467-474 Kvarn−s

Sweden is fortunate to have a great number of fairly large lakes. There are 395 lakes with a surface area exceeding 10 km within the country (1). The four largest lakes, L. Vänern, L. Vättern, L. Mälaren and L. Hjälmaren, all situated in central Sweden, have a total surface area of 9086 km, which constitutes 21.6% of the total lake area of Sweden. The drainage area of these four lakes amounts to 79␣ 845 km, which is c. 18% of the total area of Sweden. In a global perspective, L. Vänern is ranked as 29 and L. Vättern as 42 based on lake volumes. L. Mälaren and L. Hjälmaren, where the latter constitutes a part of the drainage area of L. Mälaren, are smaller and do not belong to the 50 largest lakes in the world (2). All lakes have been shaped and reshaped by several glacials that have covered Scandinavia and parts of northern Europe during the past 3 million years. The latest glacial began retreating from central Sweden c. 10␣ 000 yrs ago. The lakes provide an exceptional freshwater supply and support abundant fish communities. Their attractive sceneries and closeness to populated areas also make them important recreational resorts. When comparing the lakes, however, it is remarkable how fundamentally different they are in most respects. The range of processes that regulate the hydrology of the lakes is very broad. This can be explained by variations in morphometry and differences in the ratios between the lake area and drainage area as well as the size of the lake itself. Indeed, the only things they seem to have in common are their large size in relation to other Swedish lakes and their position within the temperate zone, which make them subject to a similar climate. Here an attempt is made to describe the structural circumstances and hydrological processes that have been identified, and to elucidate the differences. The links between water exchange and chemical response are discussed with an example from L. Vänern. The sediments have not been treated in this paper but it must be emphasized that the exchange between sediment and water is important. A number of investigations of bottom dynamics and sediment concentrations, mainly of metals, have been published by Håkanson (3–6). Furthermore, Håkanson studied Morphometry and Hydrology of the Four Large Lakes of Sweden Hans Kvarnäs