M. Langmaack et al. Applied Soil Ecology 16 2001 121–130 123
and non-destructive equipment scans the morphology of the soil surface at a resolution of 0.3 mm Helming,
1992. Without any intervening extraneous influences morphological changes observed on the soil surface
are indicative of sub-surface soil structural changes as a result of faunal activities. The effects of collembolan
and enchytraeid activities on the topography of previ- ously sealed soil surfaces were investigated through
the use of a laser microrelief meter in the present study.
This research was inspired by the results of Kladi- vko et al. 1986, Roth and Joschko 1991 and
Mando and Miedema 1997 which demonstrated the structural changes of crusted soils and the reduc-
tion of surface runoff due to earthworm burrowing and termite activities. The purpose was to investi-
gate whether soil mesofauna contribute to, or even accelerate the rehabilitation of sealed soil surfaces
through their burrowing activities. Soil core samples were inoculated with Collembola and Enchytraei-
dae in defined numbers and subjected to a simulated rainstorm. The soil type chosen is highly suscepti-
ble to surface sealing processes. Alterations in the artificially created seal were detected by measuring
the topography of the soil surface immediately af- ter the rainstorm application and at 6 and 18 month
intervals.
2. Material and methods
2.1. Experimental design In autumn 1996, 15 undisturbed soil monoliths
h:5 cm, ∅: 11 cm, A: 95 cm
2
were obtained from the Ap-horizon of a Gleyic PodzoluvisolHaplic Luvisol
derived from loess FitzPatrick, 1986; FAO, 1988 approximate German equivalent: Pseudogley-Parabra-
unerde aus Loess after basic tillage and seedbed preparation practices were performed. According to
AG Boden 1994 the soil is classified as a sandy loamy silt Uls with 26.2 sand, 60.9 silt and
12.9 clay. The arable land site is located in the sloping Solling area Lower-Saxony, Germany and
very susceptible to surface sealing and soil erosion. The annual mean precipitation is 810 mm.
As described by Schrader et al. 1997 the mono- liths were defaunated in a microwave oven for 6
min at 750 W. Comparing the convenient defaunation techniques microwaving, deep freezing and biocide
application, Huhta et al. 1989 recommended micro- waving as most effective. Only nematodes occasion-
ally recovered from microwaved treatments.
Six of the 15 monoliths were inoculated with Collembola 300 individuals of Folsomia candida ≡
30 000 m
− 2
, six with Enchytraeidae 200 individuals of Enchytraeus minutus and E. lacteus ≡ 20 000 m
− 2
and the remaining three were not inoculated. These densities are within the upper range for typical meso-
faunal populations in arable land Tischler, 1965; Didden, 1993.
At the end of the experiment all monoliths were checked for the presence of mesofauna. Control, i.e.
uninoculated monoliths were still without Enchytraei- dae and Collembola, while both taxa were reduced in
abundance in inoculated monoliths.
2.2. Rainfall simulation To create a surface seal, soil monoliths were sub-
jected to a simulated rainstorm generated with a rainfall simulator as described by Roth and Helm-
ing 1992. In brief, the rainfall simulator consists of a 1 m
2
drop-producing unit with 2500 capillar- ies mounted 7 m above the box containing the soil
monoliths. The drop size distribution was randomised around a median drop size of 2.89 mm. The rain-
fall kinetic energy produced was 25.80 J m
− 2
mm
− 1
, which corresponds to about 99.5 of natural rainfall
kinetic energy at 30 mm h
− 1
rainfall intensity Laws and Parsons, 1943.
Rainfall was applied to 10 of the 15 monoliths 4 with Collembola, 4 with Enchytraeidae, 2 uninocu-
lated for 60 min to instigate the formation of a sealed surface. The actual rainfall intensity was 29 mm h
− 1
. The soil monoliths were placed under the rainfall de-
vice at a 5 slope to prevent the soil surfaces from ponding and to allow for sampling of the generated
surface water runoff. The arrangement of the soil monoliths under the rainfall simulator with hoses for
runoff collection is shown in Fig. 1.
Thus, the experiment comprised the following treatments: four sealed and two unsealed monoliths
inoculated with Collembola, the same number of monoliths inoculated with Enchytraeidae, and two
sealed and one unsealed uninoculated no fauna monoliths.
124 M. Langmaack et al. Applied Soil Ecology 16 2001 121–130
Fig. 1. View of the platform slope 5 with soil monoliths placed 7 m below the drop-producing unit of the rainfall simulator. Soil surface run-off from each monolith was collected by hoses.
2.3. Soil surface scanning Immediately after rainfall application the surface
topography of all monoliths was measured with a non-contact laser microrelief meter, as described by
Helming 1992. In brief, the laser microrelief meter consists of an aluminium frame supporting a sledge
with a mounted laser probe, consisting of a laser source and an optical sensor. The x- and y-direction
movement of the laser probe is software-controlled and driven by two stepping motors. As the laser
probe moves, height values are collected and stored in a computer. This scanning movement allows the
topography of areas from a few cm
2
to a maximum of 1 m
2
to be digitised with 0.3 mm horizontal and 0.2 mm vertical resolutions, respectively. The result is
a surface digital elevation model DEM with regular grid spacing.
A 7 cm × 7 cm area at the centre of each monolith surface was digitised to measure the surface topogra-
phy. A grid spacing of 0.3 mm resulted in a DEM of 52 900 height values per area. For analysis purposes
the dimensionless roughness index ‘specific surface area’ SSA, representing the ratio of the surface area
measured to the projected surface on a plane perpen- dicular to the laser beam, was calculated based on
the procedures of Helming et al. 1993. Briefly, the method consists of summing up the surface area of
each 3 mm × 3 mm grid square. The surface area of each grid square was determined by calculating the
area of the four triangles derived from the four ele- vation points of the grid plus a linearly interpolated
midpoint. In previous studies the SSA index was de- termined to be a suitable parameter for the character-
isation of soil surface topographies Helming et al., 1993; Schrader et al., 1997.
The alterations of the created seal were monitored by measuring the topography of the soil surface with
the non-contact laser microrelief meter immediately after the rainstorm application time t
as well as 6 time t
6
and 18 months time t
18
later. Between the measurements, the soil monoliths were stored at
20
◦
C in dark and humid conditions Schrader et al., 1997. For comparison of the different treatments
M. Langmaack et al. Applied Soil Ecology 16 2001 121–130 125
and measurement dates the relative differences of the SSA values were calculated. By definition the lowest
possible value of SSA is 1.0 totaly plane surface: we therefore subtracted 1.0 from all SSA values be-
fore determining the percentage differences between treatments. The Mann–Whitney-U-test was used for
statistical analysis.
3. Results
