Hydrological Connectivity Evolution of Yellow River Delta Wetland Based on Hydrological Connectivity Pattern Analysis

Water is a limiting factor for the ecological protection and high-quality development of the Yellow River Delta. At present, the classification system for wetland hydrological connectivity patterns is imperfect and cannot meet practical management needs. Therefore, this paper constructs a hydrological connectivity classification index system based on three aspects-the pressure index, state index, and response index based on the "Pressure-State-Response" model and the analytic hierarchy process (AHP)-and then uses the network connectivity index to describe the dynamics of hydrological connectivity in the Yellow River Delta wetland under different connectivity patterns. The results show that (1) the hydrological connectivity patterns in the Yellow River Delta can be divided into five types as follows: artificial freshwater connectivity, artificial saltwater connectivity, natural-artificial freshwater connectivity, artificial-natural saltwater connectivity, and natural freshwater-saltwater connectivity. Among these types, the artificial freshwater connectivity is the most widely distributed, accounting for approximately 55.14% of the study area, followed by the artificial saltwater connectivity (24.68%), natural saltwater connectivity (9.45%), natural-artificial freshwater connectivity (8.1%), and natural freshwater-saltwater connectivity (2.63%). (2) From 1990 to 2020, the network closure (alpha), line point rate (beta), and network connectivity (gamma) indices of the Yellow River Delta wetland decreased from 0.95, 2.85, and 0.96 to 0.75, 2.51, and 0.83, respectively, and the overall connectivity level remained at a high level. The alpha, beta, and gamma values of the artificial freshwater connectivity pattern decreased from 0.93, 2.86, and 0.95 to 0.68, 2.36, and 0.79 and became the type with the lowest connectivity. The alpha, beta, and gamma indices of the natural-artificial freshwater, artificial saltwater, natural saltwater, and natural freshwater-saltwater connectivity patterns increased. Among these patterns, the artificial saltwater connectivity increased from 0.74, 2.37, and 0.83 to 0.93, 2.80, and 0.95 and had the highest connectivity. This paper has certain value and significance for wetland hydrology management.