| Macrophytes play an important role in maintaining the stability of ecosystem structure and function.The characteristics and biomass distribution of macrophyte community in Dongting Lake Basin are affected by hydrological connectivity.Therefore,this paper takes the large aquatic plants in Dongting Lake Basin as the research object,comprehensively considers the landscape structure and hydrological factors,constructs the hydrological connectivity evaluation system suitable for Dongting Lake,divides the Dongting Lake Basin in different hydrological periods,and studies the community structure characteristics of large aquatic plants in Dongting Lake Basin under different hydrological connectivity.The main conclusions are as follows(1)Results of hydrological connectivity Zoning:(1)on the basis of hydrological connectivity at home and abroad,the evaluation index system of Dongting lake hydrological connectivity is constructed.The evaluation indexes of the system are water level,water temperature,flow rate and node connection rate(?Index),network connectivity(?Index).The weight of each evaluation index is calculated by entropy weight method:the weight of each index in flood period is 0.199,0.200,0.198,0.204and 0.199 respectively;The weight of each index in wet season was 0.201,0.202,0.196,0.200 and 0.201 respectively;The weight of each index is 0.202,0.202,0.195,0.200and 0.201 respectively.In order to reflect the connectivity level of water system structure and hydrological and hydraulic parameters,the evaluation standard zoning of hydrological connectivity is established,which are excellent(>0.4),good(0.36?0.4),medium(0.32?0.36)and poor(0.28?0.32).(2)According to the results of water system connectivity zoning,the areas with poor hydrological connectivity(0.28?0.32)are the four areas of East Dongting Lake,including Lujiao,Bianshan,Yueyanglou and baxianqiao;The area with medium(0.32?0.36)hydrological connectivity evaluation is mostly sankou area,namely Sancha River,hudu River and Songzi river area(0.32?0.36);The areas with good hydrological connectivity(0.36?0.4)are mostly South Sishui and West Dongting Lake areas,and the main points include Potou,Jinshi,wanjiazui,yugongmiao,Xiaojiawan,xiaohezui,Muping Lake,Nanzui,Wanzi lake,jiangjiazui and HENGLING lake;The hydrological connectivity evaluation is excellent(>0.40),and there are five areas of South Dongting Lake.(2)Community structure and distribution characteristics of macrophytes in Dongting Lake:in this paper,the diversity,community characteristics and biomass distribution of macrophytes in Dongting Lake were used to characterize the community structure characteristics,so as to explore the dominant factors driving the succession of macrophytes.(1)Under different hydrological periods,the average hydrological connectivity of Dongting Lake Basin in flood period is 0.366±046,and the average hydrological connectivity in wet season is 0.379±039,and the average hydrological connectivity is 0.377 in the recession period±0.051?The results showed that the average biomass was 7.22kg/m2,the total species number was 19,and the average SW diversity index was 0.640.The average biomass distribution,species number and species diversity of Dongting Lake Community in the high water period were higher than those in the low water period(the average biomass was 2.98kg/m2,the total species number was 13,The average biomass was 2.65kg/m2,the number of species was 11,and the SW diversity index was0.537.(2)In the same hydrological period,the areas with good hydrological connectivity(0.36?0.40)had the largest number of dominant species(4 species)and the highest community species diversity(SW index was 1.032),followed by the areas with good hydrological connectivity(RHC>0.40,2 dominant species,SW index was0.481),moderate(RHC between0.32?0.36,2 dominant species,SW index was 0.443),moderate(RHC between 0.32?0.36,2dominant species,SW index was 0.443)32,one dominant species,and SW index was 0.192);The biomass distribution of macrophytes was as follows:in the areas with good hydrological connectivity(0.36?0.40)in flood period and recession period,the biomass distribution of macrophytes was the most(4.0kg/m2 and 4.9kg/m2 respectively),and in other areas,the biomass distribution of macrophytes was from high to low,and the hydrological connectivity was medium(RHC was between 0.32?0.36),4 kg/m2 and 2.3 kg/m2 in flood period and recession period),excellent(RHC>0.40,1.6 kg/m2 in flood period and 1.8 kg/m2 in recession period),poor(RHC between 0.28 and 0.32,1.5 kg/m2 in flood period and 1.7 kg/m2in recession period);In wet season,the area with the largest biomass distribution was the area with the best hydrological connectivity(>0.40)(the average biomass was 9.2kg/m2).In other areas,the biomass distribution from high to low was good(RHC was between0.36-0.40,the average biomass was 9.0kg/m2),medium(RHC was between 0.32-0.36,the average biomass was 4.2kg/m2),medium(RHC was between 0.32-0.36,the average biomass was 4.2kg/m2)and low(RHC was between 0.36-0.40,the average biomass was 9.0kg/m2)The RHC was between 0.28 and 0.32,and the average biomass was1.9kg/m2.When the hydrological connectivity was lower than 0.40,the biomass,species richness and biodiversity index of the area with higher hydrological connectivity were significantly higher than those of the area with lower hydrological connectivity(ANOVA,P<0.05).If and only in the wet season,the higher the hydrological connectivity,the more the regional biomass distribution.(3)Effects of hydrological connectivity on biomass and community structure of macrophytes:regression analysis showed that hydrological connectivity was an important factor affecting biomass and biodiversity of macrophytes in Dongting Lake(biomass R~2=0.346 and biodiversity R~2=0.445 in flood period;biomass R~2=0.346 and biodiversity R~2=0.445 in flood period);In wet season,biomass R~2=0.906 and biodiversity R~2=0.474;In the recession period,biomass R~2=0.280,biodiversity R~2=0.488).According to the correlation analysis,the influence mechanism of hydrological connectivity on macrophytes is different in different hydrological periods.During flood season,the hydrological connectivity mainly affected the macrophyte community by affecting the transparency(P<0.05)and total phosphorus content(P<0.05);In wet season,macrophyte communities were mainly affected by water transparency(P<0.01),water velocity(P<0.05)and chlorophyll content(P<0.05);During the recession period,the hydrological connectivity affected the distribution of macrophyte community by affecting the transparency(P<0.05)and chlorophyll content(P<0.01). |
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