Reconstruction of heavy metal(loid) pollution history based on dendrochemistry in Jiuzhaigou World Natural Heritage site, southwestern China

Heavy metal(loid)s are widely regarded as important environmental pollutants and have attracted extensive attention. In addition to such areas with frequent human activities as cities and industrial areas, the heavy metal(loid) pollution in remote areas lacking long-term monitoring data also deserves attention. In this study, Chinese pine ( Pinus tabuliformis ) in Jiuzhaigou World Natural Heritage was sampled to analyze concentration of Pb, Zn, Cu, As, Cd, Co, Cr, and Ni and to reconstruct pollution history. Source analysis and evaluation of the potential ecological risk of heavy metal(loid)s were also performed. Results showed that Jiuzhaigou has been polluted by heavy metal(loid)s at a relatively high level and concentrations were the highest at the location with intensive human activities (Nuorilang). Tree growth was inhibited by increased heavy metal(loid) concentration and this situation was more pronounced at high concentrations. The increased heavy metal(loid) concentrations were attributed to human activities such as forest logging, infrastructure construction, and tourism development. Heavy metal(loid) pollution reached a very high level of ecological harm at Nuorilang and a high level of ecological harm in Shuzheng and Heye villages. Overall, even at low concentrations, we demonstrated that Chinese pine can be used not only as a bioindicator for heavy metal(loid) pollution but also to infer pollution history over a relative long-term period and to enhance our understanding of the biogeochemical cycle of heavy metal(loid)s in forest ecosystems.