Patterns of water, heat, and solute flux through streambeds around small dams   总被引：1，自引：0，他引：1  

Fanelli RM  Lautz LK 《Ground water》2008,46(5):671-687

Hyporheic exchange, enhanced by complex stream channel morphology, can influence biogeochemical processing in the streambed. These processes chemically alter water passing temporarily through the streambed, which eventually returns to the stream channel and can potentially affect surface water quality. To assess the degree of biogeochemical cycling induced by complex streambed morphology, we instrumented two 20-m reaches of Red Canyon Creek, Wyoming, each containing a small log dam, with in-stream minipiezometers and temperature data loggers. We simultaneously observed pore water geochemistry and streambed temperature dynamics in several bedforms located upstream or downstream of the dams. We modeled seepage flux into the streambed using heat transport modeling.
Upstream of the dams, low-permeability sediments have settled out in low-velocity pools, and enhanced anaerobic biogeochemical cycling occurred in the streambed. Rapid flux into the streambed occurred in glides immediately above the dams, where streambed temperature dynamics and geochemistry were nearly identical to the stream. In riffle sequences downstream of the dams, the streambed was oxygen rich, showed evidence of nitrification, and temperature dynamics indicated high connectivity between the streambed and the stream. Further downstream, streambed pore water geochemistry indicated ground water discharge occurring at the pool-riffle transition. Assessing streambed biogeochemical cycling may be facilitated by coupling streambed temperature measurements with pore water geochemistry and can aid in understanding how hyporheic exchange contributes to overall stream biogeochemistry.  相似文献   

Probabilistic evaluation of seismic performance of 3‐story 3D one‐ and two‐way steel moment‐frame structures     

Hiroyuki Tagawa  Gregory MacRae  Laura Lowes 《地震工程与结构动力学》2008,37(5):681-696

This paper presents the results of a probabilistic evaluation of the seismic performance of 3D steel moment‐frame structures. Two types of framing system are considered: one‐way frames typical of construction in the United States and two‐way frames typical of construction in Japan. For each framing system, four types of beam–column connections are considered: pre‐Northridge welded‐flange bolted‐web, post‐Northridge welded‐flange welded‐web, reduced‐beam‐section, and bolted‐flange‐plate connections. A suite of earthquake ground motions is used to compute the annual probability of exceedence (APE) for a series of drift demand levels and for member plastic‐rotation capacity. Results are compared for the different framing systems and connection details. It is found that the two‐way frames, which have a larger initial stiffness and strength than the one‐way frames for the same beam and column volumes, have a smaller APE for small drift demands for which members exhibit no or minimal yielding, but have a larger APE for large drift demands for which members exhibit large plastic rotations. However, the one‐way frames, which typically comprise a few seismic frames with large‐sized members that have relatively small rotation capacities, may have a larger APE for member failure. The probabilistic approach presented in this study may be used to determine the most appropriate frame configuration to meet an owner's performance objectives. Copyright © 2008 John Wiley & Sons, Ltd.  相似文献   

Unsteady thermoelastic analysis of a circular disk with a hot central core and subjected to adiabatic conditions     

Carlos A. Rossit  Patricio A. A. Laura 《Ocean Engineering》2000,27(4)

The unsteady thermoelastic analysis of a cooling circular disk or cylinder which is originally at uniform temperature is a classical problem of the theory of thermal stresses. More recent studies consider the case of composite structural configurations. The present paper deals with a situation which, apparently, has not been previously considered: unsteady thermal stresses caused by the presence of a hot, central nucleus. The temperature field is obtained in terms of a Fourier–Bessel expansion and then, radial and tangential stresses are evaluated analytically. The problem is of basic interest in mechanical and naval engineering systems.  相似文献   

BET_EF: a probabilistic tool for long- and short-term eruption forecasting   总被引：6，自引：3，他引：3  

Warner Marzocchi  Laura Sandri  Jacopo Selva 《Bulletin of Volcanology》2008,70(5):623-632

  相似文献   

Sensitivity Analysis of Three-Dimensional Steady-State and Transient Spray Irrigation Models     

David Heebner  Laura Toran 《Ground water》2000,38(1):20-28

  相似文献   

CRAFIT: A Computer Program for Calibrating Breakthrough Curves of CRAFLUSH, a One-Dimensional Fracture Flow and Transport Model     

Laura Toran 《Ground water》2000,38(3):430-434

  相似文献   

Resisting Corporate Multiculturalism: Mapping Faculty Initiatives and Institutional‐Student Harassment in the Classroom     

Heidi J. Nast  Laura Pulido 《The Professional geographer》2000,52(4):722-737

This paper argues that calls for multicultural curricula in universities across the US can be met with strategic curricular interventions that radically confront gendered racisms across regional, national, and international racial formations. Faculty who risk making such interventions should plan for student and institutional resistances. Intersecting consumer and corporate interests desire universities to be socially nonconflictual and economical places of leisure and entertainment, not sites of critical intervention. Accordingly, we theorize how and why faculty committed to oppositional multiculturalism might be cast as transgressive. In so doing, we pay particular attention to how identity politics are quadrangulated through embodiment, performance, time, and place. We additionally discuss ways for systematically working against the grain of gendered racisms and for supporting those who are teaching multiculturalism (critically) or seen to embody it. Working against the grain is particularly important as we enter the 21st century, given the increasing diversification of faculty and student bodies in universities across the US and the attendant risks “diverse” persons take, risks generally not experienced or acknowledged by White Americans.  相似文献   

The 5,660?yBP Boquerón explosive eruption, Teide–Pico Viejo complex, Tenerife     

Olaya García  Costanza Bonadonna  Joan Martí  Laura Pioli 《Bulletin of Volcanology》2012,74(9):2037-2050

Quantitative hazard assessments of active volcanoes require an accurate knowledge of the past eruptive activity in terms of eruption dynamics and the stratified products of eruption. Teide–Pico Viejo (TPV) is one of the largest volcanic complexes in Europe, but the associated eruptive history has only been constrained based on very general stratigraphic and geochronological data. In particular, recent studies have shown that explosive activity has been significantly more frequently common than previously thought. Our study contributes to characterization of explosive activity of TPV by describing for the first time the subplinian eruption of El Boquerón (5,660?yBP), a satellite dome located on the northern slope of the Pico Viejo stratovolcano. Stratigraphic data suggest complex shifting from effusive phases with lava flows to highly explosive phase that generated a relatively thick and widespread pumice fallout deposit. This explosive phase is classified as a subplinian eruption of VEI 3 that lasted for about 9–15?h and produced a plume with a height of up to 9?km above sea level (i.e. 7?km above the vent; MER of 6.9–8.2?×?10⁵?kg/s). The tephra deposit (minimum bulk volume of 4–6?×?10⁷?m³) was dispersed to the NE by up to 10?m/s winds. A similar eruption today would significantly impact the economy of Tenerife (e.g. tourism and aviation), with major consequences mainly for the communities around the Icod Valley, and to a minor extent, the Orotava Valley. This vulnerability shows that a better knowledge of the past explosive history of TPV and an accurate estimate of future potentials to generate violent eruptions is required in order to quantify and mitigate the associated volcanic risk.  相似文献   

Enrichment of rare earth elements as environmental tracers of contamination by acid mine drainage in salt marshes: A new perspective     

Delgado J  Pérez-López R  Galván L  Nieto JM  Boski T 《Marine pollution bulletin》2012,64(9):1799-1808

Rare earth elements (REE) were analyzed in surface sediments from the Guadiana Estuary (SW Iberian Pyrite Belt). NASC (North American Shale Composite) normalized REE patterns show clearly convex curvatures in middle-REE (MREE) with respect to light- and heavy-REE, indicating acid-mixing processes between fluvial waters affected by acid mine drainage (AMD) and seawater. However, REE distributions in the mouth (closer to the coastal area) show slightly LREE-enriched and flat patterns, indicating saline-mixing processes typical of the coastal zone. NASC-normalized ratios (La/Gd and La/Yb) do not discriminate between both mixing processes in the estuary. Instead, a new parameter (E(MREE)) has been applied to measure the curvature in the MREE segment. The values of E(MREE)>0 are indicative of acid signatures and their spatial distribution reveal the existence of two decantation zones from flocculation processes related to drought periods and flood events. Studying REE fractionation through the E(MREE) may serve as a good proxy for AMD-pollution in estuarine environments in relation to the traditional methods.  相似文献   

Effects of prokaryotic diversity changes on hydrocarbon degradation rates and metal partitioning during bioremediation of contaminated anoxic marine sediments     

Rocchetti L  Beolchini F  Hallberg KB  Johnson DB  Dell'Anno A 《Marine pollution bulletin》2012,64(8):1688-1698

We investigated changes of prokaryotic diversity during bioremediation experiments carried out on anoxic marine sediments characterized by high hydrocarbon and metal content. Microcosms containing contaminated sediments were amended with lactose and acetate and incubated in anaerobic conditions up to 60 d at 20 or 35 °C. Microcosms displaying higher degradation efficiency of hydrocarbons were characterized by the dominance of Alphaproteobacteria and Methanosarcinales and the lack of gene sequences belonging to known hydrocarbonoclastic bacteria. Multivariate analyses support the hypothesis that Alphaproteobacteria are important for hydrocarbon degradation and highlight a potential synergistic effect of archaea and bacteria in changes of metal partitioning. Overall, these results point out that the identification of changes in the prokaryotic diversity during bioremediation of contaminated marine sediments is not only important for the improvement of bio-treatment performance towards hydrocarbons, but also for a better comprehension of changes occurring in metal partitioning which affect their mobility and toxicity.  相似文献