The study of long-term climatic change in the Arctic, a region both particularly sensitive to the effects of a warming climate and an important driver of global climate, is pertinent to understanding the rates and magnitude of current ecosystem changes. Analyses on geological time frames provide insight into the variability of Arctic climate, allowing a contextualized understanding of recent ecosystem changes that have been documented across the Arctic. Lake CF8, a mid-Arctic lake on Clyde Foreland, Baffin Island, contains a unique sedimentary archive of the present and last two interglacial periods, due to past non-erosive glaciation patterns, providing an opportunity to study interglacial climate trends. Diatom assemblages were analyzed through the organic sediment record of the past three interglacials. Trends in the ontogeny of this lake were revealed: the early, post-glacial environment was dominated by species of the colonial Fragilaria genera, which transitioned into high relative abundances of tychoplanktonic Aulacoseira species. Benthic/periphytic taxa, such as Psammothidium marginulatum, tended to increase in relative abundance in the mid- to late-interglacial periods. The ecological interpretation of this pattern is examined in this study, and suggests that climate drives the succession of the diatom community primarily through indirect effects on lake ice and pH. The extent of ice cover likely plays a large role in the biotic community of this lake; the diatom assemblages within the past ~ 50 years indicate increasing littoral habitat complexity with a peak in Eunotia species and a slightly acidic pH, which is discussed in relation to changing habitat availability associated with decreasing ice cover. In-lake production was examined through the use of spectrally-inferred chlorophyll a trends, which also indicate elevated production in the past ~ 50 years. As climate change becomes an increasingly significant threat to the stability of Arctic ecosystems, interest in paleoclimate records that extend into past, non-anthropogenically mediated warm periods, is increasing. This sediment record extends our understanding of past environmental trends beyond the longest records in this part of the Arctic, the Greenland ice core records, and enhances our understanding of the variability of Arctic climate. / Thesis (Master, Biology) -- Queen's University, 2009-05-06 17:04:38.302

No description available.

No description available.

Determining optimum building orientation for naturally ventilated buildings is an important concept. Obtaining the optimum orientation will determine the success of the performance of a naturally ventilated building. / This project deals with obtaining the preferred building orientation for 10 regional weather stations across the province of Ontario. Different methods were utilized to obtain the preferred building orientation: the average ventilation rate method, the percentage of ventilation rates above and below the minimum summer ventilation rates, and the consecutive hours method, ie. the number of weather events that are below the minimum summer design ventilation rate for a specific building configuration. The analysis involves six building orientations (0$ sp circ$, 30$ sp circ$, 60$ sp circ$, 90$ sp circ$, 120$ sp circ$, and 150$ sp circ$) with respect to North, and exterior temperatures greater than or equal to 20$ sp circ$C, 25$ sp circ$C, or 30$ sp circ$C. / Optimizing building orientation, to minimize the number of weather events where the ventilation rates are below the summer design ventilation rate is the general goal of this research work. / A statistical analysis was carried out based on the results obtained from the data for the frequency of ventilation rates versus the ventilation rates below the summer design ventilation rate, for all 10 Ontario weather stations, for temperatures greater than or equal to 20$ sp circ$C, and all six building orientations. The output of the statistical analysis showed that for the above mentioned temperature range, that there is a relationship between the ventilation rates below the design summer ventilation rate and building orientation.

No description available.

Limited information is available on the response of local cactus pear cultivars to environmental factors that influence fruit yield. Eleven cultivars were evaluated in three diverse agro-climatic areas over seven production seasons in the Limpopo Province to assess their environmental adaptability. Significant differences between cultivars, areas and production years for five fruit yield components were evident. A strong genotype by environment interaction was observed, although some cultivar characteristics were genetically controlled. The most suitable production area is the cool mid-altitude area of Limpopo Province. Cultivars that can be recommended for fresh fruit production are: âAlgerianâ, âAmerican Giantâ, âGymno Carpoâ, âMaltaâ, âMoradoâ, âNudosaâ and âZastronâ. Fruit yield was significantly influenced by minimum temperature and plant macro nutrients. Soil phosphorus levels above 20 mg kg-1 and applied nitrogen higher than 100 kg ha-1 year-1 had a positive effect on fruit yield. Soil pH did not influence the fruit yield of the cultivars tested. None of the cultivars tested had a winter chilling requirement to become fertile. Vegetative growth was stimulated by increased solar radiation. Cactus pear plants can be considered to be fully mature from the fifth year onwards. Environmental adaptability is related to species differences rather than plant morphological differences. Plant growth habit changed markedly in different environments. To obtain high fruit yields, it is important to match a cultivar with prevailing environmental conditions of the area. Fruit yield in cactus pear is a function of the number of fertile cladodes, the number of fruit set, the number of fruit left after thinning and individual fruit mass. Research into orchard practices, in particular pruning, and evaluation of the existing cactus pear germplasm should receive attention. As a ânewâ cultivated fruit crop it offers real solutions towards mitigation of the effects of drought in arid and semi-arid parts of Limpopo Province.

Downy Mildew (Plasmopara viticola) is known as one of the most important vineyard diseases in the Western Cape, because it has the capability to develop and spread very fast, and so cause large crop losses in certain years. In 1992 an Austrian researcher developed the Metos automatic weather station and associated software, to predict the occurrence of primary and secondary infection of downy mildew. This Metos weather stationâs software was adapted for South African climatic conditions during 1995 and is known as the Metos-2 model. The Metos-2 model however had some shortcomings that needed to be improved. The most important of this was that the model was not sensitive enough to accurately calculate infections, and furthermore it gives only a âYes/Noâ warning of possible primary and/or secondary infections. The Metos-2 model makes use of measured leaf wetness values from a leaf wetness sensor that is probably considered as one of the most inaccurate meteorological sensors. During 1995 - 2005 the Metos-2 model has been thoroughly tested and used by the disease management division of ARC Infruitec-Nietvoorbij, to warn the industry of possible downy mildew outbreaks. Results over these years have shown that more sprays were needed within the preventative spraying programs, as opposed to recommendations of the Metos-2 model, for the same or even improved control of downy mildew. On the other hand the results of the Metos-2 model compared to the Metos model, gave similar warnings for both primary and secondary infections. It is however very difficult to get clear similarities/differences between what the Metos-2 model has calculated and what had really occurred in the vineyards. This can be attributed mainly to the accumulation effect of downy mildew infections. With the development of the Downy Mildew Early Warning Model (DSVWmodel), two important changes were made, namely the leaf wetness was replaced with a mathematical, non-linear regression and the Metos-2 modelâs âYes/Noâ warnings for downy mildew infections were replaced with four classes of possible risks. The calculated leaf wetness of the DSVW-model, that uses measured relative humidity and air temperature as input values, had a significant coefficient of determination of 0.70, compared with measured leaf wetness. The DSVW-modelâs four risk classes of possible infections (primary and secondary) are as follows: zero infection (0 %), low infection (1 - 34 %), medium (35 - 74 %) and a high risk class (75 - 100 %). To test the DSVWmodelâs accuracy and reliability, historical weather data (1998 - 2003) and measured disease outbreak data in the Stellenbosch, Robertson and Paarl areas were used to run both the Metos-2 and the DSVW-models. Primary as well as secondary infections were predicted by the models. When the DSVW-model and the Metos-2 modelâs infection warnings were correlated with disease outbreaks, of the two, the DSVW-model showed consistently similar or better correlations with the measured disease outbreak data. The DSVW-model also calculated on a regular basis more primary and secondary infections, than the Metos-2 model, which at times did not warn of any downy mildew infections, although outbreaks of downy mildew did occur soon after. Producers can use the new DSVW-model with confidence, together with one or other prevention spray program, for the control of downy mildew.

Large areas of cultivated land in Ethiopia frequently suffer from drought, causing low crop yields and food insecurity. It was hypothesized that it may be possible to alleviate this problem by employing infield rain water harvesting (IRWH). Three representative semi-arid ecotopes in the Rift Valley were selected to test this hypothesis. They were the Melkassa Hypo Calcic Regosol, The Dera Calcic Fluvic Regosol and the Mieso Hypo Calcic Vertisol. The climate, topography and soils of the ecotopes were characterized in detail. Rainfall runoff studies were carried out over two rain seasons on replicated plots on these ecotopes comparing two soil surface treatments. They were conventional tillage (CT), simulating the initially fairly rough surface which results after normal tillage; and no tillage (NT), simulating the flat crusted surface expected on the runoff strip of the IRWH system. Rainfall amounts, rainfall intensity at one minute intervals, and runoff, were measured for each storm during the two rain seasons on each ecotope. The results were used to calibrate and validate the Morin & Cluff runoff model in order to enhance the extrapolation capability of the study results to other similar ecotopes. The study yielded the following useful results. · The rainfall pattern on all the ecotopes was characterized by occasional storms with fairly high amounts and high intensities (Pi) which greatly exceeded the final infiltration rates of the soil, causing a high proportion of the rain (P) to runoff (R), i.e. producing a high R/P ratio. For the NT treatment final overall R/P values for the two seasons on the Melkassa, Dera and Mieso ecotopes were 0.45, 0.52 and 0.32, respectively. These high values indicate that IRWH should produce a significant increase in yield due to its ability to reduce R to zero while concentrating the runoff in the basin area and increasing the water available for transpiration and therefore increasing yield. · Because of the textural and mineralogical properties of the topsoils, particularly the two Regosols soils; they disperse and form crusts easily when impacted by high intensity rain. The result was that after cultivation at the start of the rain season the surface of the CT treatment soon became very similar to that of the NT treatment. Accordingly no significant difference was found between the runoff from the NT and CT plots on the Melkassa Regosol and Dera Regosol. There was, however, a significant difference in this respect on the Mieso Vertisol with a more stable surface. · Runoff prediction in all the ecotopes were well done by the M & C model. · Two separate strategies were developed to estimate the maize yield increase that could be expected on the Melkassa Regosol by employing IRWH. From the nearby Melkassa Research Station it was possible to obtain maize yields for 15 seasons (1989-2003). These were used together with climate data, the CROPWAT model, and the runoff measurements, to estimate the benefit of IRWH. The two strategies produced yield increase estimates of 33% and 40% compared to CT.

No abstract available.

Very little is known about the response of Lachenalia to fertilisation when cultivated in soil. The objective of this study was therefore to quantify the effect of fertilisation on the growth, yield and quality of Lachenalia in both the nursery and pot plant phases. In order to achieve this two pot trials for the nursery phase and one pot trial for the pot plant phase were conducted in the glasshouse. For the first trial in the nursery phase the combined effect of nine nitrogen levels and three application times on the Lachenalia cultivars, Rupert and Ronina, were studied. The nitrogen was applied at levels equivalent to 0, 30, 70, 120, 180, 250, 330, 420 or 520 kg N ha -1 . Three different nitrogen application times were used namely: one third with planting and the rest 10 weeks after planting (T1); one third with planting and the other two thirds after planting (T 2) or one quarter with planting and the other three quarters after planting (T3). The leaf area of Ronina plants was larger than that of Rupert plants irrespective of nitrogen levels and application times. However, Ronina bulbs were larger and softer than Rupert bulbs. The nutrient (N, P, Ca and Mg) and carbohydrate (D-glucose, sucrose and starch) content of Rupert bulbs were higher than that of Ronina bulbs. Application of nitrogen had a positive influence on the leaf area, bulb fresh mass and circumference of both cultivars. Bulb firmness was negatively influenced by nitrogen application. The best results for most parameters were obtained when nitrogen was applied in four equal applications. In the second trial for the nursery phase the response of Rupert and Ronina to five nitrogen (0, 70, 180, 330 or 520 kg N ha -1 ) and five phosphorus (0, 10, 30, 50 or 80 kg N ha -1 ) or five potassium (0, 70, 180, 330 or 520 kg N ha -1 ) levels were studied. Neither the interaction between nitrogen and phosphorus levels nor the interaction between nitrogen and potassium levels had a large influenced on the growth and development of Lachenalia. Results obta ined in this trial with respect to the effect of nitrogen levels on the different parameters mainly confirm with the results obtained with the first trial. In the trial for the pot plant phase the effect of seven nitrogen levels (0, 30, 70, 120, 180, 250, 330, 420 or 520 kg N ha -1 ) on Lachenalia grown from 7-8 cm bulbs, whereof the fertilisation history in the nursery phase differed, was investigated. The fertilisation history of the bulbs in the nursery phase consisted of three nitrogen levels (0, 70, 250 or 520 kg N ha -1 ) combined with two nitrogen application times (T1, T2 or T3 as described earlier). The leaf area of Ronina plants was larger than that of Rupert plants. Nitrogen applied in the nursery phase promoted the leaf area of both Rupert and Ronina. Application of nitrogen in the nursery phase and in the pot plant phase increased the number of inflorescence per plant and the number of florets per inflorescence. The peduncle length increased with higher nitrogen levels in the nursery phase wherea s the peduncle diameter increased with higher nitrogen levels in the pot plant phase.