Bacteria‐sediment associations in an alpine,freshwater environment and their effects on particle size,density and settling velocity          下载免费PDF全文

David C. Barrett  Kyle R. Hodder 《地球表面变化过程与地形》2018,43(10):2232-2242

This study measures the presence of bacteria‐sediment associations (BSAs) in an alpine, glacier‐fed watershed in the Southern Coast Mountains of British Columbia, Canada. The impact of BSAs on the creation of flocculated particles and their settling velocity are quantified using a laser transmissometer. Results from the study indicate that BSAs are present in the watershed and vary over both space and time. The percentage of bacteria associated with sediment particles was found to range from < 1% to 40%. Major sources of planktonic bacteria such as agricultural land and wastewater treatment outflow co‐occur with large decreases in the BSA ratio. Laboratory analysis demonstrates that an increase in the concentration of bacteria was associated with a decrease in the volume concentration of small particles, and a decrease in both estimated density and measured settling velocity for particles in larger size classes; consistent with flocculated particles of increasing complexity arising from combinations of primary particles and/or BSAs. Paleoenvironmental reconstructions using laminated lake sediments in alpine, glacier‐fed systems benefit from a fuller understanding of the geomorphologic processes by which they formed. While bacteria are noted to enhance formation of flocculated particles in laboratory systems, their impact upon geomorphic processes in natural systems have yet to be fully explored. © 2018 The Authors. Earth Surface Processes and Landforms published by John Wiley & Sons Ltd.  相似文献   

Airborne thermal infrared videography of stream temperature anomalies from a small unoccupied aerial system          下载免费PDF全文

Kyle Fitch  Christa Kelleher  Samuel Caldwell  Ian Joyce 《水文研究》2018,32(16):2616-2619

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Estimation of the 3D correlation structure of an alluvial aquifer from surface-based multi-frequency ground-penetrating radar reflection data     

Zhiwei Xu  James Irving  Kyle Lindsay  John Bradford  Peimin Zhu  Klaus Holliger 《Geophysical Prospecting》2020,68(2):678-689

Knowledge about the stochastic nature of heterogeneity in subsurface hydraulic properties is critical for aquifer characterization and the corresponding prediction of groundwater flow and contaminant transport. Whereas the vertical correlation structure of the heterogeneity is often well constrained by borehole information, the lateral correlation structure is generally unknown because the spacing between boreholes is too large to allow for its meaningful inference. There is, however, evidence to suggest that information on the lateral correlation structure may be extracted from the correlation statistics of the subsurface reflectivity structure imaged by surface-based ground-penetrating radar measurements. To date, case studies involving this approach have been limited to 2D profiles acquired at a single antenna centre frequency in areas with limited complementary information. As a result, the practical reliability of this methodology has been difficult to assess. Here, we extend previous work to 3D and consider reflection ground-penetrating radar data acquired using two antenna centre frequencies at the extensively explored and well-constrained Boise Hydrogeophysical Research Site. We find that the results obtained using the two ground-penetrating radar frequencies are consistent with each other, as well as with information from a number of other studies at the Boise Hydrogeophysical Research Site. In addition, contrary to previous 2D work, our results indicate that the surface-based reflection ground-penetrating radar data are not only sensitive to the aspect ratio of the underlying heterogeneity, but also, albeit to a lesser extent, to the so-called Hurst number, which is a key parameter characterizing the local variability of the fine-scale structure.  相似文献   

Significance of “stretched” mineral inclusions for reconstructing P–T exhumation history     

Kyle T. Ashley  Robert S. Darling  Robert J. Bodnar  Richard D. Law 《Contributions to Mineralogy and Petrology》2015,169(6):1-9

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Modeling prograde TiO2 activity and its significance for Ti-in-quartz thermobarometry of pelitic metamorphic rocks     

Kyle T. Ashley  Richard D. Law 《Contributions to Mineralogy and Petrology》2015,169(2):1-7

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Quantifying the influence of channel sinuosity on the depositional mechanics of channelized turbidity currents: A laboratory study     

Kyle M. Straub  David MohrigJames Buttles  Brandon McElroyCarlos Pirmez 《Marine and Petroleum Geology》2011,28(3):744-760

Here we present results from a suite of laboratory experiments that highlight the influence of channel sinuosity on the depositional mechanics of channelized turbidity currents. We released turbidity currents into three channels in an experimental basin filled with water and monitored current properties and the evolution of topography via sedimentation. The three channels were similar in cross-sectional geometry but varied in sinuosity. Results from these experiments are used to constrain the run-up of channelized turbidity currents on the outer banks of moderate to high curvature channel bends. We find that a current is unlikely to remain contained within a channel when the kinetic energy of a flow exceeds the potential energy associated with an elevation gain equal to the channel relief; setting an effective upper limit for current velocity. Next we show that flow through bends induces a vertical mixing that redistributes suspended sediment back into the interiors of depositional turbidity currents. This mixing counteracts the natural tendency for suspended sediment concentration and grain size to stratify vertically, thereby reducing the rate at which sediment is lost from a current via deposition. Finally, the laboratory experiments suggest that turbidity currents might commonly separate from channel sidewalls along the inner banks of bends. In some cases, sedimentation rates and patterns within the resulting separation zones are sufficient to construct bar forms that are attached to the channel sidewalls and represent an important mechanism of submarine channel filling. These bar forms have inclined strata that might be mistaken for the deposits of point bars and internal levees, even though the formation mechanism and its implications to channel history are different.  相似文献   

On the origins of GEMS grains     

Lindsay P. Keller  Scott Messenger 《Geochimica et cosmochimica acta》2011,75(18):5336-5365

From their birth as condensates in the outflows of oxygen-rich evolved stars, processing in interstellar space, and incorporation into disks around new stars, amorphous silicates predominate in most astrophysical environments. Amorphous silicates were a major building block of our Solar System and are prominent in infrared spectra of comets. Anhydrous interplanetary dust particles (IDPs) thought to derive from comets contain abundant amorphous silicates known as GEMS (glass with embedded metal and sulfides) grains. GEMS grains have been proposed to be isotopically and chemically homogenized interstellar amorphous silicate dust. We evaluated this hypothesis through coordinated chemical and isotopic analyses of GEMS grains in a suite of IDPs to constrain their origins. GEMS grains show order of magnitude variations in Mg, Fe, Ca, and S abundances. GEMS grains do not match the average element abundances inferred for ISM dust containing on average, too little Mg, Fe, and Ca, and too much S. GEMS grains have complementary compositions to the crystalline components in IDPs suggesting that they formed from the same reservoir. We did not observe any unequivocal microstructural or chemical evidence that GEMS grains experienced prolonged exposure to radiation.We identified four GEMS grains having O isotopic compositions that point to origins in red giant branch or asymptotic giant branch stars and supernovae. Based on their O isotopic compositions, we estimate that 1-6% of GEMS grains are surviving circumstellar grains. The remaining 94-99% of GEMS grains have O isotopic compositions that are indistinguishable from terrestrial materials and carbonaceous chondrites. These isotopically solar GEMS grains either formed in the Solar System or were completely homogenized in the interstellar medium (ISM). However, the chemical compositions of GEMS grains are extremely heterogeneous and seem to rule out this possibility. Based on their solar isotopic compositions and their non-solar elemental compositions we propose that most GEMS grains formed in the nebula as late-stage non-equilibrium condensates.  相似文献   

Visualizing uncertainties in a storm surge ensemble data assimilation and forecasting system   总被引：2，自引：1，他引：1  

Thomas Höllt  M. Umer Altaf  Kyle T. Mandli  Markus Hadwiger  Clint N. Dawson  Ibrahim Hoteit 《Natural Hazards》2015,77(1):317-336

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Building the Hindu Kush: monazite records of terrane accretion,plutonism and the evolution of the Himalaya–Karakoram–Tibet orogen     

Shah Faisal  Kyle P. Larson  John M. Cottle  Jaida Lamming 《地学学报》2014,26(5):395-401

In situ U‐Th/Pb (LA‐ICP‐MS) monazite ages from the Hindu Kush of NW Pakistan provide new petrochronologic constraints on the tectonic evolution of the Himalaya–Karakoram–Tibet orogen. Monazites from two adjacent garnet + staurolite schist specimens yield multiple age populations that record the major Mesozoic and Cenozoic deformational, magmatic and metamorphic events along the southern margin of Eurasia. These include the accretion of the Hindu Kush–SW Pamir to Eurasia during the Late Triassic, followed by the accretion of the Karakoram terrane in the Early Jurassic. Younger Jurassic and Cretaceous ages record the development of an Andean‐style volcanic arc along the southern Eurasian margin, which ended with the docking of the Kohistan island arc and the emplacement of the Kohistan–Ladakh batholith during the Late Cretaceous. The initial Eocene collision of India with Eurasia was followed by widespread high‐temperature metamorphism and anatexis associated with crustal thickening within the Himalaya system in the Late Oligocene and Early Miocene.  相似文献   

Resident Attitudes Toward Timber Rattlesnakes (Crotalus horridus)     

Lindsay S. Keener-Eck  Rebecca A. Christoffel 《社会与自然资源》2020,33(9):1073-1091

Abstract

Timber rattlesnakes (Crotalus horridus) are endangered throughout the northeastern United States where multiple factors contribute to population declines. Challenges exist to managing rattlesnake populations because there is little information about human dimensions of this species or other small predators that are venomous or perceived as hazardous. Our objective was to evaluate relationships between resident attitudes and behavioral intentions toward timber rattlesnakes. A mail survey (n?=?593) was used to collect data from residents who live near a rattlesnake population in central Connecticut. Two variables defined resident attitudes toward rattlesnakes: coexistence with the species and perceived threats from the species. Rattlesnake-related factors and situational factors appeared to contribute more heavily to behavioral intentions toward rattlesnakes than general wildlife value orientations. Attitudes predicted behavioral intentions toward rattlesnakes. Results will help wildlife managers incorporate human factors into appropriate management and public outreach strategies.  相似文献