phosphorus.
Most of the copper (70–96%) in the bioretention outflow was in dissolved
form. Total and dissolved copper concentrations showed a decreasing
trend over successive storms (Fig. 3). Statistical differences
between the two treatments were detected during storm 3, 4, 5, and
6, with the Royal Classic bioretention system leaching more copper
than the Silver Springs system. Elevated copper leaching was observed
for the third storm. The bioretention systems showed net release of copper
for the first few storms, but retention of copper in the last two
storms (Table 2). Copper concentrations monitored in the outflow for
all seven storms were N20 μg/L, which exceeds the benchmark for industrial
stormwater discharge in the State of Washington of 14 μg/L
total copper (Washington State Department of Ecology, 2009).