Bacterial transport experiments in fractured crystalline bedrock   总被引：5，自引：0，他引：5  

Becker MW  Metge DW  Collins SA  Shapiro AM  Harvey RW 《Ground water》2003,41(5):682-689

The efficiency of contaminant biodegradation in ground water depends, in part, on the transport properties of the degrading bacteria. Few data exist concerning the transport of bacteria in saturated bedrock, particularly at the field scale. Bacteria and microsphere tracer experiments were conducted in a fractured crystalline bedrock under forced-gradient conditions over a distance of 36 m. Bacteria isolated from the local ground water were chosen on the basis of physicochemical and physiological differences (shape, cell-wall type, motility), and were differentially stained so that their transport behavior could be compared. No two bacterial strains transported in an identical manner, and microspheres produced distinctly different breakthrough curves than bacteria. Although there was insufficient control in this field experiment to completely separate the effects of bacteria shape, reaction to Gram staining, cell size, and motility on transport efficiency, it was observed that (1) the nonmotile, mutant strain exhibited better fractional recovery than the motile parent strain; (2) Gram-negative rod-shaped bacteria exhibited higher fractional recovery relative to the Gram-positive rod-shaped strain of similar size; and (3) coccoidal (spherical-shaped) bacteria transported better than all but one strain of the rod-shaped bacteria. The field experiment must be interpreted in the context of the specific bacterial strains and ground water environment in which they were conducted, but experimental results suggest that minor differences in the physical properties of bacteria can lead to major differences in transport behavior at the field scale.  相似文献   

Long-term performance of permeable reactive barriers using zero-valent iron: geochemical and microbiological effects   总被引：15，自引：0，他引：15  

Wilkin RT  Puls RW  Sewell GW 《Ground water》2003,41(4):493-503

Geochemical and microbiological factors that control long-term performance of subsurface permeable reactive barriers were evaluated at the Elizabeth City, North Carolina, and the Denver Federal Center, Colorado, sites. These ground water treatment systems use zero-valent iron filings (Peerless Metal Powders Inc.) to intercept and remediate chlorinated hydrocarbon compounds at the Denver Federal Center (funnel-and-gate system) and overlapping plumes of hexavalent chromium and chlorinated hydrocarbons at Elizabeth City (continuous wall system). Zero-valent iron at both sites is a long-term sink for carbon, sulfur, calcium, silicon, nitrogen, and magnesium. After about four years of operation, the average rates of inorganic carbon (IC) and sulfur (S) accumulation are 0.09 and 0.02 kg/m2/year, respectively, at Elizabeth City where upgradient waters contain <400 mg/L of total dissolved solids (TDS). At the Denver Federal Center site, upgradient ground water contains 1000 to 1200 mg/L TDS and rates of IC and S accumulation are as high as 2.16 and 0.80 kg/m2/year, respectively. At both sites, consistent patterns of spatially variable mineral precipitation and microbial activity are observed. Mineral precipitates and microbial biomass accumulate the fastest near the upgradient aquifer-Fe0 interface. Maximum net reductions in porosity due to the accumulation of sulfur and inorganic carbon precipitates range from 0.032 at Elizabeth City to 0.062 at the Denver Federal Center (gate 2) after about four years. Although pore space has been lost due the accumulation of authigenic components, neither site shows evidence of pervasive pore clogging after four years of operation.  相似文献   

Explaining the thinness of the fresh water lens in the Pleistocene carbonate aquifer on Andros Island, Bahamas     

Ritzi RW  Bukowski JM  Carney CK  Boardman MR 《Ground water》2001,39(5):713-720

Two hypotheses are explored to explain the thinness of the fresh water lens on Andros Island, Bahamas. The lens is an order of magnitude thinner than predicted by the Ghyben-Herzberg theory. One hypothesis previously posed in the literature is that the base of the lens is governed by the contact between the Lucayan Formation and the pre-Lucayan limestones. An alternate hypothesis, posed here, is that thinning is caused by the hydraulic influence of low-permeability paleosols in the Lucayan Formation. These hypotheses were explored, along with the influence of recharge and other factors, using a numerical model for variable-density flow and salt transport. In the layered system of grainstones/packstones and paleosols within the Lucayan Formation itself, the velocity vectors are nearly horizontal in the grainstones/packstones, and they are nearly vertical in the paleosols. These strata above the pre-Lucayan, all lower than it in permeability, draw the base of the lens upward to a position well above the contact by significantly reducing pressure within and below the strata relative to hydrostatic pressure. It is the loss of pressure across the paleosols that dramatically thins the fresh water lens, and thus the predominant hydraulic control on lens thickness arises from the existence of paleosols.  相似文献   

压实粘土斜坡的软化与蠕变     

Day  RW 张聪辰 《地质科学译丛》1996,13(4):76-80

本文基于南加里弗尼亚地价昂贵且土地逐渐减少，大部分建筑开始修建填土斜坡上这一事实，对压实粘土斜坡进行地下勘探和现场测试，并对压实粘土做了室内试验。从而探讨了压实粘土软化和蠕变的规律及其影响因素。  相似文献   

卫星生物气候学     

倪建红  郑志超 《地球科学进展》1991,6(6):44-48

一、引言 分析植被和气候的关系是地球科学研究的一个中心课题。最近的全球气候动力学研究已把注意力集中在加深对植被与气候相互作用的了解上。然而,在描述和评价植被活动中,测量手段的缺乏限制了生物气候学新模式的发展。  相似文献   

美国NCAR的气候系统模式（CSM0     

倪建红  焦彦军 《大气情报》1997,17(2):23-25

  相似文献   

北美观测系统计划（NAOS）     

Schl.  TW 倪建红 《大气情报》1997,17(4):34-35,36

  相似文献   

地球系统演化过程中的主要矛盾──汤懋苍教授关于“气候变化地心说”的新探索     

倪建红 《地球科学进展》1997,(3)

地球系统演化过程中的主要矛盾──汤懋苍教授关于“气候变化地心说”的新探索关键词地球系统演化，气候变化，冰期旋回１大冰期旋回（１０８年）与银、地磁耦合在地球的４６亿年演化史中，曾出现过７次大冰期，关于它的成因已经提出了很多假说，但都不能令人满意。汤懋苍...  相似文献   

Deeply Penetrating Banded Zonal Flows in the Solar Convection Zone     

Howe R  Christensen-Dalsgaard J  Hill F  Komm RW  Larsen RM  Schou J  Thompson MJ  Toomre J 《The Astrophysical journal》2000,534(2):L163-L166

We discuss the spectrum arising from synchrotron emission by fast cooling (FC) electrons, when fresh electrons are continually accelerated by a strong blast wave, into a power-law distribution of energies. The FC spectrum has so far been described by four power-law segments divided by three break frequencies nusa相似文献   

通过自由振荡了解地幔     

Schn.  RW 徐起浩 《世界地震译丛》1999,(6):80-81

大地震辐射的地震波穿过整个地球。因为这些波仅在地球内部传播,所以经历了多次反射,并且沿相反方向传播的波之间的相互干涉形成了一种驻波形态:地球的简正振型(图1)。这些“体”波也受到传播它的介质的影响。因此它也就带有关于地球弹性分布和间断位置的有价值信息。  相似文献