Cladocera w osadach pelagicznych Jeziora Biskupińskiego

• Autorzy: Szeroczyńska, Krystyna , Polcyn, Ilona

Warianty tytułu

EN

Cladocera in pelagic sediments of the Biskupińskie lake (Central Poland)]

• Języki publikacji: PL

Abstrakty

PL

Przedstawiono wyniki analizy szczątków Cladocera osadów z profilu 5, pochodzącego z głębokiej strefy Jeziora Biskupińskiego. Wyniki stanowią materiał uzupełniający dane, które uzyskano w roku 1995 z analizy osadów profilu 4 pochodzącego ze strefy litoralnej. Sedymentacja osadów odwierconych w profilu 4 obejmuje okres od fazy inicjalnej jeziora (alleröd) po czasy współczesne, a osady z profilu 5 odłożone zostały w okresach subborealnym i subatlantyckim. W związku z tym dokonane porównanie wyników dotyczy tylko neoholocenu. Duża frekwencja planktonowych osobników Cladocera w profilu 5 pozwoliła na szczegółowe prześledzenie procesu eutrofizacji jeziora, jak również wahań poziomu wody. Wydzielono 5 etapów wzrostu trofii oraz stwierdzono wyższy poziom wód w jeziorze w drugiej połowie okresu subborealnego i w okresie subatlantyckim, w czasie wędrówki ludów. Etapy wzrostu trofii są częściowo zbieżne z fazami rozwoju gospodarki ludzkiej, a określone poziomy wahań wody z wynikami badań paleohydrologicznych. Wydzielono również 3 fazy i 6 podfaz rozwoju Cladocera, które odpowiadają fazom klimatycznym oraz lokalnym fazom pyłkowym.

EN

The first analyses of the content of Cladocera within sediments of the Biskupin Lake were performed in 1994 (Szeroczyńska, 1995). The section (core 4) studied comes from the littoral zone of the lake, where sedimentation lasted from the initial phase of the lake (Alleröd) until contemporary times. These results turned out to be insufficient to conduct a full reconstruction of the lake?s history. Hypotheses on the biological development of the lake are based mainly on changes in the species composition of the plankton. The sediments of core 4 contained primarily remains of species of the littoral zone, and planktonic species consisted mainly of allochthonous material, washed in by waves. Hence, their presence and frequency were of circumstantial value, and did not present the real picture of changes which occurred in the lake during the Holocene. In 1996, in order to obtain a complete picture, an additional analysis of Cladocera remains was performed on the sediments of core 5, drilled in the pelagic zone, at a place where the water depth exceeded 10 m. Microscopic analyses were performed by I. Polcyn and interpreted by K. Szeroczyńska. The sediments were deposited only during the Subboreal and Subatlantic periods, despite relatively large thickness of 9 m. Therefore, it was possible to study the changes which occurred exclusively during the Neo-Holocene. The thickness of these sediments allowed for a detailed interpretation of the periods during which they were deposited. An analysis of subfossil Cladocera was performed on 83 samples, spaced every 2 to 10 cm. 32 Cladocera species belonging to 6 families were found. The species composition was very close to that encountered in the sediments of core 4 (Szeroczyńska, 1995). Only the count of individual species was different. The results obtained are presented graphically in percentage and absolute value diagrams (Figs. 2, 3, 4), and compared with those of the analyses of core 4 (Fig. 5). Furthermore, the diversity diagram and species composition of forms connected with a certain pH were constructed for both cores (Fig. 6). On the basis of species composition and frequency of Cladocera specimens, changes in the lake during the Subboreal and Subatlantic periods were characterised. The zones of Cladocera development were established, their numbering corresponding to that of the zones distinguished in core 4. The Subboreal period is represented by one zone (Va, b, c) of Cladocera development. The species composition and the frequency of individuals indicates that during this period the lake was dominated by planktonic forms. The share of littoral forms was small, except for the acidobiontic species Alonella excisa. During the Subboreal period this species achieved maximum development, and in the sediments of core 5 larger amounts of its remains were found, as compared to cores taken from the littoral zone. Near the end of the Subboreal period, the count of Alonella excisa declined, and this species never reached such a share among the species of Chydoridae. In the Subatlantic period, two zones of Cladocera development have been distinguished (Zone VIa, b, c, Zone VII). The lake was dominated at that time by species connected with higher trophy. It is probable that this was a period of progressive eutrophication of the lake, particularly from Zone VIb onwards. A smaller share of planktonic forms (approximately 30%, except for Bosmina longirostris), indicates a somewhat higher water level. Only in the sediments at a depth of 400-370 cm, whose sedimentation probably occurred during the Migration period, a share of planktonic forms did exceed 50% (including only 10% of Bosmina longirostris). Near the end of the Subatlantic period, a change in the species composition of Cladocera was noted. An increased share was shown again by planktonic forms (approximately 70%, including 20% of Bosmina longirostris), and the littoral forms, including Chydorus sphaericus, did not exceed 30%. This period, despite its short duration, was distinguished as a separate zone (VII), and it is also reflected in other lakes of the Polish Lowlands (Szeroczyńska, 1998a, b). The characteristics of Cladocera development in the Biskupin Lake indicate that the development of the lake was directly influenced by the climate and economic activity of man. The zones of Cladocera development found in sediments of cores 4 and 5, correspond in part with the climatic periods, as well as local pollen phases (Noryśkiewicz, 1995). The CONSLIK diagrams (Fig. 7) confirm this assignment. On the basis of the frequency of species preferring more fertile waters, 5 phases of increased trophy in the lake (two in the Subboreal and three in the Subatlantic period) were identified. These phases correspond in part with the periods of increased trophy, distinguished on the basis of diatom analyses (Bogaczewicz-Adamczak, 1995), and the phases of human influence, distinguished on the basis of palynological studies (Noryśkiewicz, 1995). It can be supposed, therefore, that the phases of increased trophy in the lake were, to a certain degree, a result of the activity of the settlers. This is confirmed by the fact that the periods of decreasing trophy correlate with phases without appreciable influence of human activity. A large frequency of planktonic remains in the sediments studied allowed for a thorough analysis of water levels in the lake, adding to the conclusions drawn from analyses of the sediments of core 4. A somewhat higher water level can be deduced from the sediments occurring at depths of 760-660 cm, 630-600 cm, 400-370 cm, as well as at the surface. A lower water level in Lake Biskupin occurred at the time of sedimentation at depths of 860-850 cm, 660-630 cm, 600-580 cm, and 380-350 cm. The above-mentioned periods of lower and higher water levels are conformable to the palaeohydrological interpretations by Niewiarowski (1995a, b) and Noryśkiewicz (1995) and, partially, to those based on the dominant planktonic or littoral diatom species (Bogaczewicz-Adamczak, 1995). As shown by analyses of subfossil Cladocera, a somewhat lower water level during the second half of the Subboreal period, as well as during the Subatlantic period, at the time of the Migration of the Peoples, is supported by palaeohydrological interpretations of other lakes (Gaillard, 1985; Niewiarowski, 1978; Ralska-Jasiewiczowa and Starkel, 1988; Szeroczyńska, 1991, 1998a).

Słowa kluczowe

PL

paleolimnologia; neoholocen; wioślarki

• Czasopismo: Studia Geologica Polonica
• Rocznik: 1998
• Tom: Vol. 112
• Strony: 105--122
• Opis fizyczny: Bibliogr. 24 poz., rys., wykr.

Twórcy

autor

Szeroczyńska, Krystyna

• Institute of Geological Sciences, Polish Academy of Sciences, ul. Twarda 51/55, 00-818 Warszawa, Poland,

autor

Polcyn, Ilona

• Institute of Geological Sciences, Polish Academy of Sciences, ul. Twarda 51/55, 00-818 Warszawa, Poland

Bibliografia

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