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Browsing by Issue Date, starting with "2022-11-11"

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  • Job crafting and job performance: the mediating effect of engagement
    Publication . Moreira, Ana; Encarnação, Tiago; Viseu, J.; Sousa, Maria José
    The main purpose of this study was to investigate whether work engagement mediates the relationship between job crafting and job performance. To this end, the following hypotheses were formulated: (1) job crafting establishes a positive and significant association with job performance; (2) job establishes a positive and significant association with work engagement; (3) work engagement establishes a positive and significant association with job performance; (4) work engagement mediates the association between job crafting and job performance. The sample was composed of 453 participants working in organisations based in Portugal. The hypotheses formulated in this study were tested by performing simple and multiple linear regressions. The results indicated that only increasing structural job resources and increasing challenging job demands established a positive and significant association with task performance. Increasing structural job resources, increasing social job resources, and increasing challenging job demands established a positive and significant association with citizenship performance and work engagement. Work engagement established a positive and significant association with task performance and citizenship performance. Only a partial mediating effect, through work engagement, was observed on the association between increasing challenging job demands and task performance, and between increasing social job resources and citizenship performance.
    2022-11-11Journal article Open Access Show more
  • Performance of Ulva sp. (Chlorophyta) at different stocking densities in recirculating aquaculture systems
    Publication . Schol, Nikki Floor; Galvão, Helena M.; Quintã, Raquel
    Aquaculture may be responsible for deterioration of surrounding natural waters, so focus of research in this field to improve sustainability is directed on the recycling of wastewater in cultivation systems. Recirculating Aquaculture Systems (RAS) show promise, but fish production is often limited because of low water quality due to the accumulation of metabolic waste. Water quality may be improved by integrating seaweed as they effectively clean the water by remediating nutrients. This study explored how to optimize RAS by measuring growth and yield performance of Ulva sp. and how this relates to water quality. An integration experiment was conducted by adding an Ulva filtration unit to outdoor RAS at different fish densities. Seaweed performance was compared by calculating growth rate, biomass yield, and nitrogen removal by biomass of the Ulva stocking densities 1, 2, and 3 kg FW m-2. Additionally, water quality parameters were compared, involving biochemical measurements and fluorescent microscopic microbial counts. The results showed that the highest growth rate was measured for Ulva stocking density 1 kg FW m-2 and the highest biomass and N yield for 2 kg FW m-2. Performance was lower with an increased fish density. The high fish density resulted in lower water quality in the RAS, with a significantly higher abundance of heterotrophic bacteria and bacterivores, a higher level of ammonia, and lower pH. No difference was detected in dissolved oxygen and phytoplankton abundance. These results demonstrate that lower Ulva stocking densities show higher performance in IRAS, but more research is required in improving the cultivation environment of Ulva to increase its capability to enhance water quality parameters.
    2022-11-11Master thesis Open Access Show more