Study On The Impact Of Aquatic Plant Restoration On The Ecological Environment Of Reciprocating Lakes

The lake is the key to the connection between rivers and lakes,which has an important impact on intercepting pollutants,purifying water,and regulating the ecosystem in Taihu Lake and surrounding lakes.With the influence of human activities in recent years,the import of exogenous nutrients has led to different degrees of eutrophication in the lake,which not only inhibits the growth of aquatic plants,destroys the ecosystem,but also hinders the utilization of the ecological function of the lake.Wanshan Lake is a typical reciprocating lake in the Taihu Lake Basin.From March to June 2019,terrain remodeling and ecological buffer zones were established in the northwest lake area of Wanshan Lake to create favorable habitat conditions and promote the recovery of aquatic plants in the lake swing area.The aquatic plants,water quality,and phytoplankton in the northwest lake area of Wanshan Lake(demonstration area,open water area,and control area)were tracked and monitored in this study.Using Biolog technology to analyze the metabolic function of the microbial community in the summer water after restoration of aquatic plants at the same time.Besides,a simulation experiment was conducted on Vallisneria natans and Potamogeton Crispus L growing alternately in summer to comprehensively analyze the impact of aquatic plant restoration on the ecological environment in Wanshan Lake.These studies will provide scientific suggestions and a theoretical basis for aquatic plant restoration and ecological management in shallow lakes.The main results are as follows:(1)From August 2019 to August 2020,monitoring the water in the northwestern of Wanshan Lake monthly shows that restoring aquatic plants is good to improve the transparency of water bodies in the demonstration area.The annual average water transparency of the demonstration area is 23% higher than that of the open water area and 30% higher than that of the control area.And multiple regression analysis showed that suspended solids(SS)are the main factor that affects water transparency,CODMn is the second.The annual average concentrations of TN,NH4+-N,and TP in the demonstration area were 32%,28%,and 28% lower than those in the open water area,respectively,and 19%,32%,and 31% lower than those in the control area,respectively.However,the restoration of aquatic plants in this study cannot reduce the CODMn content in the water body,which is related to the decomposition of aquatic plants.Tryptophan-like fluorescence(C1),hummus-like fluorescence(C2),and hummus-like fluorescence(C3)were identified by PARAFAC analysis of three-dimensional fluorescence spectrum consensus.The results of fluorescence intensity percentage and fluorescence spectral characteristic parameters(HIX,BIX,FI)showed that the DOM of Wanshan Lake was mainly composed of endogenous contributions.Moreover,extreme conditions such as sluice release(in November 2019)and continuous rainstorm(in July 2020)resulted in the great fluctuation of water quality in the northwestern of Wanshan Lake,but the water quality in the demonstration area was still better than that in the open water area and the control area.(2)By recording aquatic plants,phytoplankton quarterly and analyzing microbial functional diversity of Wanshan Lake in summer showed that types,coverage,and species diversity of aquatic plants in the demonstration area have increased after ecological restoration.The submerged plant coverage reached 37% ~49% and Vallisneria natans and Potamogeton crispus L are dominant plants.Affected by the special terrain and hydrology,the growth of aquatic plants has no obvious improvement effect on the concentration of Chl.a,but it still has a great influence on the phytoplankton community,especially the Cyanobacteria.The results also showed that Cyanobacteria,Bacillariophyta,and Chlorophyta were the main phytoplankton in the northwestern of Wanshan Lake,and the water was moderately polluted to slightly polluted.CODMn,SS,T and TN were the main environmental factors affecting the phytoplankton community.Also,the restoration of aquatic plants can promote the succession of the microbial community in the water,improve the response and utilization of microorganisms to amine carbon sources,increase the metabolic activity of microorganisms in the water,and improve the self-purification ability of water in the lake lakes.(3)The results of 100 d continuous monitoring showed that the growth of submerged plant Vallisneria natans accelerated the decomposition of Potamogeton Crispu L by simulating the alternating state of death and growth of different biomass.Adding 0.5 kg·m-3 Potamogeton Crispus L was beneficial to the growth of Vallisneria natans,increased the concentration of DO in water,and promoted the conversion and removal of nitrogen and phosphorus in water.The DTN,TN,DTP,TP and PO43--P in water were decreased by 36.09%,51.57%,68.98%,65.69% and 79.21%,respectively.However,excessive supplementation(1 kg·m-3)of Potamogeton Crispus L inhibited the growth of Vallisneria natans,leading to the decomposition of Vallisneria natans plants,thus maintaining a high level of nitrogen and phosphorus nutrients in water.0.5 kg·m-3 Potamogeton Crispu L decomposition and Vallisneria natans growth also reduced CDOM content and increased microbial activity in the water.Excessive Potamogeton Crispus L decomposition significantly increased CDOM content and inhibited microbial life activities.From a microecological point of view,the microbial community in the wated the highest utilization degree of carbon source in the medium decomposition stage of Potamogeton Crispus L.The alternating growth process of Vallisneria natans and Potamogeton Crispus L could significantly improve the utilization ability of water microorganisms to Carbohydrates,and increase the microbial functional diversity index and the utilization ability of carbon source.The results of RDA analysis also showed that TN,DTP,TP,DO and DOC were the main environmental factors affecting microbial functional diversity.In conclusion,the increase of aquatic plants significantly improved the water environment restored the ecological function of the lake,and achieved the purpose of improving the habitat quality of Wanshan Lake,which accumulated some engineering experience for the ecological restoration of the shallow lake.However,the extreme conditions have a great impact on the water the environment of Wanshan Lake and corresponding measures should be taken to control it.Besides,the control of 0.5kg·m-3 Potamogeton crispus L in summer is beneficial to improve the lake water environment and the growth of aquatic plants.