For each hourly outflow sample, we determined the leachate volume,
the pH, the electrical conductivity (EC), and the concentration of
DOC. For EC and DOC, samples were transferred into 20-mL glass vial
and stored at 4 °C. These samples were then filtered through a
0.45 μm filter and EC and UV/Vis absorption (at 465 nm) was measured.
The UV/Vis absorbance was then converted to DOC concentrations by
developing a calibration curve from a series of diluted samples where
both UV/Vis and DOC had been measured. Dissolved organic carbon
for calibration standards was measured with a TOC analyzer after acid
purging of samples (TOC-VCSH, Shimadzu, Tokyo, Japan). In addition,
for each storm a composite sample was collected by merging 80% of
each hourly outflow sample in a 500-mL Nalgene bottle. This composite
sample was analyzed for nitrate/nitrite (Systea Easy, 1-Reagent),
total Kjeldahl Nitrogen (SM 4500-N-C), total and ortho-phosphorus
(SM 4500-P-E), and total and dissolved copper (EPA 200-7). Composite
samples for each storm were analyzed by ATR-FTIR as described in the
supporting information.