Responses Of The Typical Biological Assemblages Of Estuarine Wetland To Hydrological Processes

Estuarine wetlands have always been a hot spot in the field of coastal research due to their special formation and development process,unique environment,dense population,numerous ecosystem functions and services,and rich biodiversity.The special geographical location with the confluence of brackish water and the mixing of river runoff and tidal currents makes the estuarine hydrological process a key process to maintain the material circulation and energy flow of the estuarine ecosystem,and it also plays an important role in regulate the biological assemblages of the estuarine wetlands.This study takes the Yangtze Estuary as an example to analyze the characteristics,and driving factors of the responses of the typical biological assemblages to hydrological processes in the estuarine ecosystem at different temporal and spatial scales through methods such as historical data collection,remote sensing image and sea chart analysis,and field experiments.Meanwhile,this study tries to reveal the time-lag and cumulative effects of the responses of biological assemblages to hydrological processes in estuarine wetland ecosystem.Based on this,a relatively complete research system on the responses of biological assemblages to the estuarine ecosystem's hydrological processes on multi-temporal and spatial scales is constructed to provide a scientific basis for the protection,development,and utilization of the estuary ecosystem and the sustainable development of the estuarine region.The main research results and conclusions of this study are as follows:1.On the estuarine scale,the responses of vegetation in the sandbar wetland and the intertidal wetland to the estuarine hydrological process is driven by the interaction between the sedimentary conditions and the evolution of the regional geomorphology under the control of the river runoff and sediment discharges.In this study,the evolution trends of vegetation and shoals in the sandbar wetland(Jiuduansha)and the intertidal tidal wetland(Chongming Dongtan)were similar during 1985-2015.Meanwhile,under the influence of the variations in river runoff and sediment discharges in the Yangtze Estuary,the hydrological and sediment factors in the adjacent waters of Jiuduansha and Chongming Dongtan have changed accordingly.The vegetation area was significantly correlated with the area of the shoals,the annual sediment discharges,and sediment concentration of the adjacent water(p <0.05).There was also a significant correlation between the shoals' area of Jiuduansha and Chongming Dongtan and the annual sediment discharge,the sediment concentration of the adjacent waters,and the vegetation area(p<0.05).The interaction characteristics among vegetation,hydrological processes and shoals vary among different elevations and different species.2.The responses of biological assemblages to the estuarine-scale hydrological processes have a certain time-lag and cumulative effect.In this study,the correlations between the annual sediment discharge and the area of the shoals and vegetation in Jiuduansha and Chongming Dongtan obtained by the lag correspondence analysis were also significant(p<0.05),and were higher than that of the synchronous correspondence analysis.The correlation coefficients between the annual sediment discharge and shoals and vegetations obtained by the cumulative correspondence analysis were the highest in the two-year or three-year cumulative treatment and were also higher than the result of synchronous correspondence analysis.At the same time,the time-lag are nested and different in multiple links of the responses process.3.On the habitat scale,the responses of biological assemblages to habitat hydrological processes included not only the direct responses to hydrological process intensity and water physiochemical factors but also the indirect responses to sedimentary factors affecting by hydrological process.Take the benthic macroinvertebrates as an example,in the study of semidiurnal,fortnightly,and seasonal scale,the environmental factors selected by nonlinear regression analysis that have significant effects on benthic macroinvertebrates included not only flow velocity,water depth,salinity,and other hydrological process intensity indicators and water physiochemical factors but also sedimentary factors such as the bulk density,and the grain size of the sediment.These two modes are also common in other estuarine organisms.At the same time,this study showed that most of the hydrological factors such as flow velocity and water depth varied significantly in different vegetation zones(p <0.05),and the responses of the benthic macroinvertebrates in the saline algae zone to hydrological processes was more obvious than that in the Scirpus mariqueters zone.The responses of other estuarine biological assemblages to hydrological processes and the key driving factors are generally different in different vegetation zones.This difference is closely related to the variations in hydrodynamic intensity of hydrological processes in different vegetation zones and also the interaction between vegetation and hydrological processes.4.Responses of different lifestyle groups and weight groups to hydrological processes are different.In this study,the infauna had no significant responses to fortnightly tides,while the epifauna and semi-infauna had significant responses.It also showed a similar pattern on the seasonal scale.The selected combinations of environmental factors that have a significant influence on benthic macroinvertebrates of different life-style also varied distinctly.This reflects the differences in the characteristics and mechanisms of the responses of benthic macroinvertebrates of different life-style to habitat-scale hydrological processes.Benthic macroinvertebrates living on the above and the surface of sediments are more strongly affected by hydrological processes.At the same time,benthic macroinvertebrates with a lower individual weight(<0.05g)accounted for a larger proportion in the community of neap tide period with a lower hydrodynamic intensity and a very low proportion in the spring tide period.The individual weight composition of the benthic macroinvertebrates was also different.The selected combinations of environmental factors that have a significant influence on the abundance and biomass of the lower-weight benthic fauna generally included the maximum flow velocity and the maximum water depth,while the factors that have a significant influence in the larger-weight benthic fauna generally included the average flow velocity and the average water depth.This indicates that the mechanisms of the responses of biological assemblages with different individual weights to hydrological process are different.5.The responses of biological assemblages to habitat-scale hydrological processes have distinct temporal differentiation characteristics,which is reflected in the distinctive differences in the response characteristics of the benthic macroinvertebrates at different temporal scales and also their driving factors.Semi-diurnal tides didn't change the abundance and biomass of the benthic macroinvertebrates(p?0.05),while the fortnightly tides significantly changed the abundance of the benthic macroinvertebrates(p<0.05).The selected hydrological and sedimentary physicochemical factors that have significant influence on the benthic macroinvertebrates also varied in different seasons.In addition,the time-lag effects and cumulative effects do exist in the responses of biological assemblages to habitat-scale hydrological processes.The correlation coefficient between the abundance,biomass of the benthic macroinvertebrates and hydrological and sedimentary factors in different temporal scales obtained through lagging correspondence analysis and cumulative correspondence analysis were higher than that through synchronous correspondence analysis.For example,the correlation between environmental factors and the abundance of macroinvertebrates calculated in the nonlinear regression analysis of 2semi-diurnal tidal cycles lagging treatment(R=0.281;p =0.023)and 2 accumulating semi-diurnal tidal cycles treatment(R=0.545;p=0.018)were both significantly higher than the results of synchronous correspondence analysis(R=0.138;p =0.023).The mechanism of time-lag effects and cumulative effects may be multifaceted,and further research is needed to explore.On the whole,this study illustrated that there are specific responses for the biological assemblages in the estuarine wetlands to hydrological processes in different temporal and spatial scales.Due to the scale characteristics of the estuarine hydrological process itself,the responses of biological assemblages to the hydrological process also has an obvious scale effect.It is requisite to maintain the relative stability of the regional hydrological and sedimentary conditions to protect the species diversity of the estuarine wetland ecosystem from being destroyed.To conduct biological assemblages research and surveys in estuarine ecosystems requires careful consideration of errors caused by temporal and spatial scale variations,and different vegetation types.At the same time,it's necessary to take long-term systematically ecological monitoring,specific quantification and in-depth research on the time-lag and cumulative effects of the hydrological processes.