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181.
在验证CENTURY模型对中国陆地植被净初级生产力(Net Primary Productivity,NPP)模拟能力的基础上,利用该模型探讨了1981-2008年中国陆地植被NPP的年际变异和变化趋势对CO2浓度、温度和降水变化的响应。结果表明,中国陆地植被NPP对不同气候因子的响应程度存在明显不同。其中,CO2浓度变化对植被NPP年际变异的影响不显著,但能够引起中国大部分地区植被NPP趋势系数增大;温度对中国中高纬度地区植被NPP的年际变化影响显著,但就全国范围而言,植被NPP年际变异对温度变化的响应程度总体低于对降水变化的响应程度;降水变化是对中国植被NPP变化趋势起主导作用的气候因子。此外,综合考虑温度和降水变化的影响发现,植被NPP变化趋势的响应特征类似于降水单独变化时植被NPP变化趋势的响应特征。 相似文献
182.
Bruce E. Frey J.Rubén Lara-Lara Lawrence F. Small 《Estuarine, Coastal and Shelf Science》1983,17(2):213-218
The eruption of Mt Saint Helens on 18 May 1980 resulted in a massive increase in suspended particulate material in the Columbia River Estuary, producing a substantial increase in light attenuation. Since photosynthesis in the estuarine water column is partly controlled by the depth of light penetration in the water, photosynthesis was reduced by about 75% during the period of increased turbidity. It took about five weeks for the estuary to clear. Although primary production within the estuarine water column was greatly diminished during this period, the flux of particulate carbon through the estuary was high, and the total production we estimate to have been lost amounted to only about 2% of the total particulate carbon flux just after the eruption. That the high levels of turbidity in the estuary did not induce a severe fall in the phytoplankton population is evidence that phytoplankton biomass concentrations in the Columbia River Estuary are mostly a function of import from the Columbia River, rather than a function of in situ production. 相似文献
183.
184.
Guojiang?WanEmail author Jing’an?Chen Siqin?Xu Fengchang?Wu P.?H.?Santschi 《中国科学D辑(英文版)》2005,48(4):484-496
The fundamental assumption of 210Pb sediment dating is the stable flux of 210Pbex, which was derived from atmosphere and then transferred into sediments via lake water. When the sedimentation rate is relatively
constant, the 210Pbex activity in sediments will be exponentially reduced with sedimentation age. 210Pbex in lake water is incorporated into sediments mainly via organic particulates. If the sedimentation flux of organic matter
in lake water is suddenly increased, 210Pbex will be significantly deposited and then transferred into sediments. On the one hand such sudden purification effect is obviously
unfit for the fundamental assumption of 210Pb dating; on the other hand, the sudden enhancement of 210Pbex flux would be indicative of the conspicuous variation of primary productivity of lake water. This problem will be discussed
in accordance with the variation trend of 210Pbex in the vertical profile of recent sediments of Lake Chenghai, Yunnan Province. The sediment core was collected from the deep-water
area of Lake Chenghai in June 1997. The vertical profile of 137Cs activity is characterized by a tree-peak pattern. This profile gave reliable ages, and also showed the stability of sediment
accumulation in the recent ten years. The vertical profile of 210Pbex activity displays a specific distribution of peaks, and is similar to the vertical profile of Corg. This phenomenon seems to be related to the mechanism of constraining the transfer of 210Pbex into lake sediments. The average atomic ratios of Horg/Corg and Corg/Norg in Lake Chenghai sediments are 5.51 and 7.04, respectively, indicating that the organic matter was predominantly derived
from the remains of endogenic algae. In terms of the three-stage evolutionary characteristics of organic matter in sediments,
i.e., “deposition-de-composition-accumulation”, the sedimentation fluxes (F(Corg)) of organic carbon (Corg) since 1970 were calculated by modeling. The sedimentation fluxes of 210Pbex (F(210Pbex)) in different years display good synchronous relations with the sedimentation flux of organic carbon (F(Corg)), especially in the years of 1972–1974 and 1986–1989. The variation of F(Corg) led to the variation of F(210Pbex); the variation of F(210Pbex) reflects, to some extent, the historical variation of lake productivity. 相似文献
185.
The nitrogen relations of Enteromorpha spp. growing on intertidal mud flats have been examined over a twelve-month period. Nitrogen assimilation rates using 15N have been used to calculate the production of the alga and were between 0·046 and 0·217 mg (g dry wt alga)?1 h?1 A considerable quantity of the alga was buried beneath the sediment over the growth season and was calculated to be equivalent to an input of up to 9·52 g N m?2 per month and 32 g N m?2 over one complete growth season. Based on carbon, this latter value represented an input of approximately 320 g C m?2 annually. Low rates of nitrogenase activity (acetylene reduction) were found to be associated with the Enteromorpha. The organisms responsible for the nitrogenase activity were probably heterotrophic bacteria but they did not contribute significant quantities of nitrogen to the alga. 相似文献
186.
本文着重指出了在今后处理大面积CCD图象数据过程中,所将面临的数据存贮困难问题.本文提出了一种有效的不丢失天文信息的压缩CCD图象数据的方法,对银纬b=-60°的一个天区的试验表明,压缩后的图象数据仅为原图象数据的1/30左右,并且可以十分方便地进行图象再现及再处理。在压缩数据过程中,我们在剑桥APM底片扫描机参数化施密特照相底片的基础上,重新安排了CCD图象上天体的对应参数,并视天体的大小及形状,有效地提取保存了天体周围矩阵信息. 相似文献
187.
基于MODIS资料的2000-2004年江河源区陆地植被净初级生产力分析 总被引:18,自引:2,他引:16
基于EOS/MODIS卫星遥感资料的分析表明,2000-2004年江河源地区陆地植被平均年NPP为82.04 gC.m-2,相当于同期全国陆地植被年NPP的23%,其中2001年的年NPP最小,只有78.04gC.m-2,2002年最大,为85.44 gC.m-2.根据年NPP分布显示,黄河源区的植被生长状况要好于长江源区,其中在黄河源东南部陆地植被的年NPP>250 gC.m-2,为江河源区植被年生长最大的区域;该地区的植被年NPP最小值的区域分布在长江源的西北部地区,年NPP大部分<50 gC.m-2.江河源地区植被的年NPP表现为显著的年际变化特征,不同地区年NPP的变化特征各不相同;高寒草甸的年NPP为该地区所有陆地植被年NPP中最大,其5 a平均值为89.38 gC.m-2,其次为高寒草原和灌木及草本植被;由于地处高寒地区,温度成为影响该地区陆地植被净初级生产力的主要因素. 相似文献
188.
189.
Heping LIU 《大气科学进展》2009,26(1):9-16
Corrections of density effects resulting from air-parcel expansion/compression are
important in interpreting eddy covariance fluxes of water vapor and CO2 when open-path systems
are used. To account for these effects, mean vertical velocity and perturbation of the density
of dry air are two critical parameters in treating those physical processes responsible for
density variations. Based on various underlying assumptions, different studies have obtained
different formulas for the mean vertical velocity and perturbation of the density of dry air,
leading to a number of approaches to correct density effects. In this study, we re-examine
physical processes related to different assumptions that are made to formulate the density
effects. Specifically, we re-examine the assumptions of a zero dry air flux and a zero moist
air flux in the surface layer, used for treating density variations, and their implications
for correcting density effects. It is found that physical processes in relation to the assumption
of a zero dry air flux account for the influence of dry air expansion/compression on density
variations. Meanwhile, physical processes in relation to the assumption of a zero moist air
flux account for the influence of moist air expansion/compression on density variations. In
this study, we also re-examine mixing ratio issues. Our results indicate that the assumption
of a zero dry air flux favors the use of the mixing ratio relative to dry air, while the
assumption of a zero moist air flux favors the use of the mixing ratio relative to the total
moist air. Additionally, we compare different formula for the mean vertical velocity, generated
by air-parcel expansion/compression, and for density effect corrections using eddy covariance
data measured over three boreal ecosystems. 相似文献
190.
G. K. Khachatryan M. B. Kopchikov V. K. Garanin M. V. Chukichev N. N. Golovin 《Moscow University Geology Bulletin》2009,64(2):102-110
The morphological and spectral-optical properties of diamond crystals from placers in North Timan rivers have been studied with IR-spectroscopy and cathode luminescence methods. As a result, correlation between external characteristics of diamonds (size and degree of mechanical damage) and number of optically active centers has been revealed. The habit and the type of distribution of structural defects in diamond crystals studied are comparable with those in diamonds from the Archangelsk Region and North Timan’s placers. Based on the obtained data, origin issues and possible primary sources of diamonds from North Timan’s placers are discussed. 相似文献