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排序方式: 共有173条查询结果,搜索用时 31 毫秒
51.
Amanda A. Pierce Beth L. Parker Robert Ingleton John A. Cherry 《Ground Water Monitoring & Remediation》2018,38(1):42-55
Difficult access conditions have limited techniques for groundwater system characterization and monitoring in bedrock exposed landscapes. This condition is common in the mining industry and resulted in the development of lightweight portable drills. This paper describes how these drills were used at a contaminated site to understand the groundwater flow system by adapting piezometer designs, ensuring effective seals to obtain reliable hydraulic head, hydrochemistry, and contaminant concentrations. Two drilling machines were evaluated: the Shaw Portable Core Drill? fits in a backpack and can advance continuously cored rock holes, nominal 51 millimeters (mm) diameter, to depths up to approximately 15 meters (m); and the larger Winkie Drill? requires a two or more people to mobilize and can advance continuously cored holes, nominal 48 mm diameter, to depths of approximately 45 m. The resulting small diameter coreholes were accommodated in the design of each well using a seal created by injecting grout into a semipermeable fabric sleeve. This “fabric sleeve” serves as a means to contain the grout and ensures that the entire annulus above the screen is sealed without loss of grout into the formation, allowing the well to perform as a piezometer. To develop and demonstrate this methodology for groundwater monitoring in bedrock, the two drills were used in drainages located along the slopes of an elevated sandstone outcrop near Los Angeles, California. Unique insights into the groundwater flow system of this bedrock environment, which would otherwise be unattainable, were achieved. This methodology overcomes the accessibility limitations of conventional drilling methods that prevent installation of wells in remote and rugged mountainous terrains. 相似文献
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53.
A line of Roman villas once dominated the Mediterranean coastline to the south of the Tiber river mouth near Ostia in central Italy. The Roman remains, which were constructed within a series of dune ridges, now lie up to 900 m from the current shoreline as a result of the continued evolution of the Tiber delta in response to postglacial sea level rise, sediment inputs from the Tiber river catchment and tectonic uplift. Infrared stimulated luminescence (IRSL) ages of potassium-rich feldspars extracted from dune sands are in good agreement with the independent age control provided by the Roman structures and allow us to hypothesise an increase in aggradation rates of five times since the end of the period of Roman occupation compared with the earlier Holocene. 相似文献
54.
Tree-ring reconstructed dry season rainfall in Guatemala 总被引:1,自引:0,他引:1
Anchukaitis Kevin J. Taylor Matthew J. Leland Caroline Pons Diego Martin-Fernandez Javier Castellanos Edwin 《Climate Dynamics》2015,45(5-6):1537-1546
Climate Dynamics - Drought in Guatemala has negative consequences for agriculture and potable water supplies, particularly in regions of the country with highly seasonal rainfall. General... 相似文献
55.
Alex Brown Rowena Banerjea Amanda Dawn Wynne Normunds Stivrins Marc Jarzebowski Lisa‐Marie Shillito Aleks Pluskowski 《Geoarchaeology》2015,30(6):511-527
Slavic and German colonization of the southern Baltic between the 8th and 15th centuries A.D. is well‐documented archaeologically and historically. Despite the large number of pollen profiles from Poland, few palaeoecological studies have examined the ecological impact of a process that was central to the expansion of European, Christian, societies. This study aims to redress this balance through multiproxy analysis of lake sediments from Radzyń Chełminski, Northern Poland, using pollen, element geochemistry (Inductively Coupled‐Optical Emission Spectroscopy [ICP‐OES]), organic content, and magnetic susceptibility. The close association between lake and medieval settlements presents the ideal opportunity to reconstruct past vegetation and land‐use dynamics within a well‐documented archaeological, historical, and cultural context. Three broad phases of increasing landscape impact are visible in the pollen and geochemical data dating from the 8th/9th, 10th/11th, and 13th centuries, reflecting successive phases of Slavic and German colonization. This involved the progressive clearance of oak‐hornbeam dominated woodland and the development of an increasingly open agricultural landscape. Although the castles and towns of the Teutonic Order remain the most visible signs of medieval colonization, the palynological and geochemical data demonstrate that the major phase of woodland impact occurred during the preceding phase of Slavic expansion; Germans colonists were entering a landscape already significantly altered. 相似文献
56.
Private docks are common in estuaries worldwide. Docks in Massachusetts (northeast USA) cumulatively overlie ~ 6 ha of salt marsh. Although regulations are designed to minimize dock impacts to salt marsh vegetation, few data exist to support the efficacy of these policies. To quantify impacts associated with different dock designs, we compared vegetation characteristics and light levels under docks with different heights, widths, orientations, decking types and spacing, pile spacing, and ages relative to adjacent control areas across the Massachusetts coastline (n = 212). We then evaluated proportional changes in stem density and biomass of the dominant vegetation (Spartina alterniflora and Spartina patens) in relation to dock and environmental (marsh zone and nitrogen loading) characteristics. Relative to adjacent, undeveloped habitat, Spartina spp. under docks had ~ 40% stem density, 60% stem biomass, greater stem height and nitrogen content, and a higher proportion of S. alterniflora. Light availability was greater under taller docks and docks set at a north-south orientation but did not differ between decking types. Dock height best predicted vegetation loss, but orientation, pile spacing, decking type, age, and marsh zone also affected marsh production. We combined our proportional biomass and stem elemental composition estimates to calculate a statewide annual loss of ~ 2200 kg dry weight of Spartina biomass (367 kg per ha of dock coverage). Managers can reduce impacts through design modifications that maximize dock height (> 150 cm) and pile spacing while maintaining a north-south orientation, but dock proliferation must also be addressed to limit cumulative impacts. 相似文献
57.
François-Nicolas Robinne Dennis W. Hallema Kevin D. Bladon Mike D. Flannigan Gabrielle Boisramé Christian M. Bréthaut Stefan H. Doerr Giuliano Di Baldassarre Louise A. Gallagher Amanda K. Hohner Stuart J. Khan Alicia M. Kinoshita Rua Mordecai João Pedro Nunes Petter Nyman Cristina Santín Gary Sheridan Cathelijne R. Stoof Matthew P. Thompson James M. Waddington Yu Wei 《水文研究》2021,35(5):e14086
2020 is the year of wildfire records. California experienced its three largest fires early in its fire season. The Pantanal, the largest wetland on the planet, burned over 20% of its surface. More than 18 million hectares of forest and bushland burned during the 2019–2020 fire season in Australia, killing 33 people, destroying nearly 2500 homes, and endangering many endemic species. The direct cost of damages is being counted in dozens of billion dollars, but the indirect costs on water-related ecosystem services and benefits could be equally expensive, with impacts lasting for decades. In Australia, the extreme precipitation (“200 mm day −1 in several location”) that interrupted the catastrophic wildfire season triggered a series of watershed effects from headwaters to areas downstream. The increased runoff and erosion from burned areas disrupted water supplies in several locations. These post-fire watershed hazards via source water contamination, flash floods, and mudslides can represent substantial, systemic long-term risks to drinking water production, aquatic life, and socio-economic activity. Scenarios similar to the recent event in Australia are now predicted to unfold in the Western USA. This is a new reality that societies will have to live with as uncharted fire activity, water crises, and widespread human footprint collide all-around of the world. Therefore, we advocate for a more proactive approach to wildfire-watershed risk governance in an effort to advance and protect water security. We also argue that there is no easy solution to reducing this risk and that investments in both green (i.e., natural) and grey (i.e., built) infrastructure will be necessary. Further, we propose strategies to combine modern data analytics with existing tools for use by water and land managers worldwide to leverage several decades worth of data and knowledge on post-fire hydrology. 相似文献
58.
Observations and Impacts from the 2010 Chilean and 2011 Japanese Tsunamis in California (USA) 总被引:3,自引:0,他引:3
Rick I. Wilson Amanda R. Admire Jose C. Borrero Lori A. Dengler Mark R. Legg Patrick Lynett Timothy P. McCrink Kevin M. Miller Andy Ritchie Kara Sterling Paul M. Whitmore 《Pure and Applied Geophysics》2013,170(6-8):1127-1147
The coast of California was significantly impacted by two recent teletsunami events, one originating off the coast of Chile on February 27, 2010 and the other off Japan on March 11, 2011. These tsunamis caused extensive inundation and damage along the coast of their respective source regions. For the 2010 tsunami, the NOAA West Coast/Alaska Tsunami Warning Center issued a state-wide Tsunami Advisory based on forecasted tsunami amplitudes ranging from 0.18 to 1.43 m with the highest amplitudes predicted for central and southern California. For the 2011 tsunami, a Tsunami Warning was issued north of Point Conception and a Tsunami Advisory south of that location, with forecasted amplitudes ranging from 0.3 to 2.5 m, the highest expected for Crescent City. Because both teletsunamis arrived during low tide, the potential for significant inundation of dry land was greatly reduced during both events. However, both events created rapid water-level fluctuations and strong currents within harbors and along beaches, causing extensive damage in a number of harbors and challenging emergency managers in coastal jurisdictions. Field personnel were deployed prior to each tsunami to observe and measure physical effects at the coast. Post-event survey teams and questionnaires were used to gather information from both a physical effects and emergency response perspective. During the 2010 tsunami, a maximum tsunami amplitude of 1.2 m was observed at Pismo Beach, and over $3-million worth of damage to boats and docks occurred in nearly a dozen harbors, most significantly in Santa Cruz, Ventura, Mission Bay, and northern Shelter Island in San Diego Bay. During the 2011 tsunami, the maximum amplitude was measured at 2.47 m in Crescent City Harbor with over $50-million in damage to two dozen harbors. Those most significantly affected were Crescent City, Noyo River, Santa Cruz, Moss Landing, and southern Shelter Island. During both events, people on docks and near the ocean became at risk to injury with one fatality occurring during the 2011 tsunami at the mouth of the Klamath River. Evaluations of maximum forecasted tsunami amplitudes indicate that the average percent error was 38 and 28 % for the 2010 and 2011 events, respectively. Due to these recent events, the California tsunami program is developing products that will help: (1) the maritime community better understand tsunami hazards within their harbors, as well as if and where boats should go offshore to be safe, and (2) emergency managers develop evacuation plans for relatively small “Warning” level events where extensive evacuation is not required. Because tsunami-induced currents were responsible for most of the damage in these two events, modeled current velocity estimates should be incorporated into future forecast products from the warning centers. 相似文献
59.
Large-scale human-built infrastructure is shown to alter the salinity and subtidal residual flow in a realistic numerical simulation of hydrodynamic circulation in a coastal plain estuary (Tampa Bay). Two model scenarios are considered. The first uses a modern bathymetry and boundary conditions from the years 2001–2003. The second is identical to the first except that the bathymetry is based on depth soundings from the pre-construction year 1879. Differences between the models' output can only result from changes in bay morphology, in particular built infrastructure such as bridges, causeways, and dredging of the shipping channel. Thirty-day means of model output are calculated to remove the dominant tidal signals and allow examination of the subtidal dynamics. Infrastructure is found to steepen the mean axial salinity gradient $ \partial \overline{s}/ dx $ by ~40% when there is low freshwater input but flatten $ \partial \overline{s}/ dx $ by ~25% under more typical conditions during moderate freshwater inflow to the estuary. Deepening of the shipping channel also increases the magnitude of the residual Eulerian circulation, allowing for larger up-estuary salt transport. Local bathymetry and morphology are important. Some regions within the estuary show little change in residual circulation due to infrastructure. In others, the residual circulation can vary by a factor of 4 or more. Major features of the circulation and changes due to infrastructure can be partially accounted for with linear theory. 相似文献
60.
Maria LUGARO Carolyn L. DOHERTY Amanda I. KARAKAS Sarah T. MADDISON Kurt LIFFMAN D. A. GARCÍA‐HERNÁNDEZ Lionel SIESS John C. LATTANZIO 《Meteoritics & planetary science》2012,47(12):1998-2012
Abstract– The composition of the most primitive solar system condensates, such as calcium‐aluminum‐rich inclusions (CAIs) and micron‐sized corundum grains, show that short‐lived radionuclides (SLR), e.g., 26Al, were present in the early solar system. Their abundances require a local or stellar origin, which, however, is far from being understood. We present for the first time the abundances of several SLR up to 60Fe predicted from stars with initial mass in the range approximately 7–11 M⊙. These stars evolve through core H, He, and C burning. After core C burning they go through a “Super”‐asymptotic giant branch (Super‐AGB) phase, with the H and He shells activated alternately, episodic thermal pulses in the He shell, a very hot temperature at the base of the convective envelope (approximately 108 K), and strong stellar winds driving the H‐rich envelope into the surrounding interstellar medium. The final remnants of the evolution of Super‐AGB stars are mostly O–Ne white dwarfs. Our Super‐AGB models produce 26Al/27Al yield ratios approximately 0.02–0.26. These models can account for the canonical value of the 26Al/27Al ratio using dilutions with the solar nebula of the order of 1 part of Super‐AGB mass per several 102 to several 103 of solar nebula mass, resulting in associated changes in the O‐isotope composition in the range Δ17O from 3 to 20‰. This is in agreement with observations of the O isotopic ratios in primitive solar system condensates, which do not carry the signature of a stellar polluter. The radionuclides 41Ca and 60Fe are produced by neutron captures in Super‐AGB stars and their meteoritic abundances are also matched by some of our models, depending on the nuclear and stellar physics uncertainties as well as the meteoritic experimental data. We also expect and are currently investigating Super‐AGB production of SLR heavier than iron, such as 107Pd. 相似文献