High nutrient loading and climatic parameters influence the dominance and dissimilarity of toxigenic cyanobacteria in northern bays of Lake Victoria

Eutrophication of Lake Victoria led to changes in its phytoplankton communities. However, different levels of eutrophication exist in the open lake and the bays, and between embayments. This study utilized spatial and temporal sampling of Napoleon Gulf and Murchison Bay, exhibiting different trophic conditions. Over one year, we investigated phytoplankton biomass, richness, diversity and dissimilarity, and related the dynamics of the dominant species to the limnological and climatic conditions. The results confirmed that Napoleon Gulf and Murchison Bay showed large differences in eutrophication status, with lower nutrient concentrations in Napoleon Gulf than in Murchison Bay, where a strong gradient was observed from inshore to offshore areas. These nutrient dynamics resulted in a 4 to 10 fold higher chlorophyll-a in Murchison Bay than in Napoleon Gulf. From the embayments, 135 phytoplankton taxa were recorded with no significant differences in alpha diversity. However, high dissimilarity in community structure was observed in beta diversity, mostly due to a turnover among the dominant toxigenic species. Thus, from a similar species pool, there was a shift in the dominant toxigenic cyanobacteria from Microcystis flos-aquae and M. aeruginosa in Murchison Bay, Dolichospermum circinale and Planktolyngbya circumcreta in Napoleon Gulf to D. circinale in the offshore stations. These cyanobacteria are toxigenic taxa with known health hazards. Using partial least square models, we showed that both climatic variables (e.g. wind, solar radiation) and levels of inorganic dissolved nutrients (e.g. SRP, NO₃^–, and NH₄⁺) are the main drivers of differences and dominance in cyanobacteria communities in northern Lake Victoria.     

动态测量不确定度贝叶斯评定的改进方法研究

动态测量不确定度的评定一直是比较复杂的问题,到目前为止,国内外有许多学者对这一问题进行了探索与研究,给出了一些评定的方法,但这些方法都存在自身的缺点与不足,还不能给出十分精确的评定结果。因此,通过对现有基于贝叶斯理论的动态测量不确定度评定方法进行分析,用最大熵原理改进其先验分布的选择与计算方法,从而有效提高计算后验分布的精度,最终提高不确定度的计算准确度。     

基于朴素贝叶斯和支持向量机的自适应垃圾短信过滤系统

随着短信业务的不断发展,垃圾短信的特征和内容也在不断变化,传统垃圾短信过滤系统中存在的主要问题是,短信特征和内容未能得到及时更新而导致过滤性能降低。考虑朴素贝叶斯的快速统计分类及支持向量机（SVM）的增量训练等特点,将其应用于垃圾短信过滤中,并把分析结果及时反馈给在线过滤子系统,使得系统具有更好的自适应性。实验结果表明,该方法可有效地解决当前垃圾短信过滤系统中存在的问题。     

Case Study: Mass Transport Mechanism in Kyunggi Bay around Han River Mouth, Korea

The horizontal, two-dimensional Princeton Ocean Model was modified to include the salt and heat-balance equations and wetting-and-drying scheme. It was applied to Kyunggi Bay (Korea) to reproduce mean conditions for one typical year. Extensive data were compiled and analyzed to evaluate input parameters representative of long-term mean conditions for the tide, salinity, and temperature. The model, forced by four major tidal constituents (M2, S2, K1, and O1), daily freshwater discharges, and daily net surface heat exchange, produced a reasonable reproduction of observed tidal elevations, tidal currents, and long-term mean monthly distributions of salinity and temperature. The calculated residual circulation pattern is consistent with previously observed, though limited, data collected in the vicinity of Kanghwa Island and Inchon Harbor. The model was used to study the following mass transport mechanisms: tidal nonlinearity, barotropic pressure gradient associated with freshwater discharge, and baroclinic pressure gradient due to density gradient. The residual circulation pattern, and its variations under different freshwater flow regimes, was examined.     

Endocrine disrupter--estradiol--in Chesapeake Bay tributaries

Exogenous chemicals that interfere with natural hormonal functions are considered endocrine disrupting chemicals (EDCs). Estradiol (17β-estradiol or E2) is the most potent of all xenoestrogens. Induction of vitellogenin (VTG) production in male fish occurs at E2 concentrations as low as 1 ng l⁻¹. E2 reaches aquatic systems mainly through sewage and animal waste disposal. Surface water samples from ponds, rivers (Wicomico, Manokin and Pocomoke), sewage treatment plants (STPs), and coastal bays (Assawoman, Monie, Chincoteague, and Tangier Sound – Chesapeake Bay) on the Eastern Shore of Maryland were analyzed for E2 using enzyme linked immuno-sorbent assay (ELISA). E2 concentrations in river waters varied between 1.9 and 6.0 ng l⁻¹. Highest E2 concentrations in river waters were observed immediately downstream of STPs. E2 concentrations in all the coastal bays tested were 2.3–3.2 ng l⁻¹.     

Management of Fluid Mud in Estuaries, Bays, and Lakes. II: Measurement, Modeling, and Management

Techniques for measurement, modeling, and management of fluid mud are available, but research is needed to improve them. Fluid mud can be difficult to detect, measure, or sample, which has led to new instruments and new ways of using existing instruments. Multifrequency acoustic fathometers sense neither density nor viscosity and are, therefore, unreliable in measuring fluid mud. Nuclear density probes, towed sleds, seismic, and drop probes equipped with density meters offer the potential for accurate measurements. Numerical modeling of fluid mud requires solving governing equations for flow velocity, density, pressure, salinity, water surface, plus sediment submodels. A number of such models exist in one-, two-, and three-dimensional form, but they rely on empirical relationships that require substantial site-specific validation to observations. Management of fluid mud techniques can be classified as those that accomplish: Source control, formation control, and removal. Nautical depth, a fourth category, defines the channel bottom as a specific fluid mud density or alternative parameter as safe for navigation. Source control includes watershed management measures to keep fine sediment out of waterways and in-water measures such as structures and traps. Formation control methods include streamlined channels and structures plus other measures to reduce flocculation and structures that train currents. Removal methods include the traditional dredging and transport of dredged material plus agitation that contributes to formation control and/or nautical depth. Conditioning of fluid mud by dredging and aerating offers the possibility of improved navigability. Two examples—the Atchafalaya Bar Channel and Savannah Harbor—illustrate the use of measurements and management of fluid mud.     

Management of Fluid Mud in Estuaries, Bays, and Lakes. I: Present State of Understanding on Character and Behavior

Fluid mud is a high concentration aqueous suspension of fine-grained sediment in which settling is substantially hindered. It constitutes a significant management problem in rivers, lakes, estuaries, and shelves by impeding navigation, reducing water quality and damaging equipment. Fluid mud accumulations have been observed in numerous locations worldwide, including Savannah Harbor, U.S., the Severn Estuary, U.K., and the Amazon River Delta, Brazil. This paper describes the present state of knowledge on fluid mud characteristics, processes, and modeling. Fluid mud consists of water, clay-sized particles, and organic material and displays a variety of rheological behaviors ranging from elastic to pseudo-plastic. It forms by three principle mechanisms: (1) the rate of sediment aggregation and settling into the near-bottom layer exceeds the dewatering rate of the suspension; (2) soft sediment beds fluidized by wave agitation; and (3) convergence of horizontally advected suspensions. Once formed, fluid mud is transported vertically by entrainment and horizontally by shear flows, gravity, and streaming. If not resuspended, it slowly consolidates to form bed material. Quantitative relationships have been formulated for key fluid mud formation and movement mechanisms, but they rely on empirical coefficients that are often site- or situation-specific and are not generally transferable. Research to define general relationships is needed.     

邮件服务智能代理的研究

分析邮件特征对邮件分类的影响,提出了双层分类方法并用于邮件服务智能代理.它包括邮件长度分类、邮件采集与预处理、文本分词、特征选取和邮件分类器等功能模块.此代理不仅可使邮件服务器具有自动过滤垃圾邮件的能力,也可以用于电子政务和电子商务,对邮件自动分类和转发.该双层分类方法首先对邮件按长度进行分类,然后根据邮件的不同长度类分别使用不同的贝叶斯分类器,从而实现垃圾邮件的过滤.实验表明它有效地提高了邮件分类的效率.     

The Urban Complex: Scalar Probabilities and Urban Computation

Guest-editor Anthony Burke redefines complexity in relation to the city as ‘a dynamic and luminal organisational condition “growing at the edge of chaos”’ and in so doing shifts our understanding of urban trauma as an event intrinsic to the contribution of the metropolis rather than external to it. Copyright © 2010 John Wiley & Sons, Ltd.     

Case Study for a Cohesive Sediment Transport Model for Matagorda Bay, Texas, with Coupled ADCIRC 2D-Transport and SWAN Wave Models

Tidal current and wave forces are the primary factors causing agitation, suspension, and transport of littoral materials in a bay. This paper presents a study of the circulation patterns of the water and sediment fluxes in a real bay during ordinary natural weather conditions. A coupled hydrodynamic and wave model is developed to support the research. A two-dimensional parallel advanced circulation hydrodynamic model with an extended transport module is used to calculate the water circulation within the bay, while the simulating wave nearshore model is implemented to provide the wave parameter data. The month of March 2003 is selected to represent the test case for the sediment transport model in Matagorda Bay, Tex. The presence of wave action significantly, increases the amount of suspended sediment, and consequently, more deposited sediments occur around the ship channel, where shallow shoals are located. Comparison of the simulated deposited sediments in the Matagorda ship channel with the two selected points of historical dredging data of the bay gives a maximum difference of 22%. This result suggests the need for an extensive comparison study.