Early-Stage Effects of a Beaver Dam on the Aquatic Environment in the Blanice National Nature Monument: Implications for Freshwater Pearl Mussel Conservation

Dominic Ditri

Diplomová práce

Abstract:

The Eurasian beaver (Castor fiber) is a species that was historically extirpated in the Czech Republic but is now recolonising its former range, substantially transforming aquatic and floodplain environments along the way. Although beaver activity is generally recognised for its positive effects on habitat heterogeneity and biodiversity, it may also pose a risk to sensitive species such as the critically endangered freshwater pearl mussel (Margaritifera margaritifera). However, no study to date has empirically evaluated the impact of beavers on this species and its habitat. Moreover, research on the local effects of beavers on water quality and habitat heterogeneity in the Czech Republic remains limited. This thesis partially addressed this knowledge gap by assessing the influence of a newly constructed beaver dam on basic water parameters in the Blanice River in the Bohemian Forest Mountains. Using a combination of long-term monitoring with data loggers and regular synoptic sampling, a total of 86 732 datapoints were collected over a nine-month period. The results show that beaver presence led to an overall increase in physicochemical and hydromorphological heterogeneity within the studied reach and created novel habitats for aquatic and wetland organisms. Median water temperatures in individual beaver wetlands and lagoons were up to 4.4 °C higher than in the main channel and extreme values could differ by 14.5 °C, which positively affected amphibian habitats. Although the deposition of fine sediment behind the dam had a localised negative impact on freshwater pearl mussel habitat, no broader adverse effects on water temperature, dissolved oxygen, or conductivity were detected downstream. This was the case both before and after the partial breaching of the dam midway through our study. In comparison to the remnants of the dam, the original beaver complex delayed the progression of stormflow through the study reach by 70 minutes, benefiting freshwater pearl mussel populations downstream. Overall, this study provides the first detailed assessment of beaver impacts on aquatic environments in the Czech Republic and the first quantitative evaluation of their effects on several key limiting factors for the freshwater pearl mussel based on continuous data. The results of this thesis contribute to the process of finding a solution to the coexistence between these two keystone species and provide valuable insights for the practical management of aquatic ecosystems both within the Blanice National Nature Monument and beyond.

Keywords

Eurasian beaver (Castor fiber), beaver dam, aquatic habitat, diurnal variation, freshwater pearl mussel (Margaritifera margaritifera), floodplain ponding, hydromorphology

Jazyk práce: angličtina

Datum vytvoření / odevzdání či podání práce: 19. 4. 2026

Obhajoba závěrečné práce

• Obhajoba proběhla 19. 5. 2026
• Vedoucí: Mgr. Ondřej Simon, Ph.D.
• Oponent: Michal Bílý, Ph.D.

Česká zemědělská univerzita v Praze

Fakulta životního prostředí

Magisterský studijní program:
Nature Conservation