Study On The Characteristics And Restoration Potential Of Seed Bank In Chaohu Lake And Its Main Tributaries

As the main primary producer of freshwater ecosystems,aquatic plants play an important role in maintaining the structure and function of aquatic ecosystems.Affected by human disturbance such as river–lake disconnection and water eutrophication,aquatic vegetation in Chaohu Lake Basin has been seriously degraded,and the ecological service functions have been severely lost.In order to restore the aquatic vegetation in this region,the Chaohu Lake and its four main tributaries-Nanfei River,Baishitian River,Hangbu River,and Zhegao River were selected as the research objects.Through the measurement of seed banks,aboveground vegetation,water physical and chemical parameters,sediment physical and chemical parameters,and other environmental factors,the spatial distribution characteristics and main influencing factors of seed bank in Chaohu Lake and its main tributaries were analyzed,and the feasibility of using seed banks to restore aquatic vegetation was evaluated.Finally,based on the current situation of seed bank,the restoration measures of aquatic vegetation in Chaohu Lake and its main tributaries were proposed.The main results are as follows:1)A total of forty-eight species were recorded in the aboveground vegetation investigation in the Chaohu Lake,of which submerged,floating-leaved,and emergent macrophytes were 1,5,and 10,respectively.Currently,artificially planted Phragmites australis and Salix communities have become the main community types.The aquatic macrophyte coverage of Chaohu Lake was about 0.77%.A total of 18 aquatic macrophytes were identified in the seed bank,of which the seed density of submerged,floating-leaved,and emergent macrophytes and hygrophytes was 2.05,2.05,16.93,and 9.30 ind./m~2,respectively.The aquatic macrophyte seeds of Chaohu Lake were mainly distributed in the estuary area.Only two emergent macrophyte species(Typha)germinated in the open water area.Spearman correlation analysis showed that the distance to bank was the main environmental factor that affected aquatic macrophyte diversity and seed density in the seed bank,and SD,Cond,and TP in the water also had significant effects.Based on the above results,we think that it is not feasible to promote the natural reconstruction and restoration of aquatic macrophytes in the Chaohu Lake by lower the water level and increasing the transparency of the water body,but the area near the estuary can be identified as a priority restoration area for aquatic macrophytes.Through the artificial transformation of the micro-topography,some hydrochorous seeds in the tributaries of the lake can be guided to gather in the priority restoration area,thereby avoiding the waste of seed resources.2)A total of 123 aquatic macrophytes were identified in the seed bank,of which submerged,floating-leaved,emergent macrophytes and hygrophytes were 3,3,8,and 109,and the seed density was 2.05,2.05,16.93,and 9.30 ind./m~2,respectively.Comparion of the four different types of rivers,the average density and average species number in the rural near-natural river Zhegao River were the highest,of which were 3523 ind./m~2and 23species,respectively;followed by the Hangbu River and Baishitian River,and the density was 1631 and 1378 ind./m~2,and the speices number was 20 and 17,respectively;the average density and average species number in urban river Nanfei River were the lowest,only 562 ind./m~2and 13 species,respectively.As for different order streams,there was no significant difference in seed bank density among the first,second,third,and fourth order streams,but the species number in fourth order stream was significantly higher than that in third order stream.Spearman correlation analysis showed that the total nitrogen in sediment was the main environmental factor affecting the density and species richness in the seed bank.Based on the above results,it is suggested that the submerged,floating-leaved,and emergent macrophytes should be planted in the natural habitat area with small human disturbance in the upper reaches of the river to provide a sustainable source of seed banks for the middle and lower of the river.At the same time,it is suggested to provide favorable conditions for seed colonization and growth by artificially creating microenvironment and improving the heterogeneity of the river habitats.Main scientific contributions of this thesis:this study carried out a systematic ecological investigation on the seed bank in the Chaohu Lake and its main tributaries for the first time,and evaluated the restoration potential of aquatic plant using the seed bank,and preliminary proposed the restoration strategies of aquatic vegetation in this area.