Agriculture Reference
In-Depth Information
Table 4.4.3.
Fluxes of dissolved organic carbon, nitrogen, phosphorus and sulphur (DOC, DON,
DOP and DOS) entering the mineral soil (forest floor seepage water) and in the sub-soil (seepage
water at 90 cm depth) of Lithic Rendolls covered with a European beech (Fagus sylvaticaL.) forest
during two heavy rain events in autumn 1998.
Water budget
(mm)
DOC
(g m
−
2
)
DON
(g m
−
2
)
DOP
(g m
−
2
)
DOS
(g m
−
2
)
Compartment
Period
Forest floor
seepage water
September 6-11
81
1.81
0.095
0.005
0.021
October 24-November 6
183
4.71
0.203
0.013
0.040
Seepage water
at 90 cm depth
September 6-11
73
1.60
0.080
0.005
0.018
October 24-November 6
170
4.06
0.180
0.012
0.034
water budget measured with zero-tension lysimeters directly beneath the
forest floor layer and at 90 cm depth were nearly equal (Table 4.4.3). Also
the concentrations of DOC and dissolved organic nutrients in forest floor
and sub-soil seepage water were similar, while the concentrations in
porewater (sampled with suction cups) were reduced by 29-48% compared
with the forest floor seepage water. Water budgets calculated with
WHNSIM were ~65% of those measured with zero-tension lysimeters.
Thus, calculation of fluxes from porewater data underestimated the fluxes
by 56-70% during heavy rain events. The measured sub-soil fluxes of DOC
during the two rain events exceeded the annual fluxes estimated for sites
with developed soils (Guggenberger
et al
., 1994).
In summary, shallow forest soils released large amounts of DOC
and nutrients from the forest floor and the upper mineral soil horizons.
In contrast to deeply developed soils, DOM was hardly retained in the
sub-soils and, thus, organic nutrients were exported from the solum. Loss
of DOM from the soil was greatest during rain storm events during the
growing season and in autumn.
Acknowledgement
We are grateful to L. Haumaier for recording the NMR spectra and
to H. Ciglasch, J. Dilling, A. Möller, U. Roth and A. Wetzel for their
assistance in the woods and in the laboratory. This study was funded in
part by Deutsche Forschungsgemeinschaft (ROSIG programme).
References
Aiken, G.R. and Leenheer, J.A. (1993) Isolation and chemical characterization of
dissolved and colloidal organic matter.
Chemistry and Ecology
8, 135-151.
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