Study on the distribution characteristics of sediments on the mangrove beach of the sea-viewing promenade, Zhanjiang

Mangrove forests possess significant ecological and aesthetic values. Investigating the spatial distribution characteristics of beach sediments in mangrove habitats and their relationships with hydrodynamic conditions and vegetation dynamics is crucial for sustaining the health and sustainability of mangrove ecosystems. This study aims to explore the spatial distribution characteristics of sediments in the mangrove beach of Xiashan Sea-viewing Promenade, Zhanjiang, and their relationship with hydrodynamics and mangrove vegetation. A total of 59 surface sediment samples were collected from 6 transects in the study area. The elevation of the sampling points, as well as wave and current data during the sampling period, were measured. The sediment transport trends of the 6 transects were also analyzed. The results show that the average grain size of surface sediments in the study area ranges from -0.75 to 5.15 φ; the average sorting coefficient is 1.26, indicating poor sediment sorting; the average skewness is 0.19, with positively skewed and extremely positively skewed sediments widely distributed in the study area; the kurtosis values range from 0.36 to 2.31, with an average of 1.14, and narrow kurtosis is observed on the seaward side of the southern and northern parts of the study area. The significant wave height in the study area ranges from 0.05 to 0.17 m, the wave period ranges from 1.44 to 3.38 s, and the current velocity ranges from 1.44 to 7.44 cm·s⁻¹. The surface sediment types include gravel, sand, silt, and clay, with sand being the most abundant, followed by silt, while gravel and clay are present in small amounts, with gravel only found in small quantities near the shore in the northern part of the study area. The sand content decreases from the shore to the sea, while the spatial distribution of silt shows the opposite trend. The clay content is relatively low, with a higher concentration in the seaward area. The wave action in the study area is significantly stronger than the current action, with the strongest hydrodynamic forces occurring during the early flood tide and late ebb tide, leading to an onshore sediment transport trend. This process can increase beach elevation and stability, which is beneficial for the growth and development of mangroves.