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741.
742.
Kirt E. Moody 《Estuaries and Coasts》2003,26(3):759-764
Blue crabsCallinectes sapidus in lower Chesapeake Bay are subject to high rates of predation during the late summer of their first year of growth as they
migrate out of vegetated nursery habitats. Predators, potentially contributing to this pattern, were identified in video-recorded
field observations of tethered juvenile crabs (20–25 mm carapace width). Predators were also tested in large laboratory tanks
containing similarly-sized untethered crabs as prey. Seven different predators attacked tethered crabs in the field. Only
two predators, larger blue crabs and northern puffers,Sphoeroides maculatus, consistently succeeded in preying on crabs in both field and laboratory settings. These results confirm the importance of
cannibalism on juvenile blue crabs and identify puffers as a potentially overlooked source of predation pressure. 相似文献
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747.
2002年11月30至12月4日,北京持续4天大雾天气,空气污染物在持续的稳定层结条件下,空气质量连续3天达5级以上。文中分析了大雾天气各主要污染物的变化特征,以及此次过程中天气形势的特点及演变,并对造成大雾日空气污染天气的物理量分布特征进行分析。结果表明:高空WNW气流、稳定性持续增加、逆温层结持续存在、低空风速较小、相对湿度大,导致局地污染物不能及时随大气扩散;1000~700hPa有弱的上升气流形成和维持,与500hPa高空下沉气流之间在低空的某层高度上形成稳定层结(逆温层),导致大雾及重污染的形成;850hPa为暖区,850~500hPa为冷平流,有利于大雾的形成和加重。 相似文献
748.
749.
Permeshwar S. Chauhan Mahesh C. Porwal Lalit Sharma Jay Devs.negi 《Journal of the Indian Society of Remote Sensing》2003,31(3):211-218
The review of study site have revealed the change in vegetation cover of Sal Dense to Sal Medium and Sal Open in 6 forest
Mosaics owing to biotic and abiotic conditions prevailing in the specific areas. Analysis carried out using thematic map derived
from aerial photograph of 1976 and satellite data of IRS 1C LISS III False Colour Composite (FCC) of March 1999 revealed the
cause for change in forest density classes. Deforestation, encroachment and agriculture have been identified as the underlying
causes, which have affected some specific locations to a marked extent. There has been a progressive and remarkable change
among vegetation classes from 1976 to 1999. It is evident from forest type and density map that Sal density has significantly
reduced from Sal Dense 65.61 % in 1976 to Sal Dense 11.12% in the year 1999 followed by Sal Open 11.18 % and Sal Medium 18.24
%. The overall change has been estimated to be 42.11% of the total forested area. 相似文献
750.
The Himalayas has one of the largest concentrations of glaciers outside the Polar Regions. Various reports suggest that significant number of mountain glaciers is shrinking due to climatic variations. Monitoring of these glaciers is important to assess future availability of water resources in the Himalayan region. However, Himalayan glaciers are normally difficult to monitor due to the rugged, mountainous terrain. Therefore, images of Indian Remote Sensing Satellite were used to monitor glaciers in the Baspa basin. Investigations have shown the presence of 30 glaciers in the basin, with areal extent of 167 km2. Out of these, 19 glaciers, with areal extent of 140 km2 were selected to estimate retreat. Investigation suggests that almost all glaciers are retreating in the study basin and overall 19% deglaciation has been observed from 1962 to 2001. In general, altitude distribution appears to have significant influence on glacial retreat. Glaciers located around 5000 m altitude range are showing 24% loss as compared to 14% by glaciers located in altitude range higher than 5400 m. In addition, mean altitude of glacier terminus is shifted upward by 88 m, i.e. from 4482 to 4570 m in last 39 years. The glacial volumes were estimated using regression relationship between area and depth. The investigations have suggested that 19.10 km3 of glacial water stored in the 19 glaciers in 1962, has been reduced to 14.71 km3 in 2001, respectively, an overall loss of 23 percent in a period between 1962 and 2001. These investigations suggest that all glaciers in the Baspa Basin are reducing and in long term, such reducing trend can create scarcity of water in the region. 相似文献