Windy Season Research Articles

Sociometric analysis of the role of penaeids in the continental shelf food web off Veracruz, Mexico based on by-catch

Continental shelf macrofauna are impacted by trawling and associated by-catch activities. These activities have been predicted to change the macrofaunal community structure and the resulting food web. Four food webs (three seasonal and one pooled) were constructed using shrimp by-catch samples from 21 surveys from 1991 to 1994. Network sociometric analyses were performed on the webs in order to explore structural characteristics focusing on the role of penaeids. The number of nodes varied from 43 to 73. The out-degree centrality value for the combined web was the highest. For the penaeid node, the windy season centrality was the highest (47%) and the rainy season the lowest (11%). The number of cutpoints by season was: windy four, dry two, and three for the combined web. Using the lambda sets analysis; penaeid is a key node for the structural cohesion of the trophic network. The rainy season food web is the most homogeneous and penaeid is an important node such that its elimination would cause a major structural and functional disruption to the network. These modeling exercises suggest over-fishing by trawlers would impact the continental shelf community structure and thus significantly change the existing trophic relationships.

Burial of canopy-stored seeds in the annual psammophyte Agriophyllum squarrosum Moq. (Chenopodiaceae) and its ecological significance

Agriophyllum squarrosum Moq. is a dominant annual on sand dunes in the arid regions of central Asia. A high percentage of seeds is retained on dead plants which become covered by moving sand, but little is known about the ecological significance of burial of canopy-stored seeds. We investigated the size and dynamics of the buried canopy-stored seed bank and effects of burial on seed germination. In March (during the windy season), May (beginning of the germination season), and July (middle of the growing season), the number of seeds per square meter in sample plots in the dunes was 623, 223 and 22, respectively, with 54.6, 30.6 and 12.9% of the total seeds retained on buried plant canopies. In a controlled experiment, more seedlings emerged from released (dispersed) than from canopy-stored seeds when burial depth was the same. No viable ungerminated released seeds were found, but 45-80% of the ungerminated canopy-stored seeds were viable. In general, with an increase in applied water germination of released seeds buried at a depth of 1 or 2 cm and of canopy-stored seeds buried at 1 cm increased, but regardless of watering regime few or no released seeds at 4 cm or canopy-stored seeds at 2 or 4 cm germinated. Significantly more seedlings emerged from plants buried in a horizontal than in a vertical position. Seedlings originating from buried canopy-stored seeds on an active dune accounted for only 5.4% of the total seedlings emerging, and most of them emerged later than those from released seeds. Thus, seed release is more effectively postponed in buried than in exposed canopies, and burial of canopy-stored seeds is a mechanism that helps regulate seed germination and seedling emergence of A. squarrosum on active dunes.

Agroecological and economic approach of prevention and curing of sandstorms in China

With the warming and drying of climate and desertification, sandstorms are occurring on a more frequent basis. In China, high-frequency regions of sandstorms tend to correspond with the spring wheat regions between the end of February and the end of March. During March to May each year, when sandstorms frequently occur, the seedlings of spring wheat are young and susceptible to being uprooted by the winds. There is not enough plant coverage or root depth at this early stage to hold the soil from the fierce winds. As a result, the young plant life is destroyed and leaving the top soil susceptible to being blown about when in the path of high-frequency regions of sandstorms. By contrast, the seeding time of winter wheat is about September–October corresponding to lowest-frequency period of sandstorms. From the end of February to the middle of March, the winter wheat begins to turn green (ahead of 10 day than grass). During March to May when sandstorm frequently occurs, the winter wheat has come into a mature tillering or jointing stage. By then, the leaf area index is 1–4 and height is up to 20–50 cm, by which the loose soil is more compacted and covered with the fledging wheat. The result is that the energy of the air current is gradually dissipated and the wind speed near the ground is greatly weakened. So, without bare uncovered soil being whipped by powerful winds, the resulting sandstorms are greatly mitigated or weakened. After investigating the trend of global warming, the geological history-forming mechanism of sandstorms and their temporal–spatial distributions, and test for the last few years, the result is that by replacing spring wheat with winter wheat in high-frequency sandstorm regions, the damages of sandstorm are greatly reduced. Thus, by significantly increasing the vegetal cover time of ground during the windy season, one can alleviate the hazard index of sandstorms, which is a social, ecological and economic favorable result.

Behaviour of ventilated double layer external wall briquettes under earthquake loading

Ventilated double layer briquette is used as external walls in the construction of classical as well as modern buildings that are built in regions having climates with high temperatures or rainy and windy seasons. In this construction technique, the external layer which acts as shield against rain, wind and solar rays, and internal layer are laid separately and then interconnected to each other with steel ties. The aim of using such briquettes in the construction of external walls is to obtain ventilated double layer wall by just laying single layer of briquettes. The staggering of vertical joints provides better bond and added structural strength. The hollow cores should be directly above one another so that they can be filled with additional thermal insulation materials as the wall constructed, if required. In this paper, the earthquake response of two walls, one built using the new briquette produced from normal concrete mortar and the other constructed using the proposed briquette made out of lightweight pumice concrete mortar are studied. It was found that the wall produced using lightweight pumice concrete mortar behaves better under earthquake loads and it has higher energy absorption capacity than the other.

Seasonal/Spatial Variations of the Near-Inertial Oscillations in the Deep Water of the Japan Sea

A general description of the near-inertial oscillations in the deep water of the Japan Sea has been found by analyzing observed current data accumulated over a period of ten years. The near-inertial oscillations were dominant in the deep water, and those in the southern Japan Sea, the Tsushima current region, were more energetic than those in the northern area. Their temporal variations have an annual cycle with wintertime intensifications corresponding to the windy season over the Japan Sea. In the Yamato Basin, however, the power of the near-inertial oscillations was small during spring and large during summer, in addition to the above seasonal variations. The results of a slab model showed that the wind stress could account for part of the long periodic variations such as the annual cycle of the near-inertial oscillations in the deep water, but this is not expected to be their only source. Since the surface currents in the southern Japan Sea, especially in the Yamato Basin, vary significantly both temporally and spatially, the surface layer itself also could be responsible for the generation of the near-inertial oscillations in the deep water.

Spatial distribution patterns of the soil seed bank of Stipagrostis pennata (Trin.) de Winter in the Gurbantonggut Desert of north-west China

The aim of this study was to investigate the spatial distribution patterns of soil seed bank of Stipagrostis pennata (Trin.) de Winter during different seasons in the Gurbantonggut Desert of north-west China. Results indicated that spatial patterns of the soil seed bank of S. pennata were similar to the distribution patterns of its associated standing vegetation, and there was a significant variation in soil seed densities among the different parts of the dunes. The highest soil seed density was found on the top of sampled dunes and in the soil of the underlayers of standing vegetation beds of S. pennata. The number of seeds stored in the soil decreased with distance from established stands of this grass species. Moreover, during secondary seed dispersal, which is air-borne in the windy season, a small proportion of seeds was also trapped by other plant species. Furthermore, the directional density distribution of seeds was strongly associated with the directions of the prevailing threshold wind (⩾6 m s −1), and higher soil seed densities usually occurred on the leeward side of the vegetation stands. Based on these investigations, wind is, probably, the key factor in forming the spatial patterns of S. pennata seed banks in the region. On the other hand, grazing affected the quality and quantity of S. pennata seed storage, as a result of delayed development and the above-ground shoots being damaged by grazing. This occurred in spring to early summer, which is the most suitable growth season for the grass. Nevertheless, grazing had little influence on the spatial distribution patterns of the seed bank over all seasons. Germination trials showed that the percentage of viable soil seeds increased continuously throughout summer and autumn. The results also revealed the clear ecological characteristics influencing the population distribution of S. pennata.

Investigation of wind characteristics and assessment of wind energy potential for Waterloo region, Canada

Abstract Wind energy becomes more and more attractive as one of the clean renewable energy resources. Knowledge of the wind characteristics is of great importance in the exploitation of wind energy resources for a site. It is essential in designing or selecting a wind energy conversion system for any application. This study examines the wind characteristics for the Waterloo region in Canada based on a data source measured at an elevation 10 m above the ground level over a 5-year period (1999–2003) with the emphasis on the suitability for wind energy technology applications. Characteristics such as annual, seasonal, monthly and diurnal wind speed variations and wind direction variations are examined. Wind speed data reveal that the windy months in Waterloo are from November to April, defined as the Cold Season in this study, with February being the windiest month. It is helpful that the high heating demand in the Cold Season coincides with the windy season. Analysis shows that the day time is the windy time, with 2 p.m. in the afternoon being the windiest moment. Moreover, a model derived from the maximum entropy principle (MEP) is applied to determine the diurnal, monthly, seasonal and yearly wind speed frequency distributions, and the corresponding Lagrangian parameters are determined. Based on these wind speed distributions, this study quantifies the available wind energy potential to provide practical information for the application of wind energy in this area. The yearly average wind power density is 105 W/m2. The day and night time wind power density in the Cold Season is 180 and 111 W/m2, respectively.

Assessment of wind energy potential for eletricity generation in Setchet, Hanang, Tanzania

Tanzania depends heavily on hydropower for her electricity demand and experiences power shortage during the dry seasons. Wind energy is proposed as an alternative source of electricity to the fossil fuel generators during the dry season, the latter are normally used to supplement the shortfall in hydro-electricity generation. Fossil fuel generators produce emissions that are toxic and as such degrade the environment. Wind speed data from a site called Setchet is used to illustrate that the available wind energy can be harvested to generate electricity that can supplement the shortfall of electricity. The windy season, which is from July to November, coincides with the dry season. The annual average wind speed is 8.3 m/s, a value that is sufficient to generate electricity. Wind energy that can be harvested from this annual average wind speed is 2.30X10 3 kwh per year. It is suggested that by generating electricity from wind, the already limited hydrological resources in the country could be used for irrigation schemes instead of channelling them for developing new hydropower plants. Tanz. J. Sci. Vol. 28(2) 2002: 27-32

Effect of Body Condition at Calving and its Changes During Early Lactation on Postpartum Reproductive Performance of Zebu Cows in a Tropical Environment

Delgado, R., Magaña, J.G., Galina, C. and Segura, J.C. 2004. Effect of body condition at calving and its changes during early lactation on postpartum reproductive performance of Zebu cows in a tropical environment. J. Appl. Anim. Res., 26: 23–28. A herd was monitored for two years in order to determine the effect of body condition score on the reproductive performance of Zebu cows managed under continuous mating in the tropics of Mexico. Overall cyclicity and pregnancy rates were 60.5% and 37.1% at four months pospartum, respectively. 62.9 percent of the cows were non-pregnant and of these more than 60% were in true anoestrus. Body condition score (BCS) at calving and 60 days postpartum, BCS changes, season and parity had significant effects (P<0.05) on cyclicity and pregnancy at 120 days postpartum. The odds of a cycling or pregnant cow at 120 days postpartum improved with increasing BCS grades. Cows calving in the dry or rainy season had lower odds (0.5 and 0.7, respectively) than those calving during the windy and rainy season. First calving cows had the worst performance, no differences being observed among multiparous cows.

Short time dissolved oxygen dynamics in shallow water ecosystems

Dissolved oxygen evolution over time holds information about the recent and past history of the physics, the chemistry and the biology of aquatic systems. On the daily time scale various phenomena seem to repeat with a sort of regularity, leaving a trace in the further trend of oxygen dynamics. These are the wind calm of nocturnal and early morning hours, the advent of the afternoon breezes, the micro- and macro-algae diurnal production, the chemical and biochemical processes. On the larger seasonal scale, dissolved oxygen shows an almost periodical trend. In this case, a greater dependency on the climatic events leads to the colder and windy season, while the warm and hot period is closely related to the vegetable production, which frees remarkable amounts of oxygen in the water through photosynthesis. Result of experimental measurements of dissolved oxygen, acquired with an automatic equipement on a very short time scale (30 s), are shown and discussed. The experiments were run to detect oscillating phenomena characterized by a period which is shorter than the daily occurrence, as well as stochastic phenomena, led by almost periodical drifts, which contribute substantially to the oxygen dynamics on the longer time scale. To determine these pseudo-periodicities, or time variation for the oscillation period, the analysis of the temporal distances between local maxima of oxygen concentrations has been performed. This kind of analysis is based on the hypothesis that we are dealing with a dissipative dynamical system whose evolution is similar to the behavior of some non linear oscillating systems with a control, where the control can be represented by a simple function of the temporal interval between two consecutive peaks. The result of the analysis suggests the existence of dynamics on a 6–8 h time scale.

Seasonal and interannual particle export in an African rift valley lake: A 5‐yr record from Lake Malawi, southern East Africa

A time‐sequencing sediment trap was deployed at 300–350 m in Lake Malawi, East Africa, from 1987 to 1992 to measure particulate export to the deep, anoxic hypolimnion in the northern and central lake regions. The monthly settling particulate samples provide a data set of seasonal and interannual export fluxes of organic carbon, biogenic opal, calcium carbonate, and lithogenic material. Maximum total particle fluxes (~50–400 mg m−2 d−1) occurred primarily during the dry, windy season (April through October) when algal productivity is high because of wind induced upwelling of nutrient‐enriched metalimnion and hypolimnion waters. Peak‐flux particulates contained an abundance of Aulacoseira and Stephanodiscus diatom valves and chains. The total particle mass flux during the wet, austral summer months (November through March) was consistently one to three orders of magnitude less than that measured during the dry months and consisted of mineral shards, terrestrial plant debris, and scattered diatom tests. The 5‐yr trap data provide support for the claim that the light‐dark lamination couplets, abundant in northern and central lake cores, reflect seasonal delivery to the sediments of diatom‐rich particulates during the windy months and diatom‐poor material during the wet season. However, interannual and spatial variability in upwelling and productivity patterns, as well as El Niño‐Southern Oscillation (ENSO)‐related rainfall and drought cycles, appears to exert a strong influence over the magnitude and geochemical composition of particle export to the deep hypolimnion of Lake Malawi.

The influence of the trade winds on the coastal development of the Guianas at various scale levels: a synthesis

The coastal development of the Guianas is dominated by extensive, shoreface-attached and alongshore westward migrating mudbanks. The behaviour of these mudbanks is mainly determined by a combination of the large supply of Amazon-borne silt and clay and the trade wind generated wave action. In the front zone of the mudbanks, fluid mud is formed. As a result, the incoming waves are strongly attenuated and deposition is favoured. At their rear side, compacted clay deposits are eroded by waves. The mudbanks, migrating in this manner, are the driving mechanism in the development of the smallest coastal unit, which consists of a mudbank and the eastward adjacent interbank area. Eisma et al. [Neth. J. Sea Res. 28 (1991) 181] has demonstrated that the frequency of the northeast trade wind, which blows towards the coast of the Guianas, in the windy season (January till April), shows a systematic change in time. For the period 1953–1986, there is evidence that the frequency of winds coming from directions between 50° and 80° (roughly east–northeast) increases. The same applies to the wind velocity from that direction. In the last 10 years a reversal of these trends appears to occur. For a more or less east–west directed coastal section, e.g. the coastline of Suriname, a more easterly direction of the northeast trade wind results in an increased longshore wave energy flux in the coastal waters. This causes an increase in length of the mudbanks, at the detriment of the usually eroding interbank parts of the coast. This is evidenced by the large-scale coastal development during the related period, demonstrating an increasing length of the mudbanks and consequently an increasing net accretion. It is hypothesised that this development will reverse if the new trends in wind direction and velocity develop further. At the geological scale, it is considered that a coincidence of a systematic increase of more northerly directed wind frequencies and a fall in sea level are responsible for the two erosive interruptions in the generally accreting coastal plain during the Young Holocene Period.

Seasonal trends of Paramphistomum cervi in Tabasco, Mexico

Thirty rumens were examined every month from May 1989 to April 1992 to establish seasonal trends of infection and their relationship to the climatic factors caused by Paramphistomum cervi in cattle. The cattle were chosen from three municipalities of the Sierra region in Tabasco: Jalapa, Tacotalpa and Teapa. P. cervi was found throughout the year with prevalence between 3.33 and 96.67%, and with a yearly average of 39.10%. The major period of infection was shown in Jalapa. However, the maximum mean intensity was found in Teapa. The prevalence of the infection in all three sites was similar, showing the regional trend of P. cervi infection. Cattle were infected mainly throughout the rainy and windy seasons, during summer, autumn and at the beginning of winter.

Seasonal trends of Paramphistomum cervi in Tabasco, Mexico

Thirty rumens were examined every month from May 1989 to April 1992 to establish seasonal trends of infection and their relationship to the climatic factors caused by Paramphistomum cervi in cattle. The cattle were chosen from three municipalities of the Sierra region in Tabasco: Jalapa, Tacotalpa and Teapa. P. cervi was found throughout the year with prevalence between 3.33 and 96.67%, and with a yearly average of 39.10%. The major period of infection was shown in Jalapa. However, the maximum mean intensity was found in Teapa. The prevalence of the infection in all three sites was similar, showing the regional trend of P. cervi infection. Cattle were infected mainly throughout the rainy and windy seasons, during summer, autumn and at the beginning of winter.

Comparison of thermal stratification, light attenuation, and chlorophyll-a dynamics between the ends of Lake Tanganyika

Thermal structure, light attenuation, and chlorophyll-a dynamics within the upper 100 m at the northern and southern ends of Lake Tanganyika were measured from August 1995–July 1996. Pronounced variability of thermal structure in time, depth and region were observed. During the dry windy season (June–September), the water column in the south was largely isothermal down to 100 m, while in the north stratification was detectable. Subsequently, in October, cessation of winds coincided with a reestablishment and strengthening of thermal stratification in the south, and a distinct rise of a weakened thermocline in the north was accompanied by an increase in epilimnetic concentrations of dissolved solids. The depth of photic zone was highly variable with the average position of 1% of incident photosynthetically active radiance found between 20 and 70 m, sometimes showing vertical shifts of 25 m a week. Weekly observations showed that concentrations of chlorophyll-a were rather similar at both ends of the lake. At both stations, periods of unstable or absent thermal stratification were accompanied by increased concentrations of chlorophyll-a, although in the north chlorophyll-a also peaked during periods of deep thermal stratification and low rates of mixing. Concentrations of chlorophyll-a did not show significant relationship with the available amount of underwater available photosynthetically active radiance (Im from 11–173 μEm−2 s−). We suggest that in Lake Tanganyika chlorophyll-a maxima can occur whenever growth rates exceed spatial mixing rates, that is, if mixing is less than a critical turbulence. Our observations underscore the consequences of hydrodynamic processes on biological productivity either by securing internal nutrients or by controlling the timing and magnitude of phytoplankton biomass production.

Formation and internal structure of Tamarix cones in the Taklimakan Desert

The distribution, formative process, and internal structures of Tamarix cones located in the southern part of the Taklimakan Desert were investigated over 3 years (from 1993 to 1995). Typical dunes were excavated in order to observe the internal structures of Tamarix cones. The main results obtained can be summarized as follows:•cones have developed on piedmont alluvial fans, low river terraces, and areas between oases and moving sand dunes;•The climate of the study area is extremely arid, with a windy season from March to July. During the windy season, sand materials are transported by the frequent storms and accumulated around the spp. clumps, resulting in a sand layer. In the autumn, the vegetation like spp. drops leaves that form a litter layer overlaying the sand layer. There are many sticky nodules along the leaves of spp., so fallen leaves stick together and form a cohesive litter layer. As a result, a sand layer and a litter layer form alternately once a year. If this process continues, for several years, a cone can be formed and developed;•The excavated cross-sections of cones are composed of alternating sand layers and litter layers. The thickness of both layers differ within the cross section. Layers are thicker in the central part around the trunk of the bush than in the outer part;•In the upper part of the cross section, the organic materials of the layers are very fresh, but they are decomposed in the lower parts due to the increased moisture content and the load of overlaying layers.

The status of wind energy development in Tanzania

Wind energy development in Tanzania started about 3 decades ago when some windmills were installed at several locations in the country to pump water for human and animal consumption and in a few cases for irrigation. There were some attempts to manufacture the windmills locally but these were never successful. In 1980 there were some attempts to generate electricity from wind but these also were unsuccessful.The analysed wind speed data revealed that the wind energy potential in Tanzania is fairly high. The analysis also showed that the windy season coincides with the dry season. The available wind energy at one prospective site called if harvested for the purpose of electricity generation could help to alleviate the shortage of hydroelectricity that prevails during the dry season. Wind energy experts are involved in analysing the available wind speed data and also measuring wind speed in small intervals of time at the sites that are believed to have high wind energy potential. It is also planned to draw a wind map for Tanzania.

Personal accounts: memoirs of a compulsive firesetter.

Personal accounts: memoirs of a compulsive firesetter.

Wind speed pattern and the available wind power at Basotu, Tanzania

This paper examines the wind speed pattern and the available wind power at Basotu, Tanzania. Wind speed data for two different sessions reveals that the windy season, is from June to November, with October being the windiest month. The average monthly wind power from June to November is at least 114 W/m2. The shortfall of hydroelectricity that prevails during the dry season is normally supplemented from fossil fuel generators. It is fortunate that the windy season coincides with the dry season. It is urged that the use of wind turbines to supplement the shortfall of hydroelectricity during the dry season would offset the emission of greenhouse gases from fossil fuel generators that degrade our aerial environment.

Contrasting Relationships Between Nutrients, Chlorophyll a and Secchi Transparency in Two Shallow Subtropical Lakes: Lakes Okeechobee and Apopka (Florida, USA)

ABSTRACT Ten years of monthly water quality data were compared from two large shallow lakes in Florida, USA – Lakes Okeechobee and Apopka. Seasonal changes in trophic state index (TSI) values and log-log regression models relating total phosphorus (TP), total nitrogen (TN), chlorophyll a (CHLA), and Secchi transparency (SD) were considered. The objective was to quantify the extent to which empirical models might vary due to the heterogeneous nature of benthic-pelagic coupling that can occur in shallow lakes. In the offshore region of Lake Okeechobee, TP and SD-based TSI values increase dramatically during winter, while CHLA-based TSI declines. These changes coincide with the windy season in south Florida, when average wind velocities can exceed 20 km h−1. Resuspension of bottom sediments occurs and this reduces light penetration to the extent that the growth of phytoplankton is inhibited. During summer, winds are calm, and these conditions occur less often. Log-log regression models of CHLA vs. TP have a negative slope during winter and a positive slope during summer in offshore Lake Okeechobee. The slope of SD vs. CHLA models displays the opposite seasonal pattern. Seasonal changes are considerably muted in the near-shore region, where sediments are more consolidated and where shallower depths reduce the severity of light suppression of phytoplankton growth. The magnitude of seasonal variation in TSI values in Lake Apopka is muted, perhaps because seasonal variation in wind velocity is less than in the region of Lake Okeechobee. Hypereutrophic levels of nutrients, CHLA, and SD occur year-round. The log-log regression models of CHLA vs. TP and CHLA vs. TN are highly significant, and light availability does not appear to limit rates of algal production. Frequent resuspension events may occur, but negative effects on phytoplankton may be mitigated by: (1) shallower depth; (2) a greater presence of viable algae in the surface sediments that might “seed” the water column with phytoplankton; (3) high concentrations of soluble nutrients in sediments that might stimulate algal growth; and (4) lower concentration of light-attenuating inorganic particles than in Lake Okeechobee. The results indicate that a high degree of variability in both the seasonal patterns and relationships among nutrients, CHLA, and transparency can occur in shallow subtropical lakes, even when they share common features (e.g., geographic location, large size, wind patterns). This finding has practical implications regarding the use of regression models in the context of shallow lake management. Models may be quite useful on a lake-by-lake basis (e.g., in Lake Apopka they have successfully been used in eutrophication management), but considerable care should be taken when generalizing models to other lake ecosystems.