History of hydrology alterations
Archaeological data suggest that people were already living in the area since VIII century BC. Discovered traces of 26 Stone Age settlements show that this area was densely populated. The water level of the lagoon was higher at that time, therefore people settled on the highest areas of dry land 160-170 m above sea level. Various discovered articles show that people were not only hunting and fishing, but were also familiar with agriculture. Livestock were also raised.
During the Atlantis period (VI-III century BC), there was an increase in pasture areas which were likely the result of human activities - forest burning. Areas of slash-and-burn agriculture were slowly expanding, however there were not many suitable areas as the territory was dominated by wetlands. When people started using iron, arable farming became popular, changing the original forested landscape in drier areas. More mosaic landscape developed with the rotation between field plots and birch or aspen stands which emerged in abandoned areas. Meadows and pastures were expanding in wetter areas.
Villages were forming with the increasing number of people and homesteads. Most of the settlements were established in higher surrounding areas. Household activities in the wetland area were mostly limited to the use of pastures, hunting and fishing. Biržulis and Stervas wetlands also provided an important protective function. It is believed that, in 1389, knights of the order were lured into the surrounding marshes of Biržulis.
As Varniai was growing and becoming the centre of church administration and economic life in Samogitia, surrounding areas in the XVII century were increasingly deforested, some streams were straightened and others flooded when building mills and other local workshops. Varnelė Stream was straightened when building a cathedral in Varniai. The changing environment increased the amounts of silts carried through inflows into Biržulis Lake.
At the end of the XIX century (the first map is available from 1893), there were more villages in the area than there are today. Fishing was one of the main sources of livelihood for the local population. The old inhabitants of these places, fishermen tell almost unreal stories about the abundance of fish and birds in Biržulis Lake. According to them, once the lake was teeming with fish, and it was called Viržuvis (the name meens „boiling with fish“) instead of Biržulis.
In about 1898-1900, a ditch was dug from Stervas Lake towards the southern part of Biržulis Lake. This ditch was likely to have changed the water regime in Stervas Lake. Written sources mention the reason for digging this ditch – the inability of locals to share the resources of fish migrating through Govijaus Stream between Biržulis and Stervas lakes. The ditch can be clearly seen in a topographic map of 1949.
When performing the first lake researches in 1904, Biržulis was mentioned as a lake that was shallow, overgrowing with dense vegetation, with extensive swampy areas and particularly abundant with fish, otters and birds. Very "aggressive" fishing was also mentioned.
In 1930 the water mill on the outlet Virvytė River ~1,5 km from the lake was destroyed and river bed cleaned. This slightly (literature mentions ~ 25 cm) lowered the water level of Biržulis Lake. The average water level prior to lowering could be between 151,05 and 151,5 m above sea level. Second time the outlet was cleaned and widened to 6 m in 1934. This resulted in additional decrease of water level by ~ 60 cm and openning of wide mudflats with deep layer of silt. Varnelė River above Biržulis Lake was also straightened. There were plans to drain Debesnos mire, however, the owner of the mill of Varniai demanded a compenstion, therefore such plans were not realized. After performing lake depth measurements during the winter of 1934, the maximum depth of the lake was 4.5 m, and the average - 1.24 m, while the lake itself covered an area of 726 ha, altitude - 150,2 m above sea level.
In the history of Biržulis Lake, the fifth decade of the last century is called "The great mistake of Biržulis". Then, in order to adapt the area to agricultural needs, there were plans to drain the lake completely. In 1955 the land reclamation started by once again deepening the riverbed of Virvytė River. In the northern part, the area of the lake decreased to a few hectares, while the total area of Biržulis became less than 100 ha. The Science Academy and fishing businesses objected to such reorganization, however, only Stervas Lake was saved from being drained. By contraries, water level was fixed in this lake in 1986 by building a dike and a spillway. A lake area of 135 ha was sustained with an altitude of ~152.5 m. There is no data on how much the average water level has been changed, however it seems like it led to increase in the lowest water levels and decrease in fluctuations.
In 1960-68, when it became clear that it is too complicated to achieve the set goal to adapt the drained area of Biržulis Lake for agriculture, the project task of complete drainage was changed. A decision was made to drain only the northern part of the lake, while leaving the southern part to nature (ornithological reserve was established in 1970). It was decided to slightly raise the water level in the southern part of the lake with the help of a sluice-regulator. A water body of about 120 ha had formed, where water level was maintained for several decades without clear regulation procedures.
During a period of 1974-1978, several spring and autumn floods ruined most of the cultural meadows that were sown at the peripfery of the drained northern part. The reclaimed areas became less and less used. Later, sluice-regulator became dysfunctional and was transformed into a stationary spillway. The rules for maintenance of the dammed Biržulis Lake were prepared in 1998 setting the “normally dammed water level” at 150.35 m altitude and minimal altitude at 150,20 m (lake area - 106.8 ha, average depth - 0.9 m, maximum depth - 2.35 m). (Actual levels measured during the project (2014 Nov. – 2015 Feb.) exhibit higher values ranging from 150,45 to 150,95). A lakelet of less than 10 ha with a highly fluctuating water level remains in the northern part of Biržulis.
Another wetland area that was affected by hydrology alterations in the middle of XXth century was Degėsiai bog north from Stervas Lake (part of Sterwas wetland complex). 66 ha of the bog area were drained for peat excavation. Peat was cut manually by digging 10-13 m wide, 0,5-1 m deep strips along the bog and leaving 6-8 m untouched sections in between. The peat cutting activity was soon abandoned leaving degrading peatland behind. Hydrolological conditions in the southern part (further from the ditches) partly naturalized. Northern part is still affected by ditches and peat degradation takes place. Restoration of proper hydrological conditions is one of project concrete nature conservation actions.
Land use changed during the period of hydrological alterations and after it. Until the last quarter of the twentieth century, most of Biržulis and substantial part of Stervas lakeside wetlands were used for the production of forage and bedding, and this maintained large open grassland areas of varying humidity. Majority of them were drained in the middle of the century. Later, their use rapidly declined and now most of the lakeside fields and pastures are overgrown with forests and bushes. Bushes have also invaded the drained lake areas. Wetter areas became dominated by reed and to lesser extent – by sedges.
Land use changes have also affected Debesnos mire that was extensively used (mowed, grazed) for centuries. Significant reduction in use appeared only few decades ago leading to increased forest cover. Re-establishment of self-sustaining mire management is one of project concrete nature conservation actions.
2014-2016 m. the project "Biodiversity and ecosystem restoration Biržulis, Stervas Debesnai and wetlands restoration planning and practical measures are financed by the European Economic Area Financial Mechanism and the Lithuanian budget.
The Project Manager:
Varnių regioninio parko direkcija
Dumbrių str. 3, Ožtakių k., Varnių sen.
LT-88324 Telšių r.
Director Irena Zimblienė