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91.
Magdalena M. Krol 《Advances in water resources》2011,34(4):537-549
During thermal remediation the increase in subsurface temperature can lead to bubble formation and mobilization. In order to investigate the effect of gas formation on resulting aqueous concentrations, a 2D finite difference flow and mass transport model was developed which incorporates a macroscopic invasion percolation (MIP) model to simulate bubble expansion and movement. The model was used to simulate three soil scenarios with different permeabilities and entry pressures at various operating temperatures and groundwater velocities. It was observed that discrete bubble formation occurred in all three soils, upward mobility being limited by lower temperatures and higher entry pressures. Bubble mobilization resulted in a different aqueous mass distribution than if no discrete gas formation was modeled, especially at higher temperatures. This was a result of bubbles moving upwards to cooler areas, then collapsing, and contaminating previously clean zones. The cooling effect also led to possible non-aqueous phase liquid (NAPL) formation which was not predicted using a model without discrete bubble formation. 相似文献
92.
Gullies are conceptualized in the literature as essentially fluvial forms with dimensional boundaries arbitrarily defined between rills and river channels. This notion is incompatible with the existing variability of form and process, as mass movements frequently exert a fundamental control on gully initiation and expansion, to the point of features outgrowing their original contributing area. The inability of a conceptual framework to incorporate existing observations inevitably constrains methodologies and research results. In this commentary, several examples of published results are contrasted with the prevailing assumption of an essentially fluvial nature, with the purpose of encouraging discussion on the need for a revised conceptual framework in gully erosion research. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
93.
崩岗侵蚀地貌的演变过程及阶段划分 总被引:4,自引:0,他引:4
崩岗是中国南方一种常见的土壤侵蚀类型,也是一种严重的水土流失方式,多分布于低山丘陵区的花岗岩风化壳之上.崩岗的形成和发展是2个不同的阶段,并始终受到水力和重力的作用.2种外力对比关系的不同使崩岗的演变过程具有明显的阶段性.通过选取适当的指标体现这种规律性,可以对崩岗的发展阶段进一步划分,对崩岗的治理控制具有重要的意义. 相似文献
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95.
Vegetation and topographic controls on sediment deposition and storage on gully beds in a degraded mountain area 总被引:1,自引:0,他引:1
Active gully systems developed on highly weathered or loose parent material are an important source of runoff and sediment production in degraded areas. However, a decrease of land pressure may lead to a return of a partial vegetation cover, whereby gully beds are preferred recolonization spots. Although the current knowledge on the role of vegetation on reducing sediment production on slopes is well developed, few studies exist on the significance of restoring sediment transport pathways on the total sediment budget of degraded mountainous catchments. This study in the Ecuadorian Andes evaluates the potential of vegetation to stabilize active gully systems by trapping and retaining eroded sediment in the gully bed, and analyses the significance of vegetation restoration in the gully bed in reducing sediment export from degraded catchments. Field measurements on 138 gully segments located in 13 ephemeral steep gullies with different ground vegetation cover indicate that gully bed vegetation is the most important factor in promoting short‐term (1–15 years) sediment deposition and gully stabilization. In well‐vegetated gully systems ( ≥ 30% of ground vegetation cover), 0.035 m3 m–1 of sediment is deposited yearly in the gully bed. Almost 50 per cent of the observed variance in sediment deposition volumes can be explained by the mean ground vegetation cover of the gully bed. The presence of vegetation in gully beds gives rise to the formation of vegetated buffer zones, which enhance short‐term sediment trapping even in active gully systems in mountainous environments. Vegetation buffer zones are shown to modify the connectivity of sediment fluxes, as they reduce the transport efficiency of gully systems. First calculations on data on sediment deposition patterns in our study area show that gully bed deposition in response to gully bed revegetation can represent more than 25 per cent of the volume of sediment generated within the catchment. Our findings indicate that relatively small changes in landscape connectivity have the potential to create strong (positive) feedback loops between erosion and vegetation dynamics. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
96.
This paper compares the performance of analytical and numerical approaches for modeling DNAPL dissolution with biodecay. A solution derived from a 1-D advective transport formulation (“Parker” model) is shown to agree very closely with high resolution numerical solutions. A simple lumped source mass balance solution in which with decay is assumed proportional to DNAPL mass (“Falta1” model) over- or underpredicts aqueous phase biodecay depending on the magnitude of the exponential factor governing the relationship between dissolution rate and DNAPL mass. A modification of the Falta model that assumes decay proportional to the source exit concentration is capable of accurately simulating source behavior with strong aqueous phase biodecay if model parameters are appropriately selected or calibrated (“Falta2” model). However, parameters in the lumped models exhibit complex interdependencies that cannot be quantified without consideration of transport processes within the source zone. Combining the Falta2 solution with relationships derived from the Parker model was found to resolve these limitations and track the numerical model results. A method is presented to generalize the analytical solutions to enable simulation of partial mass removal with changes in source parameters over time due to various remedial actions. The algorithm is verified by comparison with numerical simulation results. An example application is presented that demonstrates the interactions of partial mass removal, enhanced biodecay, enhanced mass transfer and source zone flow reduction applied at various time periods on contaminant flux reduction. Increasing errors that arise in numerical solutions with coarse discretization and high decay rates are shown to be controlled by using an adjusted decay coefficient derived from the Parker analytical solution. 相似文献
97.
生态地球化学:从调查实践到应用理论的系统工程 总被引:30,自引:1,他引:29
生态地球化学是以多目标区域地球化学调查为基础,以生态地球化学评价、生态地球化学评估、生态地球化学预警和生态地球化学修复为主体的系统工程。文章系统地介绍了我国近年来生态地球化学研究成果,对长江流域河流生态系统、山西农田生态系统,北京城市生态系统,鄱阳湖、洞庭湖、太湖等湖泊湿地生态系统的区域生态地球化学评价进展进行了归纳总结。文章从区域尺度上综述了土壤碳库,土壤元素基准值和土壤背景值,土壤污染等级划分等基础研究方面的进展。面向未来,指出了生态地球化学发展趋势,提出生态地球化学研究需要进一步延伸和发展的领域。 相似文献
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100.
地下水NO -3污染的微生物修复实验研究 总被引:5,自引:0,他引:5
随着农业的发展,尤其是化肥和农药的超量施用,产生了一系列的环境问题,已危及地下水的质量安全。大量的氮素没有被农作物吸收,经微生物硝化作用后,以硝态氮的形式进入土体和地下水。浅层地下水已普遍受到氮素不同程度的污染。本文以硝态氮污染为例,在实验室探索了硝态氮污染地下水微生物修复的实验方法,通过室内模拟含水层地下水静止条件和流动条件下,利用优选的菌群制剂和少量营养碳源,对试验区高含NO-3地下水的修复试验效果是显著的,去除率可达90%~100%。其作用还是持续的,静止条件下试验进行到256d时,其去除率仍达89 74%;流动条件下试验进行到112d时,试验主孔下游的观测孔3#、4#中的去除率也还有16 22%和27 26%。试验结果为野外现场原位微生物修复提供了技术支撑。 相似文献