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211.
William C. Johnson Karen L. Willey Joseph A. Mason David W. May 《Quaternary Research》2007,67(3):474-486
The middle Wisconsinan Gilman Canyon Formation at the Buzzard's Roost type locality in southwestern Nebraska was investigated to document the stratigraphy and to reconstruct the environmental and climate record. The Gilman Canyon Formation was subdivided into three loess units and three soils, with radiocarbon ages constraining it between about 40 ka and 25 ka. Stable carbon isotope ratios, magnetic susceptibility, and carbon content were used to define and characterize soils within both the Gilman Canyon Formation and underlying Illinoian Loveland Loess. At the height of soil development within the Gilman Canyon Formation, climate was supporting C4-dominated grassland, with July temperatures equal to or exceeding those of today. Soil-forming intervals within the Loveland Loess, including the Sangamon Soil, also exhibited relative increases in C4 biomass. Climate, as recorded in the Gilman Canyon Formation, is corroborated by regional proxy data. The formation accumulated during MIS 3, and concurrent soil formation coincided with a summer insolation maximum. 相似文献
212.
Robert J. Kieber William J. Cooper Joan D. Willey G. Brooks Avery Jr. 《Journal of Atmospheric Chemistry》2001,39(1):1-13
Diurnal and seasonal variations in atmospheric hydrogen peroxideconcentrations wereinvestigated during a summer and winter cruise aboard the R.V. `Endeavor' atthe BermudaAtlantic Time Series Station. Rainwater peroxide concentrations in Augustdisplayed dielvariability while no temporal H2O2 pattern was evidentin March rain. Averageconcentrations in March were also significantly lower than August whichindicates photochemicalprocesses are involved in controlling hydrogen peroxide concentrations inmarine rainwaterfalling over the open ocean. The range of gas phase hydrogen peroxideconcentrations wasbetween 1 and 6 ppbv and also exhibited a strong diurnal pattern during bothAugust and Marchwith concentration maxima in the early evening. The influence of atmosphericdeposition onsurface seawater hydrogen peroxide levels was also evaluated. Hydrogenperoxide depth profileswere measured on four separate occasions before and after rain events duringthe Augustsampling period. The input of rainfall hydrogen peroxide was observedthroughout the 25 metermixed layer with surface concentrations two fold larger in the morning aftera rain event. Theintegrated increase in hydrogen peroxide after the rain from 0 to 90 meterswas 1,720 molalmost all of which could be accounted for by the peroxide added from rain.The data presentedin this study represent the first detailed, simultaneous measurements ofhydrogen peroxide inmarine air, rain and surface seawater. 相似文献
213.
Raul Rodríguez Xavier Navarro M. Carmen Casas Angel Redaño 《Theoretical and Applied Climatology》2013,114(1-2):1-8
The rainfall spatial organization in the metropolitan area of Barcelona (Spain) has been studied from records of an urban rain gauge network in the period 1994–2009. Using statistical and regional analysis techniques, correlation between data recorded by the different rain gauges has been calculated, and the effective number of independent stations (n eq) equivalent to the used network has been determined. It has been found out that for durations longer than 20 min, the areal rainfall return period observed for a storm registered by the network approximately decreases by a factor of 1/n eq in relation to the current point rainfall intensity–duration–frequency relationships for the metropolitan area of Barcelona. Using objective analysis techniques, continuous precipitation fields have been generated on a regular grid with a spatial resolution of 300?×?300 m for the storms registered by the rain gauges from 1994 to 2009, for durations from 10 min to 24 h. The precipitation fields obtained have been useful to estimate the characteristic areal reduction factors in the metropolitan area of Barcelona. A direct relationship has been found between the areal reduction factor for all the area corresponding to the urban rainfall network of Barcelona and the effective number of n eq for every duration considered. 相似文献
214.
The new European Marine Strategy Directive: difficulties, opportunities, and challenges 总被引:1,自引:0,他引:1
Borja A 《Marine pollution bulletin》2006,52(3):239-242
215.
Off‐reef planktivorous reef fishes respond positively to decadal‐scale no‐take marine reserve protection and negatively to benthic habitat change
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The effects of no‐take marine reserve (NTMR) protection and changes in benthic habitat on fusiliers (family Caesionidae) were investigated at four small Philippine offshore islands on time scales of 10–31 years. Fusiliers are highly mobile, schooling, medium‐sized planktivorous fish that generally feed “off‐reef.” For these reasons, and given the small size of the NTMRs (3.6–37.5 ha) in this study, it was predicted that fusilier density would be unlikely to show clear effects of NTMR protection, or to respond to changes in benthic habitat. In contrast to predictions, clear NTMR effects were observed on fusilier density at three of the four NTMRs, with durations of protection from 14 to 31 years. Furthermore, the study provided strong evidence that benthic variables, specifically cover of live hard coral and dead substratum, affect the density of fusiliers. This effect of benthic habitat on density was highlighted by several major environmental disturbances that caused shifts in the benthic habitat from live hard coral to dead substratum. For two of the three most abundant species of fusiliers individually, and for all three of them combined (Pterocaesio pisang + Caesio caerulaurea + Pterocaesio digramma/tessellata), as live hard coral cover decreased, fish density decreased. It is hypothesized that these “off‐reef” daytime feeders may have such a strong association with live hard coral cover because they use this habitat as nocturnal sleeping sites. Multivariate analyses indicated that, across all sites and times sampled, cover of live hard coral and dead substratum accounted for 38% of the variation in fish assemblage structure. These results are important as there are very few reports in the published literature of strong effects of NTMR protection or changes in benthic habitat on the density and assemblage structure of fusiliers. 相似文献
216.
217.
The European Water Framework Directive (WFD) establishes a framework for the protection and improvement of estuarine and coastal waters, trying to achieve 'good surface water status at the latest 15 years after the date of entry into force of this Directive'. One of the biological elements that should be analysed is the benthos and, as such, the WFD normative definitions describe the aspects of the benthic communities that must be included in the ecological status assessment of a water body. Therefore, it is essential to include, in the assessment, the different metrics that address those parameters identified in the normative definitions for each of the ecological status classes. In this contribution the use of the AMBI, richness and diversity, combined with the use, in a further development, of factor analysis together with discriminant analysis, is presented as an objective tool (named here M-AMBI) in assessing ecological quality status. This assessment requires previous classification of water bodies and typologies, together with the definition of reference conditions; this is undertaken in this contribution using historical data, expert judgement and multivariate analysis. The study has been undertaken by examining changes in benthic communities in the Basque Country, over the last decade, as a case-study, to demonstrate the accuracy and potential of these methodologies. 相似文献
218.
Geochemical and statistical analysis of trace metals in atmospheric particulates in Wuhan, central China 总被引:3,自引:0,他引:3
Weiwei Lv Yanxin Wang Xavier Querol Xinguo Zhuang Andrés Alastuey Angel López Mar Viana 《Environmental Geology》2006,51(1):121-132
The geochemical characteristics of trace metals (As, Cr, Co, Cd, Cu, Mn, Ni, Pb, V and Zn) in PM10 in Wuhan, the biggest metropolitan in central China, as well as their sources and contributions were analyzed. As PM10 has been the principal contaminant of air in Wuhan for years, concentrations of trace metals were measured in PM10 using high-volume samplers at one urban (Hankou) and one industrial (Changqian) site in Wuhan between September 2003 and September 2004. Based on the results, PM10 in Wuhan is characterized by relatively high levels of As, Cd, Mn, Pb and Zn compared with other Asian cities. The time-series of these elements indicated that As, Cu and Zn at both sites have similar trends, whereas Pb levels showed different patterns due to different emission sources. Factor analysis was applied to the datasets focusing on the apportionment of the mass of selected trace metals. Results indicate that Pb, Cd and As have a common source (smelting) at both sites, whereas the sources of Ni vary from coal combustion and steel in Changqian to mineral and traffic in Hankou. 相似文献
219.
Single crystals of CaAl4Si2O11 were synthesised at 1,500?°C and 14 GPa in a multi-anvil press, and the structure of the phase determined by single-crystal X-ray diffraction at room conditions. The structure-type is that of the “hexagonal barium ferrites”. The space group of the average structure is P6 3 /mmc and the cell parameters are a?=?5.4223(4) Å, c?=?12.7041(6) Å, V?=?323.28(5) Å3, with Z?=?2, and its density is 3.905?g?cm?3, which is reasonable for a high-pressure alumino-silicate phase. The 22 oxygen and two calcium atoms within the unit-cell form an approximate hexagonal-close-packed array. Ten of the twelve octahedral interstices within this array that have only oxygen atoms for apices are filled with Si and/or Al. M1 octahedra share edges to form a spinel-like sheet of octahedra. The average bond length ?=?1.833 Å suggests mixed occupancy by Si and Al. The M1 octahedral sheets are linked by shared corners to pairs of face-sharing M2 octahedra containing Al, with ?= 1.918 Å. The remaining two cations of the unit-cell contents statistically occupy four tetrahedrally-coordinated interstices, which occur as face-sharing pairs. The average bond length for these sites (1.742 Å) suggests that they are occupied by Al, although Si occupancy cannot be excluded by the data. It is proposed that only one interstice of each pair is locally occupied, with the possibility of some short-range ordering of such occupancies. Complete long-range order leading to the acentric space group P6 3 mc is excluded by the data, as is the possibility of the average structure being comprised of merohedral (0?0?0?1) twins of P6 3 mc symmetry. 相似文献