Kinetics of Mn(II) oxidation by Leptothrix discophora SS1     

Jinghao ZhangLeonard W Lion  Yarrow M Nelson  Michael L ShulerWilliam C Ghiorse 《Geochimica et cosmochimica acta》2002,66(5):773-781

The kinetics of Mn(II) oxidation by the bacterium Leptothrix discophora SS1 was investigated in this research. Cells were grown in a minimal mineral salts medium in which chemical speciation was well defined. Mn(II) oxidation was observed in a bioreactor under controlled conditions with pH, O₂, and temperature regulation. Mn(II) oxidation experiments were performed at cell concentrations between 24 mg/L and 35 mg/L, over a pH range from 6 to 8.5, between temperatures of 10°C and 40°C, over a dissolved oxygen range of 0 to 8.05 mg/L, and with L. discophora SS1 cells that were grown in the presence of Cu concentrations ranging from zero to 0.1 μM. Mn(II) oxidation rates were determined when the cultures grew to stationary phase and were found to be directly proportional to O₂ and cell concentrations over the ranges investigated. The optimum pH for Mn(II) oxidation was approximately 7.5, and the optimum temperature was 30°C. A Cu level as low as 0.02 μM was found to inhibit the growth rate and yield of L. discophora SS1 observed in shake flasks, while Cu levels between 0.02 and 0.1 μM stimulated the Mn(II) oxidation rate observed in bioreactors. An overall rate law for Mn(II) oxidation by L. discophora as a function of pH, temperature, dissolved oxygen concentration (D.O.), and Cu concentration is proposed. At circumneutral pH, the rate of biologically mediated Mn(II) oxidation is likely to exceed homogeneous abiotic Mn(II) oxidation at relatively low (≈μg/L) concentrations of Mn oxidizing bacteria.  相似文献   

Processes in microbial transport in the natural subsurface     

Timothy R. Ginn  Brian D. Wood  Kirk E. Nelson  Timothy D. Scheibe  Ellyn M. Murphy  T.Prabhakar Clement   《Advances in water resources》2002,25(8-12)

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Paleohydrology of arid southeastern maui, hawaiian islands, and its implications for prehistoric human settlement     

Jonathan Stock  James CoilPatrick V. Kirch 《Quaternary Research》2003,59(1):12-24

Arid slopes on the southeastern side of Maui are densely covered with archaeological remains of Hawaiian settlement from the late prehistoric to early postcontact period (ca. A.D. 1500-1860). Permanent habitation sites, agricultural features, and religious structures indicate perennial occupation and farming in a subregion called Kahikinui, yet there is presently no year-round water source. We explore the possibility that postcontact deforestation led to the loss of either (1) perennial channel flow or (2) perennial springs or seeps. To investigate the first possibility, we estimated ancient peak flows on 11 ephemeral channels in Kahikinui using field measurements and paleohydrology. Peak-flow estimates (3-230 m³/s) for a given drainage area are smaller than those for current perennial Maui streams, but are equivalent to gauged peak flows from ephemeral and intermittent streams in the driest regions of Hawai’i and Maui islands. This is consistent with the long-term absence of perennial channel flow in Kahikinui. On the other hand, others have shown that canopy fog-drip in Hawai’i can be greater than rainfall and thus a large part of groundwater recharge. Using isolated live remnants and snags, we estimate the former extent of the forest upstream from archaeological sites. We use rough estimates of the loss of fog-drip recharge caused by deforestation and apply a simple, steady-state hydrologic model to calculate potential groundwater table fall. These order-of-magnitude estimates indicate that groundwater could have fallen by a minimum of several meters, abandoning perennial seeps. This is consistent with archaeological evidence for former perennial seeps, such as stonewalls enclosing potential seeps to protect them. Although longer-term reductions in rainfall cannot be ruled out as a factor, deforestation and loss of fog-drip recharge are obvious and more immediate reasons for a recent loss of perennial water in Kahikinui, Maui.  相似文献   

The shifting territory of government: some insights from the Rural White Paper   总被引：2，自引：0，他引：2  

Jonathan Murdoch 《Area》1997,29(2):109-118

Summary In this paper it is proposed that the territory of governance is currently being reconfigured by the state. The state is pulling back from a universalist, welfare role, which entailed comprehensive governance of the whole national territory. Now a much more selective form of government is coming into being, concerned with 'community', 'diversity' and 'locality'. This is not, however, simply a belated recognition by the state that these are ever more important features of socio-spatial life: rather, it is part of the reconfiguration of the territory of government as the state invokes these characteristics in order to modify its ways of governing. Using Foucault's concept of governmentality–that is the means used by the state to 'problematise' life within its territorial borders and then act on the basis of these problematisations—the recent case of the Rural White Paper is examined. It is proposed that this is a very clear example of a governmental retreat from a comprehensive role in the governance of rural areas and shows how the state now seeks to govern 'through communities'.  相似文献   

Fluvial process and the establishment of bottomland trees   总被引：1，自引：0，他引：1  

Michael L. Scott  Jonathan M. Friedman  Gregor T. Auble 《Geomorphology》1996,14(4):327-339

The effects of river regulation on bottomland tree communities in western North America have generated substantial concern because of the important habitat and aesthetic values of these communities. Consideration of such effects in water management decisions has been hampered by the apparent variability of responses of bottomland tree communities to flow alteration. When the relation between streamflow and tree establishment is placed in a geomorphic context, however, much of that variability is explained, and prediction of changes in the tree community is improved.The relation between streamflow and establishment of bottomland trees is conditioned by the dominant fluvial process or processes acting along a stream. For successful establishment, cottonwoods, poplars, and willows require bare, moist surfaces protected from disturbance. Channel narrowing, channel meandering, and flood deposition promote different spatial and temporal patterns of establishment. During channel narrowing, the site requirements are met on portions of the bed abandoned by the stream, and establishment is associated with a period of low flow lasting one to several years. During channel meandering, the requirements are met on point bars following moderate or higher peak flows. Following flood deposition, the requirements are met on flood deposits ;high above the channel bed. Flood deposition can occur along most streams, but where a channel is constrained by a narrow valley, this process may be the only mechanism that can produce a bare, moist surface high enough to be safe from future disturbance. Because of differences in local bedrock, tributary influence, or geologic history, two nearby reaches of the same stream may be dominated by different fluvial processes and have different spatial and temporal patterns of trees. We illustrate this phenomenon with examples from forests of plains cottonwood (Populus deltoides ssp. monilifera) along meandering and constrained reaches of the Missouri River in Montana.  相似文献   

Data buoy measurements of phytoplankton dynamics in southampton water, UK, a temperate latitude estuary with high nutrient inputs     

Paul N. Wright  David J. Hydes  Mary Lou Lauria  Jonathan Sharples  Duncan A. Purdie 《Ocean Dynamics》1997,49(2-3):203-211

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Advection Within Shallow Pore Waters of a Coastal Lagoon, Florida   总被引：2，自引：0，他引：2  

Jaye E. Cable  Jonathan B. Martin  Peter W. Swarzenski  Mary K. Lindenberg  Joel Steward 《Ground water》2004,42(7):1011-1020

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An attenuation model for distant earthquakes     

Adrian Chandler  Nelson Lam 《地震工程与结构动力学》2004,33(2):183-210

Large magnitude earthquakes generated at source–site distances exceeding 100km are typified by low‐frequency (long‐period) seismic waves. Such induced ground shaking can be disproportionately destructive due to its high displacement, and possibly high velocity, shaking characteristics. Distant earthquakes represent a potentially significant safety hazard in certain low and moderate seismic regions where seismic activity is governed by major distant sources as opposed to nearby (regional) background sources. Examples are parts of the Indian sub‐continent, Eastern China and Indo‐China. The majority of ground motion attenuation relationships currently available for applications in active seismic regions may not be suitable for handling long‐distance attenuation, since the significance of distant earthquakes is mainly confined to certain low to moderate seismicity regions. Thus, the effects of distant earthquakes are often not accurately represented by conventional empirical models which were typically developed from curve‐fitting earthquake strong‐motion data from active seismic regions. Numerous well‐known existing attenuation relationships are evaluated in this paper, to highlight their limitations in long‐distance applications. In contrast, basic seismological parameters such as the Quality factor (Q‐factor) could provide a far more accurate representation for the distant attenuation behaviour of a region, but such information is seldom used by engineers in any direct manner. The aim of this paper is to develop a set of relationships that provide a convenient link between the seismological Q‐factor (amongst other factors) and response spectrum attenuation. The use of Q as an input parameter to the proposed model enables valuable local seismological information to be incorporated directly into response spectrum predictions. The application of this new modelling approach is demonstrated by examples based on the Chi‐Chi earthquake (Taiwan and South China), Gujarat earthquake (Northwest India), Nisqually earthquake (region surrounding Seattle) and Sumatran‐fault earthquake (recorded in Singapore). Field recordings have been obtained from these events for comparison with the proposed model. The accuracy of the stochastic simulations and the regression analysis have been confirmed by comparisons between the model calculations and the actual field observations. It is emphasized that obtaining representative estimates for Q for input into the model is equally important.Thus, this paper forms part of the long‐term objective of the authors to develop more effective communications across the engineering and seismological disciplines. Copyright © 2003 John Wiley & Sons, Ltd.  相似文献   

Channel adjustments of the lower Trinity River,Texas, downstream of Livingston Dam     

Jonathan D. Phillips  Michael C. Slattery  Zachary A. Musselman 《地球表面变化过程与地形》2005,30(11):1419-1439

Channel cross‐sectional changes since construction of Livingston Dam and Lake Livingston in 1968 were studied in the lower Trinity River, Texas, to test theoretical models of channel adjustment, and to determine controls on the spatial extent of channel response. High and average flows were not significantly modified by the dam, but sediment transport is greatly reduced. The study is treated as an opportunistic experiment to examine the effects of a reduction in sediment supply when discharge regime is unchanged. Channel scour is evident for about 60 km downstream, and the general phenomena of incision, widening, coarsening of channel sediment and a decrease in channel slope are successfully predicted, in a qualitative sense, by standard models of channel response. However, there is no consistent channel response within this reach, as various qualitatively different combinations of increases, decreases or no change in width, depth, slope and roughness occur. These multiple modes of adjustment are predicted by the unstable hydraulic geometry model. Between about 60 km and the Trinity delta 175 km downstream of the dam, no morphological response to the dam is observed. Rather than a diminution of the dam's effects on fluvial processes, this is due to a fundamental change in controls of the fluvial system. The downstream end of the scour zone corresponds to the upstream extent of channel response to Holocene sea level rise. Beyond 60 km downstream, the Trinity River is characterized by extensive sediment storage and reduced conveyance capacity, so that even after dam construction sediment supply still exceeds transport capacity. The channel bed of much of this reach is near or below sea level, so that sea level rise and backwater effects from the estuary are more important controls on the fluvial system than upstream inputs. Copyright © 2005 John Wiley & Sons, Ltd.  相似文献   

The effective number of cycles of earthquake ground motion     

Jonathan Hancock  Julian J. Bommer 《地震工程与结构动力学》2005,34(6):637-664

The seismic response of any system that accumulates damage under cyclic loading is dependent not only on the maximum amplitude of the motion but also its duration. This is explicitly recognized in methods for estimating the liquefaction potential of soil deposits. Many researchers have proposed that the effective number of cycles of the ground motion is a more robust indicator of the destructive capacity of the shaking than the duration. However, as is the case with strong‐motion duration, there is no universally accepted approach to determining the effective number of cycles of motion, and the different methods that have been proposed can give widely varying results for a particular accelerogram. Definitions of the effective number of cycles of motion are reviewed, classified and compared. Measurements are found to differ particularly for accelerograms with broad‐banded frequency content, which contain a significant number of non‐zero crossing peaks. The key seismological parameters influencing the number of cycles of motion and associated equations for predicting this quantity for future earthquakes are identified. Correlations between cycle counts and different duration measures are explored and found to be rather poor in the absence of additional parameters. Copyright © 2004 John Wiley & Sons, Ltd.  相似文献