Brief hydrographic description of Lammin-Suo peatland

The Lammin-Suo peatland (lake Ozernoye) is located on the watershed between the basins of the rivers Chornaya and Sestra (the Gulf of Finland basin, Fig. 10). Major portion of the surface runoff from the peatland drains into the river Sister. Hydrographic net of the Lammin-Suo peatland consists of five brooks and one temporary stream. They all are draining the massif and are the elements of the primary hydrographic net of this watershed territory. As for the hydrography of the territory in question, there are three bog lakes and four overgrown (buried) lakes with residual water lenses (Fig. 11).

Fig..10 Location of the peatland station

Fig. 11. Hydrographic setting of Lammin-Suo

Presented in Table 1 are the hydrographic specifications of the brooks which drain the Lammin-Suo peat massif. Table 2 contains a typology of bog landscapes in the catchment areas of the brooks.

The heads of all the brooks that flow out of the peat massif originate at the edge of its periphery, in a strip 10 to 30 meters wide, where there is a depression which concentrates a bog water runoff (Fig. 11). Open channels of the streams appear only at the boundary of the bog.

 

Table 1. Hydrographic specifications of the brooks

Brook

Catchment area, sq.km

Forest percentage (dry land + bog)

Bogginess, percentage

Lake percentage

Yuzhny

1.18

31.4 (8.5+22.9)

91.5

0.0

Zapadny-1,2

0.32

78.4 (28.1+50.3)

66.3

5.6

Severny

0.37

93.5 (17.3+76.2)

78.6

4.1

Vostochny

0.10

36.0 (18.0+18.0)

82.0

0.0

Table 2. Bog landscapes: composition and area inside the brook’s reception basin

Brook

Groups of bog microlandscapes, percentage

Forest

Moss-forest

Moss

Moss-grass

Mixed

Yuzhny

17

9

>1

52

12

Zapadny-1,2

19

16

15

16

<1

Severny

11

24

22

8

14

Vostochny

9

45

-

16

12

The head of the brook Yuzhny originates at the south-eastern margin of the peatland. The surface runoff from the southern part of the bog accumulates in a flat depression which passes into a channel-forming stage, in fact – into the brook Yuzhny. Running then through an influent channel of a forebay in a hydrographic structure the stream crosses an earth-filled dam. A runoff gauge post is equipped with a hydrometric flume with a discharge capacity of 1 cubic m per 1 second. During a low stream flow period the runoff measurements are effected through the use of a V-notch weir with a cut-out angle of 90°.

The brook Severny flows out of the north-eastern part of the bog massif, then cuts a low esker across and flows into a small interesker low bog, wherein a furrow of the channel is practically unseen. A sheet piling is constructed right at the edge of this bog where it shuts off a narrow channel-like furrow of the brook (presumably of anthropogenic origin), crossing a relatively deep saddle of a high esker. A thin-walled weir with a cut-out angle of 90° is installed at the end of the influent channel with a stilling reservoir. Then the brook Severny emerges out and into a relatively wide water-logged valley of the brook Bolotny and flows into the latter. In a low stream flow period, as soon as a confluence of the brooks takes place, a discharge of the brook Severny into the estuary is over 70 per cent of a total runoff. The brook Severny is about 300 meters long.

As for the brook Bolotny, which starts on a kame terrace, some 150 meters up from the place where the brook Severny joins it, the brook has been once rigged with a hydrometric gauge section which is similar to the one described above. Hydrological observations were performed on this hydrometric section in the eighties of the last century. Moving currentwise, the brook Bolotny runs along the north-eastern periphery of the massif in question in a deep interesker depression, taking water from numerous springs of the right-bank high esker named Leninskie Gory ridge (some 1700 meters long, 20-25 meters high), which separates the brook from the Lammin-Suo peatland. As it leaves the kame-esker upland with a rather flashy flow the brook Bolotny joins the brook Sorochi which, being a right-bank tributary of the Sister river, flows out of the lake Simaginskoye. 

Two brooks named Zapadny-1 and Zapadny-2 drain the western part of the Lammin-Suo peatland massif. The waters that flow down to the bog’s margin find their way to the neighboring paludal forest wherein drainage ditches once had been digged. It is a couple of such drainage ditches that intercepts the bog’s runoff. Then moving upwards on a higher level, the said runoff passes into the influent channels of the hydrometric structures (Zapadny-1 and Zapadny-2 respectively) rigged with thin-walled V-notch weirs with the same cut-out angle of 90°.

Then the streams run on a lower fenny land where the drainage ditches are often cut off by paludal formations. Below, the streams are taken into a net of old and neglected main drains: these give rise to the brook Smolyanets which flows into the lake Grand Simaginskoye attributed to the basin of the Chornaya river and this, in turn, empties into the Gul of Finland. The total length of the brooks up to the place of confluence with the lake is 2.7 kilometers.

The brook Vostochny flows out of the north-eastern edge of the bog and enters the Kopeyechka paludal tract which includes an overgrown paludal-lacustrine lake Kopeyechka and lake No. 3. In fact, this is not a brook but rather a creek, less than 50 meters long, which crosses an isthmus of inorganic soil and through which the peat waters of the Lammi-Suo massif drain into the Kopeyechka paludal tract. The latter is drained by infiltration through a high esker right into the brook Bolotny of the river Sister’s basin.

The brook Vostochny has not formed any hollow under the action of concentrated runoff in the bog massif, it just flows directly out of the bog. At the head of the brook, where its bed has been cleared out at the beginning of the seventies of the last century with a view to construct there a runoff gauge plot, some 50-60 cm above the bed there is an ever-growing layer of sphagnum peat, wherefrom a drainage takes place. 

Fig. 12.  A weir

A temporary stream that manifests itself most clearly on a terrain drains a fenny area on the south-western edge of the peatland which belongs to the brook Yuzhny’s catchment area. A surface runoff there is observed during the spring floods only, when thawing waters accumulate in the waterlogged edge of the bog massif and flow down along its lower (fenny) portion.

In the recent years, as a result of laying a temporary timber transport road, there have been noticeable changes in a flow régime of this stream. In springtime the bog waters are blocked by the road and a zone of waterlogging becomes larger. It is only if an overflow level is reached that the thawing waters are partially discharged into a drainage network located behind the road. This is the reason why the composition of bog vegetation shifts towards hydrophilic species, both on the side of the bog and downwards the road.

Fig. 13. Gauging station

In the recent years, due to the increasing watering of the southern part of the peatland, two more minor temporary watercourses from the bog appear in the spring period. They are plotted at a distance of 180 meters and 300 meters respectively along the range of an electric power transmission line on the right bank of the brook Yuzhny. These are the areas where the hydro-amelioration ditches are in the most close proximity to the peatland, which facilitates the flowing of water into the drainage network.

At a distance of 460 meters along the passage of the power line on the side of the left bank of the brook Yuzhny there is the first unnamed tributary that runs into the brook down and below the gauging section. Should one rely only on the results of interpreting the plan views of terrain, without a ground survey, then the upper reaches of this unnamed brook could be mistakenly attributed to the catchment area of the brook Yuzhny. Presently the catchment area of this unnamed brook is about 10 hectares. The rate of peat accumulation in the southern periphery of the peatland is higher than in its south-eastern part, for it becomes more waterlogged in low-water seasons. This is partly because of those earth-dam filling works when construction of a gauging station on the brook Yuzhny was done at the end of the forties of the last century.

Further accretion of the peat deposit in the bog massif is likely to cause an increase in the catchment area of the left unnamed tributary. It will include a part of the left-bank of the brook Yuzhny’s springhead, a part of the brook Vostochny catchment area and also one part of the bog with a tributary that has formed an extensive dry-valley basin, wherefrom a runoff is currently infiltrating (like the drain from the Kopeyechka tract) into the brook Bolotny. Figure 11 shows this part of the bog massif as unshaded because it has not been attributed to any of investigated bog reception basins so far.

Lakes

There are two paludal-lacustrine basins in the bog massif: a group of the lakes Two Sisters (Fig. 14), including the lakes Pitievoye and Kupalnoye (formerly known as Muna-Lammin) separated by a narrow uplift of a mineral outcrop of a bed with a peat cofferdam on the surface, and distal lake No. 3 (Fig. 15) near the eastern edge of the bog. Also found within the confines of the bog massif are four hidden basins covered with a quaking mat (Fig. 11). They differ in a stage of weediness of waters and a state of paludification.

Fig. 14. Lakes 2 Sisters

Genetically all these seven reservoirs are well-preserved remains of the Early Holocene lake which was located in the postglacial depression and its shallow-water fragments later turned out to be the focuses of primary paludification. Long-term mean water stage of the palaeolake was some 2 meters below a current water level of the lakes Two Sisters. These reservoirs are located in the deepest portions of the palaeolake basin (at the kame-esker contact) and are considered to be parental. 

Fig. 15. Lake №3

The lakes which are covered by quaking mat are residual water lenses with a high content of suspended organic matter and occasionally separated by a horizontal layer of peat. The lakes are products of overgrowing and subsequent paludification from above, and their location, therefore, can be pinpointed from the satellite images. If compared to other lakes, the overgrown lakes Sukhoye and Torfyanoye were subject to paludification to the utmost degree. However, estimation of a relative content of organic matter was done rather approximately by using a probe and it is clear that to make an unbiased definition of this parameter peat samplers are needed in future. Nearly all the surface of both lakes is covered by a moss-forest microlandscape. Recorded on the surfaces of overgrown lakes Kopeyechka and Besdonnoye are the open moss-grass microlandscapes with early indications of ridge-and-islet forming processes. Also gaping water holes still remain on the overgrown surfaces of the said lakes. The holes have a remarkably ideal ‘coin’ configuration. Again, the overgrown lake Kopeyechka is to be considered the youngest one regarding the time when its swamping waters have closed its surface in.

 

Table 3. Hydrographic specifications of lakes

Lake

Water table area, sq.m

Volume of lake, cub.m

Depth, average/maximum, m

Kupalnoye

17900

66900

3.7/10.1

Pityevoye

15300

65750

4.3/12.2

No. 3

5600

13200

2.35/5.7

How quickly the lake basins overgrow depends upon their position in terms of geomorphology. Thus the lake Kupalnoye’s basin has undergone the most intense paludification, whereas thickness of bottom sediments in the relatively deepest lake Pityevoye is by far less. These two lakes have become boggy mainly from the peatland side. Observed on the surface of the lakes are numerous fragments of quaking mat in the form of floating peat islets, which definitely means a downwards paludification. Lake No. 3 has become paludal least of all, since practically all its bank line borders on the dry land of esker. A bog invades only at a narrow contact with the now buried bog lake Kopeyechka.

All reservoirs are localized in the north-western and north-eastern peripheries that separate the peatland from the kame-esker uplift. The most water-logged horizons of the overgrown lakes Kopyechka and Besdonnoye are an aqueous medium with suspended organic matter, while those of the overgrown lakes Sukhoye and Torfyanoye contain highly liquefied peat.

Fig.16. Bathymetric chart of lake Pityevoye

Fig. 17. Bathymetric chart of lake Kupalnoye

Fig. 18. Bathymetric chart of lake No. 3