Browsing by Author "Asaeda, Takashi"

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    AquaEco 40 (2006) Decomposition of Zizania latifolia AGB and BGB
    (2013-04) Sanderson, Brian; Shilla, Daniel; Fujino, Takeshi; Asaeda, Takashi
    Decomposition of aboveground and belowground organs of the emergent macrophyte Z.latifolia wasinvestigated using a litterbag technique for a period of 359 days in a freshwater marsh in Japan. Above-ground parts were classified into: leaves, sheaths and stems. Belowground parts were classified into: hor-izontal rhizomes (new rhizome, hard rhizome, soft rhizome) and vertical rhizome (stembase). The decayrate (k) was 0.0036 day)1, 0.0033 day)1and 0.0021 day)1for leaves, sheaths and stems, respectively. Forbelowground parts, the decay rate varied considerably from 0.0018 day)1to 0.0079 day)1, according todifferences in the initial chemical compositions of rhizomes. After 359 days of decay, new rhizomes lost94% of their original dry mass, compared with a loss of 48 –84% for the other rhizomes. There was asignificant positive relationshi p between litter quality and decay rate for horizontal rhizomes. For the newrhizomes, which had an internal nitrogen content of 24.2 mg N g)1dry mass, the mass loss was 40% higherthan that of soft rhizomes, which had an internal N content of 9.8 mg N g)1dry mass. Over the period of359 days, the nitrogen concentration in all rhizome types decreased to levels lower than initial values, butthe phosphorus concentration remained constant after an initial leaching loss. Most nitrogen and phos-phorus were lost during the first 45 days of decay. Changes in carbon to nitrogen (C:N) and carbon tophosphorus (C:P) ratios basically followed inversed trends of the nitrogen and phosphorus concentrations.
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    Decomposition Rate of Submerged Plants
    (Springer Link, 2013-04) Shilla, Daniel; Asaeda, Takashi; Fujino, Takeshi; Sanderson, Brian
    Breakdown and nutrient dynamics of submerged macrophytes were studied in Myall Lake, Australia. Mass loss of Myriophyllum sulsagineum was the lowest (64.90%) among the studied macrophytes during the 322 days followed by charophytes (60.79%), whereas Najas marina and Vallisneria gigantea lost 91.15 and 86.02% of their respective initial mass during that time. The overall exponential breakdown rates of Najas marina and Vallisneria gigantea were similar, with k-values of 0.24 and 0.23 day 1 , respectively. These rates were significantly higher than the break down rates of charophytes (0.007 day 1 ) and M. sulsagineum (0.008 day 1 ). During growth phase, water column depicted lower nutrient concentrations while during decay period, significant increase in water column nutrients resulted. Release of nutrients from decomposing macrophytes and incorporation of these nutrients into sedimentary phase as well as uptake of nutrients by the growing macrophytes, can present a considerable cycling pathway of nutrients in Myall lake system. The results of this study suggest that different submerged macrophytes may differ appreciably in quality and may exhibit different decomposition rates, patterns and nutrient dynamics in aquatic ecosystems in general, and Myall lakes in particular.
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    Hydrobiologia 541 (2005) Decomposition of Eichhornia crassipes
    (2013-04) Sanderson, Brian; Shilla, Daniel; Fujino, Takeshi; Asaeda, Takashi
    The water hyacint h (Eichhornia crassipes (Mart.) Solms.) plants in lakes and reservoirs have gained con-siderable attention in tropical and sub-tropical parts of the world due to its rapid growth. The amount ofnutrients released from the dead plant materials is of particular interest. Thus, decomposition of waterhyacinth plant parts under aerobic conditions was studied in the laboratory. Roots , petioles, and leaves ofwater hyacinth were enclosed separately in one litre polypropylene bottles which contained 500 ml of lakewater. 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 throughday 61, with almost 92.7 and 97.3% of the dry mass removed, respectively. Weight loss due to bacterialactivities during 94 days decomposition was 22.6, 3.9, and 30.5% from leaf, petiole, and root litter.Decomposition of litter in lake water indica ted that after 94 days 0.6, 0, and 0.6 g m)2of leaf, petiole, androot N was dissolved in leachate, while 23.1, 14.4, and 6.0 g m)2of leaf, petiole, and root N was eithervolatilized or remained as particulate organic N. Moreover, 0.2, 0, and 0.1 g m)2of leaf, petiole, and root Premained dissolved in the leachate, while 3.1, 3.4, and 1.1 g m)2of leaf, petiole, and root P was eitherprecipitated or remained as particulate organic P. The carbon dynamics during the decomposition indicatedthat 7.4, 28.8, and 3.7 g m)2of leaf, petiole, and root C remained dissolved in the leachate afte r 94 dayswhile 228.0, 197.6, and 107.4 g m)2of leaf, petiole, and root C was either diffused or remained as par-ticulate organic C. These findings are useful for quantifying the nutrient cycles of very shallow lakes withwater hyacinth under aerobic water environment. Further examination of the fate of the plant litter as itmoves down in deep anaerobic water environment, is necessary to understand the leaching process better
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    Modelling Faecal Streptococci Mortality in Constructed Wetlands Implanted with Eichhornia Crassipes
    (2008) Kalibbala, Martin; Mayo, Aloyce W.; Asaeda, Takashi; Shilla, Daniel
    Faecal streptococci mortality was investigated in a water hyacinth (Eichhornia crassipes) constructed wetland pond. The wetland was 7.5 m long, 1.5 m wide and 1.0 m deep, and was implanted with E. crassipes. In order to assess the performance of the system towards bacterial mortality, a mathematical model, based on plug flow philosophy was developed. The model incorporated the role of factors, namely solar intensity, pH, dissolved oxygen, temperature, sedimentation, and root attached growth. Model analysis strongly suggests that bacterial mortality rate constant was largely influenced by two factors, namely solar intensity and root biofilm attachment, with both contributing approximately 70.5% of removal. The contribution of other factors like temperature, dissolved oxygen, pH and sedimentation on bacterial mortality rate were less significant. For example, dissolved oxygen, pH and sedimentation contributed 5%, 8% and 0.82%, respectively. Thus, the sedimentation factor was omitted from the model because of its insignificant contribution. The same was done for temperature, due to low ambient temperature range (3.1°C) in the study area. The overall model bacterial removal efficiency was 83%.
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    Phosphorus speciation in Myall Lake sediment, NSW, Australia
    (2009-03) Shilla, Daniel; Asaeda, Takashi; Kalibbala, Martin
    The amount of phosphorus and its fractions in the sediment of Lake Myall, NSW, Australia, was assessed using a sequential extraction technique. Five sedimentary phosphorus reservoirs were measured, namely loosely sorbed phosphorus (NH4Cl–P), iron associated phosphorus (BD–P), calcium bound phosphorus (HCl–P), metal oxide bound phosphorus (NaOH–P) and residual phosphorus (organic and refractory P, Res-P). Samples were taken from the deep and shallow sites of the lake. During the analysis, the average concentrations of each fraction of phosphorus was calculated. The results depicted that the total phosphorus (TP) content and chemically extractable phosphorus in both fine and coarse sediment fractions from the deep sites of the lake were significantly higher than those of the shallow sites, except for HCl–P extracted from the fine sediment fraction. Sediment TP was also strongly and positively correlated to sediment Fe. The phosphorus in the sediment mainly consisted of BD–P and Res-P, while NH4Cl–P and HCl–P only contributed a minor part. The rank order of the different phosphorus extracts was similar for the two sites, namely Residual-P>BD–P>NaOH–P>HCl–P>NH4Cl–P.