Spatial Distribution and Ecological Risk Assessment of Heavy Metals in the Sediment of a Tropical Mangrove Wetland on Hainan Island, China

Abstract

Mangroves have a high ecological service value and play an important role in achieving carbon neutrality. However, mangrove wetland soil quality is constantly being affected, and the ecological services provided are gradually declining due to the threat of various pollutants, especially heavy metal pollution. Exploring the sources and ecological risks of heavy metals in mangrove sediments will be helpful in improving mangrove protection. In 2020, sediments were collected from terrestrial and aquatic areas of Dongzhai Harbor mangrove wetland in Hainan, China, and were analyzed for the concentrations of nine heavy metals (As, Cd, Cr, Cu, Hg, Pb, Ni, Zn, Co). The results showed that there were obvious spatial distributions of heavy metals in sediments. The high concentrations of heavy metals occurred largely in terrestrial areas and in 0–20 cm of the sediment surface layer. Correlation analysis and cluster analysis indicated that As mainly originated from ships and aquaculture in the harbor waters, Cd and Hg from agriculture, Cr, Cu, Ni, Zn and Co from the weathering of parent rocks, and Pb from soot emitted from metal smelters and automobile exhaust. The individual potential ecological risk index (Eir) indicated that contaminating elements were mainly Cd and Hg. The potential ecological risk index (RI) and multiple probable effect concentrations quality (mPECQs) indicated that the areas with high heavy metal concentration and the 0–20 cm range of sediment surface layer were more susceptible to heavy metal contamination. Although there were no obvious ecological risks in the area, these results could facilitate the understanding of the distribution of heavy metal pollution in mangroves and provide information to achieve sustainable development of mangroves.

Distribution of Heavy Metals in Surface Sediments of a Tropical Mangrove Wetlands in Hainan, China, and Their Biological Effectiveness

“…Dongzhai Harbor Mangrove Wetland is in Haikou City, Hainan Province, northeast of Hainan Island, with a tropical maritime monsoon climate. The average annual temperature is 17.1 • C, the average annual precipitation is 1676 mm, and the all-weather irregular tides have an average tidal range of approximately 1 m (Figure 1) [12]. Dongzhai Harbor is a drowned-valley-type harbor formed by the collapse of the 1605 Qiongshan earthquake, and is injected by small streams such as the Zhuxi River, Qiaotou River, and Yanfeng River.…”

“…The environmental pressure on mangrove wetlands is increasing due to the increase in the population, the development of industrial and agricultural production in cities and watersheds, and especially the extensive selection of bay estuaries as sewage disposal sites for coastal cities, which has led to a large amount of pollutants entering the estuarine area [10,11]. In 2020, Mao et al [12], through the analysis of nine heavy metals in mangrove wetland sediments in Dongzhai Harbor, found that the content of heavy metals such as Cd, Cr, Cu, Ni, Zn, and Co in this area exceeded the standard, and the potential ecological risk and the quality of the concentration of the multiple possible impacts showed that the area with high concentrations of heavy metals and the surface of the sediment in the range of 0-20 cm were more susceptible to contamination by heavy metals. Studies have shown that the distribution of heavy metals in mangrove wetland sediments is closely related to changes in land-use patterns [13].…”

Research status of heavy metal pollution evaluation in urban wetlands in China

“…Ma Yongling [21] collected the sediment digestion of Wuhe Wetland and determined 6 kinds of heavy metals (As, Cd, Cu, /b110>Hg, Pb, and Zn). The results show that the heavy metal content in the surface sediments of Wuhe wetland is mostly higher than that of the environmental background value, and the potential ecological risk assessment shows that the potential ecological hazard index in the sediments of Wuhe wetland is extremely strong ecological hazard.…”