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1.
Ger Van Graas 《Organic Geochemistry》1986,10(4-6)
Biomarker distributions in a suite of asphaltenes and kerogens have been analysed by flash pyrolysis directly coupled to a GCMS system. Attention has been focussed on biomarkers of the sterane and triterpane types. The sample suite under investigation consists of sediments with different kerogen types and some crude oils. Biomarker distributions in the pyrolysates have been compared with the “free” biomarkers in the corresponding saturated hydrocarbon fractions.The analyses show significant differences between the distributions of the free biomarkers and those in the pyrolysates. The latter have lower amounts of steranes while diasteranes are absent or present at low concentrations only. In the triterpane traces a shift of maximum intensity from C30 (free compounds) to C27/C29 is observed. Furthermore, the pyrolysates contain a set of triterpenes (not present among the free compounds), and there is a selective loss of “non-regular” triterpanes that are present in the saturated hydrocarbon fractions. The observed differences between pyrolysates and free hydrocarbons can be explained partly by the processes occurring during pyrolysis such as bond rupture and subsequent stabilisation of primary pyrolysis products. To a certain extent these differences also show that maturation processes occurring in sediments have effects on free biomarker molecules different from those on molecules that are enclosed in a macromolecular matrix (kerogen or asphaltenes).Differences between biomarker distributions of asphaltene and kerogen pyrolysates are relatively small. A comparison with the pyrolysates from extracted whole sediments suggests that these differences are mainly caused by interactions between the organic material and the mineral matrix during pyrolysis.Oil asphaltenes behave differently from sediment asphaltenes as their pyrolysates are more similar to the corresponding saturated hydrocarbon fractions, i.e. the differences described above are observed to a much smaller extent. This different behaviour appears to be the result of coprecipitation of a part of the maltene fraction with the oil asphaltenes. 相似文献
2.
Summary
Discharge from a small grassland catchment in Ireland is simulated with the atmospheric land-surface scheme SEWAB. Hydrological
processes are parameterized to represent surface runoff and baseflow generation and soil moisture storage changes. Surface
ponding and infiltration are explicitly described in order to account for the rapid response of streamflow to precipitation
events. The annual discharge, the evapotranspiration and individual flood flows are accurately modelled. The simulation of
soil moisture at various depths is close to the observations from time domain reflectometer measurements. An analysis of the
significance of individual hydrological processes for discharge simulation from the small catchment found the ponding process
to be essential for time periods of less than 12 hours. A depth dependent saturation hydraulic conductivity improves the simulations
on all time scales.
Received October 25, 2000/Revised February 16, 2001 相似文献
3.
Over the last century, afforestation in Ireland has increased from 1% of the land area to 10%, with most plantations on upland drained blanket peatlands. This land use change is considered to have altered the hydrological response and water balance of upland catchments with implications for water resources. Because of the difficulty of observing these long‐term changes in the field, the aim of this study was to utilize a hydrological model to simulate the rainfall runoff processes of an existing pristine blanket peatland and then to simulate the hydrology of the peatland if it were drained and afforested. The hydrological rainfall runoff model (GEOtop) was calibrated and validated for an existing small (76 ha) pristine blanket peatland in the southwest of Ireland for the 2‐year period, 2007–2008. The current hydrological response of the pristine blanket peatland catchment with regard to streamflow and water table (WT) levels was captured well in the simulations. Two land use change scenarios of afforestation were also examined, (A) a young 10‐year‐old and (B) a semi‐mature 15‐year‐old Sitka Spruce forest. Scenario A produced similar streamflow dynamics to the pristine peatland, whereas total annual streamflow from Scenario B was 20% lower. For Scenarios A and B, on an annual average basis, the WT was drawn down by 16 and 20 cm below that observed in the pristine peatland, respectively. The maximum WT draw down in Scenario B was 61 cm and occurred in the summer months, resulting in a significant decrease in summer streamflow. Occasionally in the winter (following rainfall), the WT for Scenario B was just 2 cm lower than the pristine peatland, which when coupled with the drainage networks associated with afforestation led to higher peak streamflows. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
4.
Brendon Blue Claire Gregory Kiely McFarlane Marc Tadaki Petra van Limburg‐Meijer Nick Lewis 《New Zealand geographer》2012,68(1):62-66
The fair and effective governance of freshwater is an increasingly prominent issue in New Zealand. Emerging from a complex of cultural, economic and biophysical narratives, freshwater geographies are multiple, varied and increasingly acknowledged as worthy of interdisciplinary scrutiny. In this commentary, we reflect on a series of generative spaces that we – as group of postgraduate geographers (plus supporting staff) – created to engage with the multiplicity of freshwater meanings both within and beyond the academy. Through this evolving epistemic‐political project, we significantly reframed our own understandings about what freshwater ‘is’ and how it ought to be governed. By pursuing a deeper understanding of how the world gets made, we expand our ability to know and make it differently. 相似文献
5.
6.
James M. Eaton Nicola M. McGoff Kenneth A. Byrne Paul Leahy Ger Kiely 《Climatic change》2008,91(3-4):317-334
Using both historic records and CORINE land cover maps, we assessed the impact of land cover change on the stock of soil organic carbon (SOC) in the Republic of Ireland from 1851 to 2000. We identified ten principal land cover classes: arable land, forest, grassland, heterogeneous agricultural areas/other, nonvegetated semi-natural areas, peatland, suburban, urban, water bodies, and wetland. For each land cover class, the SOC stock was estimated as the product of SOC density and land cover area. These were summed to calculate a national SOC budget for the Republic of Ireland. The Republic of Ireland’s 6.94 million hectares of land have undergone considerable change over the past 150 years. The most striking feature is the decrease in arable land from 1.44 million ha in 1851 to 0.55 million ha in 2000. Over the same time period, forested land increased by 0.53 million ha. As of 2000, agricultural lands including arable land (7.85%), grassland (54.33%), and the heterogeneous agricultural areas/other class (7.91%) account for 70.09% of Irish land cover. We estimate that the SOC stock in the Republic of Ireland, to 1 m depth, has increased from 1,391 Tg in 1851 to 1,469 Tg in 2000 despite soil loss due to urbanization. This increase is largely due to the increase of forested land with its higher SOC stocks when compared to agricultural lands. Peatlands contain a disproportionate quantity of the SOC stock. Although peatlands only occupy 17.36% of the land area, as of 2000, they represented 36% of the SOC stock (to 1 m depth). 相似文献
7.
Ger van Graas Jan M.A. Baas B. van de Graaf J.W. de Leeuw 《Geochimica et cosmochimica acta》1982,46(11):2399-2402
The thermodynamic stabilities of thirteen cholestane isomers have been computed using molecular mechanics. The calculated composition of a mixture of these isomers at thermodynamic equilibrium is in agreement with the composition of a cholestane isomerate. From the calculated stabilities the extent to which isomerisation reactions can proceed during maturation can be predicted. The GLC retention order on non-polar phases of 20R/S isomeric pairs has been estimated from the preferred geometries of the molecules which are also obtained by molecular mechanics. 相似文献
8.
Prof. H. Ambühl Das Gerät ist erhältlich bei Fa. Dr. H. Züllig 《Aquatic Sciences - Research Across Boundaries》1983,45(2):502-504
A device is described which can be used where working equipment has to be instantly activated (i.e. without time delay) under
water. The latch with an adjustable spring, on which the instrument is fastened, can be released by jerking on the supporting
cable or by suddenly stopping the lowering motion, thereby instantly activating the working equipment.
相似文献
9.
Gerard Kiely John D. Albertson Marc B. Parlance William E. Eichinger 《Boundary-Layer Meteorology》1996,77(3-4):267-284
The flux of sensible heat from the land surface is related to the average rate of dissipation of temperature fluctuations in the atmospheric surface layer through the temperature variance budget equation. In many cases it is desirable to estimate the heat flux from measurement or inference of the dissipation rate. Here we study how the dissipation rate scales with atmospheric stability, using three inertial range methods to calculate the dissipation rate: power spectra, second order structure functions, and third order structure functions. Experimental data are analyzed from a pair of field experiments, during which turbulent fluctuations of velocity and temperature were measured over a broad range of neutral and unstable atmospheric flows. It is shown that the temperature dissipation rate scales with a single convective power law continuously from near-neutral to strongly unstable stratification. The dissipation scaling is found to nearly match production in the near-neutral region, but to be consistently lower than production in the more convective regimes. The convective scaling is shown to offer a simplified means of computing sensible heat flux from the dissipation rate of temperature variance.Also at Johns Hopkins University, Baltimore, MarylandAlso at Los Alamos National Laboratory, Los Alamos, New Mexico. 相似文献
10.
Dr. H. R. Bürgi Das Gerät ist erhältlich bei Fa. Dr. H. Züllig 《Aquatic Sciences - Research Across Boundaries》1983,45(2):505-507
A new set of nets in twin arrangement for quantitative layer-sampling of crustaceans is presented and compared to a volume
sampler, as regards capturing characteristics. Due to a favorable geometry and clearly defined opening of the net, there is
no loss due to flight reaction nor water backup.
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