Influence Scope of Potamogeton crispus Population on Lake Waterquality during the Growth Period in Xuanwu Lake, China

Potamogeton crispus has a significant effect on the purification of contaminated water and can improve the stability of aquatic ecosystems, but much research work was carried out under controlled conditions. The water quality indexes were measured to determine whether the purification effect under natural conditions can achieve the same effect as under controlled conditions in this study. The physical and chemical indicators of the water around the P. crispus population were monitored to study the range of impact of P. crispus population during the logarithmic growth period on the water in Xuanwu Lake, Nanjing City. These indicators included pH, secchi disc transparency, turbidity, dissolved oxygen, total nitrogen, ammonia, and total phosphate. The result showed that P. crispus population played an important role in improving lake water quality. P. crispus population increased dissolved oxygen concentration, improved transparency, reduced turbidity, absorbed nutrients from the water column. The transparency, turbidity, and pH value could be affected to 40% of the width of P. crispus population, while dissolved oxygen concentration could be affected to the same width of the population. But the nitrogen and phosphorus concentration could be affected to 10% of the population. In vertical space, the influence of P. crispus population on the surface water was greater than that of the bottom water. According to this study, the gap between P. crispus population can be controlled at 20% of the population width, which can effectively reduce nutrient concentration, improve water transparency and dissolved oxygen content, improve water quality. In the process of ecological restoration with P. crispus population, the width of P. crispus population should be controlled and prevent the spread by regular harvesting, blocking with the net, and so on. The gap between populations should also be determined according to the population width.