Spatiotemporal Patterns of Heavy-Metal Pollution in Coastal Pinqing Lagoon (Southern China): Anthropogenic and Hydrological Effect

Abstract

Coastal lagoons connecting the land and sea provide essential ecosystem services. However, emerging environmental issues such as environmental pollution and ecological degradation from rapid socio-economic development in coastal zones of south China are becoming increasingly prevalent. This study examined the spatiotemporal variation, sources, assessments, and driving forces of heavy metals based on core and surface sediments collected from Pinqing Lagoon, a coastal lagoon in South China. Sediment cores (PQ1, PQ2, and PQ3) showed distinct vertical variations in the content of Cu, Cd, Zn, Pb, As, and Sb with an average coefficient of variation (C.V.) of 0.25. However, a relatively lower vertical variation (C.V. mean = 0.13) was shown by the other elements (Mn, V, Ni, Cr, and Co). Although Cu was the chief pollutant heavy metal and it had mean values of 1.6 and 1.7 for the enrichment factor (EF) and contamination factor (CF), respectively, Cd posed the highest ecological risk (Eri mean = 36.34). A century-scale anthropogenic disturbance and growing industrial activities in the lagoon area have caused heavy-metal pollution in Pinqing Lagoon. Wastewater discharge into the lagoon over the past 30 years has further aggravated the pollution. The land-use pattern changes in the catchment and removal of polluting industries resulted in a shift in the center of gravity of heavy-metal pollution in the surface sediment of the lagoon. When integrated with the available data, significant pollution gradients were observed suggesting that the pollution level of Pinqing Lagoon was slightly higher than the marginal sea (Honghai Bay) but significantly lower than the adjacent inland water bodies (Gongping and Chisha Reservoirs). This difference attributes unique hydrodynamic conditions to the Pinqing Lagoon, which consistently mitigates environmental pollution by lying at the interface between inland water and the coastal sea in South China. These conditions resulted in the relatively low contamination degree (CD mean = 7.5) and the low ecological risk index (RI mean = 70) over the past 150 years in Pinqing Lagoon.