Estimating groundwater recharge for an arid karst system using a combined approach of time‐lapse camera monitoring and water balance modelling          下载免费PDF全文

Stephan Schulz  Gerrit H. de Rooij  Nils Michelsen  Randolf Rausch  Christian Siebert  Christoph Schüth  Mohammed Al‐Saud  Ralf Merz 《水文研究》2016,30(5):771-782

Groundwater is the principal water resource in semi‐arid and arid environments. Therefore, quantitative estimates of its replenishment rate are important for managing groundwater systems. In dry regions, karst outcrops often show enhanced recharge rates compared with other surface and sub‐surface conditions. Areas with exposed karst features like sinkholes or open shafts allow point recharge, even from single rainfall events. Using the example of the As Sulb plateau in Saudi Arabia, this study introduces a cost‐effective and robust method for recharge monitoring and modelling in karst outcrops. The measurement of discharge of a representative small catchment (4.0 · 10⁴ m²) into a sinkhole, and hence the direct recharge into the aquifer, was carried out with a time‐lapse camera. During the monitoring period of two rainy seasons (autumn 2012 to spring 2014), four recharge events were recorded. Afterwards, recharge data as well as proxy data about the drying of the sediment cover are used to set up a conceptual water balance model. The model was run for 17 years (1971 to 1986 and 2012 to 2014). Simulation results show highly variable seasonal recharge–precipitation ratios between 0 and 0.27. In addition to the amount of seasonal precipitation, this ratio is influenced by the interannual distribution of rainfall events. Overall, an average annual groundwater recharge for the doline (sinkhole) catchment on As Sulb plateau of 5.1 mm has estimated for the simulation period. Copyright © 2015 John Wiley & Sons, Ltd.  相似文献   

A mobile multi-depth borehole sensor set-up to study the surface-to-base seismic transfer functions     

Edwin A. Obando  Nils Ryden  Peter Ulriksen 《Engineering Geology》2011,(3):246

The best method to evaluate the seismic site response is by means of borehole vertical arrays that use earthquake records from different depths. In this paper we introduce the implementation of a single borehole sensor system (synchronized to a sensor on the surface) that is fixed at variable depths within a single well. This system is used for recording small amplitude earthquake signals at variable stiffness conditions in depth to compute empirical borehole transfer functions. The computed average empirical borehole transfer functions allow the estimation of an S-wave velocity model that is constrained using the frequency peak observed in the H/V ratio curve.Pairs of surface and borehole earthquake records were obtained with the borehole sensor placed at − 10, −20, −50, and − 100 m depth in a test site in Managua, Nicaragua. The average velocity of the final model down to − 100 m appeared to be in good agreement with the average velocity computed via cross-correlation using the surface and borehole signals. Likewise, an inverted MASW profile and H/V ratio at the same site agree with the S-wave velocity model obtained.  相似文献   

Changes in dissolved silica mobilization into river systems draining North America until the period 2081–2100     

Nils Moosdorf  Jens Hartmann  Ronny Lauerwald 《Journal of Geochemical Exploration》2011

Dissolved silica (DSi) is an important control on algae abundance and species composition both in freshwater and marine ecosystems. Although continental and global budgets for DSi exist, understanding of the spatial variability of DSi cycles needs to be improved on those scales. In this study, an empirical model of DSi mobilization into river systems is extrapolated on a 1.4 km² grid to North America. To analyze changes in DSi mobilization patterns, DSi mobilization is estimated regionally for present day runoff and a runoff projection ensemble for the period 2081–2100. The model predicts present day annual DSi fluxes for the monitored area within 6% of the calculated fluxes. Possible biases by processes not directly represented by applied geodata are discussed (e.g. land use and ecosystem influences) and found to be only minor on the regional scale. Uncertainty of the results is discussed based on a literature review. The projected DSi-mobilization rates at high latitudes for the present day conditions may be overestimated. However, the projected change rate for the period 2081–2100 might even be underestimated, due to e.g. increased thawing in certain permafrost regions, which was not included in the model.  相似文献   

The origin of skarn beds, Ryllshyttan Zn�CPb�CAg + magnetite deposit, Bergslagen, Sweden     

Nils F. Jansson  Rodney L. Allen 《Mineralogy and Petrology》2011,103(1-4):49-78

Thin- to medium-bedded, stratiform calc-silicate deposits (banded skarns) are a peculiar, but important, component of the supracrustal successions in the Palaeoproterozoic Bergslagen mining district of central Sweden. They are referred to as ??skarn-banded leptites?? in the literature and are common in areas and at stratigraphic levels that contain iron oxide and base metal sulphide deposits. The stratigraphic hanging wall of the stratabound Ryllshyttan Zn?CPb?CAg + magnetite deposit at Garpenberg, contains approximately 100?C150?m of interbedded aluminous skarn beds and rhyolitic ash-siltstones. The skarn beds are mineralogically variable and dominantly composed of grandite, spessartine, epidote, actinolite, quartz, clinopyroxene, and locally magnetite. Integrated field-mapping, and whole-rock lithogeochemical, microscopic and mineral chemical analyses suggest that the stratiform skarn beds are the products of at least two discrete hydrothermal events and subsequent metamorphism. The first event comprised accumulation in a quiescent subaqueous environment, below wave base, of calcareous and ferruginous sediments rich in Fe, Mn, Ca, and Mg. These chemical sediments were deposited concurrently with rhyolitic ash-silt sedimentation, thus forming a (now metamorphosed) laminated calcareous Fe formation with both a detrital rhyolitic component and rhyolitic siltstone interbeds. Positive Eu-anomalies and negative Ce-anomalies for normalized rare earth element analyses of skarn beds suggest that the iron may have been derived from exhalation of hot and reduced hydrothermal fluids, which upon mixing with more oxidized seawater, precipitated Fe oxides and/or carbonates that settled from suspension to the seafloor. The size of the positive Eu-anomalies of the chemical sediments are modified by the content of rhyolitic volcaniclastic material, which has a negative Eu anomaly, such that positive Eu-anomalies are only observed in skarn beds that possess a minor volcaniclastic component. Subsequently, the calcareous Fe formations were subjected to post-depositional alteration by hydrothermal fluids, locally yielding more manganoan and magnesian assemblages. The Mn-alteration is manifested by lateral gradations from epidote-grandite-clinopyroxene±magnetite rocks into significantly more Mn-rich quartz-spessartine rocks and massive andradite rocks over distances of less than 10?cm within individual skarn beds. Magnesian alteration is manifested by the development of discordant zones of pargasite para-amphibolites and formation of stratiform pargasite rocks texturally similar to the interlaminated grandite-epidote-ferroan diopside rocks. The latter increase in abundance towards the Ryllshyttan deposit and are associated with pre-metamorphic/pre-tectonic K?CMg?CFe±Si alteration (now biotite-phlogopite-garnet-cordierite-pargasite rocks) that is related to base metal mineralization. The zone of Mn- and Mg-altered skarn beds extends beyond the zone of pervasive K?CMg?CFe±Si alteration around Ryllshyttan. This suggests that the skarn bed progenitors, or their sedimentary contacts against rhyolitic ash-siltstones, acted as conduits to outflowing hydrothermal fluids. The chemical and mineralogical imprint, imposed on affected beds by alteration, may serve as indicators of proximity to intense K?CMg?CFe±Si alteration envelopes around other base metal sulphide deposits in Bergslagen. The last recorded event comprised syn-tectonic veining of competent massive andradite skarn beds. The veins contain quartz-albite-epidote-ferroan diopside-actinolite assemblages.  相似文献   

Coupling spatial geochemical and lithological information to distinguish silicate and non-silicate chemical weathering fluxes     

Jens Hartmann  Nils Moosdorf 《Applied Geochemistry》2011

Lithological maps have been proved to be a useful tool to evaluate regional and global matter fluxes from chemical weathering. However, lithological classes provide aggregated information of mineralogical, geochemical, sedimentary or diagenetic properties. Thus, using a limited number of lithological classes introduces by their definition a bias to the analysis of weathering fluxes, specifically in the case of multilithological catchments. Here it is shown that the coupling of geochemical with lithological information may help to better identify the sources of the weathering fluxes, using the example of dissolved Ca to better distinguish weathering rates of silicate and non-silicate minerals.  相似文献   

Forecasts of hydrological parameters over the Mackenzie River Basin: Sensitivity to initial conditions,horizontal resolution and forecast range     

Nils Ek  Harold Ritchie 《大气与海洋》2013,51(4):675-710

Abstract

As part of the Global Energy and Water Cycle Experiment, Canadian global spectral forecast model predictions of surface water and energy fluxes over the Mackenzie River basin are examined. Two nine‐member ensemble forecasts of one month duration are produced with the operational model, for a spring and a summer case, at a horizontal resolution of about 100 km (T95). The sensitivity to initial conditions is measured by the degree to which the individual forecasts in the ensembles vary one from another. The evolution in time of this estimated error (ensemble standard deviation) is determined for the surface energy and water accumulations, averaged over the basin. For comparison the calculations are repeated for the Mississippi basin and over North America. The greatest sensitivity is found for the net accumulation of precipitation minus evaporation. The spring ensemble is redone at a coarser horizontal resolution (T47), and the results are similar. The forecast uncertainty (ensemble standard deviation) of the area‐averages over the basin appear to be unaffected by this change, although the ensemble mean values are sensitive to the change in resolution. The ensemble standard deviation makes a significant, abrupt increase toward the end of the second week into the forecasts. This investigation suggests a need for an improved model, if the forecasts’ useful range is to extend to one month. Available upgrades to the land‐surface, precipitation and evaporation schemes will be used in subsequent work, and the forecasts reported here will serve as a baseline for comparison.  相似文献   

Atmospheric winter response to a projected future Antarctic sea-ice reduction: a dynamical analysis     

Jürgen Bader  Martin Flügge  Nils Gunnar Kvamstø  Michel D. S. Mesquita  Aiko Voigt 《Climate Dynamics》2013,40(11-12):2707-2718

Several studies have analysed the atmospheric response to sea-ice changes in the Arctic region, but only few have considered the Antarctic. Here, the atmospheric response to sea-ice variability in the Southern Hemisphere is investigated with the atmospheric general circulation model ECHAM5. The model is forced by the present and a projected future seasonal cycle of Antarctic sea ice. In September, the mean atmospheric response exhibits distinct similarities to the structure of the negative phase of the Southern Annular Mode, the leading mode of Southern Hemisphere variability. In the reduced Antarctic sea-ice integration, there is an equatorward shift of the Southern Hemisphere mid-latitude jet and the storm tracks. In contrast to a recent previous study, our findings indicate that a substantial impact of Southern Hemispheric future sea-ice reduction on the mid-latitude circulation cannot be ruled out.  相似文献   

Chromite oxidation by manganese oxides in subseafloor basalts and the presence of putative fossilized microorganisms     

Ivarsson M  Broman C  Holm NG 《Geochemical transactions》2011,12(1):5-10

Chromite is a mineral with low solubility and is thus resistant to dissolution. The exception is when manganese oxides are available, since they are the only known naturally occurring oxidants for chromite. In the presence of Mn(IV) oxides, Cr(III) will oxidise to Cr(VI), which is more soluble than Cr(III), and thus easier to be removed. Here we report of chromite phenocrysts that are replaced by rhodochrosite (Mn(II) carbonate) in subseafloor basalts from the Koko Seamount, Pacific Ocean, that were drilled and collected during the Ocean Drilling Program (ODP) Leg 197. The mineral succession chromite-rhodochrosite-saponite in the phenocrysts is interpreted as the result of chromite oxidation by manganese oxides. Putative fossilized microorganisms are abundant in the rhodochrosite and we suggest that the oxidation of chromite has been mediated by microbial activity. It has previously been shown in soils and in laboratory experiments that chromium oxidation is indirectly mediated by microbial formation of manganese oxides. Here we suggest a similar process in subseafloor basalts.  相似文献   

The spin evolution of nascent neutron stars     

Anna L. Watts  Nils Andersson 《Monthly notices of the Royal Astronomical Society》2002,333(4):943-951

The loss of angular momentum owing to unstable r-modes in hot young neutron stars has been proposed as a mechanism for achieving the spin rates inferred for young pulsars. One factor that could have a significant effect on the action of the r-mode instability is fallback of supernova remnant material. The associated accretion torque could potentially counteract any gravitational-wave-induced spin-down, and accretion heating could affect the viscous damping rates and hence the instability. We discuss the effects of various external agents on the r-mode instability scenario within a simple model of supernova fallback on to a hot young magnetized neutron star. We find that the outcome depends strongly on the strength of the magnetic field of the star. Our model is capable of generating spin rates for young neutron stars that accord well with initial spin rates inferred from pulsar observations. The combined action of r-mode instability and fallback appears to cause the spin rates of neutron stars born with very different spin rates to converge, on a time-scale of approximately 1 year. The results suggest that stars with magnetic fields ≤10¹³ G could emit a detectable gravitational wave signal for perhaps several years after the supernova event. Stars with higher fields (magnetars) are unlikely to emit a detectable gravitational wave signal via the r-mode instability. The model also suggests that the r-mode instability could be extremely effective in preventing young neutron stars from going dynamically unstable to the bar-mode.  相似文献   

Evolving turbulence and magnetic fields in galaxy clusters     

Kandaswamy Subramanian  Anvar Shukurov  Nils Erland L. Haugen 《Monthly notices of the Royal Astronomical Society》2006,366(4):1437-1454

  相似文献