Characteristics of Hydrological Connectivity and Its Ecological Effects in a Typical Tidal Channel System of the Yellow River Delta

Salt marsh is a transitional area between land and sea，Its primary productivity is high, and it is the habitat of many important species. It plays an important role in maintaining the function of wetland and the global ecological balance. The structure and the ecological function had been greatly influenced by climate change and human activities. The hydrological connectivity of tidal channel is one of the key ecological process for coastal wetlands, and is also an important way to maintain and repair it. In this paper, through field investigation and in situ observation of a typical tidal channel system with major and minor tributaries in the Yellow River Delta, the characteristics of hydrological connectivity and the distribution of soil and biological characteristics under different gradients of hydrological connectivity were analyzed. The results show that the intensity of hydrological connectivity is affected by the shape of the tidal channel and topography, in which the frequency of flooding, the cumulative duration of flooding are significantly correlated with the topography and the shape of tidal channel. Soil moisture content and salinity are affected by the strength of hydrological connectivity significantly. Moisture content in the period of spring tides is greater than the neap tides, the area of high flooding frequency is greater than the low frequency, while the salinity of the soil is greatly influenced by the flooding frequency. The more frequent flooding helps to alleviate the salinity stress. The distribution of biomass of Suaeda salsa with the gradient of hydrological connectivity was basically consistent with the seed flow and the density of soil seed bank, both high frequency flooding area is greater than low frequency flooding area, It can be seen that the distribution of Suaeda salsa mainly depends on the adaptability of the process of plant life cycle to the features of hydrological connectivity.