Accumulation of Heavy Metals in a Coastal Wetland Natural Reserve in the Estuarine Wetlands of Tianjin, China

Abstract

The condition about the heavy metal contamination of wetland soil has become a hot research topic in wetland science. The research on heavy metal contamination is of great importance for coastal wetland management and for monitoring the intensity of human activities. This paper aims to provide information on the concentration levels of heavy metals within different land use types in a coastal wetland in China. Topsoil (0– 20cm) about different land use types was sampled in Tianjin Palaeocoast and Wetland National Natural Reserve (TJPWNR), China. The chemical properties of the soil and the concentrations of heavy metals in the different sample areas within TJPWNR were investigated in 2007. To investigate the level of pollution, total concentrations of heavy metals such as As, Cd, Cu, Pb, Zn, and Cr were analyzed by applying the method of inductively coupled plasma atomic absorption spectrometry to assess and compare contamination levels of the sampling spots. The average concentrations of As, Cu, Pb, Zn, Cr, and Cd in the surface soil were respectively 19.846, 36.147, 32.656, 100.1, 86.43 and 0.207 mg/kg. Compared with those from other typical wetlands in coastal China, the heavy metal is at a mediate level, which is consistent with the fact that the Tianjin coastal wetland is highly exploited and suffers extreme impacts from human activities. An overall common trend in heavy metal accumulation was shown to have the following decreasing order, with few exceptions: FS>VCS>HIS>WS. Our research demonstrates that the mean concentrations of heavy metals are higher in areas of intensive human activities and farmland than those in wetland soil and vegetation community soil, which suggests that human activities cause larger effects; no significant differences were observed for other heavy metals. The comprehensive contamination indices indicate low contamination levels in the four land use types. The results of this analysis suggest that land use types can play significant role in heavy metal contamination.