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81.
Determining sediment provenance allows a better understanding of fluvial palaeo-dynamics, and identifying involved watersheds, at broad spatio-temporal scales. Conventional approaches for source identification are usually based on the physical, mineralogical, geochemical, magnetic or isotopic properties of sediments. Rapid, non-destructive and, in well-established contexts, highly accurate, mid-infrared spectroscopy is an alternative method for investigating sediment sources. The present research objectives are: (i) to use the mid-infrared spectroscopy method to discriminate the provenance of fine sediments, by applying discriminant analysis on a large set of reference samples from three different watersheds in the Upper Rhine area (associated with the Rhine, Ill and Vosges tributaries); (ii) to clarify whether the provenance spectra signatures are influenced by riverine depositional contexts (bars versus banks) and, to some extent, by grain size and/or high organic matter content; and (iii) to apply the mid-infrared spectroscopy – discriminant analysis method to a study of fluvial palaeo-dynamics and determine the provenance of palaeo-channel infillings. Three main sedimentary sources, divided into eight sub-categories, have been characterized by 196 modern reference samples from 78 collecting sites. Discriminant analysis displayed a strong separating power by classifying correctly the origin of samples without any inter-group overlap, independently from the geomorphological context (bar or bank) and associated slight changes in organic matter contents or grain size. Mid-infrared spectroscopy – discriminant analysis investigations of the palaeo-channel infill, complemented by radiocarbon dates and mineralogical data, allowed reconstructing general trends for the local morpho-sedimentary dynamics over the last ca 12 millennia. 相似文献
82.
Beerkan multi-runs for characterizing water infiltration and spatial variability of soil hydraulic properties across scales 总被引:1,自引:1,他引:0
Laurent Lassabatere Simone Di Prima Rafael Angulo-Jaramillo Saskia Keesstra David Salesa 《水文科学杂志》2019,64(2):165-178
A method is presented for characterizing the spatial variability of water infiltration and soil hydraulic properties at the transect and field scales. The method involves monitoring a set of 10 Beerkan runs distributed over a 1-m length of soil, and running BEST (Beerkan estimation of soil transfer parameters) methods to derive hydraulic parameters. The Beerkan multi-runs (BMR) method provides a significant amount of data at the transect scale, allowing the determination of correlations between water infiltration variables and hydraulic parameters, and the detection of specific runs affected by preferential flow or water repellence. The realization of several BMRs at several transects on the same site allows comparison of the variation between locations (spatial variability at the field scale) and at the transect scale (spatial variability at the metre scale), using analysis of variance. From the results, we determined the spatial variability of water infiltration and hydraulic parameters as well as its characteristic scale (transect versus field). 相似文献
83.
When fine particles are involved, cohesive properties of sediment can result in flocculation and significantly complicate sediment process studies. We combine data from field observations and state-of-the-art modeling to investigate and predict flocculation processes within a hypertidal estuary. The study site is the Welsh Channel located at the entrance of the Dee Estuary in Liverpool Bay. Field data consist of measurements from a fixed site deployment during 12–22 February 2008. Grain size, suspended sediment volume concentration, and current velocity were obtained hourly from moored instruments at 1.5 m above bed. Near-bottom water samples taken every hour from a research vessel are used to convert volume concentrations to mass concentrations for the moored measurements. We use the hydrodynamic model Proudman Oceanographic Laboratory Coastal Ocean Modelling System (POLCOMS) coupled with the turbulence model General Ocean Turbulence Model (GOTM) and a sediment module to obtain three-dimensional distributions of suspended particulate matter (SPM). Flocculation is identified by changes in grain size. Small flocs were found during flood and ebb periods—and correlate with strong currents—due to breakup, while coarse flocs were present during slack waters because of aggregation. A fractal number of 2.4 is found for the study site. Turbulent stresses and particle settling velocities are estimated and are found to be related via an exponential function. The result is a simple semiempirical formulation for the fall velocity of the particles solely depending on turbulent stresses. The formula is implemented in the full three-dimensional model to represent changes in particle size due to flocculation processes. Predictions from the model are in agreement with observations for both settling velocity and SPM. The SPM fortnight variability was reproduced by the model and the concentration peaks are almost in phase with those from field data. 相似文献
84.
Innovative Germicidal UV and Photocatalytic System Dedicated to Aircraft Cabin Eliminates Volatile Organic Compounds and Pathogenic Micro‐Organisms
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85.
86.
We report on a field test of a transportable version of a superconducting gravimeter (SG) intended for groundwater storage monitoring. The test was conducted over a 6-month period at a site adjacent to a well in the recharge zone of the karstic Edwards Aquifer, a major groundwater resource in central Texas. The purpose of the study was to assess requirements for unattended operation of the SG in a field setting and to obtain a gravimetric estimate of aquifer specific yield. The experiment confirmed successful operation of the SG, but water level changes were small (<0.3 m) leading to uncertainty in the estimate of specific yield. Barometric pressure changes were the dominant cause of both water level variations and non-tidal gravity changes. The specific yield estimate (0.26) is larger than most published values and dependent mainly on low frequency variations in residual gravity and water level time series. 相似文献
87.
AbstractThis paper aims at revisiting the use of non-dimensional representations for catchment change and model robustness analysis. As well as being helpful for catchment classification according to hydroclimatic conditions, the Turc-Budyko representation enables visualization of temporal changes in these conditions and/or modification of the hydrological behaviour of the catchment. This brings a new perspective to hydrological analysis, different from the classical time series plots, which helps when interpreting catchment functioning with respect to hydroclimatic constraints. These tools do not require statistical analyses of observed series and are therefore very simple to implement. Four case studies are considered here to illustrate the use of the Q/P = f(P/Ep) graph. When combined with the inter-annual Turc-Mezentsev formula, this visual framework enables anticipation of potential difficulties for models based on the same hypotheses, solely using the analysis of observed data. 相似文献
88.
Brunet Morgane Moretti Laurent Le Friant Anne Mangeney Anne Fernández Nieto Enrique Domingo Bouchut Francois 《Natural Hazards》2017,85(2):1189-1208
Natural Hazards - In November 2015, China government announced that the national carbon emissions trading market is expected to start in 2017. Carbon emission trading system is a raising concern... 相似文献
89.
Laurent Millet Charline Giguet-Covex Valérie Verneaux Jean-Claude Druart Thierry Adatte Fabien Arnaud 《Journal of Paleolimnology》2010,44(4):963-978
This paper presents the recent history of a large prealpine lake (Lake Bourget) using chironomids, diatoms and organic matter
analysis, and deals with the ability of paleolimnological approach to define an ecological reference state for the lake in
the sense of the European Framework Directive. The study at low resolution of subfossil chironomids in a 4-m-long core shows
the remarkable stability over the last 2.5 kyrs of the profundal community dominated by a Micropsectra-association until the beginning of the twentieth century, when oxyphilous taxa disappeared. Focusing on this key recent period,
a high resolution and multiproxy study of two short cores reveals a progressive evolution of the lake’s ecological state.
Until AD 1880, Lake Bourget showed low organic matter content in the deep sediments (TOC less than 1%) and a well-oxygenated
hypolimnion that allowed the development of a profundal oxyphilous chironomid fauna (Micropsectra-association). Diatom communities were characteristic of oligotrophic conditions. Around AD 1880, a slight increase in the
TOC was the first sign of changes in lake conditions. This was followed by a first limited decline in oligotrophic diatom
taxa and the disappearance of two oxyphilous chironomid taxa at the beginning of the twentieth century. The 1940s were a major
turning point in recent lake history. Diatom assemblages and accumulation of well preserved planktonic organic matter in the
sediment provide evidence of strong eutrophication. The absence of profundal chironomid communities reveals permanent hypolimnetic
anoxia. From AD 1995 to 2006, the diatom assemblages suggest a reduction in nutrients, and a return to mesotrophic conditions,
a result of improved wastewater management. However, no change in hypolimnion benthic conditions has been shown by either
the organic matter or the subfossil chironomid profundal community. Our results emphasize the relevance of the paleolimnological
approach for the assessment of reference conditions for modern lakes. Before AD 1900, the profundal Micropsectra-association and the Cyclotella dominated diatom community can be considered as the Lake Bourget reference community, which reflects the reference ecological
state of the lake. 相似文献
90.
Patrícia Kováčová Laurent Emmanuel Natália Hudáčková Maurice Renard 《International Journal of Earth Sciences》2009,98(5):1109-1127
Stable isotope data of the foraminiferal carbonate shells and bulk sediment samples from the Central Paratethys were investigated
to contribute to better knowledge of the paleoenvironmental changes in Badenian (Middle Miocene). Five benthic (Uvigerina semiornata, U. aculeata, Ammonia beccarii, Elphidium sp. and Heterolepa dutemplei) and three planktonic taxa (Globigerina bulloides, G. diplostoma and Globigerinoides trilobus), characterising the bottom, intermediate and superficial layers of the water column, were selected from the Vienna Basin
(W Slovakia). The foraminiferal fauna and its isotope signal point out to temperature-stratified, nutrient-rich and consequently
less-oxygenated marine water during the Middle/Late Badenian. Negative carbon isotope ratios indicate increased input of 12C-enriched organic matter to the bottom of the Vienna Basin. Positive benthic δ18O implies that the global cooling tendency recorded in the Middle Miocene has also affected the intramountain Vienna Basin.
In this time, the Central Paratethys has been in the process of isolation. Our stable isotope trend suggests that the communication
with Mediterranean Sea has been still more or less active on the south of Vienna Basin (Slovak part) in the Late Badenian,
whereas the seawater exchange towards north was apparently reduced already during the Middle Badenian. 相似文献