Although Lake Vänern is the largest freshwater reservoir in Western Europe, it remains relatively unknown to the scientific community outside of Scandinavia. Therefore, we aim to give a brief outline of the lake and its geological history, in particular the landscape transformation, resource utilization, pollution history, and environmental development of the region. The landscape around Lake Vänern was shaped into its present form during the latest glaciations some 10,000 years ago. Large variation exists in its tributaries, with forest in the north and agricultural areas in the south. Human influence on the landscape was relatively small until the mid-18th century. Later, in the mid-19th century, the agriculture, forestry and shipping industries underwent large transformations as the towns around the lake grew and the economy changed. Development of fishing equipment, processes and changes in catching methods industrialized the fishing industry after mid-20th century. In the 1960s the lake was considered to be one of the most heavily mercury-polluted lakes in the world. After the passing of the first national environmental protection law in Sweden the lake turned into a success story: It has been declared to be healthy. However, old pollution still affects the fishing industry. With this new focus on the environment, the scientific community started to be interested in the lake. The lake has also played a very important role as the largest hydropower reservoir in Sweden. Here, too, the environmental question is in focus and the effects of the water regulation are still under debate. The result has been loss of biodiversity and an increased risk of an inflow of invasive species from international shipping. However, still many questions remain to be answered regarding the lake and effect of ongoing climate change on the sustainable development of the lake region.
Since the first settlements were established within the Lake Vänern region some 6,000 years ago, the lake has played an important role in the life of people in this region. The first description of the water system of Lake Vänern was published in 1555. Olaus Magnus wrote:
The streams and rivers fall out into the lake with a great thunder and swirl. Because its lengthy shores are surrounded by mountains, one cannot anywhere find an outflow more than in one place. In this place the current is so rapid and noisy that it can be heard from a distance of more than 20 Italian miles.(Magnus 1555, second book, Chapter 30, our translation)
Lake Vänern is Europe’s third-largest lake, after Lake Ladoga and Lake Onega in Russia. Few international scientists have paid it any significant interest. As a consequence, most research on Lake Vänern has been carried out by domestic natural scientists, regional authorities, museums, and various government departments (Drotz et al., 2012a). The collective scientific knowledge about Lake Vänern is therefore small. Here we aim to give a brief historical outline of the natural and cultural heritage of the Lake Vänern region.
Lake Vänern is the largest freshwater body in Sweden and the largest lake within the European Union; it has a water surface of 5,650 km2, a drainage basin covering a total of 46,800 km2, a coastline of 4,800 km, and a freshwater archipelago made up of over 22,000 islands, islets, and boulders. The lake contains one third of Sweden’s freshwater reserves (Figure 1). Lake Vänern is situated in the southwest part of Sweden and is connected to the North Sea along the Kattegat coast. The only outlet from the lake to Skagerrak is via the Göta River. The lake itself lies in the middle of a water system that is 720 km long and has its sources in the watershed of northern Sweden and neighboring districts in Norway which collects in Lake Rogen (Jakobsson and Berg, 2006). From there the water flows via the Klarälv River into Lake Vänern.
Värmlandssjön is the larger of the two basins in Lake Vänern. As the smaller basin, the Dalbosjön, it is also large enough for counterclockwise geostrophic currents to occur throughout the summer (Kvarnäs, 1975). Vertical movements of water within the basins are assumed to be of little importance, except in spring and autumn, when lower and upper water masses are mixed with each other and also intermixed between the basins (Håkanson, 1977). During spring thermal bars develops around the coastlines and in summer a thermocline is established. This temporarily lowers the water exchange between the shore area and the pelagic zone, resulting in a difference in the water quality between these areas (Dahl and Wilson, 2004). Lake Vänern’s physical environment is therefore very likely to be affected by the expected climate change (Weyhenmeyer, 2004; Holgersson et al., 2007), which will in turn have a large ecological effect on Lake Vänern (Blenckner et al., 2010).
The bedrock in the landscape around and beneath Lake Vänern consists mostly of gneiss. Within Lake Vänern there is a sharp boundary between two different gneiss regions: in the West a younger layer of gray form rocks that originated relatively shallow in the Earth’s crust, and in the East an older reddish form of rock that originated much deeper. The Sveconorwegian orogeny gave rise to the mylonite zone which lies across the lake in a north to south direction along the east side of Värmlandsnäs and Kållandsö. The zone arose about 1,000 million years ago when several continents collided and the supercontinent Rodinia was created (Bingen et al., 2008). Over millions of years the mountain chain eroded to an almost flat surface, but the depression in the bedrock remained and can be seen at the bottom of Lake Vänern (Figure 2). Later, this landscape ended up in the northern hemisphere due to plate-tectonic movements and went through a series of ice ages. It was especially during the latest glaciation period that the landscape was shaped into what it is today (Dennegård et al., 1987). The ice sheet lay several kilometers thick over the region. About 8,000 to 10,000 years ago Lake Vänern was carved out due to the land uplift, and the present lake was created (Björck, 1995; Lambeck, 1999). However, the region is still changing. Because of bedrock depression the lake is still slowly tipping towards the southwest. The land uplift is about 3.5 meters per thousand years in the north and about 2.6 meters in the south (Lundqvist, 1998).
The different landscapes and the people living around the lake
The landscape round Lake Vänern’s tributaries differs. In the north, rivers run through forests, and in the south, streams flow through agricultural landscapes. The lake is situated within the boreo-nemoral zone which is limited to the north by the Limes norrlandicus, a biogeographical border between the south boreal zone and the nemoral zone (Fries, 1980). However, the northern part of the drainage basin lies in the boreal zone. The northernmost source of the water shed is in the alpine zone. The height difference within the total drainage basin is large and reaches its highest point in the Norwegian mountains at 1,700 meters above sea level and the lowest point in Lake Vänern at 45 meters above sea level. The Lake Vänern drainage basin thus has a great variation in local climate.
The landscape within the drainage basin has also been affected and changed by humans over the course of history, as can be seen in the current landscape (Heijkensköld, 1981; Gustavsson et al., 2007) along the tributaries and the development of the society (Råsled, 2007). Before modernization in the mid-19th century (Gadd, 2011) the local landscape was important for the daily production of food and fiber: it provided arable fields, meadows, forests, and water. Here we exemplify the land use from the map of Årås (Wallringh, 1968), which is situated at the outlet of the Gullspång River near the town of Mariestad (Figure 2). The map and in particular the cartographer’s notes give a good picture of how the landscape was utilized in late 17th century. Årås was a manor and therefore wealthier than the average farm. All the same, situated in a landscape dominated by forests, the small arable fields only produced crops enough to meet the household’s needs. The extensive meadow and grazing areas tell us that cattle farming was more important. The importance of fishing is shown by the presence of permanent fishing structures. A tavern also added to the income. Iron ore and iron played an important part in this district. Årås had a water-powered hammer mill with two furnaces. The woodland was an important source of charcoal for the hammer mill (Niklasson et al., 2011). The Årås forest consisted of spruce (Picea abies), pine (Pinus sylvestris), birch (Betula pendula), and alder (Alnus glutinosa), whereas some tree species are pointed out as missing – oak (Quercus robur), beech (Fagus sylvatica), hazel (Corylus avellana), and lime (Tilia cordata). Apart from charcoal and grazing space, we can expect that the forest provided timber, firewood, foliage (for fodder), and bark (for handicraft and roofing).
The landscape transformation
Driven by changes in technology and the land consolidation process, the landscape around Vänern underwent the same major changes as the rest of southern Sweden starting in the mid-19th century (Helmfrid, 1961; Gadd, 1983). These changes helped to feed a growing population. The cost was a considerable loss in biodiversity when meadows and wetlands in the south were transformed into enormous arable fields and old-growth forests in the north were progressively turned into spruce and pine plantations. Prior to the agricultural revolution the plains around Lake Vänern were varied and species-rich landscapes. The extensive wetlands in particular were a paradise for insects, frogs, and birds. For the farmers this was a challenging landscape, however. In good years it was a rich landscape that allowed for plenty of cattle to be bred and sold; but the clayey soils were easily flooded and famines struck the area when the crops failed. Heavy rains in the early 1830s and the famine that followed provided an impetus for modernizing the landscape (Håkansson, 1997). The resulting new landscape was primarily grain-producing and today is one of Sweden’s most important agricultural districts.
At the end of the 19th century most of the population of Sweden still lived in rural areas, but trade and shipping along the rivers and tributaries is already documented in the early Middle Ages, when marketplaces began to emerge along the shores of Lake Vänern (Råsled, 2007). The first town to receive town privileges and with it the legal right to conduct its business around Lake Vänern was the town of Lidköping in 1446 (Figure 2). Other towns around the lake received their privileges later: Mariestad in 1583, Karlstad in 1584, Brätte (predecessor to Vänersborg) around 1584, Kristinehamn in 1642, Åmål in 1643, Vänersborg in 1644, Trollhättan in 1916 and Säffle in 1951. It is estimated that at the beginning of the 20th century approximately 130,000 people lived in the municipalities around Lake Vänern. Today the numbers have grown and to around 300,000, and the lake supplies water to more than 800,000 people every day.
Floods and regulation
In the autumn of 2000, Arvika in western Värmland at Glafsfjorden suffered one of the most extensive floods that have hit Sweden in modern times. Because Lake Vänern has the world’s longest official data series on water levels, dating back to1807, we know that this flood was not historically unique. Earlier floods greatly affected the population: the submersion of water meadows and fields often resulted in severe famines. The attempts to understand Vänern’s fluctuating water levels were driven by the wish to control the water (Jakobsson, 2007, 2010). Later, at the beginning of the 20th century, flood protection was no longer the main driver for water regulation. Instead, it was the value of electricity production in the state-owned hydropower plant on Göta River. Finally, in 1937, the state hydropower company Vattenfall was authorized to regulate Lake Vänern (Jakobsson, 2010). The regulation amplitude is between 43.16 and 44.85 meters above sea level. Seventy-five years later the biological and ecological implications of this decision are not fully known. Reeds have spread and become denser in many bays and archipelagos. However, the coverage of bushes and trees on islands and shores has also greatly increased since the 1970s and is today a very serious concern (Finsberg and Paltto, 2004). The cause of this overgrowth is not clear and may depend on factors in addition to water regulation, such as climate change, excess nitrogen, and decreased grazing.
Shipping and the transport route
Shipping, like most aspects of society, maintained essentially the same traditional forms from the Middle Ages to the 18th century, and it played a central role in the village communities around Lake Vänern (Nilsson, 1996). Boats were the main method of transporting locally produced merchandise to different markets. Exchange between the northern and southern parts of the Vänern region included iron and wood in return for agricultural products or livestock (Holmström, 1996). The early existence of iron works in Värmland is one of the most important factors in the development of trade and shipping in the region. In 1800 the first channel bypassing the Trollhättan Falls was opened for navigation, and Lake Vänern came in direct contact with the North Sea for the first time. Thirty-two years later, a water connection to Lake Vättern and the Baltic Sea was opened, the Göta Canal (Hallberg, 1993). Thirty-six years later the Dalsland Canal opened a waterway into the Norwegian lake systems (Rollof, 1979).
During the 1850s, boats owned by the village communities disappear from the estate inventories and instead steamship companies become increasingly more common (Nilsson, 1996). In the 1950s there were still a large number of older vessels of between 80 and 200 tons navigating the lake (Hallberg, 1993). However, the competition from land transport—railway and trucks—was noticeable. Today the ships that enter the lake weigh up to 4,400 tons. Shipping goods are dominated by artificial fertilizer and forestry products; petroleum products, coal, and low-value commodities for the various industries are also common. In spite of the new ships it was not until 1974 that year-round navigation was introduced in Lake Vänern.
Today there is a growing discussion about increasing the international ship traffic to Lake Vänern (Hallman, 2011). At the same time, it has been documented that human-mediated transport contributes to the spread of alien invasive species (Herborg et al., 2003). This is a large problem for many countries since the Secretariat of the Pacific Regional Environment Program has estimated that more than 5,000 species of aquatic organisms may be transported around the world each day in ballast water. In spite of this, alien invasive species are not currently a major problem in Lake Vänern (Josefsson and Andersson, 2001). A contributing factor for this may be that the climate or water chemistry is not sufficiently favorable for many of the potential invasive species to gain a foothold in Lake Vänern. However, it does not mean that the Lake is free from invaders. A recent example is the Chinese Mitten Crab, Eriocheir sinensis (Drotz et al., 2010, 2012b; Czerniejewski et al., 2012).
Fishing in Lake Vänern
In the mid-19th century, fishing in Vänern moved away from the shore to more open water outside the islands. The nets in those days were made of homespun linen cord, and the fishing boats were rowed or sailed (Aarsrud, 1991; Degerman, 2004; Nilsson and Drotz, 2012). When transporting their catch during the summer, fishermen used ice, kept the fish in containers of water, or simply left them exposed to the air on the bottom of the boat. The distance between the fishing areas and trading places was a limiting factor for the amount of fish that was caught and sold. The development of stronger boats and new fishing equipment and techniques, together with increased processing and marketing of fish products, has led to specialization within the commercial fishing industry that started in the 1960s.
In the 1950’s the fishing community was struggling to survive. Catches were decreasing, presumably as a result of declining fish populations due to sulfite and mercury pollution from industrial wastewater that leaked into the lake. In addition, a lowered public demand for fish contributed to a drop in prices. However, the fish catches still had increased nearly six-fold during the period 1920 to 1960 (Degerman, 2004). The switch from cotton to nylon cord used in fishing gear was very successful and had created a strong belief in a prosperous future for the fishing industry at the end of the 1950s. In the 1960s the government and local fishermen started a project for finding new catch methods and sale possibilities. With the aim of expanding to the smoked fish market, some fishermen started to trawl for vendace (Coregonous albula). At this time Artur Johansson from the north of Sweden heard about the trawling project by chance; his involvement would affect the entire fishing industry (Nilsson and Drotz, 2012). The fishermen increased their income fourfold by selling the roe instead of the fish. As a result, the catch per year of vendace increased strongly up to 1980s. The vendace also had an advantage over bottom-feeding or carnivorous fishes since it was not affected by the mercury pollution. The provisional permission for testing trawling in the lake lasted for an amazing 42 years (Degerman, 2004). Today, the two most economically important fish species are pike-perch (Stizostedion lucioperca) and vendace. A total of 72 commercial fishermen are active in Lake Vänern, and of these, one-seventh are located in Spiken, Europe’s largest inland port for lake fishing. The total catch in Lake Vänern is on average approximately 550 tons in recent years.
Pollution history and a newborn environmental awareness
Because Lake Vänern is quite deep, it can, in terms of water presence etc. be equated to a sea. If polluted water causes damage, here and there, the damage is only caused by local conditions near the river outflow. By and large, Lake Vänern’s capacity to receive polluted water without any harm is unlimited …(Sondén, 1914, our translation)
The paper and pulp mill’s discharge of waste material and mercury into Lake Vänern was extensive during the first part of the 20th century (Lindeström, 2001; Wihlborg and Danielsson, 2006). Elevated levels of mercury were documented in fish as early as 1965 (Westöö, 1966). As a consequence, in 1967 Stig Tejning started to analyze mercury levels in the blood cells, plasma, hair, and nails from the local populations around the lake. All fishermen had elevated levels of mercury in their bodies (Tejning, 1967). The levels were not alarmingly high, but even so it was recommended that residents restrict their consumption of the fish from the lake (Becker et al., 2007). A more modern attitude towards the environment had developed during the 1950s and 60s which resulted in the passing of Sweden’s first environmental protection laws in 1969. Now Lake Vänern came into focus nationally for the first time. County councils and the National Environmental Protection Board carried out an examination of the state of health of the lake (Lundström et al., 1978). The new environment protection law had great influence on the lake’s recovery (Karlsson, 2012). Authorities and industry alike were forced into a new environmental consciousness. Mercury was banned, government subsidies were granted for environmental protection measures, and new technologies were developed.
During the 1970s sewage treatment was vastly improved. In industry, wastewater purification was developed and production methods improved (Danielsson et al., 2001). The large and visible discharges of fibers and wastewater lessened. Levels of phosphorus decreased and water transparency increased (Wilander and Persson, 2001; Willén, 2001). Concentrations of organic material decreased drastically in the lake and discharges containing mercury have stopped. Despite the decreasing levels of toxins in fish, e.g. mercury, DDT and PCB, concentrations of toxins are still higher than normal in the lake, and fatty fish are subject to limiting recommendations for human consumption (Becker et al., 2007). Even without being purified, the water in the lake is today drinkable far from land.
Due to the lake’s history of pollution, continuous monitoring of the environment of Lake Vänern started in 1973 and was reviewed in 1996 (Christensen, 2011). The environmental program has a fixed element and a variable element. The fixed element consists of regular yearly inspections and regular inspections that take place at less frequent intervals. The variable element consists of projects designed to examine and enhance the lake’s environment, together with campaign-type surveys, for example when there has been a temporary disturbance to the environment. The Swedish Meteorological and Hydrological Institute (SMHI) collects data on the water level of the lake and the water flow in its surrounding rivers on a regular basis. Other regular studies focus on hazardous substances in fish, estimations of fish stock using echo sounding, and taking inventory of nesting birds on skerries.
Now new clouds emerge on the horizon, with a changing climate, changing water regulation policies, and new lifestyles. We are left with many questions regarding what the future holds. Are we really equal to the task of establishing sustainable development within the Lake Vänern region?
The authors Marcus K. Drotz, Eva Gustavsson, and Lars Göran Nilsson thank the municipality of Lidköping for financial support.