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The mire is in a completely natural state hydrologically. In the larger mineral soil islands and around the mire there have been forest loggings in the 1970s, but the timber was transported along winter roads to be floated along the river Kepa and further along the river Kem, without causing significant W h i t e s e a d n a l n i F L a k e O n e g o L a k e L a d o g a ecological changes in the mire. In general, there is very little human impact in the area due to its extremely difficult accessibility. Only along the rivers the inhabitants of the nearby Jyskyjrvi village have been hunting and collecting berries. Tourists have visited the area also only in the vicinity of the rivers in connection with boat and canoe tours.

Ypyssuo mire has been included in a proposal for new Ramsar areas in Russia (Botch & Kuznetsov 1999). In this connection it became evident that further knowledge of this huge mire system is needed to promote the decision about including Ypyssuo mire in the Ramsar list of internationally valuable wetlands. On the basis of the large pristine mire area, Ypyssuo mire has also been included in the nature reserve plans of Karelian Republic, despite lacking concrete knowledge about the biodiversity of the area.

Since the last glacial period, 455 Pg of organic carbon have accumulated in northern peatlands (Gorham 1991). Peatlands constitute more than 30% of the global store of soil carbon and their sheer bulk makes them important environmental buffers. Peatlands both consume and produce greenhouse gases, and they are a major sink for carbon dioxide (CO2) and a net source of methane (CH4) (Martikainen 1996). However, little is known about the variability of carbon sequestration in peat through time and in response to climate change (Moore et al. 1998). Understanding the rate of carbon accumulation is necessary both in estimating the size of carbon reserves and in terms of their relevance to climate change, CO2 sequestration and global warming..

Material and methods Mapping of complexes, vegetation and flora. Mire complexes of Ypyssuo mire have been mapped using black and white aerial photos from the year 1978 in the scale 1:17 000. The photos are uncorrected, but it was possible to place the structures in a map base in the scale 1:25 000 in the mire ecosystems laboratory of the Karelian Research Centre. Altogether 9 different vegetation units were distinguished, as well as the string-flark patterns of aapamires and hummock-hollow patterns of bogs. On the basis of this aerial photo interpretation, added with a Landsat TM7 satellite image interpretation, a general mire complex map of Ypyssuo mire system was compiled.

In the western part of the mire, the vegetation was mapped in the field in August 2003 in an area of about 1400 hectares, using the Finnish mire site classification. The accuracy of the mapping was on the level of mire type system normally used for practical forestry planning, containing 35 site types (Laine & Vasander 2005) instead of the more accurate botanical site type system, containing almost 100 mire site types (e.g. Ruuhijrvi 1983; Eurola et al. 1984, 1994). The site types were named in the field on the basis of microreliefs and plant composition, but according to the Finnish mapping tradition used for practical purposes, they were not documented by making relevs. In this study species composition of each pattern was recorded as a part of floristic study. In addition to field observations, black and white aerial photo interpretation was used to define the boundaries of vegetation patterns.

Vascular plant and bryophyte flora inventory was made in the mapped area and in the southern part of the mire system near the river Kem. In the inventory, all different sites, which could be identified in aerial photos and in the field, were checked. The nomenclature follows Hmet-Ahti et al. (1998) for vascular plants, Ulvinen et al. (2002) for bryophytes.

Peat sampling and field analyses. Mire stratigraphy was studied along one transect in the southern part of the mire system in 1954 by Nadezhda Lebedeva, Karelian Research Centre (Fig. 2).

Fig. 2. Mire massifs in the Ypyssuo mire system.

In August 2003, mire stratigraphy was studied at 10 study sites in the western and southern margins of the mire. In April 2004 additional peat sampling was made at five more study sites, covering the whole mire system. Samples were taken for five macrofossil profiles (Fig. 3). The peat samples were taken with a Russian peat corer (Tolonen 1967).

Fig. 3. Coring points in Ypyssuo mire system. The bar shows the location of the mire profile cored by Nadezhda Lebedeva in 1954.

The vertical peat carbon accumulation of Ypyssuo mire was examined by using geophysical methods: ground penetrating radar, conductivity and temperature probing, and peat columns of known age, mass and carbon content. For methods used in this study see Hnninen (1992) and Puranen et al.

(1997 and 1999). Basal morphology was largely based on about 23 kilometres of ground penetrating radar profiling, in addition to conventional coring.

Twenty-eight samples for radiocarbon dating were taken from various parts of the mire system. The ages of basal peat were determined at 9 survey points just above the mineral soil or gyttja. The vertical dynamics of peat and carbon accumulation were studied by dating 6 peat profiles. The AMS radiocarbon determinations were made at the Poznan Radiocarbon Laboratory of Poland. The C ages were calibrated after Stuiver & Reimer (1993). In addition, the water content, dry bulk density, carbon content, ash content and pH value were determined from laboratory samples.

Ground penetrating radar is an electromagnetic measuring device used to examine media of low electrical conductivity. Remarkable attenuation takes place in electrically conductive media (conductivity 10 mS/m). The radar antenna transmits a short electromagnetic pulse of radio frequency (40-MHz) into the medium. When the pulse reaches an electric interface in the medium, some of the energy will be reflected back while the rest will proceed forwards. The radar system will then measure the time elapsed between wave transmission and reflection. This is repeated at short intervals while the antenna is in motion, and the output signals are drawn consecutively by means of an intensity recorder, which thus produces a continuous profile of the electric interfaces in the medium.

High-frequency antennae (>500 MHz) allow a better resolution of thin layers, but shallow penetration depth, while low-frequency antennae have a coarser resolution, but their penetration depth is markedly better.

The first ground penetrating radar was acquired in Finland in 1981 and was initially used mainly for peatland investigations. Ground penetrating radar is mainly used for measuring the thickness of peat deposits. The stratigraphy of aapamires has been studied by ground penetrating radar among others by Hnninen (1992) and of raised bogs by Suomi & Mkil (2000).

Results 1. Biodiversity of Ypyssuo mire at different levels Mire system and mire massifs. Ypyssuo mire system consists of numerous mire massifs, concerning to two main mire types: aapamires and bogs (Fig. 4). There are two enormous aapamires, one covering about hectares in the southern part of the mire, and another approximately equally large in the north-eastern part of the mire. The aapamires of Ypyssuo mire have a clear string-flark pattern. In the north-eastern aapamire the slope is very gentle, and the flarks are very large covering about 80 % of the area of the mire massif. In the southern aapamire the flarks are narrow, taking less than % of the area. The central parts of of aapamires are partly meso-eutrophic flark fens, but mainly oligo-mesotrophic flark fens according to traditional Finnish mire site type classification. In the southern part of the mire system there is also an extensive rich flark fen with Sphagnum contortum, Scorpidium scorpioides and Pseudo-calliergon trifarium, covering about 1000 hectares. In the marginal parts of aapamires there are also pine bogs and spruce mires.

The bogs mainly do not have a well developed hummock-hollow pattern, but in the northern part of the mire inside a curve of the river Kepa there is a large bog which in the central part has developed as a concentric bog.

In addition to the three main massifs there are numerous separate small aapamires, eccentric bogs and Sphagnum fuscum bogs. The other bogs also have minerotrophic strips, and indicators of minerotrophy like Carex rostrata as relics of former more clearly minerotrophic conditions, and they can be considered as transition mires.

Vegetation. The plant cover of mire massifs and systems is normally studied on two levels those are community level and mire site level. The community diversity of Ypyssuo mire is quite high. 20 associations of described from Karelian mires with using topological and ecological method (Kuznetsov, 2003). The further investigation of this mire system are to increase the number of presented communities.

The structure of vegetation of Ypyssuo on mire sites level was mapped in the western central part of the mire system in an area covering some hectares (Fig.4). The main vegetation units were poor sedge fens in the marginal parts of aapamires, moderately rich flark fens in the centres of aapamires and Sphagnum fuscum Chamaedaphne calyculata bogs in the watersheds of the flow of mire water. In the southern part of the mapped area there was a large spruce mire, which was generally defined as Equisetum sylvaticum spruce mire. The pattern is large, and highly variable according to ecohydrological conditions. In areas with abundant water flow there was more luxurious vegetation and also some ground water influence. The tree layer was completely pristine with no signs of any human impact. Huge very old pines are characteristic.

Flora. The flora of Ypyssuo mire is relatively poor, despite the diversity of site types and abundance of moderately rich sites. Altogether 78 species of vascular plants were found in mire sites, and 55 species of bryophytes. In addition, in the marginal forests, and especially on the shores of the river Kepa there was a high number of species. There are only few northern species like Petasites frigidus and Ranunculus lapponicus, and no clearly southern species.

Species included in the Red Data Book of East Fennoscandia (Kotiranta et al.

1998) and Karelian Republic ( & 1995) are Carex laxa, C.

livida and Dactylorhiza traunsteineri.

Fig. 4. Vegetation map of a small area in the western part of Ypyssuo mire system. The abbreviations of mire site types are as follows:

KoLN Koivulettoneva Birch sedge intermediate fen ChKeR Vaiverokeidasrme Chamaedaphne hummock hollow bog RhRiN Ruohoinen rimpineva Herb flark fen SN Saraneva Sedge fen IR Isovarpurme Dwarf shrub pine bog (Ledum) RiSN Rimpinen saraneva Flark sedge fen RiN Rimpineva Flark Fen MkK Metskortekorpi Equisetum sylvaticum spruce mire RhSN Ruohoinen saraneva Herb sedge fen RhNR Ruohoinen nevarme Herb pine sedge fen RiLN Rimpinen lettoneva Flark sedge intermediate fen RaIR Rahkainen isovarpurme Sphagnum fuscum swarf shrub pine bog 2. Development history of the mire system Dynamics. The formation of mire system is started ca 10,000 years ago (age is calibrated) inside expanede and flat depressions with eutrophic and mesoeutrophic sedge-horsetail and sedge-Hypnum communities formed the corresponding layers of bottom peat layers. The lifetime of similar communities varies in diferet parts of mire system that is confirmed by peat stratighraphy and C14 datings of separate peate layers (Fig. 5, 6) The same time some other kind of mires started to develop in this region. Often they have lacustrine development stage ( ., 1979; , 1981).

During the following 4,000 years the mire system filled all the depressions. The composition gradually changes via Carex into CarexSphagnum dominated peat, with Scheuchzeria palustris and Menyanthes as additional constituents at the surface, indicating rather wet conditions. The influence of the bottom basin has decreased and the mire has developed in a more oligotrophic direction. Succesion rate and trends varies in different parts of system. See example from microfossil diagram from column 7 (Fig. 7) collected from a flark in southern part of the system (Fig. 3). Five stages (or palaeocommunities) can be seen from the plant remainings structure. This part of mire was strongly flooded and stagnated during the last 3,000 years. It is confirmed by the prevailing of Scheuchzeria palustris and Carex limosa in upper peat layers. The dominance of these species is also shows the decreasing Fig. 5. Stratigraphic profile along the transect studied in 1954.

Symbols: eutrophic peat types (1-7): 1- woody-Carex, 2- woody-Equisetum, 3- woody-Phragmites, 4- woody-Scheuchzeria, 5- Carex, 6- Carex- Equisetum, 7-Carex-Sphagnum; mesotrophic peat types (8-14): 8- woody-Carex, 9- Eriophorum, 10- Carex- Scheuchzeria, 11- Carex- Equisetum, 12- Carex-Herbs, 13- Carex, 14- Sphagnum; 15- water, 16- sand, 17- clay, 18- coring points, 19- degree of decomposition (%) Fig. 6. Stratigraphy of coring points in Ypyssuo Symbols: eutrophic peat types (1-12): 1- woody-Carex, 2- woody-Equisetum, 3- woodyMenyanthes, 4- woody- Menyanthes-Carex, 5- Carex, 6- Carex- Menyanthes, 7- Carex-Equisetum, 8- Carex-Scheuchzeria, 9- Carex-Sphagnum, 10- Scheuchzeria-Sphagnum, 11- Sphagnum, 12- Bryales; mesotrophic peat types (13-15): 13- Carex, 14- Sphagnum, 15- Eriophorum- Sphagnum;

ombrotrophic peat types (16-18): 16- Hollow Sphagnum, 17- complex Sphagnum, 18- Fuscum;

19- degree of decomposition (%), 20- age (cal. BP), 21- coring points.

of mineral nutrient level during this development stage. Some similar reconstructions are conducted from other peat columns and are to publish soon in a special paper.

The average depth of the peat layer is 2,4 metres, including the slightly humified surface layer (H1-H4), with 0,6 m average thickness. The greatest peat thickness is about 4,0 m. The average degree of humification (H) according to von Post's scale 1-10 is 4,7. Humification is moderate or high (H5-H9) in the layers underlying the surficial peat. Numerous charcoal layers were found in the bottom peat layers in the marginal parts of of Ypyssuo.

Fig. 7. Macrofossil diagram on coring point Stages (palaeocommunities): I eutrophic Carex lasiocarpa Equisetum fluviatile.- Warnstorfia sp.+Caliergon sp.+Scorpidium scorpioides, II mesotropic (M) Carex lasiocarpa Sphagnum sect. Subsecunda, III Carex lasiocarpa Equisetum fluviatile, IV M Carex limosa Scheuchzeria palustris, V Carex lasiocarpa M enyanthes 3. Carbon accumulation The average rate of peat growth in Ypyssuo has been 0,2 mm yr-1 and the net apparent carbon accumulation 11,4 g m-2 yr-1 (Figs 8 and 9). Frequent mire fires have slowed down vertical peat accumulation. It is typical of sedgedominated peat deposits that the dry matter content and carbon content are highest in the layer underlying the surficial peat (Mkil et al. 2001). The peat layer is also driest in Ypyssuo at the depth where the rate of peat growth was only 0,15 mm yr-1.

Samples for laboratory analyses have been taken at four points. The average ash content (% of dry mass) is 4,7% (2,2-12,9), the water content (% of wet mass) is 89,3% (78,4-98,4), and the dry bulk density 104,2 kg per mire m3.

The carbon and nitrogen content (% of dry mass) are 53,1% (46,1-60,7) and 2,29% (1,31-3,17), respectively.

The total area of Ypyssuo covers about 50 000 hectares, containing 1,x 109 m3 of peat in situ and 66 million tons of carbon. Thus the sheer bulk of virgin Ypyssuo makes it an important environmental buffer.

0,0,0,0,0,0,0,0,Peat increment 0 1000 2000 3000 4000 5000 6000 7000 8000 9000 Age (cal BP) Fig. 8. Average peat increment rate as a function of time at five dated profiles.

Carbon accumulation 0 1000 2000 3000 4000 5000 6000 7000 8000 9000 Age (cal BP) Fig.9. Carbon accumulation rate as a function of time at five dated profiles.

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