we use >330 data points together with mixed-effect models to indicate that (i) human
activity modes significantly influence the Cu and Mn but not Zn, Fe, Pb and Cd levels, and (ii) annual
mean temperature (AMT) only significantly influences Cu and Pb levels, while annual precipitation (AP)
only significantly affects Fe, Cu and Mn levels. Given these differences, we suggest that the impacts of
human activity modes and climate on heavy metal “spread” in groundwater are biased.