PROJECT DESCRIPTION
BACKGROUND
The ecological functioning of the Ljubljanica River corridor – upstream and downstream of the Ljubljana urban area – towards the confluence with the Sava River, and further upstream along the Sava, has been heavily degraded. This section of the river is a habitat for a fragmented and heavily endangered population of Danube salmon (Hucho hucho), as well as populations of Danube roach (Rutilus pigus) and striped chub (Leuciscus souffia). The Ljubljanica River acts as a corridor, linking the limestone headwater areas and alluvial plain areas of the Sava. Due to its unique character, the Ljubljanica River and its corridor has remained a vital habitat for numerous endangered species, in spite of it being one of the most degraded rivers in Slovenia. Currently, it represents a habitat for 26 native fish species, including several species listed in the Habitats Directive (Eudontomyzon mariae, Barbus meridionalis, Rhodeus sericeus amarus, Cobitis taenia, Cottus gobio, as well as the three mentioned above). Eco-hydrological conditions in the Ljubljanica River corridor help maintain unique habitat conditions in the Ljubljansko Barje wetlands in a fragile ecological equilibrium.
OBJECTIVES
The Ljubljanica Connects project aimed to improve the coherence of the Natura 2000 network by restoring the functionality of the Ljubljanica River as a corridor linking the upstream Ljubljansko Barje site, the Sava-Medvode-Kresnice site and floodplain areas, especially to enable migration of the fish species Danube roach, Danube salmon and striped chub. It aimed to achieve this by removing barriers to fish migration, improving water management infrastructure, and putting in place a water monitoring system. The project aimed to carry out an ecohydrological survey and develop hydrological models to serve as the basis for a management plan, identify threats at the project sites, and implement river restoration actions and habitat conservation work to improve the ecological status of the river and to meet the requirements of the Water Framework Directive.
RESULTS
The Ljubljanica Connects project reconstructed two dysfunctional fish passes and removed other migratory barriers along the Ljubljanica River in Slovenia, to reconnect fragmented populations of three target fish species, Danube salmon (Hucho hucho), Danube roach (Rutilus pigus) and striped chub (Leuciscus souffia). Monitoring activities using Internet-connected cameras then confirmed that these fish were migrating along both fish passes.
Reconstruction of two old fish passes, at the Fužine weir and Ambrožev trg barrier, which had caused fish populations to be fragmented into two sub-populations, re-established river connectivity. This re-opened a fish migration corridor between two Natura 2000 network sites and increased the spawning habitat accessible to migrating fish. The work re-connected the upstream Ljubljansko Barje Natura 2000 site with floodplain areas downstream of the urban area of Ljubljana, and the Sava-Medvode-Kresnice Natura 2000 site. Project results showed that despite some interruptions in the functionality of the fish pass in Fužine, a total of 12 different fish species were recorded using the reconstructed fish passes in both directions, including the three target fish species. The Ljubljanica River corridor will therefore now function as an important passage or stepping stone for many species, connecting the upstream Ljubljansko Barje site with floodplain areas.
Fish continue to be monitored in the reconstructed fish passes using the innovative system developed during the project. Innovations included the use of infra-red technology for monitoring at night, advanced camera technology, special software that estimates fish size, and a system for transmitting the images on-line to a website continuously in real-time. The project beneficiary stored more than 200 000 photos taken in the fish passes, and approximately 20% of these were used to determine fish species. From this data, the project team concluded that fragmented populations of fish species had been reconnected through the reconstructed fish passes. The innovative monitoring method has great potential for use in other fish passes in Slovenia and elsewhere in the EU. The method is not harmful to fish (non-invasive), and provides reliable and continuous data on fish passage at relatively low cost.
The fish pass restoration included installing deflectors at the exits, which preventing the ingress of debris but allowed fish to leave, reducing damage and maintenance costs. The project restored a sill at Zalog and raised its height by 20 cm to directly improve the quality of surface water in the oxbows situated upstream, by increasing water level which decreased the heating rate of water and increased the concentration of dissolved oxygen.
The modernisation of the lifting system at the Ambrožev trg barrier enables very precise water level regulation, crucial in cases of high waters and therefore an important flood protection and climate change adaptation measure. For the purposes of assessment, forecasting and management of flood risks, the project team developed hydrological and hydraulic models of the Ljubljanica River, in line with the EU Floods Directive.
The project significantly contributed to achieving the goals of the Habitats Directive, through measures to improve the population status of three Natura 2000 fish species and their prey species. Project actions should also increase the water quality in the Ljubljanica River, especially by increasing oxygen levels, a key objective of the Water Framework Directive.
Online streaming of fish activity was a successful awareness-raising tool concerning fish and freshwater ecosystems. The project team involved students and schoolchildren in activities, and employed young researchers. The local society of anglers attracted more members on account of strengthened fish populations, especially for Danube salmon. Other recreational activities along the river are also expected to increase.
Further information on the project can be found in the project's layman report and After-LIFE Conservation Plan (see "Read more" section).
