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181.
IntroductionCarbondioxide(CO2 )isaprincipalgreenhousegasandthereforetheirair waterexchangesareimportantproblemsinterrestrialecosystemsforclimatechangestudy(Frankignoulle ,1 998;Chimel,2 0 0 1 ) .ThedirectionofCO2 gasexchange(evasionorinvasion)isdependentonthedirectionoftheCO2concentrationgradientbetweentheairandthesurfacewater;themagnitudeoftheexchangedependsadditionallyonthegasexchangecoefficient,k.Alloflakesinland ,withitssmallareabutlargeatmosphericCO2 fluxrange ,playanimportantroleinev… 相似文献
182.
我国若干湖泊水库的营养状态指数TSI_c及其与各参数的关系 总被引:18,自引:4,他引:18
基于我国20多个湖泊水库的不同营养状态特征,首次得出了适用于我国若干湖泊的营养状态指数TSIc及其与各参数的关系,通过对这些湖泊的TSIc与TSIm值比较,指出TSIc比TSIm更适合于描述生物量与营养盐呈线性响应的我国这类湖泊的营养状态,此外还提出用相关加权法综合不同参数的营养状态指数,并用一个“综合”状态式来表示湖泊的营养状态。 相似文献
183.
V. Nikora R. Nokes W. Veale M. Davidson G. H. Jirka 《Environmental Fluid Mechanics》2007,7(2):159-172
The hydrodynamics of super- and sub-critical shallow uniform free-surface flows are assessed using laboratory experiments
aimed at identifying and quantifying flow structure at scales larger than the flow depth. In particular, we provide information
on probability distributions of horizontal velocity components, their correlation functions, velocity spectra, and structure
functions for the near-water-surface flow region. The data suggest that for the high Froude number flows the structure of
the near-surface layer resembles that of two-dimensional turbulence with an inverse energy cascade. In contrast, although
large-scale velocity fluctuations were also present in low Froude number flow its behaviour was different, with a direct energy
cascade. Based on our results and some published data we suggest a physical explanation for the observed behaviours. The experiments
support Jirka’s [Jirka GH (2001) J Hydraul Res 39(6):567–573] hypothesis that secondary instabilities of the base flow may
generate large-scale two-dimensional eddies, even in the absence of transverse gradients in the time-averaged flow properties. 相似文献
184.
Abstract–Pollen of 42 plant species from 17 families has been found in the food stores of Seladonia subaurata nests, with 61–86% of the pollen being accounted for by the Compositae. The foragers are characterized by strict flower preferences: more than 90% of the pollen in each cell belongs to two or three, sometimes four, plant species. At the eusocial stage of the existence of a colony, two or three foragers usually provision each cell. In especially large colonies, foragers are divided into groups and provision several cells during the day. 相似文献
185.
Abstract: We tested the hypothesis that variation in the sensitivity of animals to habitat change is explained by ecological traits (life‐history traits, trophic level, and mobility). We measured the sensitivity of insectivorous mammals (shrews and bats) and their prey (arthropods active at the soil surface and nocturnal aerial arthropods) to three aspects of agricultural intensification in a matched‐pair experimental design: increased use of agrochemicals (comparison of organic and conventional cereal crops, with pairing for the size of the boundary hedge), change in grassland management from hay to silage (with pairing for the size of the boundary hedge), and increased field size due to hedgerow loss (with boundary‐field comparisons as a proxy). We assessed the sensitivity of taxa as the difference in their relative abundance between pairs of high‐ and low‐intensity sites for each aspect of agricultural intensification. We used phylogenetically informed analyses to explore cross‐species relationships between our measures of sensitivity and seven ecological traits of animals (e.g., trophic level, mobility, and reproductive rate). Several traits were related to the sensitivity of animals to agricultural intensification. These traits were mainly associated with fast life histories (high reproductive output and low trophic level) and low mobility. Trophic level of adults was related to sensitivity to habitat change for all three aspects of agricultural intensification, but the direction of the relationship differed between the three aspects of intensification. The significance of the relationship between other ecological traits and sensitivity to intensification varied for the three aspects of agricultural intensification. Our results show that some ecological traits can be used to preselect taxa that are predicted to be sensitive to habitat change, and their sensitivity can be tested empirically for use as biotic indicator taxa. Understanding which traits are related to sensitivity to habitat change is vital because sensitivity is important in determining a taxon's ability to survive in dynamic environments. 相似文献
186.
Abstract: We tested the unsustainable fishing hypothesis that species in assemblages of fish differ in relative abundance as a function of their size, growth rates, vagility, trophic level, and diet by comparing species composition in historical bone middens, modern fisheries, and areas closed to fishing. Historical data came from one of the earliest and most enduring Swahili coastal settlements (approximately AD 750–1400). Modern data came from fisheries near the archeological site and intensively harvested fishing grounds in southern Kenya. The areas we sampled that were closed to fishing (closures) were small (<28 km2) and permanent. The midden data indicated changes in the fish assemblage that are consistent with a weak expansion of fishing intensity and the unsustainable fishing hypothesis. Fishes represented in the early midden assemblages from AD 750 to 950 had longer life spans, older age at maturity, and longer generation times than fish assemblages after AD 950, when the abundance of species with longer maximum body lengths increased. Changes in fish life histories during the historical period were, however, one‐third smaller than differences between the historical and modern assemblages. Fishes in the modern assemblage had smaller mean body sizes, higher growth and mortality rates, a higher proportion of microinvertivores, omnivores, and herbivores, and higher rates of food consumption, whereas the historical assemblage had a greater proportion of piscivores and macroinvertivores. Differences in fish life histories between modern closures and modern fishing grounds were also small, but the life histories of fishes in modern closures were more similar to those in the midden before AD 950 because they had longer life spans, older age at maturity, and a higher proportion of piscivores and macroinvertivores than the modern fisheries. Modern closures and historical fish assemblages were considerably different, although both contained species with longer life spans. 相似文献
187.
188.
Shin-jen Cheng 《Journal of the American Water Resources Association》2010,46(6):1171-1191
Cheng, Shin-jen, 2010. Inferring Hydrograph Components From Rainfall and Streamflow Records Using a Kriging Method-Based Linear Cascade Reservoir Model. Journal of the American Water Resources Association (JAWRA) 46(6):1171–1191. DOI: 10.1111/j.1752-1688.2010.00484.x Abstract: This study investigates the characteristics of hydrograph components in a Taiwan watershed to determine their shapes based on observations. Hydrographs were modeled by a conceptual model of three linear cascade reservoirs. Mean rainfall was calculated using the block Kriging method. The optimal parameters for 42 events from 1966-2008 were calibrated using an optimal algorithm. Rationality of generated runoffs was well compared with a trusty model. Model efficacy was verified using seven averaged parameters with 25 other events. Hydrograph components were characterized based on 42 calibration results. The following conclusions were obtained: (1) except for multipeak storms, a correlation between base time of the surface runoff and soil antecedent moisture is a decreasing power relationship; (2) a correlation between time lag of the surface flow and soil antecedent moisture for single-peak storms is an increasing power relationship; (3) for single-peak events, times to peak of hydrograph components are an increasing power correlation corresponding to the peak time of rainfall; (4) the peak flows of hydrograph components are linearly proportional to that of total runoff, and the peak ratio for the surface runoff to total runoff is approximately 78 and 13% for subsurface runoff to total runoff; and (5) the relationships of total discharges have direct ratios between hydrograph components and observations of total runoffs, and a surface runoff is 60 and 32% for a subsurface runoff. 相似文献
189.
Studies on the population ofRana arvalis Nilss. frogs performed in the radioactively contaminated area near Lake Berdanish in 1993 revealed a number of features indicating
that the contents of nutrients in the organisms of adults and juveniles is low. The analysis of simultaneously collected data
on food supply to this population showed that the structure of food chains in the study area is simplified and the diversity
and biomass of soil invertebrates (the main food for amphibians) are sharply reduced. These factors account for food deficiency,
which manifests itself in a low level of stomach filling and individual energy reserves of the frogs and is reflected in their
population characteristics. 相似文献
190.