Hannu Pajunen

Turvekerrostuman paksuuskasvu eräällä trooppisella suolla Burundissa

Pajunen H. Turvekerrostuman paksuuskasvu eräällä trooppisella suolla Burundissa.

Tiivistelmä

In the highlands of Burundi are mires more than 20 m deep. The great depth results either from high growth rate of deposits or from long accumulation time. Samples for radiocarbon datings have been taken from the depths of 5, 10, 15 and 20 meters (Table 1). The investigated mire is in the valley of the Buyongwe river, at an altitude of 1 400 m, where the mean annual temperature is about 18°C and precipitation about 1 150 mm (Lebedev 1970). The lower part of the peat deposit (10— 20 m) consists of well-humified (H 7—8) woody peat. The upper part (0—10 m) is formed of less humified (H 5—6) papyrus peat. Many undecomposed logs are at a depth of 5 to 10 m. 14C-age of the deepest sample is 8 650±120 years. Average long-term growth rate is 2.31 mm per year. The increase in growth rate from bottom to surface is partly apparent, partly real. The apparent increase comes from the fact that the lower part has been compressed. The real increase results from changes in the peat-forming vegetation. In its earlier phase the mire had tree cover. Later the vegetation changed to papyrus with a richer yield. The long-term growth rate in this mire has been about five times higher than in Eurasian mires (Zurek 1976). The 20 m thick peat deposit has accumulated during the last 8 700 years. The climate has been rather constant all the time. The absence of logs in the top meters is the result of human acitivity. Altitude effects peat formation. In low lying areas the decomposition of plant matter is faster than its production. There-fore peat cannot form. Plants with the richest yield cannot grow on mires at high altitude. The most favorable altitude for high growth rate seems to be from 1 300 to 2 300 m. The depth of this mire results from high growth rate rather than from long accumulation time.

Vastaanotettu 31.10.2017 Julkaistu 1.1.1981

Katselukerrat 2479

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