Quantification of the relation between surface morphodynamics and subsurface sedimentological product in sandy braided rivers     

Natalie O. Parker  Gregory H. Sambrook Smith  Philip J. Ashworth  James L. Best  Stuart N. Lane  Ian A. Lunt  Christopher J. Simpson  Roberte. Thomas 《Sedimentology》2013,60(3):820-839

This study uses digital elevation models and ground‐penetrating radar to quantify the relation between the surface morphodynamics and subsurface sedimentology in the sandy braided South Saskatchewan River, Canada. A unique aspect of the methodology is that both digital elevation model and ground‐penetrating radar data were collected from the same locations in 2004, 2005, 2006 and 2007, thus enabling the surface morphodynamics to be tied explicitly to the associated evolving depositional product. The occurrence of a large flood in 2005 also allowed the influence of discharge to be assessed with respect to the process–product relationship. The data demonstrate that the morphology of the study reach evolved even during modest discharges, but more extensive erosion was caused by the large flood. In addition, the study reach was dominated by compound bars before the flood, but switched to being dominated by unit bars during and after the flood. The extent to which the subsurface deposits (the ‘product’) were modified by the surface morphodynamics (the ‘process’) was quantified using the changes in radar‐facies recorded in sequential ground‐penetrating radar surveys. These surveys reveal that during the large flood there was an increase in the proportion of facies associated with bar margin accretion and larger dunes. In subsequent years, these facies became truncated and replaced with facies associated with smaller dune sets. This analysis shows that unit bars generally become truncated more laterally than vertically and, thus, they lose the high‐angle bar margin deposits and smaller scale bar‐top deposits. In general, the only fragments that remain of the unit bars are dune sets, thus making identification of the original unit barform problematic. This novel data set has implications for what may ultimately become preserved in the rock record.  相似文献   

Civil society and urban food insecurity: analyzing the roles of local food organizations in Johannesburg     

Natalie Koch 《Urban geography》2013,34(1):109-130

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Microbial contamination monitoring and control during human space missions   总被引：2，自引：0，他引：2  

Rob Van Houdt  Kristel Mijnendonckx  Natalie Leys 《Planetary and Space Science》2012,60(1):115-120

The ubiquity and resilience of microorganisms makes them unavoidable in most environments including space habitats. The impaired immune system of astronauts in flight raises the level of concern about disease risk during human space missions and additionally these biological contaminants may affect life support systems and hardware. In this review, the microbial contamination observed in manned space stations and in particular the International Space Station ISS will be discussed, demonstrating that it is a microbiologically safe working and living habitat. Microbial contamination levels were in general below the implemented quality standards, although, occasional contamination hazard reports indicate that the current prevention and monitoring strategies are the strict minimum.  相似文献   

Seasonal snow cover decreases young water fractions in high Alpine catchments     

Natalie Ceperley  Giulia Zuecco  Harsh Beria  Luca Carturan  Anthony Michelon  Daniele Penna  Joshua Larsen  Bettina Schaefli 《水文研究》2020,34(25):4794-4813

Estimation of young water fractions (F_yw), defined as the fraction of water in a stream younger than approximately 2–3 months, provides key information for water resource management in catchments where runoff is dominated by snowmelt. Knowing the average dependence of summer flow on winter precipitation is an essential context for comparing regional drought severity and provides the hydrological template for downstream water users and ecosystems. However, F_yw estimation based on seasonal signals of stable isotopes of oxygen and hydrogen has not yet explicitly addressed how to parsimoniously include the seasonal shift of water input from snow. Using experimental data from three high-elevation, Alpine catchments (one dominated by glacier and two by snow), we propose a framework to explicitly include the delays induced by snow storage into estimates of F_yw. Scrutinizing the key methodological choices when estimating F_yw from isotope data, we find that the methods used to construct precipitation input signals from sparse isotope samples can significantly impact F_yw. Given this sensitivity, our revised procedure estimates a distribution of F_yw values that incorporates a wide range of possible methodological choices and their uncertainties; it furthermore compares the commonly used amplitude ratio approach to a direct convolution approach, which circumvents the assumption that the isotopic signals have a sine curve shape, an assumption that is generally violated in snow-dominated environments. Our new estimates confirm that high-elevation Alpine catchments have low F_yw values, spanning from 8 to 11%. Such low values have previously been interpreted as the impact of seasonal snow storage alone, but our comparison of different F_yw estimation methods suggests that these low F_yw values result from a combination of both snow cover effects and longer storage in the subsurface. In contrast, in the highest elevation, glacier dominated catchment, F_yw is 3–4 times greater compared to the other two catchments, due to the lower storage and faster drainage processes. A future challenge, capturing spatio-temporal snowmelt isotope signals during winter baseflow and the snowmelt period, remains to improve constraints on the F_yw estimation technique.  相似文献   

For still possible cities: a politics of failure for the politically depressed     

Natalie Osborne 《The Australian geographer》2019,50(2):145-154

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Intercomparison of soil pore water extraction methods for stable isotope analysis and interpretation of hillslope runoff sources     

Natalie Orlowski  Dyan L. Pratt  Jeffrey J. McDonnell 《水文研究》2019,33(22):2939-2954

Intercomparison of soil pore water extraction methods for stable isotope analysis has been a focus of recent studies in relation to plant source waters, which found a wide isotopic variance depending on the extraction method. Few studies have yet explored extraction effects for mobile pore waters that relate to hillslope runoff. This is because it is extremely difficult in natural systems to control the boundary conditions in order to assess and compare impacts of pore water extraction on resulting hillslope flow. With our new semicontrolled experiments on outdoor mini‐hillslopes, we studied mixing and runoff processes by means of stable isotopes of water and quantified relations between pore water extraction methods. We tested the null hypothesis that nondestructive and destructive pore water sampling methods sample the same soil water pool. Three hillslopes were mounted on load cells, filled with loamy sand textured soils from the Landscape Evolution Observatoryat Biosphere 2, equipped with soil moisture and temperature sensors, a bottom outflow, and a surface runoff gauge for isotope sampling. We followed the precipitation isotopic composition over and through the soil profile. One hillslope was instrumented with suction cups, on the second we installed sampling ports for in‐situ soil water vapour measurements, and the third hillslope was sampled destructively for applying the centrifugation and vapour equilibrium methods. All hillslopes were sampled at four depths (0–10, 10–20, 20–30, and 30–40 cm) at three different downslope positions. ²H and ¹⁸O analyses were performed via laser spectroscopy. We found no isotopic differences between rainfall, surface runoff, and bottom outflow. The in situ vapour ports' soil isotope data showed the widest spread over all hillslope positions and depths. Centrifugation's and suction cups' isotope results plotted closest to the local meteoric water line and within the range of hillslope runoff and bottom outflow data. Hillslope position did not influence the soil isotope results. These results suggest caution be used in the field when selecting an extraction technique for matching soil waters to runoff waters. Soil suction lysimeters and centrifugation appeared to be the most appropriate tools in this regard.  相似文献   

Dynamic domain kinematic modelling for predicting interflow over leaky impeding layers     

Menberu Meles Bitew  C. Rhett Jackson  David C. Goodrich  Seth E. Younger  Natalie A. Griffiths  Kellie B. Vaché  Benjamin Rau 《水文研究》2020,34(13):2895-2910

Traditional Boussinesq or kinematic simulations of interflow (i.e., lateral subsurface flow) assume no leakage through the impeding layer and require a no-flow boundary condition at the ridge top. However, recent analyses of many interflow-producing landscapes indicate that leaky impeding layers are common, that most interflow percolates well before reaching the toe slope, and therefore, the downslope contributing length is shorter than the hillslope length. In watersheds characterised by perched interflow over a low conductivity layer through permeable topsoil, interflow with percolation may be modelled with a kinematic wave model using a mobile upslope boundary condition defining the hillslope portion contributing interflow to valleys. Here, we developed and applied a dynamic interflow model to simulate interflow using a downslope travel distance concept such that only the active contributing length is modelled at any time. The model defines a variable active area based on the depth of the perched layer, the topographic slope and the ratio of the hydraulic conductivity of topsoil to that of the impeding layer. It incorporates a two-layer soil moisture accounting water balance analysis, a pedo-transfer function, and percolation and evaporation routines to predict interflow rates in continuous and event-based scenarios. We tested the modelling concept on two sets of data (2-year dataset of rainfall observations for the continuous simulation and a multi-day irrigation experiment for the event simulation) from a 121-m-long open interflow collection trench on an experimental hillslope at the Savannah River Site, South Carolina. The continuous model simulation partially represented the observed interflow hydrograph and perched water depth in the experimental hillslope with correlation coefficients of 0.85 and 0.35, respectively. Model performance improved significantly at event-scale analysis. The modelling approach realistically represents interflow dynamics in hillslopes with leaky impeding layers and can be integrated into catchment-scale hydrology models for more detailed hillslope process modelling.  相似文献   

How do Local People Value Rural Waterways? A Study in the Upper Catchments of South East Queensland’s Rivers     

Katherine Witt  Helen Ross  Sylvie Shaw  Natalie Jones  David Rissik  Breanna Pinner 《社会与自然资源》2019,32(6):638-656

In Integrated Catchment (or Watershed) Management, the impacts of upstream conditions and actions on downstream environments and people is a key issue. Knowing upstream people’s values towards waterways is, therefore, important for community engagement and the development of publicly acceptable management approaches. This qualitative study applies Kellert’s framework of relational values to explore the types and diversity of people’s values towards the upper catchments of South East Queensland, Australia, and tests the “universality” of Kellert’s framework. We found the full range of values identified by Kellert with some variations and elaborations in content. People living, working, and enjoying recreation in the upper catchments have affection for their local waterways and a moral inclination to protect them. This extends our understanding of how people value these waterways, which is more often depicted in terms of utilitarian and economic value. The findings provide managers with new opportunities for engaging with local communities and waterway users.  相似文献   

Noble gas composition,cosmic-ray exposure age, 39Ar-40Ar,and I-Xe analyses of ungrouped achondrite NWA 7325          下载免费PDF全文

Jens Hopp  Natalie Schröter  Olga Pravdivtseva  Hans-Peter Meyer  Mario Trieloff  Ulrich Ott 《Meteoritics & planetary science》2018,53(6):1150-1163

Northwest Africa (NWA) 7325 is an anomalous achondrite that experienced episodes of large-degree melt extraction and interaction with melt under reducing conditions. Its composition led to speculations about a Mercurian origin and provoked a series of studies of this meteorite. We present the noble gas composition, and results of ⁴⁰Ar/³⁹Ar and ¹²⁹I-¹²⁹Xe studies of whole rock splits of NWA 7325. The light noble gases are dominated by cosmogenic isotopes. ²¹Ne and ³⁸Ar cosmic-ray exposure ages are 25.6 and 18.9 Ma, respectively, when calculated with a nominal whole rock composition. This ³⁸Ar age is in reasonable agreement with a cosmic-ray exposure age of 17.5 Ma derived in our ⁴⁰Ar/³⁹Ar dating study. Due to the low K-content of 19 ± 1 ppm and high Ca-content of approximately 12.40 ± 0.15 wt%, no reliable ⁴⁰Ar/³⁹Ar age could be determined. The integrated age strongly depends on the choice of an initial ⁴⁰Ar/³⁶Ar ratio. An air-like component is dominant in lower temperature extractions and assuming air ⁴⁰Ar/³⁶Ar for the trapped component results in a calculated integrated age of 3200 ± 260 (1σ) Ma. This may represent the upper age limit for a major reheating event affecting the K-Ar system. Results of ¹²⁹I-¹²⁹Xe dating give no useful chronological information, i.e., no isochron is observed. Considering the highest ¹²⁹Xe*/¹²⁸Xe_I ratio as equivalent to a lower age limit, we calculate an I-Xe age of about 4536 Ma. In addition, elevated ¹²⁹Xe/¹³²Xe ratios of up to 1.65 ± 0.18 in higher temperature extractions indicate an early formation of NWA 7325, with subsequent disturbance of the I-Xe system.  相似文献   

White mica trace element and boron isotope evidence for distinctive infiltration events during exhumation of deeply subducted continental crust     

Natalie E. Sievers  Carrie A. Menold  Marty Grove  Matthew A. Coble 《International Geology Review》2017,59(5-6):621-638

ABSTRACT

Previous study of subducted continental crust within the Luliang Shan terrane in Northwest China has documented metasomatic formation of thick, hydrated phengite + garnet-rich selvages at the interface between mafic eclogite blocks and quartzofeldspathic host gneiss. Whole rock concentrations of Cs and Ba within the selvage are enriched by two orders of magnitude relative to the eclogite blocks and host gneiss. We performed in situ ion microprobe analyses of Li, Be, B, Rb, Sr, Cs and Ba and δ¹¹B of phengite within the Luliang Shane terrane to better constrain the source(s) of the infiltrating fluid. The phengite within the selvage are enriched in Li, Cs and Ba and yield δ¹¹B values between ?30‰ and ?9‰, values that are lower than mantle values. High Ba/Rb, Cs/Rb coupled with low B/Be, B/Li and highly negative δ¹¹B values indicate that the high-pressure fluid that formed the selvage was derived from highly devolatilized rocks within the subduction channel. In contrast, muscovite, which crystallized in the adjacent host gneiss during a subsequent lower pressure phase of fluid infiltration at approximately 0.9 GPa depths, has much lower Li, Cs and Ba relative to the high-pressure phengite. These retrograde muscovite have very high concentrations of B (up to 5500 ppm) and Be (up to 50 ppm) and high (?2 to +8‰) δ¹¹B values that are consistent with crystallization from a fluid derived from shallower and less devolatilized regions of the subduction zone. Additional host gneiss samples, regionally distributed and kilometres away from the studied area lack the B-rich signature and indicate that the late stage fluids were likely localized to the region near the studied traverse.  相似文献