刈割对千岛湖生态浮床植物生长与氮素净化效率的影响

生态浮床是一种净化水体氮磷污染的高效人工强化技术，刈割是生态浮床管理的重要措施。为探究深水水库中刈割管理对生态浮床植物生长及氮素去除效率的影响，以华东地区最大深水水库千岛湖为例，选取沉水植物绿色狐尾藻 (Myriophyllum aquaticum) 和挺水植物水芹 (Oenanthe javanica) 为研究对象，分别对2种植物进行刈割和未刈割处理，构建生态浮床系统，进行水质净化培养实验。结果表明：刈割处理对水芹和绿色狐尾藻生长的影响不同，刈割后水芹相对增长率加快，经25 d生长干重翻了约一倍，未刈割水芹后期观察到部分叶片凋零、株高降低；绿色狐尾藻刈割后干重无明显增加，水下部分萎缩，在此状态和水质背景下很难恢复；刈割处理能明显促进水芹水上部分茎叶对氮素的吸收，占比从13.85%提升至25.37%；绿狐尾藻茎秆的刈割会影响水下根系的正常生长，整体降低氮素去除效率；浮床植物的种植明显增强了水体反硝化脱氮能力，水体溶解性氮气增量 (△[N₂]) 较对照高3.52~6.98 μmol·L⁻¹。但刈割对于植物根系反硝化速率存在负面影响，刈割后水芹和绿狐尾藻水体△[N₂]分别降低约13.74%和21.77%。以上结果表明，生态浮床系统对深水水库水体具有良好的脱氮效果，但针对不同的植物应采取不同的管理方式，选用水芹作为浮床植物时应进行及时刈割，促进植物生长对氮素的吸收；而刈割对绿色狐尾藻可能是一种不可逆的伤害，建议在生长期结束时进行整株收获，中途不宜收割。该研究结果可为深水水库生态浮床的科学应用和管理提供参考。

Influence of mowing on the growth and nitrogen purification efficiency of ecological floating bed plants in Qiandao Lake

Ecological floating bed is a high-efficiency artificial enhancement technology to purify nitrogen and phosphorus pollution in water column, while mowing is the key measure for the management. In order to investigate the influence of mowing management on the growth and nitrogen removal efficiency of ecological floating bed plants in deep-water reservoirs, Qiandao Lake was taken as an example. Submerged plant Myriophyllum aquaticum (M. aquaticum) and emerging plant Oenanthe javanica (O. javanica) were selected as the reserach objects, and the two plants were treated with and without mowing treatment respectively. The ecological floating bed system was constructed and the water purification culture experiment was carried out. The results showed that mowing treatment had different impacts on the growth of M. aquaticum and O. javanica. The relative growth rate of O. javanica accelerated after mowing, and the dry weight doubled after 25 days. Partial leaf withering and plant height reduction were observed in the late stage of uncut O. javanica without mowing. The dry weight increase of M. aquaticum was not obvious after mowing, and the submerged part shrunk, which was difficult to recover in this state and water quality background. Mowing treatment significantly promoted the uptake of nitrogen by the water portion of the stems of O. javanica, from 13.85% to 25.37%, while that of M. aquaticum affected the normal growth of the submerged root system and reduced the overall nitrogen removal efficiency. Planting of floating bed plants significantly enhanced the denitrification and nitrogen removal capacity, and the increment of dissolved nitrogen in the water body (△[N2]) was 3.52~6.98 μmol·L−1 higher than that of the control. However,mowing negatively affected the denitrification rate of the plant root system, and the △[N2] of O. javanica and M. aquaticum decreased by about 13.74% and 21.77% respectively after mowing. This study showed that the ecological floating bed system had good denitrification effect on deep-water reservoirs, but different management methods should be adopted for different plants, and watercress should be harvested in time to promote plant growth for nitrogen uptake. When O. javanica was chosen as a floating bed plant, timely harvesting management should be carried out to promote nitrogen uptake by plant growth. While mowing may be an irreversible damage to M. aquaticum, so it was recommended to harvest the whole plant at the end of the growth period, and should not be harvested midway. The results of the study can provide scientific support for the scientific application and management of ecological floating beds in deep-water reservoirs.