Artikkelit kirjoittajalta Martti Korpijaakko

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

Dry density of peat — the quantity of dry matter of peat held in unit of volume of peat in situ — depends on several factors, the most important of which are peat type, degree of humification (comp. e.g. Päivänen 1969, Korpijaakko and Rad-forth 1972) and water content (Korpijaakko 1975). Thus knowing of peat types and their degree of humification is not enough for accurate evaluation of the amount of dry matter contained in a peat deposit. Undisturbed samples of known volume from different depths and sites are needed. A piston sampler for this purpose has been developped and applied in the Geological Survey of Finland. The sampler is a modified version of the stationary piston sampler used mainly for palynologieal studies in the Geological Survey. When the coring is performed the piston-cone component of the sampler is kept stationary while the sharpened cylinder is pushed down. Thus the vacume caused by the piston helds peat core on its place while the cylinder cuts it off from the surrounding matter. Because of the strong vacuum effect good samples are obtained also from wett deposit. The diameter of the new sampler is 10 cm (Fig. 1). The cylinder component is devided into three parts. The one in the center is the sample cylinder proper. Its length is 20 cm. The lowest part is 10 cm long. The peat held in this part prevents water from running out from the sample cylinder while the sampler is hoistened. The length of the topmost part of the cylinder is 20 cm. Its function is to hold at the end of the sampling procedure the piston- cone component plus the peat which was disturped while the sampler was pushed down. The cylinder parts are jointed with nuts, which are rotated on to the upper part when the sample is removed. Cylinders are made off stainless steel. Transparent plastic cylinders have been used, too. They are good only in the peat deposits with no sunken logs. The sample cylinder is driven into peat with a rammer. The sampler is hoisted with tongs, which are also used to keep piston-cone component stationary while taking a sample. The equipment is portable. 3—4 men are needed in sampling.

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