Hydrological Connectivity And Its Influence On Vegetation In The Coast Wetland In The Yellow River Delta

Hydrological connectivity is one of the most important and basic factors in the coastal wetland which influences the eco-hydrological processes.Revealing the hydrological connectivity and its influence on the vegetation structures in the Yellow River Delta provides important information and theoretical guides for the wetland protection and restoration in this area.The current research aims to parameterize hydrological connectivity in the coast wetlands and reveal its influence on the vegetation in the Yellow River Delta.The soil moisture and topographic data were collected,and combined with the graph theory network science to develop new methods for parameterization the fine(1m~2),meso(100 m~2)and broad(10~6 m~2)scales'hydrological connectivity in the intertidal flat area(IF),supratidal marsh area(TM),semi-artificial pound(AP)and river side(RS)areas.The vegetation character and spatial structure in population,community and landscape scale were also analyzed and linked to the fine,meso and landscape hydrological connectivity.In the fine scale,.point hydrological connectivity index is developed based on the soil moisture conditions,and the indices in IF,TM,AP and RS are 1.162,0.495,0.610 and 1.217 respectively;the point centrality degree index based on soil moisture and graphic theory in the four areas are 7.871,5.340,7.977 and4.172 respectively.In the meso scale,the TOFCI(Topographic Over Field Capacity Index)index developed by soil moisture,topographic conditions and graph theory can capture the characteristic in the research area,and the index values in IF,TM,AP and RS are 0.871,0.551,0.483 and 1.531 respectively,In the broad scale,the LTOFCI(Landscape Topographic Over Field Capacity Index)network were constructed based on the soil moisture,topographic conditions and network science model.Then the parameter estimation was conducted as the hydrological index for the meso scale and the values in in IF,TM,AP and RS are 2.496,0.969,0.829and 1.814 respectively.In the fine scale,hydrological connectivity in RS>IF while in the other scales indices in these two areas are almost the same.Besides,in meso and fine scales,hydrological connectivity in AP>IF while in the broad scale,IF>AP.For vegetation population,the mean diameter and biomass of Suaeda salsa are positively correlated with the hydrological connectivity while the density is negatively correlated with the hydrological connectivity.The biomass and density of Phragmites australis in the dysconnectivity plots are higher than the connectivity plots.Besides,the spatial structure of P.australis in the dysconnectivity plots are also more complicated and denser than which in the connectivity plots.Hydrological connectivity and soil salinity are two driving factors of vegetation communities.The salinity decided the distribution of communities while hydrological connectivity influence the vegetation cover rate,biomass and the spatial structure especially in the high salinity areas(IF and TM).The vegetation cover rate,biomass of the communities increases with the hydrological connectivity so does the complication and density of the spatial structure.In the landscape scale,the higher vegetation patch size distributed in the higher connectivity areas and the complication as well as the density of the spatial structure.While we still find that in the lower soil density area,the vegetation patches are more regular,and the spatial structures are denser.Hydrological connectivity influence on the vegetation structures showed significant scale effects.According to the multi-fracture analysis on scale effects,in AP,the hydrological connectivity variability in different scale came from higher index values,for TM and RS,the variability mainly came from the lower index values.In the areas with stronger hydrological connectivity,the variability of hydrological connectivity influence on the biomass and vegetation cover rate mainly came from the point with small fitting error values.For the vegetation spatial structures,the variability of hydrological connectivity influence on the structure density for small and broad scales mainly came from the point with small fitting error values while for the meso scale it came from larger error values.For the structure connectedness,the variability came from large fitting error values in the meso scale while in the brad scale,it came from small fitting error values.Besides,the hydrological connectivity showed more significant influence on the vegetation cover,biomass and vegetation spatial structures in the high soil salinity area and the influence shows a threshold-like pattern:in the lower hydrological connectivity areas,the linkage is stronger?The conclusion of this research can be used to identify the potential degradation patches in the coastal wetlands,and it can also provide the theoretical guide for the wetland restoration.