Influence Of Tidal Ditch Morphology Changes On Hydrological Connectivity In The Liaohe Estuary Wetland

Hydrological connectedness is a crucial mechanism for moving materials,information,and energy between wetland water bodies and is a key sign of the stability of wetland ecosystems.The tidal ditch,the most active micro-geomorphic unit in the salt marsh wetland,exchanges materials,energy,and information with the sea during high and low tides,and its morphological features play a significant role in determining the wetland’s hydrological connectivity.The hydrological connectivity process that results in the formation of the Liaohe estuary wetlands,which are comprised of various rivers,including the Liao River,the Daling River,and the Xiaoling River,is intricate.Due to both natural and human pressures,the hydrological connection of the wetlands has recently been severely impacted.In order to identify significant areas of hydrological connectivity and to clarify the evolution of hydrological connectivity,This study is based on the connectivity index and the Morphological Spatial Pattern Analysis(MSPA)model to investigate the actual hydrological connectivity of the Liaohe estuary wetlands in time and space,analyse its dynamics,identify important areas of hydrological connectivity and clarify the evolution of hydrological connectivity;quantitatively characterize the morphological changes of the tidal flats and tidal channels in the study area between 1985 and 2020;investigate how the morphological changes of the tidal channels improve the hydrological connectivity of the wetlands and identify the main influencing factors The study’s findings are as follows:(1)The hydrological connectivity of Liaohe estuary wetlands was at a low and unstable level during 1985-2020;the landscape type of hydrological connectivity of Liaohe estuary wetlands changed dramatically during the study period.1985-2010 was a period of decline,during which wetlands were mainly transformed into non-wetlands,the area of wetlands in the core area decreased,the fragmentation of the landscape intensified and the wetlands in the core area became more fragmented.The hydrological connectivity of wetlands declined as the fragmentation of the landscape intensified;the recovery period from 2010 to 2020 was dominated by the transformation of non-wetlands to wetlands,with the core area of wetlands increasing and the hydrological connectivity gradually restored.These areas play an important role in maintaining the hydrological connectivity of the wetlands in the Liaohe estuary.(2)The morphological characteristics of the tidal channels have obvious spatial and temporal heterogeneity.The upper reaches of the Liaohe estuary are dominated by branching tidal channels,while the tidal channels at the left and right bank estuaries are distributed on the tidal flats in the form of "tidal trees" and roundabouts,and the highest tidal channel grade is 5.During the period 1985-2020,the length,curvature and drainage efficiency of tidal channels fluctuate downwards;the density,frequency and branching rate of tidal channels fluctuate upwards;and the number of tidal channels first decreases and then increases.The development of the tidal ditch network tends to be unstable.(3)The total tidal channel length,tidal channel density and tidal channel curvature are the key factors influencing the structural connectivity of wetlands;the average return channel flow length OPL,tidal channel density,tidal channel frequency and tidal channel branching rate are the key factors influencing the functional connectivity of wetlands.Tidal channel density had the most significant effect on structural connectivity,with IIC increasing linearly with increasing tidal channel density;OPL had the most significant effect on functional connectivity,with PC decreasing exponentially with increasing OPL.