Study on spatio-temporal variation and hydrological connectivity of tidal creek evolution in Yancheng coastal wetlands

The ecological changes have attracted extensive international attention at Jiangsu Yancheng coastal wetland on the west coast of the Pacific Ocean in recent decades. Tidal creek is an important channel for material exchange between sea and land and plays an important role in the connectivity of water in coastal wetlands. The tidal flats from Sheyang Port to Liangduo Estuary in Jiangsu Province were selected and divided into five sub-study areas using each port as a split point. Based on the remote sensing image data from 1987 to 2020, this study used seven parameters (grade, number, length, density, curvature, bifurcation ratio, and drainage efficiency) to analyze the spatio-temporal divergence patterns and hydrological connectivity of tidal creek network. The results showed that (1) the area of tidal flat was reduced from 1024.87 to 352.05 km2, the total length of the tidal creek was directly reduced from 1061.27 to 640.74 km, the average density increased from 1.00 to 1.82 km/km2, and the total number increased by 33% in 1987-2020, indicating the tidal creeks tended to be "short, fragmented, and parallelized." (2) The development degree of tidal creek networks showed a trend of gradually increasing from north to south, in which the γ index in areas II and V were closer to 1/3 of tree shape after 2002, indicating that the development of tidal creeks in these two areas was better. (3) The spatial heterogeneity of hydrological connectivity levels of tidal creeks in the study area was obvious, which gradually increased from north to south. In 2020, Area I was the lowest, and ICmin was 0.14, and Area V was the highest, and ICmax was 0.90. (4) Reclamation was the main factor leading to the shrinkage and degradation of tidal creeks, but it also increased tidal creek density and hydrological connectivity per unit area; the expansion of Spartina alterniflora had a certain influence on the development of tidal creeks. The results of this study are expected to provide data support for understanding and predicting the evolution of the morphological characteristics of tidal creeks under the influence of human and natural activities and provide scientific reference for the protection and restoration of hydrological connectivity in coastal wetlands.