Characteristics of DOM exported in hillslope lateral
subsurface flow
Indices of aromaticity (SUVA254) of old-growth DOM
export were 14% higher (3.46 vs. 3.00) and humification index (HIX) was
nearly twice that of DOM exported from the second-growth forest (12.24
vs. 6.63). The DOM exported from the old-growth hillslope had a mean
fluorescence index (FI) of 1.14 compared to 1.52 from the second-growth
hillslope. Fluorescence regional integration modelling (FRI) confirms
the patterns shown by the EEMs indices (Fig 2). FDOM corresponding to
amino acids (RI and RII) and microbial exudates (RIV) were higher in
exports from the second-growth hillslope. Conversely, plant-derived
fulvic- and humic-like hydrophobic organic acids (RIII and RV) were
higher in exports from the old-growth hillslope.
Indices of FDOM chemical character (FI and HIX) were similar in exports
from the two hillslopes at the onset of subsurface flow but diverged
over time (Fig 3a and 3b). Across the subsurface flow season, FI
decreased by half the possible range in the old-growth hillslope. The
proportion of complex organic acids in FDOM exports (based on HIX),
increased 3-fold during the flow period. In contrast, the chemical
character of FDOM exported from the second-growth hillslope remained
relatively uniform (Fig 3a and 3b).