Nitrate-induced changes and effect of varying total nitrogen to total phosphorus ratio on the phytoplankton community in Lake Chivero, Zimbabwe: Microcosm experiments

Microcosm experiments were conducted to assess nitrate-induced changes and the effect of varying the ratio of total nitrogen to total phosphorus (TN:TP) on the winter and late summer phytoplankton communities in Lake Chivero, Zimbabwe. In both winter and summer, nitrate addition altered species composition from a cryptophyte-dominated to a chlorophyte-dominated assemblage and increased chlorophyll a concentration and total algal biomass. The shift in algal dominance and increase in chlorophyll a concentration and total algal biomass also occurred in the control showing that isolation from allogenic processes like turbulence had an effect on phytoplankton structure. Microcystis aeruginosa, a common cyanobacterium in Lake Chivero, did not assume dominance in any of the treatments. From an application perspective it is interesting that varying nitrate loadings in microcosms favoured chlorophytes rather than increasing undesirable cyanobacteria. Nutrient manipulation can be used as a management option to avoid cyanobacteria occurrence, by maintaining either cryptophytes or chlorophytes. However, the practicality of such an intervention needs to be assessed

Response of phytoplankton assemblages isolated for short periods of time in a hyper-eutrophic reservoir (Lake Chivero, Zimbabwe)

The response of phytoplankton assemblages isolated in enclosures for short periods of time was examined in hyper-eutrophic Lake Chivero (Harare, Zimbabwe), to determine the factors that influenced the structure of the phytoplankton community, after noticing a marked decline in the dominance of Microcystis aeruginosa in recent years. The phytoplankton assemblage in the lake during summer, winter and the end of winter was dominated by Cryptomonas sp. and Cyclotella sp., with an average relative abundance of > 95%, based on phytoplankton biomass estimations. Isolation in summer resulted in the exclusion of Cyclotella sp., a decline of Cryptomonas sp. and an increase in M. aeruginosa and Anabaena sp. In winter, when M. aeruginosa was absent in the inoculum, isolation resulted in an increase in Cryptomonas sp. biomass and a decline of Cyclotella sp. At the end of winter Cryptomonas sp. initially increased but later declined following the increase in chlorophytes. The non-equilibrium state in Lake Chivero caused pioneer species to dominate rather than M. aeruginosa.Keywords: Microcystis aeruginosa, non-equilibrium state, pioneer species, turbulenc

Mapping wetland characteristics for sustainable development in Harare: The case of Borrowdale West, Highlands, National Sport stadium and Mukuvisi Woodlands wetlands

Wetland ecosystems are under threat from agriculture and urbanisation, affecting water supply and quality in urban areas like the City of Harare. With the need to protect wetlands that remain, the spatial extent of the Highlands, Borrowdale West, Mukuvisi and National Sports wetlands was established. LANDSAT and SPOT Satellite imagery were used to map the spatial extent on the wetlands and to take note of the temporal changes that occurred between 1989 and 2009. Supervised classification was used to classify the images. High resolution Google earth imagery were then downloaded and used as baseline data for mapping the wetlands using the Cowardin wetland classification system 1979 and the Land Capability Classification system for wetness. Maps showing the physical characteristic of the wetlands were then produced. Results indicated that area under wetlands has been shrinking over the years. Using the wetland classification system it was found out that much of the area under wetland should not be used for any other landuse purpose other than wetland protection. However the study found out that urban expansion projects are currently modifying the wetlands. The Highlands wetland has been drained and road construction is currently in progress while a Hotel is under construction on the National sports wetland covering 287 012 m2 of the wetland. This study provides information on the current physical state of the wetlands, which can be the basis for wetland protection and management by policy makers and managers. Key Words:  Wetland, Spatial extent, Physical characteristics, Classification, Landuse, Protection and Managemen

Designing of an intelligent fuzzy logic system for accretion prevention in Sponge iron SL/RN rotary KILN based 100TPD DRI process

Sponge iron is an intermediate product of steel formed during direct reduction of iron ore with aid of regulated temperatures and pressures within a rotary kiln. The greatest challenge is the direct measurement of kiln shell temperatures due to the catastrophic accumulation of sintered particles of solid bed which form rings at places along the length of the kiln thus hindering material flow. The accretion reduces productivity, damage kiln lining and reduces the production period as well as reduction in product quality. This process requires a controller which will be able to control with imprecise and partial data input; and be able to achieve the desired product quality under dynamic process conditions thus a Fuzzy Controller was used for the proposed design. The main goal of the research was to predict the rate of accretion build up within the kiln and minimize it with aid of a Fuzzy Control System cascaded to an already existing Programmable Logic Controller. A 16.2% build up rate was achieved as compared to the most appreciated 27% thus nearly a 10% decrease, a result which can improve the campaign period by approximately 48 hours which will be a 200 tons of sponge iron

Occurrence and diversity of arbuscular mycorrhizal fungi colonising off‐season and in‐season weeds and their relationship with maize yield under conservation agriculture

Weeds are responsible for major crop losses worldwide but can provide beneficial agroecosystem services. This study aimed to elucidate how arbuscular mycorrhizal fungi (AMF) in weeds respond to host identity and conservation agricultural practices. The study was carried out at two locations in Southern Africa during off-season and in-season maize cultivation. Off-season AMF root colonisation, diversity indices and community composition significantly differed among weed species at both locations. Glomus sp. VTX00280 explains most of the AMF community differences. In-season, implementation of conventional tillage with mulching alone (CT + M) or together with crop rotation (CT + M + R) resulted in a 20% increase in AMF colonisation of the constantly occurring weed species, Bidens pilosa (BIDPI) and Richardia scabra (RCHSC), com- pared with conventional tillage plus rotations (CT + R). The diversity of AMF was highest under no-tillage plus mulching (NT + M). Off-season and in-season AMF structures of both BIDPI and RCHSC were not related, but 39% of the taxa were shared. Structural equation modelling showed a significant effect of the cropping system on weed AMF diversity parameters and weed and maize root colonisation, but no significant influence of weed root AMF traits and maize colonisation was detected on maize yield. This may be explained by the improvement in weed competitive ability, which may have offset the AMF-mediated benefits on yield. Our findings highlight that implementing M and CR to CT and NT positively affected weed AMF colonisation and diversity. The similarity between the off-season and in-season AMF composition of weeds supports the fact that weeds functionally host AMF during the non-crop period

Investigation of the effects of lubricant fat content on drawn copper wires

The Lean Manufacturing goal of reducing waste and increasing productivity has made it a necessity to produce good quality products in manufacturing industries at a low cost. In the cable manufacturing companies this can be achieved by optimising the wire drawing process. One way to meet the desired quality of the drawn wires is to improve lubricant efficiency through installation of an automatic, continuous lubricant fat content control system on the drawing machine. The paper shows a method of finding the optimum lubricant concentration for producing good quality copper wires using Taguchi experiments. Taguchi experiments are employed to analyse the effects of different lubricant fat content levels on the tensile strength and lubricant temperature. The results from the experiments indicated that the tensile strength of the wire is affected by low lubricant fat content. The lower the lubricant fat content: the lower the tensile strength drawing lubricant resulting in numerous wire breakages that affect the quality of the final product, namely the cable

Model reference adaptive control system for moisture regulation in cotton ginning

Moisture content (mc) within the cotton fibre is an important aspect for all stages of the ginning process. However due to the process dynamics, mc is currently being controlled by regulating the water and air temperatures from the Humidifiers. Human intervention and lack of consistence on set-points determination has resulted in inconsistent mc during humidification. This procedure requires a control system which will be able to adjust the process set-points automatically by eliminating the need for human intervention. In this paper a robust Model Reference Adaptive Control (MRAC) system for a Samuel Jackson Humidifier is presented. This system improves upon the existing system by creating a closed loop controller with parameters that can be updated to change the response from reference model. The control parameters are then updated based on this error thus the parameters converge to ideal values that cause the plant response to match the response of the reference model

Design of an automated grinding media charging system for ball mills

The parameters of mill load (ML) not only represent the load of the ball mill, but also determine the grinding production ratio (GPR) of the grinding process. Monitoring and recognition of milling conditions have significant effect on the operating efficiency, product quality, and energy and grinding media consumption for the milling circuit. This paper presents an automated grinding media charging system incorporating a multi-agent system developed in Java Agent Development Environment (JADE). A control logix program is designed to determine the precise quantities of grinding media to be charged in an incremental manner such that shock loading is avoided. The multi-agent system created in JADE monitors the power drawn and the mill load of the ball mill such that proper charging conditions are established. High quality of the regulation process is achieved through utilization of the control logix and the multi-agent system

A homozygous ADAMTS2 nonsense mutation in a Doberman Pinscher dog with Ehlers Danlos syndrome and extreme skin fragility

An eight-week old Doberman Pinscher was diagnosed with Ehlers Danlos syndrome based on the dog's hyper-mobile carpal, tarsal and stifle joints and abnormal skin. The skin was loose and hyper-elastic with several wounds and large atrophic scars. The dog was euthanized after a severe degloving injury from minimal trauma. A whole-genome sequence, generated with DNA from the dog's blood, contained a rare, homozygous C-to-T transition at position 2408978 on chromosome 11. This transition is predicted to alter the ADAMTS2 transcript (ADAMTS2:c.769C>T) and encode a nonsense mutation (p.Arg257Ter). Biallelic ADAMTS2 mutations have caused a type of Ehlers Danlos syndrome known as dermatosparaxis in other species