Pekka Pakarinen , Kimmo Tolonen

Pintaturpeen kasvunopeudesta ja ajoittamisesta

Pakarinen P., Tolonen K. Pintaturpeen kasvunopeudesta ja ajoittamisesta.

Tiivistelmä

Sphagnum f uscum hummocks have been studied in a southern Finnish ombrotrophic bog in Kuhmoinen (62°N). The annual increments of Sphagnum have been distinguished by means of cyclic pigmentation (cf. Bellamy & Rieley 1967), branching pattern (cf. Maimer 1962) and changes in growth-direction due to pressure of snow-cover. These «innate markers» (cf. Clymo 1970) can be found in scattered individuals of S. fuscum particularly in the less compact parts of hummocks. In addition, Polytrichum affine (= strictum) growing mixed with Sphagnum was utilised as a re-ference mark for the increments (cf. Long-ton 1972). With the combination of these methods it was possible to date a Sphagnum fuscum hummoc down to ca. 50 years old layers (Fig. 3). In the same site, volume samples were taken and analyzed in a vertical profile (Fig 4). It appears that the growth rate of surface peat decreases with depth (maximum gradient in the top 10 cm layer) indicating a progress of humification process and autocompaction (Aaby & Tauber 1975). It is concluded that the pine method used earlier (Borggreve 1889, Saarinen 1933) gives not comparable values of growth-rate of surface peat particularly if pines of different age are used. It is also suggested that the long-term growth curves of peat accumulation (cf. Tolonen 1973, Zurek 1976) should not be extended to the surface but instead to the level where compaction process has terminated, i.e. often at 30—50 cm below surface. The «moss dating method» was also applied to Sphagnum fuscum hummocks in several other bogs in southern Finland. The preliminary results indicate a considerable variability in the vertical distribution of growth rates, even within one hummock, but the overall picture is similar as in Fig. 4. From the profile dated with moss method the peat samples were also analysed for cesium-137 and potassium. As illustrated by Fig. 5, 137Cs has become enriched to the Sphagnum layer (as also potassium) supposedly by an active uptake mechanism. Thus the peak of 137Cs fallout in 1963 (see Fig. 5) cannot be used as a dating method in peat profiles in contrast to lake sediments (cf. Pennington et al. 1973).

Vastaanotettu 31.10.2017 Julkaistu 1.1.1977

Katselukerrat 570

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