Evaluation of sampling methods for the estimation of structural indices in forest stands

The paper is about the accurate (i.e. unbiased and precise) and efficient estimation of structural indices in forest stands. We present SIAFOR, a computer programme for the calculation of four nearest-neighbour indices, which describe the spatial arrangement of tree positions, the distribution pattern of species, and the size differentiation between trees. The study uses SIAFOR as a sampling simulator in eight completely stem-mapped forest stands of varying area and structural complexity. We statistically evaluate two sample types (distance and plot sampling), comparing sampling error, bias and minimum sample size for index estimation. We introduce the concepts of measurement expansion factor (MEF) and design expansion factor (DEF) for the technical evaluation of sample type efficiency (optimal sample type). Results indicate that sampling error can reach high levels and that minimum sample sizes for index estimation often amply exceed the limit of 20% of tree density or 20 trees per species per hectare, that we set as the highest feasible sample size in normal situations. We found clear feasibility limits (in terms of minimal tree densities and reachable accuracy levels) for the estimation of all investigated indices. Generally, equal or higher sample sizes are needed for plot sampling than for distance sampling to reach equal accuracy levels. Nevertheless, plot sampling resulted more efficient for the estimation of tree size differentiation at low to medium accuracy levels. For all other investigated indices distance sampling resulted more efficient than plot sampling. Minimum sample size increases with accuracy and is negatively correlated with tree density. At a given accuracy level minimum sample size is highest for the estimation of relative mingling and lowest for tree size differentiation; furthermore it is generally lower in large stands than in small ones. Because of the consistency of our conclusions in all of the investigated stands, we think they apply in most stands of similar area (between 1 and 10 ha) and species diversity (not more than four species).     

湖南城市洪涝易损性诊断与评估

首先从孕育洪涝灾害的环境变异性、社会经济灾敏性、城市土地利用对洪涝的放大作用，防洪标准和人为设障等方面对湖南城市洪涝的易损性进行了总体诊断。然后，选取人口密度、工业产值密度、道路网密度、排水管道密度、建成区绿地率等指标，运用模糊综合评判对之进行了定量评估。将全省城市洪涝的易损性程度划分为5个等级；高度易损性，较高度易损性、中度易损性、较低度易损性、低度易损性。研究结果表明：湖南城市洪涝易损性程度总体水平高，因此，湖南洪涝防治要从以农村为重点转向以城市为重点，加大城市洪涝治理力度；湖南城市洪涝易损性程度等级与城市规模之间没有对应关系，因此，湖南城市洪涝防治应因地制宜。     

The contamination of fish with chlorinated hydrocarbons in Portugal: continental coast and Azores islands

In a baseline study, muscle and liver from important commercial fish belonging to different trophic levels were analysed for organochlorines. Samples of sole, sardine and hake were collected from seven locations off the Continental coast and greater forkbeard and horse mackerel off two Azores islands. Residues of ppDDT, ppDDE and PCBs were present in all muscle and liver samples. ppDDD occurred in all liver samples and in most muscle samples, except in sole where it occurred in 29% of the samples. Dieldrin was detected less frequently and did not occur in samples from the Azores. The residue levels were generally similar to those detected in related species from the North Sea, except for samples of sole collected between the Tagus and Sado estuaries where much higher residues were obtained. In view of the low consumption of insecticides in the Azores, it is proposed that long-range transport of organochlorines by winds and/or marine currents is responsible for their presence in this area. The organochlorine residues found in these fish showed no relationship with their position in the food chain but the values did increase with the quantity of lipids present. An unknown compound analysed by GC-MS interfered with DDE quantification in one sample of greater forkbeard.     

Belgian MSWI fly ashes and APC residues: a characterisation study

Municipal Solid Waste Incineration (MSWI) produces different sorts of residues, bottom ash, fly ashes and Air Pollution Control (APC) residues. Generally, fly ashes and APC residues are mixed at the MSWI plant and manage as a sole residue. In this study, fly ashes and APC residues have been sampled separately at different Belgian MSWI plant and analysed by X-ray fluorescence in order to highlight the composition differences that may appear between the solids. Ca and Cl are found to be the major elements in most of the samples. Lithophilic elements, such as Al and Si, are richer in furnace and boiler ashes, as can be expected. Leaching tests also show differences between the residues; leachates from furnace and boiler ashes are alkaline while those from bag filter residues present a pH value of 6, which impacts the leaching of heavy metals (Pb and Zn). The results suggest that it could be advantageous to manage fly ashes and APC residues separately by adjusting the treatment to their specificities.     

Etude sur l'activite initiale et la persistance d'un larvicide experimental a base de bacillus thuringiensis var. israelensis et d'une preparation commerciale contenant l'insecticide organophosphore temephos

Abstract

The larvicide activity of the experimental preparation SAN 402 I WDC containing B. Thuringiensis var. Israelensis and that of Abate 500 E (44 % temephos) were tested on the larvae of Aedes aegypti. The studies were performed on the following media : distilled water, pure and buffered at pH 9, 7 and 4 and pond water whether or not free from materials in suspension. The activity of both preparations is not influenced by the composition of the media, exception made for the presence of materials in suspension. The persistance varies according to the kind of the media and the concentration level. It is in general rather low. Both preparations behave rather similar, the microbial insecticide however is more influenced by the presence of materials in. suspension.     

Long-term perspectives on world metal use—a system-dynamics model

In this paper, a system dynamics model is described, which simulates long-term trends in the production and consumption of metals (i.e. iron/steel and an aggregate of metals of medium abundance) in relation to impacts such as ore-grade decline, capital and energy requirements and waste flows. This metal model can be of assistance in exploring the issue of sustainability of metal resource use. Application of the model to historical trends shows it to be fairly capable of reproducing the long-term trends in the 1900–1990 period, among others on the basis of two intensity of use curves applied to 13 world regions. For future trends, a set of perspective-based long-term scenarios has been constructed that represent the major paradigms in resource use. These scenarios highlight some of the uncertain factors in the relation between economic growth, metal resource exploitation and use, and energy and environmental consequences. They also indicate that apparently similar metal flows in society may be the result of quite different and sometimes contrary assumptions on metal demand, production patterns and resource base characteristics. Such analyses contribute to a more open and transparent discussion on the issue at hand by adding quantitative explications to qualitative views.     

The assessment of electromigration as a new technique to study diffusion of radionuclides in clayey soils

For the performance assessment study of a geological disposal of High Level Waste (HLW) in clayey formations, migration studies are essential. For low permeability soils (clays), classical diffusion studies take a very long time. In order to reduce the experimental time, we propose an electrical field as driving force to accelerate the migration of ionic species. This paper reports the assessment of the electromigration technique as a powerful new and fast technique for migration studies. The apparent molecular diffusion coefficient can be derived by two independent methods using the migration parameters obtained from an electromigration experiment, namely the apparent dispersion coefficient and the apparent convection velocity. First, it can be calculated from the velocity of the migrating species by the Einstein relation. But, corrections are necessary for electroosmotic flow. The apparent electroosmotic mobility is experimentally determined as 2.2·10⁻⁹ m²/Vs. Second, it can be calculated from the relation between the apparent dispersion coefficient and the total apparent convection velocity. But it is necessary to know the dispersion length of the medium. The dispersion length for Boom Clay is experimentally determined as 8·10⁻⁵ m. Because of the serious reduction in time, it becomes possible to run series of experiments at different electrical fields to obtain averaged values for the apparent molecular diffusion coefficient according to the two methods. Experiments at different electrical fields have another advantage: the intercept of the linear relationship between the total apparent convection velocity and the apparent dispersion coefficient gives the apparent molecular diffusion coefficient. The apparent molecular diffusion coefficients obtained for ⁸⁵Sr, ¹³¹I and HTO are respectively 0.8·10⁻¹¹, 15·10⁻¹¹, and 24·10⁻¹¹ m²/s. These values are confirmed by pure diffusion experiments. The excellent agreement with the apparent molecular diffusion coefficients obtained by classical diffusion tests clearly demonstrates the feasibility of the electromigration technique for the determination of diffusion coefficients.