the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 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.
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- CC1: 'Comment on egusphere-2025-1184', Mateusz Stolarczyk, 11 Jun 2025 reply
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RC1: 'Comment on egusphere-2025-1184', Gabriel Singer, 30 Sep 2025
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General comments:
The abstract currently cannot stand on its own, i.e., it is not understandable on its own without having read more text of the manuscript. Needs to be rewritten. In the introduction please be much clearer about the actual research questions/hypotheses of your study. For instance, it is unclear what is “an environmental response to beaver dams”, meaning a change in upstream-downstream gradients in physicochemistry? Or do you mean a change after-before (in a temporal sense!) at larger spatial scale? Take care to robustly derive your study´s questions from past work AND explain them in an understandable way. The three questions are currently a slightly loose list without much connection and with poor derivation.
A weakness of the study is its focus on upstream-downstream comparisons without any controls. Water chemical conditions may change a lot between two sites along a stream continuum, independent of beaver dams. The study investigates only stream sites with beaver dams and compares data from above and below. There was no investigation before beaver dams were constructed, nor are there any control sites where no dams exist. I acknowledge that a full before-after-control-impact (BACI) study design was deemed infeasible, but such shortcomings of the study design must at least be discussed. Typically, in studies lacking controls, a higher level auf causality is needed for hypothesized processes, here in this case all processes that may affect physicochemical conditions. For ions without much explanation for change in beaver ponds, the current design does not allow to strongly pin down beavers as being the origin for any change, especially if the direction of change was not consistent. This should be reflected in the discussion.
The paper also suffers from a relatively inefficient presentation of results. There are too many figures. Consider moving some figures to the Supplement and look for ways to more efficiently present data (e.g. do not use separate tables for PCA variable loadings, but rather include these as a separate panel in the figure). Consider removing, shortening the more detailed results on dam cascades or vertical profiles or move to supplement to give the paper more focus. Some plots are simply superfluous and don´t present much exciting (e.g. SEC in Fig 10).
The discussion of the various anaerobic processes should be organized along the redox ladder.
The lower differences from upstream to downstream compared to upstream-pond may to some extent be related to the fact that downstream samples are from a well-mixed turbulent stream but pond sampling was likely not done in a spatially “integrative” way. Thus, pond samples may not represent average pond conditions. This needs discussion, also in light of anyway existing vertical profile data.
I strongly recommend authors to discuss the observed beaver pond effects in the light of residence time of water in the ponds. Doing this may offer a chance to integrate pond/stream size effects and seasons (differences in stream discharge). It may even be able to integrate geomorphic pond type (for which I find any observed differences inadequately derived as well as discussed anyway). Residence time in concert with temperature may be able to explain a lot.
Overall, I urge authors to shorten the paper and find more efficient wording in particular in the discussion. This will make the paper more accessible to a larger audience.
More specific comments:
55: “attenuation of downstream …. concentrations” – please express more clearly, do you mean compared to upstream? Then is it measured relative to a control? Or does this imply some before-after comparison as well? The same problem applies to the text in the abstract.
58: maybe two sentences instead of semicolon?
60-65: Could be worthwhile to dive deeper into whether these studies aiming at investigating “reductions” and thus working with upstream-downstream differences actually follow BACI-study designs to statistically robust conclusions.
66: maybe explain a bit better why and how geomorphic factors could actually have such an influence.
115: explain pond-to-channel ratio
155: were both the original data and the differences (percent change) used in the same PCA? Please provide justification why this procedure would make sense.
161: There is no N in this formula.
171: Variables are all concentrations or differences thereoef. I suggest to not mix untransformed with log-transformed variables in the same PCA. Concentrations may just all be log-transformed, as they are often log-normal distributed anyway. I cannot see any step in PCA where significance tests would become relevant. And to use significance for normality tests is a questionable approach anyway, as normally one “hopes” for high P to identify a variable as “not identifiable as not normal”. Try to work without those debated and criticized tests. Same applies to Shapiro-Wilk used prior to ANOVA.
178-180: Before doing hard-core hypothesis tests, please cleanly derive why these hypotheses would anyway make sense to be tested in the intro. The derivation of your questions and subsequent hypotheses needs to be clearer. Currently it seems that the factor “pond type” was defined after the study was done.
199: Reword “controls the values”, not appropriate wording to describe PCA results.
Fig 3: What are the various regions indicating? Information for A,A/B, etc. missing from the legend. I suggest you also present factor loadings as arrows, could be done in a separate plot (panel).
Fig 4: This figure does not allow to recognize which points belong to the same pond and date, i.e. the paired nature of the data is not shown (or “used” because in fact its consideration could make data analysis stronger). Consider working with differences or connections between points.
Table 4: This table presents A LOT OF P-values. Since the same dataset was used multiple times, some P-value adjustment (e.g. Bonferroni) should be done. Certainly, P-values >0.05 (<0.1) should not be reported. I fear that not too many P-values will remain significant then, making clear why this strategy of extensive dataset testing may not be the best. Also, stronger analysis may take into account multiple factors (pond type, age, seasons) at once.
269: Was this PCA entirely done with “differences”? A graph of variable scores as arrows as a panel in Fig 6 may be more efficient than Table 5. I suggest to not speak of “water samples” in the legend of Fig 6 as two samples were needed to create one point in these graphs, as I understand. The site codes in fig 6 are hard to distinguish.
285: Similar comments apply to this PCA as to the previously presented one.
Chapter 3.4. needs to be incorporated in the Discussion.
354: pointing out high TOC only makes sense in comparison to upstream.
365: any idea about CH4 in these ponds? It would make sense to organize the discussion of the various anaerobic processes along the redox ladder.
366: ammonification is a fairly specific process and not a synonym for OM oxidation.
370: Prefer “aerobic/anaerobic” for microbial processes, but “oxic/anoxic” or low/high redox potential for environmental conditions.
Fig 12: Very appreciated conceptual figure. Consider using coloring the pond sequence in a color gradient instead of arrows?
Citation: https://doi.org/10.5194/egusphere-2025-1184-RC1
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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.