Faculty of Engineering
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Publication Embargo Impact of calcium and magnesium on growth and morphological acclimations of Nitella: implications for calcification and nutrient dynamics(Taylor & Francis, 2010-12-01) Gomes, P. I. A; Asaeda, TThe impact of calcium (Ca) and magnesium (Mg) on the growth and morphology of a Charophyte, Nitella pseudoflabellata, and the influence of Mg on calcification and phosphorous (P) speciation were studied in laboratory experiments for variable concentrations (≤q120 mg · L−1) of Ca and Mg. It was clearly identified that Mg aided shoot elongation. An increase in Ca concentrations produced intensified shoot elongation also, but at a lesser rate than the equivalent levels of Mg. Depending on the availability of Ca and Mg, the morphological appearance differed significantly, suggesting significant levels of ecoplasticity. Furthermore, Mg was observed to produce less calcite encrustation. Plant P-speciation suggested a higher Mg concentration corresponding to a more water-soluble and less carbonate-bound P fraction. This indicates that upon senescence and decomposition, a large fraction of P is supplied to the water column; ultimately behaving similar to a typical vascular plant.Publication Embargo Spatial and temporal heterogeneity of Eragrostis curvula in the downstream flood meadow of a regulated river(EDP Sciences, 2009) Gomes, P. I. A; Asaeda, TWe studied the spatiotemporal trends of Eragrostis curvula (Schrad.) Nees in a flood meadow of a regulated river. The response variables, including the abundance of colonies, colony sizes, flowering spikes, biomass and root structure were checked against a set of environmental variables. These variables included distance from the river, substrate conditions (stony to sandy), soil nutrients (total nitrogen, phosphorous and calcium) and soil moisture. Relationships were evidenced using redundancy analysis. Response variables were found to be distinctive and based on substrate conditions (i.e. stony or sandy). The variables ‘distance from the river’ and ‘soil phosphorous’ contributed significantly to the overall variance. Stony habitats were observed to have lower soil nutrient levels and were characterised by monospecific stands of E. curvula, while the high nutrient levels of sandy habitats promoted heterogeneous herbaceous vegetation growth. Primary production, especially belowground, was measured to be significantly higher (t-test, P<0.05) in stony habitats. Spatiotemporal trends suggested that, irrespective of the number of colonies, E. curvula demonstrated significant levels of adaptation to micro-environments through biomass allocation and the morphological plasticity of its roots. The study results suggest that river regulation and the subsequent reduction in the frequency of inundation, in addition to the reduction of nutrients and fine sediment supply downstream, give a competitive edge to E. curvula over other herbaceous species.Publication Embargo Phytoremediation of heavy metals by calcifying macro-algae (Nitella pseudoflabellata): implications of redox insensitive end products(Pergamon, 2013-08-01) Gomes, P. I. A; Asaeda, TTo evaluate the phytoremediation of heavy metals in water and understand the biochemistry of end products of calcifying macro algae (charophytes), an 84-wk laboratory experiment was conducted. Eighteen microcosms were maintained with and without plants. These were given different heavy metal treatments: no heavy metals, 0.2 mg L−1 Cr6+ and 0.01 mg L−1 Cd. Accumulation observed to be 0.06% Cr by dry weight and for Cd it was 0.02%. The bioconcentration factors were 3000 and 25 000 for Cr and Cd, respectively. Ratios of heavy metal accumulation in alkaline (i.e., calcified areas) to acidic areas of plants were 6 to 4 (for Cr) and 1 to 1 (for Cd). This elucidated an association between heavy metal accumulation and calcification. This was validated by sequential extraction of sediments. It was shown that in microcosms with plants, the heavy metals were mainly in redox insensitive and less bioavailable carbonate bound form (39–47%). This was followed by organic-bound form (23–34%). Carbonate bound end products will ensure long term storage of heavy metals and after plant senescence these will not re-enter the water column.Publication Embargo Phycoremediation of Chromium (VI) by Nitella and impact of calcium encrustation(Elsevier, 2009-07-30) Gomes, P. I. A; Asaeda, TThis article discusses the applicability of the Charophyte, Nitella pseudoflabellata in the remediation of Cr (VI) contaminated waters at different calcifying potentials. Its growth was found to be positively correlated with Ca in water (CaW), but marginally significant in the presence of Cr (VI) in water (CrW). High CaW resulted in calcite encrustation on the plant cell wall. CaW was found to be aiding Cr (VI) fixation in the long run, as this correlated positively with both CaW and CrW. However, Ca interfered with passive Cr (VI) accumulation in live plant matter at low CrW concentrations (≤0.2 mg/L). Biosorption by dead plant matter seemed to be the major mechanism as the dead plant organs contained >1 mg/g Cr dry weight of plant. Cr (VI) concentrations greater than 0.4 mg/L were too toxic, showing maximum quantum efficiency of PSII photochemistry (Fv/Fm) values < 0.63. The opposite was noticed (Fv/Fm > 0.76) when Cr (VI) was less than 0.2 mg/L. Elongation curve patterns based on shoot lengths showed similar scenarios. In all cases high CaW units with calcite encrustation found to be least affected by Cr (VI) toxicity. Optimum remediation was obtained using a combination of high Ca and Cr (VI) in the case of passive (short-term) operation and low Ca and Cr (VI) for active (long-term) operation. Under the passive scenario, plants accumulated above 1.2 mg/g Cr dry weight whereas in the active case, accumulation was 0.8 mg/g Cr dry weight. We conclude that Nitella-mediated Cr (VI) remediation is a promising technique within the range and conditions investigated.Publication Embargo Tree colonization trends on a sediment bar after a major flood(John Wiley & Sons, Ltd., 2011-10) Asaeda, T; Gomes, P. I. A; Sakamoto, K; Rashid, M. HTree mortality and regeneration in riparian areas are greatly influenced by flooding. The elevational distribution of Salix spp. and Robinia pseudoacacia were investigated by observing densities and standing conditions before and after a major flood on a sediment bar in the middle reaches of the Arakawa River in Kumagaya, Japan. The subsequent tree recruitment was also examined. R. pseudoacacia was easily washed away with the eroded sediment, whereas Salix spp. was found to be more tolerant. Both species were able to survive even after collapsing, provided that their roots were fully or partially embedded in the sediment. Re-shooting of collapsed trees, rather than emergence from saplings (either by seeds or vegetative fragments), was observed to be the major method of recruitment after the flood. Therefore, tree density before the flood was unchanged, unless the trees were subject to washing away. Salix spp. recruitment was mainly observed in low-lying areas and R. pseudoacacia in elevated areas. Recruitment from saplings was species-specific. Salix spp. at high elevations originated mainly from shoot fragments as they need high levels of moisture for seed germination and at higher elevations, sediment moisture content is very low. R. pseudoacacia, on other hand, originated mainly from roots and seeds. At a given elevation, past recruitment patterns indicated that the annual recruitment of trees increased with tree density up to a particular threshold of recruitment density. Further increases in tree density beyond that optimum value resulted in a decline in recruitment. Furthermore, threshold density was observed to increase along with elevation for R. pseudoacacia while declining with Salix spp. Copyright © 2010 John Wiley & Sons, Ltd.Publication Embargo Spatial and temporal tree colonization in a midstream sediment bar and the mechanisms governing tree mortality during a flood event(John Wiley & Sons, Ltd., 2010-10) Asaeda, T; Gomes, P. I. A; Takeda, EReduced disturbances in regulated rivers can result in stable tree colonisation in downstream reaches. We examined spatial and temporal tree colonisation on a midstream sediment bar, focussing on three dominant taxa: Salix spp. (primarily Salix gilgiana), Robinia pseudoacacia and Albizia julibrissin. We developed allometric relationships for tree height, tree age and tree diameter at breast and knee height, as well as relationships between above and below-ground biomass. The spatial profiles for all individual trees of these taxa were obtained before and after a major flood in September 2007. Pre-flood data indicate that R. pseudoacacia colonize the highest elevations, A. julibrissin lower elevations and Salix spp. the lowest elevations of the three taxa. The oldest trees at each elevation were found to have survived 1.8–2.5 m inundation in past floods. Results of investigations subsequent to the flood event in September 2007 suggest that trees can survive flooding as long as their roots remain embedded in the soil. Individuals of Salix spp. experienced higher levels of inundation, but showed the greatest survival. This is probably due to morphological acclimations, particularly deep root systems and high elasticity of shoots. Considering inundation depths, erosion depths and sediment particle sizes in tree habitats, we found that sediment mobilization was the major cause of tree mortality. Thus, the ability of Salix spp. to colonize coarse sediments greatly contributed to its survival, as coarse sediments result in significantly less tractive force. Copyright # 2009 John Wiley & Sons, Ltd.Publication Open Access Colour-based estimation of rhizome age in Phragmites australis(Kluwer Academic Publishers, 2004-10) Karunaratne, S; Asaeda, T; Toyooka, SThe colour of different age groups of Phragmites australis (Cav.) Trin. ex Steudel rhizomes was studied from April through October 2000 at approximately one-month intervals to propose a more efficient method to identify the rhizome age based on the Munsell colour-order system. Seven rhizome age-classes were recognized, from <1 to 6 years old, based on descriptions published in the scientific literature. During April and May sampling, spectral reflectance between 400 and 700 nm of different rhizome ages was measured at 10 nm intervals, using a spectral colorimeter. Rhizomes of different ages were assigned colours by selecting one/two shortest Euclidian distances between the mean spectral reflectance of each rhizome age category and the Munsell colours on the four-dimentional subspace, made by Principal Component Analysis of the spectral reflectance data of 1289 Munsell colours. The Munsell colour for new to six-year-old rhizomes changed from yellow to yellow-red, and the value decreased from new to six-year-old rhizomes, indicating a darkening with ageing. The age of rhizomes collected from April through October was estimated using the colour key, in addition to the age attribution based on branching hierarchy. Between 87% and 100% of the rhizomes attributed to a certain age class based on branching hierarchy were assigned to the same age class using colours during all sampling dates. There was a strong correlation (r = +0.96) between rhizome age estimated by branching hierarchy and colour. At each sampling, bulk density, an indicator of rhizome storage levels, measured as a verification of age identification, varied among the age categories indicating distinct differences in storage levels. These results confirmed that rhizomes of a specific age category could be assigned a distinct colour, which remains more or less unchanged throughout the growing season. Thus, colour can be used as a primary criterion in the estimation of the age of P. australis rhizomes.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.