Assessing the impact of human activities on heavy metal pollution in mangrove wetland surface waters: A case study of the Zhangjiangkou Estuary

Mangrove ecosystems are among the most biologically diverse and productive marine ecosystems globally, with significant ecological and environmental functions. Nonetheless, research into heavy metal pollution in mangrove wetland surface waters remains limited. In this study, surface water and sediment porewater samples were collected from 24 stations within the Zhangjiangkou estuary and mangrove area. Cu (89.51 ± 54.78 μg/L) and Pb (61.86 ± 39.68 μg/L) concentration were the highest in water, followed by Ni (27.28 ± 2.42 μg/L), Cr (19.62 ± 3.64 μg/L), Hg (7.38 ± 2.00 μg/L), Cd (6.61 ± 0.40 μg/L). With the exception of Hg, the concentrations of all heavy metals were highest in the upstream and downstream of the study area, with lower concentrations observed in the middle reaches. Cu and Pb are clearly influenced by anthropogenic sources, with Pb concentrations at locations proximal to bridges, railways, and fishing activities exceeding 50 % of the total Pb concentration, while Cu concentrations in the downstream and upstream of the river and areas within mangrove forests accounted for 30 %-74 % of the total Cu concentration. Principal component analysis (PCA) suggests that the primary sources of heavy metals were transportation and agriculture mixed sources (accounting for 62.68 %) and mariculture pollution (accounting for 37.32 %). Cu and Pb concentration exceeded the third category seawater quality standards, highlighting an overall unfavorable pollution status.