the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 07 Aug 2025
Hydrography of intertidal environments in Schleswig-Holstein, Germany
Abstract. The current status of intertidal waters in the wake of ongoing global change was assessed in a baseline study with a 36 month time series of water level, temperature, and salinity measurements from Bottsand lagoon on the Baltic Sea coast, and on the mudflats off Schobüll at the North Sea coast of Schleswig-Holstein, Germany. Extreme events, storm surges and heat waves were also recorded in a temporal resolution of 20 minutes. At Bottsand lagoon, the temperatures followed the air temperatures in winter, and were higher than the air temperatures in spring and summer. The annual averages varied from 12.1 to 12.6 °C, the air temperatures varied from 11.1 to 11.2 °C. The salinities showed one or two months periods of consistently higher or lower values in winter and spring. The annual averages ranged from 14.7 to 16.9 units. The lagoon showed a different variability than that of the open Baltic surface waters, where the temperatures and salinities were lower in summer and higher in winter. The seasonal salinity differences were less developed in the mid 1960s, when the connectivity of the lagoon with the Baltic Sea was less restricted, and a sandy shoal in the lagoon was not present. In Husum Bight off Schobüll, water temperatures were lower than the air temperatures in winter and higher in spring and summer. The annual average water temperatures ranged from 10.8 to 11.4 °C, and the air temperatures from 9.9 to 10.2 °C. High waters were warmer during the day than at night-time in spring and early summer only. The annual average salinities off Schobüll ranged from 24.0 to 27.2 units. The values were higher in summer and lower in winter. This seasonal cycle was related to variations in the Elbe river runoff, which largely influences the salinity in the south-eastern German Bight. The same seasonal cycle was recorded in the Sylt Roads time series. Cross-correlations of the records revealed that it takes seven weeks for an Elbe river freshwater pulse to reach Schobüll, and three weeks more to proceed to Sylt. On average, the salinities were 2.7 units lower off Schobüll than off Sylt, which mirrors a pervasive gradient of landward decreasing salinities in the Wadden Sea. They were induced by a local, low-salinity lens on top of tidal waters, fed by groundwater seepage or by freshwater runoff. A cross correlation with the precipitation record revealed salinity decreases about one week after high precipitation. The cumulative salt marsh submergence times per period of observation, i.e. inundation frequencies, were very variable at the lower boundaries of the lower and upper salt marsh vegetation zones. The inundation frequencies were consistently higher at Bottsand than at Schobüll, where the same halophyte assemblages prevailed. As the average salinity was 10 units higher at Schobüll, the differences of inundation frequencies suggest that a certain salinity has to be maintained in the soils to sustain specific halophyte assemblages. A mass occurrence of small Pacific oyster shells was observed before the vegetation boundary off Schobüll in spring 2024. The data suggested an oyster spatfall triggered by the North Sea heat waves in summer 2023, with temperatures exceeding 23 °C, and a subsequent wipe-out during a period of salinities lower than 18 units after an Elbe river discharge event in January 2024. The biotic responses to environmental extremes highlighted the vulnerability of Wadden Sea ecosystems at times of Global Change.
Competing interests: At least one of the (co-)authors is a member of the editorial board of Biogeosciences. The peer-review process was guided by an independent editor, and the authors also have no other competing interests to declare.
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.-
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The requested preprint has a corresponding peer-reviewed final revised paper. You are encouraged to refer to the final revised version.
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Interactive discussion
Status: closed
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CC1: 'Comment on egusphere-2025-2672', Julia Lübbers, 26 Aug 2025
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AC3: 'Reply on CC1', Joachim Schönfeld, 10 Oct 2025
CC1: 'Comment on egusphere-2025-2672', Julia Lübbers, 26 Aug 2025
I am positively surprised to see such a long and detailed hydrographic study from the North Sea and Baltic Sea coasts of Schleswig-Holstein. In the context of global warming, such baseline studies are crucial for understanding the effects and consequences of rising sea levels. Schleswig-Holstein may seem less prominent compared to major coastal areas like New York City, but this makes the availability of such a continuous record even more impressive and valuable for future research.
Reply: we sincerely thank Julia Lübbers for her comments and suggestions.
This study is of high quality, and I strongly recommend publication. I have only a few major comments and suggestions:
Photographs of the installed loggers: Including photos or schematics of the logger installations would help readers better understand how they were set up in the field.
Reply: we have taken images of the logger installations in the field and are going to provide them in the Supplement to the revised version of the manuscript.
Damage to the fishing rod at Schobüll: How confident are the authors that the fishing rod broke naturally rather than being damaged by human interference? Since the logger was installed near a pier, could curious passers-by have interacted with it? Would it be safer to place loggers farther away from public access to avoid possible disturbance?
Reply: human footprints were not recognised around the measuring point off Schobüll during our inspection visits in winter or after damage of the rods. Such footprints stay in the mud for two weeks or more. Also, the top segment of a rod broke off once in summer. The fracture was so high that no one could reach it. Consequences of installing the measuring points further away from the general public are longer approaches in difficult terrain and difficulties with levelling over long distances and unstable ground.
Evidence for the mass oyster mortality: The manuscript mentions a "mass occurrence of empty oyster shells" at the Schobüll station. Could the authors provide quantitative estimates (e.g., number of shells per square metre) or photographs to document this observation and confirm that it was indeed a mass mortality event?
Reply: we have screened the 63-2000 µm size fraction of foraminiferal monitoring samples taken annually at the vegetation boundary off Schobüll in late October or early November. Indeed the concentration of shell fragments in the 0-1 cm surface sediment was 53 per 10 cm3 in 2023 and 304 per 10 cm3 in 2024, i.e. six times higher. The values have to be taken with caution because the 2024 sample was taken more than six months later than the shell lag was observed, and the surface area was 2 x 10 cm2, hence very small as compared to a footprint.
The shell fragments were identified by naked eye in the field as fragments of juvenile Pacific oysters. When we attempted to quantify their abundance, we discovered under the binocular microscope that we have mistaken barnacle plates with oyster shell fragments. They belong to Austrominius modestus, an invasive barnacle, which proliferates at warm temperatures and is endangered by temperatures below -5°C (O’Riordan et al., 2020). A period of strong frost between 29-Nov-2023 and 1-Dec-2023, with daily mean temperatures of up to -10.2°C, may well have caused a mass die-off, which may have produced the shell lag we have observed. The manuscript is going to be corrected accordingly during the revision. The basic conclusion that the biota are very much affected by extreme events is still valid.
Overall, this is an impressive study that will serve as an important reference for future coastal monitoring. I hope the authors will continue this valuable time-series work for many years to come.
Citation: https://doi.org/10.5194/egusphere-2025-2672-AC3
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AC3: 'Reply on CC1', Joachim Schönfeld, 10 Oct 2025
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RC1: 'Comment on egusphere-2025-2672', Anonymous Referee #1, 17 Sep 2025
‘Hydrography of intertidal environments in Schleswig-Holstein, Germany’- submitted by Schönfeld et al., provided important temporal dataset of basic parameters of water and air in this study. Using the new dataset, along with a compilation of published dataset of 1960s, this manuscript showed short-term and long-term changes in the marginal marine environment.
Although the manuscript provided incredible amount of dataset, in my opinion, the manuscript has not been presented well. Abstract and conclusion contain too many texts; it needs to be concise. Also, discussion and conclusion do not provide significant outcome instead of having extensive dataset.
The materials and methods section is very important as throughout the manuscript data used were obtained from sensors and corers. So, it’s wise to explain the accuracy and precision of each parameter and how it was determined. However, this section is little bit messy and inconsistent in many aspects. Please see my comments below. I suggest summarizing all analytical data (accuracy, precision etc) for all parameters in a table.
Para 160, first sentence: What is the relevance of this sentence?
Explain what P/T and C/T loggers are. What does it mean by P, T and C.
Para 175, 180, first sentence: Cite Figure 1
Para 200. How were accuracy determined? It’s not clear to me how accuracy is shown by range and average. Please explain? What’s the unit of salinity? I assume it is a practical salinity unit. Please clarify. Accuracy is generally reported in percentage.
Para 205: Here precision is in percentage, but earlier paragraph external reproducibility is shown in real unit numbers. I suggest please be consistent throughout the methodology. It should be better to report everything in percentage, otherwise it’s difficult for reader to understand the flow.
Para 205 second line: Here salinity in unit but in next line it’s in per mil. Be consistent. Either psu or per mil.
Para 255, last sentence: This is a negative statement. Either remove this statement. If you are doubtful about the published data, don’t use it.
Para 270, fourth line: I assume 1.06% of total salinity dataset. Salinity unit is also sometime expressed as %. So please clarify.
Para 275, first line: Rewrite! It reads 0.08% salinity lost/changed in water.
Para 300, first line: sometimes temp in C, sometimes in K. Be consistent. in fig 2, max water temperature shows a value less than 30. Please check the values given here or check the figure.
Para 300 last line: No need to write 1sigma each time.
Figure 4 caption: in b panel, only one station has been plotted as only one red and blue pattern. It’s not clear what stations. I assume for Holtenau.
Para 420 first line: low air temperature in winter.
Figure 7: in text temperature changes are discussed first, but in figure it comes in the lower panel. inconsistency!
Section 4.2. title: In results and everywhere, title is focused on Schobüll . Now Husum Bight. Not consistent
Para 600, last line: initial hypothesis of what? Not linked properly
Para 605: This is a result, not conclusion of the study
Citation: https://doi.org/10.5194/egusphere-2025-2672-RC1 -
AC1: 'Reply on RC1', Joachim Schönfeld, 10 Oct 2025
RC1: 'Comment on egusphere-2025-2672', Anonymous Referee #1, 17 Sep 2025
‘Hydrography of intertidal environments in Schleswig-Holstein, Germany’- submitted by Schönfeld et al., provided important temporal dataset of basic parameters of water and air in this study. Using the new dataset, along with a compilation of published dataset of 1960s, this manuscript showed short-term and long-term changes in the marginal marine environment.
Reply: we are grateful for the thorough review and in particular appreciate the recognition of relevance of our contribution.
Although the manuscript provided incredible amount of dataset, in my opinion, the manuscript has not been presented well. Abstract and conclusion contain too many texts; it needs to be concise. Also, discussion and conclusion do not provide significant outcome instead of having extensive dataset.
Reply: indeed, we created a large data set. As anything was new and many unexpected features were observed, they need to be documented and reported in text and figures. This is a matter of case for any baseline study. We concede that both, Abstract and Conclusions chapters can be shortened without loss of evidence and information. We are going to do that during the revision of the paper.
The materials and methods section is very important as throughout the manuscript data used were obtained from sensors and corers. So, it’s wise to explain the accuracy and precision of each parameter and how it was determined. However, this section is little bit messy and inconsistent in many aspects. Please see my comments below. I suggest summarizing all analytical data (accuracy, precision etc) for all parameters in a table.
Reply: we concede that the middle part of Chapter 2.2 Hydrographical measurements between lines 161 and 192 may be difficult to follow. According to the advise of Reviewer 1, it is worthwhile to re-structure this part in that we first report the measuring points, then describe the assembly, after that the operation procedures, and finally create a short, new paragraph reporting the sensor accuracy. A new Table is not deemed necessary as only these three parameters were measured. Corers were not applied.
Para 160, first sentence: What is the relevance of this sentence?
Reply: we are convinced that it is necessary to report which devices were used at first.
Explain what P/T and C/T loggers are. What does it mean by P, T and C.
Reply: the abbreviations are deemed self-explanatory, but this is seemingly not the case. Therefore, we are going to reformulate the sentence to: "As in earlier studies, Odyssey® C/T and P/T data loggers (Dataflow Systems Ltd., Christchurch, New Zealand) were used to measure water level (P), temperature (T), and salinity (C).".
Para 175, 180, first sentence: Cite Figure 1
Reply: this could be done but may be misleading as the map in Figure 1 is too low in resolution, and the geographical coordinates are given in any way.
Para 200. How were accuracy determined? It’s not clear to me how accuracy is shown by range and average. Please explain? What’s the unit of salinity? I assume it is a practical salinity unit. Please clarify. Accuracy is generally reported in percentage.
Reply: the sensor accuracy was determined under laboratory conditions, which is explained in the sentences before. The salinity is dimensionless and has to be expressed as "units". This has been discussed thoroughly in an earlier paper already (Schönfeld, 2018, there page 385). At best, we are going to provide this reference here. Reporting the accuracy as percentage is not correct, because no single-point calibration was applied.
Para 205: Here precision is in percentage, but earlier paragraph external reproducibility is shown in real unit numbers. I suggest please be consistent throughout the methodology. It should be better to report everything in percentage, otherwise it’s difficult for reader to understand the flow.
Reply: this is a misunderstanding. We referred to the manufacturer's data sheet here. This is going to be specified in the revised version of the paper.
Para 205 second line: Here salinity in unit but in next line it’s in per mil. Be consistent. Either psu or per mil.
Reply: this is again a misunderstanding. The salinity of the seawater standards we used was measured with an Optimare Precision Salinometer that has been calibrated with IAPSO Standard Seawater. Therefore, the unit "permil" can be assigned to these values (Supplement Table S3). As this could be misleading, it is certainly better to omit the unit in the revised version of the paper.
Para 255, last sentence: This is a negative statement. Either remove this statement. If you are doubtful about the published data, don’t use it.
Reply: the senior author knew Professor Lutze in person. He was very accurate and we do not doubt his data. We simply say for clarity that the methodology was not reported. It might be better to replace the term "methodology of" by "the instruments used for" in the revised version of the paper.
Para 270, fourth line: I assume 1.06% of total salinity dataset. Salinity unit is also sometime expressed as %. So please clarify.
Reply: "1.06 % of the time from the total salinity record" would be correct. We are going to change this in the revised version.
Para 275, first line: Rewrite! It reads 0.08% salinity lost/changed in water.
Reply: see above. "of 0.08 % of the data from the salinity record." would be correct. We are going to change that.
Para 300, first line: sometimes temp in C, sometimes in K. Be consistent. in fig 2, max water temperature shows a value less than 30. Please check the values given here or check the figure.
Reply: it is a matter of common sense that temperature levels are to be reported in degree centigrade, while differences or intervals are to expressed in Kelvin. Figure 2 presents the daily mean temperatures as noted in the figure caption, while the values given in Line 296 are the extremes. We think it is unnecessary to say "-0.7°C (minimum value) to 31.8°C (maximum value)".
Para 300 last line: No need to write 1sigma each time.
Reply: we respectfully disagree. Otherwise the value can be mistaken with the total data range.
Figure 4 caption: in b panel, only one station has been plotted as only one red and blue pattern. It’s not clear what stations. I assume for Holtenau.
Reply: Reviewer 1 is right, the figure caption is ambiguous. It rather should read "Figure 4. Water level at Bottsand and Holtenau (a), temperature, and salinity during the Centennial Flood at Bottsand (b). The red arrows in (a) mark the salinity rises observed at Bottsand". We are going to change this in the revised version of the manuscript.
Para 420 first line: low air temperature in winter.
Reply: we agree and are going to add "in winter" in the revised version.
Figure 7: in text temperature changes are discussed first, but in figure it comes in the lower panel. inconsistency!
Reply: as a convention, we always plotted the salinities in the top panel (see Figures 2 and 3).
Section 4.2. title: In results and everywhere, title is focused on Schobüll . Now Husum Bight. Not consistent
Reply: Schobüll is located on the north-eastern side of part of inner Husum Bight. This has been stated in Line 112 already.
Para 600, last line: initial hypothesis of what? Not linked properly
Reply: the initial hypothesis of the present study has been given in Line 66. We could add a sentence in Line 601, at the end of the paragraph, saying that "Temperatures and salinities of intertidal waters indeed showed a different variability than those of surface waters further off shore.", just for clarification.
Para 605: This is a result, not conclusion of the study
Reply: the values are repeated here to fuel the reader's imagination. They could be omitted and the sentence could read "The mean difference of on-site manually measured and data logger recorded values is deemed acceptable with reference to the profound environmental dynamics observed.", taking the risk that other readers would ask themself where in the Results section did they say that.
Citation: https://doi.org/10.5194/egusphere-2025-2672-AC1
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AC1: 'Reply on RC1', Joachim Schönfeld, 10 Oct 2025
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RC2: 'Comment on egusphere-2025-2672', Anonymous Referee #2, 23 Sep 2025
The manuscript entitled “Hydrography of intertidal environments in Schleswig-Holstein, Germany” by Schönfeld et al. reports on a study assessing the current status of marine marginal environments using a 36-month time series of abiotic variables measured from two systems located at the Baltic Sea and the North Sea. The authors used a large temporal dataset resulting from an impressive sampling effort. The authors also reported changes in salt marsh and oyster occurrence. This is an interesting and important article. It offers valuable insights into short and long-term changes in marginal habitats. The contribution of this research to filling out gaps on the impacts of global change on fragile ecosystems is well-described and meets the criteria laid down for publication in Biogeosciences. The manuscript is generally well-written and could be accepted after some revisions. My main concern is about the lack of information regarding the ecology of salt marshes and Pacific oyster in the Introduction. Responses of these to organisms to extreme events are indeed discussed. The Materials and Methods section should also provide details about the sampling strategy employed to document biotic responses (salt marsh and Pacific oyster populations) to extreme events. Finally, the conclusion is too long, and in some instances, this section presents information that should appear in the Results section (For instance, see lines 604-606 and lines 640-642).
Citation: https://doi.org/10.5194/egusphere-2025-2672-RC2 -
AC2: 'Reply on RC2', Joachim Schönfeld, 10 Oct 2025
RC2: 'Comment on egusphere-2025-2672', Anonymous Referee #2, 23 Sep 2025
The manuscript entitled “Hydrography of intertidal environments in Schleswig-Holstein, Germany” by Schönfeld et al. reports on a study assessing the current status of marine marginal environments using a 36-month time series of abiotic variables measured from two systems located at the Baltic Sea and the North Sea. The authors used a large temporal dataset resulting from an impressive sampling effort. The authors also reported changes in salt marsh and oyster occurrence. This is an interesting and important article. It offers valuable insights into short and long-term changes in marginal habitats. The contribution of this research to filling out gaps on the impacts of global change on fragile ecosystems is well-described and meets the criteria laid down for publication in Biogeosciences.
Reply: we thank the Reviewer 2 for the positive review appreciate the recognition of our efforts to create the time series presented in this paper.
The manuscript is generally well-written and could be accepted after some revisions. My main concern is about the lack of information regarding the ecology of salt marshes and Pacific oyster in the Introduction.
Reply: the ecology of the salt marshes is beyond the scope of the present study. Geochemical microbial and faunistic data would have to be included, which are mostly not available. The floral successions have been documented in the literature much better. They are of relevance to the present study because halophytes directly respond to the hydrographical dynamics we have captured, e.g. inundation frequency. Therefore, we have summarized the past and present state of the salt marshes in the 1.1 Geographical and environmental setting chapter.
Responses of these to organisms to extreme events are indeed discussed. The Materials and Methods section should also provide details about the sampling strategy employed to document biotic responses (salt marsh and Pacific oyster populations) to extreme events.
Reply: there was no intention neither a sampling strategy to document biotic responses to extreme events. It would have employed a biomonitoring scheme with short sampling intervals, which is beyond the knowledge and physical capacities of the authors. None-the-less, observations were made by accident, in particular the shell lag before the groynes off Schobüll where one could walk upon much easier than on the prevailing mud. This observation was set into a context by exploring the hydrographical data we have obtained.
Finally, the conclusion is too long, and in some instances, this section presents information that should appear in the Results section (For instance, see lines 604-606 and lines 640-642).
Reply: indeed, the Conclusion chapter could be shortened in places. The values in lines 604 to 606 were repeated to fuel the reader's imagination. They could be omitted, taking the risk that other readers would ask themself where in the Results section did they say that..
Citation: https://doi.org/10.5194/egusphere-2025-2672-AC2
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AC2: 'Reply on RC2', Joachim Schönfeld, 10 Oct 2025
Interactive discussion
Status: closed
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CC1: 'Comment on egusphere-2025-2672', Julia Lübbers, 26 Aug 2025
I am positively surprised to see such a long and detailed hydrographic study from the North Sea and Baltic Sea coasts of Schleswig-Holstein. In the context of global warming, such baseline studies are crucial for understanding the effects and consequences of rising sea levels. Schleswig-Holstein may seem less prominent compared to major coastal areas like New York City, but this makes the availability of such a continuous record even more impressive and valuable for future research.
This study is of high quality, and I strongly recommend publication. I have only a few major comments and suggestions:
- Photographs of the installed loggers: Including photos or schematics of the logger installations would help readers better understand how they were set up in the field.
- Damage to the fishing rod at Schobüll: How confident are the authors that the fishing rod broke naturally rather than being damaged by human interference? Since the logger was installed near a pier, could curious passers-by have interacted with it? Would it be safer to place loggers farther away from public access to avoid possible disturbance?
- Evidence for the mass oyster mortality: The manuscript mentions a "mass occurrence of empty oyster shells" at the Schobüll station. Could the authors provide quantitative estimates (e.g., number of shells per square metre) or photographs to document this observation and confirm that it was indeed a mass mortality event?
Overall, this is an impressive study that will serve as an important reference for future coastal monitoring. I hope the authors will continue this valuable time-series work for many years to come.
Citation: https://doi.org/10.5194/egusphere-2025-2672-CC1 -
AC3: 'Reply on CC1', Joachim Schönfeld, 10 Oct 2025
CC1: 'Comment on egusphere-2025-2672', Julia Lübbers, 26 Aug 2025
I am positively surprised to see such a long and detailed hydrographic study from the North Sea and Baltic Sea coasts of Schleswig-Holstein. In the context of global warming, such baseline studies are crucial for understanding the effects and consequences of rising sea levels. Schleswig-Holstein may seem less prominent compared to major coastal areas like New York City, but this makes the availability of such a continuous record even more impressive and valuable for future research.
Reply: we sincerely thank Julia Lübbers for her comments and suggestions.
This study is of high quality, and I strongly recommend publication. I have only a few major comments and suggestions:
Photographs of the installed loggers: Including photos or schematics of the logger installations would help readers better understand how they were set up in the field.
Reply: we have taken images of the logger installations in the field and are going to provide them in the Supplement to the revised version of the manuscript.
Damage to the fishing rod at Schobüll: How confident are the authors that the fishing rod broke naturally rather than being damaged by human interference? Since the logger was installed near a pier, could curious passers-by have interacted with it? Would it be safer to place loggers farther away from public access to avoid possible disturbance?
Reply: human footprints were not recognised around the measuring point off Schobüll during our inspection visits in winter or after damage of the rods. Such footprints stay in the mud for two weeks or more. Also, the top segment of a rod broke off once in summer. The fracture was so high that no one could reach it. Consequences of installing the measuring points further away from the general public are longer approaches in difficult terrain and difficulties with levelling over long distances and unstable ground.
Evidence for the mass oyster mortality: The manuscript mentions a "mass occurrence of empty oyster shells" at the Schobüll station. Could the authors provide quantitative estimates (e.g., number of shells per square metre) or photographs to document this observation and confirm that it was indeed a mass mortality event?
Reply: we have screened the 63-2000 µm size fraction of foraminiferal monitoring samples taken annually at the vegetation boundary off Schobüll in late October or early November. Indeed the concentration of shell fragments in the 0-1 cm surface sediment was 53 per 10 cm3 in 2023 and 304 per 10 cm3 in 2024, i.e. six times higher. The values have to be taken with caution because the 2024 sample was taken more than six months later than the shell lag was observed, and the surface area was 2 x 10 cm2, hence very small as compared to a footprint.
The shell fragments were identified by naked eye in the field as fragments of juvenile Pacific oysters. When we attempted to quantify their abundance, we discovered under the binocular microscope that we have mistaken barnacle plates with oyster shell fragments. They belong to Austrominius modestus, an invasive barnacle, which proliferates at warm temperatures and is endangered by temperatures below -5°C (O’Riordan et al., 2020). A period of strong frost between 29-Nov-2023 and 1-Dec-2023, with daily mean temperatures of up to -10.2°C, may well have caused a mass die-off, which may have produced the shell lag we have observed. The manuscript is going to be corrected accordingly during the revision. The basic conclusion that the biota are very much affected by extreme events is still valid.
Overall, this is an impressive study that will serve as an important reference for future coastal monitoring. I hope the authors will continue this valuable time-series work for many years to come.
Citation: https://doi.org/10.5194/egusphere-2025-2672-AC3
-
RC1: 'Comment on egusphere-2025-2672', Anonymous Referee #1, 17 Sep 2025
‘Hydrography of intertidal environments in Schleswig-Holstein, Germany’- submitted by Schönfeld et al., provided important temporal dataset of basic parameters of water and air in this study. Using the new dataset, along with a compilation of published dataset of 1960s, this manuscript showed short-term and long-term changes in the marginal marine environment.
Although the manuscript provided incredible amount of dataset, in my opinion, the manuscript has not been presented well. Abstract and conclusion contain too many texts; it needs to be concise. Also, discussion and conclusion do not provide significant outcome instead of having extensive dataset.
The materials and methods section is very important as throughout the manuscript data used were obtained from sensors and corers. So, it’s wise to explain the accuracy and precision of each parameter and how it was determined. However, this section is little bit messy and inconsistent in many aspects. Please see my comments below. I suggest summarizing all analytical data (accuracy, precision etc) for all parameters in a table.
Para 160, first sentence: What is the relevance of this sentence?
Explain what P/T and C/T loggers are. What does it mean by P, T and C.
Para 175, 180, first sentence: Cite Figure 1
Para 200. How were accuracy determined? It’s not clear to me how accuracy is shown by range and average. Please explain? What’s the unit of salinity? I assume it is a practical salinity unit. Please clarify. Accuracy is generally reported in percentage.
Para 205: Here precision is in percentage, but earlier paragraph external reproducibility is shown in real unit numbers. I suggest please be consistent throughout the methodology. It should be better to report everything in percentage, otherwise it’s difficult for reader to understand the flow.
Para 205 second line: Here salinity in unit but in next line it’s in per mil. Be consistent. Either psu or per mil.
Para 255, last sentence: This is a negative statement. Either remove this statement. If you are doubtful about the published data, don’t use it.
Para 270, fourth line: I assume 1.06% of total salinity dataset. Salinity unit is also sometime expressed as %. So please clarify.
Para 275, first line: Rewrite! It reads 0.08% salinity lost/changed in water.
Para 300, first line: sometimes temp in C, sometimes in K. Be consistent. in fig 2, max water temperature shows a value less than 30. Please check the values given here or check the figure.
Para 300 last line: No need to write 1sigma each time.
Figure 4 caption: in b panel, only one station has been plotted as only one red and blue pattern. It’s not clear what stations. I assume for Holtenau.
Para 420 first line: low air temperature in winter.
Figure 7: in text temperature changes are discussed first, but in figure it comes in the lower panel. inconsistency!
Section 4.2. title: In results and everywhere, title is focused on Schobüll . Now Husum Bight. Not consistent
Para 600, last line: initial hypothesis of what? Not linked properly
Para 605: This is a result, not conclusion of the study
Citation: https://doi.org/10.5194/egusphere-2025-2672-RC1 -
AC1: 'Reply on RC1', Joachim Schönfeld, 10 Oct 2025
RC1: 'Comment on egusphere-2025-2672', Anonymous Referee #1, 17 Sep 2025
‘Hydrography of intertidal environments in Schleswig-Holstein, Germany’- submitted by Schönfeld et al., provided important temporal dataset of basic parameters of water and air in this study. Using the new dataset, along with a compilation of published dataset of 1960s, this manuscript showed short-term and long-term changes in the marginal marine environment.
Reply: we are grateful for the thorough review and in particular appreciate the recognition of relevance of our contribution.
Although the manuscript provided incredible amount of dataset, in my opinion, the manuscript has not been presented well. Abstract and conclusion contain too many texts; it needs to be concise. Also, discussion and conclusion do not provide significant outcome instead of having extensive dataset.
Reply: indeed, we created a large data set. As anything was new and many unexpected features were observed, they need to be documented and reported in text and figures. This is a matter of case for any baseline study. We concede that both, Abstract and Conclusions chapters can be shortened without loss of evidence and information. We are going to do that during the revision of the paper.
The materials and methods section is very important as throughout the manuscript data used were obtained from sensors and corers. So, it’s wise to explain the accuracy and precision of each parameter and how it was determined. However, this section is little bit messy and inconsistent in many aspects. Please see my comments below. I suggest summarizing all analytical data (accuracy, precision etc) for all parameters in a table.
Reply: we concede that the middle part of Chapter 2.2 Hydrographical measurements between lines 161 and 192 may be difficult to follow. According to the advise of Reviewer 1, it is worthwhile to re-structure this part in that we first report the measuring points, then describe the assembly, after that the operation procedures, and finally create a short, new paragraph reporting the sensor accuracy. A new Table is not deemed necessary as only these three parameters were measured. Corers were not applied.
Para 160, first sentence: What is the relevance of this sentence?
Reply: we are convinced that it is necessary to report which devices were used at first.
Explain what P/T and C/T loggers are. What does it mean by P, T and C.
Reply: the abbreviations are deemed self-explanatory, but this is seemingly not the case. Therefore, we are going to reformulate the sentence to: "As in earlier studies, Odyssey® C/T and P/T data loggers (Dataflow Systems Ltd., Christchurch, New Zealand) were used to measure water level (P), temperature (T), and salinity (C).".
Para 175, 180, first sentence: Cite Figure 1
Reply: this could be done but may be misleading as the map in Figure 1 is too low in resolution, and the geographical coordinates are given in any way.
Para 200. How were accuracy determined? It’s not clear to me how accuracy is shown by range and average. Please explain? What’s the unit of salinity? I assume it is a practical salinity unit. Please clarify. Accuracy is generally reported in percentage.
Reply: the sensor accuracy was determined under laboratory conditions, which is explained in the sentences before. The salinity is dimensionless and has to be expressed as "units". This has been discussed thoroughly in an earlier paper already (Schönfeld, 2018, there page 385). At best, we are going to provide this reference here. Reporting the accuracy as percentage is not correct, because no single-point calibration was applied.
Para 205: Here precision is in percentage, but earlier paragraph external reproducibility is shown in real unit numbers. I suggest please be consistent throughout the methodology. It should be better to report everything in percentage, otherwise it’s difficult for reader to understand the flow.
Reply: this is a misunderstanding. We referred to the manufacturer's data sheet here. This is going to be specified in the revised version of the paper.
Para 205 second line: Here salinity in unit but in next line it’s in per mil. Be consistent. Either psu or per mil.
Reply: this is again a misunderstanding. The salinity of the seawater standards we used was measured with an Optimare Precision Salinometer that has been calibrated with IAPSO Standard Seawater. Therefore, the unit "permil" can be assigned to these values (Supplement Table S3). As this could be misleading, it is certainly better to omit the unit in the revised version of the paper.
Para 255, last sentence: This is a negative statement. Either remove this statement. If you are doubtful about the published data, don’t use it.
Reply: the senior author knew Professor Lutze in person. He was very accurate and we do not doubt his data. We simply say for clarity that the methodology was not reported. It might be better to replace the term "methodology of" by "the instruments used for" in the revised version of the paper.
Para 270, fourth line: I assume 1.06% of total salinity dataset. Salinity unit is also sometime expressed as %. So please clarify.
Reply: "1.06 % of the time from the total salinity record" would be correct. We are going to change this in the revised version.
Para 275, first line: Rewrite! It reads 0.08% salinity lost/changed in water.
Reply: see above. "of 0.08 % of the data from the salinity record." would be correct. We are going to change that.
Para 300, first line: sometimes temp in C, sometimes in K. Be consistent. in fig 2, max water temperature shows a value less than 30. Please check the values given here or check the figure.
Reply: it is a matter of common sense that temperature levels are to be reported in degree centigrade, while differences or intervals are to expressed in Kelvin. Figure 2 presents the daily mean temperatures as noted in the figure caption, while the values given in Line 296 are the extremes. We think it is unnecessary to say "-0.7°C (minimum value) to 31.8°C (maximum value)".
Para 300 last line: No need to write 1sigma each time.
Reply: we respectfully disagree. Otherwise the value can be mistaken with the total data range.
Figure 4 caption: in b panel, only one station has been plotted as only one red and blue pattern. It’s not clear what stations. I assume for Holtenau.
Reply: Reviewer 1 is right, the figure caption is ambiguous. It rather should read "Figure 4. Water level at Bottsand and Holtenau (a), temperature, and salinity during the Centennial Flood at Bottsand (b). The red arrows in (a) mark the salinity rises observed at Bottsand". We are going to change this in the revised version of the manuscript.
Para 420 first line: low air temperature in winter.
Reply: we agree and are going to add "in winter" in the revised version.
Figure 7: in text temperature changes are discussed first, but in figure it comes in the lower panel. inconsistency!
Reply: as a convention, we always plotted the salinities in the top panel (see Figures 2 and 3).
Section 4.2. title: In results and everywhere, title is focused on Schobüll . Now Husum Bight. Not consistent
Reply: Schobüll is located on the north-eastern side of part of inner Husum Bight. This has been stated in Line 112 already.
Para 600, last line: initial hypothesis of what? Not linked properly
Reply: the initial hypothesis of the present study has been given in Line 66. We could add a sentence in Line 601, at the end of the paragraph, saying that "Temperatures and salinities of intertidal waters indeed showed a different variability than those of surface waters further off shore.", just for clarification.
Para 605: This is a result, not conclusion of the study
Reply: the values are repeated here to fuel the reader's imagination. They could be omitted and the sentence could read "The mean difference of on-site manually measured and data logger recorded values is deemed acceptable with reference to the profound environmental dynamics observed.", taking the risk that other readers would ask themself where in the Results section did they say that.
Citation: https://doi.org/10.5194/egusphere-2025-2672-AC1
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AC1: 'Reply on RC1', Joachim Schönfeld, 10 Oct 2025
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RC2: 'Comment on egusphere-2025-2672', Anonymous Referee #2, 23 Sep 2025
The manuscript entitled “Hydrography of intertidal environments in Schleswig-Holstein, Germany” by Schönfeld et al. reports on a study assessing the current status of marine marginal environments using a 36-month time series of abiotic variables measured from two systems located at the Baltic Sea and the North Sea. The authors used a large temporal dataset resulting from an impressive sampling effort. The authors also reported changes in salt marsh and oyster occurrence. This is an interesting and important article. It offers valuable insights into short and long-term changes in marginal habitats. The contribution of this research to filling out gaps on the impacts of global change on fragile ecosystems is well-described and meets the criteria laid down for publication in Biogeosciences. The manuscript is generally well-written and could be accepted after some revisions. My main concern is about the lack of information regarding the ecology of salt marshes and Pacific oyster in the Introduction. Responses of these to organisms to extreme events are indeed discussed. The Materials and Methods section should also provide details about the sampling strategy employed to document biotic responses (salt marsh and Pacific oyster populations) to extreme events. Finally, the conclusion is too long, and in some instances, this section presents information that should appear in the Results section (For instance, see lines 604-606 and lines 640-642).
Citation: https://doi.org/10.5194/egusphere-2025-2672-RC2 -
AC2: 'Reply on RC2', Joachim Schönfeld, 10 Oct 2025
RC2: 'Comment on egusphere-2025-2672', Anonymous Referee #2, 23 Sep 2025
The manuscript entitled “Hydrography of intertidal environments in Schleswig-Holstein, Germany” by Schönfeld et al. reports on a study assessing the current status of marine marginal environments using a 36-month time series of abiotic variables measured from two systems located at the Baltic Sea and the North Sea. The authors used a large temporal dataset resulting from an impressive sampling effort. The authors also reported changes in salt marsh and oyster occurrence. This is an interesting and important article. It offers valuable insights into short and long-term changes in marginal habitats. The contribution of this research to filling out gaps on the impacts of global change on fragile ecosystems is well-described and meets the criteria laid down for publication in Biogeosciences.
Reply: we thank the Reviewer 2 for the positive review appreciate the recognition of our efforts to create the time series presented in this paper.
The manuscript is generally well-written and could be accepted after some revisions. My main concern is about the lack of information regarding the ecology of salt marshes and Pacific oyster in the Introduction.
Reply: the ecology of the salt marshes is beyond the scope of the present study. Geochemical microbial and faunistic data would have to be included, which are mostly not available. The floral successions have been documented in the literature much better. They are of relevance to the present study because halophytes directly respond to the hydrographical dynamics we have captured, e.g. inundation frequency. Therefore, we have summarized the past and present state of the salt marshes in the 1.1 Geographical and environmental setting chapter.
Responses of these to organisms to extreme events are indeed discussed. The Materials and Methods section should also provide details about the sampling strategy employed to document biotic responses (salt marsh and Pacific oyster populations) to extreme events.
Reply: there was no intention neither a sampling strategy to document biotic responses to extreme events. It would have employed a biomonitoring scheme with short sampling intervals, which is beyond the knowledge and physical capacities of the authors. None-the-less, observations were made by accident, in particular the shell lag before the groynes off Schobüll where one could walk upon much easier than on the prevailing mud. This observation was set into a context by exploring the hydrographical data we have obtained.
Finally, the conclusion is too long, and in some instances, this section presents information that should appear in the Results section (For instance, see lines 604-606 and lines 640-642).
Reply: indeed, the Conclusion chapter could be shortened in places. The values in lines 604 to 606 were repeated to fuel the reader's imagination. They could be omitted, taking the risk that other readers would ask themself where in the Results section did they say that..
Citation: https://doi.org/10.5194/egusphere-2025-2672-AC2
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AC2: 'Reply on RC2', Joachim Schönfeld, 10 Oct 2025
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Joachim Schönfeld
Hermann W. Bange
Helmke Hepach
Svenja Reents
The requested preprint has a corresponding peer-reviewed final revised paper. You are encouraged to refer to the final revised version.
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I am positively surprised to see such a long and detailed hydrographic study from the North Sea and Baltic Sea coasts of Schleswig-Holstein. In the context of global warming, such baseline studies are crucial for understanding the effects and consequences of rising sea levels. Schleswig-Holstein may seem less prominent compared to major coastal areas like New York City, but this makes the availability of such a continuous record even more impressive and valuable for future research.
This study is of high quality, and I strongly recommend publication. I have only a few major comments and suggestions:
Overall, this is an impressive study that will serve as an important reference for future coastal monitoring. I hope the authors will continue this valuable time-series work for many years to come.