A novel framework to assess the hydrological connectivity of lake wetlands in plain river networks with dense hydraulic facilities: Comparing natural and disturbed states over a century

The proliferation of hydraulic facilities worldwide has greatly hindered the lake wetlands ecosystem services through impacting hydrological connectivity. However, developing a general method to evaluate hydrological connectivity in the plain river-lake wetlands networks heavily influenced by hydraulic facilities remains challenging. In this study, we present a novel framework for the hydrological connectivity evaluation of lake wetlands whilst considering different types of hydraulic facilities. By generalising lake wetlands into patches and rivers into edges, a river topological network connecting lake wetlands was constructed based on graph theory, and connectivity indices were calculated through three dimensions: individual patches - inter-patches - and study area, respectively. Using detailed historical topographic maps and high-resolution satellite data, this new framework, combining graph theory and connectivity indices, is applied to a river-lake wetlands district with dense sluices/pumping stations in eastern China. Results show that (1) Although the number of lake wetlands remained relatively stable over the past century, the average area decreased by 18.44%, and the density of hydraulic engineering boomed to 2.2/km2. (2) The increases in hydraulic facilities and the decrease in lake wetlands areas significantly reduced the degree of hydrological connectivity, resulting in the overall connectivity value decreasing from 0.97 in the 1910s to 0.45 in 2019. (3) The importance of the same lake wetlands patch has progressively heightened in the last hundred years. This study provides an effective method for quantifying hydrological connectivity in plain river-lake wetlands with dense hydraulic facilities and could shed light on lake wetlands protection and restoration.