洱海湖滨带挺水植物残体腐解特征及其环境效应初探

Decomposition Characteristics of Emergent Aquatic Plant Residues from the Lakeshore of Erhai Lake and their Environmental Effects

采用试验模拟的方法,研究洱海4种主要挺水植物茭草(Zizania caduciflora)、香蒲(Typha latifolia)、水葱(Scirpusvalidus)和芦苇(Phragnites australis)在水体中的腐解特征.结果表明:在21 d的腐解试验中,水葱腐解速率最快,茭草和香蒲其次,芦苇最慢;挺水植物单位干物质TN释放量表现为水葱>茭草≈香蒲>芦苇,TP释放量表现为水葱>茭草>香蒲>芦苇;4种植物TP释放率均高于TN,腐解出的TP进入水体的比例也明显高于TN.水体中ρ(TN),ρ(TP)及ρ(CODCr)均在腐解初期(1～3 d)快速上升,pH和ρ(DO)快速下降;随后,ρ(TN),ρ(TP)及ρ(CODCr)均缓慢下降,pH和ρ(DO)则缓慢回升.结合洱海湖滨带挺水植物空间分布的调查结果,估算全湖湖滨带4种挺水植物中TN和TP的总质量分别为17.622和2.870 t,其中茭草和香蒲中的TN和TP分别占91%和95%,对茭草和香蒲进行适时、适宜的收割对改善湖滨带的水质具有重要的意义.

The decomposition characteristics of four types of main emergent aquatic plants,Zizania caduciflora,Typha latifolia,Phragnites australis and Scirpus validus,from the lakeshore of Erhai Lake were studied using experimental simulation.The results showed that during the decomposition processes over 21 days,the decomposition rate of S.validus was the largest among these aquatic plants,the next were those of Z.caduciflora and T.latifolia,and the least was that of P.australis.The order of total nitrogen amount released from the four aquatic plants（per dry weight） was S.validus,Z.caduciflora/T.latifolia and P.australis.The order of total phosphorus amount released was S.validus,Z.caduciflora,T.latifolia and P.australis.The percentage of nitrogen decomposed was lower than that of phosphorus,and the proportion of decomposed total phosphorus entering the water was higher than that of total nitrogen.The mass concentrations of total nitrogen,total phosphorus and CODCr in the water increased rapidly during the initial stage of the plant decomposition processes（1-3 d）,and then decreased slowly.However,the values of pH and the mass concentration of DO decreased quickly during the initial stage,and then increased slowly.Combined with spatial distribution investigation of emergent aquatic plants in the lakeshore of Erhai Lake,the weights of total nitrogen and total phosphorus contained in these four emergent aquatic plants were estimated to be 17.622 and 2.870 t respectively,and the proportions of total nitrogen and total phosphorus contained in Z.caduciflora and T.latifolia were 91% and 95% respectively.The timely and appropriate harvesting of Z.caduciflora and T.latifolia in the lakeshore of Erhai Lake has great significance for improving water quality.