Artikkelit kirjoittajalta Jukka Häikiö

The effect of water content and degree of humification on dry density of peat has been shortly dealt with. Term dry density of peat is being used here to express the quantity of dry matter of peat held in a unit of volume of peat in situ. The material was collected from different parts of Finland both from virgin and drained mires (Fig. 1). Figures 3 and 7 are based on material collected from Eastern-Canadian raised bogs (Korpijaakko 1975). Sampling was conducted using a piston sampler designed for taking volumetric peat samples (Korpijaakko 1981). To determine water content and dry density peat samples were dried at 105 °C. Water content is given as per cent of fresh weight except for Canadian material as per cent of volume. Dry density is expressed as kg/m3 or g/cm3. Ash content of Sphagnum peat samples varies between 1 and 2 % and Carex peat between 3 and 4 %. It is not substracted from the weight. There is a clear positive correlation between the degree of humification and dry density of Sphagnum peat (comp. e.g. Päivänen 1969, Korpijaakko ja Radforth 1972, Tolonen ja Saarenmaa 1979, Mäkilä 1980). This is deliniated by a straight regression line for Finnish peats in Figure 2 and for Canadian peats in Figure 3. The slight difference on the course of the lines is due to the fact that Finnish samples come from the conditions that regularly prevail in Finnish mires where as part of Canadian samples are obtained from a exceptionally dry and consolidated deposite near a five meters high peat cliff in Point Escuminac, New Brunswick. For sedge peat there is no significant correlation between degree of humification and dry density (Fig. 4). This comes from the fact that sedge peat differently from Sphagnum peat is rather dence in its structure already in low degree of humification. Thus only minor changes of weight per volume takes place when humification advances. There is a strong negative correlation between water content and dry density of both Sphagnum and Carex peat. Within the limits of water content met in Finnish peatlands (80—95 %) the correlations can be depicted with straight regression lines (Figs. 5 and 6). When the water content of peat in situ gets still much lower than this, the regression lines will curve to the left closing to certain maximum values of dry density. As to Sphagnum peat there would be several curves representing different degrees of humification as is shown in Fig. 7. For Carex peat, because of the lack of correlation between the degree of humification and dry density, there will still be only one curve, that would follow at its wet end the data points shown in Fig. 6. The evaluation of the content of dry matter and further the energy content of a peat deposit can not be based on the knowing of peat types and degrees of humification alone. Dry density values of different kinds of peat in the deposit have to be determined. The most reliable results are obtained if the calculations are based on a sufficient quantity of volumetric samples. If they are not available the diagrams such as in Figures 5 and 6 could be utilized. The preassumption is that good enough peat samples are available for correct determination of water content on weight bases.

• Korpijaakko, Sähköposti: ei.tietoa@nn.oo
• Häikiö, Sähköposti: ei.tietoa@nn.oo
• Leino, Sähköposti: ei.tietoa@nn.oo