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1.
This article reviews the wood fuels situation in the Sahel and the findings of various needs assessment methodologies, especially as these are relevant to the numerous programmes to introduce improved cooking technologies in the region. Most people in West Africa, especially in poor and rural areas, rely primarily on wood fuels and crop wastes for energy needs, with devastating environmental consequences. Most wood is used in cooking. The quantity of fuel used depends on the type of fireplace, utensils used, how and when food is prepared, food preparation methods, types of fuels, how fuelwood is collected, and special customs surrounding the family fire — all of which are intimately associated with the economic, cultural and social fabric of Sahelian societies. Conventional fuel consumption and resource surveys have yielded useful information about quantitative energy needs in the Sahel, but increasingly sociocultural studies are being used to ensure that stove designs will meet the needs of the end-user. Economic analssis is also necessary to establish the dimensions of wood scarcity, to assess the financial attractiveness to consumers of alternative fuels and stoves, and in evaluating the costs and benefits to society of proposed national woodstoves programmes.  相似文献   

2.
Climate models and results, especially for paleo-climatic scale are reviewed. It is concluded that the climatic system is more stable than it was thought to be when Budyko-Sellers type models first came into existence. Even a 2% decrease in solar radiation may not result in White Earth due to negative feed-backs. A decrease in CO2 to about 200 ppm can result in White Earth. A doubling of CO2 increases the surface temperature by an order of 1°C. The total climatic system which is nonlinear can exhibit very long period internal oscillations, even of the order of 1,00,000 years though none of the time constants involved are in that range individually.  相似文献   

3.
On an uranium-mining-influenced area, sunflowers (Helianthus annuus) were grown on a small-scaled plot. Subsamples of sunflowers were harvested 34, 66, 96, 108, 140, and 170 days after sowing. Contents of Cd, Co, Cr, Cu, Fe, Mn, Ni, Pb, Th, U, Zn, and rare earth elements (REEs, La–Lu) were determined in the sunflower shoots, as well as total and bioavailable contents of these 25 elements in the soil taken on the day of sowing and after the last harvest. Shoot contents alone were not sufficient to evaluate the extraction capacity of the sunflowers. Instead total extracted masses (product of biomass and element content) had to be calculated. The total extracted mass increased for most of the elements until 140 days after sowing. Bioconcentration factors (BCFs) as ratio between element content in shoot and soil, were calculated for this time to evaluate the phytoextraction efficiency. BCFs ≥1 (relating total soil contents) and thus a very effective extraction was calculated for Cd. The BCFs, based on mobile soil contents, were ≥1 for all elements, except for U and REEs (La–Lu). Consequently, the sunflower is able to extract many elements effectively from the direct harmful soil fraction. To reduce the contents of Cd and Ni down to levels, where the mining-influenced area could be classified as arable land would require 55 and 207 sunflower growth cycles. Although this is quite a long time, the uranium-mining-influenced area could be successively remediated, while growing biofuel crops, without interfering with food production.  相似文献   

4.
Soil quality evaluation under different land management practices   总被引：5，自引：0，他引：5  
Sustainable agricultural production requires prudent management backed by reliable information that accurately elucidates the complex relationships between land management practices and soil quality trends. Therefore, this study investigates the influence of management on soil properties acquired at different depths, and yields, at five different field sites within Ohio, USA. The principal management systems considered were no till with or without manure and cover crops, natural vegetation (NV) or forest, and conventional tillage (CT) defined as farms with surface residue cover (<30 %). Analyses of variance (ANOVA), correlation analyses, stepwise regression, and the principal component analyses (PCA) were used to elucidate and model the link between four different management practices and the soil physical and chemical properties. The ANOVA results indicate that the available water capacity and electrical conductivity (EC) were the major variables affected by management. In contrast, soil pH, bulk density (ρ b), porosity, soil organic carbon (SOC), and total nitrogen (TN), were invariable with management, yet only pH and EC did not significantly vary with the interaction of soil type and management effects. In comparison, the PCA results suggest that SOC, TN, porosity, ρ b, and EC were the major determining factors controlling yield variability. Interestingly, the derived models revealed that the highest yields, notably 10 and 2.7 Mg ha?1 for corn (Zea mays L.) and soybean (Glycine max (L.) Merr.) occurred in soils under CT management. Quantifying the nexus between soil properties and management choices as demonstrated in this study, can provide critical insight for sustainable agricultural production.  相似文献   

5.
The role of zooplankton in a salt marsh ecosystem was studied in Flax Pond, Old Field, N. Y., a 30-hectare tidal pond adjacent to Long Island Sound. Various marine crustaceans accounted for over 95% of the zooplankton caloric biomass in all but three months, in which ctenophores (Mnemiopsis leidyi) accounted for about 20%. Mass balance analysis of crustacean biomass showed a seasonal trend with increased “consumption” by the marsh from July to November. Analysis of groups (or species) for all months showed total numbers were reduced by passing through, or interacting with, the marsh. The most abundant group for each sample date also was significantly reduced from outflowing waters for all months, as were the group copepodids and miscellaneous calanoids from July to November. The energy requirements for the crustacean zooplankton community could have been supplied amply by the estimated standing crop of phytoplankton in the marsh. Phytoplankton net primary production was low, but it was ample to satisfy crustacean energy needs in all months. Crustaceans and phytoplankton alone were not enough to support estimated ctenophore nutrition requirements in summer. Therefore, detritus may also have been an important ctenophore food source.  相似文献   

6.
A parametric crop yield model YIELD, which was developed by Prof. W. Terjung and his team at UCLA, was applied to calculate yield and water consumption for corn in Saudi Arabia. The model employs climatic and environmental data in order to simulate yield for several crops in different places all over the world. A network of 22 stations provided climatic data averaged over a period of 17 years (1967–1983). The nonclimatic data was derived from the FAO soil map of the world and the writer's personal experience. The main objectives of this paper are: [1] to determine suitable places and times for planting corn, under rainfed and irrigated conditions in Saudi Arabia; [2] to contrast irrigation water for corn in each province; and [3] to assess the potential yield for corn in the country in a year. This study concluded that highest yields of corn under fully-irrigated conditions (primary growing season) occurred in the mountainous region in SW Saudi Arabia (about 12,000 kg/ha, and more than 18,000 in Nimas) while lowest yields occurred in Tabuk and Al-Khawsh (about 4,000 kg/ha). Yields in most of the other stations were (5,000–8,000 kg/ha). Under rainfed conditions crop failed in all regions except in the SW region in which yields range between 2,000 kg/ha in Al-Khawsh and — 6,000 kg/ha as in Nimas. According to the findings of this study, the most suitable months for corn sowing in Saudi Arabia are December and January.  相似文献   

7.
Net annual productivity of tall and medium form cordgrass,Spartina alterniflora, was estimated by a new clip sampling method in a sloping foreshore salt marsh at Wallops Island, Virginia. This method measured live standing crops only, to avoid problems of measuring dead biomass inherent in other methods. Losses from live standing crops by shoot mortality and by leaf shedding were estimated from these measurements and added separately to production of live tillers and of live culms. This allowed quantification of various components of production.Spartina tillering in different zones of the marsh produced 62 to 211 g dry weight per m2 per yr. Tiller mortality removed 37 to 106 g per m2 per yr from live standing crops. Culms produced 348 to 1,132 g per m2 before flowering and die-back. Culm mortality removed 28 to 246 g per m2 before flowering. Leaf shedding removed an additional 83 g per m2 in tall formSpartina. Altogether, net annual productivity These estimates are much higher than previous estimates of productivity and standing crops inSpartina marshes nearby.  相似文献   

8.
Simulating the temporal-spatial distribution of areas suitable for crops is an important part of analyzing the effects of climate change on crop growth, reducing the vulnerability of crop growth, and assessing the adaptability of crop growth to climate change. This study selected climate factors that affect the growth of wheat, maize and rice, and it combined surface soil and ground elevation factors as environment variables, as well as data from agricultural observation stations as species variables. The MaxEnt ecological model was used to identify suitable areas for these three crops during the period of 1953-2012. The areas suitable for the three crops were analyzed to determine the temporal-spatial distribution of major food crops and to estimate the difference in crop growth adaptability under climate change. The results showed the following: ① The response to climate change of the areas suitable for food crops could be ranked from strongest to weakest as follows: wheat, rice, and maize. ② On the same space-time scale, for the growth of wheat and rice, the southern agricultural regions, mountainous areas and plateaus were relatively unsuitable for a wider variety of crops than the northern agricultural regions, plains and basins. ③ The adaptability of wheat increased in the major agricultural regions slightly. The adaptability of maize increased in the northern agricultural regions and decreased in the southern agricultural regions, respectively. The adaptability of rice was stable in the southern agricultural regions, and it decreased in the Huang-Huai-Hai region and increased in the northeastern region. ④ Over 60 years, the ability of the major food crops to adapt to climate change increased in the northeast region, Gansu-Xinjiang region, Southwest region and Loess Plateau region, but the adaptability of major food crops decreased in the Huang-Huai-Hai region and the Mid-and-Lower Reaches of the Yangtze River. ⑤ The suitable areas of maize and rice were significantly correlated with planting areas and yields, respectively, which provided feasibility for simulating the distribution of suitable areas on maize and rice in different climate scenarios in the future. The suitable area of wheat is not significantly related to the planting area and yield. In the future, we will take more factors to model the suitable area of wheat accurately.  相似文献   

9.
Five different refraction formulas were applied to SiO2 polymorphs in order to determine the most suitable refractive index-density relation. 13 SiO2 polymorphs with topological different tetrahedral frameworks are used in this study including eight new low density SiO2 polymorphs — so called “guest free porosils”. These SiO2 polymorphs cover a density range from 1.76 to 2.92 g/cm3. The mean refractive indices (ovn) of the porosils have been determined by the immersion method, the densities (ρ) were calculated from the unit cell parameters. Assuming the polarizability (α) of all SiO2 polymorphs to be constant the general refractivity formula $$\{ 2\overline {11} 0\} \langle 0001\rangle $$ turned out to be the most suitable for SiO2 polymorphs. Regression analysis yields an electronic overlap parameter b=1.2(1).  相似文献   

10.
Itaipu Lake, which includes the Itaipu hydroelectric power plant, is one of the largest dams in the world and has a strong relationship with its surroundings. The flooded area has multiple uses such as navigation, recreation, water abstraction for industrial, urban and agricultural irrigation. The lake is located at the frontier between Brazil, Argentina and Paraguay. In this study, superficial sediments collected from nine sampling sites were analysed for grain size, organic matter and 16 priority polycyclic aromatic hydrocarbons (PAHs) using high-performance liquid chromatography (HPLC) with fluorescence detector. The total concentration of PAHs in the dry sediment ranged from 35.21 to 685.37 µg kg?1. Diagnostic ratios showed that the possible source of PAHs in the Itaipu Lake could be pyrolitic and petrogenic. The potential toxicity of sediment of PAHs varied from not detected to 127.70 µg g?1, suggesting that some adverse ecological effects would arise due to PAHs in these sediments.  相似文献   

11.
The paper presents the nature of variations of tropospheric and total ozone column retrieved from the Convective Cloud Differential (CCD) technique, Ozone Monitoring Instrument (OMI), and Total Ozone Mapping Spectrometer (TOMS) data, National Aeronautics and Space Administrations (NASA), USA, respectively; surface temperature, relative humidity, total rainfall, ozone precursors (non-methane hydrocarbon, carbon monoxide, nitrogen dioxide, and sulphur dioxide) that are collected from India Meteorological Department (IMD), Alipore, Kolkata; solar insolation obtained from Solar Geophysical Data Book and El-Niño index collected from National Climatic Data Center, US Department of Commerce, National Oceanic and Atmospheric Administration, USA. The effect of these climatic parameters and ozone precursors on ozone variations is critically analyzed and explained on the basis of linear regression and correlation. It has been observed that the maximum, minimum and mean temperature, relative humidity, solar insolation, tropospheric, and total ozone column (TOC) showed slight increasing tendencies from October 2004 to December 2011, while total rainfall and El-Niño index showed little decreasing tendencies for the same period. Amongst selected climatic parameters and ozone precursors, the solar insolation and the average temperature had a significant influence on both, the tropospheric ozone and total ozone column formation. The solar insolation had contributed more in tropospheric ozone than in total ozone column; while El-Niño index had played a more significant role in total ozone column build up than in tropospheric ozone. Negative correlation was observed between almost all ozone precursors with the tropospheric and total ozone. The tropospheric ozone and total ozone column were also significantly correlated. The level of significance and contribution of different climatic parameters are determined from correlation technique and Multiple Linear Regression (MLR) method. The related chemical kinetics for ozone production processes has been critically described.  相似文献   

12.
Uraninite from the metamorphic deposit investigated is divided into two groups on the basis of its occurrence and physical and chemical properties. Uraninite of the first group occurs as distorted crystals in the form of elongated cubesa {100}; the second group occurs mainly in the form of rhombo-dodecahedrad {100}, all belonging to the GaF2 type in the isometric system. The chemical formulae are 8UO2·UO3·PbO for the first group and 5UO2·UO3·PbO for the second. Isotopic dating yields 1,900 and 300 m. y. for the formation time of uraninite in this deposit. The former value corresponds to the main mineralization period and the latter represents the reformation event.  相似文献   

13.
The hypothesis thatTypha domingensis (cattail) can invade tidal marshes only after soil salinities are substantially reduced was tested experimentally by comparing the salt tolerance of seeds, seedlings, and plants reared from rhizomes. Germination rates for four southern California populations reached 100% in fresh water, decreasing to 2% at 20‰. The salt tolerance of seeds from three coastal populations was lower than that of the Salton Sea population. Salt tolerance of plants grown in the lab did not increase with age for seedlings up to 8 weeks old. Rhizome-bearing plants had greatly decreased growth at 10‰ and no growth at 25‰ However, rhizomes of about 5% of the plants survived 9 months at 45‰. The seeds and seedlings are salt sensitive, which explains why invasion into tidal marshes is restricted to prolonged periods of low soil salinity. The older, rhizome-bearing plants are salt tolerant, which explains how invading plants persist persist under hypersaline conditions.  相似文献   

14.
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15.
A detailed survey showed that groundwater fluoride was 6.1ppm in the Talupula area of the Anantapur district in southern India which is higher than is normally observed in groundwater elsewhere in India but not so extreme as that reported in Andhra Pradesh (up to 21 mg L-1). Groundwater is used for irrigating agricultural crops as well as for drinking which may expose its population to higher concentrations of fluoride through their diet. A preliminary study examined the concentrations of fluoride in five agricultural crops in the Talupula area and the soil beneath agricultural crops. The stem and leaves of Heliathusannuas, Arachishypogaea, Morusalba, Lychopersiconesculantum, and Phaseolus vulgaris were examined for fluoride and heavy metal accumulation. Heavy metal (Zn, Cu and Pb) accumulation in the stem and leaves were examined to determine if there was any correlation between their uptake and that of fluoride. In the soil beneath the crops, fluoride concentrations ranged from 6.53±0.44 to 8.23±1.22 ppm and a significant accumulation of fluoride was observed in the stems (13.2±2.0 to 23.9±3.6 ppm; p < 0.001) and leaves (16.4±1.9 to 61.5±4.5 ppm) of the agricultural plants. A significant accumulation of fluoride was observed from the stem to the leaves for all plants (p < 0.03) except Helianthus annuas. Copper also displayed significant accumulation from the soil to the stems in some of the plants tested but there was no significant accumulation of zinc or lead. A significant translocation from the stem and accumulation in the leaves was not observed for Cu or Pb but there was significantly higher zinc in the leaves of Arachishypogaea and Morusalba when compared to their stems. This study demonstrated that agricultural plants grown under field conditions and irrigated with groundwater high in fluoride will accumulate fluoride, but that fluoride is unlikely to have a significant effect on Cu, Zn or Pb accumulation in the stems and leaves of agricultural plants of the area. While drinking water is still the major cause of fluorosis in southern India, consumption of foods with high fluoride concentrations may also increase the risk of fluorosis.  相似文献   

16.
The history of climate change and related driving mechanisms of the Gonghe Basin, northeastern Qinghai-Tibetan Plateau, China, was reconstructed in the Holocene epoch, based on the comprehensive analysis of multi-proxies consisting of magnetic susceptibility, grain size, and geochemical elements from eolian and peat deposits at different altitudes. The results indicate that Holocene climate change at different altitudes is both consistent and different: a synchronous record of an increased warm–humid phase (10.0–8.5 ka) and a cold phase around 8.2 ka in the Early Holocene; an optimal warm–humid condition in marginal mountains of the Gonghe Basin in the Mid-Holocene; and a gradual decline in temperature and humidity in the Late Holocene. The Gonghe Basin interior in the Mid-Holocene was relatively arid, with increased moisture in the Late Holocene. On this basis, we compared our results to the paleoclimatic record in the low-latitude Asian monsoonal region, which indicates that, in addition to the Asian summer monsoonal strength having influenced regional climate change, the upward and subsidence motion of airflow over the Qinghai-Tibetan Plateau induced by topographic conditions, evaporation, and the feedback effect by the substrate was also influential. The latter was especially important for spatial–temporal differences in Middle and Late Holocene climatic changes at different altitudes.  相似文献   

17.
Assemblages of ichthyofauna of shallow inshore habitats along Californía’s central coast are described in terms of species composition, abundance, and life-style categories. A total of 22,334 fishes from 65 species and 27 families was collected with otter trawls at six sites in the main channel and tidal creeks of Elkhorn Slough, a tidal embayment and seasonal estuary, and two nearshore ocean stations in Monterey Bay during 44 months between August 1974 and June 1980. Greater than 90% of the catch comprised 10 species. The four dominant species,Cymatogaster aggregata, Leptocottus armatus, Phanerodon furcatus, andEmbiotoca jacksoni, occurred during most or all seasons and were classified as residents or partial residents. Several abundant species were marine immigrants that seasonally use the slough as spawning and nursery grounds; this resulted in higher abundance and species richness during summer. Species collected during winter largely were slough residents. Species compsosition and richness varied with distance from the slough entrance. The ocean assemblage was most different, and its similarity to other stations decreased progressively with distance inland and into the tidal creeks. During our study, 5,074 fishes were collected by beach seine in Bennett Slough, a remote shallow marsh basin adjacent to the entrance of Elkhorn Slough. Species richness was relatively low and three euryhaline species accounted for >80% of the total catch. The species assemblage was most similar to those at the tidal creek and most shallow stations of Elkhorn Slough. Resident species numerically dominated assemblages in Bennett Slough and the most inland areas of Elkhorn Slough. The high relative abundance of marine-related fishes (classified as marine, marine immigrant, and partial resident), entering Elkhorn Slough early in life or as spawning adults indicates the importance of this habitat to nearshore fish assemblages.  相似文献   

18.
Corbicula manilensis was found in the gizzards of 24 ducks of 5 species taken from the James River, Virginia, between 1973 and 1976. Percent average volume in these species ranged from trace to 6%. This is the first known occurrence of this exotic clam in the food of duck in Chesapeake Bay. A total of 135 other food items was identified from the 116 gizzards of 9 species that were examined. Food that predominated includedCyperus spp.,Leersia oryzoides, Polygonum spp., andZea mays. The great diversity of food consumed in this fresh tidal section of the James River indicates the high value of these wetlands to waterfowl. *** DIRECT SUPPORT *** A01BY015 00008  相似文献   

19.
The increased rate of annual temperature in the Qinghai-Tibetan Plateau exceeded all other areas of the same latitude in recent decades. The influence of the warming climate on the alpine ecosystem of the plateau was distinct. An analysis of alpine vegetation under changes in climatic conditions was conducted in this study. This was done through an examination of vegetation greenness and its relationship with climate variability using the Advanced Very High Resolution Radiometer satellite imagery and climate datasets. Vegetation in the plateau experienced a positive trend in greenness, with 18.0 % of the vegetated areas exhibiting significantly positive trends, which were primarily located in the eastern and southwestern parts of the plateau. In grasslands, 25.8 % of meadows and 14.1 % of steppes exhibited significant upward trends. In contrast, the broadleaf forests experienced a trend of degradation. Temperature, particularly summer temperature, was the primary factor promoting the vegetation growth in the plateau. The wetter and warmer climate in the east contributed to the favorable conditions for vegetation. The alpine meadow was mostly sensitive to temperature, while the steppes were sensitive to both temperature and precipitation. Although a warming climate was expected to be beneficial to vegetation growth in the alpine region, the rising temperature coupled with reduced precipitation in the south did not favor vegetation growth due to low humidity and poor soil moisture conditions.  相似文献   

20.
Heavy metals are governed by parent material of soils and influenced by the soil physicochemical properties and soil and crop management practices. This paper evaluates total heavy metal concentrations in rainfed soils under diverse management practices of tropical India. Vertisols (clayey soils with high shrink/swell capacity) had the highest concentrations of heavy metals. However, chromium (Cr) content was above the threshold value in Aridisol [calcium carbonate (CaCO3)]-containing soils of the arid environments with subsurface horizon development. Concentration increased at lower depths (>30 cm). Basaltic soils showed higher concentrations of nickel (Ni), copper (Cu) and manganese (Mn). Cadmium (Cd), cobalt (Co), Cu and Mn concentrations were higher in soils cultivated to cotton, whereas Cr concentration was above the threshold level of 110 mg kg?1 in food crop cultivated soils. As the specific soil surface is closely related to clay content and clay type, soil’s ability to retain heavy metals is more closely tied to the specific surface than to the soil cation exchange capacity. Higher positive correlations were found between heavy metal concentrations and clay content [Cd(r = 0.85; p ≤ 0.01); Co (r = 0.88; p ≤ 0.05); Ni (r = 0.87; p ≤ 0.01); Co (r = 0.81; p ≤ 0.05); Zn (r = 0.49; p ≤ 0.01); Cr (r = 0.80; p ≤ 0.05); Mn (r = 0.79; p ≤ 0.01)]. The amounts of nitrogen–phosphorus–potassium applied showed a positive correlation with Co and Ni (r = 0.62; p ≤ 0.05). As several soils used for growing food crops are high in Ni, Cr and Mn, the flow of these metals in soil–plant–livestock/human chain needs further attention.  相似文献   

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