Characteristics of Nutrients and Influence Factors of Aquatic Macrophytes in the Ditches of Raised Fields in Baiyang Lake

The concentrations of nutrients of plants and water quality were investigated in the ditches of raised fields in Baiyang Lake. The 20 study sites spread throughout the entire area of the raised fields. There were 14 species of aquatic macrophytes growing in different areas of the platforms and ditches. Only 2 emergent plant species were grown in the ditches because of limited light and space in the ditches. Eight submerged plant species and 4 floating plant species that preferred the still water were found at the same time. The nutrient concentrations differed among the 14 macrophytes in the ditches, leading to the different effects on nutrient accumulation. Some plants had higher nutrient concentrations than the others, such as Phragmites australis, Spirodela phlyhiza, Hydracharis dubta, Ceratophyllum spicatum, Potamogeton crispus, Potamogeton malaianus and Myrio? phyllum spicatum. Phragmites australis, Nelumbo nucifera, Salvinia natans, Chara sp., Potamogeton malaianus, Potamogeton lucens and Myriophyllum spicatum had a lower decomposition rate than the others due to the higher C/N, C/P and N/P ratios. Periodically harvesting these plants will help reduce the siltation of lakebed and slow the process of terrestralization. The types of aquatic macrophytes and their abilities to assimilate nutrients are influenced by various environmental factors. Water in all the ditches of raised fields was weakly alkaline and lower than 1.5 m, but had significant differences in nutrient levels, transparency and disolved oxygen content among the 20 sample sites. The results showed a positive correlation between the concentrations of total nitrogen and total phosphorus in the lake water. Water nutrient concentrations and light conditions were considered as 2 important impact factors in this research. The nutrient concentrations of plants had significantly positive correlation with water nitrogen and phosphorous concentrations, and markedly negative relationship with transparency. Nutrient uptake by aquatic macrophytes could be improved effectively by changing the structure of the raised fields and the water conditions.