Isotope hydrology and water sources in a heavily urbanized stream     

Christian Marx  Dörthe Tetzlaff  Reinhard Hinkelmann  Chris Soulsby 《水文研究》2021,35(10):e14377

Complex networks of both natural and engineered flow paths control the hydrology of streams in major cities through spatio-temporal variations in connection and disconnection of diverse water sources. We used spatially extensive and temporally intensive sampling of water stable isotopes to disentangle the hydrological sources of the heavily urbanized Panke catchment (~220 km²) in the north of Berlin, Germany. The isotopic data enabled us to partition stream water sources across the catchment using a Bayesian mixing analysis. The upper part of the catchment streamflow is dominated by groundwater (~75%) from gravel aquifers. In dry summer periods, streamflow becomes intermittent in the upper catchment, possibly as a result of local groundwater abstractions. Storm drainage dominates the responses to precipitation events. Although such events can dramatically change the isotopic composition of the upper stream network, storm drainage only accounts for 10%–15% of annual streamflow. Moving downstream, subtle changes in sources and isotope signatures occur as catchment characteristics vary and the stream is affected by different tributaries. However, effluents from a wastewater treatment plant (WWTP), serving 700,000 people, dominate stream flow in the lower catchment (~90% of annual runoff) where urbanization effects are more dramatic. The associated increase in sealed surfaces downstream also reduces the relative contribution of groundwater to streamflow. The volume and isotopic composition of storm runoff is again dominated by urban drainage, though in the lower catchment, still only about 10% of annual runoff comes from storm drains. The study shows the potential of stable water isotopes as inexpensive tracers in urban catchments that can provide a more integrated understanding of the complex hydrology of major cities. This offers an important evidence base for guiding the plans to develop and re-develop urban catchments to protect, restore, and enhance their ecological and amenity value.  相似文献   

From land cover-graphs to urban structure types     

Irene Walde  Sören Hese  Christian Berger  Christiane Schmullius 《International journal of geographical information science》2014,28(3):584-609

Urban structure types (UST) are an initial interest and basic instrument for monitoring, controlling and modeling tasks of urban planners and decision makers during ongoing urbanization processes. This study focuses on a method to classify UST from land cover (LC) objects, which were derived from high resolution satellite images. The topology of urban LC objects is analyzed by implementing neighborhood LC-graphs. Various graph measures are examined by their potential to distinguish between different UST, using the machine learning classifier random forest. Additionally the influence of different parameter settings of the random forest model, the reduction of training samples, and the graph measure importance is analyzed. An independent test set is classified and validated, achieving an overall accuracy of 87%. It was found that the height of the building with the highest node degree has a strong impact on the classification result.  相似文献   

First GOCE gravity field models derived by three different approaches   总被引：28，自引：10，他引：18  

Roland Pail  Sean Bruinsma  Federica Migliaccio  Christoph F?rste  Helmut Goiginger  Wolf-Dieter Schuh  Eduard H?ck  Mirko Reguzzoni  Jan Martin Brockmann  Oleg Abrikosov  Martin Veicherts  Thomas Fecher  Reinhard Mayrhofer  Ina Krasbutter  Fernando Sans��  Carl Christian Tscherning 《Journal of Geodesy》2011,85(11):819-843

Three gravity field models, parameterized in terms of spherical harmonic coefficients, have been computed from 71 days of GOCE (Gravity field and steady-state Ocean Circulation Explorer) orbit and gradiometer data by applying independent gravity field processing methods. These gravity models are one major output of the European Space Agency (ESA) project GOCE High-level Processing Facility (HPF). The processing philosophies and architectures of these three complementary methods are presented and discussed, emphasizing the specific features of the three approaches. The resulting GOCE gravity field models, representing the first models containing the novel measurement type of gravity gradiometry ever computed, are analysed and assessed in detail. Together with the coefficient estimates, full variance-covariance matrices provide error information about the coefficient solutions. A comparison with state-of-the-art GRACE and combined gravity field models reveals the additional contribution of GOCE based on only 71 days of data. Compared with combined gravity field models, large deviations appear in regions where the terrestrial gravity data are known to be of low accuracy. The GOCE performance, assessed against the GRACE-only model ITG-Grace2010s, becomes superior at degree 150, and beyond. GOCE provides significant additional information of the global Earth gravity field, with an accuracy of the 2-month GOCE gravity field models of 10?cm in terms of geoid heights, and 3?mGal in terms of gravity anomalies, globally at a resolution of 100?km (degree/order 200).  相似文献   

Influence of grass soil cover on water runoff and soil detachment under rainfall simulation in a sub‐humid South African degraded rangeland     

Pascal Podwojewski  Jean Louis Janeau  Séraphine Grellier  Christian Valentin  Simon Lorentz  Vincent Chaplot 《地球表面变化过程与地形》2011,36(7):911-922

In most regions of the world overgrazing plays a major role in land degradation and thus creates a major threat to natural ecosystems. Several feedbacks exist between overgrazing, vegetation, soil infiltration by water and soil erosion that need to be better understood. In this study of a sub‐humid overgrazed rangeland in South Africa, the main objective was to evaluate the impact of grass cover on soil infiltration by water and soil detachment. Artificial rains of 30 and 60 mm h^?1 were applied for 30 min on 1 m² micro‐plots showing similar sandy‐loam Acrisols with different proportions of soil surface coverage by grass (Class A: 75–100%; B: 75–50%; C: 50–25%; D: 25–5%; E: 5–0% with an outcropping A horizon; F: 0% with an outcropping B horizon) to evaluate pre‐runoff rainfall (Pr), steady state water infiltration (I), sediment concentration (SC) and soil losses (SL). Whatever the class of vegetal cover and the rainfall intensity, with the exception of two plots probably affected by biological activity, I decreased regularly to a steady rate <2 mm h^?1 after 15 min rain. There was no significant correlation between I and Pr with vegetal cover. The average SC computed from the two rains increased from 0·16 g L^?1 (class A) to 48·5 g L^?1 (class F) while SL was varied between 4 g m^?2 h^?1 for A and 1883 g m^?2 h^?1 for F. SL increased significantly with decreasing vegetal cover with an exponential increase while the removal of the A horizon increased SC and SL by a factor of 4. The results support the belief that soil vegetation cover and overgrazing plays a major role in soil infiltration by water but also suggest that the interrill erosion process is self‐increasing. Abandoned cultivated lands and animal preferred pathways are more vulnerable to erosive processes than simply overgrazed rangelands. Copyright © 2011 John Wiley & Sons, Ltd.  相似文献   

Using lumped conceptual rainfall-runoff models to simulate daily isotope variability with fractionation in a nested mesoscale catchment   总被引：1，自引：0，他引：1  

Christian Birkel  Doerthe Tetzlaff  Sarah M. Dunn  Chris Soulsby 《Advances in water resources》2011,34(3):383-394

This paper presents 19 months of stable isotope (δ²H and δ¹⁸O) data to enhance understanding of water and solute transport at two spatial scales (2.3 km² and 122 km²) in the agricultural Lunan catchment, Scotland. Daily precipitation and stream isotope data, weekly lake and spring isotope data and monthly groundwater isotope data revealed important insights into flow pathways and mixing of water at both scales. In particular, a deeper groundwater flow path significantly contributes to total streamflow (25-50%). Upstream lake isotope dynamics, susceptible to evaporative fractionation, also appeared to have an important influence on the downstream isotope composition. This unique tracer data set facilitated the conceptualization of a lumped catchment-scale flow-tracer model. The incorporation of hydrological, mixing and fractionation processes based on these data improved simulations of the stream δ²H isotope response at the catchment outlet from 0.37 to 0.56 for the Nash-Sutcliffe statistic. The stable isotope data successfully aided model conceptualization and calibration in the quest for a simple water and solute transport model with improved representation of process dynamics.  相似文献   

How important is it to integrate riverine suspended sediment chemical composition with depth? Clues from Amazon River depth-profiles   总被引：1，自引：0，他引：1  

Julien Bouchez  Maarten Lupker  Christian France-Lanord 《Geochimica et cosmochimica acta》2011,75(22):6955-6970

The vertical variability in mineralogical, chemical and isotopic compositions observed in large river suspended sediments calls for a depth-integration of this variability to accurately determine riverine geochemical fluxes. In this paper, we present a method to determine depth-integrated chemical particulate fluxes of large rivers, based on river sampling along depth-profiles, and applied to the Amazon Basin lowland tributaries. The suspended particulate matter (SPM) concentration data from depth-profiles is modeled for a number of individual grain size fractions using the Rouse model, which allows to predict the grain size distribution of suspended sediment throughout the whole river cross-section. Then, using (1) the relationship between grain size distribution and the Al/Si ratio (2) relationships between the Al/Si ratio and the chemical concentrations, the chemical composition of river sediment is predicted throughout the river cross-section, and integrated to yield the depth-integrated chemical particulate flux for a number of chemical elements (e.g. Si, Al, Fe, Na, REEs, …). For elements such as Al, Fe, REEs, Th, the depth-integrated flux is around twice as high as the one calculated from river surface sample characteristics. For Na and Si, the depth-integrated flux is three times higher than the “surface” estimate, due to the enrichment of albite and quartz at the bottom of the river. Depth-integrated ⁸⁷Sr/⁸⁶Sr composition of suspended sediment, also predictable using this method, differs by more than 10⁻³ from the surface sample composition.Finally, potential implications of depth-integrated estimates of Amazon sediment chemistry are explored. Depth-integration of particulate ⁸⁷Sr/⁸⁶Sr isotopic ratios is necessary for a reliable use of Sr isotopes as a provenance tracer. The concept of steady-state weathering of a large river basin is revisited using depth-integrated sediment composition. This analysis shows that, in the Amazon Basin river, the previously observed discrepancy between (1) weathering intensities of channel surface sediment and (2) silicate-derived dissolved fluxes is only slightly accounted for by the vertical variability of suspended sediment weathering intensities. This observation confirms that most large rivers basins are not eroding at steady-state.  相似文献   

Crustal contamination and PGE mineralization in the Platreef,Bushveld Complex,South Africa: evidence for multiple contamination events and transport of magmatic sulfides     

Christian Ihlenfeld  Reid R. Keays 《Mineralium Deposita》2011,46(7):813-832

Diamond drill core traverses across the Platreef were carried out at Tweefontein, Sandsloot, and Overysel in order to establish the relationship between crustal contamination and platinum group element (PGE) mineralization. The footwall rocks are significantly different at each of these sites and consist of banded iron formation and sulfidic shales at Tweefontein, of carbonates at Sandsloot, and of granites and granite gneisses at Overysel. As demonstrated in this study, Platreef rocks are characterized by two stages of crustal contamination. The first contamination event occurred prior to emplacement of the magma and is present in Platreef rocks at all three sites, as well as in the Merensky Reef. This event is readily identified on trace element spidergrams and trace element ratio scattergrams. The second contamination event was induced by interaction of the Platreef magma with the local footwall rocks. It is most easily identified at Tweefontein, where there is a large increase in the FeO content of the Platreef rocks, and at Sandsloot, where there is a large increase in their CaO and MgO contents, relative to Bushveld rocks that are uncontaminated by the local footwall rocks. At Overysel, the second contamination event did not result in pronounced changes in the major element composition of the Platreef rocks, but can be detected in their trace element chemistry. A strong inverse relationship between PGE tenors and S/Se ratios is interpreted to suggest that the PGE-rich sulfides were formed prior to emplacement of the Platreef magmas through assimilation of crustal S and became progressively enriched in the PGE during transport. Rather than promoting S-saturation, interaction of the Platreef magma with the footwall rocks diluted the metal tenors of the sulfides. Although both the Platreef and the Merensky Reef magmas were contaminated by the same crustal contaminant and were probably PGE-rich, they have radically different Pd/Pt ratios. Their Pd/Pt ratios suggest that whereas the Merensky Reef magma became PGE-rich due to dissolution of PGE-rich sulfides segregated from a pre-Merensky magma that had undergone relatively little fractionation prior to reaching S-saturation, the pre-Platreef magma had undergone greater fractionation prior to the sulfide saturation event, thereby increasing its Pd/Pt ratio. We suggest that the magmas that formed the Platreef and Merensky Reef may have simply been carrier magmas for sulfides that had formed elsewhere in the plumbing system of the Bushveld Complex by the interaction of earlier generations of magmas with the crustal rocks that underlie the Complex.  相似文献   

Texture and anisotropy analysis of Qusaiba shales     

Waruntorn Kanitpanyacharoen  Hans‐Rudolf Wenk  Frans Kets  Christian Lehr  Richard Wirth 《Geophysical Prospecting》2011,59(3):536-556

Scanning and transmission electron microscopy, synchrotron X‐ray diffraction, microtomography and ultrasonic velocity measurements were used to characterize microstructures and anisotropy of three deeply buried Qusaiba shales from the Rub’al‐Khali basin, Saudi Arabia. Kaolinite, illite‐smectite, illite‐mica and chlorite show strong preferred orientation with (001) pole figure maxima perpendicular to the bedding plane ranging from 2.4–6.8 multiples of a random distribution (m.r.d.). Quartz, feldspars and pyrite crystals have a random orientation distribution. Elastic properties of the polyphase aggregate are calculated by averaging the single crystal elastic properties over the orientation distribution, assuming a nonporous material. The average calculated bulk P‐wave velocities are 6.2 km/s (maximum) and 5.5 km/s (minimum), resulting in a P‐wave anisotropy of 12%. The calculated velocities are compared with those determined from ultrasonic velocity measurements on a similar sample. In the ultrasonic experiment, which measures the effects of the shale matrix as well as the effects of porosity, velocities are smaller (P‐wave maximum 5.3 km/s and minimum 4.1 km/s). The difference between calculated and measured velocities is attributed to the effects of anisotropic pore structure and to microfractures present in the sample, which have not been taken into account in the matrix averaging.  相似文献   

Impact of recent climatic change on growth of low elevation eastern Mediterranean forest trees   总被引：3，自引：1，他引：2  

Dimitrios Sarris  Dimitrios Christodoulakis  Christian K?rner 《Climatic change》2011,106(2):203-223

Evidence is presented of how Pinus halepensis Miller from dry habitats at <300 m elevation of four Greek island regions have responded to climatic conditions of the last two centuries. We compared historical periods of low growth due to low precipitation with the recent period of significant precipitation decline. In all cases trees?? growth patterns across the twentieth century were consistent with trends in annual (rather than seasonal) precipitation, with lowest values in both precipitation and radial growth during the last two decades of the twentieth century, the worst conditions for tree growth in more than 200 years. The data are compared with trends across different vegetation belts of the northern Mediterranean basin. Drought related tree mortality in Greece in 2000 and 2007 coincided with the most severe fire outbreaks on record. IPCC WG I (2007) climate scenarios for the Mediterranean suggest a further decline in precipitation, particularly in the eastern regions. Should this occur, growth reduction in trees, tree mortality and damage from forest fires are likely to become more severe.  相似文献   

Raman study of apatite amorphised with swift heavy ions under various irradiation conditions     

Christian Weikusat  Ulrich A. Glasmacher  Beatrice Schuster  Christina Trautmann  Ronald Miletich  Reinhard Neumann 《Physics and Chemistry of Minerals》2011,38(4):293-303

Crystallographically oriented Durango fluorapatites were exposed to swift heavy ions (Xe, Ta, Au, U) at different irradiation conditions. Beam-induced sample modifications were investigated with respect to the effect of fluence (10⁹–10¹³ ions/cm²), electronic energy loss (18–27 keV/nm), and pressure (3.6–11.5 GPa) applied during irradiation. In situ high-pressure irradiation was performed in diamond anvil cells. Confocal Raman spectroscopy was used to trace the occurring changes in the crystal lattice. Fragmentation of the crystal specimen depends on the orientation and sample thickness and was found to scale with energy loss and fluence. The radiation damage for irradiation along the c-axis was found to be larger than for the 〈hk0〉 direction, independent of the confining pressure. Observations on samples irradiated at high pressures indicate a stabilising effect, leading to reduced amorphisation in comparison to the samples irradiated without pressure.  相似文献