Pekka Pakarinen

Ravinteiden pidättyminen kohosoiden hapettomiin turvekerroksiin

Pakarinen P. Ravinteiden pidättyminen kohosoiden hapettomiin turvekerroksiin.

Tiivistelmä

Chemical analyses of anaerobic ombrotrophic Sphagnum peats are presented from four southern Finnish raised bogs. Some characteristics of the study sites and samples are outlined in Table 1. Ranking of the elemental concentrations in Table 2 indicates that among the "trace metals", iron (380 ppm = 0.38 mg/g of dry peat) shows a greater mean concentration in deep ombrotrophic peat layers than the "macronutrients"" phosphorus (160 ppm) and potassium (100 ppm). The lowest averages were found for zinc (8.5 ppm), lead (6.0 ppm), manganese (5.7 ppm) and copper (1.3 ppm). Estimates of long-term accumulation rates of elements in peat (Table 2) are based on volume samples from radiocarbon or pollen-dated profiles (cf. Tolonen 1971, 1977). The average rate of nitrogen accumulation (3.6 kg ha-1 yr-1) appears to be somewhat lower than the corresponding values from Denmark (Jörgensen 1927), Sweden (Mattson & Koutler-Andersson 1955) and Germany (Aletsee 1967). A tentative comparison to watershed studies (Verry 1975, Kauppi 1979) suggests that roughly equal amounts of phosphorus are accumulated by ombrotrophic peat and lost by runoff waters, while in the case of nitrogen the retention by peat is relatively greater. The mean rate of past peat accumulation in the study material (50 g m-2 yr-1, cf. Table 1) is approximately 1/4 of the current mean annual production of Sphagnum fuscum (195 g m-2 yr-1, cf. Pakarinen 1978a) in the same area. A similar comparison of the past accumulation rates of chemical elements (Table 2) with the current retention (consumption) rates by the living moss layer (Pakarinen 1978a,b) gives the following order of elements (peat/moss % ratio in parentheses): N(26.4) > Mg(16.7) > Fe(14.5) > Ca(14.4) > P(11.9) > Zn(8.1) > Pb(7.2) > Cu(5.0) > Mn(0.8) > K(0.6). This comparison suggests that manganese and potassium are to a great extent depleted from peat (by recycling or leaching), while nitrogen is accumulated at about the same relative rate as organic matter. The relatively low percentage values of some elements (Zn, Pb, Cu) probably indicate an increase in atmospheric metal deposition in this century (cf. Aaby & Jacobsen 1979). Detailed budget calculations may not be possible, because no direct information is available on the atmospheric fallout or on the leaching rates 1000 or 2000 years ago. In any case it appears that on annual basis the past accumulation rates of chemical elements (exc. N) in ombrotrophic bogs are quite small. This study has been supported by the Natural Science Research Council, Academy of Finland (macronutrients) and by the Nessling Foundation (trace elements). "

Vastaanotettu 31.10.2017 Julkaistu 1.1.1981

Katselukerrat 2655

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