Sedimentological Analysis of Regional Differentiation and Sediment Provenance in the Lu’erhuan River Sea Area of Qinzhou Bay, Guangxi Province

Globally, coastal regions are vital areas of human activity and, as such, are centers of population growth and urban and economic development. Long-term human development has had a major impact on the ecological environment of coastal zones. Therefore, exploring the distribution and provenance of marine sediment types in coastal areas heavily influenced by human activities can provide scientific evidence and references for the current and future ecological management of these sensitive environments. For this reason, we conducted an analysis of the sediment grain size, endmembers, and organic matter content and geochemical elements in the Lu’erhuan River-Malan Island-Sandun Island area in the eastern part of Qinzhou Bay, a region heavily influenced by human activities. The sediment grain size clearly differs throughout the study site and the material provenances and hydrodynamic conditions also vary, likely due to the local environmental conditions and the significant impact that human activities have had on the area. The finest-grained sediment is imported from either inland or coastal areas via rivers and weak tidal currents, the next finest component comes from coastal areas through weak tidal currents, and the moderately coarse component mainly originates from nearby beaches. The two coarsest-grained sediment components are influenced by the combination of human activities, tidal currents and waves and enter the water via erosion. The organic matter provenance resembles that of the sediment components, exhibiting varied characteristics. Due to the combination of natural and human activities in the bay, the organic matter in the upper reaches of the Lu’erhuan River originates from the river and coastal paddy fields, with obvious terrigenous characteristics; the organic matter in northern Malan Island mainly comes from external sources related to oyster farming, while the organic matter in eastern Sandun Island is mainly produced endogenously by marine plankton. Al, Ti, Fe, Mg, K, Ga and other elements indicate that terrestrial sediments are significantly disturbed by human activities. However, Mn reflects the marine distribution of terrestrial sediments from the Lu’erhuan River to Jishuimen. Ca and Sr, which are indicators of marine sediments, are distributed in the eastern offshore area of Sandun Island, which is connected to open waters. Due to the influence of human activities, As and Cd are highly enriched in the study area, while Cu is less affected by human activities