Decomposition And Nutrient Dynamics Of Phragmites Australis Litter In The Wuliangsu Lake

The decomposition of lake aquatic plant litter affects litter deposition and nutrient release into water and sediments. Consequently, the aquatic environment of the lakes affected. Litter bag technique was used to study the litter decomposition, nutrient dynamics and affecting factors of Wuliangsu Lakeshore vegetation zone’s dominant species-Phragmites australis litter. The hybrid evolutionary algorithm (HEA) was implemented to model, analyze and forecast population dynamics and affecting factors of Phragmites australis litter decomposition. The results shows that:1. The mass losing of decomposition litter was rapid and only 52.44% of the dry mass remained at the end of the experiment during 270 days. The decomposition rate is 0.00268d"1.The time needed for 50% of dry mass decomposition in the plant tissues is 0.83 year, and the time needed for 95% of dry mass decomposition is 3.19 year.2. In the process of decomposition, the N in litter has the dynamics characteristics of release-accumulation-release process, while the P and C have been in a release state during decomposition. The decomposition rates and nutrient content variations were simultaneously influenced by the quality of the litter as well as the environmental factors (water temperature, dissolved oxygen and pH), which were significantly correlated with the litter decomposition and nutrient dynamic during the process of decomposition.3. The predicting of models obtained with HEA showed the best results for Phragmites australis litter decomposition resulting in coefficients of determination(r2) between the predicted and measured data of 0.90-0.99.4. Mass loss(ML) has positive relationship with WT. The N release favors low pH (pH<8.326); When DO≤5.688, N/P is relatively low (below 14),which is not sensitive to changes of pH, but is positively related to the DO. With the increase of WT within the range of 0-6.1%, the N/P goes up to a high value quickly at the beginning and then drops down gradually with the change of WT. When DO> 5.688, N/P is increase with the change of WT and eventually reaches a peak value 24.787; when WT> 16.978, the P has negative relationship with DO, namely P release fast under the condition of high dissolved oxygen; when WT≤16.978, WT is negatively related to low value of P, namely temperature promote P release. The net release of P elements happened.