Biological Conservation Implications of Water-level Fluctuations in a Wetland of International Importance: Lake Kerkini, Macedonia, Greece

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Abstract
Kerkini Lake in Greece, a reservoir maintained principally for agricultural irrigation purposes on the Strymon River, has been classified as a ‘Wetland of International Importance’ according to the Ramsar Convention. Hydrological conditions favoured the formation of a shallow, very productive lake, rich in species diversity and biotic abundance. The importance of the wetland lay in its complex zonation of various habitats which mainly consisted of: shallow open water with sand-strips, beaches, and mud-flats; shallow-water areas with communities of emergent vegetation; a lowland hardwood riparian forest mainly ofSalixandTamarixspecies; a shrub-swamp; and extensive wet meadows. The diversity of habitats supported a rich waterbird fauna for breeding, stationing during migration, and wintering.Nevertheless, in 1982 a new high-dam was constructed, higher embankments along the banks of the Lake were established, and other works were carried out (to increase the water capacity of the reservoir), in response to irrigation demands. No consideration was given to the wetland resources. Operation of the new dam resulted in changes in the flooding etc. regime, with severe impact on the biotic resources of the wetland, especially by waterlevel increases of more than 5 m in less than 4 months during spring — the critical growing- and breedingseason. Wetland heterogeneity and the mosaic structure of water-land-vegetation were thereby lost.Now the riparian forest is diminishing in area and declining in productivity, the reed-swamp with emergent macrophytes has been lost, and wet meadows have also disappeared. Deep flooding and the loss of these habitats is reflected in marked decline in the densities of migratory waterbird populations and, most important, in drastic shrinkage in the populations of breeding species. Similar impact is observed in the dramatic decline of fish species diversity and abundance. In general, nowadays, Kerkini presents an alarming example of loss of biodiversity and accelerating impoverishment of its former biotic resources.In view of the projected plans to increase further the water-storage capacity of the Lake by raising its waterlevel, measures are urgently needed: (a) for preventing such actions; (b) for restoring and maintaining marsh conditions, and (c) for ecologically sound management and sustainable use of the wetland resources.