Badania diatomologiczne i geochemiczne późno glacjalnych i holoceńskich osadów z Przedniego Stawu w Dolinie Pięciu Stawów Polskich (Tatry)

Abstract

W osadach późnoglacjalnych (diatomofazy PS1-PS5) zanotowano dużą zmienność okrzemek w obrębie rodzajów: Fragilaria, Navicula, Nitzschia, Diploneis, Pinnularia i Amphora oraz maksimum występowania Cyclotella sp. w diatomofazie PS2. W holocenie (diatomofazy PS6-PS10) obserwuje się wzrost udziału okrzemek planktonicznych, początkowo Cyclotella quadriiuncta?, następnie Asterionella formosa, a dalej Melosira distans. Z badań geochemicznych wynika, że w osadach póżnoglacjalnych w zonach 2 i 3 zaznacza się wysoka koncentracja B, Ti, Mo i V, a w zonie 5 maksymalny udział Pb, B i V. W holocenie w zonach 6, 8 i 10 notuje się wysoką zawartość Cu i V, a w zonach 8 i 10 B i Mn. Wymienione diatomofazy i zony geochemiczne przedstawiono na tle fitofaz określonych metodą palinologiczną (K. Krupiński, praca w druku).

DIATOMOLOGICAL AND GEOCHEMICAL STUDIES ON LATE GLACIAL AND HOLOCENE SEDIMENTS FROM THE PRZEDNI STAW LAKE IN THE DOLINA PIĘCIU STAWÓW POLSKICH VALLEY (TATRA Mts)

Diatomological and geochemical studies of about 3·meter sequence of sediments from the Przedni Staw Lake (Figs 1-5) showed that they are highly varying in composition and frequency of diatoms (Fig. 6), content of organic matter (Fig. 7) and trace elements (Figs 8-10) as well as in mineral composition (Figs 11-12).

The recorded changes in composition and frequency of diatoms characteristic for Late Glacial sediments (diatom phases PS1-PS5) evidence highly differentiated physico-chemical and biological conditions which were presumably related to marked climatic changes in the Tatra Mts. The changes at first resulted in retreat of glaciers from area of the Przedni Staw Lake as first innumerous diatoms adopted to life under extremely disadvantageous conditions (Fragilaria, Navicula, Denticula and others) here appeared already in the oldest phase of the Late Glacial (PS1). Planktonic diatoms of the genus Cyclolella (PI. I. Fig; 1-14) appeared along with amelioration d the conditions which suggests some what longer vegetation time and amelioration of light and thermic conditions in the diatom phase PS2 (BÝlling?). The next diatom phases (PS3-PS5) display changes leading alternatively to deterioration and amelioration (in diatom phase PS4 - AllerÝd) of ecological conditions, presumably connected with only partial thawing of the lake ice in summer time. This could explain the lack of phytoplankton in this part of Late Glacial sequence. The genera Fragilaria, Navicula, Nitzschia, Diploneis, Pinnularia and Amphora predominate here (PI. III - V).

Late Glacial sediments display two geochemical zones (zones 2, 3) with high content of trace elements B, Ti, Mn and V, and zone 5 characterized by the maximum increase in concentration of Pb, B and V, coinciding with the Younger Dryas.

A more radical amelioration of climate which has taken place at the beginning of the Holocene, is traceable in the diatom phase PS6. In that diatom phase a short-lasting bloom of Cyclotella quadriiuncta? (PI. II, Figs 1-14) may be noted. In turn, the diatom succession of the diatom phase PS7 appears markedly similar to the Late Glacial in presence of flora Fragilaria and Navicula. The phase optimal for development of diatoms is characterized by the bloom of Asterionella formosa (diatom phase PS8) at the turn of the Atlantic and Subboreal times. High share of Melosira distans in the latest Holocene diatom phases PS9 and PS10 evidences changes towards cooling and a slight increase in acidity of water in this lake.

Horizons with reduced concentration of trace elements (B, Pb, Cu, Ti, V, Cr and Mn), recorded in Holocene sediments, may be linked with similar climatic conditions lasting for some time in the zones 7 and 9. In turn, high concentration of Cu and V, displayed by sediments of the zones 6, 8 and 10, and B, Cr and MD in the zones 8 and 10 may be linked with increase in amount of organic matter in the studied sediments.