Effects of submerged plant restoration on methane release in Lake Xuanwu, a typical urban lake

湖泊是温室气体甲烷(CH₄)的重要释放源之一，削减湖泊CH₄释放对缓解全球气候变化意义重大。沉水植物恢复作为控制湖泊富营养化的重要手段，可能同时具备削减CH₄释放的效果。为验证上述假设，本研究选取江苏省南京市典型城市湖泊玄武湖作为研究对象，利用顶空-平衡法开展了为期一年的野外观测研究，并结合室内培养实验，比较了玄武湖沉水植物恢复区与未恢复区CH₄释放、产生和氧化的差异以及沉水植物恢复在其中的可能作用。研究结果显示：玄武湖未恢复区水-气界面CH₄扩散通量的变化范围为23.5~6076.1 μmol/(m·d)，年平均值为(1244.0±1317.6) μmol/(m·d)。未恢复区的CH₄释放主要受温度、多种营养盐（总磷、总氮、亚硝态氮、氨氮）、叶绿素a浓度等影响；恢复区的CH₄扩散通量显著低于未恢复区，其年平均值仅为未恢复区的23.8%，该区域的CH₄释放主要受温度、总磷等影响。沉水植物恢复可能通过以下两种途径削减了CH₄释放：（1）沉水植物的恢复显著降低了各类营养盐与叶绿素a浓度（总磷、总氮和叶绿素a分别下降了80.2%、73.6%和72.2%），进而削减了CH₄的排放；（2）沉水植物的恢复显著地降低了沉积物不同温度下的产甲烷潜势与其温度敏感性，同时还提高了甲烷氧化潜势，使得净CH₄释放减少。本研究可为湖泊修复与碳汇能力提升的协同提供重要参考。;Lakes are one of the major sources of emissions of greenhouse gas methane (CH₄). Reducing CH₄ emission from lakes is critical to mitigate global climate change. Submerged plant restoration, as an important means to control lake eutrophication, may also contribute to reducing CH₄ release. To verify the above hypothesis, Lake Xuanwu, a typical urban lake in Nanjing, Jiangsu Province, was selected as the research object in this study. A one-year in-situ investigation, combined with the incubation test, was conducted to compare the differences in CH₄ release, production and oxidation between the submerged plant restored and unrestored areas in Lake Xuanwu and the possible role of submerged plants in it. The results showed that the diffusion flux of CH₄ at the water-air interface in the unrestored area of Lake Xuanwu ranged from 23.5 μmol/(m·d) to 6076.1 μmol/(m·d), with the annual mean of (1244.0±1317.6) μmol/(m·d). The CH₄ release in the unrestored area was mainly affected by temperature, various nutrients (total phosphorus, total nitrogen, nitrite and ammonia nitrogen), and chlorophyll-a concentration. The CH₄ diffusion flux in the restored area was significantly lower than that in the unrestored area, and its average annual value was only 23.8% in the unrestored area. The CH₄ release in this area was mainly affected by temperature and total phosphorus. Submerged plants may mitigate CH₄ emissions through two pathways: (1) Submerged plant restoration significantly reduced the concentration of various nutrients and chlorophyll-a (total phosphorus, total nitrogen and chlorophyll-a decreased by 80.2%, 73.6% and 72.2%, respectively), thus reducing the emission of CH₄; (2) Submerged plant restoration significantly reduced the methanogenesis potential in sediments at different temperatures and temperature sensitivity, and also increased the methane oxidation potential, resulting in less CH₄ release. This study provides valuable insights into the synergistic enhancement of lake restoration and carbon sequestration capacity.