hydrostatic forces (e.g. tidal and wave effects), or directly by lithospheric forces (e.g. tectonic and thermal forces). Several techniques for measuring in situ pore pressures in the upper few metres of sediments have been developed, and one instrument, the PUPPI, will operate autonomously in water depths up to 6000 m. Basic sediment properties and processes can already be inferred from pore pressure responses using this technique. However, further application and development could greatly enhance its capability, especially for long-term monitoring of sediment conditions. In this Chapter, pore pressure measurement techniques are briefly reviewed and problems are highlighted. An outline is given of some of the many ways in which pore pressure measurements could be used to gain further insight into geological processes and to determine some of the pertinent sediment properties more accurately for engineering applications.     

珠江三角洲思贤滘水文泥沙特征和现代演变

根据思贤滘的水文泥沙、地形和底质资料,分析了思贤滘的河床底质类型、分布规律、沉积物粒度组成、重矿物含量以及河床演变特征等,讨论了思贤滘的泥沙运移特点,指出西江和北江的推移质均已进入思贤滘,但未通过,因此,对思贤滘凹岸堤围的险段岁修工程不容忽视;并对思贤滘的整治规划提出了不设闸的刍议。     

The Western Boundary of the Equatorial Pacific Upwelling: Some Consequences of Climatic Variability on Hydrological and Planktonic Properties

The longitude of the western limit of the equatorial Pacific upwelling is a key parameter for studies of carbon budget and pelagic fisheries variability. Although it is well defined at the surface on the equator by a salinity front and a sharp variation of the partial pressure of CO₂, data from two equatorial cruises make it clear that this hydrological limit does not necessarily coincide with the boundary of the nitrate and chlorophyll enriched area. In January-February 1991 during a non-El Niño period, when trade winds and the South Equatorial current (SEC) were favorable to upwelling, the two limits were at the same longitude. Conversely, in September-October 1994 during El Niño conditions, when the equatorial upwelling had stopped, the nitrate and chlorophyll enriched zone was found a few degrees of longitude east of the hydrological boundary (5.5° at the surface and 2.5° for the 50 m upper layer), whereas no such offset was observed for zooplankton biomass. A simple model, based on the HNLC (High Nutrient - Low Chlorophyll) ecosystem functioning, was initialized with nitrate uptake measurements and estimates of upwelling break duration. The model results support the hypothesis that zonal separation of the limits arises from biological processes (i.e. nitrate uptake and phytoplankton grazing) achieved during that upwelling break.     

Dependence of thermal conductivity of snow on microstructure

A geometrical model, including different geometrical shapes influencing thermal conductivity of snow is proposed. The geometrical model has been assumed to comprise of unit cells having solid (ice) inclusion as an aggregation of spherical, cylindrical or cubical shapes with vertical connection, arranged in a cubic packing. From the geometrical model and one-dimensional heat transfer theory, the effective thermal conductivity has been computed. For this purpose, coupled one-dimensional heat transfer equations have been solved for steady-state condition to account for conduction in ice, conduction in air and latent heat transfer due to water vapour sublimation through air. The model demonstrates the dependency of thermal conductivity on density, grain-spacing, grain contact ratio and temperature. Spherical inclusions give highest conductivity while cubical inclusion estimates lowest value for the same density. Thermal conductivity has been found increasing sharply near to the packing density for all three shapes. Empirical model results and results obtained from existing microstructure based models have also been compared with the present model.     

Surface energy balance of seasonal snow cover for snow-melt estimation in N-W Himalaya

This study describes time series analysis of snow-melt, radiation data and energy balance for a seasonal snow cover at Dhundi field station of SASE, which lies in Pir Panjal range of the N-W Himalaya, for a winter season from 13 January to 12 April 2005. The analysis shows that mean snow surface temperature remains very close to the melting temperature of snow. It was found close to −1°C for the complete observational period which makes the snow pack at Dhundi moist from its beginning. The average air temperature over this period was found to be 3.5°C with hourly average variation from −5.5°C to 13°C. The snow surface at this station received a mean short wave radiation of 430W m⁻², out of which 298W m⁻² was reflected back by the snow surface with mean albedo value of 0.70. The high average temperature and more absorption of solar radiation resulted in higher thermal state of the snowpack which was further responsible for faster and higher densification of the snowpack. Net radiation energy was the major component of surface energy budget with a mean value of 83W m⁻². Bulk transfer model was used to calculate turbulent fluxes. The net energy was utilized for satisfying cold content and snow-melt by using measured snow surface temperature and density of snow pack. The mean square error between calculated and measured daily snow-melt was found to be approximately 6.6mm of water equivalent.