Research Papers - Department of Civil Engineering
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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 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.