SUPERVISOR: Thomas HEIN

PROJECT ASSIGNED TO: Johannes KOWAL

In central Europe, todays rivers have commonly been subjected to severe human interferences and as a result have failed to achieve a good ecological status in a drastically high number of cases (European Union 2000; Grizzetti et al. 2017). While the aquatic flora and fauna is impacted by stressors such as morphological alterations, pollution, invasive species or water abstraction (BMLFUW 2021), the ecological resilience of the overall river meta-ecosystem increasingly depends on its interconnectedness in order to compensate for local habitat loss or degradation (Aarts et al. 2004). However, the construction of dams, hydraulic structures for navigation as well as flood protection measures have led to a severe fragmentation of most river networks. As a result, dispersal mechanisms as well as life history strategies are impaired or inhibited. This impact has to be recognized as an urgent threat not only from an ecological perspective (Seliger and Zeiringer 2018) but also concerning human interests since ecosystem services largely depend on the effective functioning of biophysical processes (Ekka et al. 2020). Nevertheless, measures to improve the connectivity have only been implemented during the past 20 years.

Continuum interruptions, which have to be considered as a four-dimensional stressor (longitudinal, lateral, vertical, temporal) generally address fluxes of energy, materials, organisms and environmental conditions. As a part of the Christian Doppler Laboratory for Meta Ecosystem Dynamics in Riverine Landscapes (CDL MERI) and the EU-project MERLIN (Mainstreaming Ecological Restoration of freshwater-related ecosystems in a Landscape context: INnovation, upscaling and transformation), this PhD thesis focuses on the longitudinal as well as the lateral dimension and is furthermore based on the meta-ecosystem concept (Loreau et al. 2003; Gounand et al. 2018; Cid et al. 2022). This theoretical approach emphasises the crucial importance of exchange processes between ecosystems, especially within the context of restoration and conservation. From this point of view, both long-term connectivity changes and recent conditions are investigated, evaluating whether or not some of the ecological effects of river fragmentation or restoration measures can be quantified on the reach and catchment scale. For this purpose, structural and functional connectivity is assessed based on well-established indices (Pascual-Hortal and Saura 2006; Rodeles et al. 2021; Cote et al. 2009; Yi et al. 2017; Baldan et al. 2022). Using the Austrian Danube and its tributaries as a study site, those indices are linked to changes within the meta-community of different taxonomic groups such as the fish fauna and are further compared to parameters that characterize the status of biological quality elements.

The Austrian Danube and its tributaries can today be described as a socio-ecohydrological system (Hein et al. 2021). Restoring the original natural state is neither possible nor compatible with the requirements of a modern society and therefore, the challenge lies in creating integrative management plans that considers ecological aspects as well as the needs of all relevant stakeholders. Hence, it is absolutely crucial to design and implement measures based on a meta-ecosystem approach rather than focusing on individual potentially disconnected areas. By providing novel insight into the effects of connectivity changes, this Ph.D. thesis will contribute to a knowledge foundation based on which integrative management plans for the Austrian Danube and its tributaries can be developed. In addition, the results will provide implications for future research making it a highly valuable contribution to the field of freshwater ecology.

Reaches with high and low longitudinal connectivity in the Austrian Danube and the lower parts of its most relevant tributaries. The overall connectivity is based on asymmetric passability of transversal structures (structural connectivity) as well as assumed dispersal capabilities of typical fish species (functional connectivity).

Publication bibliography

Aarts, Bram G. W.; van den Brink, Fred W. B.; Nienhuis, Piet H. (2004): Habitat loss as the main cause of the slow recovery of fish faunas of regulated large rivers in Europe: the transversal floodplain gradient. In River Res. Applic. 20 (1), pp. 3–23. DOI: 10.1002/rra.720.

Baldan, Damiano; Cunillera-Montcusí, David; Funk, Andrea; Hein, Thomas (2022): Riverconn: An R Package to Assess River Network Fragmentation. In SSRN Journal. DOI: 10.2139/ssrn.4096555.

BMLFUW (2021): Nationaler Gewässerbewirtschaftungsplan 2021 [National River Basin Management Plan 2015]. Bundesministerium für Land- und Forstwirtschaft, Umwelt und Wasserwirtschaft [Federal Ministry Republic Austria Agridulture, Forestry, Regions and Water Management].

Cid, Núria; Erős, Tibor; Heino, Jani; Singer, Gabriel; Jähnig, Sonja C.; Cañedo-Argüelles, Miguel et al. (2022): From meta-system theory to the sustainable management of rivers in the Anthropocene. In Frontiers in ecology and the environment 20 (1), pp. 49–57. DOI: 10.1002/fee.2417.

Cote, David; Kehler, Dan G.; Bourne, Christina; Wiersma, Yolanda F. (2009): A new measure of longitudinal connectivity for stream networks. In Landscape Ecol 24 (1), pp. 101–113. DOI: 10.1007/s10980-008-9283-y.

Ekka, Anjana; Pande, Saket; Jiang, Yong; van der Zaag, Pieter (2020): Anthropogenic Modifications and River Ecosystem Services: A Landscape Perspective. In Water 12 (10), p. 2706. DOI: 10.3390/w12102706.

European Union (2000): Directive 2000/60/EC of the European Parliament and of the Council establishing a framework for the Community action in the field of water policy. EU Water Framework Directive (WFD).

Gounand, Isabelle; Harvey, Eric; Little, Chelsea J.; Altermatt, Florian (2018): Meta-Ecosystems 2.0: Rooting the Theory into the Field. In Trends in ecology & evolution 33 (1), pp. 36–46. DOI: 10.1016/j.tree.2017.10.006.

Grizzetti, Bruna; Pistocchi, Alberto; Liquete, Camino; Udias, Angel; Bouraoui, Faycal; van de Bund, Wouter (2017): Human pressures and ecological status of European rivers. In Scientific reports 7 (1), p. 205. DOI: 10.1038/s41598-017-00324-3.

Hein, Thomas; Hauer, Christoph; Schmid, Martin; Stöglehner, Gernot; Stumpp, Christine; Ertl, Thomas et al. (2021): The coupled socio-ecohydrological evolution of river systems: Towards an integrative perspective of river systems in the 21st century. In The Science of the total environment 801, p. 149619. DOI: 10.1016/j.scitotenv.2021.149619.

Loreau, Michel; Mouquet, Nicolas; Holt, Robert D. (2003): Meta-ecosystems: a theoretical framework for a spatial ecosystem ecology. In Ecol Letters 6 (8), pp. 673–679. DOI: 10.1046/j.1461-0248.2003.00483.x.

Pascual-Hortal, Lucía; Saura, Santiago (2006): Comparison and development of new graph-based landscape connectivity indices: towards the priorization of habitat patches and corridors for conservation. In Landscape Ecol 21 (7), pp. 959–967. DOI: 10.1007/s10980-006-0013-z.

Rodeles, Amaia A.; Galicia, David; Miranda, Rafael (2021): A simple method to assess the fragmentation of freshwater fish meta-populations: Implications for river management and conservation. In Ecological Indicators 125, p. 107557. DOI: 10.1016/j.ecolind.2021.107557.

Seliger, Carina; Zeiringer, Bernhard (2018): River Connectivity, Habitat Fragmentation and Related Restoration Measures. In Stefan Schmutz, Jan Sendzimir (Eds.): Riverine Ecosystem Management. Cham: Springer International Publishing, pp. 171–186.

Yi, Yujun; Cheng, Xi; Yang, Zhifeng; Wieprecht, Silke; Zhang, Shanghong; Wu, Yingjie (2017): Evaluating the ecological influence of hydraulic projects: A review of aquatic habitat suitability models. In Renewable and Sustainable Energy Reviews 68, pp. 748–762. DOI: 10.1016/j.rser.2016.09.138.