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901.
Hideo Kawai 《Journal of Oceanography》2005,61(2):235-246
At present, the barotropic buoyant stability parameter has been derived from a vertical virtual displacement of a water parcel. The barotropic inertial stability parameter in the eccentrically cyclogeostrophic, basic current field was derived in 2003 from a horizontal cross-stream virtual displacement of a parcel. By expressing acceleration of a parcel due to a virtual displacement, which is arbitrarily sloping within a vertical section across the basic current, in terms of natural coordinates, we derived the vertical component of baroclinic buoyant stability parameter B
2
2, the horizontal component of baroclinic inertial stability parameter I
2
2, the baroclinic joint stability parameter J
2, its buoyant component B
2 and its inertial component I
2. B
2 is far greater than I
2
2, and when neglecting relative vorticity except for vertical shear, a downward convex curve of J
2 plotted against the slope of a virtual displacement follows a trend of B
2 curve. If a parcel displaces along a horizontal surface or an isopycnal surface, however, B
2 vanishes, and J
2 becomes equal to I
2. Actual parcel is apt to displace not only along the bottom slope, but also along the sea surface and an isopycnal interfacial surface, which is approximately equivalent to an isentropic surface, preferred by lateral mixing and exchange of momentum. Such actual displacement makes B
2 vanishing, and grants I
2 an important role. The present analysis of I
2 examining effects due to curvature and horizontal and vertical shear vorticities are useful in deepening our understanding of baroclinic instability in actual oceanic streams. 相似文献
902.
VishwambharPrasadSati 《山地科学学报》2005,2(1):76-85
Agricultural practices are the main stay of the people of Uttranchal. Out of the total population,more than 75% people are engaged either with the main occupation of agriculture or its allied practices,dominated by traditional subsistence cereal farming.Among them, the main crops are rice, wheat, millet,barley, all types of pulses, all types of oilseeds and almost all types of fruits. The crops, vegetables and fruits of all varieties are grown in the different climatic zones such as tropical, temperate, and cold because, the region is characterized by the different altitudinal zones elevated from 200 m to more than 8000m. As a result, different climates are found from hot tropical to sub temperate and chilly cold. Pulses varieties are grown extensively. Among vegetables,potato, onion, carrot, all types of green leaf vegetables,brinzal, pumpkin, ladyfinger, pea, gram, radish,ginger, garlic, etc, are grown widely. All fruit varieties are grown in the different altitudinal zones. The mainfruits are orange, malta (a big size of orange),elephant citrus, lemon and all other types of citrus,apple, stone fruits including peach and pears, manykinds of nuts, and the fruits which are grown in the low lying areas. In spite of feasible climatic conditions,agricultural dominant society, and availability of all types of crops, the production and productivity of these crops are very low, even they are unable to meet the grain-need of the people in Uttaranchal. Agricultural crops are grown almost in all the altitudinal zones -- from the low-lying areas, which are called ‘Ga. ngarh‘, to the highly elevated region,where the legendary term is given as ‘Danda‘. The growing seasons vary according to the heights. The present paper aims to discuss the agricultural practices including cropping season, cropping pattern,land use, production of cropsagricultural system in thisand ecological aspect of Himalayan state and suggest some measures for developing farming system,which could lead the sustainability, in terms of meeting the food grain needs of the people on the one hand and restoring the ecological balance on the other. 相似文献
903.
Village is an important implementation unit of national poverty alleviation and development strategies of rural China, and identifying the poverty degree, poverty type and poverty contributing factors of each poverty-stricken village is the precondition and guarantee of taking targeted measures in poverty alleviation strategies of China. To respond it, we construct a village-level multidimensional poverty measuring model, and use indicator contribution degree indices and linear regression method to explore poverty factors, while adopting Least Square Error (LSE) model and spatial econometric analysis model to identify the villages’ poverty types and poverty difference. The case study shows that: (1) Spatially, there is obvious territoriality in the distribution of poverty-stricken villages, and the poverty-stricken villages are concentrated in contiguous poverty-stricken areas. The areas with the highest VPI, in a descending order, are Gansu, Yunnan, Guizhou, Guangxi, Hunan, Qinghai, Sichuan, and Xinjiang. (2) The main factors contributing to the poverty of poverty-stricken villages in rural China include road construction, terrain type, frequency of natural disasters, per capita net income, labor force ratio, and cultural quality of labor force. The main causes of poverty include underdeveloped road construction conditions, frequent natural disasters, low level of income, and labor conditions. (3) Chinese poverty-stricken villages include six main subtypes, and most poverty-stricken villages are affected by multiple poverty-forming factors, reflected by a relatively high proportion of the three-factor dominant type, four-factor coordinative type, and five-factor combinative type. (4) There exist significant poverty differences in terms of geographical location and policy support, and the governments still need to carry out targeted poverty alleviation measures according to local conditions. The research can not only draw a macro overall poverty-reduction outline of impoverished villages in China, but also depict the specific poverty characteristics of each village, helping the government departments of poverty alleviation at all levels to mobilize all kinds of anti-poverty resources. 相似文献
904.
Atmospheric lead(Pb) and other trace metals can transport over long distance and deposit on remote alpine ecosystems. In this work, the soil profiles, litter and dominant mosses along a large altitude were collected on Ao Mountain, Central China, to obtain the spatial distributions of Pb in these materials, decipher the possible factors controlling the distribution, and quantitatively distinguish the natural versus anthropogenic sources of Pb through the Pb isotopic tracing and biomonitoring. The results show that soil Pb concentrations(mg/kg) decreased significantly with depth, and they were markedly higher in the O(42.6± 2.7) and A(36.4 ± 2.2) horizons than in the litter(7.20 ± 1.9) and mosses(28.0 ± 3.9). The Pb enrichment in the surface soils(O and A horizons),litter and mosses existed in the relatively high altitudes, which was attributed to the influences from atmospheric wet deposition, plants, soil physicochemical properties and human activity. ThePb isotopic ratios identified the Pb sources as originating mainly from Chinese coal combustion,mining and smelting. Atmospheric Pb from southeastern, southwestern and northwestern regions could be deposited in the alpine ecosystem by long distance atmospheric transport. The anthropogenic Pb reached over 50% in the O and A horizons, and over 70% in the litter and mosses, which corresponded to the concentrations of 26.9, 17.7, 5.92 and 21.2 mg/kg, respectively. The results indicate that the mutual effects of climate and regional human activity could increase the Pb accumulation in remote alpine ecosystems. 相似文献
905.
Emiliya P. Kirilova Maarten van Hardenbroek Oliver Heiri Holger Cremer André F. Lotter 《Journal of Paleolimnology》2010,43(4):829-842
We present a palaeolimnological study encompassing five centuries of trophic-state change of the dike-breach lake De Waay
located on the Rhine-Meuse delta (the Netherlands). Diatom-inferred total phosphorus (TP) concentrations indicate hypertrophic
epilimnetic conditions (>300 μg l−1 TP) since the formation of the lake in the fifteenth century until the end of the eighteenth century. Cladocera data support
the reconstructed trophic state and indicate turbid conditions in lake De Waay during this period. High inferred TP concentrations
as well as the amount of Ti in the sediment reflect numerous flooding events. From the nineteenth century onwards reconstructed
TP concentrations decreased to 40–150 μg l−1 due to improvements in sewage and dike systems that considerably diminished direct river flooding and seepage-derived nutrients.
As a consequence, the increased stability of littoral habitats led to an increased diversity of the Cladocera assemblages.
The most significant decrease in TP concentrations to ~40 μg l−1 occurred between about 1900 and 1930. This mesotrophic phase was a consequence of the isolation of the lake from catchment
drainage and the introduction of a highly elaborate flood control during this period. However, since the mid twentieth century
a eutrophication trend is preserved in the record, likely related to increased agricultural activity in the vicinity of the
lake. Our results emphasize that land-use and trophic-state history must be taken into account when evaluating the ecological
status of lakes for water management and protection actions, especially for lakes in landscapes that are strongly modified
by human action. 相似文献
906.
Arbab I. Arbab 《Astrophysics and Space Science》2009,323(2):181-184
In the framework of unifying gravity and electromagnetism, we have shown that accelerating objects emit gravitational wave
as those determined by Larmor formula for the accelerating charged particle. We have found new formulae for the power of Gravitational
waves radiated by spinning and orbiting objects. The minimum wavelength of the gravitational wave emitted by an object of
mass m and radius R is
. 相似文献
907.
Latitudinal variation of leaf morphological traits from species to communities along a forest transect in eastern China 总被引:2,自引:0,他引:2
Comprehensive information on geographic patterns of leaf morphological traits in Chinese forests is still scarce. To explore the spatial patterns of leaf traits, we investigated leaf area (LA), leaf thickness (LT), specific leaf area (SLA), and leaf dry matter content (LDMC) across 847 species from nine typical forests along the North-South Transect of Eastern China (NSTEC) between July and August 2013, and also calculated the community weighted means (CWM) of leaf traits by determining the relative dominance of each species. Our results showed that, for all species, the means (± SE) of LA, LT, SLA, and LDMC were 2860.01 ± 135.37 mm2, 0.17 ± 0.003 mm, 20.15 ± 0.43 m2 kg–1, and 316.73 ± 3.81 mg g–1, respectively. Furthermore, latitudinal variation in leaf traits differed at the species and community levels. Generally, at the species level, SLA increased and LDMC decreased as latitude increased, whereas no clear latitudinal trends among LA or LT were found, which could be the result of shifts in plant functional types. When scaling up to the community level, more significant spatial patterns of leaf traits were observed (R 2 = 0.46–0.71), driven by climate and soil N content. These results provided synthetic data compilation and analyses to better parameterize complex ecological models in the future, and emphasized the importance of scaling-up when studying the biogeographic patterns of plant traits. 相似文献
908.
The lipids in a sediment core from Lake Valencia, a hypereutrophic freshwater lake in Venezuela, are examined to understand
environmental changes over the last ∼13,000 years. From the latest Pleistocene to the earliest Holocene, total organic carbon
(TOC) substantially increased from 2.2 to 10%, while total organic carbon over total nitrogen (TOC/TN) decreased from as high
as 34 to as low as 10. Correspondingly, the concentration of terrestrially derived triterpenoids markedly decreased, and the
dominant n-alkane shifted from C31 to C23 or C25. During the same period, algal biomarkers such as botryococcenes, dinosterol, isoarborinol, C20 HBIs and 1,15C32 keto-ol markedly increased in abundance. These changes suggested a greater contribution of algal organic matter at the onset
of the Holocene, which was concurrent with increasing rainfall and the formation of a permanent lake (Lake Valencia) in the
Aragua Valley, Venezuela. The age profile of Paq, a n-alkane based proxy, showed large oscillations (0.20–0.81), reflecting historical variations in source strength of submerged/floating
vs. terrestrial/emergent OM inputs. An abrupt increase in tetrahymanol abundance at ∼7,260 cal years BP suggests the establishment
of an oxic–anoxic boundary in the lake’s water column. After reaching its maximum abundance at ∼2,100 cal year BP, botryococcenes,
a biomarker of Botryococcus braunii, gradually decreased to below the detection limit in the uppermost sediments, while different algal/microbial biomarkers
such as diploptene, dinosterol and isoarborinol substantially increased. These different historical profiles of algal/microbial
biomarkers reflect different responses of source organisms to environmental changes throughout this period. The δ13C determinations presented exceptionally enriched values for botryococcene isomers (−7.7 to −15.1‰), indicating the utilization
of bicarbonate as carbon sources in an extremely productive ecosystem. 相似文献
909.
Glen M. MacDonald David F. Porinchu Nicolas Rolland Konstantine V. Kremenetsky Darrell S. Kaufman 《Journal of Paleolimnology》2009,41(1):129-141
Instrumental climate records from the central Canadian treeline zone display a pattern of variation similar to general Northern
Hemisphere temperature trends. To examine whether this general correspondence extends back beyond the instrumental record,
we obtained a sediment core from Lake S41, a small lake in the Northwest Territories of Canada at 63°43.11′ N, 109°19.07′ W.
A radiocarbon-based chronology was developed for the core. The sediments were analyzed for organic-matter content by loss-on-ignition
(LOI), biogenic-silica content (BSi), and chironomid community composition to reconstruct July air temperature and summer
water temperature. The paleolimnological records were compared with records of atmospheric CO2 concentration, solar variability, and hemispheric temperature variations over the past 2000 years. The results of the analyses
suggest that widely-documented long-term variations in Northern Hemisphere temperature associated with radiative forcing,
namely the cooling following the medieval period during the Little Ice Age (LIA), and twentieth century warming, are represented
in the central Canadian treeline zone. There is also evidence of a brief episode of warming during the eighteenth century.
As evidenced by LOI and BSi, the twentieth century warming is typified by increased lake productivity relative to the LIA.
Depending upon the measure, the increased productivity of the twentieth century nearly equals or exceeds that of any other
period in the past 2000 years. In contrast, the rate of chironomid head capsule accumulation decreased and remained low during
the twentieth century. Although the chironomid-inferred temperature reconstructions indicate cooling during the LIA, they
present no evidence of greatly increased temperatures during the twentieth century. Warming during the twentieth century might
have enhanced lake stratification, and the response of the chironomid fauna to warming was attenuated by decreased oxygen
and lower temperatures in the hypolimnion of the more stratification-prone lake.
相似文献
Glen M. MacDonaldEmail: |
910.
Effects of an ecological conservation and restoration project in the Three-River Source Region,China 总被引:3,自引:3,他引:3
The first-stage of an ecological conservation and restoration project in the Three-River Source Region (TRSR), China, has been in progress for eight years. However, because the ecological effects of this project remain unknown, decision making for future project implementation is hindered. Thus, in this study, we developed an index system to evaluate the effects of the ecological restoration project, by integrating field observations, remote sensing, and process-based models. Effects were assessed using trend analyses of ecosystem structures and services. Results showed positive trends in the TRSR since the beginning of the project, but not yet a return to the optima of the 1970s. Specifically, while continued degradation in grassland has been initially contained, results are still far from the desired objective, ‘grassland coverage increasing by an average of 20%–40%’. In contrast, wetlands and water bodies have generally been restored, while the water conservation and water supply capacity of watersheds have increased. Indeed, the volume of water conservation achieved in the project meets the objective of a 1.32 billion m3 increase. The effects of ecological restoration inside project regions was more significant than outside, and, in addition to climate change projects, we concluded that the implementation of ecological conservation and restoration projects has substantially contributed to vegetation restoration. Nevertheless, the degradation of grasslands has not been fundamentally reversed, and to date the project has not prevented increasing soil erosion. In sum, the effects and challenges of this first-stage project highlight the necessity of continuous and long-term ecosystem conservation efforts in this region. 相似文献