A primary study of the decomposition of reed (Phragmites australis Cav.) leaves in the Schelde under experimental conditions
Hongwei, Y. (1996). A primary study of the decomposition of reed (Phragmites australis Cav.) leaves in the Schelde under experimental conditions. MSc Thesis. VUB: Brussel. 67 pp.
In the experiment presented in this thesis, the leaf hanging method was used for the study of the initial decomposition (6 weeks) of reed Phragmites australis (Cav.) leaves under aerobic condition. The development of micro-organisms associated with the process of the decomposition were observed. The adequacy of single and double negative exponential function model describing the mass loss of decaying leaves was compared. Dry weight (DW), particulate total carbon (PTC) and particulate organic carbon (POC) of leaf pieces were a significant (ANOVA, p < 0.05) linear function of leaf area measured. The regressions were significantly (ANOVA, p < 0.05) different between the respective weeks of the experiment. Although the single negative exponential model fitted the DW, PTC and POC data of leaf pieces significantly (ANOVA, p < 0.05), the double negative exponential model fitted significantly more adequate to describe the decomposition rate of leaves (Multiple regression test, p < 0.05). The specific decomposition rate (k = 0.018 day-1) determined by fitting the single negative function model to DW of leaves pieces was comparable to literature values. In the first week of decomposition, about 20 % DW and POC of leaves pieces were lost. This loss probably mostly represents leaching of water-soluble components. After this rapid decomposition stage, the decomposition rate declined and about 30 % of both DW and POC of leaf pieces was lost due to the activity of micro-organisms in the last 5 weeks. The decomposition of reed leaves greatly stimulated the development of population of micro-organisms. The abundance of free bacteria in the water with reed leaves was significantly (ANOVA, p < 0.05) higher than that in water without reed leaves after the submergence of leaves. With exception of the second and third week, the abundance of bacteria attached on the decomposing leaves showed an increasing tendency, which represent the high importance of bacteria during the period of initial decomposition. The abundance of micro(zoo)plankton in the water with reed leaves was significantly (ANOVA, p< 0.05) higher than that in the water without reed leaves during the period of the incubation except during the third week. The concentration of POC in the water with leaves showed a significantly increasing tendency (Spearman Rank, p< 0.05). This was probably due to both the increase of the concentration of detritus derived from the submerged leaves and abundance of micro(zoo)plankton. With exception of the second and third week, the concentration of POC in water with leaves was significantly higher than that in water without leaves throughout the period of the incubation (ANOVA, p< 0.05).
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