Soil erosion by water is one of the most important
factors affecting contemporary landscape changes
within the lowland geoecosystems in Central Europe. Soil erosion by water mainly depends on: rainfalls
(especially its intensity and erosivity), length of slope and its inclination, type of cultivation and usage
of land, anti-erosion treatments and susceptibility of
soils to erosion. The aim of conducted research was
to evaluate conditioning and magnitude of secular
and extreme soil erosion processes in the Drawsko
Lakeland with special considering of rainfall erosivity
index (EI30). The main goal was realised through several research tasks. The first task involved examination of surface runoff and slope wash conditionings,
course and quantity in the testing plot located within
the Chwalimski Potok catchment. The second task
was related to evaluate rainfall impact to soil erosion
by water processes. It was realised by computation
rainfall characteristics: intensity, kinetic energy and
erosivity. In order to assess secular and extreme soil
erosion impact to land relief changes, research were
provided with additional details by conducting three
field experiments with simulated rainfall.
Stationary observation and quantitative researches
of soil erosion (at testing plots) have been conducting
within the Chwalimski Brook catchment for three
hydrological years (2012–2014). The slope with the
test area is located within the 1st order catchment being a subsystem of the Młynski Brook catchment and
then followed by the upper Parsęta catchment. This
area covers 4.8 hectares and is characterised by short
slopes with small height variances up to 10 meters.
Historically, the area was covered with agricultural
crops, currently they cover about 10% of the area. The
slope is covered with gleyic retisols and its average inclination is about 4 degrees with its south-east exposure. The measuring system of soil erosion covered
5 testing plots with different agricultural use (bare
fallow, meadow, potatoes, spring and winter crops).
Plots are 42 metres long and 4 metres width. In the
bottom edge of each plot catchers with volume of 800
dm3 were installed. In this research, only data from
black fallow were considered. Such tillage is recognised as a standard in soil erosion studies. Two experiments have been conducted in this testing plot. The
third one has been conducted on slope located within
an area of undulated morainic plateau in the Kłuda
catchment. The slope is characterised by greater height variances than in Chwalimski Brook catchment.
The slope, where the experiment has been conducted,
is situated within local closed depression and is covered by sands underlain by boulder clay. Its average
slope is about 10° with its southwest exposure.
Although annual precipitation in the three-year
measurement period was comparable with mean
value from multi-year period (1987–2014), its intensity and erosivity were distinguishably lower. Such
rainfall conditions are not favourable for extreme
soil erosion by water processes, thus any relief forms
from such geomorphological processes were not observed in the Drawsko Lakeland.
Due to lack of that kind of forms, in 2013 and
2014, three field experiments were conducted. The
main aim of experiments was to evaluate the impact
of high intensity rainfall on soil surface. The first
experiment consisted of 5, the second and the third
of 4 rainfall simulations. The rainfall was created by
using a purpose-built rain simulator, consisting of 3
and 6 sprinklers placed around the testing plot. Despite the slope inclination in the Kłuda catchment
was 2.5 times steeper than Chwalimski Potok’s slope, surface runoff attained smaller volume, because
of remarkably higher infiltration rate.
In 2012–2014, surface runoff and soil loss has occurred 8 times each year. The maximal monthly surface runoff volume was registered in February 2012,
and it equalled 10.1 dm3
m−2 and the maximal soil
loss value was registered in May 2013 and equalled
3,198 kg ha−1. Annual runoff volumes were between
31.2 dm3
m−2 in 2012 and 38.8 dm3
m−2 in 2013, whereas annual soil loss values ranged from 740 kg ha−1
in 2012 to 5,700 kg ha−1 in 2013. Soil erosion values
caused by simulated rainfall during field experiments
were similar or significantly higher than annual values. Surface runoff was between 31.2 dm3
m−2 in the
first experiment and 34.2 dm3
m−2 in the second one,
whilst soil loss was between 4,632 kg ha−1 and 8,637
kg ha−1.
The achieved experiment results have been compared with soil erosion rate achieved from stationary observations. The results show that runoff and soil
loss considerably increase during rainfalls with high
amount, intensity and erosivity. Furthermore, individual extreme erosive events may exceed annual (secular) soil erosion processes. Conducted stationary
research indicates that annual soil erosion primarily
depends on individual rainfall and erosive events,
which considerably exceed mean values.
In order to evaluate the soil susceptibility to erosion by water in the Drawsko Lakeland, high resolution potential and actual soil erosion risk maps were
prepared. The qualitative assessment of soil erosion
risk was based on geoinformation technologies. The
model considers following conditions affecting the
size of soil erosion: slope steepness and aspect, topographic factor LS (unit upslope contributing area),
lithology, rainfall erosivity (Modified Fournier Index
calculated from monthly and annual precipitation
data) and land use and land cover from Corine Land
Cover 2006. To prepare the map of potential soil erosion risk, land use from Corine Land Cover was not
considered. Thematic maps have been reclassified
into a 4-degree division. The results of the soil erosion risk assessment in the Drawsko Lakeland reveal
the fact that a majority of its area is characterized by
moderate or low erosion risk levels. Areas with high
erosion risk are mostly located in the northern part
of the Lakeland.
The achieved results from stationary observations
and field experiments may indicate that the soil loss
magnitude significantly increases during rainfall
with higher intensity, greater totals and accumulated
in time rainfall events. This may confirm the high
potential of soil erosion by water processes of above-
-average magnitude and intensity in the discharge of
material from agricultural used slopes.
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