Box 9K Restoration: Lake Hornborgasjön (Sweden)

Lake Hornborgasjön, Sweden

Source: M Moser, IWRB


Substantial changes to the hydrological and ecological management of Lake Hornborgasjön (Site 384 on Map 9.7) have been initiated in order to restore the area to its former importance for bird conservation. Degradation of the site began in the early nineteenth century with drainage to increase the area of arable land. The level of the lake was lowered some 2 m between 1803 and 1993, as a result of canalisation for conducting water away from the site. Regularly flooded areas were greatly reduced, and in summer open water was found only in the canal and a few lagoons. The basin was filled with decomposing plant material and the former lake became invaded by reed and scrub. Original ecological functions became substantially altered and there was widespread concern for the decline in breeding birds in an area which had formerly been of considerable ornithological interest. Restoration of the lake required a raising of the water level, implemented in two stages, by a total of 1.5 metres (Bjork, 1973), with the creation of dikes to protect surrounding arable land. Ten years later the plans were modified, reducing the water-level rise to 0.85 m and abandoning the diking proposals in favour of creating more marginal habitats, natural vegetation patterns and shallow water areas to encourage submerged vegetation. Flood meadows were also favoured to provide a source of seeds for ducks. More shallow water would also be of benefit to birds in restricting fish populations and thereby reducing competition for food resources. Reed clearance was a priority for management. The final government sanction for the plans was approved in 1990. The rise in water level is due to be completed by 1995. In 1991 it was already reported (Herzeman and Larsson, 1991) that some 7 km2 of reeds had been cleared and open water areas re-established. Some 2200 hectares of surrounding land have been acquired by the Swedish Environmental Protection Agency in order to regulate management activities and preclude damaging operations. Already improvements have been recorded in breeding bird populations. Dunlin (Calidris alpina), ruff (Philomachus pugnax), little gull (Larus minutus) and black tern (Chlidonias niger) have begun nesting since the start of the restoration programme (Grimmett and Jones, 1989).