Although both this study and Hou et al. (2014) were conducted in YRD, the study
areas were not exactly the same. The flux of each pathway was updated with more recent or appropriate data compiled from the literature and statistical yearbooks. The calculated net flux also indicated the temporal trend of heavy metal concentration in farmland topsoil. The net flux resulted in the net mass change of heavy metal in topsoil in a year, which was equivalent to the annual change rate of heavy metal concentrations in topsoil, i.e., temporal trend.