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781.
The goal of this study was to investigate the influence of one variable, natural organic matter, on residual gasoline saturation in sandy soils. Capillary pressure-saturation (Pc−S) relationships (air-gasoline) were determined for three physically-similar sandy soils, with different organic carbon contents (0.086%, 0.89% and 1.65%) and residual gasoline saturations were compared. Two initial moisture conditions, residual water saturation and air-dry, were evaluated. One soil type was packed to two different bulk densities. Visualization of the soils using cryo-scanning electron microscopy was performed to aid in better understanding the role of the organic matter in the soil. The results showed that soils with higher organic contents had higher residual gasoline saturations when starting with an initially air-dry soil. Increasing the bulk density of the same air-dried soil resulted in an increase in residual gasoline saturation. In the presence of a residual water saturation, however, residual gasoline saturations were virtually identical for the three soils and independent of bulk density; approximately 5–10 times lower than in soil that was initially air-dry. The presence of the residual water effectively coated the surface of the soil thereby reducing or eliminating gasoline/soil interactions. Some residual water may also be occupying very small pore spaces, making these locations inaccessible to the gasoline. 相似文献
782.
Huang XD El-Alawi Y Penrose DM Glick BR Greenberg BM 《Environmental pollution (Barking, Essex : 1987)》2004,130(3):453-463
Phytoremediation of creosote-contaminated soil was monitored in the presence of Tall fescue, Kentucky blue grass, or Wild rye. For all three grass species, plant growth promoting rhizobacteria (PGPR) were evaluated for plant growth promotion and protection of plants from contaminant toxicity. A number of parameters were monitored including plant tissue water content, root growth, plant chlorophyll content and the chlorophyll a/b ratio. The observed physiological data indicate that some plants mitigated the toxic effects of contaminants. In addition, in agreement with our previous experiments reported in the accompanying paper (Huang, X.-D., El-Alawi, Y., Penrose, D.M., Glick, B.R., Greenberg, B.M., 2004. A multi-process phytoremediation system for removal of polycyclic aromatic hydrocarbons from contaminated soil. Environ. Poll. doi: 10.1016/j.envpol.2003.09.031), PGPR were able to greatly enhance phytoremediation. PGPR accelerated plant growth, especially roots, in heavily contaminated soils, diminishing the toxic effects of contaminants to plants. Thus, the increased root biomass in PGPR-treated plants led to more effective remediation. 相似文献
783.
This paper presents results of a numerical investigation of soil vapor extraction (SVE) systems at the laboratory scale. The SVE technique is used to remove volatile chlorinated hydrocarbons (VCHC) from the water-unsaturated soil zone. The developed numerical model solves equations of flow, transport and interfacial mass transfer regarding an isothermal n-component and three-phase system. The mathematical model is based on a simple pore network and phase distribution model and designed to be scaled by a characteristic length. All mathematical expressions are structured into VCHC specific and VCHC non-specific parameters. Furthermore, indicators are introduced that help to separate thermodynamic equilibrium from thermodynamic non-equilibrium domains and to determine the controlling physical parameters. For numerical solution, the system of partial differential equations is discretized by a finite volume method and an implicit Euler time stepping scheme. Computational effort is reduced notably through techniques that enable spatial and temporal adaptivity, through a standard multigrid method as well as through a problem-oriented sparse-matrix storage concept. Computations are carried out in two dimensions regarding the laboratory experiment of Fischer et al. [Water Resour. Res. 32 (12) 1996 3413]. By varying the characteristic length scale of the pore network and phase distribution model, it is shown that the experimental gas phase concentrations cannot be explained only by the volatility and diffusivity of the VCHC. The computational results suggest a sorption process whose significance grows with the aqueous activity of the less or non-polar organic compounds. 相似文献
784.
Estimating erosion in a riverine watershed bayou liberty-tchefuncta river in louisiana 总被引:1,自引:0,他引:1
Martin A Gunter JT Regens JL 《Environmental science and pollution research international》2003,10(4):245-250
GOAL, SCOPE, BACKGROUND: Sheet erosion from agricultural, forest and urban lands may increase stream sediment loads as well as transport other pollutants that adversely affect water quality, reduce agricultural and forest production, and increase infrastructure maintenance costs. This study uses spatial analysis techniques and a numerical modeling approach to predict areas with the greatest sheet erosion potential given different soils disturbance scenarios. METHODS: A Geographic Information System (GIS) and the Universal Soil Loss Equation (USLE) were used to estimate sheet erosion from 0.64 ha parcels of land within the watershed. The Soil Survey of St. Tammany Parish, Louisiana was digitized, required soil attributes entered into the GIS database, and slope factors determined for each 80 x 80 meter parcel in the watershed. The GIS/USLE model used series-specific erosion K factors, a rainfall factor of 89, and a GIS database of scenario-driven cropping and erosion control practice factors to estimate potential soil loss due to sheet erosion. RESULTS AND DISCUSSION: A general trend of increased potential sheet erosion occurred for all land use categories (urban, agriculture/grasslands, forests) as soil disturbance increases from cropping, logging and construction activities. Modeling indicated that rapidly growing urban areas have the greatest potential for sheet erosion. Evergreen and mixed forests (production forest) had lower sheet erosion potentials; with deciduous forests (mostly riparian) having the least sheet erosion potential. Erosion estimates from construction activities may be overestimated because of the value chosen for the erosion control practice factor. CONCLUSIONS: This study illustrates the ease with which GIS can be integrated with the Universal Soil Loss Equation to identify areas with high sheet erosion potential for large scale management and policy decision making. RECOMMENDATIONS: The GIS/USLE modeling approach used in this study offers a quick and inexpensive tool for estimating sheet erosion within watersheds using publicly available information. This method can quickly identify discrete locations with relatively precise spatial boundaries (approximately 80 meter resolution) that have a high sheet erosion potential as well as areas where management interventions might be appropriate to prevent or ameliorate erosion. 相似文献
785.
During numerical simulation of air flow in the vadose zone, it was noticed that a small sinusoidal pressure would cause a gradual one-way migration of the pore gas. This was found to be a physical phenomenon, not a numerical artifact of the finite element simulation. The one-way migration occurs because the atmospheric pressure, and hence the air density, is slightly greater when air is flowing into the ground than when air is flowing out of the ground. A simple analytic theory of the phenomenon is presented, together with analytic calculations using actual barometric pressure data. In soil of one Darcy permeability, the one-way migration is of the order of a few tenths of a meter per year for either plane flow from ground surface or for radial flow from an open borehole. The migration is sufficiently small that it will have no practical consequences in most circumstances; however, investigators who conduct detailed numerical modeling should recognize that this phenomenon is not a numerical artifact in an apparently linear system. 相似文献
786.
787.
不同措施在防治山地果园水土流失及面源污染中的应用研究 总被引:3,自引:0,他引:3
通过施用生物毯、生物带和秸秆覆盖3种措施,模拟人工降雨,测定山地果园的水土流失量,比较不同措施在防治山地果园水土流失中的效果.结果表明,在降雨强度为1.33 mm/min时,与对照相比生物毯和秸秆覆盖能减少50%以上的氮磷流失量,生物带减少氮磷流失量也达到30%以上;在降雨强度为2.33 mm/min时,秸秆覆盖防治水土流失的效果最好;在高降雨强度(2.33mm/min)时,各种措施防治效果降低,但效果仍然明显,对磷的防治效果好于对氮的防治效果,与对照相比生物毯能减少44.5%的磷流失量.山地果园水土流失相当严重,施用生物毯和秸秆覆盖能有效防治山地果园的面源污染. 相似文献
788.
The spatial patterns of soil organic carbon (SOC) are closely related to the global climate change. In quantifying the spatial patterns of SOC density, the concept of uncertainty of the SOC density values at unsampled locations is particularly important because such uncertainty can be propagated into the subsequent global climate change modelling and has fundamental impacts on the ultimate results of the model. A total of 361 SOC density data of topsoil (0–20 cm) in Hebei province and sequential indicator simulation (SIS) were applied to perform a conditional stochastic simulation in this study to quantitatively assess the uncertainty of mapping SOC density. The results showed that a great variation exists in the SOC density data. The conditional variance of 500 realizations generated by SIS was larger in mountainous areas of the study area where the SOC density fluctuated the most, and the uncertainty was smaller on the plain area where SOC density was consistently small. Realizations generated by SIS can represent the possible spatial patterns of SOC density without smoothing effect. A set of realizations can be used to explore all possible spatial patterns of SOC density and provide a visual and quantitative measure of the spatial uncertainty of mapping SOC density. With a given threshold of SOC density, SIS can quantitatively assess both local uncertainty and spatial uncertainty of SOC density that is greater the threshold. 相似文献
789.
The role of glomalin, a protein produced by arbuscular mycorrhizal fungi, in sequestering potentially toxic elements 总被引:21,自引:0,他引:21
González-Chávez MC Carrillo-González R Wright SF Nichols KA 《Environmental pollution (Barking, Essex : 1987)》2004,130(3):317-323
Naturally occurring soil organic compounds stabilize potentially toxic elements (PTEs) such as Cu, Cd, Pb, and Mn. The hypothesis of this work was that an insoluble glycoprotein, glomalin, produced in copious amounts on hyphae of arbuscular mycorrhizal fungi (AMF) sequesters PTEs. Glomalin can be extracted from laboratory cultures of AMF and from soils. Three different experiments were conducted. Experiment 1 showed that glomalin extracted from two polluted soils contained 1.6-4.3 mg Cu, 0.02-0.08 mg Cd, and 0.62-1.12 mg Pb/g glomalin. Experiment 2 showed that glomalin from hyphae of an isolate of Gigaspora rosea sequestered up to 28 mg Cu/g in vitro. Experiment 3 tested in vivo differences in Cu sequestration by Cu-tolerant and non-tolerant isolates of Glomus mosseae colonizing sorghum. Plants were fed with nutrient solution containing 0.5, 10 or 20 microM of Cu. Although no differences between isolates were detected, mean values for the 20 microM Cu level were 1.6, 0.4, and 0.3 mg Cu/g for glomalin extracted from hyphae, from sand after removal of hyphae and from hyphae attached to roots, respectively. Glomalin should be considered for biostabilization leading to remediation of polluted soils. 相似文献
790.
Introduced Birds and the Fate of Hawaiian Rainforests 总被引:3,自引:0,他引:3
Abstract: The Hawaiian Islands have lost nearly all their native seed dispersers, but have gained many frugivorous birds and fleshy-fruited plants through introductions. Introduced birds may not only aid invasions of exotic plants but also may be the sole dispersers of native plants. We assessed seed dispersal at the ecotone between native- and exotic-dominated forests and quantified bird diets, seed rain from defecated seeds, and plant distributions. Introduced birds were the primary dispersers of native seeds into exotic-dominated forests, which may have enabled six native understory plant species to become reestablished. Some native plant species are now as common in exotic forest understory as they are in native forest. Introduced birds also dispersed seeds of two exotic plants into native forest, but dispersal was localized or establishment minimal. Seed rain of bird-dispersed seeds was extensive in both forests, totaling 724 seeds of 9 native species and 2 exotics with over 85% of the seeds coming from native plants. Without suitable native dispersers, most common understory plants in Hawaiian rainforests now depend on introduced birds for dispersal, and these introduced species may actually facilitate perpetuation, and perhaps in some cases restoration, of native forests. We emphasize, however, that restoration of native forests by seed dispersal from introduced birds, as seen in this study, depends on the existence of native forests to provide a source of seeds and protection from the effects of ungulates. Our results further suggest that aggressive control of patches of non-native plants within otherwise native-dominated forests may be an important and effective conservation strategy. 相似文献