C and N exports in lateral subsurface flow
Lateral subsurface flow from the second-growth forest started earlier,
ran later, and generated nearly twice the total runoff compared to the
old growth forest (Fig 1a, Table 2). Concentrations of DOC and TDN
exported in lateral subsurface flow from the old-growth forest were 5
and 3 times higher than those from the second-growth forest and C:N
(DOC/TDN) was also higher in old-growth exports (Table 2, Fig 1b and c),
likely resulting from direct leaching of O-horizon and transport through
shallow, subsurface flowpaths. Peak DOC and TDN concentrations for the
old-growth forest export occurred during the mid-May peak in subsurface
runoff and then declined (Fig 1). In contrast, the DOC and TDN
concentrations in lateral subsurface flow exported from the
second-growth hillslope were uniformly low throughout the flow period.
Annual subsurface flux of C and N were 10 and 8 times higher from the
old-growth hillslope (Table 2).