Browsing by Author "Asaeda, T"

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item: Conference-Full-text
Consequences of flow turbulence : Biomass partitioning and Plastic responses in morphology
(2013-11-12) Ellawala, C; Asaeda, T; Kawamura, K
Water movement has a major influence on plant growth in aquatic ecosystems. Although the plants growing in shallow lakes and wetlands are not experiencing mean flow, they also experience water movement as flow turbulence. The objective of the current study was to observe the variations of morphology and biomass partitioning in Egeria densa and Chara fibrosa when exposed to three different turbulence levels. Chara fibrosa has been observed to have shorter internodal lengths, less number of internodes when exposed to increased turbulence, while reducing the lateral branching. Egeria densa has been observed to reduce biomass gain and lateral branching while increasing the shoot:root ratio. Morphological variations of C. fibrosa and E. densa are more or less similar while their responses to flow turbulence directed towards their survival in respective condition.
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Control of algal blooms in reservoirs with a curtain: A numerical analysis
(Elsevier, 2001) Asaeda, T; Pham, HS; Nimal Priyantha, DG; Manatunge, J; Hocking, GC
Two vertical curtains, having depths to cover the epilimnion thickness, were installed across the Terauchi Dam Reservoir in the western island of Japan to curtail the nutrient supply from nutrient-rich inflows to the downstream epilimnion of the reservoir. The withdrawal level was also regulated to keep the downstream epilimnion away from the nutrient supply. This method markedly reduced algal blooming in the reservoir downstream of the curtains during spring and summer. The physical and biological processes in the reservoir ecosystem were analysed using the 2-D reservoir model DYRESM and chemical and biological submodels, to predict the water quality and algal species composition in the reservoir. The horizontal variability was maintained in the model by dividing the horizontal layer into parcels. Temperature, chlorophyll-a, soluble phosphorus, nitrate, ammonium, dissolved oxygen, biochemical oxygen demand, internal nitrogen, internal phosphorus were considered as state variables in the model. The simulated results revealed the mechanism of how algal blooming is reduced, during early spring high algal concentrations consume large amounts of nutrients, which reduces the nutrient supply to the downstream zone of the reservoir, whereas during late spring and summer, nutrient dispersion from the upstream epilimnion to the downstream epilimnion is curtailed by the curtains, markedly reducing algal blooming in the downstream zone.
item: Article-Abstract
Control of algal blooms in reservoirs with a curtain: a numerical analysis
Asaeda, T; Pham, HS; Priyantha, DGN; Manatunge, JMA; Hocking, GC
Two vertical curtains, having depths to cover the epilimnion thickness, were installed across the Terauchi Dam Reservoir in the western island of Japan to curtail the nutrient supply from nutrient-rich inflows to the downstream epilimnion of the reservoir. The withdrawal level was also regulated to keep the downstream epilimnion away from the nutrient supply. This method markedly reduced algal blooming in the reservoir downstream of the curtains during spring and summer. The physical and biological processes in the reservoir ecosystem were analysed using the 2-D reservoir model DYRESM and chemical and biological submodels, to predict the water quality and algal species composition in the reservoir. The horizontal variability was maintained in the model by dividing the horizontal layer into parcels. Temperature, chlorophyll-a, soluble phosphorus, nitrate, ammonium, dissolved oxygen, biochemical oxygen demand, internal nitrogen, internal phosphorus were considered as state variables in the model. The simulated results revealed the mechanism of how algal blooming is reduced, during early spring high algal concentrations consume large amounts of nutrients, which reduces the nutrient supply to the downstream zone of the reservoir, whereas during late spring and summer, nutrient dispersion from the upstream epilimnion to the downstream epilimnion is curtailed by the curtains, markedly reducing algal blooming in the downstream zone.
item: Article-Full-text
Decomposition and mineralization of Eichhornia crassipes litter under aerobic conditions with and without bacteria
Gamage, NPD; Asaeda, T
The water hyacinth (Eichhornia crassipes (Mart.) Solms.) plants in lakes and reservoirs have gained considerable attention in tropical and sub-tropical parts of the world due to its rapid growth. The amount of nutrients released from the dead plant materials is of particular interest. Thus, decomposition of water hyacinth plant parts under aerobic conditions was studied in the laboratory. Roots, petioles, and leaves of water hyacinth were enclosed separately in one litre polypropylene bottles which contained 500 ml of lake water. To study the influence of bacteria on the decomposition, antibiotics were added to half of the bottles. We observed that decomposition of leaves and petioles without antibiotics were relatively rapid through day 61, with almost 92.7 and 97.3% of the dry mass removed, respectively. Weight loss due to bacterial activities during 94 days decomposition was 22.6, 3.9, and 30.5% from leaf, petiole, and root litter. Decomposition of litter in lake water indicated that after 94 days 0.6, 0, and 0.6 g m)2 of leaf, petiole, and root N was dissolved in leachate, while 23.1, 14.4, and 6.0 g m)2 of leaf, petiole, and root N was either volatilized or remained as particulate organic N. Moreover, 0.2, 0, and 0.1 g m)2 of leaf, petiole, and root P remained dissolved in the leachate, while 3.1, 3.4, and 1.1 g m)2 of leaf, petiole, and root P was either precipitated or remained as particulate organic P. The carbon dynamics during the decomposition indicated that 7.4, 28.8, and 3.7 g m)2 of leaf, petiole, and root C remained dissolved in the leachate after 94 days while 228.0, 197.6, and 107.4 g m)2 of leaf, petiole, and root C was either diffused or remained as particulate organic C. These findings are useful for quantifying the nutrient cycles of very shallow lakes with water hyacinth under aerobic water environment. Further examination of the fate of the plant litter as it moves down in deep anaerobic water environment, is necessary to understand the leaching process better.