| 04 Apr 2025
The effect of beaver ponds on water physico-chemical composition in the Carpathians (Poland and Slovakia)
Abstract. In recent decades, the population of the Eurasian beaver (Castor fiber) has undergone a rapid recovery from near extinction to abundance across vast areas of Europe. The ability of this species to build dams makes its reintroduction an important environmental factor in the recolonised areas. This study investigated nine beaver-inhabited streams distributed across the Western Carpathians to assess the effects of geomorphic type, age of beaver pond sequence and seasonality on the physico-chemical changes to water in and below beaver ponds.
In general, greater reductions in NO3- and SO42- were observed with increasing temperatures during the warm period (spring–summer). A comparison of two distinct types of beaver ponds revealed that there was a greater decrease in NO3- and Ca2+ in overflowing ponds and a greater decrease in pH downstream to these ponds compared to in-channel reservoirs. Beaver pond sequence age was positively related to decrease in dissolved oxygen, SO42- and pH. Biogeochemical processes involving organic matter accumulated in beaver ponds, that include decomposition, aerobic/anaerobic oxidation and CaCO3 precipitation, are responsible for changes of these physico-chemical parameters in stream water. The natural development of extensive beaver ponds and their persistence may be crucial for sustaining water purification processes. Further research based on a more frequent sampling strategy should aim to identify the biogeochemical processes that occur in beaver ponds under specific hydro-meteorological conditions: during low flow periods, snowmelt and rainfall events.
The article “The effect of beaver ponds on water physico-chemical composition in the Carpathians (Poland and Slovakia)” examines how Eurasian beaver dams influence stream water chemistry in the Western Carpathians. Based on seasonal sampling of streams with varying geomorphology, pond types, and dam ages, the study found that beaver ponds significantly alter water parameters by reducing dissolved oxygen and nitrate levels, promoting sulfate reduction, increasing ammonium concentration, lowering pH, and in some cases facilitating calcium removal through precipitation. These effects are most pronounced during warm seasons and in older or overflowing ponds, where microbial and chemical processes intensify. The results underscore the important role of beaver ponds in modifying water quality. These valuable findings enhance our understanding of the complex influence of beaver activity on various environmental components, emphasizing the ecological significance of beaver-engineered habitats.
However, after reading the above study, several questions and comments arise regarding the conducted research, which may serve as useful guidance for the implementation of other research topics related to this subject:
1. Following an analysis of the results, conclusions, and the overall content of the paper, I would suggest considering a slight modification of the title (if it possible) to more accurately reflect the impact of beaver dams on the physico-chemical properties of stream water, rather than on the ponds as a whole. In my opinion, the ponds are a secondary consequence of dam construction, with the dam itself serving as the primary factor driving environmental modifications.
2. Sampling was conducted seasonally and did not account for hydrologically dynamic periods such as snowmelt or heavy rainfall events, which are known to cause substantial shifts in water flow and sediment transport. These events could temporarily alter or intensify the biogeochemical processes within beaver ponds, potentially affecting nutrient fluxes, oxygen dynamics, and pH levels. Incorporating high-resolution or event-based sampling in future research would provide a more comprehensive understanding of the short-term yet ecologically significant changes associated with such hydrological disturbances.
3. While the study offers valuable interpretations regarding biogeochemical processes in beaver ponds, it relies largely on indirect inference of organic matter dynamics and microbial activity. Direct measurements of parameters such as microbial community composition and microbial activity were not included, which limits the ability to fully validate the proposed mechanisms driving changes in water chemistry. Incorporating such data - through methods like enzyme activity assays or DNA sequencing - would strengthen the conclusions by providing process-level evidence and a clearer understanding of the microbial and organic matter contributions to the observed physico-chemical transformations.
4. The manuscript appropriately highlights the role of aquatic and riparian vegetation in nutrient cycling, particularly in relation to nitrate (NO₃⁻) reduction during the spring–summer period; however, this aspect was not quantitatively addressed. I agree that plant uptake likely contributes to observed nutrient dynamics, but this raises further questions about how pond age influences species diversity and vegetation cover? Specifically, is there a noticeable difference in plant growth or species composition between younger and older ponds, especially during the summer months? Addressing these questions with quantitative vegetation data would enhance understanding of biotic factors driving nutrient transformations in beaver ponds.