Heavy Metal Concentrations in the Surface Water of a Crater Lake in Southern China

This study continuously monitored the concentrations of five heavy metals (Cu, Zn, Pb, Cr, and Cd) in the surface water of the famous crater lake in Southern China based on a once a week sampling frequency of four locations from June 2018 to May 2019. The concentrations of these heavy metals and their seasonal variations were discussed by correlating with the lake’s water temperature, pH, and rainfall. The results showed that the weekly Cu, Zn, Pb, Cr, and Cd concentrations ranged from 0.31 to 1.10 µg/L, 0.10 to 2.03 µg/L, 0.01 to 0.50 µg/L, 0.39 to 2.71 µg/L, and 0.00 to 0.86 µg/L, respectively. The mean annual metal concentrations of lake water were in decreasing order of Cr > Zn > Cu > Pb > Cd and within the permissible levels of national water quality guidelines. There was no significant seasonal variation in the heavy metal concentration between the wet and dry seasons. However, except for Cr, the other metals’ mean concentrations were slightly higher in the wet season than the dry season, likely due to rainfall-related inputs. Based on correlation analysis, water temperature and pH may have influenced the concentrations of Zn and Cu, respectively, while the concentration of both metals was not affected by rainfall and showed high fluctuations throughout the sampling period, suggesting airborne related dust source inputs. Conversely, Pb concentration was influenced mainly by rainfall and temperature and is likely rain-related source inputs. Meanwhile, the negative correlation between the Cr concentration and pH value of lake water suggests that Cr is mainly derived from sediments. In contrast, the Cd concentration is not related to these factors as its content is generally a reflection of background value. Finally, the characteristics of these five heavy metals in this closed hydrological system of the Huguang Maar Lake suggest that atmospheric deposition and weathering-related inputs are important in evaluating heavy metal concentration levels in a close lake system for sustainable protection of its ecosystem.