南四湖菹草生长周期对内源磷释放的影响

The effect of growth cycle of Potamogeton crispus on internal phosphorus release in Nansihu Lake

沉水植物对于“沉积物-水”界面(SWI)的磷(P)循环起着重要的作用,但目前关于沉水植物生长周期对沉积物-水界面磷释放过程的影响研究较少.本研究以南四湖优势沉水植物菹草为研究对象,在菹草的生长周期内分别于4个湖区菹草丰富且具有代表性的采样点获取其11月(生长期)、4月(泛滥期)、8月(衰亡期)的原位沉积物柱样,结合表层水体水质、间隙水、沉积物磷赋存形态等研究,分析菹草在生长、泛滥及衰亡过程中对于内源磷释放的影响.结果表明:①表层水体中总磷(TP)浓度和活性磷在SWI释放通量在菹草11月(生长期)、4月(泛滥期)、8月(衰亡期)分别为(0.04±0.02)、(0.08±0.01)、(0.11±0.02)mg·L^(-1)和(0.18±0.36)、(0.91±0.76)、(0.18±0.20)mg·m^(-2)·d^(-1).说明菹草生长期内源磷的释放得到削弱,而菹草泛滥衰亡后,内源磷释放风险增大;②菹草生长不同时期沉积物磷的释放受铁(Fe)和硫(S)的还原作用交替控制;③沉积物铁结合态磷(Fe-P)与弱结合态磷(LP)与磷释放通量呈正相关,说明沉积物LP释放与Fe-P厌氧溶解是南四湖磷释放的主要途径.以上结果有助于探明沉水植物生长周期内源磷释放特征,为南四湖水环境管理提供理论依据.

Submerged plants play an important role in the phosphorus(P)cycling at the sediment-water-interface(SWI),but there is limited research on the effects of the growth cycle of submerged plants on the P release at the SWI.This study takes the dominant submerged plant Potamogeton crispus in Nansihu Lake as the research object.During the growth cycle of Potamogeton crispus,in situ sediment samples were obtained from representative sampling points in four lake areas with abundant Potamogeton crispus in November(growth period),April(flood period),and August(decay period).Based on the study of the quality of surface water and interstitial water,and the composition of sediment phosphorus,the impact of Potamogeton crispus on internal phosphorus release were analysed during growth,flooding,and decay processes.The results showed that:①The total phosphorus(TP)concentrations and labile P release fluxes at the SWI were(0.04±0.02),(0.08±0.01),(0.11±0.02)mg·L^(-1),and(0.18±0.36),(0.91±0.76),(0.18±0.20)mg·m^(-2)·d^(-1)in November,April,and August,respectively.It indicates that the loading of internal P were weaken during the growth period of Potamogeton crispus but a high risk of P release during blooming and decays process;②The P release from sediment at different growth stages of Potamogeton crispus was alternately controlled by the reduction of iron(Fe)and sulfur(S);③Sediment iron bound phosphorus(Fe-P)and weakly bound phosphorus(LP)were positively correlated with P release flux,indicating that sediment LP release and Fe-P anaerobic dissolution were the main pathways for P release in Nansihu Lake.The results help to explore the characteristics of internal P loading during the growth cycle of submerged plants and provide a theoretical basis for the environment management of Nansihu Lake.