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241.
Surface and groundwater pollution by organochlorine compounds in a typical soybean system from the south Pampa,Argentina 总被引:3,自引:0,他引:3
Mariana Gonzalez Karina S. B. Miglioranza Valeria M. Shimabukuro Orlando M. Quiroz Londoño Daniel E. Martinez Julia E. Aizpún Víctor J. Moreno 《Environmental Earth Sciences》2012,65(2):481-491
Organochlorine pesticides (OCPs) use has been restricted or forbidden in Argentina since 1998 and technical endosulfan is
the last currently used OCPs on the soybean-wheat production. As they persist in soil for several years after application,
OCPs constitute a source of environmental pollution. This work aims to assess OCPs contamination of groundwater (Gw) and streamwater
(Sw) in the Quequén Grande River watershed from south Argentinean Pampas in relation to the hydrogeological characteristics.
OCPs were analyzed in Sw, Gw, surface bottom sediments, soils and borehole cutting sediments (Cs) by gas chromatograph-electron
capture detector. Pesticide distribution in Cs was dependent on the characteristic of the non-saturated zone. Leached pesticides
over 3 m in Cs showed the pattern: HCHs = endosulfan > chlordanes > DDTs, and from 3 to 6 m heptachlor was the main group
as a consequence of the past use of this compound in the area, mainly on potato crops. Endosulfan reaches Gw during application
season as well as during flooding events while a retard effect was observed for Sw. Levels of α- and β-isomers were in certain
cases above national (7 ng L−1) and international (3 ng L−1) limits for aquatic biota protection. As the endosulfan sulfate metabolite was present in Gw and Sw and due to its high toxicity,
it should be considered in the establishment of water quality criteria for human and environmental protection. 相似文献
242.
At present, approximately 1500 asteroids are known to evolve inside or sticked to the exterior 1:2 resonance with Mars at a ? 2.418 AU, being (142) Polana the largest member of this group. The effect of the forced secular modes superposed to the resonance gives rise to a complex dynamical evolution. Chaotic diffusion, collisions, close encounters with massive asteroids and mainly orbital migration due to the Yarkovsky effect generate continuous captures to and losses from the resonance, with a fraction of asteroids remaining captured over long time scales and generating a concentration in the semimajor axis distribution that exceeds by 20% the population of background asteroids. The Yarkovsky effect induces different dynamics according to the asteroid size, producing an excess of small asteroids inside the resonance. The evolution in the resonance generates a signature on the orbits, mainly in eccentricity, that depends on the time the asteroid remains captured inside the resonance and on the magnitude of the Yarkovsky effect. The greater the asteroids, the larger the time they remain captured in the resonance, allowing greater diffusion in eccentricity and inclination. The resonance generates a discontinuity and mixing in the space of proper elements producing misidentification of dynamical family members, mainly for Vesta and Nysa-Polana families. The half-life of resonant asteroids large enough for not being affected by the Yarkovsky effect is about 1 Gyr. From the point of view of taxonomic classes, the resonant population does not differ from the background population and the excess of small asteroids is confirmed. 相似文献
243.
Kathryn E. Davis Rodney L. Anderson Daniel J. Scheeres George H. Born 《Celestial Mechanics and Dynamical Astronomy》2011,109(3):241-264
This paper presents a method to construct optimal transfers between unstable periodic orbits of differing energies using invariant
manifolds. The transfers constructed in this method asymptotically depart the initial orbit on a trajectory contained within
the unstable manifold of the initial orbit and later, asymptotically arrive at the final orbit on a trajectory contained within
the stable manifold of the final orbit. Primer vector theory is applied to a transfer to determine the optimal maneuvers required
to create the bridging trajectory that connects the unstable and stable manifold trajectories. Transfers are constructed between
unstable periodic orbits in the Sun–Earth, Earth–Moon, and Jupiter-Europa three-body systems. Multiple solutions are found
between the same initial and final orbits, where certain solutions retrace interior portions of the trajectory. All transfers
created satisfy the conditions for optimality. The costs of transfers constructed using manifolds are compared to the costs
of transfers constructed without the use of manifolds. In all cases, the total cost of the transfer is significantly lower
when invariant manifolds are used in the transfer construction. In many cases, the transfers that employ invariant manifolds
are three times more efficient, in terms of fuel expenditure, than the transfer that do not. The decrease in transfer cost
is accompanied by an increase in transfer time of flight. 相似文献
244.
Martijn Woltering Pia Atahan Kliti Grice Henk Heijnis Kathryn Taffs John Dodson 《Quaternary Research》2014
Branched glycerol dialkyl glycerol tetraether (GDGT) distributions observed in a sediment core from Lake McKenzie were utilized to quantitatively reconstruct the pattern of mean annual air temperature (MAAT) from coastal subtropical eastern Australia between 37 and 18.3 cal ka BP and 14.0 cal ka BP to present. Both the reconstructed trend and amplitude of MAAT changes from the top of the sediment core were nearly identical to a local instrumental MAAT record from Fraser Island, providing confidence that in this sediment core branched GDGTs could be used to produce a quantitative record of past MAAT. The reconstructed trend of MAAT during 37 to 18.3 cal ka BP and timing of the Last Glacial Maximum (LGM) in the Lake McKenzie record were in agreement with previously published nearby marine climate records. The amplitude of lower-than-present MAAT during the LGM potentially provides information on the latitude of separation of the Tasman Front from the East Australian current in the subtropical western Pacific. The Lake McKenzie record shows an earlier onset of near modern day warm temperatures in the early Holocene compared to marine records and the presence of a warmer than present day period during the mid-Holocene. 相似文献
245.
Flood management decision-makers face significant challenges as the climate changes. The perceptions of those affected by floods are critical to the successful implementation of adaptation responses; risk perceptions are affected by how information is communicated and, in turn, perceptions influence expectations on flood risk managers to respond. The links between flood experience, risk perception, and responses by individual households were examined in the Hutt Valley, New Zealand, through a household survey, a workshop and interviews with local government practitioners. Two propositions were tested: (1) that flood experience can influence flood risk perceptions; and (2) that flood experience can stimulate increased risk reduction and adaptation actions where changing climate risk is likely. Perceptions of responsibility for flood management were also examined. The study found that previous flood experience contributes to heightened perception of risk, increased preparedness of households, greater willingness to make household-level changes, greater communication with councils, and more advocacy for spatial planning to complement existing structural protection. Flood-affected households had a stronger preference for central government and communities having flood risk responsibilities, in addition to local government. Those who lacked experience were more likely to be normalised to their prior benign experiences and thus optimistic about flood consequences. These results suggest that harnessing positive aspects of experience and communication of changing risk through engagement strategies could help shift the focus from citizens’ expectation that governments will always provide protection, to a citizen–local government–central government dialogue about the changing character of flood risk and its implications, and build a ‘risk conscious’ society in which ‘sharing and bearing’ is considered desirable. 相似文献
246.
Roger Gonzalez-Herrera Eden Martinez-Santibañez Julia Pacheco-Avila Armando Cabrera-Sansores 《Environmental Earth Sciences》2014,72(8):2879-2886
The application of agrochemicals in crops can cause pollution of aquifers, especially those with a shallow water table and covered by thin soils; such is the case of Yucatan, Mexico. Information about the requirements and application of fertilizers to major irrigation and rainfed crops as well as the volume of water consumed in growing were used to determine the potential amount of nitrate delivered to groundwater. The research reported in this paper was conducted in the metropolitan area of the city of Merida, in Yucatán, Mexico, where groundwater plays an important role since it is the main source of supply, due to the lack of surface water in the region. In addition, the vulnerability of this aquifer is threatened by the various activities taking place in the municipalities, which emphasize agriculture, located within the groundwater basin. This activity is analyzed as a source of contamination given the concentration of NO3 ? present in groundwater intended for human consumption. The results show that the contribution of farming that enriches the presence of nitrates in the aquifer is different for each municipality in the study area. For the ZMM, the average nutrient leaching is 44 % of the original mass applied; it could be diluted approximately 12 times, in the groundwater. 相似文献
247.
Muller高原位于巴布亚新几内亚南部高地,以发育大漏斗(giant doline)群而闻名.这些漏斗中许多具有可与新不列巅岛Nakanai山地的超级漏斗(megadoline)和中国南方喀斯特天坑相媲美的特大规模和形态,都属"岩盖(caprock)"型漏斗.Muller高原的地质、自然地理和水文环境可与Nakanai山地环境和中国南方喀斯特区环境相对比.本文讨论了Muller高原上三个大漏斗群(Rogorepo,Mamo和Atea)的形成机制.Muller高原的大漏斗,像Nakanai的超级漏斗和中国天坑一样,形成于更新世.Muller高原漏斗的形成环境与其它大漏斗有许多相似性.然而,它却不可能演化成像Nakanai超级漏斗一样壮丽,像中国天坑那样具有极高美学价值,其原因在于石灰岩地层中有不纯非石灰岩夹层. 相似文献
248.
de Oliveira AJ Hollnagel HC Lima Mesquita Hde S Fontes RF 《Marine pollution bulletin》2007,54(7):921-927
Physical and chemical characteristics of intertidal sediments and their relationships with bacteria and cyanobacteria were analyzed at four stations at Pereque Beach. Granulometric analysis showed that Pereque beach has sediment that is classified as sand. The lowest value of the sediment C/N rates (6.08), mainly due to a higher concentration of organic nitrogen, was found at the northern part of Pereque Beach, where organic matter of marine source was more prominent. In this area, density (9.6x10(6)cells cm(-3)), biomass (1992.04ngC cm(-3)) and activity of bacteria were higher than at the southern end. In contrast, cyanobacteria density varied from 2.0 to 4.0x10(5)cells cm(-3), with biomass and total chlorophyll a of the sediment being higher at the southern part, where there are water input from Pereque River and higher organic matter of continental origin. The variability in the microbial population is discussed in the light of the sediment granulometry, organic matter quality, fresh water inflow and pollution. 相似文献
249.
Historical contamination and sources of organochlorine pesticides in sediment cores from Quanzhou Bay, Southeast China 总被引:8,自引:0,他引:8
Three sediment cores were collected from the top to the mouth of Quanzhou Bay, Southeast China, in order to establish sources and historical trends of organochlorine pesticides (OCPs) in the region. The spatial distribution of OCPs in surface sediments implies that Quanzhou Bay received the contamination inputs not only from rivers near the shore, but also from outside the bay. The variation profiles of concentrations clearly showed that OCPs were widely used between 1960s and 1980s in China. A recent increasing trend was found in all cores despite their ban in China in 1983. Different ratios of (DDD+DDE)/DDTs indicated that DDTs at the top of the bay were mainly derived from long-term weather soils, while DDTs near the mouth of the bay were mainly derived from fresh inputs from outside the bay. Higher percentage of gamma-HCH in HCHs deposited after 1990 implies that lindane may have been used recently around Quanzhou Bay. 相似文献
250.
Julia Semprich Nina S. C. Simon Yuri Yu. Podladchikov 《International Journal of Earth Sciences》2010,99(7):1487-1510
Constraints on density as a function of pressure, temperature, and composition are crucial to understand isostatic movements
during geodynamic processes. Here, we provide a systematic series of density diagrams extracted from thermodynamic calculations
for a variety of crustal compositions within a wide P–T range. We quantify systematic density changes in collisional settings for relevant compositional variations and attempt to
simplify the density–composition relationships. Rock densities depend strongly on pressure, temperature, and composition.
Densities at some selected pressure–temperature conditions increase linearly with increasing Al2O3 as well as MgO/FeO contents in pelitic rocks. Al- and Fe-rich pelites yield the highest densities, which is mostly due to
the formation of garnet but also depends on other minerals and changes of reactions. The effect of loading on densities is
investigated, and we show that for deep burial, a meta-pelite rich in Fe and Mg yields much larger density changes than a
dry basalt and that the burial of such a rock with a composition close to typical lower crust may result in significant negative
buoyancy. Metamorphism of hydrous lower crust due to pressurization and heating thus leads to densification of thickened lower
crust, while heating of dry crust leads to a decrease in density. Hence, water-loaded isostatic subsidence due to metamorphism
of water-saturated lower crust is substantial and increases with the thickness and depth of the reacting layer, while dry
compositions show much less or only transient densification and subsidence. The density change due to thermal expansion, an
extensively used concept in geodynamic models, predicts uplift under the same P–T conditions and is an order of magnitude smaller than the density variation calculated from petrologically consistent diagrams. 相似文献