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891.
The profiles of cortisol, testosterone, ll-ketotestosterone and 17α, 20β- dihydroxy-4-pregnene-3-one in mule rainbow trout reared under constant water temperature and natural photoperiod were determined by radioimmunoassay. Gonads of male rainbow trout reached maturity when the fish were two years old. Changes in the plasma levels of both sex steroid hormones and cortisol were closely related to the GSI. Plasma levels of testosterone, 11-ketotestostemne and 17a, 2013-dihydroxy 4-pregnene-3-one showed a clear peak in the annual breeding season, when the GSI reached their maxima. Plasma cortisol levels also showed clearly seasonal changes in both two- and three-year-old fish. The results suggest that the elevated plasma levels of cortisol may not just be due to stresses during the breeding season but have certain physiological functions in the reproduction of rainbow trout. 相似文献
892.
基于逐日气象干旱指数,构建了可以反映某一时段内气象旱涝强度的标准化阶段气象旱涝强度指数 (staged meteorological drought intensity index, ISD) 和阶段气象旱涝时间分布状态的标准化阶段气象旱涝空间分布差异指数 (staged meteorological drought discrepancy index, ISDD)。以构建昆明月尺度的ISD和ISDD为例说明了阶段气象旱涝指数的构建方法,通过对不同时段降水距平百分率、ISD, ISDD和标准降水指数 (standardized precipitation index, ISP) 的对比分析,结合降水及逐日气象干旱指数 (multi-scale standardized precipitation index, IMSP) 的演变,验证了ISD和ISDD的有效性。对于任一站点的不同时间尺度,两个指数可以在日尺度到年尺度乃至更大的时间尺度上进行计算,通过Boltzmann函数来构建ISD和ISDD的方法具有很好的拓展应用性,其他气象干旱指数也可以采用该方法来构建阶段干旱指数。 相似文献
893.
在对国内气象旅游资源评估方法分析研究的基础上,从气象旅游资源相关因素中,筛选出了7个指标,创建了气象旅游资源评估指标体系,提出了评估方法。计算每个评估指标的实际数值并进行标准化处理。采用专家咨询和层次分析法相结合的方法对评估指标体系中的每一级指标赋予相应的权重,最终构建出气象旅游资源评估模型。在实例研究中,以大连为例,选取葫芦岛、东港、鞍山和岫岩等4个城市为对照,结合多年的气候统计数据,分别计算5个城市的气象旅游资源评估指数,并进行横向对比分析,找出各城市气象旅游资源的优势和不足。 相似文献
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897.
Levels of organochlorine pesticides in natural water along the Yangtze River,from headstream to estuary,and factors determining these levels 总被引:1,自引:0,他引:1
Chen Liu Guo-Li Yuan Zhong-Fang Yang Tao Yu Xue-Qi Xia Qing-Ye Hou Long Chen 《Environmental Earth Sciences》2011,62(5):953-960
Organochlorine pesticides (OCPs), including hexachlorocyclohexane and dichlorodiphenyltrichloroethane, were monitored in 37
samples of water collected along the Yangtze River, the third longest river in the world (6,300 km). The total concentration
of OCPs (∑OCPs) in the river water ranged from 0.11 to 27.37 ng/L. It was interesting to discover that, except for some sites
near industrial cities, levels of OCPs in the water samples were very similar along the whole river. Significantly, OCPs were
detected in Tuotuo River (the origin of Yangtze River) even though OCPs have never been used in this area because of its 4,540 m
height above sea level. Furthermore, it was found that ∑OCPs was related to temperature and altitude along the river. We assume
OCPs are transported along the Yangtze River, and the factors affecting this process are discussed. 相似文献
898.
A model for evaluating the influence of water and salt on vegetation in a semi-arid desert region,northern China 总被引:1,自引:0,他引:1
Dong Hui Cheng Wen Ke Wang Xun Hong Chen Guang Cai Hou Hong Bin Yang Ying Li 《Environmental Earth Sciences》2011,64(2):337-346
A model, influence of water and salt on vegetation (IWSV), was developed to evaluate their influence on plant species. The
main function of this model was to calculate a comprehensive index value for evaluating the suitability of plant growth. This
model consists of five explanatory variables (vadose zone moisture content, vadose zone salinity, vadose zone lithology, depth
to the water table, and groundwater mineralization) and two response variables (plant species and their cover). A set of independent
data on three plant species, Artemisia ordosica, Salix psammophila, and Carex enervis, which are dominant species in the Mu Us Desert of northern China, were used to validate the model. Validation results show
an overall correct prediction for the distribution of these three species. The results demonstrated that the IWSV model can
be a useful tool for groundwater management and nature conservation in a semi-arid desert region, especially for predicting
the vegetation distribution in areas with groundwater extraction. 相似文献
899.
Supercooled water with temperatures below freezing point,was identified from hydrographic data obtained by Chinese and Australian expeditions to Prydz Bay,Antarctica,during the austral summer.The study shows that most supercooled waters occurred at depths of 63-271 m in the region north of the Amery Ice Shelf(AIS) front.The maximum supercooling was 0.16°C below the in-situ freezing point.In temperature and salinity ranges of-2.14--1.96°C and 34.39-34.46,respectively,the water was colder and fresher than peripheral shelf water.The supercooled water had less variability in the vertical profiles compared to shelf water.Based on analysis of their thermohaline features and spatial distribution,as well as the circulation pattern in Prydz Bay,we conclude that these supercooled waters originated from a cavity beneath the AIS and resulted from upwelling just outside of the AIS front.Water emerging from the ice shelf cools to an extremely low temperature(about-2.0°C) by additional cooling from the ice shelf,and becomes buoyant with the addition of melt water from the ice shelf base.When this water flows out of the ice shelf front,its upper boundary is removed,and thus it rises abruptly.Once the temperature of this water reaches below the freezing point,supercooling takes place.In summer,the seasonal pycnocline at-100 m water depth acts as a barrier to upwelling and supercooling.The upwelling of ice shelf outflow water illuminates a unique mid-depth convection of the polar ocean. 相似文献
900.
1 INTRODUCTION Measuring the velocity of ocean currents is one of the most important tasks in physical oceanography research. Many centuries ago, mariners had begun to obtain the sea surface cur- rents from vessel drift records. As early as in 1870s instr… 相似文献