The behavior of heavy metals (Cd, Cu, Zn, Cr, Pb),
nutrients (organic C, P, and N parameters), and major
ions was investigated during percolation of roof runoff water
through an artificial infiltration site. The concentrations
of the various components were determined in rainwater,
roof runoff, and infiltrating water at various depths in
the soil. The concentrations of most parameters in roof
runoff were highest during the “first flush” at the beginning
of rain events. Despite rapid infiltration caused by strong
preferential flow, differences were still observed in infiltration
behavior between individual compounds. Cl-, NO3
-,
SO4
2-, ortho-phosphate, and the major part of DOC behaved
essentially conservatively during infiltration, whereas
NH4
+ concentration decreased probably as a consequence
of nitrification. The concentrations of Ca, Mg, Na, K, and
alkalinity were regulated by dissolution of soil material. The
change in concentrations of Cu, Cd, and Cr during
infiltration was mostly due to the concentration dynamics
of roof runoff inflow water with only limited retention by
soil, indicating the high mobility of these metals in the
unsaturated zone. In the short term, Pb and Zn showed
the opposite behavior with strong retention in the upper soil
layers as determined by the large decrease in their
concentrations measured in the lysimeters compared with
those in the runoff water. However, in the long term,
zinc and lead were also transported through the deeper
soil layers of the unsaturated zone. The high mobility of Cu
and Cd can be attributed to complexation by ligands in
solution, and of Cr to the presence of Cr(VI) species. The
artificial infiltration site used in this study was designed
according to recommended standards for water infiltration;
nevertheless its design turned out to be sub-optimal for
the retention of heavy metals and for some of the organic
and inorganic compounds.
