Intensity of soil water erosion in Holocene in loess

Aplikovaná a antropogenní
Geomorfologický
sborník 2 geomorfologie
ČAG, ZČU v Plzni, 2003
Intensity of soil water erosion in Holocene in loess areas of
Poland
Krystyna Dwucet, Zbigniew Śnieszko
e-mail: [email protected]
University of Silesia, Faculty of Earth Sciences60 Będzińska Str., Sosnowiec, Poland
Rainwash in loess arable lands is the predominating slope process in
temperate climatic zone. Reconstruction of rainwash intensity in the past can
be the base to estimate the intensity of anthropopression of ancient
agricultural cultures. Detailed studies of geological profiles indicate reg ional
and microregional differentiation in rainwash intensity from the early
cultivation of loess areas (Fig.1).
Fig. 1. Range of loess in Poland:
a) localisation of profiles with deposits originated from soil erosion
b) localisation of research sites
Data concerning the rainwash process in last 10 thousand years were
obtained by investigation on deposits accumulated at the lowest parts
of the slopes (delluvium), in dry valley bottoms (delluvium and prolluvium)
and river valley bottoms (overbank alluvium) ( ŚNIESZKO, 1995). Observations
of heavy rainfalls effects and analyses of Cs 137 decay in present delluvium and
overbank alluvium (RODZIK J., JANICKO G., ZAGÓRSKI P., ZGŁOBICKI 1998,
STARKEL L., ed. 1997, STARKEL L., ed 2001) were the bases for the rainwash
intensity reconstruction for the last 50 years.
The current rate of rainwash in loess arable lands in Polish Uplands
decidedly increase during torrential rains (Table 1).
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Table. 1. The current rate of rainwash in loess arable lands in Polish Uplands
Measured quantity
Order of quantity
t/km2
Average ratio of 24 hours’ denudation on loess
(plough lands) of Lublin Upland:
(ZGŁOBICKI 2001)
0,0X
(JÓZEFACIUK&JÓZEFACIUK 1996)
0,00X-0,X
Efficiency of rainwash during heavy rainfalls:
Piaski Szlacheckie (MARUSZCZAK, TREMBACZOWSKI,
X000,0
1956)
X000,0
Dzierzkowice (BURACZYŃSKI, WOJTANOWICZ, 1971)
the Kalinka catchment (CZYŻOWSKA, 1997)
Upland plateau
X0,0
Slope
X0000,0
Locally at footslopes and in valley bottoms the accumulation of a layer
of more than ten cm thick (exceptionally of several score cm) takes place after
one heavy rainfall only (CZYŻOWSKA, 1997). Deep furrows, being the initial
forms of gullies, are also locally formed. A single heavy rainfall couses the
insignificant accumulation in most of the area. Repeated rainfalls leads to the
formation of layers of delluvium, prolluvium at footslopes and alluvium,
which are presently met in geological profiles.
Little accretion of delluvium and flood alluvium had been observed in the
all investigated Holocene sedimentary profiles (corresponding with soil
erosion on loesses of Polish Uplands) till the appearance of the first traces
of agriculture (Fig. 2). 14C datings of the oldest Holocene delluvium indicates
the local differentiation in age of slope processes acceleration connected with
human impact.
Cultivation on loess uplands in Poland has already started in the Neolithi c
Age. Since then the prolluvial-delluvial covers, rills and gullies has locally
formed with different intensity and in different periods (Fig. 3). The volume
of material accumulated as weel as their extent were directly related to the
arable land area, the way of land use and contemporary climatic conditions.
The factors mentioned above require detailed palaeogeographical analysis and
good recognition of economical relations in the past in particular settlement
microregions (vide KRUK, MILISAUSKAS, ALEXANDROWICZ, ŚNIESZKO, 1996,
ABŁAMOWICZ D., ŚNIESZKO Z., 2001). Therefore these investigations are
carried out in multidisciplinary groups of scientists, always with cooperation
of archaeologists.
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Fig. 2. Geological
structure
of
selected profiles of
the
Holocene
deposits in Polish
uplands:
1 – regosoils, 2 –
laminated deposits,
3 – laminated
deposits
with
gravels and debris,
4 – deposits of
massive structure,
5
–
relict
chernozem, 6 –
tree trunks
Fig. 3. Phases of soil erosion stated in geological profiles:
V – number of registered events
T – time
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Total thickness of the Holocene delluvial-prolluvial deposits accumulated
in presently dry valley floors reaches sometimes up to 10 m. Most often the
sediments are built of two series of different age, divided by a fossil soil.
The lower series overlies Late Vistulian-Holocene mollisol. The age and type
of fossil soil overlain by the upper series are differentiated. Profiles with only
one layer of deposit related to redeposition of soil also occur. The OSL
method was recently used to Holocene delluvium dating ( ŚNIESZKO Z.,
BLUSZCZ A., PORĘBA G., 2003 in press). The age of delluvial lower series
dated by means of this method varies in broad range.
Lower covers were most often formed in the Middle Ages, covers
correlated with the settlement of Funnel Beaker Cultur e occur locally, and
with Lusatian settlement are rarely met. The upper cover most often refers to
the last hundred years of intensive land use.
The oldest lower covers are met in geological profiles in areas actively
exploited in agricultural way in the period of Neolithic agriculture
culmination (KPL – from 5 to 4 thousand years BP). These results were
obtained investigating the nearest neighbourhood of the Neolithic settlement
in Bronocice in the Małopolska Upland (KRUK, MILISAUSKAS,
ALEXANDROWICZ, ŚNIESZKO, 1996). In loessic areas, which in Neolithic Ages
were not occupied by plough lands, the lower series of deposits was created
much later. It was most often observed not before the Middle Ages, e xcept
one case when it was documented in the Bronze Age.
In almost whole loess area in Poland the general deposit accretion
corresponding to soil erosion falls to the period of ground size reduction and
introduction of root plants. The intensive rainwash g oes on up to present
times. To estimate the size of mechanical denudation, which took place in
the latter part of the 20 th century, the results of investigation on thickness of
deposits corresponding to soil erosion and containing isotope of Cs 137 are
recently used. Measurements of caesium content in deposits developed in the
mid-60s and probably the first profile of delluvium in the loessic area was
dated by this method in experimental plot in Huldenberg ( MUCHER 1985).
From 6-m succession of prolluvial-delluvial deposits, have accumulated for
the last 900 years, the upper layer of 54 cm thick refers to the period of
merely 30 years. Similar results are obtained in profiles in Poland. In profile
of delluvial-prolluvial deposits investigated in Biała (Głubczyce Plateau)
the anthropogenic caesium occurs in the layer of 50 cm thick ( ŚNIESZKO,
BLUSZCZ, PORĘBA, 2003).
Investigations with Cs 137 indicate the uncomparably larger accumulation
rate of deposits derived from soil erosion in th e period of last 50 years than in
the former anthropogenic periods in Holocene. It is the result of deep
ploughing as well as the large importance of root vegetation in the
acceleration of rainwash processes.
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Results of investigation on soil erosion in the Holocene indicate that apart
from direct influence of climatic factors on the size of final rainwash effects
the anthropogenic conditions are of essential importance.
Not every way of land use had similar effect in the mobilisation of “soil
erosion”. Management of flat slope foot areas and terraces in the early
Neolithic Ages as well as also later in the period of the intensive settlement in
the past did not cause the essential increase in rainwash intensity at settled
loessic areas. Deforestation and ploughing on slopes caused rapid acceleration
of soil material transport into depressions. This process was started in many
loessic areas already in the period KPL (Neolithic Ages). Its course was
influenced by the size of settlement groups, localisation of fi eld roads,
settlement intensity, duration of colonies and camping sites, localisation of
plough lands, techniques of cultivation.
Optimum conditions for more intensive rainwash existed when frequency
of torrential rains increased during periods directly a fter harvesting and during
agrotechnical measures to prepare sowing and when the amount of snow
precipitation increased at large deforestation on slope. To investigate relations
between economic impact and climate on “soil erosion” the progress in
climatic reconstruction is of large importance.
At present stage there is the lack of base to call the processes of “soil
erosion” common in any of settlement phases in the past. For particular areas
it is possible to designate large impact on slope in KPL as well as in the
Lusatian culture. There are many documents testifying to such phenomena in
the beginning of the second thousand years of AD. Undoubtedly the common
acceleration concerns the period from introducing of potato cultivation and
then introduction of plough and mechanical equipment.
References
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Aplikovaná a antropogenní geomorfologie
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Autoreferat pracy doktorskiej. Lublin.
Streszczenie
Wydajność procesów wodnej erozji gleb w holocenie na obszarach
lessowych Polski
W pracy przedstawiono aktualny stan badań nad skutkami spłukiwania współczesnego i
w przeszłości w obszarach lessowych Wyżyn Polskich (rys. 1). Poddano analizie
współczesne uwarunkowania środowiskowe sprzyjające spłukiwaniu i znaczenie zasady
aktualizmu dla interpretacji dynamiki tych procesów w przeszłości.
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