| As one of the most important rivers in China,the Yangtze River plays an vital role in the economic development,the social progress,cultural prosperity and ecological health,etc.However,the Yangtze River has been facing with ecosystem degradation in the last few decades.Construction of embankments and sluice gates and water pollution,have severely threatened the natural hydrological regime,resulting in a significant decrease of natural hydrological connectivity and a longer water change cycle,the Yangtze floodplain lakes have gradually been eutrophication status.The quarrying and dredging have decreased the connection between the Yangtze River and foodplain lakes,the changing water cycle is quite different in different lake regions.As a significant assemblage in floodplain ecosystem,the differences of macroinverbrate community in different regional scale are of great importance for floodplain conservation and management.Exchanging rates of water is viewed as one of the quantitative indices of hydrological connectivity.Systematical investigations of macroinvertebrates-water exchange rate need to be carried out in floodplain-scale and lake-scale.Hence,we tried to explain the differences of macroinverbrate community in floodplain-scale and lake-scale(the lake focus on the Dongting Lake).Besides,we analyzed the differences of water exchange rate between the Yangtze River and floodplain lakes,and in different lake regions in the Dongting Lake.Finally we tried to figure out the ecological responses of macroinvertebrate composition to water exchange rate in different scales.The results are mainly as follows:1.A preliminary system of the macroinvertebrate community structure in floodplain-scale has been analyzed.The 31 Yangtze floodplain lakes have been classified into five types according to the lake classification given by Pan.A total of 146 macroinvertebrate taxa belonging to 95 genera,38 families,24 orders,9 classes and 5 phyla were identified from 31 lakes.The lakes were dominated by species of Bivalvia,being 52.7%of the total species richness.However,there were significant differences in the species richness and species composition.Species richness was highest in the river-connected lakes that have connected with the Yangtze River,and the lakes were dominated by species of Bivalvia,Gastropoda and Insecta.While the algal lakes that have severally threatened by human activities,had the lowest species number and had dominant groups of tolerant oligochaetes and chironomids.2.The responses of macroinvertebrate to the disturbed hydrological connectivity in floodplain scale have been systematically analyzed.We exmined the effectiveness of species richness and taxonomic distinctness(TD,?+ and ?+)indices in determining anthropogenic effects based on the five lake groups in 31 shallow lakes in the Yangtze floodplain.The spatial pattern of species richness was largely influenced by lake area rather than by water quality.In contrast,the TD indices were insensitive to lake area and responded more readily to water quality than species richness.The ?+and ?+of entire taxa were significantly related to the Ch1 a,TP and TN.Besides,the responses of macroinvertebtates along hydrological disturbance gradients showed that the algal lakes had the highest A+value(the algal lakes had the worst hydrological connectivity and the most serious human disturbance).In constrast,the river-connected lakes had the lowest ?+ value and equally distributed species(the river-connected lakes had the greatest hydrological connectivity and the least human disturbance).3.The seasonal community features of macroinvertebrates in lake scale about the Dongting Lake have been systematical analyzed.The diversity of species in April was higher than in October.Altogether 88 taxa of macroinvertebrates were identified in April and altogether taxa 40 were identified in October.The functional feeding group was basically the same in April and October.The results of alpha diversity index showed that there were no differences in two seasons about Margalef diversity,Pielou evenness index and Shannon-Wiener diversity.The macroinvertebrates of phylogenetic dissimilarity value in April was lower than in October.Besides,sample distributions of NMDS in April were more intensive than in October,and the spatial difference of community in October was greater than in April.4.The community features and influencing factors of macroinvertebrates in lake scale about the Dongting Lake have been systematical confiremed.The primary influencing factors of macroinvertebrates in lakes was hydrological connectivity,capacity of water exchange,and the secondary factor was trophic status.(1)A great hydrological connectivity can support the water as carries for transportation of matter,energy and organism.It can provide the aquatic organism with essential material and energy.Different water exchange in different regions has an influence on the distribution pattern of macroinvertebrate.(2)Along environmental gradients,the distribution of macroinvertebrates was quite different.The water temperature was one of the influencing factors of macroinvertebrates in the same water exchange regions.The regions with low water temperature were gathered with cold water species like oligochaete.The nutrient concentration was the key factors of macroinvertebrates in regions with low hydrological connectivity.The regions with low TN concentration were gathered with clean species(like Ephemera sp.).(3)Regression analysis indicated that the species richness of macroinvertebrate was high in areas with high water age,because one of the factors affecting species diversity of macroinvertebrate was the degree of water exchange.Besides,there was a significant relationship between water age of macroinvertebrate and beta diversity,alpha diversity index in the Donting Lake.It is shown that the water age and Shannon-Wiener index,Pielou evenness index was relationship of a single peak curve.Shannon-Wiener index and Pielou evenness were first increased and then decreased.And the trend of beta diversity index is decreasing. |
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