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241.
陆地生态系统与全球变化相互作用的研究进展   总被引:36,自引:3,他引:36  
全球变化及其对生态系统特别是陆地生态系统的影响已经严重地影响到人类生存环境与社会经济的可持续发展 ,引起了各国政府、科学家及公众的高度关注。文中从CO2 浓度倍增、温度变化、水分变化、水热与CO2 协同作用、辐射变化、臭氧变化以及人为干扰等气候环境变化对植物光合生理、生长发育、物质分配、水分利用、碳氮代谢等的影响方面阐述了全球变化影响生态系统的过程与机理 ;从地理分布范围、物候、结构与功能、生态系统的稳定性等方面分析了中国植被、森林生态系统、草原生态系统与农田生态系统对全球变化的响应 ;从植被变化引起的动力条件与热力条件的变化及植被固碳潜力的变化探讨了植被对于气候的反馈作用。在此基础上 ,基于当前全球变化研究前沿 ,提出了未来关于陆地生态系统与全球变化相互作用研究需要重视的方面 ,尤其是关于生态系统对全球变化响应的阈值研究应引起高度重视。  相似文献   
242.
The Great Plains landscape is less topographically complex than most other regions within North America, but diverse aquatic ecosystems, such as playas, pothole lakes, ox-bow lakes, springs, groundwater aquifers, intermittent and ephemeral streams, as well as large rivers and wetlands, are highly dynamic and responsive to extreme climatic fluctuations. We review the evidence for climatic change that demonstrates the historical importance of extremes in north–south differences in summer temperatures and east–west differences in aridity across four large subregions. These physical driving forces alter density stratification, deoxygenation, decomposition and salinity. Biotic community composition and associated ecosystem processes of productivity and nutrient cycling respond rapidly to these climatically driven dynamics. Ecosystem processes also respond to cultural effects such as dams and diversions of water for irrigation, waste dilution and urban demands for drinking water and industrial uses. Distinguishing climatic from cultural effects in future models of aquatic ecosystem functioning will require more refinement in both climatic and economic forecasting. There is a need, for example, to predict how long-term climatic forecasts (based on both ENSO and global warming simulations) relate to the permanence and productivity of shallow water ecosystems. Aquatic ecologists, hydrologists, climatologists and geographers have much to discuss regarding the synthesis of available data and the design of future interdisciplinary research. © 1997 John Wiley & Sons, Ltd.  相似文献   
243.
Freshwaters in different regions show many similarities and differences in their responses to climatic warming. Bases for comparison include reports from regional committees, long-term records for several sites where climate has warmed in the past two decades and other human alterations to freshwaters that simulate some of the expected results of climatic warming, such as reservoir construction. Palaeoecological studies of freshwaters under climatic warming and differences in communities under different climatic regimes are also considered. Major changes in the physical, chemical and biological characteristics of lakes occur. Many of the changes to lakes and streams are the result of strong effects of climatic warming on terrestrial catchments. Inputs from catchments can be either dampened or amplified by in-lake processes, in some cases causing counter-intuitive responses, such as the acidification of streams but alkalinization of lakes in areas where supplies of base cations are limited. Consideration of land–water interactions and interactions between climatic warming and other human stresses are important for the accurate prediction of the effects of climatic change. © 1997 John Wiley & Sons, Ltd.  相似文献   
244.
Variability and unpredictability are characteristics of the aquatic ecosystems, hydrological patterns and climate of the largely dryland region that encompasses the Basin and Range, American Southwest and western Mexico. Neither hydrological nor climatological models for the region are sufficiently developed to describe the magnitude or direction of change in response to increased carbon dioxide; thus, an attempt to predict specific responses of aquatic ecosystems is premature. Instead, we focus on the sensitivity of rivers, streams, springs, wetlands, reservoirs, and lakes of the region to potential changes in climate, especially those inducing a change in hydrological patterns such as amount, timing and predictability of stream flow. The major sensitivities of aquatic ecosystems are their permanence and even existence in the face of potential reduced net basin supply of water, stability of geomorphological structure and riparian ecotones with alterations in disturbance regimes, and water quality changes resulting from a modified water balance. In all of these respects, aquatic ecosystems of the region are also sensitive to the extensive modifications imposed by human use of water resources, which underscores the difficulty of separating this type of anthropogenic change from climate change. We advocate a focus in future research on reconstruction and analysis of past climates and associated ecosystem characteristics, long-term studies to discriminate directional change vs. year to year variability (including evidence of aquatic ecosystem responses or sensitivity to extremes), and studies of ecosystems affected by human activity. © 1997 John Wiley & Sons, Ltd.  相似文献   
245.
Hypersaline habitats in Chile, from marine solar salt pans to saline lagoons and pools in Andean salars, were prospected in search of Artemia populations. These saline ecosystems were characterized through physico-chemical parameters and ionic composition of their brines. Biometrics of cysts and nauplii, as well as morphometrics by using multivariate discriminant analysis for adult specimens evidenced that the Chilean populations of brine shrimp belong to A. franciscana. Cross-breeding results supported the former hypothesis of conspecific Chilean populations, and their differences with A. persimilis, also endemic to the New World, but restricted to Argentinean sites.  相似文献   
246.
The Institute of Biology investigations of morphological diversity of bacteriae with the aid of electronic microscopy are used for the purposes of ecological monitoring. The results obtained allow to recommend this method to be widely applied.It has been demonstrated that for oligotrophic lake Baikal microflora consists mainly from ultra-microscopic cocci. Where the river Selenga inflows into Baikal morphological diversity of bacteriae is much wider. Bacterioplankton of Irkutsk reservoir by morphological characteristics is very similar to one of lake Baikal In meso-eutrophic Bratsh reservoir bacteriuplankton is more morphologically diversified. There are flexibacteriae, vibrios. Caulobacter sp. cells occurring in its water body.In the places of waste waters'' income to river. Angara morphological diversity of bacteriae is high and various forms with projections etc. can be observed.  相似文献   
247.
好氧不产氧光合细菌(aerobic anoxygenic photosynthesis bacteria,AAPB)是广泛分布于海洋、湖泊及河流等典型水域生境中的异养原核生物,能够以环境中有机物为营养物质来获取细胞生长及代谢所需的能量,同时借助自身独特的菌绿素完成光合作用产能但不合成氧气,在物质循环与能量流动中扮演着重要角色.近年,越来越多的AAPB种属被陆续报道,基于光合基因,例如光合反应中心M亚基(pufM)的分子系统发育分析显示,大部分AAPB属于α-、β-及γ-变形菌,且丰度及多样性随生境的不同而呈现时空地理格局异质性.本文对AAPB的栖息环境与生长特性、丰度与分布、生态功能以及环境驱动因子等方面的研究进展进行了回顾和综述.目前,针对水库生态系统AAPB的研究鲜见报道,作者建议开展水库生境中AAPB多样性分布、环境驱动因素及生态功能研究,丰富对于水生生态系统中功能微生物种群生态结构与代谢功能的认识.  相似文献   
248.
Evapotranspiration (ET) from riparian vegetation can be difficult to estimate due to relatively abundant water supply, spatial vegetation heterogeneity, and interactions with anthropogenic influences such as shallower groundwater tables, increased salinity, and nonpoint source pollution induced by irrigation. In semiarid south-eastern Colorado, reliable ET estimates are scarce for the riparian corridor that borders the Arkansas River. This work investigates relationships between the riparian ecosystem along the Arkansas River and an underlying alluvial aquifer using ET estimates from remotely sensed data and modelled water table depths. Results from a calibrated, finite-difference groundwater model are used to estimate weekly water table fluctuations in the riparian ecosystem from 1999 to 2009, and estimates of ET are calculated using the Operational Simplified Surface Energy Balance (SSEBop) model with over 200 Landsat scenes covering over 30 km2 of riparian ecosystem along a 70-km stretch of the river. Comparison of calculated monthly SSEBop ET to estimated alfalfa reference ET from local micrometeorological station data indicated statistically significant high linear correspondence (R2 = .87). Daily calculated SSEBop ET showed statistically significant moderate linear correspondence with data from a local weighing lysimeter (R2 = .59). Simulated monthly SSEBop ET values were larger in drier years compared with wetter years, and ET variability was also larger in drier years. Peak ET most commonly occurred during the month of June for all 11 years of analysis. Relationships between ET and water table depth showed that peak monthly ET was highest when groundwater depths were less than about 3 m, and ET values were significantly lower for groundwater depths greater than 3 m. Negative sample Spearman correlation highlighted riparian corridor locations where ET increased as a result of decreased groundwater depths across years with different hydroclimatic conditions. This study shows how a combination of remotely sensed riparian ET estimates and a regional groundwater model can improve our understanding of linkages between riparian consumptive use and near-river groundwater conditions influenced by irrigation return flow and different climatic drivers.  相似文献   
249.
250.
Páramos are high‐altitudinal neotropical ecosystems located in the upper regions of the northern Andes. Their hydrology is characterized by an extraordinarily high run‐off ratio. One major contributing mechanism is thought to be fog occurrence, which is common in the páramos and occurs by the cooling of near‐surface moist air, as it is forced to higher elevations by topography. However, field‐based observations and quantification of this flux are rare. We present results of monitoring of occult precipitation, understood as the combination of fog and drizzle inputs, combined with meteorological and soil moisture monitoring for periods between 7 to 17 months in 6 sites distributed over 3 páramos catchments in Colombia: three sites in Romerales (Quindío), two in Chingaza (Cundinamarca), and one in Belmira (Antioquia). Occult precipitation inputs were measured with cylindrical fog gauges with a cover on top. We estimate occult precipitation inputs to add between 7% and 28% to rainfall inputs in the study sites. Our results also show that occult precipitation has a large temporal and spatial variability, both within one site and between sites, which make it difficult to upscale and quantify at a catchment scale. Nevertheless, occult precipitation can be important for downstream water supply given that these inputs are especially concentrated during periods with low rainfall. Lastly, we also find evidence for an increase in soil moisture related to occult precipitation during a dry period in Romerales páramo.  相似文献   
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