Exploring large wood retention and deposition in contrasting river morphologies linking numerical modelling and field observations          下载免费PDF全文

Virginia Ruiz‐Villanueva  Bartłomiej Wyżga  Hanna Hajdukiewicz  Markus Stoffel 《地球表面变化过程与地形》2016,41(4):446-459

Large wood tends to be deposited in specific geomorphic units within rivers. Nevertheless, predicting the spatial distribution of wood deposits once wood enters a river is still difficult because of the inherent complexity of its dynamics. In addition, the lack of long‐term observations or monitored sites has usually resulted in a rather incomplete understanding of the main factors controlling wood deposition under natural conditions. In this study, the deposition of large wood was investigated in the Czarny Dunajec River, Polish Carpathians, by linking numerical modelling and field observations so as to identify the main factors influencing wood retention in rivers. Results show that wood retention capacity is higher in unmanaged multi‐thread channels than in channelized, single‐thread reaches. We also identify preferential sites for wood deposition based on the probability of deposition under different flood scenarios, and observe different deposition patterns depending on the geomorphic configuration of the study reach. In addition, results indicate that wood is not always deposited in the geomorphic units with the highest roughness, except for low‐magnitude floods. We conclude that wood deposition is controlled by flood magnitude and the elevation of flooded surfaces in relation to the low‐flow water surface. In that sense, the elevation at which wood is deposited in rivers will differ between floods of different magnitude. Therefore, together with the morphology, flood magnitude represents the most significant control on wood deposition in mountain rivers wider than the height of riparian trees. Copyright © 2015 John Wiley & Sons, Ltd.  相似文献   

Root properties of vegetation communities and their impact on the erosion resistance of river dikes   总被引：1，自引：0，他引：1       下载免费PDF全文

Wouter Vannoppen  Jean Poesen  Patrik Peeters  Sarah De Baets  Bart Vandevoorde 《地球表面变化过程与地形》2016,41(14):2038-2046

Predicted climate change and the associated sea level rise poses an increased threat of flooding due to wave overtopping events at sea and river dikes. To safeguard the land from flooding it is important to keep the soil erosion resistance at the dikes high. As plant roots can be very effective in reducing soil erosion rates by concentrated flow, the main goal of this study is to explore the variability in root system characteristics of five dike vegetation communities along the Scheldt River (Belgium) and to assess their effectiveness in controlling soil erosion rates during concentrated flow. This study is the first one to investigate systematically the erosion‐reducing potential of the root properties of representative dike vegetation communities in a temperate humid climate. Results show that the presence of Urtica dioica resulted in large differences in root length density (RLD) among dike vegetation communities. Observed RLD values in the topsoil ranged from 129 to 235 km m^‐3 for dike vegetation communities without U. dioica, while smaller values ranging from 22 to 58 km m^?3 were found for vegetation communities with U. dioica. The erosion‐reducing effect of the dike vegetation communities was estimated based on a global Hill curve model, linking the RLD to the soil detachment ratio (SDR; i.e. the ratio of the soil detachment rate for root‐permeated topsoils to the soil detachment rate for root‐free topsoils). Concentrated flow erosion rates are likely to be reduced to 13–16% of the erosion rates for root‐free topsoils if U. dioica is absent compared to 22–30% for vegetation communities with U. dioica. Hence, to maintain a high resistance of the soil against concentrated flow erosion it is important to avoid the overgrowth of grassland by U. dioica through an effective vegetation management. Copyright © 2016 John Wiley & Sons, Ltd.  相似文献   

Modeling uncertainty of moving objects on road networks via space–time prisms     

Bart Kuijpers 《International journal of geographical information science》2013,27(9):1095-1117

Moving objects produce trajectories, which are typically observed in a finite sample of time‐stamped locations. Between sample points, we are uncertain about the moving objects's location. When we assume extra information about an object, for instance, a (possibly location‐dependent) speed limit, we can use space–time prisms to model the uncertainty of an object's location.

Until now, space–time prisms have been studied for unconstrained movement in the 2D plane. In this paper, we study space–time prisms for objects that are constrained to travel on a road network. Movement on a road network can be viewed as essentially one‐dimensional. We describe the geometry of a space–time prism on a road network and give an algorithm to compute and visualize space–time prisms. For experiments and illustration, we have implemented this algorithm in MATHEMATICA.

Furthermore, we study the alibi query, which asks whether two moving objects could have possibly met or not. This comes down to deciding if the chains of space–time prisms produced by these moving objects intersect. We give an efficient algorithm to answer the alibi query for moving objects on a road network. This algorithm also determines where and when two moving objects may have met.  相似文献   

Pesticides Removal by Filtration over Cactus Pear Leaves: A Cheap and Natural Method for Small‐Scale Water Purification in Semi‐Arid Regions     

Abraha Gebrekidan  Hannah Nicolai  Liese Vincken  Mekone Teferi  Tsehaye Asmelash  Tadesse Dejenie  Samuel Zerabruk  Kindeya Gebrehiwet  Hans Bauer  Josef Deckers  Patricia Luis  Luc De Meester  Bart van der Bruggen 《洁净——土壤、空气、水》2013,41(3):235-243

This study aims to examine the efficiency of Opuntia ficus‐indica for removing organochlorine pesticides from surface waters. Adsorption properties such as size, dose, and time of O. ficus‐indica for aldrin, dieldrin, and dichlorodiphenyltrichloroethane (DDT) were studied through stirring and column methods. Because of their high affinity and swelling characteristics, dried O. ficus‐indica was studied in stirring while fresh unpeeled O. ficus‐indica was applied in both stirring and column experiments and proved to be well‐suited to column application. Before removing pesticides, the column was flashed with distilled water eliminate the turbidity and smell from fresh unpeeled cactus. The removal of pesticides increased with an increasing adsorbent dose and decreased with adsorbent particle sizes. The optimum adsorbent dose is 10 g for dried and 15 g for fresh unpeeled O. ficus‐indica. The experimental results show that O. ficus‐indica possesses strong adsorption ability for aldrin, dieldrin, and DDT, and the adsorption isotherm data obeyed the Freundlich model. The results of our small‐scale experiments suggest a strong potential to develop local small‐scale water treatment units that can be used at the level of individual households or local communities, using a widely available adsorbent.  相似文献   

Characterisation of organic matter and microbial communities in contrasting arsenic-rich Holocene and arsenic-poor Pleistocene aquifers,Red River Delta,Vietnam     

Wafa M. Al Lawati  Athanasios Rizoulis  Elisabeth Eiche  Christopher Boothman  David A. Polya  Jonathan R. Lloyd  Michael Berg  Patricio Vasquez-Aguilar  Bart E. van Dongen 《Applied Geochemistry》2012

High concentrations of geogenic As in the groundwaters of south and SE Asia, which are used as drinking waters, are causing severe health impacts to the exposed human populations. It is widely accepted that As mobilisation from sediments into these shallow reducing groundwaters requires active metal-reducing microbes and electron donors such as organic matter (OM). Although OM in such Holocene aquifers has been characterised, there is a dearth of data on Pleistocene aquifers from the same areas. Reported here are preliminary studies of OM and microbial communities present in two aquifers, one of Pleistocene and one of Holocene age, with contrasting concentrations of As (viz. Pleistocene: low As <10 μg/L; Holocene: high As up to 600 μg/L) from Van Phuc village in the Red River Delta, Vietnam. Results revealed OM inputs from multiple sources, including potential contributions from naturally occurring petroleum seeping into the shallow aquifer sediments from deeper thermally mature source rocks. Although concentrations vary, no noticeable systematic differences in biomarker distribution patterns within the OM were observed between the two sites. Microbial analyses did not show a presence of microbial communities previously associated with As mobilisation. All clone libraries were dominated by α-, β-, and γ-Proteobacteria not known to be able to reduce Fe(III) or sorbed As(V). Furthermore, representatives of the Fe(III)-reducing genus Geobacter could only be detected at very low abundance by PCR, using highly selective 16S rRNA gene primers, supporting the hypothesis that metal reduction is not a dominant in situ process in these sediments. No correlation between As concentration in groundwater and OM composition nor microbial community in the host sediments was found. This suggests that either (i) As is not being significantly mobilised in situ in these sediments, instead As appears to be mobilised elsewhere and transported by groundwater flow to the sites or (ii) sorption/desorption processes, as implicated by geochemical data from the cores, play a critical role in controlling As concentrations at these sites.  相似文献   

3D modeling of light interception in heterogeneous forest canopies using ground-based LiDAR data     

Dimitry Van der Zande  Jan Stuckens  Willem W. Verstraeten  Simone Mereu  Bart Muys  Pol Coppin 《International Journal of Applied Earth Observation and Geoinformation》2011

  相似文献   

Preliminary results of a finite-element,multi-scale model of the Mahakam Delta (Indonesia)   总被引：1，自引：1，他引：0  

Benjamin de Brye  Sébastien Schellen  Maximiliano Sassi  Bart Vermeulen  Tuomas Kärnä  Eric Deleersnijder  Ton Hoitink 《Ocean Dynamics》2011,61(8):1107-1120

  相似文献   

Evidence of a Mixed-Layer Dynamics Contribution to the Entrainment Process     

Cyrille Flamant  Jacques Pelon  Bart Brashers  Robert A. Brown 《Boundary-Layer Meteorology》1999,93(1):47-73

The internal thermal boundary layer developing over the Mediterranean during a cold-air outbreak associated with a Tramontane event has been studied by means of airborne lidar, in situ sensors, and a modelling approach that consisted of nesting the University of Washington (UW) planetary boundary-layer (PBL) model in an advective zero-order jump model. This approach bypasses some of the deficiencies associated with each model: the absence of the dynamics in the mixed layer for the zero-order jump model and the lack of an inversion at the PBL top for the UW PBL model. Particular attention is given to the parameterization of the entrainment flux at the PBL top. Values of the entrainment closure parameter derived with the model when matching PBL structure observations are much lower than those derived with standard zero-order jump models. They also are in good agreement with values measured in different meteorological situations by other studies. This improvement is a result of the introduction of turbulent kinetic energy production in the mixed layer.  相似文献   

Identifying slope processes over time and their imprint in soils of medium‐high mountains of Central Europe (the Karkonosze Mountains,Poland)          下载免费PDF全文

Jaroslaw Waroszewski  Markus Egli  Dagmar Brandová  Marcus Christl  Cezary Kabala  Malgorzata Malkiewicz  Jakub Kierczak  Bartłomiej Glina  Paweł Jezierski 《地球表面变化过程与地形》2018,43(6):1195-1212

Soils in mountainous areas are often polygenetic, developed in slope covers that relate to glacial and periglacial activities of the Pleistocene and Holocene and reflect climatic variations. Landscape development during the Holocene may have been influenced by erosion/solifluction that often started after the Holocene climatic optimum. To trace back soil evolution and its timing, we applied a multi‐methodological approach. This approach helped us to outline scenario of soil transformation. According to our results, some aeolian input must have occurred in the late Pleistocene. During that time and the early Holocene, the soils most likely had features of Cryosols or Leptosols. Physico‐chemical and mineralogical analyses have indicated that the material was denudated (between late Boreal to the Atlantic) from the ridge and upper‐slope positions forming a colluvium at mid‐slope positions. Later, during the Sub‐Boreal, mass wasting of the remains of silt material deposited at the end of the Pleistocene age on the ridge top seems to have occurred. In addition, the cool and moist conditions caused the deposition of a colluvium at the lower‐slope positions. The next phase was characterized by the transformation of Leptosols/Cambisols into Podzols at upper‐slope or shoulder positions and to Albic Cambisols at mid‐slope positions. During the Sub‐Boreal period, Stagnosols started to form at the lower part of the slope catena. Overall, the highest erosion rates were calculated at the upper‐slope position and the lowest rates at mid‐slope sites. Berylium‐10 (¹⁰Be) data showed that the Bs, BC/C were covered during the Holocene by a colluvium with a different geological composition which complicated the calculation of erosion or accumulation rates. The interpretation of erosion and accumulation rates in such multi‐layered materials may, therefore, be hampered. However, the multi‐methodological reconstruction we applied shed light on the soil and landscape evolution of the eastern Karkonosze Mountains. Copyright © 2017 John Wiley & Sons, Ltd.  相似文献   

Examining the Use of USEPA's Generic Attenuation Factor in Determining Groundwater Screening Levels for Vapor Intrusion          下载免费PDF全文

Yijun Yao  Iason Verginelli  Eric M. Suuberg  Bart Eklund 《Ground Water Monitoring & Remediation》2018,38(2):79-89

A value of 0.001 is recommended by the United States Environmental Protection Agency (USEPA) for its groundwater‐to‐indoor air Generic Attenuation Factor (GAFG), used in assessing potential vapor intrusion (VI) impacts to indoor air, given measured groundwater concentrations of volatile chemicals of concern (e.g., chlorinated solvents). The GAFG can, in turn, be used for developing groundwater screening levels for VI given target indoor air quality screening levels. In this study, we examine the validity and applicability of the GAFG both for predicting indoor air impacts and for determining groundwater screening levels. This is done using both analysis of published data and screening model calculations. Among the 774 total paired groundwater‐indoor air measurements in the USEPA's VI database (which were used by that agency to generate the GAFG) we found that there are 427 pairs for which a single groundwater measurement or interpolated value was applied to multiple buildings. In one case, up to 73 buildings were associated with a single interpolated groundwater value and in another case up to 15 buildings were associated with a single groundwater measurement (i.e., that the indoor air contaminant concentrations in all of the associated buildings were influenced by the concentration determined at a single point). In more than 70% of the cases (390 of 536 paired measurements in which horizontal building‐monitoring well distance was recorded) the monitoring wells were located more than 30 m (and one up to over 200 m) from the associated buildings. In a few cases, the measurements in the database even improbably implied that soil gas contaminant concentrations increased, rather than decreased, in an upward direction from a contaminant source to a foundation slab. Such observations indicate problematic source characterization within the data set used to generate the GAFG, and some indicate the possibility of a significant influence of a preferential contaminant pathway. While the inherent value of the USEPA database itself is not being questioned here, the above facts raise the very real possibility that the recommended groundwater attenuation factors are being influenced by variables or conditions that have not thus far been fully accounted for. In addition, the predicted groundwater attenuation factors often fall far beyond the upper limits of predictions from mathematical models of VI, ranging from screening models to detailed computational fluid dynamic models. All these models are based on the same fundamental conceptual site model, involving a vadose zone vapor transport pathway starting at an underlying uniform groundwater source and leading to the foundation of a building of concern. According to the analysis presented here, we believe that for scenarios for which such a “traditional” VI pathway is appropriate, 10^?4 is a more appropriately conservative generic groundwater to indoor air attenuation factor than is the EPA‐recommended 10^?3. This is based both on the statistical analysis of USEPA's VI database, as well as the traditional mathematical models of VI. This result has been validated by comparison with results from some well‐documented field studies.  相似文献