Faculty of Engineering
Permanent URI for this communityhttps://rda.sliit.lk/handle/123456789/4203
Browse
5 results
Search Results
Publication Embargo Mathematical modeling as a tool in aquatic ecosystem management(American Society of Civil Engineers, 2002-04) Karunaratne, S; Asaeda, TThe capacity of an existing model to simulate the growth (biomass) of a reed [Phragmites australis (Cav) Trin. ex Stuedel] in fresh water habitats using published field data and the incorporation of a submodel to estimate seasonal variation in reed mineral–nutrient content was investigated. This new feature also enabled one to estimate plant removal of mineral–nutrients from sediments. Model-predicted and observed shoot, rhizome, and root biomass showed concordance correlation coefficients of 0.97, 0.52, and 0.99, respectively. The nutrient analysis study showed that the annual uptakes of nitrogen and phosphorus from sediment by P. australis in the Denmark Vejlerne Nature Reserve were 143.9 and 16.1 kg ha−1, respectively. The simulated results also showed that at the time of peak standing stock of minerals, shoots contained 40 and 22.5% of whole plant N and P, respectively. This suggested that the use of the common reed in wastewater treatment plants allows removal of nitrogen more easily than phosphorus, because a higher percentage of nitrogen is bound with the easily removable shoot parts.Publication Open Access Age-specific seasonal storage dynamics of Phragmites australis rhizomes: a preliminary study(Kluwer Academic Publishers, 2004-10) Karunaratne, S; Asaeda, T; Yutani, KAge-specific seasonal rhizome storage dynamics of a wetland stand of Phragmites australis (Cav.) Trin. ex Steud. in Japan, were investigated from April to October 2000. For each sampling date, above- and below-ground biomass and age-specific rhizome bulk density, ?rhiz were measured. Seven rhizome age classes were recognized, from <1 year to six years old, based on their position within the branching hierarchy as main criteria and rhizome color, condition of nodal sheaths and condition of the shoots attached to vertical rhizomes as secondary criteria. P. australis stand was moderately productive, having a net aerial and below-ground production of 1980 and 1240 g m−2, respectively, and a maximum mean shoot height of 2.33 ± 0.12 m. In spring, shoot growth started at the expense of rhizome reserves, decreasing the rhizome biomass as well as ?rhiz. Both parameters reached the seasonal minimum in May followed by a subsequent increase, indicating a translocation of reserves to rhizomes from shoots after they become self supporting. For each sampling date, ?rhiz increased with rhizome age. Given that the quantity of reserves remobilized by the rhizomes for spring shoot growth, as assessed by the drop in bulk density from April to May, were positively correlated (r = 0.97, P < 0.05) with rhizome age, it is proposed that for spring shoot formation older rhizomes remobilize stored reserves more actively than younger ones. Given that the accumulation of rhizome reserves (rise in bulk density) from May to August, May to September or May to November was negatively correlated (r = 0.97, 0.92 and 0.87, respectively, P < 0.05) with rhizome age, it seemed possible that younger rhizomes were ‘recharged’ at a higher rate than older ones. These resource allocation mechanisms pertaining seasonal rhizome storage dynamics are of paramount importance in formulating management and conservation strategies of wetlands and aquatic habitats. Our results indicate that a harvest of above-ground biomass from May to June would be more effective in reducing the growth than a harvest in July to August or later, when rhizome reserves have already been replenished. However, the latter may remove a larger shoot bound nutrient stock, still preserving a healthy stand for the subsequent years.Publication Open Access Verification of a mathematical growth model of Phragmites australis using field data from two Scottish lochs(Springer Netherlands, 2000-12) Karunaratne, S; Asaeda, TA growth model of Phragmites australis was verified using two independent sets of published field data. The model simulates the growth pattern of a well-established, monospecific stand of P. australis in the absence of genetic diversity and environmental stresses of mainly nutrient and water deficiency. The model formulated using first order differential equations was combined with plant phenology and comprises five subroutines in which photosynthetically active radiation, shoot, root, rhizome and new rhizome biomass are calculated. Using the model, experimental results were reproduced within reasonable limits having concordance correlation coefficients of more than 0.75 for 70% of the output parameters, which was the main objective of the study. The modelled efficiencies of PAR were 7.15% and 3.09%, as opposed to 7.7% and 2.53% in experimental estimations, for Loch of Foffar and Loch of Balgavies, respectively. Production and seasonal fluxes of dry matter of P australis in Scottish lochs were estimated using the modelled quantities for the 1975 growing season in g m 2. They showed that 31% and 37% of total net photosynthate translocated to rhizomes before shoot senescence began in Loch of Forfar and Loch of Balgavies, respectively. Also in both lochs approximately 45% of total downward translocation came from accumulated shoot dry matter during senescence, while the rest came from photosynthesis before the shoots started to senesce.Publication Embargo Shoot regrowth and age-specific rhizome storage dynamics of Phragmites australis subjected to summer harvesting(Elsevier, 2004-04-01) Karunaratne, S; Asaeda, T; Yutani, KShoots of a monospecific wetland stand of Phragmites australis (Cav.) Trin. ex Steud. in Central Japan were harvested during two summer months in June (June-cut stand) and July (July-cut stand) and their effects on the stand morphology, above- and below-ground biomass and rhizome storage level (in terms of age-specific rhizome bulk density, ρrhiz), were investigated between themselves and to an uncut control stand. Both harvesting treatments increased leaf production and decreased shoot height, stem diameter, and the storage accumulation capacity of older rhizome age categories, the June-cut stand showing the lowest ρrhiz. Even though the year-end age-specific rhizome reserve level did not reach to that of uncut stand values, both treatments accelerated the post-harvest rhizome reserve accumulation rates (i.e. rate of ρrhiz increment) stimulated by shoot harvesting, especially in younger rhizomes and were negatively and linearly correlated with rhizome age. The study identified the seasonal changes of the rhizome reserve quality as essential for proper vegetation management. July or August is the appropriate harvesting time for plant stands used in phytoremediation and wastewater treatment, where a larger shoot-bound nutrient stock is removed, while preserving a healthy stand for the subsequent years. A harvest in May to June would be more effective in reducing the growth, and repeated June-cutting may likely weaken the stand beyond repair after several years.Publication Embargo Dynamic modeling of the growth of Phragmites australis: model description(Elsevier, 2000-08-01) Asaeda, T; Karunaratne, SA dynamic model was developed to simulate the growth dynamics of a monospecific stand of Phragmites australis in freshwater ecosystems. Five state variables (biomass of shoots, inflorescence, roots, old rhizomes and new rhizomes) were selected to illustrate the growth of P. australis. Growth was described using mathematical relationships. The net growth of the plant stand was the integral effect of photosynthesis, respiration, mortality and assimilate translocation between shoots and below-ground plant organs. Below-ground biomass (i.e. rhizome and root biomass) before the growth commencement, daily total global radiation and daily mean air temperature were input data. The model is capable of simulating the seasonal variation of above-ground biomass (shoots, stems, leaves and panicles), leaf area index, rhizome, new rhizome, root biomass and shoot height with correlation coefficients close to 1.0 for most of the parameters. The model estimated the conversion efficiency of photosynthetically active radiation varying from 3.76 to 7.19% from northern temperate regions to warmer southern temperate regions. The carbon budget was constructed using the modelled predictions. Analysis of annual net production and fluxes showed that irrespective of the varying climatic conditions, the percentage of annual fluxes of an event, as a proportion of the total photosynthetic production remained almost same. The respiration of shoots, as well as rhizomes and roots, was shown to consume a considerable amount of photosynthetic production: 25% by shoot respiration and 40% by rhizome and root respiration.