Research Papers - Department of Civil Engineering

Permanent URI for this collectionhttps://rda.sliit.lk/handle/123456789/598

Browse

Filters

20043

Advanced Search

Filter by

Settings

End date: 2009Subject: search.filters.subject.Bulk density

Search Results

Now showing 1 - 3 of 3
  • Thumbnail Image
    PublicationOpen Access
    Colour-based estimation of rhizome age in Phragmites australis
    (Kluwer Academic Publishers, 2004-10) Karunaratne, S; Asaeda, T; Toyooka, S
    The 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.
  • Thumbnail Image
    PublicationOpen Access
    Age-specific seasonal storage dynamics of Phragmites australis rhizomes: a preliminary study
    (Kluwer Academic Publishers, 2004-10) Karunaratne, S; Asaeda, T; Yutani, K
    Age-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.
  • Thumbnail Image
    PublicationEmbargo
    Shoot regrowth and age-specific rhizome storage dynamics of Phragmites australis subjected to summer harvesting
    (Elsevier, 2004-04-01) Karunaratne, S; Asaeda, T; Yutani, K
    Shoots 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.