important in separating classes [16]. PCA also allows for the evaluation
of relationships between observed variables [17,18]. These statistical
techniques have been applied to data from a variety of research fields,
including environmental and soil sciences [14], but with almost no report
on their use to characterize releases of heavy metals after simulated
acid rain (SAR), especially the evaluation of the relationships between
variables and the application of two-dimensional (2-D) HCA heat map.
In this study, we conducted batch column experiments with SAR solutions
and nine natural urban soils from Guangzhou. The aims of this
study were to: (1) assess the risk of heavy metals (Cd, Pb, Cu, and Zn)
in urban soils for water quality affected by SAR; (2) use 2-D HCA heat
map and PCA to cluster soils in terms of heavy metal releases from
soils after SAR; (3) investigate the changes in speciation fractions of
heavy metals in urban soils affected by SAR; and (4) identify how soil
properties affect the releases of heavy metals in response to SAR.