GROWTH DIFFERENCES BETWEEN HYDRILLA VERTICILLATA AND MYRIOPHYLLUM SPICATUM AND THE EFFECTS ON WATER ENVIRONMENT IN NEWLY BUILT WATER SUPPLY LAKES IN CHANGSHU CITY

In order to explore the effect of submerged macrophytes community construction on the water environment of newly built water supply lakes, a comparative study was conducted on the growth of Hydrilla verticillata and Myriophyllum spicatum under artificial planting conditions and their effects on water quality and chlorophyll a(Chl.a) in the newly built emergency water supply lake from May to November 2019 in Changshu City, Jiangsu Province, China. The results showed that the two kinds of submerged macrophytes could grow normally in the experimental lake, and their biomass showed an upward trend from May to September, but H. verticillata was in a rapid growth period from May to July, while M. spicatum was in a rapid growth period from July to September. The decay period of H. verticillata was earlier than that of M. spicatum, and the decay process was shorter. In November, H. verticillata withered completely, while M. spicatum was still in the middle stage of decay. The concentration of Chl.a could be effectively reduced during growth period of two submerged macrophytes, inhibiting phytoplankton growth, while the results were opposite during the period of decline in Autumn. The comprehensive membership function value calculated by total phosphorus(TP), total nitrogen(TN), chemical oxygen demand(COD_Mn), Chl.a, dissolved oxygen(DO) and Water transparency(SD) showed that the water quality of submerged macrophytes group was better than that of the control group during the period of vigorous growth, while deteriorating during decline period. Pearson analysis showed that the biomass of H. verticillata had a significantly negative correlation with Chl.a, and the biomass of H. verticillata and M. spicatum had a significantly negative correlation with TP. This study can provide theoretical support for selecting, planting and harvesting of submerged macrophytes during lake restoration in the middle and lower Yangtze River Basin.