Home About us Contact | |||
Rainy Season (rainy + season)
Kinds of Rainy Season Selected AbstractsImpact of the Cropping Systems of a Minor Dry Season on the Growth, Yields and Nitrogen Uptake of Maize (Zea mays L) Grown in the Humid Tropics during the Major Rainy SeasonJOURNAL OF AGRONOMY AND CROP SCIENCE, Issue 6 2003U. R. Sangakkara Abstract A field study evaluated the residual effect of a cropping system in two minor (dry) seasons on the productivity pattern and nitrogen utilization of a maize crop grown in the subsequent major (wet) seasons. The cropping systems established in the minor seasons, where evaporation exceeds rainfall, were either monocultures of maize (Zea mays L), or maize intercropped with either common bean (Phaseolus vulgaris L) or sunhemp (Crotolaria juncea L). In addition, monocultures of two green manures, namely sunhemp (Crotolaria juncea) or Tithonia (Tithonia diversifolia), were established. The residues of maize and beans and the green manures were incorporated at the end of the minor season; at the onset of rains in the major season, maize crops were established on the same plots. Germination of maize was not affected by the previous cropping system. In contrast, crop growth and yields of maize and nitrogen utilization were affected by the previous cropping system. Optimum growth and highest yields were procured in maize that was grown after a green manure crop. Similarly, although the yields were high, the planting of a green manure crop reduced nitrogen utilization by maize in the major season, thereby indicating its potential contribution to sustainability, due to its lower mining of soil nitrogen. On the basis of the results of this two-year study, the impact of cropping systems in minor seasons on the productivity of maize, a very important highland cereal in the tropics, grown under rain-fed conditions in a major season, is presented. [source] Size traits and site conditions determine changes in seed bank structure caused by grazing exclusion in semiarid annual plant communitiesECOGRAPHY, Issue 1 2006Yagil Osem 1. Contrasting patterns of change in the seed bank of natural grasslands are frequently found in response to grazing by domestic herbivores. Here, we studied the hypotheses that a) patterns of change in seed bank density and composition in response to grazing depend on spatial variation in resource availability and productivity, and b) that variation among species in patterns of seed bank response to grazing is linked to differences in species size traits (i.e. size of plant, dispersal unit and seed). 2. Effects of sheep grazing exclusion on the seed bank were followed during five years in a semiarid Mediterranean annual plant community in Israel. Seed bank density and composition were measured in autumn, before the rainy season, inside and outside fenced exclosures in four neighboring topographic sites differing in vegetation characteristics, soil resources and primary productivity: Wadi (dry stream terraces, high productive site), Hilltop, South- and North-facing slopes (less productive sites). 3. Topographic sites differed in seed density (range ca 2500,18000 seed m,2) and in seed bank response to grazing exclusion. Fencing increased seed density by 78, 51 and 18% in the Wadi, South- and North-facing slopes, respectively, but had no effect in the Hilltop. At the species level, grazing exclusion interacted with site conditions in determining species seed bank density, with larger or opposite changes in the high productive Wadi compared to the other less productive sites. 4. Changes in seed bank structure after grazing exclusion were strongly related to species size traits. Grazing exclusion favored species with large size traits in all sites, while seed density of tiny species decreased strongly in the high productive Wadi. Species with medium and small size traits showed lesser or no responses. 5. The size of plants, dispersal units and seeds were strongly correlated to each other, thus confounding the evaluation of the relative importance of each trait in the response of species to grazing and site conditions. We propose that the relative importance of plant size vs seed size in the response to grazing changes with productivity level. [source] Permeability of receptive fig fruits and its effects on the re-emergence behaviour of pollinatorsECOLOGICAL ENTOMOLOGY, Issue 2 2010HU HAO-YUAN 1. Figs and pollinating fig wasps provide a model system for studying mutualism. The permeability of the syconium changes during receptivity or between seasons, which may affect the behaviour of pollinators. Fig fruits are permeable during receptivity, and in some species, pollinators can enter and re-emerge after oviposition/pollination. We studied the relationship between fig permeability and pollinator re-emergence behaviour with a functional dioecious fig, Ficus hispida and the obligate pollinator Ceratosolen solmsi marchali. 2. The relationship reflects the interaction of figs and pollinators in the mutualism and also the conflicts of interests between the two partners: figs benefit from the enclosed fig fruits which have low permeability, but pollinators benefit from their re-emergence behaviour, which requires high fig permeability. 3. The results showed that at the end of receptivity, the permeability of fig fruits lowered rapidly with changes to the ostiole structures, and re-emergence rate was low, with more re-emerging pollinators trapped in the ostiolar bracts. Our results also showed that in the rainy season, the length of receptivity was shorter and fig permeability was lower. The re-emergence rates were also lower than those in the dry season. The results elucidated that figs' interests dominated in the conflicts between fig and pollinating wasp. 4. Based on a new criteria which employed the classification of pollinators found dead in the ostiolar bracts and which involved a survey of 6 monoecious and 12 dioecious fig species, we found that re-emergence behaviour was prevalent among fig species, and was more prevalent in functional dioecious figs than monoecious ones. [source] Dung beetles in a Central Amazonian rainforest and their ecological role as secondary seed dispersersECOLOGICAL ENTOMOLOGY, Issue 3 2002Ellen Andresen Abstract 1. The role of several factors that affect the composition of the dung beetle assemblages in an Amazonian rainforest was quantified, together with the effect of these factors on the role that dung beetles play as secondary seed dispersers. 2. A total of 61 dung beetle species was captured during 3360 h of trapping. During nocturnal trapping periods, more dung beetles, of larger mean size, and more species were captured per trap than during diurnal trapping periods. 3. During the rainy season, more dung beetle species were captured per trap than during the dry season, but the number of individuals and their mean size did not vary between seasons. 4. Bait size had a significant effect on the mean number of beetles and mean number of species but not on mean beetle size. As bait size increased from 5, 10, 25, to 50 g, more beetles and more species were captured per trap. 5. Between 6 and 73% of plastic beads, used as seed mimics, were buried by dung beetles at depths that ranged from 0.5 to 7 cm. Both the proportion of beads buried and burial depth decreased with increasing bead size, and increased with increasing amounts of dung surrounding each bead (5, 10, and 25 g). 6. The proportion of buried seeds for three species varying in size between 5 and 27 mm, increased with increasing dung beetle size, using beetles of seven sizes, varying between 10 and 25 mm. 7. Seeds surrounded by dung were buried more often and more deeply when placed on the forest floor during the late afternoon than when placed during the early morning. Seeds were also buried more often when placed on the forest floor during the rainy season than when placed during the dry season, but season had no effect on burial depth. 8. Forests in Central Amazonia hold a rich dung beetle community that plays an active role in secondary seed dispersal, and consequently in plant regeneration. The interaction between seeds and beetles is complex because it is affected by many factors. [source] Hydrological connectivity in coastal inland systems: lessons from a Neotropical fish metacommunityECOLOGY OF FRESHWATER FISH, Issue 1 2010P. H. M. De Macedo-Soares de Macedo-Soares PHM, Petry AC, Farjalla VF, Caramaschi EP. Hydrological connectivity in coastal inland systems: lessons from a Neotropical fish metacommunity. Ecology of Freshwater Fish 2010: 19: 7,18. © 2009 John Wiley & Sons A/S Abstract,,, We assessed the influence of hydrological connectivity in structuring fish communities through seasonal samplings of environmental variables and fishes in a coastal lagoon and associated pools in the Restinga de Jurubatiba National Park, Brazil. Community structure attributes such as species richness, numerical density and biomass, Shannon,Wiener diversity index and evenness were compared between periods of the lowest and highest hydrological connectivity, while the environmental gradient and fish zonation were explored through ordination techniques. The greater hydrological connectivity established in the rainy season promoted the homogenisation of most environmental variables and fish species, which differed markedly from the arrangement observed in the dry season. Despite variation in fish species composition, community attributes showed non-significant differences between the dry and rainy seasons. The patterns of composition and numerical density in pools were strongly influenced by local factors, especially salinity, dissolved oxygen, total phosphorous concentration and water colour in the dry season, in addition to total nitrogen concentration and depth in the rainy season. Comparable to the role played by flood pulses in river-floodplain systems, the hydrological connectivity in these tropical coastal waterbodies seems to strongly influence fish community structure, and, therefore to determine regional biodiversity. [source] Seasonal distribution and species composition of daytime biting mosquitoesENTOMOLOGICAL RESEARCH, Issue 2 2009Waseem AKRAM Abstract Adults and immatures of Aedes mosquito populations were collected at temperatures between 40 and 44°C (summer), while larvae were collected at 0°C (winter). Major mosquito activities were observed from February to mid-December at various collection sites that yielded high populations of Aedes spp. from May to September, and high populations of Culex spp. and Anopheles spp. from March to September. In June to July, mosquito activity was suspended because the relative humidity was high (70%); a result of the monsoon rains. In August, with temperature ranging from 38 to 42°C, the populations of Culex, Anopheles and Aedes began to increase (36.8, 32.1 and 26.3%, respectively). Population estimates (through standard prototype Centers for Disease Control (CDC) and Biogents (BG)-sentinel) and species composition of Aedes in forest habitats indicated a rapid increase in the populations of Ae. albopictus (52.3%), Ae. aegypti (19.1%) and Ae. vittatus (28.5%) following the rainy season in July. Areas positive for Ae. albopictus had identical population levels and distribution ranges of Ae. vittatus, however, there were no Ae. aegypti in Ae. albopictus areas from August to September. The population level, seasonal distribution, habitat and areas of adult activity marked by global positioning system (GPS) coordinates are being used for reference and for species composition data of Anopheles spp. (2), Culex spp. (10) and Aedes spp. (5) in addition to associated temperature, relative humidity and physico-chemical factors of larval habitat. Global meteorological changes have caused an expansion of the active period, leading to the mosquito's possibility of being a vector of disease increasing, resulting in the spread of dengue fever. [source] Assessing the impact of pollution on the Japaratuba river in Brazil using the Drosophila wing spot testENVIRONMENTAL AND MOLECULAR MUTAGENESIS, Issue 2 2007Silmara de Moraes Pantaleão Abstract The Drosophila melanogaster somatic mutation and recombination test (SMART) was used to assess the genotoxicity of surface (S) and bottom (B) water and sediment samples collected from Sites 1 and 2 on the Japaratuba River (Sergipe, Brazil), an area impacted by a petrochemical industrial complex that indirectly discharges treated effluent (produced water) into the river. The genotoxicity tests were performed in standard (ST) cross and high bioactivation (HB) cross flies and were conducted on samples taken in March (dry season) and in July (rainy season) of 2003. Mutant spot frequencies found in treatments with unprocessed water and sediment samples from the test sites were compared with the frequencies observed for similar samples taken from a clean reference site (the Jacarecica River in Sergipe, Brazil) and those of negative (ultrapure water) controls. While samples from the Japaratuba River generally produced greater responses than those from the Jacarecica River, positive responses were detected for both the test and reference site samples. All the water samples collected in March 2003 were genotoxic. In July 2003, the positive responses were restricted to water samples collected from Sites 1 B and 2 S in the ST cross. The genotoxicity of the water samples was due to mitotic recombination, and the samples produced similar genotoxic responses in ST and HB flies. The spot frequencies found in the July water samples were considerably lower than those for the March water samples, suggesting a seasonal effect. The only sediment samples that were genotoxic were from Site 1 (March and July) and from the Jacarecica River (March). The genotoxins in these samples produced both somatic mutation (limited to the Site 1 sample in HB flies) and recombination. The results of this study indicate that samples from both the Japaratuba and Jacarecica Rivers were genotoxic, with the most consistently positive responses detected with Site 1 samples, the site closest to the putative pollution source. Environ. Mol. Mutagen. 48:, 2007. © 2007 Wiley-Liss, Inc. [source] Grassland communities on a Sahelian peneplain in Burkina FasoFEDDES REPERTORIUM, Issue 1-2 2008J. V. Müller Dr. A detailed phytosociological analysis of grassland communities of a Sahelian peneplain in Burkina Faso (West Africa) is presented. The floristic structure of the vegetation was documented with 113 relevés, which were classified manually and in addition ordinated to characterize main floristic gradients. The topographical situation from high-lying areas of the peneplain with erosion of material to low-lying areas with accumulation of material turned out to be the most important differentiating factor in the data set. All grassland communities are dominated by annual grasses and have large distribution ranges. They colonize sandy-silty, loamy to clayey soils and can be water-saturated or repeatedly inundated during the rainy season, while dry, non-inundated habitats are also colonized. Many grasses are valuable fodder plants and are appreciated by livestock , the peneplain is economically highly important as a grazing ground. Whereas exozoochorous annual species are constantly present companions, perennial herbaceous species are almost completely missing. Stands were grouped into one alliance Panico laeti-Echinochloion colonae and only two phytocoenoses: a rankless Schoenefeldia gracilis -community (with two subcommunities: a typical subcommunity with a large ecological amplitude from sandy-silty to loamy soils, and an Aristida funiculata -subcommunity on sandy, dry, non-inundated soils) and Eragrostietum pilosae. The Eragrostietum pilosae grows in the low-lying areas of the peneplain and connects between communities of seasonally inundated lakes and the grasslands on the upper parts of the pene- plain. Following the topography, the two plant communities form a large transition (zonation complex). It is widespread across the study area and contains the diagnostic species of both plant communities. The plant communities are compared with other Sahelian grass-dominated plant communities, and with plant communities from the Sahara and the (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) Grasfluren einer sahelischen Rumpffläche in Burkina Faso In diesem Beitrag wird eine detaillierte pflanzensoziologische Analyse der Grasfluren einer sahelischen Rumpffläche in Burkina Faso (Westafrika) präsentiert. Die floristische Struktur der Vegetation wurde mit 113 pflanzensoziologischen Aufnahmen dokumentiert. Diese wurden zunächst manuell klassifiziert und anschließend einem Ordinationsverfahren unterzogen, um die wichtigsten Gradienten im floristischen Datensatz aufzuzeigen. Die topographische Geländesituation der Rumpffläche, beginnend mit hochgelegenen Bereichen mit Materialaustrag bis in die Niederungen mit Materialeintrag, wurde als wichtigster differenzierender Faktor des floristischen Datensatzes identifiziert. Alle untersuchten Pflanzengesellschaften der Grasfluren haben große Verbreitungsgebiete und werden von annuellen Gräsern dominiert. Sie sind auf sandig-schluffigen, lehmigen bis tonigen Böden zu finden. Sie können in der Regenzeit entweder wassergesättigt oder wiederholt überflutet sein. Die Grasfluren sind auch auf trockenen, nicht überfluteten Standorten nachgewiesen. Viele der Grasarten sind vom Weidevieh geschätzte Futterpflanzen , die Rumpffläche dient als wirtschaftlich bedeutendes Weideland. Exozoochore, einjährige Arten sind hochstet als Begleiter vorhanden. Hingegen fehlen mehrjährige, krautige Arten fast vollständig. Die Bestände konnten einem pflanzensoziologischen Verband Panico laeti-Echinochloion colonae und zwei Pflanzengesellschaften zugeordnet werden. Die ranglose Schoenefeldia gracilis -Gesellschaft kommt in zwei Untereinheiten vor: eine typische Untereinheit mit breiter ökologischer Amplitude von sandig-schluffigen bis lehmigen Böden, und eine Aristida funiculata Untereinheit auf trockenen, sandigen, nicht überfluteten Böden. Das Eragrostietum pilosae kommt in den tiefliegenden Bereichen Sudanian zone. A close floristic relationship of Sahelian grassland communities with Saharan vegetation could be shown. der Rumpffläche vor und vermittelt zwischen den Pflanzengesellschaften temporärer Seen und den Grasfluren der hochgelegenen Bereiche der Rumpffläche. Der Geländesituation folgend bilden beide Pflanzengesellschaften einen breiten Übergangsbereich (Zonationskomplex). Dieser Übergangsbereich ist im Untersuchungsgebiet weit verbreitet und enthält diagnostische Arten beider Pflanzengesellschaften. Die beschriebenen Einheiten werden mit anderen grasdominierten Pflanzengesellschaften des Sahels sowie der Sahara und der Sudanzone verglichen. Eine enge floristische Beziehung der sahelischen Grasfluren mit Vegetationseinheiten der Sahara wird aufgezeigt. [source] Impact of the fish Garra on the ecology of reservoirs and the occurrence of Microcystis blooms in semi-arid tropical highlands: an experimental assessment using enclosuresFRESHWATER BIOLOGY, Issue 8 2009TADESSE DEJENIE Summary 1.,Many man-made reservoirs in the semi-arid highlands of Northern Ethiopia (Tigray) are characterised by the occurrence of intensive blooms of cyanobacteria and a dominance of small riverine fishes belonging to the genus Garra. 2.,We carried out enclosure experiments to test for the effect of these small fish on abiotic characteristics, phytoplankton biomass and zooplankton community structure in the pelagic of two reservoirs (Gereb Awso and Tsinkanet). Two experiments were carried out in each of the reservoirs, one at the end of the rainy season (highest water level) and one at the end of the dry season (lowest water level). 3.,The presence of Garra in general increased the amount of suspended matter, nutrient concentrations (total nitrogen and total phosphorus), phytoplankton and Microcystis biomass (including the proportion of Microcystis in the phytoplankton community), and reduced water transparency. The positive effect of the presence of Garra on nutrient concentrations and phytoplankton productivity indicate that Garra has the potential to affect food web functioning indirectly through bottom-up effects, by enhancing nutrient concentrations through sediment resuspension and excretion of nutrients. Indeed, population densities of the cladoceran zooplankton taxa Ceriodaphnia and Diaphanosoma also showed an overall increase in enclosures with Garra. 4.,However, our data also provide some evidence for a potential of Garra to exert top-down control on large bodied daphnids (Daphnia carinata, D. barbata), although such effect varied among experiments. The limited capability of Garra to control zooplankton communities mainly reflects the low efficiency of these small, riverine and benthos-oriented fish in foraging on zooplankton and suggests the existence of an unoccupied niche for zooplanktivorous fish in the majority of the reservoirs. 5.,Although the main effects of Garra on the pelagic food web seemed to be mediated by bottom-up mechanisms, our results also indicate that one of the key variables, the relative abundance of Microcystis, was impacted by Daphnia -mediated trophic cascade effects. [source] Phytoplankton production and growth rate in Lake Tanganyika: evidence of a decline in primary productivity in recent decadesFRESHWATER BIOLOGY, Issue 11 2007STEPHANE STENUITE Summary 1. This study focused on phytoplankton production in Lake Tanganyika. We provide new estimates of daily and annual primary production, as well as growth rates of phytoplankton, and we compare them with values published in former studies. 2. Chlorophyll- a (chl- a) in the mixed layer ranged from 5 to 120 mg chl- a m,2 and varied significantly between rainy and dry seasons. Particulate organic carbon concentrations were significantly higher in the south basin (with 196 and 166 mg C m,3 in the dry and the rainy season, respectively) than in the north basin (112 and 109 mg C m,3, respectively). 3. Carbon : phosphorus (C : P) ratios varied according to season. Phosphorus limitation seemed to occur more frequently than nitrogen limitation, especially during the rainy season. Severe P deficiencies were rare. 4. Measured particulate daily primary production ranged from 110 to 1410 mg C m,2 day,1; seasonal contrasts were well marked in the north basin, but less in the south basin, where primary production peaks occurred also in the rainy season. Estimates of annual primary production, based on daily primary production calculated from chl- a and water transparency, gave values lower than those reported in previous studies. Picophytoplankton accounted on average for 56% of total particulate production in the south basin during the wet season of 2003. 5. Phytoplankton growth rates, calculated from primary production, ranged from 0.055 to 0.282 day,1; these are lower than previously published values for Lake Tanganyika. [source] Stem hydraulics mediates leaf water status, carbon gain, nutrient use efficiencies and plant growth rates across dipterocarp speciesFUNCTIONAL ECOLOGY, Issue 4 2009Jiao-Lin Zhang Summary 1Stem vascular system strongly influences structure and functioning of leaves, life-history, and distribution of plants. Xylem structure and hydraulic conductivity of branches, leaf functional traits, and growth rates in 17 dipterocarp species in a mature plantation stand were examined to explore the functional relationships between these traits. 2Maximum hydraulic conductivity on the bases of both sapwood and leaf area (kL) were positively correlated with midday leaf water potential in the rainy season, stomatal conductance, area-based maximum photosynthetic rate, photosynthetic N (PNUE) and P use efficiencies (PPUE), and mean height and diameter growth rates. Moreover, kL was positively correlated with mesophyll thickness and mass-based maximum photosynthetic rate. These results revealed the mechanistic linkage between stem hydraulics and leaf photosynthesis through nutrient use efficiency and mesophyll development of leaves. 3A detrended correspondence analysis (DCA) using 37 traits showed that the traits related to stem hydraulics and leaf carbon gain were loaded on the first axis whereas traits related to light harvesting were loaded on the second axis, indicating that light harvesting is a distinct ecological axis for tropical canopy plants. The DCA also revealed a trade-off between photosynthetic water use efficiency and hydraulic conductivity along with PNUE and PPUE. 4The congeneric species were scattered fairly close together on the DCA diagram, indicating that the linkages between stem hydraulics, leaf functional traits, and plant growth rates are phylogenetically conserved. 5These results suggest that stem hydraulics mediates leaf water status, carbon gain, nutrient use efficiencies, and growth rates across the dipterocarp species. The wide variation in functional traits and growth rates among these dipterocarp species along with the trade-offs mentioned above provide a possible explanation for their co-existence in tropical forest communities. [source] Defoliation alters water uptake by deep and shallow roots of Prosopis velutina (Velvet Mesquite)FUNCTIONAL ECOLOGY, Issue 3 2003K. A. Snyder Summary 1Prosopis velutina Woot. (Velvet Mesquite) at a site with limited groundwater availability derived a greater percentage of water from shallow soil at the onset of the summer rainy season than did trees at a site with greater availability of groundwater. Predawn leaf water potentials (,pd) were not a strong indicator of shallow water use for this species with roots in multiple soil layers. 2We experimentally defoliated P. velutina plants to determine if reduced-canopy photosynthesis would alter vertical patterns of root activity. After natural rain events, hydrogen isotope ratios of xylem sap indicated that defoliated P. velutina took up a greater percentage of its water from shallow soils than did undefoliated plants. 3Irrigation with deuterium-labelled water further demonstrated that undefoliated plants were able to use shallow soil water. Defoliation appeared to affect the ability of trees to use deep-water sources. 4Reduced carbon assimilation limited water uptake from deep soil layers. These data highlight that there are internal physiological controls on carbon allocation that may limit water uptake from different soil layers. During periods of high vapour pressure deficit or soil drought, when leaf gas exchange and carbon assimilation decline, this may create positive feedbacks where plants are unable to forage for deep water due to carbon limitations. [source] Embryo of an annual fish (Austrolebias charrua) in the last dormancy stage, diapause IIIGENESIS: THE JOURNAL OF GENETICS AND DEVELOPMENT, Issue 1 2009Article first published online: 22 JAN 200 Embryo of an annual fish (Austrolebias charrua) in the last dormancy stage, diapause III. The embryo, surrounded by a transparent vitelline envelope, is in the pre-hatching stage. A prominent eye and part of the pigmented body and tail are apparent. Why annual fishes? Annual fishes (Order Cyprinodontiformes) are a special kind of teleost, found in Africa and South America, with developmental strategies closely related to their life cycle. These fishes inhabit temporary pools that undergo drying during summer, when all adults die. The embryos remain buried in the bottom mud and are resistant to desiccation. In the subsequent rainy season they hatch a few hours after the pool is flooded and a new reproductive cycle begins. This developmental pattern is characterized by the presence of a unique stage between cleavage and embryogenesis, dispersion-aggregation of blastomeres and because the embryos show reversible developmental arrests (diapauses) at different stages. Annual fish embryos are transparent, large, hardy and easy to maintain in the laboratory. Adults show continuous production of eggs and juveniles reach sexual maturity a few weeks after hatching (an unusual condition in fishes). Their particular developmental features confer unique opportunities for research on cell behavior during early development, the effect of environmental factors on development, the regulation of diapauses and the mechanisms involved in sex determination, among others topics. Image provided by Nibia Berois, Universidad de la República, Montevideo, Uruguay. [source] Nutrient constraints to tropical agroecosystem productivity in long-term degrading soilsGLOBAL CHANGE BIOLOGY, Issue 12 2008SOLOMON NGOZE Abstract Soil degradation is one of the most serious threats to sustainable crop production in many tropical agroecosystems where extensification rather than intensification of agriculture has occurred. In the highlands of western Kenya, we investigated soil nitrogen (N) and phosphorus (P) constraints to maize productivity across a cultivation chronosequence in which land-use history ranged from recent conversion from primary forest to 100 years in continuous cropping. Nutrient treatments included a range of N and P fertilizer rates applied separately and in combination. Maize productivity without fertilizer was used as a proxy measure for indigenous soil fertility (ISF). Soil pools of mineral nitrogen, strongly bound P and plant-available P decreased by 82%, 31% and 36%, and P adsorption capacity increased by 51% after 100 years of continuous cultivation. For the long rainy season (LR), grain yield without fertilizer declined rapidly as cultivation age increased from 0 to 25 years and then gradually declined to a yield of 1.6 Mg ha,1, which was maintained as time under cultivation increased from 60 to 100 years. LR grain yield in the old conversions was only 24% of the average young conversion grain yield (6.4 Mg ha,1). Application of either N or P alone significantly increased grain yield in both the LR and short rainy (SR) seasons, but only application of 120 kg N ha,1 on the old conversion increased yield by >1 Mg ha,1. In both SR and LR, there was a greater average yield increment response to N and P when applied together (ranging from 1 to 3.8 Mg ha,1 for the LR), with the greatest responses on the old conversions. The benefit,cost ratio (BCR) for applying 120 kg N ha,1 alone was <1 except on the old conversions, while BCRs were>1 for applying 25 kg P ha,1 alone at all levels of conversion for both seasons. Application of both N (120 kg N ha,1) and P (25 kg P ha,1) on the old conversions resulted in the greatest BCRs. This study clearly indicates that maize productivity responses to N and P fertilizer are significantly affected by the age of cultivation and its influence on ISF, but that loss of productivity can be restored rapidly when these limiting nutrients are applied. Management strategies should consider ISF and economic factors to determine optimal N and P input requirements for achieving and sustaining profitable crop production on degraded soils. [source] Seasonal changes in radiation and evaporation implied from the diurnal distribution of rainfall in the Lower MekongHYDROLOGICAL PROCESSES, Issue 9 2008Kumiko Tsujimoto Abstract Solar radiation is an important input to many empirical equations for estimating evaporation, which in turn plays an important role in the hydrologic cycle in the Lower Mekong River Basin due to the high evaporation potential of the tropical monsoon climate. Few proper meteorological data exist for the Lower Mekong River Basin, however, and the region's meteorological conditions, including seasonal variation in radiation and evaporation, have not been clarified. In this study, ground-based hourly hydrometeorological data were collected at three observation stations located in different land-use types (urban district, paddy area, and lake) in the Lower Mekong River Basin. These data were analysed to investigate the seasonal variation in radiation and evaporation related to the diurnal distribution of rainfall. Contrary to common expectations, our results showed that rainy and dry seasons had nearly the same amount of solar radiation in the Lower Mekong River Basin because (1) rainy seasons had a relatively larger amount of extraterrestrial radiation; (2) no rain fell on nearly half of the days during rainy seasons; and (3) the amount of solar radiation on rainy days reached 88% of that on non-rainy days. The third factor was attributed to the high frequency of evening rainfall. Furthermore, this rainfall,radiation relationship meant that rainy seasons had a large amount of net radiation due to the low reduction ratio of solar radiation and an increase in long-wave incoming radiation. Accordingly, rainy seasons had a high evaporation potential. Moreover, for the rain-fed rice paddies that prevail in this region, sufficient radiation during the rainy season would be a great advantage for rice growing. Copyright © 2008 John Wiley & Sons, Ltd. [source] Water fluxes at a fluctuating water table and groundwater contributions to wheat water use in the lower Yellow River flood plain, ChinaHYDROLOGICAL PROCESSES, Issue 6 2007Jianfeng Yang Abstract Capillary upflow from and deep percolation to a water table may be important in crop water supply in irrigated areas of the lower Yellow River flood plain, north China. These fluxes at the water table and the variations of the capillary upflow in relation to crop evapotranspiration need to be investigated to quantify the effect of a water table on soil water balance and to improve agricultural water management. A large weighing lysimeter was used to determine daily crop evapotranspiration, daily capillary upflow from and daily percolation to a fluctuating water table during a rotation period with wheat growing in a dry season and maize in a rainy season. The water table depth varied in the range 0·7,2·3 m during the maize growth period and 1·6,2·4 m during the wheat growth period. Experimental results showed that the capillary upflow and the percolation were significant components of the soil water balance. Three distinctly different phases for the water fluxes at the water table were observed through the rotation period: water downward period, the period of no or small water fluxes, and water upward period. It implied that the temporal pattern of these water fluxes at the water table was intimately associated with the temporal distribution of rainfall through the rotation period. An empirical equation was determined to estimate the capillary upflow in relation to wheat evapotranspiration and root zone soil water content for local irrigation scheduling. Coupled with the FAO-Penman,Monteith equation, the equation offers a fast and low cost solution to assess the effect of capillary upflow from a water table on wheat water use. Copyright © 2007 John Wiley & Sons, Ltd. [source] Hydrological and biogeochemical processes in a changing Amazon: results from small watershed studies and the large-scale biosphere-atmosphere experimentHYDROLOGICAL PROCESSES, Issue 12 2006Christopher Neill Abstract The Amazon Basin is the world's largest tropical forest region and one where rapid human changes to land cover have the potential to cause significant changes to hydrological and biogeochemical processes. The Large-Scale Biosphere-Atmosphere Experiment in Amazonia (LBA) is a multidisciplinary, multinational research program led by Brazil. The goal of LBA is to understand how the Amazon Basin functions as a regional entity in the earth system and how these functions are changing as a result of ongoing human activity. This compilation of nine papers focuses on a central LBA question in the area of nutrient dynamics and surface water chemistry,how do changes in land use alter fluxes of dissolved and particulate materials from uplands across riparian zones and down the channels of river corridors? These papers cover work conducted in small watersheds on a wide range of topics within the spirit and geographical focus area of LBA: water balance and runoff generation, nutrient transformations in riparian zones and stream channels, carbon fluxes in water moving from land to water and the influence of soils on flowpath structure and stream chemistry. Important new insights can be gained from these and other studies. Forest clearing for pastures results in a decrease in soil hydraulic conductivity that forces water into surficial flowpaths throughout most of the rainy season across wide regions of the Amazon. Riparian zones along small forest streams appear to be very effective in removing nitrate arriving from the uplands, while forest streams take up nitrate at very low rates, allowing them to travel downstream for long distances. Although substantial, the contribution of dissolved organic C (DOC) to the carbon flux from forests to streams appears to be lower than the flux of dissolved inorganic C that is subsequently outgassed as CO2. Remaining key challenges within LBA will be to synthesize existing data sets on river networks, soils, climate, land use and planned infrastructure for the Amazon to develop models capable of predicting hydrologic and biogeochemical fluxes at a variety of scales relevant to the development of strategies for sustainable management of the Amazon's remarkable forest, soil and freshwater resources. Copyright © 2006 John Wiley & Sons, Ltd. [source] Hydrological impacts of forest conversion to agriculture in a large river basin in northeast ThailandHYDROLOGICAL PROCESSES, Issue 14 2001J. Wilk Abstract Small-scale experiments have demonstrated that forest clearance leads to an increase in water yield, but it is unclear if this result holds for larger river basins (>1000 km2). No widespread changes in rainfall totals and patterns were found in the 12 100 km2 Nam Pong catchment in northeast Thailand between 1957 and 1995, despite a reduction in the area classified as forest from 80% to 27% in the last three decades. Neither were any detectable changes found in any other water balance terms nor in the dynamics of the recession at the end of the rainy season. When a hydrological model calibrated against data from the period before the deforestation was applied for the last years of the study period (1987,1995), runoff generation was however underestimated by approximately 15%, indicating increased runoff generation after the deforestation. However, this was mainly due to the hydrological response during one single year in the first period, when the Q/P ratio was very low. When excluding this year, neither analysis based on the hydrological model could reveal any significant change of the water balance due to the deforestation. More detailed land-use analysis revealed that shade trees were left on agricultural plots as well as a number of abandoned areas where secondary growth can be expected, which is believed to account for the results. Copyright © 2001 John Wiley & Sons, Ltd. [source] Factors explaining the abundance of rodents in the city of Luang Prabang, Lao PDR, as revealed by field and household surveysINTEGRATIVE ZOOLOGY (ELECTRONIC), Issue 1 2008Prasartthong PROMKERD Abstract A field and a household survey, the latter of which included inspections and interviews with the residents of a total of 1370 properties, were conducted in 2004 in 30 villages of the city of Luang Prabang, Lao PDR, in order to assess the degree of rodent infestation and to identify potential factors influencing infestations. Roof rats, Rattus rattus, and the Polynesian rat, Rattus exulans, were the only rodents found in the city, and trapping results showed a clear dominance of roof rats (80,90% of all individuals). Measurements of rodent activity using tracking patches correlated positively with the trapping data, and revealed a significantly higher degree of rat infestation during the rainy season (September) than during the dry season (November). If households in the vicinity of the sampling locations were considered, villagers' accounts of indoor rodent infestations recorded during the household survey correlated positively with measurements of rodent activity. At least every second household reported indoor infestations. Using explorative statistical analyses (classification trees, factor analysis) we checked the predictive or explanatory value of up to 28 variables assessed during household inspections for villagers' observations on rodent infestation as the dependent variable. Trophic factors such as exposed food (indoors) and garbage (outdoors), and structural features such as open ceilings (indoors) and rat harborage in gardens (outdoors) ranked highest as explanatory variables. Assessment of a small sample of roof rat droppings collected inside houses revealed the presence of the potential disease agents Salmonella javiana, Cryptosporidium parvum, Giardia duodenalis and the parasitic nematode Calodium hepaticum (syn. Capillaria hepatica). These results underline the need for an appropriate rodent management strategy for the city, whereby simple sanitation and rodent-proofing measures could be cheap means of reducing rat infestation rates. [source] Applying discontinuous deformation analysis to assess the constrained area of the unstable Chiu-fen-erh-shan landslide slopeINTERNATIONAL JOURNAL FOR NUMERICAL AND ANALYTICAL METHODS IN GEOMECHANICS, Issue 5 2007Jian-Hong Wu Abstract Chiu-fen-erh-shan landslide is a remarkable slope failure occurred during the Chi-Chi earthquake in 1999. In November of 2002, abnormal geomorphologic features, including buckling and ground subsidence, were observed on the lower slope of the Chiu-fen-erh-shan landslide. This study attempts to assess the constrained area of a future collapsing on the slope using a dynamic discrete numerical analysis method, discontinuous deformation analysis (DDA). The simulation results show that the depression in front of the toe of the slope provides a space for arresting the whole sliding rocks when only the unstable lower slope fails. However, as the whole slope slides, the rock fragments move farther into the memorial park and can impact other facilities resulting in the enlarging of constrained area. The authority should prohibit people from entrancing the constrained area in the rainy season. Copyright © 2006 John Wiley & Sons, Ltd. [source] Simulation of the intraseasonal and the interannual variability of rainfall over West Africa with RegCM3 during the monsoon periodINTERNATIONAL JOURNAL OF CLIMATOLOGY, Issue 12 2010M. B. Sylla Abstract Intraseasonal and interannual variability of rainfall is simulated using the International Centre for Theoretical Physics (ICTP) Regional Climate Model (RegCM3) over West Africa. The intraseasonal variability of rainfall showing three distinct phases and the monsoon jump is well reproduced in the simulation. In addition, the regional model shows that while the monsoon rainbelt moves to the Sahel, the African Easterly Jet (AEJ) undergoes a northward migration and a weakening from June to August, when the core is at its northernmost location. This coexists with the appearance and the strengthening of the Tropical Easterly Jet (TEJ), the development and increased activity of the African Easterly Waves (AEWs), and the intensification and northward shift of the ascent between the AEJ and the TEJ core levels and axis. Similarly, the simulated interannual variability of rainfall over West Africa, the Guinea region, and the Sahel, as well as the variability of atmospheric features during contrasting wet and dry years, is also well captured. In fact, in the simulation during dry years the AEWs activity is decreased while the AEJ is strengthened and migrates southward, the TEJ becomes weaker, and the ascent between the levels of the AEJ and the TEJ decreases. The simulated rainfall variability and the behavior of the related features during the rainy season and during contrasting wet and dry years are in line with previous studies that used observations and reanalysis. We conclude that this model performance is of sufficient quality for application to the study of climate processes and mechanisms over West Africa. Copyright © 2009 Royal Meteorological Society [source] Global summer monsoon rainy seasonsINTERNATIONAL JOURNAL OF CLIMATOLOGY, Issue 12 2008Suping Zhang Abstract A concise and objective definition of monsoon rainy season characteristics is proposed for worldwide monsoon regions. The result highlights six major summer monsoon rainy season domains and the mean dates of the local onset, peak and withdrawal phases of the summer monsoon rainy season. The onset phases occur progressively later poleward in the continental domains but primarily eastward in the oceanic monsoon regions. The rainy season retreats equatorward over the continental and oceanic monsoon regions. The length of the rainy season decreases poleward and shorter rainy season can also be found over the outskirts of warm water. Some exceptions exist in terms of the characteristics of rainy season, e.g. the westward advance of rainy season over North Africa and an apparently prolonged rainy season in the Korean peninsula. The results here are basically compatible with those obtained in previous studies on regional monsoons. A definition of the seasonal wind overturning is proposed. Combining rainfall and winds, we stratify the global monsoon into strong and weak categories. The strong monsoons are typically in the regions with both concentration of summer rainfall and annual reversal of low-level winds, while the weak monsoon features only a contrasting wet,dry season. Seemingly, some mid-latitude regions with wind reversals are not monsoonal because of the reversals being opposite to the monsoon overturning and the rainfall patterns being more or less Mediterranean. The comparison between the monsoon domains derived from Climate Prediction Center (CPC) Merged Analysis of Precipitation (CMAP) and the 40-year European Centre for Medium-Range Weather Forecasts Re-Analysis (ERA-40), the Japanese 25-year Reanalysis (JRA-25) and National Centers for Environmental Prediction (NCEP) datasets show good capabilities of the reanalyses in demarcation of the major monsoon rainy season domains in the tropics and subtropics. But the reanalyses are less realistic in the mid-latitudes of Eurasia and North America. The result here provides the simple yet objective definitions of monsoon domain, onset, peak and withdrawal which are useful for validation of GCMs. Copyright © 2008 Royal Meteorological Society [source] Pre-rainy season moisture build-up and storm precipitation delivery in the West African SahelINTERNATIONAL JOURNAL OF CLIMATOLOGY, Issue 7 2008J. Bayo Omotosho Abstract The salient differences between the years of above and below normal precipitation, particularly within the long period of 1972,1990 with persistently decreasing Sahelian rainfall, are investigated for Kano, a Nigerian station within the Sahel. Daily rainfall data from 1916 to 2000, storm records from 1951 to 2000 and radiosonde data for three dry and three wet years are used in this study. Results confirm previous findings that the African Easterly Jet (AEJ) located in the 700,600 mb layer is stronger during the dry than in wet years. Significantly, however, it is shown that during the wet years, there is stronger and deeper early season (April,June) build-up of moisture below the AEJ. Furthermore, throughout the period from April to August, the middle troposphere was almost always drier than normal during the dry years and moist than normal in the wet years. Consequent upon these, the storms, which deliver almost all the rainfall in the Sahel, produce at least 150% more precipitation during the wet than in the dry years, though the June to September or annual total number of storms differs by only about 30%. Finally, during the dry years, the onset of rainfall is found to be generally very late compared to the long-term mean, with shorter length of the rainy season. Copyright © 2007 Royal Meteorological Society [source] Seasonal march and its spatial difference of rainfall in the PhilippinesINTERNATIONAL JOURNAL OF CLIMATOLOGY, Issue 6 2007I. Akasaka Abstract On the basis of the pentad rainfall data averaged from 1961 to 2000, the seasonal march of rainfall in the Philippines is analyzed in this study. The relation to the atmospheric circulation at the 850 hPa level is also discussed. To investigate the temporal and spatial features of rainfall, the Empirical orthogonal function (EOF) analysis was applied to rainfall data. The result showed two dominant modes in the seasonal march of rainfall. The first mode reveals the increase of rainfall amount in the entire Philippines during summer monsoon while the second mode represents the contrast between the west and east coasts in the seasonal march of rainfall. The rainy season starts simultaneously over the entire west coast in the middle of May and withdraws gradually from northern stations around November. And on the east coast, the rainfall amount increases in autumn and winter rather than in summer. These regional differences between west and east coasts are considered to correspond to the seasonal change of Asian summer monsoon and orographic effect. The seasonal march of rainfall in the Philippines is characterized by the sudden change of atmospheric circulation around the Philippines. Particularly, the onset and peak of rainy season on the west coast are influenced by the eastward shift of the subtropical high and the evolution of the monsoon trough with southwesterly, respectively. The increase of rainfall on the east coast is related with the weakened monsoon trough around early September. Copyright © 2006 Royal Meteorological Society [source] Modulation of the intraseasonal rainfall over tropical Brazil by the Madden,Julian oscillationINTERNATIONAL JOURNAL OF CLIMATOLOGY, Issue 13 2006Everaldo B. De Souza Abstract Fifteen years (1987,2001) of rain gauge-based data are used to describe the intraseasonal rainfall variability over tropical Brazil and its associated dynamical structure. Wavelet analysis performed on rainfall time series showed significant peaks centered roughly in periods of 30,70 days, particularly in the eastern southeastern Amazon and northern northeast Brazil. A significant enhancement of precipitation with maximum anomalies in a northeastward oriented band over tropical Brazil is evidenced from empirical orthogonal function (EOF) analysis of 30,70-day filtered rainfall anomalies during rainy season (January to May). Lagged/lead composites revealed that, on a global scale, the Madden,Julian oscillation (MJO) is the main atmospheric-mechanism modulator of the pluviometric variations on intraseasonal timescale in the eastern Amazon and northeast Brazil. A coherent northward expansion of rainfall across tropical Brazil is evident during the passage of MJO over South America. Regionally, the establishment of a quasi-stationary deep convection band triggered by the simultaneous manifestation of south Atlantic convergence zone (SACZ) and intertropical convergence zone (ITCZ) explains the intensified rainfall over these regions. Such regional mechanisms are dynamically embedded within the eastward-propagating MJO-related large-scale convective envelope along tropical South America/the Atlantic Ocean. These features occur in association with a significant intraseasonal evolution of the lower-level wind and sea-surface temperature (SST) patterns, particularly in the Atlantic Ocean, including a coherent dynamical connection with atmospheric circulation, deep convective activity over South America and rainfall over tropical Brazil. Copyright © 2006 Royal Meteorological Society [source] Interannual variability in rainy season characteristics over the Limpopo region of southern AfricaINTERNATIONAL JOURNAL OF CLIMATOLOGY, Issue 14 2005C. J. C. Reason Abstract This study focuses on the interannual variability of dry spell frequencies, dry and wet spell characteristics and onset dates of the austral summer rainy season over the Limpopo region (22,25 °S, 27,32 °E) of northern South Africa. These characteristics of the rainy season are of considerable interest to farmers, water resource managers and other user groups. The Limpopo region supports a large rural population dependent on rain-fed agriculture as well as significant biodiversity, particularly in the Kruger National/Limpopo Transfrontier Park. It is also a region prone to devastating floods and droughts. Evidence is presented that summer dry spell frequency and onset date are related to ENSO via changes in regional circulation. Niño 3.4 sea surface temperature (SST) anomalies appear to show a robust relationship with dry spell frequency during the 1979,2002 period analysed. Anomalies in onset date of the rainy season during 1979,2002 appear to be inversely related to Niño 3.4 SST, with the relationship strengthening after 1986. These results suggest that there may be some predictability in these parameters, particularly in dry spell frequency during austral summer, based on existing skill in predicting tropical Pacific SST. Copyright © 2005 Royal Meteorological Society. [source] Australian drought: the interference of multi-spectral global standing modes and travelling wavesINTERNATIONAL JOURNAL OF CLIMATOLOGY, Issue 6 2003Warren B. White Abstract Extreme drought has devastated the flora, fauna, and regional economy in rangeland grazing districts over Australia for 3,5 years duration every 20 to 30 years throughout the 20th century. We investigate the source of drought occurring in five example grazing districts in eastern and central Australia. We find year-to-year variability in grazing district rainfall (GDR) during the summer rainy season (November to March) composed of quasi-biennial, interannual, quasi-decadal, and interdecadal signals from 1900 to 1999. However, the longer period signals dominate, accounting for the interdecadal quasi-periodicity of the drought/flood cycle. We find these GDR signals associated with corresponding global standing modes and travelling waves in covarying sea-surface temperature (SST) and sea-level pressure (SLP) anomalies. These global SST/SLP modes/waves influence the GDR signals by altering the troposphere moisture flux converging onto the grazing districts from regional tropical and extra-tropical oceanic source regions. We construct statistical models to determine whether the evolution of these global SST/SLP modes/waves over the oceanic source regions can hindcast corresponding GDR signals from one year to the next. When these models allow for modulation of the modes/waves, they hindcast ,1/3 of the variance in the GDR indices at 1 year lead, including the drought episodes. We find drought resulting from the constructive interference of the dry phases of the quasi-decadal and interdecadal global SST/SLP modes/waves, accompanied by a weakening of year-to-year variability associated with either weak quasi-biennial and interannual modes/waves or their destructive interference. Copyright © 2003 Royal Meteorological Society [source] Spatial variation in the duration of the rainy season in monsoonal AustraliaINTERNATIONAL JOURNAL OF CLIMATOLOGY, Issue 14 2001Garry D. Cook Abstract Climatological research in the tropics of northern Australia has focused particularly on the Australian summer monsoon. However, the timing of many ecologically important processes is determined not by the monsoon but by extra-monsoonal rainfall events. These events produce a temporal pattern of wet and dry spells that is at least as important ecologically as the amount of rain. We defined the rainy season as that period when the probability of 10-day dry spells was less than 0.5, and the wet season as that period within the rainy season when the probability of dry spells was less than 0.1. We applied these criteria to seven stations along a strong north,south rainfall gradient spanning more than 12° of latitude in tropical north Australia. The duration of the rainy and wet seasons in northern Australia decreases with increasing latitude. The timing and duration of these seasons were also affected by the El Niño,Southern Oscillation (ENSO). The relative contribution of temporally isolated rainfall events to both the duration of the rainy season and the amount of rainfall increases with latitude. The geographic variation in these seasons corresponds to many patterns occurring in natural ecosystems. We argue that understanding the extra-monsoon rainfall events is critical to understanding how climate variation affects natural ecosystems. Copyright © 2001 Royal Meteorological Society [source] Consumer preferences and fungal and mycotoxin contamination of dried cassava products from GhanaINTERNATIONAL JOURNAL OF FOOD SCIENCE & TECHNOLOGY, Issue 1 2001Peter W. Wareing Summary Members of one hundred and twenty five households from 19 villages producing dried cassava products were interviewed in Ghana. Kokonte was the most important cassava product in 19% of the households processing it. Most kokonte was produced between January and March. Mould growth during processing or storage was a problem during June and July, which is part of the rainy season. Most producers and market traders preferred non-mouldy kokonte, although many (59%) would consume a mouldy product. There was a price premium for non-mouldy kokonte. The most commonly isolated fungi were yeasts and Cladosporium spp. (44 out of 49 samples). Other fungi isolated included Aspergillus spp. (20 samples); Penicillium spp. (15 samples) and Fusarium spp. (30 samples). Sterigmatocystin was detected in 10 samples at 0.17,1.67 mg kg,1; patulin in 4 samples at 0.55,0.85 mg kg,1; cyclopiazonic acid in 4 samples at 0.08,0.72 mg kg,1; penicillic acid in 5 samples at 0.06,0.23 mg kg,1 and tenuazonic acid in 3 samples at 0.02,0.34 mg kg,1. Mycotoxin contamination of mouldy kokonte was a potential problem; there is therefore the need to improve kokonte processing to avoid mould growth. [source] Effect of the Environmental Factors on the Caloric Content of Benthic and Phytophilous Invertebrates in Neotropical Reservoirs in the Paraná State, BrazilINTERNATIONAL REVIEW OF HYDROBIOLOGY, Issue 3 2010Yara Moretto Bagatini Abstract The complexity of the relations between the organisms and the environment are reflected through the energy content. So we tested the hypothesis on body energy content variation in invertebrates and its relation with some environmental factors (season, habitat type, trophic status and trophic guild). We expected higher energy values for phytophilous fauna, rainy season, in reservoirs with higher trophic levels and for herbivorous invertebrates. The results showed the influence of seasonality and trophic status of the reservoir on the energy content of invertebrates, which was higher in the rainy season and in the mesotrophic reservoirs, due to the input of allochthonous material during this season, confirming our initial prediction. A higher caloric content was recorded for carnivorous and detritivorous invertebrates. The differences between the trophic guilds were primarily related to the opportunistic feeding behavior, which may be considered as one of the main factors controlling the energy flow of benthic and phytophilous invertebrates. (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] |