Geomorfologický Aplikovaná a antropogenní 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: kdwucet@wnoz.us.edu.pl 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). 17
Table. 1. The current rate of rainwash in loess arable lands in Polish Uplands Measured quantity Order of quantity t/km 2 Average ratio of 24 hours denudation on loess (plough lands) of Lublin Upland: (ZGŁOBICKI 2001) (JÓZEFACIUK&JÓZEFACIUK 1996) Efficiency of rainwash during heavy rainfalls: Piaski Szlacheckie (MARUSZCZAK, TREMBACZOWSKI, 1956) Dzierzkowice (BURACZYŃSKI, WOJTANOWICZ, 1971) the Kalinka catchment (CZYŻOWSKA, 1997) Upland plateau Slope 0,0X 0,00X-0,X X000,0 X000,0 X0,0 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). 14 C 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. 18
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 19
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 Culture 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, except 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 goes 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. 20
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 ABŁAMOWICZ D., ŚNIESZKO Z., 2001: Osadnictwo kultur rolniczych w dorzeczu środkowej Kłodnicy a atrakcyjność krajobrazu. Sprawozdania Archeologiczne T. 53. BURACZYŃSKI J., WOJTANOWICZ J., 1971: Rozwój wąwozów lessowych w okolicy Dzierzkowic na Wyżynie Lubelskiej pod wpływem gwałtownej ulewy w czerwcu 1969 roku. Annales UMCS Sec. B. 26, 6, s. 135 162. CZYŻOWSKA E., 1997: Stan badań nad rolą ekstremalnych opadów w ewolucji wyżyn lessowych. W: Rola gwałtownych ulew w ewolucji rzeźby Wyżyny Miechowskiej (na przykładzie ulewy w dniu 15 września 1995 r.). Ed. L. Starkel. Dokumentacja geograficzna, t. VIII, Wrocław JÓZEFACIUK Cz., JÓZEFACIUK A., 1996: Erozja i melioracje przeciwerozyjne. Biblioteka Monitoringu Środowiska. Warszawa. S. 5 144. KRUK J., MILISAUSKAS S., ALEXANDROWICZ S.W. & ŚNIESZKO Z., 1996 : Osadnictwo i zmiany środowiska naturalnego wyżyn lessowych. Studium archeologiczne i paleogeograficzne nad neolitem w dorzeczu Nidzicy. Inst. Arch. i Etnol. PAN Kraków. MARUSZCZAK H., TREMBACZOWSKI J., 1956: Geomorfologiczne skutki gwałtownej ulewy w Piaskach Szlacheckich koło Krasnegostawu. Ann. UMCS. Ser B. 11, 4, s. 129 151. 21
MUCHER H, J., 1985 : A study on loess- derived anthropogenic colluvia at the experimental plot Huldenberg, Belgium. Preliminary results of a micromorphological approach. W: The Huldenberg Experimental Field. Excursion Guide. Workshop on Soil Erosion and Hillslope Hydrology with Emphasis on Higer Magnitude Events. Leuven 27 30 March 1985. RODZIK J., JANICKO G., ZAGÓRSKI P. & ZGŁOBICKI 1998: Deszcze nawalne na Wyżynie Lubelskieji ich wpływ na rzeźbę obszarów lessowych. W: Geomorfologiczny i sedymentologiczny zapis lokalnych ulew. Ed. L. STARKEL. Dokumentaja geograficzna. Wrocław. STARKEL L. (ed.), 1997: Rola Gwałtownych ulew w ewolucji rzeźby Wyżyny Miechowskiej (Na przykładzie ulewy w dniu 15 września 1995 roku). Wrocław. STARKEL L., (ed 2001): Geomorfologiczny i sedymentologiczny zapis lokalnych ulew. Dokumentacja Geograficzna. 11. Wrocław. ŚNIESZKO Z., 1995: Ewolucja obszarów lessowych Wyżyn Polskich w czasie ostatnich 15 000 lat. Pr. Uniw. Śl. 1496. S. 5 122. ŚNIESZKO Z., BLUSZCZ A., PORĘBA G., 2003: Podstawy badań wieku holoceńskich osadów proluwialno- deluwialnych na obszarach lessowych Wyżyn Polskich. (In press.) ZGŁOBICKI W., 2001: Dynamika współczesnych procesów stokowych w północnozachodniej części Wyżyny Lubelskiej w świetle wyników badań metodą cezową ( 137 Cs ). 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. 22