Sedimentary records of environmental evolution in Dongzhai Port mangrove swamps (South China) over the last hundred years: Insights from corrections of grain-size effects.

Mangrove sediments play a vital role in the biogeochemical processes of elements by behaving as both sources and/or sink for nutrients and trace metals. Under the combined impacts of grain-size effects and human activities, it is difficult to accurately assess the sources and degree of pollutants. For this purpose, two cores were collected from a mangrove swamps of Dongzhai Port (South China) and analyzed for temporal distributions of grain size, nutrients, major and trace elements, and Pb activities. Due to the significant vertical variation of grain size with depth, linear regression analysis was conducted based on trace metals (i.e., Pb, Cr, Ni, Cu, Cd, Zn) and normalized element Al to reconstruct local environmental background. The results showed that the contents of Cu, Cd, and Zn in the surface layers exhibited significantly increasing trends since the 1980s, with maximum contents of 9.06, 0.16, and 228.66 μg g, and their enrichment factors up to 1.52, 1.40, and 1.50, respectively. It should be attributed to shrimp farming and domestic sewage, indicating slight anthropogenic inputs. The evolution process was divided into three stages in Dongzhai Port over the last 100 years: before 1980 AD, 1980-2000 AD, and from 2000 AD to the present, corresponding to the stages of natural deposition, domestic pollution, and aquaculture pollution, respectively.