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91.
This paper critically reviews and intercompares land surface schemes (LSSs) as used in atmospheric general circulation models
(AGCMs) to simulate soil moisture and its response to a warmer climate, and potential evapotranspiration approaches as used
in operational soil moisture monitoring and in predicting the response of soil moisture to a warmer climate. AGCM predictions
of overall soil moisture change are in broad agreement but disagree sharply in some regions. Intercomparison projects have
sought to evaluate the LSSs used by AGCMs for both accuracy and consistency. These studies have found that different LSSs
can produce very different simulations even when supplied with identical atmospheric forcing. As well, LSSs that produce similar
surface results from present-day or control climates often diverge when forced with climatic change data. Furthermore, no
single LSS has been identified that produces an adequate simulation of all of temperature, moisture, evapotranspiration and
runoff. AGCM LSSs must resolve the surface energy balance (SEB) in order to compute realistic heat fluxes between with the
atmospheric model. LSSs have been used with AGCMs in both on-line (fully coupled) and off-line modes. In off-line climatic
change experiments, AGCM predictions of atmospheric temperature and precipitation have been used, along with model downward
radiative fluxes at the surface, to drive their own uncoupled LSS. However, there are simple non-energy-balance methods for
estimating evapotranspiration that have been traditionally used in agricultural and meteorological applications. These schemes
compute a potential evapotranspiration (PE) based on temperature and/or net radiation inputs, with the PE modified based on
the availability of soil moisture. Operational PE approaches have also been used with AGCM data in off-line climate change
experiments. The advantages of this approach are that it is simpler and requires less information, although (like the off-line
SEB approach) it leaves out the simulation of feedbacks between the surface and the atmosphere.Although the SEB approach is
essential for LSSs that must be coupled to AGCMs, this does not necessarily make it superior to an off-line operational PE
LSS when it comes to quantities such as soil moisture. The quality of current observational data is insufficient to demonstrate
that either approach is better than the other. Both approaches should continue to be used and intercompared when predicting
the impacts of climatic change on soil moisture. 相似文献
92.
Dorothy L. Parker Takami Morita Rebecca Verity James K. McCarthy 《Geochimica et cosmochimica acta》2007,71(23):5672-5683
To examine the pathways that form Mn(III) and Mn(IV) in the Mn(II)-oxidizing bacterial strains Pseudomonas putida GB-1 and MnB1, and to test whether the siderophore pyoverdine (PVD) inhibits Mn(IV)O2 formation, cultures were subjected to various protocols at known concentrations of iron and PVD. Depending on growth conditions, P. putida produced one of two oxidized Mn species - either soluble PVD-Mn(III) complex or insoluble Mn(IV)O2 minerals - but not both simultaneously. PVD-Mn(III) was present, and MnO2 precipitation was inhibited, both in iron-limited cultures that had synthesized 26-50 μM PVD and in iron-replete (non-PVD-producing) cultures that were supplemented with 10-550 μM purified PVD. PVD-Mn(III) arose by predominantly ligand-mediated air oxidation of Mn(II) in the presence of PVD, based on the following evidence: (a) yields and rates of this reaction were similar in sterile media and in cultures, and (b) GB-1 mutants deficient in enzymatic Mn oxidation produced PVD-Mn(III) as efficiently as wild type. Only wild type, however, could degrade PVD-Mn(III), a process linked to the production of both MnO2 and an altered PVD with absorbance and fluorescence spectra markedly different from those of either PVD or PVD-Mn(III). Two conditions, the presence of bioavailable iron and the absence of PVD at concentrations exceeding those of Mn, both had to be satisfied for MnO2 to appear. These results suggest that P. putida cultures produce soluble Mn(III) or MnO2 by different and mutually inhibitory pathways: enzymatic catalysis yielding MnO2 under iron sufficiency or PVD-promoted oxidation yielding PVD-Mn(III) under iron limitation. Since PVD-producing Pseudomonas species are environmentally prevalent Mn oxidizers, these data predict influences of iron (via PVD-Mn(III) versus MnO2) on the global oxidation/reduction cycling of various pollutants, recalcitrant organic matter, and elements such as C, S, N, Cr, U, and Mn. 相似文献
93.
Adam Carter Benjamin van Wyk de Vries Karim Kelfoun Patrick Bachèlery Pierre Briole 《Bulletin of Volcanology》2007,69(7):741-756
A clear model of structures and associated stress fields of a volcano can provide a framework in which to study and monitor
activity. We propose a volcano-tectonic model for the dynamics of the summit of Piton de la Fournaise (La Reunion Island,
Indian Ocean). The summit contains two main pit crater structures (Dolomieu and Bory), two active rift zones, and a slumping
eastern sector, all of which contribute to the actual fracture system. Dolomieu has developed over 100 years by sudden large
collapse events and subsequent smaller drops that include terrace formation. Small intra-pit collapse scars and eruptive fissures
are located along the southern floor of Dolomieu. The western pit wall of Dolomieu has a superficial inward dipping normal
fault boundary connected to a deeper ring fault system. Outside Dolomieu, an oval extension zone containing sub-parallel pit-related
fractures extends to a maximum distance of 225 m from the pit. At the summit the main trend for eruptive fissures is N80°,
normal to the north–south rift zone. The terraced structure of Dolomieu has been reproduced by analogue models with a roof
to width ratio of approximately 1, suggesting an original magma chamber depth of about 1 km. Such a chamber may continue to
act as a storage location today. The east flank has a convex–concave profile and is bounded by strike-slip fractures that
define a gravity slump. This zone is bound to the north by strike-slip fractures that may delineate a shear zone. The southern
reciprocal shear zone is probably marked by an alignment of large scoria cones and is hidden by recent aa lavas. The slump
head intersects Dolomieu pit and may slide on a hydrothermally altered layer known to be located at a depth of around 300 m.
Our model has the summit activity controlled by the pit crater collapse structure, not the rifts. The rifts become important
on the mid-flanks of the cone, away from pit-related fractures. On the east flank the superficial structures are controlled
by the slump. We suggest that during pit subsidence intra-pit eruptions may occur. During tumescence, however, the pit system
may become blocked and a flank eruption is more likely. Intrusions along the rift may cause deformation that subsequently
increases the slump’s potential to deform. Conversely, slumping may influence the east flank stress distribution and locally
control intrusion direction. These predictions can be tested with monitoring data to validate the model and, eventually, improve
monitoring. 相似文献
94.
Adam Tickell 《Area》1998,30(1):83-90
95.
This is the second part of a study conducted to determine whether polymeric sampling tubing can affect organic analyte concentrations during a sampling event. In this part of the study, we looked for sorption and desorption of tricholoroethylene (TCE) and leaching of organic constituents in water pumped through five types of polymeric tubing. The materials tested were a rigid fluoropolymer, a flexible fluoropolymer, low-density polyethylene (LDPE), and two plasticized polypropylene tubings. The effects of tubing length and flow rate were examined.
The least sorptive tubings, both initially and at equilibrium, were the fluoropolymers. However, in some instances the LDPE tubing had little effect on TCE concentrations. This was when a slow flow rate was used to sample relatively shallow wells (50 feet [15 m] or less) or when a faster flow rate (1 L/min) was used to sample wells that are less than 500 feet (152 m). Further testing is recommended using more sorptive analytes.
Using high performance liquid chromatography (HPLC), we were unable to detect any constituents leaching from any of the tubings used in these studies, even when a slow flow rate was used. However, desorption of sorbed analytes is a concern for all the tubings tested, including the rigid fluoropolymer. 相似文献
The least sorptive tubings, both initially and at equilibrium, were the fluoropolymers. However, in some instances the LDPE tubing had little effect on TCE concentrations. This was when a slow flow rate was used to sample relatively shallow wells (50 feet [15 m] or less) or when a faster flow rate (1 L/min) was used to sample wells that are less than 500 feet (152 m). Further testing is recommended using more sorptive analytes.
Using high performance liquid chromatography (HPLC), we were unable to detect any constituents leaching from any of the tubings used in these studies, even when a slow flow rate was used. However, desorption of sorbed analytes is a concern for all the tubings tested, including the rigid fluoropolymer. 相似文献
96.
97.
98.
Alfonso V. Botello Enrique F. Mandelli Steve Macko Patrick L. Parker 《Geochimica et cosmochimica acta》1980,44(3):557-559
The stable carbon isotope composition sedimentary organic carbon was determined in the sediments of seven coastal lagoons of the Gulf of Mexico, Mexico. For most of the lagoons the δ13C values for sediments ranged from ?20.1 to ?23.9%. Anomalously low values, ?26.8 to 29.3%. were determined in sediments of two of the studied lagoons, probably due to the presence of organic carbon from anthropogenic sources, naturally absent in these environments. The δ13C values determined in the tissues of oysters collected at the same time in the different lagoons were very similar to those recorded in the sediments. 相似文献
99.
Adam Kovach Harold W. Fairbairn Patrick M. Hurley Miguel A.S. Basei Umberto G. Cordani 《Precambrian Research》1976,3(5):471-480
Rb/Sr whole rock as well as K/Ar whole rock and mineral age determinations have been carried out on drill core samples obtained from the crystalline basement underlying the Amazonas and Maranhão Basins in Brazil. The data confirm the existence of an ancient basement under the Upper and Middle Amazonas Basin. The primary age of the granitic rocks is estimated at about 1560 Ma which correlates with recent age data obtained on granitic rocks on both sides of the Amazonas syneclise. In some areas the K/Ar ages show a decrease probably due to the effect of the Nickerie thermal episode described previously in the Guayana Shield.In the basement of the interconnected Lower Amazonas and Maranhão Basins Late Precambrian (Caririan) metamorphism and igneous activity seems to have been pervasive. The data allow the continuation of the Brazilian age province known in northeastern Brazil under the Maranhão Basin, linking this province to the Brasilia-Paraguay orogenic belt of similar age. 相似文献
100.
Organic carbon from sediments collected in Texas seagrass meadows was enriched in 13C by an average of 6.6% relative to organic carbon from offshore sediments. Within the South Texas hay system examined. δ13C values became increasingly more typical of offshore sediments with increasing distance from seagrass meadows. This permits the use of carbon isotope data as a measure of the relative contributions of seagrasses and plankton to sedimentary organic matter. 相似文献