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21.
Sediment resuspension in two adjacent shallow coastal lakes: controlling factors and consequences on phosphate dynamics 总被引：1，自引：0，他引：1
Inmaculada de Vicente Luis Cruz-Pizarro Francisco J. Rueda 《Aquatic Sciences - Research Across Boundaries》2010,72(1):21-31
A combination of field measurements, modelling and laboratory experiments was used to evaluate the potential impact of sediment
resuspension on phosphorus (P) dynamics. The study was carried out in two adjacent shallow coastal lakes (Lake Honda and Lake
Nueva) which, due to their geographic proximity (only 200 m apart), are subject to equal meteorological forcing and represent
ideal systems to study how morphometry and sediment properties relate to wind events. The focusing factors (a measure of the
fluxes of sediment into the water column through resuspension) estimated by comparing settling fluxes measured in surface
sediment traps with those measured in bottom traps, were significantly larger (approximately 34% larger) in Lake Honda (LH;
1.18) than in Lake Nueva (LN; 0.88). Our model estimates of resuspension fluxes (E) were also ca. 40% larger in LH than in LN, in agreement with the observed focusing factors. The larger resuspension fluxes
encountered in LH, in comparison with LN, can mainly be explained by differences in lake morphometry. Still, they could arise
from differences in grain size distribution or in benthic algae concentration encountered in the lake sediments. By means
of adsorption experiments in the laboratory, we show that resuspension events will have different effects on P-dynamics in
LH and LN. While the resuspended material from LH tends to adsorb phosphate (PO4
3−), removing it from the water column, in LN the resuspended sediments tend to increase the availability of PO4
3− in solution. These differences arise from (1) higher concentrations of PO4
3− in water in LH compared to LN; and (2) larger PO4
3−adsorption capacity of the LH sediments as a result of the more abundant iron oxyhydroxides and clay. 相似文献
22.
A new steel framing system for seismic protection of timber platform frame buildings. Implementation with hysteretic energy dissipators 
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下载免费PDF全文 This paper describes a new seismic protection system for timber platform frame buildings, either for new construction or retrofit. The system consists in connecting the timber frame to a steel structure that includes hysteretic energy dissipators designed to absorb most of the seismic input energy thus protecting the timber frame and the other steel members; alternatively, the system might use other types of dissipative devices. The steel structure consists of four steel stacks (located at each of the four façades) and steel collectors embracing each slab; the stacks and the collectors are connected, at each floor level, through the energy dissipators. The steel structure is self‐supporting, that is, the timber frame is not affected by horizontal actions and can be designed without accounting for any seismic provision; in turn, the steel members do not participate in the main load‐carrying system. The timber‐steel interface is designed to avoid any stress concentration in the transfer of horizontal forces and to guarantee that the yielding of the dissipators occurs prior to any timber failure. The energy dissipation capacity of the suggested system is discussed, and an application example on a six‐story timber building is presented; this case corresponds to highly demanding conditions because of the relatively large building height and weight, the high local seismicity, and the soft soil condition. This research belongs to a wider project aiming to promote the structural use of timber by improving the seismic capacity of wooden buildings; this research includes experiments and advanced numerical simulation. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献
23.
Federico Torcal Antonio M. Posadas Mario Chica & Inmaculada Serrano 《Geophysical Journal International》1999,139(3):703-725
Geostatistics offers various techniques of estimation and simulation that have been satisfactorily applied in solving geological problems. In this sense, conditional geostatistical simulation is applied to calculate the probability of occurrence of an earthquake with a lower than or equal magnitude to one determined during a seismic series. It is possible to calculate the energy of the next most probable earthquake from a specific time, given knowledge of the structure existing among earthquakes occurring prior to a specific moment. 相似文献
24.
Federico Torcal Antonio M. Posadas & Inmaculada Serrano 《Geophysical Journal International》1999,139(3):726-742
Seismic series can be taken as examples of correlated unstationary sets of time-stochastic sequences. We investigate the possibility of estimating what is most probable to occur subsequently, if we know the events that have occurred up to a given moment.
The stochastic methods can be used with data of the seismic series, irrespective of their genesis and origin. Using three stochastic methods, namely (1) simulating the likelihood of occurrence by conditional geostatistical simulation; (2) developing a stochastic analysis of the energy release by means of energy packages; and (3) calculating the occurrence time of the most probable next earthquake, we were able to simulate the occurrence of earthquakes that took place during the Alborán Sea seismic series (1997–1998).
We conclude that it is possible to set limits on the time of occurrence and energy release, understood as the magnitude of the most probable earthquake, during the development of a seismic sequence and prior to the actual occurrence of the earthquake. 相似文献
The stochastic methods can be used with data of the seismic series, irrespective of their genesis and origin. Using three stochastic methods, namely (1) simulating the likelihood of occurrence by conditional geostatistical simulation; (2) developing a stochastic analysis of the energy release by means of energy packages; and (3) calculating the occurrence time of the most probable next earthquake, we were able to simulate the occurrence of earthquakes that took place during the Alborán Sea seismic series (1997–1998).
We conclude that it is possible to set limits on the time of occurrence and energy release, understood as the magnitude of the most probable earthquake, during the development of a seismic sequence and prior to the actual occurrence of the earthquake. 相似文献
25.
Mark F. Bautista 《Marine Chemistry》1985,16(4):369-377
Diurnal and diel rates of nitrogen fixation (acetylene reduction) were measured in an intertidal marine mat community consisting of Microcoleus chthonoplastes, Lyngbya aestuarii, and an underlying layer of anaerobic bacteria (probably photosynthetic, fermentative, and sulfate reducing bacteria). The community is located on Shackleford Banks, a barrier island off the coast of North Carolina. Rates of nitrogenase activity during the diurnal period were generally highest in the morning. Rates measured during the day, but incubated in the dark, at times equalled those of samples incubated continuously in the light. Fixation also occurred at night. Mat samples deprived of light prior to the acetylene reduction assay continued to reduce acetylene during the night and into the following day, although at lower rates than samples exposed to light. The persistence of dark nitrogenase activity serves as evidence that reducing power initially generated through photosynthesis can be stored and subsequently utilized through heterotrophic metabolism. Although cyanobacteria are responsible for light-mediated nitrogenase activity, non-photosynthetic bacterial contributions to dark-mediated nitrogenase activity cannot be ruled out. 相似文献
26.
The taphonomic and archeological implications of massive mortality patterns of guanaco (Lama guanicoe) populations due to winter stress are discussed, considering both local and regional scales. The presentation has its focus in the Lake Cardiel basin, Southern Patagonia, Argentina. Winter stress is not an unusual event in Patagonian ecosystems and it produces a seasonal and predictable output: a huge number of dead guanacos in certain loci.Five faunal assemblages formed in 2000 are discussed, three in rock shelters and two at open-air settings, considering guanaco individuals/bone preservation, age and sex structure, death positions, degree of interment, carnivore damages, trampling marks, and the association between guanaco individuals/bones and archeological material (mainly lithic artifacts). Conditions exist for the commingling of naturally formed guanaco bone assemblages and archeological materials. The taphonomic signature of this mortality pattern is analysed, and criteria developed that allow identification of the potential mixture between archeological material and modern guanaco bones. From an archeological point of view, the potential scavenging opportunities brought by these guanaco mortality events to hunter-gatherer populations are explored.In sum, the results of this study are twofold. First, it brings new data on the regional taphonomy of guanacos and its implications for the archeological record. Second, it invites consideration of these mass mortality events in the context of strategies employed by hunter-gatherer populations to cope with their environment. 相似文献
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Between 2008 and 2010, the island of Majorca (Spain) experienced the coldest and wettest winters of the last 40 years. Accumulated rainfall was twice the average and values of intense rainfall up to 296 mm/24?h were recorded, very similar to those calculated for a return period of 100 years. Additionally, high precipitation coincided with anomalous, low temperatures, with abundant snowfall and freezing in the highest zones of the Tramuntana Range, in the northwest sector of the island. As a result, 34 mass movements were recorded on the range, which seriously affected the road network in an area of great importance for tourism, as it welcomes 8.5 million visitors each year. Fourteen rockfalls, 1 rock avalanche, 15 landslides and 4 karstic collapses were inventoried. The geological structure, formed by a series of NW overlapping thrusts, determines the distribution as well as the failure pattern of the movements. Thus, the northern face of the range registered 68% of the mass movements: nine rockfalls with planar failure took place as well as all the landslides recorded. Likewise, south-facing slopes have been affected by longer runout rockfalls with a wedge-type failure. The thorough analysis of the meteorological data shows that most of the movements have taken place after antecedent rainfall over 800?mm. Additionally, the rockfalls have also occurred after several freeze–thaw cycles, being a determining and unusual factor in this warm region. Intense rainfall >90 mm/24?h also caused rockfalls as well as exceptional very intense rainfall >120 mm/24?h caused landslides. The results aim to contribute to the design of an early warning system coordinating emergency, infrastructure services and meteorological centres in a region of high risk. 相似文献
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Juan Bautista Belardi Gisela Cassiodoro Rafael Goi Michael D. Glascock Alejandro Súnico 《Geoarchaeology》2015,30(3):223-237
Hunter‐gatherer mobility and spheres of interaction are important characteristics worthy of investigation in Patagonian archaeology. One way to approach these is by studying the distribution of lithic archaeological materials. Siltstone (limolite) artifacts are found along the western strip of southwestern Patagonia, Argentina. Based on geomorphological studies and the high density of archaeological material, a source was located along the western margin of Cardiel Lake. Neutron activation analysis of samples from the source and archaeological sites in several neighboring basins allowed us to model its circulation. Siltstone's archaeological distribution indicates that its regional circulation had a southerly direction dating from the early Holocene. This southern vector shows an important difference when compared to the distribution of obsidian from Pampa del Asador, which has a broader circulation pattern. This could be related to a greater availability of high‐quality lithic materials north of the siltstone source. This work also contributes to the construction of a lithic source database for southern Patagonia. 相似文献