Influence of sediment grain size and mineralogy on testate amoebae test construction

Testate amoebae are increasingly used for environmental monitoring as well as paleoenvironmental reconstructions. Paleoecological interpretations of testate amoebae assemblages depend on the understanding of the ecological processes operating today. We then ask the question of the link between testate structure and its environment. This study analyses both the grain size and mineralogical assemblage of tests of common species belonging to the genus Centropyxis and Difflugia. It is concluded that grain size is a limiting factor for test construction, whereas mineral composition is not. Hence, when analyzing agglutinated testate amoebae for paleoenvironmental reconstructions, it should be taken into account the mean grain size of the sediment. A non-appropriate grain-size probably inhibits the development of a testate amoebae specific assemblage.     

Shallow water SPH for flooding with dynamic particle coalescing and splitting

In this paper an adaptive algorithm for Smoothed Particle Hydrodynamics (SPH) for the Shallow Water Equations (SWEs) is presented. The area of a particle is inversely proportional to depth giving poor resolution in small depths without particle refinement. This is a particular limitation for flooding problems of interest here. Higher resolution is created by splitting the particles, while particle coalescing (or merging) improves efficiency by reducing the number of the particles when acceptable. The new particle coalescing procedure merges two particles together if their area becomes less than a predefined threshold value. Both particle splitting and coalescing procedures conserve mass and momentum and the smoothing length of new particles is calculated by minimizing the density error of the SPH summation. The new dynamic particle refinement procedure is assessed by testing the numerical scheme against analytical, experimental and benchmark test cases. The analytical cases show that with particle splitting and coalescing typical convergence rates remain faster than linear. For the practical test case, in comparison to using particle splitting alone, the particle coalescing procedure leads to a significant reduction of computational time, by a factor of 15. This makes the computational time of the same order as mesh-based methods with the advantage of not having to specify a mesh over a flood domain of unknown extent a priori.     

Deciphering signals of late Holocene fluvial and aeolian supply from a shelf sediment depocentre off Senegal (north‐west Africa)

High‐resolution climatic records of the late Holocene along the north‐west African continental margin are scarce. Here we combine sediment grain size, elemental distribution and mineral assemblage data to trace dust and riverine sources at a shallow‐marine sediment depocentre in the vicinity of the Senegal River mouth. The aim is to understand how these terrigenous components reflect climate variability during the late Holocene. Major element contents were measured and mineral identification was performed on three sub‐fractions of our sediment core: (i) fluvial material < 2 µm, (ii) aeolian material of 18–63 µm and (iii) a sub‐fraction of dual‐origin material of 2–18 µm. Results show that more than 80% of the total Al and Fe terrigenous bulk content is present in the fluviogenic fraction. In contrast, Ti, K and Si cannot be considered as proxies for one specific source off Senegal. The Al/Ca ratio, recording the continental river runoff, reveals two dry periods from 3010 to 2750 cal a BP and from 1900 to 1000 cal a BP, and two main humid periods from 2750 to 1900 cal a BP and from 1000 to 700 cal a BP. The match between (i) intervals of low river runoff inferred by low Al/Ca values, (ii) reduced river discharge inferred by integrated palynological data from offshore Senegal and (iii) periods of enhanced dune reactivation in Mali confirms this interpretation. Copyright © 2011 John Wiley & Sons, Ltd.     

关于下蜀黄土分类新方法及其承载力探讨

下蜀黄土是我国区域性分布的一种特殊性土，是在干旱气候条件下由风力堆积而成。单一地采用塑性指数（Ip)对其进行分类是显进管于简单而不能反映其特征。本文综合其活动性指数及粘粒含量进行分类的新方法，有利于对下蜀黄土进行评价。同时因其粉粒含量超过50％，受“袜度效应”影响，不能简单地套用粘性土公式，笔者总结了以往下蜀土分布地区采用的粘性土，新黄土公式，注意到Ip,Ps与fo,fk的相关性，提出了fo=100βPs 40α经验公式。     

Mathematical attributes of some soil–water characteristic curve models

Numerous mathematical models have been proposed in the research literature to represent soil–water characteristic curve data. A number of proposed mathematical models are summarized and the significance of each of the associated soil parameters is illustrated. The advantages and disadvantages of the various mathematical models are outlined. The derivatives for each of the model equations are presented along with comments regarding the efficiency of the best-fit regression procedures.The models using three soil parameters models proved to be superior for representing the wide range of soil suctions required in solving geotechnical problems. Regression analyses using three soil parameters were shown to be numerically more stable, converging with a reasonable number of iterations.     

Electron Probe Microanalysis of Environmental Samples: Preparation of Reference Materials, Correction for Particle Size Effects and Representative Results on Sediments Recovered from Snow, Power Station Fly Ash and Bone Samples

In this paper we report the results of electron probe X-ray microanalysis (EPMA) that was used to study environmental materials. The mode of preparation and certification of reference samples based on a basaltic glass matrix for environmental applications of EPMA is described. These samples were prepared containing scandium, strontium and barium (from 0.03 up to 7% m/m) and an evaluation was made of homogeneity, their stability to local heating, followed by analysis by independent methods for certification of composition. Matrix correction procedures for the EPMA technique have been developed for particles having a size commensurable with the volume of X-ray generation. An analytical equation for the size factor is proposed and two techniques for selecting optimum conditions for the analysis of environmental samples by EPMA are reported. These procedures provided satisfactory results when utilized in analysing sediments recovered from snow, coal fly ash and the bones of animals and fish, results from which can be used as indicators for evaluating the pollution level of the lower atmosphere, surface and ground water, as well as revealing pollution mechanisms.     

Correction factors for estimating suspended sediment export from loess catchments

This study focuses on problems related to estimating the exact exported suspended sediment quantity and quality from flow‐proportional samples taken at a fixed height at the outlet of a small, agricultural catchment in central Belgium. First, a correction factor is introduced to estimate the real suspended sediment concentration. This factor depends on the stream depth and the grain size distribution of the sediment and is necessary because of the presence of a concentration gradient in the stream. Secondly, water depth is corrected for the sediment volume, and thirdly, the grain size distribution of the exported sediment is corrected. The application of these correction factors leads to a reduction of the estimated total sediment export by 18 per cent (from 4810 Mg over a period of three years to 3930 Mg). Furthermore, the importance of small grain size fractions increases, leading to higher enrichment ratios for the clay fraction and lower ratios for the sand fraction. Suspended sediment export is thus more selective than was previously thought. Due to the overestimation of the sediment export, total phosphorus losses from the catchment are also overestimated by 17 per cent. This paper therefore emphasizes that point sampling of suspended sediment is biased and that a method should be incorporated to correct the sediment export in terms of quantity and quality. Copyright © 2001 John Wiley & Sons, Ltd.     

Effect of spatial pattern on nutrient reduction in the Liaohe Delta

The effect of spatial pattern on the nutrient reduction is investigated based on the spatial simulation model developed for the study area of the Liaohe Delta, China. Four scenarios are designed to test the effect of different landscape components on the nutrient reduction in the reed marsh: Canal density, reed area size, reed area shrinking pattern, and pumping station position. Based on a spatial model designed for the study area, the nutrient reduction in each case of these scenarios is simulated. The results indicate that each factor brings less than 10% change in the total nutrient reduction rate. More canals will not help much to improve nutrient reduction. Smaller areas are more efficient than larger ones. The shrinkage pattern is better than others in keeping a higher nutrient reduction rate. It is also more efficient to keep the pumping station near the border of the area to be irrigated. These conclusions provide theoretical supports to strategy makers for local land use planning, and contribute to the understanding of the relationship between landscape patterns and functions.     

Effect of spatial pattern on nutrient reduction in the Liaohe Delta

Landscape pattern analysis has been a major topic in landscape ecology[1-4]. Many quantitative methods have also been designed to describe the pattern, in order to get an overall idea of how the landscape is structured, and what is the effect of different patterns on large scale ecological processes[5-11]. So far this kind of research has mainly focused on habitat analysis, or site selection of wild animals, in the scope of nature conservation[12-13]. But few pattern analyses have been made on…