Sava River, Slovenia
The Sava River, a major tributary of the Danube and the longest river flowing through Slovenia (221 km out of 990 km), has formed extensive alluvial plains whose groundwater provides drinking water to about 15 % of the Slovenian population.
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A chain of alluvial aquifers in Slovenia forms an ‘interstitial highway’ that connects the Alpine, Dinaric, and Continental biogeographical regions and hosts a rich and diverse groundwater fauna. Moreover, the alluvial deposits within the Sava River catchment, and further downstream those of the Danube, constitute a major dispersal corridor for groundwater fauna between the Balkan Peninsula and the broader region of Southeastern Europe, particularly the Pannonian Basin.
In Slovenia the lower reaches of the Sava River alluvial are fragmented by series of hydropower dams and exposed to intensive agriculture.
Diverse groundwater fauna
In addition to supplying clean and safe drinking water to a large proportion of the population within the Sava River catchment, these ecosystems sustain an exceptional diversity of groundwater fauna (stygofauna). At least 50 species have been recorded in and around Ljubljana alone, within an area approximately 15 km in length.
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The fauna is zoogeographically highly diverse. Some species are widespread across Europe. Others, such as Bogidiella albertimagni Hertzog, 1933, inhabit gravelly hyporheic zones and shallow groundwater systems throughout central and southern Europe. Other taxa are predominantly associated with Dinaric karst aquifers.
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The genus Niphargus is the most species-rich taxon. Copepods of the genera Acanthocyclops, Diacyclops, and Nitrocrella are also well represented. Ostracod Fabaeformicandona aemonae is named after the city of Ljubljana. Among the most ancient lineages are syncarids, including Bathynella and Parabathynella.
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However, much of the biodiversity within other parts of the Sava alluvium remains unexplored.
The Sava River alluvial aquifer under, and north and northwest of the city of Ljubljana is known as Ljubljansko polje. Large part of this aquifer lies directly beneath the city and the rest is mostly covered by agricultural land.
Balancing environmental and economic interests
As in many other regions worldwide, river valleys offer flat terrain and fertile soils suitable for agriculture, making them highly attractive for human settlement and industrial development. Urbanization, industrialization, and intensive agriculture lead to groundwater pollution, habitat fragmentation, and alterations of groundwater levels, posing serious threats to alluvial biodiversity throughout the Sava River catchment.
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Slovenia has well-established legislation protecting karst caves as habitats for subterranean biota. In contrast, alluvial aquifers are protected only indirectly, primarily through measures safeguarding the quality and quantity of drinking water. Effective conservation of these ecosystems requires improved knowledge of the distribution and ecology of interstitial species. The implementation of innovative monitoring tools, such as eDNA, could substantially enhance the protection of these unvisible ecosystems.
One of the GREG sampling sites northwest from Ljubljana.
Words by Dr. Nataša Mori
Photos by Davorin Tome & Živa Vehovar