Axi-symmetric simulation of soil vapor extraction influenced by soil fracturing

Fracturing, either pneumatic or hydraulic, is a method to improve the performance of soil vapor extraction (SVE) in relatively low permeability soils (< 10(-5) cm/s). A two-dimensional model is presented to simulate trichloroethylene (TCE) soil vapor extraction modified by fracturing. Flow and transport is modeled using mobile macropore and micropore networks, which also have been identified in the literature as dual porosity, dual permeability, or heterogeneous flow models. In this model, fluids can flow in both the macropore and micropore networks. This represents a more general model compared to immobile micropore, mobile macropore models presented thus far in the literature for vapor flow and transport in two dimensions. The model considers pressure- and concentration-driven exchange between the macropore and micropore networks, concentration-driven exchange between the gas and sorbed phases within each network, and equilibrium exchange between the gas and water and a sorbed phase within each network. The parameters employed in an example simulation are based on field measurements made at a fractured site. Considered in the simulations were the influence of the volume percentage of fractures, the length of fractures, the relative location of the water table, and the influence of pulsed pumping. For these simulations, internetwork concentration-driven exchange most significantly affected mass removal. The volume percentage of fractures more significantly influence flow and mass removal than the length of fractures. The depth of the water table below the contamination plume only significantly influenced flow and mass removal when the water table was within 60 cm of the bottom of the contaminated soil in the vadose zone for the parameters considered in this study. Pulsed pumping was not found to increase the amount of mass removed in this study.     

Effects of skin and hydraulic fractures on SVE wells

Soil vapor extraction (SVE) systems are intended to cause substantial volumes of air to flow through the subsurface with the purpose of removing volatile contaminants. The effectiveness of SVE can be influenced by any effect that changes the specific gas capacity (discharge as a function of vacuum) of a well. Skins of low permeability material enveloping a well bore are widely recognized to affect the performance of wells used to recover water, natural gas, or petroleum, and skin can also significantly diminish the performance of an SVE well. Skins a few mm thick consisting of material whose gas phase permeability is 0.01 of the formation can reduce the specific gas capacity of an SVE well by factors of 2 to 10 or more. Hydraulic fractures created in the vicinities of shallow wells commonly resemble sand-filled layers shaped like flat-lying disks or gently dipping saucers. The contrast between the gas-phase permeability of the sand in the fracture and that of the formation is particularly important, with significant effects requiring the ratio to be greater than approximately 50. Shallow hydraulic fractures filled with several tenths of m3 of sand in formations that are several orders of magnitude less permeable than that of the enveloping formation should increase specific gas capacity by factors of 10 or more. Field tests of the effects of hydraulic fractures on the performance of SVE were conducted by creating four wells intersecting fractures and a suite of control wells created using conventional methods in silty saprolite. Specific gas capacities ranged over more than an order of magnitude for 10 wells completed within a small area (2 m2) and at the same depth. Specific capacities correlate to the drilling method that was used to create the bore for the well: lowest values occurred in wells drilled with a machine auger, slightly better results were obtained using a Shelby tube, and the best results were obtained from conventional wells bored with a hand auger. Skin factors determined for wells created with a machine auger could be explained by a layer 1 cm thick that has 0.007 times the permeability of the enveloping material, which could readily have been created during the drilling procedure. Specific capacities of wells intersecting hydraulic fractures were 5 to 100 times more than those of conventional wells. The large difference in performance appears to be due in part to the beneficial effects of the fracture, and in part to the detrimental effects of well skin.     

Diversity pattern and spatial scale: a study of a tropical rain forest of Malaysia

Scale is emerging as one of the critical problems in ecology because our perception of most ecological variables and processes depends upon the scale at which the variables are measured. A conclusion obtained at one scale may not be valid at another scale without sufficient knowledge of the scaling effect, which is also a source of misinterpretation for many ecological problems, such as the design of reserves in conservation biology.This paper attempts to study empirically how scaling may affect the spatial patterns of diversity (tree density, richness and Shannon diversity) that we may perceive in tropical forests, using as a test-case a 50 ha forest plot in Malaysia. The effect of scale on measurements of diversity patterns, the occurrence of rare species, the fractal dimension of diversity patterns, the spatial structure and the nearest-neighbour autocorrelation of diversity are addressed. The response of a variable to scale depends on the way it is measured and the way it is distributed in space.We conclude that, in general, the effect of scaling on measures of biological diversity is non-linear; heterogeneity increases with the size of the sampling units, and fine-scale information is lost at a broad scale. Our results should lead to a better understanding of how ecological variables and processes change over scale.     

Manipulation of nest-box density affects extra-pair paternity in a population of blue tits (<Emphasis Type="Italic">Parus caeruleus</Emphasis>)

We tested the effect of manipulation of breeding density on the occurrence of extra-pair paternity in a blue tit (Parus caeruleus) population during two consecutive years. In a homogeneous oak forest, nest-box manipulation provided a high density plot (plot A, 1.10 and 1.32 pairs/ha) and a low density plot (plot B, 0.43 and 0.46 pairs/ha). Microsatellite analysis on 91 broods revealed a higher proportion of extra-pair paternity in broods in plot A (mean of 17.2%) than in plot B (mean of 11.4%). A correlative approach showed that the proportion of extra-pair young in broods was affected by the number of breeding neighbours within 100 m around the nest-box, by the distance to the nearest breeding neighbour and by an additional plot effect. However, the nearest neighbours accounted for only 39.3% of extra-pair paternities and distance to extra-pair fathers was significantly higher than the nearest neighbour distance in both plots. This implies that the effect of density on the occurrence of extra-pair paternities is associated with active female choice to enhance the brood fitness. Although there were more extra-pair young in broods when density was high, the number of extra-pair fathers did not increase and stayed close to one. We suggest that density increases the cost of mate guarding by males, thereby increasing the possibility for females to solicit extra-pair paternities to the cuckolding male they have chosen. Finally, we discuss why correlatives approaches do not always show evidence for an effect of breeding density on extra-pair paternity occurrence.Communicated by M. Soler     

A Concentric Analysis of the Impact of Urbanization on the Threatened European Tree Frog in an Agricultural Landscape

Abstract:  Pond-breeding amphibians are affected by site-specific factors and regional and landscape-scale patterns of land use. Recent anthropogenic landscape modifications (drainage, agriculture intensification, larger road networks, and increased traffic) affect species by reducing the suitable habitat area and fragmenting remaining populations. Using a robust concentric approach based on permutation tests, we evaluated the impact of recent landscape changes on the presence of the endangered European tree frog ( Hyla arborea ) in wetlands. We analyzed the frequency of 1 traffic and 14 land-use indices at 20 circular ranges (from 100-m up to 2-km radii) around 76 ponds identified in western Switzerland. Urban areas and road surfaces had a strong adverse effect on tree frog presence even at relatively great distances (from 100 m up to 1 km). When traffic measurements were considered instead of road surfaces, the effect increased, suggesting a negative impact due to a vehicle-induced effect. Altogether, our results indicate that urbanization and traffic must be taken into account when pond creation is an option in conservation management plans, as is the case for the European tree frog in western Switzerland. We conclude that our easy-to-use and robust concentric method of analysis can successfully assist managers in identifying potential sites for pond creation, where probability of the presence of tree frogs is maximized.     

The Effect of Fragment Shape and Species' Sensitivity to Habitat Edges on Animal Population Size

Abstract:  Habitat fragmentation causes extinction of local animal populations by decreasing the amount of viable "core" habitat area and increasing edge effects. It is widely accepted that larger fragments make better nature reserves because core-dwelling species have a larger amount of suitable habitat. Nevertheless, fragments in real landscapes have complex, irregular shapes. We modeled the population sizes of species that have a representative range of preferences for or aversions to habitat edges at five spatial scales (within 10, 32, 100, 320, and 1000 m of an edge) in a nation-wide analysis of forest remnants in New Zealand. We hypothesized that the irregular shapes of fragments in real landscapes should generate statistically significant correlations between population density and fragment area, purely as a "geometric" effect of varying species responses to the distribution of edge habitat. Irregularly shaped fragments consistently reduced the population size of core-dwelling species by 10–100%, depending on the scale over which species responded to habitat edges. Moreover, core populations within individual fragments were spatially discontinuous, containing multiple, disjunct populations that inhabited small spatial areas and had reduced population size. The geometric effect was highly nonlinear and depended on the range of fragment sizes sampled and the scale at which species responded to habitat edges. Fragment shape played a strong role in determining population size in fragmented landscapes; thus, habitat restoration efforts may be more effective if they focus on connecting disjunct cores rather than isolated fragments.     

气态有机物组成对生物过滤及菌体密度的影响

以堆肥-火山灰为填料的生物过滤器连续处理含甲苯、乙酸乙酯和异丙醇的气体,观测生物过滤效果和填料的菌系状态变化.结果表明:在甲苯和乙酸乙酯共存的条件下,生物过滤器优先去除乙酸乙酯;当进气中同时存在甲苯、乙酸乙酯和异丙醇时,优先去除乙酸乙酯和异丙醇.填料中各种微生物的菌体密度与过滤去除的有机物组成和浓度有关.霉菌和酵母菌竞争利用乙酸乙酯和异丙醇的能力较强,放线菌和细菌对甲苯的竞争利用能力较强.进气中高浓度的有机物会使填料中的菌体密度增大.在处理甲苯、乙酸乙酯和异丙醇的生物过滤器的各段填料中,菌体密度按细菌、霉菌、酵母菌、放线菌的顺序而降低. 图 1表 3参 17     

Analysis of lead in soils adjacent to an interstate highway in Tampa,Florida

In order to assess the amount and distribution of lead pollution in soils adjacent to a major interstate highway serving the city of Tampa, Florida, a total of 224 samples were collected from 32 transects perpendicular to the roadway. The lead content was measured using atomic absorption spectrophotometry. The highest levels of lead were found at distances of 81, 243, and 729 cm from the road. The results show that there is a weak negative correlation between soil lead and the distance from the roadside, as well as with traffic density. The weakness of the relationship is a result of confounding variables such as turbulence and other microclimatic factors, downslope movement of soils overtime, and human action such as construction and highway landscaping. Nevertheless, over one-third of the samples collected in the study area contain more than 500 g g^–1 lead, levels considered to be hazardous by the United States Centers for Disease Control and the Environmental Protection Agency.     

高镍杂铜低温生产电解铜粉试验

用杂铜电解生产铜粉时，电解液的温度一般可控制在２０￣６０℃。本文介绍了在３０℃较低温度和６００￣１２００Ａ／ｍ＾２的较低电流密度下，用杂铜电解生产铜粉的试验过程。试验结果表明：低温和低铜离子浓度对生产细粒铜粉有利，而料低电流密度在保证铜粉粒度的情况下，对节约电能有利。     

呼和浩特市大气气态和颗粒物上正构烷烃的研究

采用聚氨基甲酸乙酯和玻璃纤维滤膜采集样品并测定。大气中总正构烷烃的浓度分布、气／固分布比与季节变化、污染源有关。在呼市大气中总正构烷烃（Ｃ１５－Ｃ３３），夏季主要存在气态中（７８％），而冬季主要存在于颗粒物上（８３％）。内蒙古草原大气对照样品中，气态中总正构烷烃在冬夏两季所占百分比都约为５０％。市区冬季大气颗粒物上的总正构烷烃浓度比其它城市结果高出１－２个数量级。