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821.
A precise monitoring of snow surface height in the region of Lambert Glacier basin-Amery Ice Shelf,East Antarctica 总被引:2,自引:0,他引:2
I.Allison 《中国科学D辑(英文版)》2005,48(1):100-111
The net surface snow accumulation on the Antarctic ice sheet is determined by a combination of precipitation, sublimation and wind redistribution. We present a one-year record of hourly snow-height measurements at LGB69 (70°50'S, 77°04'E, 1850 m a.s.l.). east side of Lambert Glacier basin (LGB), and 4 year record at G3 (70°53'S, 69°52'E, 84 m a.s.l.), Amery Ice Shelf (AIS). The measurements were made with ultrasonic sensors mounted on automatic weather stations installed at two sites. The snow accumulation at LGB69 is approximately 70 cm. Throughout the winter, between April and September, there was little change in surface snow height (SSH) at the two sites. The negative SSH change is due to densification at LGB69, and is due to both ablation and densification at G3. The strongest accumulation at two sites occurred during the period between October and March (accounting for 101.6% at LGB69), with four episodic increasing events occurring during 2002 for LGB69, and eight events during 1999-2002 for G 相似文献
822.
823.
Histogram and variogram inference in the multigaussian model 总被引:1,自引:4,他引:1
Xavier Emery Julián M. Ortiz 《Stochastic Environmental Research and Risk Assessment (SERRA)》2005,19(1):48-58
Several iterative algorithms are proposed to improve the histogram and variogram inference in the framework of the multigaussian model. The starting point is the variogram obtained after a traditional normal score transform. The subsequent step consists in simulating many sets of gaussian values with this variogram at the data locations, so that the ranking of the original values is honored. The expected gaussian transformation and the expected variogram are computed by an averaging operation over the simulated datasets. The variogram model is then updated and the procedure is repeated until convergence. Such an iterative algorithm can adapt to the case of tied data and despike the histogram. Two additional issues are also examined, referred to the modeling of the empirical transformation function and to the optimal pair weighting when computing the sample variogram. 相似文献
824.
V. I. Danilov-Danilyan 《Water Resources》2005,32(5):572-579
The causes of freshwater deficiency are considered, the main causes being poor environmental conditions and excessive water consumption. The problem of water deficiency is shown to be insoluble without the development of intense water use, conservation, and protection. Based on studying water as a commodity, it is asserted that the market mechanism is not sufficient to cope with water deficiency. The potential of the international water market is shown to be very limited in contrast to the market of water-efficient processes and water-retaining products. 相似文献
825.
Comprehensive assessment of ecotoxicological situation in the Volga River basin is presented. Concentrations of organic and inorganic toxic substances are cited. Basic clinic and postmortem symptoms of intoxication in fish are described; changes in the cellular structure of their organs and tissues, as well as disturbances in hemogenesis, developing under the effect of toxic agents, are characterized. Based on the dose-effect dependences, calculated according to the values of the total concentration of toxic substances, standardized to MPC, and criteria of the physiological state of fish, cases of exceedance of the critical concentrations of pollutants are demonstrated for the investigated river sections.__________Translated from Vodnye Resursy, Vol. 32, No. 4, 2005, pp. 410–424.Original Russian Text Copyright © 2005 by Moiseenko, Gashkina, Sharova, Pokoeva. 相似文献
826.
M. Roy-Barman C. Jeandel M. Souhaut M. Rutgers van der Loeff I. Voege N. Leblond R. Freydier 《Earth and Planetary Science Letters》2005,240(3-4):681-693
230Th, 232Th and 234Th were analyzed in sinking particles collected by moored and drifting sediment traps in the NE Atlantic Ocean (POMME experiment) in order to constrain the phase(s) carrying Th isotopes in the water column. It reveals a contrasted behaviour between 234Th and 230Th. 234Th is correlated to the particulate organic carbon suggesting that it is primarily scavenged by organic compounds in the surface waters. 230Thxs is correlated with Mn, Ba and the lithogenic fraction that are enriched in small suspended particles and incorporated in the sinking particulate flux throughout the water column. The lack of correlation between 230Thxs and CaCO3 or biogenic silica (bSi) indicates that CaCO3 and bSi are not responsible for 230Th scavenging in the deep waters of this oceanic region. 230Th is generally correlated with the lithogenic content of the trapped material but this correlation disappears in winter during strong atmospheric dust inputs suggesting that lithogenic matter is not directly responsible for 230Th scavenging in the deep waters or that sufficient time is required to achieve particle–solution equilibration. MnO2 could be the prevalent 230Thxs-bearing phase. The narrow range of Kd_MnO2Th obtained for very contrasted oceanic environments supports a global control of 230Thxs scavenging by MnO2 and raises the possibility that the 230Th–231Pa fractionation is controlled by the amount of colloidal MnO2 in seawater. 相似文献
827.
The importance of sampling frequency in the course of monitoring of mutagenic pollution of small rivers is shown, the Kotorosl River (a tributary of the Volga River) being taken as an example. In working out a sampling program, due consideration should be given for seasonal variations of the river hydrological regime and input of pollutants. Incorrect choice of sampling frequency may lead to one of the principal reasons for improper assessment of toxicogenetic situation. A water sampling program has been proposed for the Kotorosl River studies based on monitoring.__________Translated from Vodnye Resursy, Vol. 32, No. 3, 2005, pp. 347–351.Original Russian Text Copyright © 2005 by Fomicheva, Prokhorova. 相似文献
828.
Comparative characteristic of several microelements (Ni, Cu, Sr, Al, Zn, Co, Mn, Pb, Cd, Hg, As) found in fish (case study of breams in the Volga basin reservoirs) is presented. Regularities of accumulation of these elements in fish depending on their concentration in the water are analyzed. Main disturbances in fish caused by the accumulation of microelements in their organs and tissues are considered. 相似文献
829.
The Boao coastal system along the eastern coast of Hainan Island is a dynamic delta-tidal inlet-barrier formed during the late Holocene. The delta developed inside a shallow lagoon barred by a sandy barrier with a narrow, shallow tidal inlet opening. Two major distributary channels separated by small islands characterize the delta. The lagoon is silting up receiving and trapping sediments from both the river and, in minor measure during storms, through the tidal inlet opening and barrier washovers. The barrier at the tidal inlet is highly dynamic and changes its form, accreting (migrating spit) against the inlet during fair-weather conditions and being eroded during storms and river floods.The delta has almost completely filled the lagoon and major concerns exist on the effect that ongoing large development plans may have on the environment. These concerns include the effect on floods and rate of siltation once banks of the islands have been stabilized and floodwater and sediment load are impeded from spreading over the lowlands, and the effect of increasing pollutant loads from the new facilities on the ecosystems of the increasingly restricting lagoon water and on the seashores. 相似文献
830.
I. MARIANNE LAGERKLINT GUNHILD ROSQVIST OTTO HERMELIN KIRK MAASCH 《Geografiska Annaler: Series A, Physical Geography》2005,87(1):111-124
ABSTRACT. A new high-resolution, alkenone-de-rived record of sea-surface temperature (SST) change covering the last 26000 years was obtained from the east-equatorial Atlantic off the Congo River. Temperature fluctuations correspond to climate change recorded in other marine and terrestrial archives of the region. The maximum temperature difference between 26000 years BP ago and the Holocene climate optimum around 6000 years BP was 4.3°C, corroborating other SST estimates from the same area. The coldest conditions were followed by a warming that began at 24000 calendar years BP, a time when Northern Hemisphere ice sheets were still at their maximal position. This comparatively early warming is in agreement with previous findings from the east-equatorial South Atlantic. After a relatively stable period between 21500 and 14500 calendar years BP, a second warming began at 14500 calendar years BP which coincides with the onset of the African Humid Period. A cool period at 11500 calendar years BP halted this warming but the trend of increasing temperatures began again at 10000 calendar years BP, this time through large-scale oscillations. The warmest time, around 6000 calendar years BP, was followed by a modest cooling that coincides with the end of the African Humid Period and the onset of Neoglaciation on the African continent. Following this the record shows two distinct warming-cooling cycles during the late Holocene. 相似文献