the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 21 Mar 2025
In situ-measured benthic fluxes of dissolved inorganic phosphorus in the Baltic Sea
Abstract. Sedimentary recycling of phosphorus is a key aspect of coastal eutrophication. Here, we present data on benthic fluxes of dissolved inorganic phosphorus (DIP) from the Baltic Sea, an area with a long eutrophication history. The presented dataset contains 499 individual fluxes measured in situ with three types of benthic chamber landers at 59 stations over 20 years, and data cover most of the Baltic Sea sub-basins (Hylén et al., 2025; https://doi.org/10.5281/zenodo.14812160). The dataset further contains information about bottom-water dissolved oxygen (O2) concentrations, sedimentary organic carbon (OC) content and sediment type. The DIP fluxes differ considerably between basins depending on OC loading and the level of O2 depletion and generally increase from the coast to the central basins. Several stations have been visited on multiple occasions, also at times with different O2 concentrations, which enables investigation of the immediate effects of shifting bottom-water O2 concentrations on the benthic DIP release. The Baltic Sea-wide benthic DIP release is estimated to be 391 – 489 kton y-1 based on a data integration based on sediment type and O2 conditions during three years with varying extents of hypoxia and anoxia (2004, 2013 and 2018). The dataset reveals a lack of flux measurements in winter months, coastal areas and sandy sediments; these should be targeted in future studies. Overall, the data is of high quality and will be important for marine management and studies on mechanisms in benthic phosphorus cycling.
Competing interests: Sebastiaan van de Velde is a member of the editorial board of the journal. The authors declare that they have no other conflicts of interest.
Publisher's note: Copernicus Publications remains neutral with regard to jurisdictional claims made in the text, published maps, institutional affiliations, or any other geographical representation in this paper. While Copernicus Publications makes every effort to include appropriate place names, the final responsibility lies with the authors. Views expressed in the text are those of the authors and do not necessarily reflect the views of the publisher.- Preprint
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Status: open (until 02 Sep 2025)
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RC1: 'Comment on essd-2025-146', Beata Szymczycha, 08 May 2025
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I find the manuscript highly informative, as it provides a comprehensive long-term dataset on benthic phosphorus fluxes in the Baltic Sea, offering valuable insights into nutrient cycling and contributing to more effective management of coastal eutrophication. I also appreciate the discussion of the study's limitations and the well-considered suggestions for future research directions.
General Comments:
- In the first sentence of the abstract, I recommend avoiding exclusive emphasis on coastal eutrophication, as phosphorus recycling is a process of broader significance across marine ecosystems. Furthermore, the majority of the data presented in the study are not from coastal environments, so a more general framing would be more appropriate.
- Please provide the source of the oxygen data used in Figure 1. If the data were collected as part of this study and extrapolated, a detailed description of the methodology should be included in the Methods section.
- According to many standard recommendations for phosphate sample collection and preservation, filtration (typically at 0.45 µm) is required to remove suspended particles and microorganisms. If unfiltered samples were used, a turbidity blank must be applied to correct for potential interference. Additionally, acidification is generally not advised for phosphate preservation. Given that various collection and preservation methods appear to have been used in this study, please discuss the uncertainties this introduces into the fluxes and extrapolations.
- I assume that samples were analyzed in different laboratories. If so, please provide detailed information on the accuracy and precision of the analytical methods used, as this can significantly affect the comparability of the results and calculations.
- The authors state that the dataset has limited use for interpreting seasonal trends. However, it would be interesting to deliberate a bit on the temporal variability at stations where monthly coverage was substantial, such as KH104.
Editorial Comments:
- Consider whether the use of the symbol “>” is necessary when the full range (0–63 µM O₂) is already explicitly stated.
Citation: https://doi.org/10.5194/essd-2025-146-RC1 -
RC2: 'Comment on essd-2025-146', Anonymous Referee #2, 26 Aug 2025
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This manuscript offers a valuable compilation of dissolved inorganic phosphorus (DIP) flux measurements collected across multiple research cruises, encompassing diverse spatial and temporal scales. While portions of the data have been previously published or referenced in various forms, the authors present a new perspective that yields novel insights into DIP flux patterns. The work makes a meaningful contribution to the field and, following appropriate revisions, merits publication in this journal. See my general comments:
Abstract
Line 30: When you say that the data is of high quality. Question is in terms of what? I don’t think this quality was estimated, even though everything was likely done correctly. Although I agree that the present study compiling DIP fluxes is important for evaluating and implementing the Marine Strategy Directives, I am less convinced of its novelty in studying the mechanism of phosphorus cycling.
Introduction
Lines 63-64: The sentence is redundant and suggests omitting.
Lines 67-68: The sentence is redundant and suggests omitting. The description of the Gulf of Finland needs to be reformulated.
Lines 72-73: Again, I don’t necessarily need to include information on catchment, as you don’t discuss it later.
Line 77: What gives this sentence? The following sentence provides a more straightforward explanation for the accumulation of higher P in the water column.
Line 99: digit in “O2” should be in subscript.
Lines 107-110/Line 146-150: Could you briefly discuss whether using different chambers could raise some differences in measured fluxes?
Lines 155-157: Could you state/discuss briefly that a different sample treatment had no effect on the level of DIP in the sample and measurement accuracy?
Line 178: Make a space between the dot and “Positive”.
Results and Discussion
Line 255: Could you add parentheses to the range of months for each season?
Lines 234-235: Maybe I have missed, but I am curious how authors obtained a common value from “non-significant” and “significant” values for the same site/area.
Lines 234-240: Would it be beneficial for authors to describe more variability in DIP fluxes and present the variation coefficients?
Figures
Figure 3: The digit in “O2” should be in subscript
Citation: https://doi.org/10.5194/essd-2025-146-RC2
Data sets
In situ measured benthic fluxes of dissolved inorganic phosphorus in the Baltic Sea Astrid Hylén, Nils Ekeroth, Andrew Dale, Mikhail Kononets, Wytze Lenstra, Anders Tengberg, Sebastiaan van de Velde, Stefan Sommer, Caroline Slomp, and Per Hall https://doi.org/10.5281/zenodo.15002521
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