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701.
Christine A. PearcyDarren A. Chevis T. Jade HaugHolly A. Jeffries Ningfang YangJianwu Tang Deborah A. GrimmKaren H. Johannesson 《Applied Geochemistry》2011,26(4):575-586
Sediments from the Aquia aquifer in coastal Maryland were collected as part of a larger study of As in the Aquia groundwater flow system where As concentration are reported to reach levels as high as 1072 nmol kg−1, (i.e., ∼80 μg/L). To test whether As release is microbially mediated by reductive dissolution of Fe(III) oxides/oxyhydroxides within the aquifer sediments, the Aquia aquifer sediment samples were employed in a series of microcosm experiments. The microcosm experiments consisted of sterilized serum bottles prepared with aquifer sediments and sterilized (i.e., autoclaved), artificial groundwater using four experimental conditions and one control condition. The four experimental conditions included the following scenarios: (1) aerobic; (2) anaerobic; (3) anaerobic + acetate; and (4) anaerobic + acetate + AQDS (anthraquinone-2,6-disulfonic acid). AQDS acts as an electron shuttle. The control condition contained sterilized aquifer sediments kept under anaerobic conditions with an addition of AQDS. Over the course of the 27 day microcosm experiments, dissolved As in the unamended (aerobic and anaerobic) microcosms remained constant at around ∼28 nmol kg−1 (2 μg/L). With the addition of acetate, the amount of As released to the solution approximately doubled reaching ∼51 nmol kg−1 (3.8 μg/L). For microcosm experiments amended with acetate and AQDS, the dissolved As concentrations exceeded 75 nmol kg−1 (5.6 μg/L). The As concentrations in the acetate and acetate + AQDS amended microcosms are of similar orders of magnitude to As concentrations in groundwaters from the aquifer sediment sampling site (127-170 nmol kg−1). Arsenic concentrations in the sterilized control experiments were generally less than 15 nmol kg−1 (1.1 μg/L), which is interpreted to be the amount of As released from Aquia aquifer sediments owing to abiotic, surface exchange processes. Iron concentrations released to solution in each of the microcosm experiments were higher and more variable than the As concentrations, but generally exhibited similar trends to the As concentrations. Specifically, the acetate and acetate + AQDS amended microcosm typically exhibited the highest Fe concentrations (up to 1725 and 6566 nmol kg−1, respectively). The increase in both As and Fe in the artificial groundwater solutions in these amended microcosm experiments strongly suggests that microbes within the Aquia aquifer sediments mobilize As from the sediment substrate to the groundwaters via Fe(III) reduction. 相似文献
702.
S. Y. Wang S. W. Sloan M. L. Huang C. A. Tang 《Rock Mechanics and Rock Engineering》2011,44(2):179-198
Using a numerical modelling code, rock failure process analysis, 2D, the progressive failure process and associated acoustic
emission behaviour of serial and parallel rock samples were simulated. Both serial- and parallel sample models are presented
for investigating the mechanism of rock pillar failure. As expected, the numerical results show that not only the stiffness,
but also the uniaxial compressive strength of the rock plays an important role in pillar instability. For serial pillars,
the elastic rebound of a rock pillar with higher uniaxial compressive strength can lead to the sudden failure of an adjacent
rock pillar with lower uniaxial compressive strength. The failure zone forms and develops in the pillar with lower uniaxial
compressive strength; however, the failure zone does not pass across the interface of the two pillars. In comparison, when
two pillars have the same uniaxial compressive strengths but different elastic moduli, both serial pillars fail, and the failure
zone in the two pillars can interact, passing across the interface and entering the other pillar. For parallel pillars, damage
always develops in the pillar having the lower uniaxial compressive strength or lower elastic modulus. Furthermore, in accordance
with the Kaiser effect, the stress-induced damage in a rock pillar is irreversible, and only when the previous stress state
in the failed rock pillar is exceeded or the subsequent applied energy is larger than the energy released by the external
loading will further damage continue to occur. In addition, the homogeneity index of rock also can affect the failure modes
of parallel pillars, even though the uniaxial compressive strength and stiffness of each pillar are the same. 相似文献
703.
MD06-3050岩芯位于西非律宾海吕宋岛以东本哈姆高原,利用钙质超微化石下透光带种属Florisphaera profunda占总颗石的相对卡度,恢复了中更新世以来该海区的上层水体结构演化特征.结果显示,西菲律宾海区自1040ka以来,温跃层/营养跃层经历了由浅-深-浅-深的长周期变动.可能是由于全球碳库的长周期变化... 相似文献
704.
We highlighted the flexibility of using unstructured mesh together with the local refinement by a resistivity model with complicated topography. The effect of topography is emphasized. Based on this, we calculated a specific class of layered models and found that the accuracy is not always satisfactory by utilizing the standard approach. As an improvement, we employed the layered earth as the reference model to calculate the wavenumbers. The comparison demonstrates that the accuracy is considerably improved... 相似文献
705.
706.
Carla BOSSARD 《山地科学学报》2011,8(6):794-807
This paper reports the first photosynthetic study of marestail in Jiuzhaigou. In this work, we used PAM fluorometry to examine
photosynthetic rates of submerged and emerged marestail in three lakes. Three lakes were studied across a gradient of water
temperature, with low water temperature conditions in Grass Lake and Arrow Bamboo Lake, and higher water temperature in Five
Colored Lake. In the field, electron transport rates (ETRmax) were measured as rapid light curves (RLCs) by in situ yield measurements. Submerged and emerged marestail showed higher
photosynthetic activity in Five Colored Lake compared to the other lakes, a response consistent with the adaptation of marestail
in Five Colored Lake to high water temperature. The optimal temperature for photosynthesis of submerged marestail in Jiuzhaigou
was about 12 °C. Nonphotochemical quenching (NPQ) of submerged and emerged marestail increased with increasing water temperature.
Maximum quantum yield (F
v/F
m) of submerged marestail in Five Colored Lake showed full recovery at 1700 h due to higher NPQ. Further, the chlorophyll a for submerged marestail was the highest in Grass Lake and the lowest in Five Colored Lake. These results indicate that in
different lakes the function of these aquatic plants is associated with a diversity of place-dependent environmental conditions,
especially water temperature that leads to pronounced differences in the plant’s ecophysiological reactions. 相似文献
707.
Ji-ning Song Lin Lu Bin Teng Han-il Park Guo-qiang Tang Hao Wu 《Ocean Engineering》2011,38(11-12):1308-1322
Laboratory tests have been conducted on vortex-induced vibration (VIV) of a long flexible riser towed horizontally in a wave basin. The riser model has an external diameter of 16 mm and a total length of 28.0 m giving an aspect ratio of about 1750. Reynolds numbers ranged from about 3000 to 10,000. Fiber optic grating strain gages are adopted to measure the dynamic response in both cross-flow and in-line directions. The cross-flow vibrations were observed to vibrate at modes up to 6 and the in-line reached up to 12. The fundamental response frequencies can be predicted by a Strouhal number of about 0.18. Multi-mode responses and the asymmetry of the bare pipe response in uniform flow were observed and analyzed. The experimental results confirmed that the riser pipe vibrated multi-modally despite it being subject to a uniform current profile and all of the excited modes vibrated at the Strouhal frequency. The asymmetrical distribution of displacement mainly resulted from the modal composition. Higher harmonics of the VIV response such as the third, fourth and fifth harmonics frequencies were found to be steady over the entire duration of the test even if they varied along the length of the riser pipe. 相似文献
708.
Chemical and Strontium Isotopic Compositions of the Hanjiang Basin Rivers in China: Anthropogenic Impacts and Chemical Weathering 总被引:1,自引:0,他引:1
The Hanjiang River, the largest tributaries of the Changjiang (Yangtze) River, is the water source area of the Middle Route
of China’s South-to-North Water Transfer Project. The chemical and strontium isotopic compositions of the river waters are
determined with the main purpose of understanding the contribution of chemical weathering processes and anthropogenic inputs
on river solutes, as well as the associated CO2 consumption in the carbonate-dominated basin. The major ion compositions of the Hanjiang River waters are characterized by
the dominance of Ca2+ and HCO3
−, followed by Mg2+ and SO4
2−. The increase in TDS and major anions (Cl−, NO3
−, and SO4
2−) concentrations from upstream to downstream is ascribed to both extensive influences from agriculture and domestic activities
over the Hanjiang basin. The chemical and Sr isotopic analyses indicate that three major weathering sources (dolomite, limestone,
and silicates) contribute to the total dissolved loads. The contributions of the different end-members to the dissolved load
are calculated with the mass balance approach. The calculated results show that the dissolved load is dominated by carbonates
weathering, the contribution of which accounts for about 79.4% for the Hanjiang River. The silicate weathering and anthropogenic
contributions are approximately 12.3 and 6.87%, respectively. The total TDS fluxes from chemical weathering calculated for
the water source area (the upper Hanjiang basin) and the whole Hanjiang basin are approximately 3.8 × 106 and 6.1 × 106 ton/year, respectively. The total chemical weathering (carbonate and silicate) rate for the Hanjiang basin is approximately
38.5 ton/km2/year or 18.6 mm/k year, which is higher than global mean values. The fluxes of CO2 consumption by carbonate and silicate weathering are estimated to be 56.4 × 109 and 12.9 × 109 mol/year, respectively. 相似文献
709.
Zhenghong Tang Samuel D. BrodyRuopu Li Courtney QuinnNan Zhao 《Ocean & Coastal Management》2011,54(5):415-426
Local jurisdictions play a critical role in climate change mitigation and adaptation. This study analyzes the theoretical framework of locally driven climate change actions and uses geographic information system (GIS) to map local jurisdictions’ climate change policy efforts in three Pacific states - California, Oregon, and Washington. The results of our study indicate statistically significant differences in geographic clusters and variations across jurisdictions. An Ordinary Least Squares (OLS) regression model was used to examine climate risk, emission stress, and socioeconomic context variables to detect influence on local climate change policy efforts. The explanatory results indicate that coastal proximity, population density, vehicles emission, and education variables significantly influence local jurisdictions’ climate change actions. The findings contribute to local organizational decision model research and can help local communities to develop more effective climate change policies. 相似文献
710.
Eko Siswanto Junwu Tang Hisashi Yamaguchi Yu-Hwan Ahn Joji Ishizaka Sinjae Yoo Sang-Woo Kim Yoko Kiyomoto Keiko Yamada Connie Chiang Hiroshi Kawamura 《Journal of Oceanography》2011,67(5):627-650
A bio-optical dataset collected during the 1998?C2007 period in the Yellow and East China Seas (YECS) was used to provide alternative empirical ocean-color algorithms in the retrieval of chlorophyll-a (Chl-a), total suspended matter (TSM), and colored dissolved organic matter (CDOM) absorption coefficients at 440 nm (ag440). Assuming that remote-sensing reflectance (Rrs) could be retrieved accurately, empirical algorithms for TChl (regionally tuned Tassan??s Chl-a algorithm) in case-1 waters (TChl2i in case-2 waters), TTSM (regionally tuned Tassan??s TSM algorithm), and Tag440 or Cag440 (regionally tuned Tassan??s or Carder??s ag440 algorithm) were able to retrieve Chl-a, TSM, and ag440 with uncertainties as high as 35, 46, and 35%, respectively. Applying the standard SeaWiFS Rrs, TChl was not viable in the eastern part of the YECS, which was associated with an inaccurate SeaWiFS Rrs retrieval because of improper atmospheric correction. TChl behaved better than other algorithms in the turbid case-2 waters, although overestimation was still observed. To retrieve more reliable Chl-a estimates with standard SeaWiFS Rrs in turbid water (a proxy for case-2 waters), we modified TChl for data with SeaWiFS normalized water-leaving radiance at 555 nm (nLw555) > 2 mW cm?2 ??m?1 sr?1 (TChl2s). Finally, with standard SeaWiFS Rrs, we recommend switching algorithms from TChl2s (for case-2 waters) to MOCChl (SeaWiFS-modified NASA OC4v4 standard algorithm for case-1 waters) for retrieving Chl-a, which resulted in uncertainties as high as 49%. To retrieve TSM and ag440 using SeaWiFS Rrs, we recommend empirical algorithms for TTSM (pre-SeaWiFS-modified form) and MTag440 or MCag440 (SeaWiFS Rrs-modified forms of Tag440 or Cag440). These could retrieve with uncertainties as high as 82 and 52%, respectively. 相似文献