Identification Of Key Obstruct Factors Of Hydrological Connectivity And Its Effect Of The Yellow River Estuary Wetland

The Yellow River estuary wetland is the broadest,most complete and youngest wetland ecosystem for warm temperatures,providing a good ecological environment for animals to inhabit,reproduce,migration and wintering.However,with the rapid development of coastal economy,the increasing interference activities of oil exploitation and reclamation have led to the significant reduction of wetland hydrological connectivity,and ultimately restricted the normal functioning of wetland ecosystem.As a result,resulting in different degrees of wetland degradation.Therefore,this paper studies the change of tidal from 1995 to 2019,analyzes the temporal evolution characteristics of hydrological connectivity of the Yellow River estuary wetland,divides the regions according to the density of tidal in 2019,and studies the spatial evolution characteristics of hydrological connectivity;Pearson correlation analysis and principal component analysis were used to identify the key factors of hydrological connectivity obstruction;Finally,combined with soil properties,plant community characteristics and landscape connectivity,the ecological effects of hydrological connectivity barrier were analyzed,in order to provide basic data and scientific support for the management,protection and restoration of the Yellow River estuary wetland.The results are as follows:(1)Affected by the diversion of the Yellow River,the extensive expansion of Spartina alterniflora community and the seawater erosion on the south bank,the length of the tidal decreased from 620.62 km to 316.74 km,and the density of the tidal decreased from 0.82 km/km~2 to 0.45 km/km~2 from 1995 to 2019.From 1995 to 2019,the mean value ofαwas 0.023,βwas 1.043,γwas 0.349,and the hydrological connectivity was weak.The eastern region with the weakest human activities had the highest hydrological connectivity,while the northern region was highly affected by human activities,resulting in the weakest hydrological connectivity.(2)Road and S.alterniflora community are the key factors for the obstruction of wetland hydrological connectivity.The Pearson correlation showed that the length and density of road and the area and density of S.alterniflora community were significantly negatively correlated with the length and density of tidal;the road,density,S.alterniflora community area and density were negatively correlated with the hydrological connectivity index.(3)Under the condition of road barrier in saltwater area,the closer to the roadside,the higher the contents of soil organic carbon(SOC)and total nitrogen(TN).At 0-5 m from the roadside,the contents of SOC and TN were 11.34±3.20 g/kg and 0.51±0.18 g/kg,respectively.The difference of SOC and TN content from sea to land is not obvious in saltwater area under multiple barriers.The SOC and TN contents of Phragmites australis community,P.australis mixed with Tamarix chinensis community and T.chinensis community were 6.86,2.43,1.21 and 2.61,1.42,2.36 times of those in the restricted area.Compared with Suaeda salsa community,S.alterniflora community was conducive to nutrient accumulation.(4)The highest species richness was 8 species at 0-5 m of road edge,the highest Shannon Wiener index was 1.47,and the lowest evenness index was 0.54.With the increased of the number of roads,the variation of species number was not obvious.The coverage,density and height of P.australis were higher at the hydrological connectivity than at hydrological blocked area.The density of Tamarix chinensis mixed with P.australis community,T.chinensis community was higher than that of the hydrological connectivity,and the order of vegetation growth was different.(5)The expansion of roads and S.alterniflora community,weakened the hydrological connectivity,resulting in the reduction of natural wetland area and serious landscape fragmentation.From 1995 to 2019,the range of IIC(Integral index of connectivity)was0.04-0.11,the range of PC(Probability of connectivity)was 0.13-0.33,and the range of LCP(Landscape coincidence probability)was 0.17-0.42.Pearson correlation showed that the length and density of roads were negatively correlated with the landscape connectivity index.The area and density of S.alterniflora community were negatively correlated with landscape connectivity index.