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91.
T. Brad C. Obergfell B. M. van Breukelen N. M. van Straalen W. F. M. Röling 《Ground Water Monitoring & Remediation》2013,33(4):69-78
We examined the spatiotemporal changes of microbial communities in relation to hydrochemistry variation over time and space in an aquifer polluted by landfill leachate (Banisveld, The Netherlands). Sampling in 1998, 1999, and 2004 at the same time of the year revealed that the center of the pollution plume was hydrochemically rather stable, but its upper fringe moved to the surface over time, especially at distances greater than 40 m away from the landfill. Complex and spatiotemporal heterogeneous bacterial and eukaryotic communities were resolved using denaturing gradient gel electrophoresis (DGGE) of 16S and 18S rRNA gene fragments. Large fluctuations were noted in the eukaryotic communities associated with strongly polluted and cleaner groundwater. The bacterial communities in strongly polluted samples were different from those in cleaner groundwater in 1998 and 1999, but no longer in 2004. The temporal variation in microbial communities was greater than the spatial variation: the 1998 bacteria communities in strongly polluted groundwater were more related to each other than to those recovered in 1999 and 2004. During the three sampling periods, the bacterial communities were more stable close to the landfill than at larger distances from the landfill. Overall, pollution appears to have only a minor influence on microbial communities. The considerable spatiotemporal variation in microbial community composition may contribute to better biodegradation of pollutants. Designing management strategies for natural attenuation of aquifer pollution will benefit from further long‐term, high‐density monitoring of changes in microbial communities, their diversity and physiological properties, in relation to changes in hydrochemistry. 相似文献
92.
Rapid temporal variability of SO2 and SO in the Venus 85–100 km mesosphere (Sandor, B.J., Clancy, R.T., Moriarty-Schieven G.H. [2007]. Bull. Am. Astron. Soc. 39, 503; Sandor, B.J., Clancy, R.T., Moriarty-Schieven, G.H., Mills, F.P. [2010]. Icarus 208, 49–60) requires in situ sources and sinks for these molecules. While many loss mechanisms are recognized, no process for in situ production is known. Observational investigations to find, or constrain other potential sulfur reservoirs offer one method toward understanding the applicable photochemistry. Here, we report upper limits for gas-phase H2SO4 (sulfuric acid) abundances in Venus’ 85–100 km upper mesosphere, derived from 16 ground-based sub-mm spectroscopic observations in the period 2004–2008. Unlike the ubiquitous sulfuric acid solid/liquid aerosol, the gas phase would be photochemically active, potentially both source and sink for SO and SO2. H2SO4 is retrieved from sub-mm lines located in the same bandpass as the SO2 and SO lines described by Sandor et al. (Sandor, B.J., Clancy, R.T., Moriarty-Schieven, G.H., Mills, F.P. [2010]. Icarus 208, 49–60). H2SO4 upper limits reported here are thus simultaneous and spatially coincident with measurements of SO2 and SO, providing for analysis of the three sulfur species collectively. The average H2SO4 abundance over 16 observations is 1 ± 2 ppb (i.e. <3 ppb). Upper limits for individual observations range from 3 to 44 ppb, where quality of the observing weather is the dominant constraint on measurement precision. The sum of H2SO4, SO2 and SO varies widely. In one comparison, the sum [H2SO4 + SO2 + SO] measured on one date differs by 10-σ from the sum measured 2 months later. We conclude that upper mesospheric sulfur atoms are not conserved among the three molecules, that H2SO4 is not a significant sulfur reservoir for balancing the observed variations of [SO2 + SO], and is not relevant to the (still unknown) photochemistry responsible for observed behavior of SO2 and SO. Having ruled out H2SO4, we infer that elemental sulfur is the most probable candidate for the needed third reservoir. 相似文献
93.
Ecological and morphological response of brackish tidal marshland to the next century of sea level rise: Westham Island, British Columbia 总被引:2,自引:0,他引:2
In response to climatic warming, eustatic sea level has been predicted to rise by about 50 cm in the next century. While feedbacks between vegetation growth and sediment deposition tend to allow marshes to maintain their morphology under a constant rate of sea level rise, recent observations of marsh deterioration suggest that changes in the rate of sea level rise may induce loss of economically and ecologically important marshland. We have developed a three dimensional model of tidal marsh evolution that couples vegetation growth and sediment transport processes including bed accretion and wave erosion. We use the model to simulate the response of marshes and tidal flats along the Fraser River Delta, British Columbia to 100 yr forecasts of sea level change. Under low sea level-rise scenarios, the delta and its marshes prograde slightly, consistent with historical measurements. While accretionary processes greatly mediate the response to increased rates of sea level rise, vegetation zones transgress landward under median and high sea level rise rate scenarios. In these scenarios, low marsh erosion and constriction of high marsh vegetation against a dyke at its landward edge result in a 15–35% loss of marshland in the next century. Several important behavioral changes take place after 2050, suggesting that predictions based on field observations and short term model experiments may not adequately characterize (and sometimes underestimate) long-term change. In particular, the replacement of highly productive high marsh vegetation by less productive low marsh vegetation results in continued reduction of the system's total biomass productivity, even as the rate of loss of vegetated area begins to decline. 相似文献
94.
Michael J. Truex Vince R. Vermeul David T. Adamson Mart Oostrom Lirong Zhong Rob D. Mackley Brad G. Fritz Jake A. Horner Tim C. Johnson Jonathan N. Thomle Darrell R. Newcomer Chris D. Johnson Michal Rysz Tom W. Wietsma Charles J. Newell 《Ground Water Monitoring & Remediation》2015,35(3):34-45
Heterogeneity of hydraulic properties in aquifers may lead to contaminants residing in lower‐permeability zones where it is difficult to deliver remediation amendments using conventional injection processes. The focus of this study is to examine use of a shear‐thinning fluid (STF) to improve the uniformity of remedial amendment distribution within a heterogeneous aquifer. Previous studies have demonstrated the significant potential of STFs for improving remedial amendment delivery in heterogeneous aquifers, but quantitative evaluation of these improvements from field applications is lacking. A field‐scale test was conducted that compares data from successive injection of a tracer in water followed by injection of a tracer in an STF to evaluate the impact of the STF on tracer distribution uniformity in the presence of permeability contrasts within the targeted injection zone. Data from tracer breakthrough at multiple depth‐discrete monitoring intervals and electrical resistivity tomography (ERT) showed that inclusion of STF in the injection solution improved the distribution of the injected fluid within the targeted treatment zone. One improvement was a reduction in the movement of injected fluids through high‐permeability pathways, as evidenced by slower breakthrough of tracer at monitoring locations where breakthrough in baseline tracer‐only injection data was faster. In addition, STF‐amended injection solutions arrived faster and to a greater extent in monitoring locations within low‐permeability zones. ERT data showed that the STF injection covered a higher percentage of a two‐dimensional cross section within the injection interval between the injection well and a monitoring well about 3 m away. 相似文献
95.
Brad E. Rosenheim Peter K. Swart Philippe Willenz 《Geochimica et cosmochimica acta》2009,73(18):5308-5319
A revised calibration is presented relating the oxygen isotope composition of the aragonite-secreting sclerosponge Ceratoporella nicholsoni, oxygen isotope composition of seawater, and ambient water temperature. This new relationship has been obtained using high-resolution δ18O data measured in sclerosponges from the Bahamas and Jamaica compared to ambient temperature measurements and δ18O values of seawater from the two locations, both measured and published. New data improve an existing calibration which was determined using measurements of salinity rather than directly measured δ18O values of the seawater and was composed of measurements from different species of sclerosponge and other aragonite-secreting organisms. The updated calibration (n = 12, r2 = 0.95) is:
T(°C)=16.1(±3.1)-[6.5(±1.1)](δarag-δsw),