Review Reports - Reduction of Internal Phosphorus Load in New Lakes by Pretreatment of the Former Agricultural Soil—Methods, Ecological Results and Costs

Round 1

Reviewer 1 Report

Reviewer’s Comments on the Paper Entitled “Reduction of internal Phosphorus load in new lakes by pretreatment of the former agricultural soil”

I have gone through the manuscript of the above paper. This paper focuses on reduction of internal Phosphorus load in new lakes established on fertilized land formerly used for agricultural purposes by three simple and cost-effective soil pretreatments. The authors concluded that that the release of P when establishing new lakes on former agricultural soil can be minimized using simple and cost-effective methods.

The study is interesting. The authors have synthesized the information nicely. The scope of the paper is well presented. Similarly, the question of the study is clear. Here I provided some minor comments that need to be considered during the revision.

Minor comments:

Abstract: Though the main aim is the comparison of three simple and cost-effective soil pretreatments, it is not directly mentioned in the abstract section. e.g., which method is the best?

Line 106-114: The objects are not clearly stated. What is novelty of the work compared to the other studies? Why did not you mention the N and Fe in the abstract? I recommend to rewrite this section.

Line 128: Please add the landuse map of study area.

Figure 1: please re scale the y to allow representing the better figures.

Figure 2: please move the figure after citation in the text

Please strengthen the conclusion. I believe there is much more to conclude from his work.

Author Response

Dear Reviewer, I hereby resubmit the revised manuscript titled:

“Reduction of Internal Phosphorus Load in New Lakes by Pretreatment of the Former Agricultural Soil – Methods, Ecological Results and Costs”.

The following reply will address answers to the review comments after 1. revision on the paper previously entitled “Reduction of internal Phosphorus load in new lakes by pretreatment of the former agricultural soil”.

The revised manuscript is attached

and below the reply to this reviewer report follow the replies to the other review reports, as a context to changes in the attached file. replies are colored red.

We thank you very much for the valuable comments, recommendations and insights. We have tried to address all comments to the best of our ability and understanding. Below you find all reviewer comments followed by our revisions, answers to comments and arguments for the choices made in the revised manuscript submitted. We hope and believe that these changes will sufficiently improve the paper qualifying it for publication.

Reply Review report:

Comments and Suggestions for Authors

Reviewer’s Comments on the Paper Entitled “Reduction of internal Phosphorus load in new lakes by pretreatment of the former agricultural soil”

Minor comments:

Abstract: Though the main aim is the comparison of three simple and cost-effective soil pretreatments, it is not directly mentioned in the abstract section. e.g., which method is the best?

Changes have been made to Line 25-26 and 31 to clarify the aim to compare the effect of the pretreatment methods. Since all tested pretreatments stopped the release of P at this site, further studies on other soil types are required to be able to determine which method will be best suited under the prevailing conditions.

Line 106-114: The objects are not clearly stated. What is novelty of the work compared to the other studies? Why did not you mention the N and Fe in the abstract? I recommend to rewrite this section.

Changes have been made to the abstract where N and Fe are included in Line 25-26, and a sentence describing the aim of the pretreatments have been included in the section “These pretreatments were applied to decrease P release following flooding and investigate if these methods constitute tools able to alleviate rapid eutrophication of reservoirs and possibly avoid or postpone the need of lake restorations after establishment” Line 120-123).

Line 128: Please add the landuse map of study area.

The Land use of the catchment is now included in the revised Figure 1, and the information is stated in the method section 2.1. Line 140-142.

Figure 1: please re scale the y to allow representing the better figures.

We assume that the comment refers to Figure 3?
The y-axis of frame A of Figure 3 is now rescaled to allow better visualization of both the P-flux of the control and pretreatments

Figure 2: please move the figure after citation in the text

Figure 1, Figure 2 and Figure 3 are now inserted after the first citation

Please strengthen the conclusion. I believe there is much more to conclude from his work.

The conclusion is expanded to include the limited P release from the untreated soil and the pretreatments effect on Fe and N release “The P release of the untreated agricultural soil was limited to the first 100 days of inundation and only a small fraction of the potentially mobile-P pool of the soil was released indicating that some agricultural land could be inundated without posing a threat of severe nutrient release and that the potentially mobile-P pool may be overestimated by the extraction procedure. Moreover, dissolution of Fe from CFH-12 was limited, suggesting that the product could be applied to alleviate P release from shallow lakes without immediate risk of toxic effects. Soil pretreatment of all three methods affect the N exchange between soil and water, most likely by limiting the availability of labile organic compounds and CFH-12 may initially constitute an electron source increasing ammonification.” Line 558-566.

Review report 2

Comments and Suggestions for Authors

This is a very nice paper about possible methods of reduction of P release from flooded agricultural soils after re-establishment of lakes. The paper is well prepared. The results are described and discussed with details. Together with estimated costs the paper presents a full perspective of applying the proposed methods in the environment.

However, there are 2 general issues which I believe the Authors should consider:

The term „new lakes” is confusing. I suggest „reservoirs” for newly created water bodies. This would be much more clear.

The designation “new lake” is retained since the study is performed as part of a project about new lakes established with a variety of purposes, not only as a water storage reservoir. Reservoir may refer to water storage facilities not characterized as lakes due to e.g. impermanent water coverage. The new lakes are reestablished where former reclaimed natural lakes were placed, some are established specifically to improve biodiversity, others are leftovers of mineral excavations or technical facilities and reservoirs with the aim to retain nutrients and to store water. “New lakes” are in this context used to broadly include these diverse manmade permanent waterbodies. “reservoir” is though included as a keyword Line 38.

The Authors should refer to potential toxicity of iron (or its lack).

References to the toxic effects of Fe is added to the introduction “Elevated Fe concentrations due to lake restoration measures can lead to toxic effects in both plants and animals (Bakker et al. 2016). Line 72-73.
The issue of potential toxicity of Fe is further discussed in the discussion ”The dissolved Fe could potentially lead to toxic effects, however, the low DFe release compared to control soil indicated no immediate risk of toxic effects to flora and fauna in the water column posed from pretreatment with CFH-12 (Bakker et al. 2016)” Line 464-466.

The way the experimental design was described is somehow confusing to me and forced me to read the “Materials and methods” section few times. The most confusing is “In-situ soil-water flux”. To me it means, the flux was measured in situ. But it wasn`t. Something like "Nutrients and Fe flux from inundated soil" would be less confusing? “Long term incubation experiment” does not reflect meaning of this experiment. I suppose “Flooding experiment” or something similar would be more informative and less confusing. Please consider this issue. Adding these two types of experiments in the Fig. 1 would be also very helpful!

The designation “in situ soil-water flux” are changed into “inundated soil flux”/”inundated soil experiment” and the designation of “long-term incubation experiment” is changed to “flooding experiment” as recommended
Figure 1 is revised as recommended

I have number of detailed but "small" questions, mainly to the way the methods were described, and doubts which I listed below:

Line 29. Consider „land” instead of „soil”.

Revised as requested

Line 97. “Stability” instead of “capacity” would be more appropriate here.

Revised as requested

Line 98-100. Why is CFH-12 less redox sensitive? Please explain here. Please define what this material is. Is it amorphous Fe(OH)₃?

Lyngsie et al. (2014) found through X-ray diffraction analysis (XRD) CFH-12 to consist of poorly ordered Fe-oxides with a high proportion of oxalate extractable Fe. CFH-12 was also shown to contain considerable amounts of Ca and Mg carbonates. Fuchs et al. (2018) found CFH-12 to be less redox sensitive compared to Fe(OH)₃ since cores added CFH-12 did not release significantly more Fe compared to control sediment under anoxic conditions, while this was the case of Fe(OH)₃. They also found that CFH-12 does not release sorped P under anoxic conditions, however, no explanation concerning the composition of CFH-12 to explain the lower redox sensitivity was given.
The characterization from Lyngsie et al. 2014 of CFH-12 as “consisting of poorly ordered Fe oxides containing magnesium (Mg) and Ca carbonates” have been added to Line 106-107.

Line 104. On the other hand, in reductive conditions typically found in wetlands during flooding, limestone was described to effectively reduce P mobility in soils (https://doi.org/10.1016/S0925-8574(99)00027-0).

This comment has been considered and the statement is changed by adding “…limestone to effectively reduce P mobility under reduced conditions typically prevalent in flooded soils (Ann et al. 1999)” at Line 113-115.

Line 137. (1) Title of section 2.2. should be „Experimental site and soil treatments” or something similar to indicate the fact, that description of treatments is provided here. If not, consider adding one separate subsection just for pretreatments (2) I would like to see in this section more information about the sand used (eg. composition; you refer to low content of Fe in the discussion), the same for CFH-12.

Title of section 2.2. changed to “Experimental site and soil treatments” as recommended
In relation to the Fe content of the sand, this was measured during the sequential extraction in this study and is now stated in the results at Line 307. The grain size and information of specific surface area of CFH-12 is included in Line 169 as well as the information added in the introduction from Lyngsie et al. 2014, stating the composition of CFH-12 of poorly ordered Fe oxide and Mg and Ca carbonates.

Line 54 – Consider adding „metals” after „with” („strong association with metals, eg. …”)

Revised as requested

Line 61 – „hydr-” instead of „Hydr-”

Revised as requested

Fig. 1. An arrow connecting frames (analysis and experiments ) with experimental site would make the figure and the experimental design more clear. To be consistent, this figure should also provide some general information about what was measured in the water samples (station W).

The recommendations are included in the revised Figure 1, which is split into 4 frames connected with arrows and information about water sampling at W is provided.

Fig 1 on the page 8 should be Figure 3.

Revised as requested

Line 146. What was the estimated amount of sand added per m² of the soil? Please add this information in the paper. In this form this would be comparable with dosage given for CFH-12 and would allow the reader to better follow your discussion about costs of both materials.

The amount of sand added is now included in Line 165. Corresponding to 99 kg m^-2

Line 169-173. Data on plant available P for this soil was not provided in the paper. It was mentioned again in line 429, but I could not find the values in the paper.

Data on plant available P was provided as the P number in Table 1 and is now included in the result section “The Olsen-P in the untreated soil of the plow layer was 0.013-0.029 mg P g DW^-1 within the experimental site.” Line 281.

Line 181-183. I suggest adding some navigation to further sections. For example: „ (…) were incubated in a 207 days …… flux experiment (see section 2.4.2 for details) (….)” and „were sliced in depth intervals and extracted….. (see section 2.4.3 for details).”.

Navigation to following sections are added as recommended

Line 189. Why 15 C degree? Please explain. What was the interval for nutrients flux? Please add this information in the paper. In this section I would also like to see detailed explanation how was the flux calculated, including the “cumulative” flux.

Temperatures of 15 C degree was used to approximate the average temperature of the summer season (1/5-30/9) where the efflux of P from the soil can be expected to be most important for the ecological state of the lake, this explanation is added in the method section Line 209.
Explanations of interval between flux sampling and calculation of the flux is extended “Soil-water fluxes of nutrients were measured at regular intervals 21 times during the experiment, initially measured 3-2 times a week gradually extended to approximately once every second week at the end of the experiment. The fluxes were calculated as the difference between initial amounts and amounts present at the following sampling, with each end amount serving as the initial amount of the following flux interval, constituting a continual flux corrected for amounts removed during sampling and added to keep the volume of water constant. The fluxes between each sampling was presented as cummulated fluxes of each core.” Line 211-216

Line 203. Please repeat again here, when the cores were taken for subsequent incubation experiment.

As recommended, it is indicated that the cores were collected prior to flooding and a citation to section 2.4.1. describing the core sampling is included.

Line 212-218. (1) According to my knowledge, nrP is considered non-mobile fraction (non-reactive), whereas NaOH-DIP is mobile. (2) It is not clear how the HA-P-NaOH was determined. Please add this information in the paper.

The definition of mobile-P from Reitzel 2005 is used, defining the potentially mobile-P pool as the sum of H₂O-DIP, BD-DIP, H₂O-nrP, BD-nrP and NaOH-nrP. nrP is non-reactive to molybdate-complexing but consists of poly-P and labile organic compounds, some of which easily oxidizes releasing molybdate reactive DIP, thus considered easily decomposable and mobile in lake sediments. In the extraction procedure utilized mobile-P associated to reducible Fe was distinguished by the BD extraction from non-mobile Al bound P in the NaOH-DIP fraction.
An extended explanation of the determination of HA-P-NaOH is added “Then addition of NaOH extracted P associated to e.g. Al (P-NaOH) and P bound in humic acids (HA-P-NaOH), separated by acidification and filtration on Gf/C filters (1.2 µm) subsequently combusted and determined as TP” Line 240.

Line 230 and section 2.6 in general. (1) It would advisable to add here, what was the aim of doing monitoring of water quality after the reservoir was established. When I started to read the paper I thought, this was done to observe the trophy development in a very initial period of the lake functioning. Then I realised that the results were placed in Table 1 as means, with some lake`s characteristics, which suggests that this monitoring was conducted just to characterize the lake in general. Thus, I believe this should be clearly claimed, what was the aim of performing measurements of the lake water quality. (2) How were DOC and chlorophyll measured? Please add this information in the paper. (3) Were water samples taken from the surface? Of from the near-bottom “layer”? Or as integrated samples? Please provide this information in the paper. (4) In Table 1, where results of these measurements are reported, also sulphate concentration is provided. Please add sulphates to the list of parameters in section 2.6 together with method of determination. (5) Please add info, what was the depth at station “W” (the max depth is given in the Table 1, but it would be more comfortable to have this depth given in this section).

The aim of the water sampling is specified in section 2.6. “ … to characterize the water quality of Lake Roennebaek, see Table 1” Line 261.
Methods for determination of DOC, Chlorophyl-a, total alkalinity and sulphate is added as requested, Line 263-268.
As requested, it is stated that the water samples were collected from the bottom water and the depth at W is stated, Line 263

Line 237. Statistical analysis is not clear. Was one way ANOVA used to compare the cumulative flux calculated for the entire incubation period? This is not clear. What was the “average daily flux”? Was this just an average from all the daily fluxes recorded within the incubation period? Please explain in the text.

The one-way ANOVA was used to compare the cumulated fluxes after 207 days incubation (at the end of the experiment)
The average daily flux refers to the flux of the flooding experiment 180 days after flooding and the flux of the inundated experiment after 180 days inundation. The “average” is due to measurements on several cores not a daily flux averaged over the entire incubation of the flooding experiment. These fluxes are presented in table 2. The explanation of Section 2.7. is revised.

Line 264. It is not clear what “organic content” is. This is probably LOI. However, when reading this paragraph I first thought it is organic P pool. Moreover, LOI was not mentioned to be measured in the profiles of treated soils (section 202).

The determination of LOI in each depth interval is mentioned in Section 2.4.3. Line 247.
The designation “organic content” is changed to LOI in Line 302 and 303.

Line 271. (1) Please provide results from ANOVA in the pictures A, B, C and D (results of F tests with degrees of freedom). (2) No data for TDP are presented here, although it was measured according to the information in section 194. In the Discussion You mention that TDP was dominated by DIP. If You believe adding TDP will not be informative, just add a caveat below the Fig. 3 why TDP was not presented here. The same comment refers to Table 2. (3) Please add an enlarged figure A to show how DIP flux looked for treatments.

I am not completely sure what was meant by (1), but I have now designated statistical significant differences between treatments in the revised Figure 3 and added F, degrees of freedom and p-values in the Figure text.
A caveat is included in the Figure description of Figure 3 and Table 2 “TDP was not included since 99% of TDP was constituted by DIP and no extra information would follow from including TDP in the figure.”.

Line 309. Word “estimated” is confusing and raises the question "How was it estimated and how precise this estimation was?" Consider “calculated” instead. Was this the “average daily flux” mentioned in the line 240?

“estimated” is changed to “calculated” to avoid confusion
Yes, the average daily flux mentioned in Section 2.7. referred to this flux, which now is designated “daily flux 180 days after flooding”.

Line 327. Should it be “According to our results…”?

No, this was a mistake and now removed

Line 387. “P released” - should be removed.

Another typo, now removed

Review report 3

Reduction of internal phosphorus load in new lakes by pretreatment of the former agricultural soil (Review) The strength of the research was performing the experiment using several methods, determining the ecological effect and estimating costs. I have no objections to the research methodology. The obtained results were discussed and their impact on the possibility of reducing eutrophication of lakes was determined. The results are presented in a fairly legible way using tables and charts. The research was conducted in Danish conditions, but I think the results may be helpful in counteracting the effects of eutrophication in other countries of the region.

Remarks 1) Please consider changing the title of the paper (for example): Reduction of Internal Phosphorus Load in New Lakes by Pretreatment of the Former Agricultural Soil – Methods, Ecological Results and Costs

The comment has been taken into consideration and the title have been changed accordingly. New title “Reduction of Internal Phosphorus Load in New Lakes by Pretreatment of the Former Agricultural Soil – Methods, Ecological Results and Costs”.

2) I suggest that Figure 1 should be titled (e.g.) ‘The experimental site’ and the word ‘Explanations’ should precede the descriptions (lines 129-136). Include figure 1 in subsection 2.2.

The revised Figure 1 is now titled, as recommended, with the title “Lake Roennebaek overview” and Frame C) specifically views the experimental site.
Figure 1 is moved to Section 2.2. and ‘Explanations’ are added to the figure description (which is revised slightly due to changes of Figure 1) as suggested, Line 151.

3) Differences: Lake area 7.9 ha (table 1) or 8 ha (line 119)? What is correct?

The average lake area is 7.9, however the area will variate during the year due to large seasonal water influx differences. Line 134 is now changed to 7.9.

4) It should changed: … Pretreating Lake Roennebaek (Line 423) - … pretreating Lake Roennebaek

This typo is now changed

5) I express my doubt whether the Authors were able to thoroughly analyze 108 literature items.

we have not addressed this comment

Reviewer 2 Report

However, there are 2 general issues which I believe the Authors should consider:

The term „new lakes” is confusing. I suggest „reservoirs” for newly created water bodies. This would be much more clear.
The Authors should refer to potential toxicity of iron (or its lack).
The way the experimental design was described is somehow confusing to me and forced me to read the “Materials and methods” section few times. The most confusing is “In-situ soil-water flux”. To me it means, the flux was measured in situ. But it wasn`t. Something like "Nutrients and Fe flux from inundated soil" would be less confusing? “Long term incubation experiment” does not reflect meaning of this experiment. I suppose “Flooding experiment” or something similar would be more informative and less confusing. Please consider this issue. Adding these two types of experiments in the Fig. 1 would be also very helpful!

I have number of detailed but "small" questions, mainly to the way the methods were described, and doubts which I listed below:

Line 29. Consider „land” instead of „soil”.

Line 97. “Stability” instead of “capacity” would be more appropriate here.

Line 98-100. Why is CFH-12 less redox sensitive? Please explain here. Please define what this material is. Is it amorphous Fe(OH)₃?

Lin3 54 – Consider adding „metals” after „with” („strong association with metals, eg. …”)

Line 61 – „hydr-” instead of „Hydr-”

Fig 1 on the page 8 should be Figure 3.

Line 169-173. Data on plant available P for this soil was not provided in the paper. It was mentioned again in line 429, but I could not find the values in the paper.

Line 203. Please repeat again here, when the cores were taken for subsequent incubation experiment.

Line 327. Should it be “According to our results…”?

Line 387. “P released” - should be removed.

Author Response

Dear Reviewer, I hereby resubmit the revised manuscript titled:

“Reduction of Internal Phosphorus Load in New Lakes by Pretreatment of the Former Agricultural Soil – Methods, Ecological Results and Costs”.

The revised manuscript is attached

and below the reply to this reviewer report follow the replies to the other review reports, as a context to changes in the attached file. replies are colored red.

Reply review report

Comments and Suggestions for Authors

However, there are 2 general issues which I believe the Authors should consider:

The term „new lakes” is confusing. I suggest „reservoirs” for newly created water bodies. This would be much more clear.

The designation “new lake” is retained since the study is performed as part of a project about new lakes established with a variety of purposes, not only as a water storage reservoir. Reservoir may refer to water storage facilities not characterized as lakes due to e.g. impermanent water coverage. The new lakes are reestablished where former reclaimed natural lakes were placed, some are established specifically to improve biodiversity, others are leftovers of mineral excavations or technical facilities and reservoirs with the aim to retain nutrients and to store water. “New lakes” are in this context used to broadly include these diverse manmade permanent waterbodies. “reservoir” is though included as a keyword Line 38.

2. The Authors should refer to potential toxicity of iron (or its lack). References to the toxic effects of Fe is added to the introduction “Elevated Fe concentrations due to lake restoration measures can lead to toxic effects in both plants and animals (Bakker et al. 2016). Line 72-73.The issue of potential toxicity of Fe is further discussed in the discussion ”The dissolved Fe could potentially lead to toxic effects, however, the low DFe release compared to control soil indicated no immediate risk of toxic effects to flora and fauna in the water column posed from pretreatment with CFH-12 (Bakker et al. 2016)” Line 464-466.

3.The way the experimental design was described is somehow confusing to me and forced me to read the “Materials and methods” section few times. The most confusing is “In-situ soil-water flux”. To me it means, the flux was measured in situ. But it wasn`t. Something like "Nutrients and Fe flux from inundated soil" would be less confusing? “Long term incubation experiment” does not reflect meaning of this experiment. I suppose “Flooding experiment” or something similar would be more informative and less confusing. Please consider this issue. Adding these two types of experiments in the Fig. 1 would be also very helpful!The designation “in situ soil-water flux” are changed into “inundated soil flux”/”inundated soil experiment” and the designation of “long-term incubation experiment” is changed to “flooding experiment” as recommended. Figure 1 is revised as recommended

I have number of detailed but "small" questions, mainly to the way the methods were described, and doubts which I listed below:

Line 29. Consider „land” instead of „soil”.

Revised as requested

Line 97. “Stability” instead of “capacity” would be more appropriate here.

Revised as requested

Line 98-100. Why is CFH-12 less redox sensitive? Please explain here. Please define what this material is. Is it amorphous Fe(OH)₃?

Lyngsie et al. (2014) found through X-ray diffraction analysis (XRD) CFH-12 to consist of poorly ordered Fe-oxides with a high proportion of oxalate extractable Fe. CFH-12 was also shown to contain considerable amounts of Ca and Mg carbonates. Fuchs et al. (2018) found CFH-12 to be less redox sensitive compared to Fe(OH)₃ since cores added CFH-12 did not release significantly more Fe compared to control sediment under anoxic conditions, while this was the case of Fe(OH)₃. They also found that CFH-12 does not release sorped P under anoxic conditions, however, no explanation concerning the composition of CFH-12 to explain the lower redox sensitivity was given.
The characterization from Lyngsie et al. 2014 of CFH-12 as “consisting of poorly ordered Fe oxides containing magnesium (Mg) and Ca carbonates” have been added to Line 106-107.

This comment has been considered and the statement is changed by adding “…limestone to effectively reduce P mobility under reduced conditions typically prevalent in flooded soils (Ann et al. 1999)” at Line 113-115.

Title of section 2.2. changed to “Experimental site and soil treatments” as recommended
In relation to the Fe content of the sand, this was measured during the sequential extraction in this study and is now stated in the results at Line 307. The grain size and information of specific surface area of CFH-12 is included in Line 169 as well as the information added in the introduction from Lyngsie et al. 2014, stating the composition of CFH-12 of poorly ordered Fe oxide and Mg and Ca carbonates.

Line 54 – Consider adding „metals” after „with” („strong association with metals, eg. …”)

Revised as requested

Line 61 – „hydr-” instead of „Hydr-”

Revised as requested

The recommendations are included in the revised Figure 1, which is split into 4 frames connected with arrows and information about water sampling at W is provided.

Fig 1 on the page 8 should be Figure 3.

Revised as requested

The amount of sand added is now included in Line 165. Corresponding to 99 kg m^-2

Line 169-173. Data on plant available P for this soil was not provided in the paper. It was mentioned again in line 429, but I could not find the values in the paper.

Data on plant available P was provided as the P number in Table 1 and is now included in the result section “The Olsen-P in the untreated soil of the plow layer was 0.013-0.029 mg P g DW^-1 within the experimental site.” Line 281.

Navigation to following sections are added as recommended

Temperatures of 15 C degree was used to approximate the average temperature of the summer season (1/5-30/9) where the efflux of P from the soil can be expected to be most important for the ecological state of the lake, this explanation is added in the method section Line 209.
Explanations of interval between flux sampling and calculation of the flux is extended “Soil-water fluxes of nutrients were measured at regular intervals 21 times during the experiment, initially measured 3-2 times a week gradually extended to approximately once every second week at the end of the experiment. The fluxes were calculated as the difference between initial amounts and amounts present at the following sampling, with each end amount serving as the initial amount of the following flux interval, constituting a continual flux corrected for amounts removed during sampling and added to keep the volume of water constant. The fluxes between each sampling was presented as cummulated fluxes of each core.” Line 211-216

Line 203. Please repeat again here, when the cores were taken for subsequent incubation experiment.

As recommended, it is indicated that the cores were collected prior to flooding and a citation to section 2.4.1. describing the core sampling is included.

The definition of mobile-P from Reitzel 2005 is used, defining the potentially mobile-P pool as the sum of H₂O-DIP, BD-DIP, H₂O-nrP, BD-nrP and NaOH-nrP. nrP is non-reactive to molybdate-complexing but consists of poly-P and labile organic compounds, some of which easily oxidizes releasing molybdate reactive DIP, thus considered easily decomposable and mobile in lake sediments. In the extraction procedure utilized mobile-P associated to reducible Fe was distinguished by the BD extraction from non-mobile Al bound P in the NaOH-DIP fraction.
An extended explanation of the determination of HA-P-NaOH is added “Then addition of NaOH extracted P associated to e.g. Al (P-NaOH) and P bound in humic acids (HA-P-NaOH), separated by acidification and filtration on Gf/C filters (1.2 µm) subsequently combusted and determined as TP” Line 240.

The aim of the water sampling is specified in section 2.6. “ … to characterize the water quality of Lake Roennebaek, see Table 1” Line 261.
Methods for determination of DOC, Chlorophyl-a, total alkalinity and sulphate is added as requested, Line 263-268.
As requested, it is stated that the water samples were collected from the bottom water and the depth at W is stated, Line 263

The one-way ANOVA was used to compare the cumulated fluxes after 207 days incubation (at the end of the experiment)
The average daily flux refers to the flux of the flooding experiment 180 days after flooding and the flux of the inundated experiment after 180 days inundation. The “average” is due to measurements on several cores not a daily flux averaged over the entire incubation of the flooding experiment. These fluxes are presented in table 2. The explanation of Section 2.7. is revised.

The determination of LOI in each depth interval is mentioned in Section 2.4.3. Line 247.
The designation “organic content” is changed to LOI in Line 302 and 303.

I am not completely sure what was meant by (1), but I have now designated statistical significant differences between treatments in the revised Figure 3 and added F, degrees of freedom and p-values in the Figure text.
A caveat is included in the Figure description of Figure 3 and Table 2 “TDP was not included since 99% of TDP was constituted by DIP and no extra information would follow from including TDP in the figure.”.

“estimated” is changed to “calculated” to avoid confusion
Yes, the average daily flux mentioned in Section 2.7. referred to this flux, which now is designated “daily flux 180 days after flooding”.

Line 327. Should it be “According to our results…”?

No, this was a mistake and now removed

Line 387. “P released” - should be removed.

Another typo, now removed

Review report 2

Comments and Suggestions for Authors

Reviewer’s Comments on the Paper Entitled “Reduction of internal Phosphorus load in new lakes by pretreatment of the former agricultural soil”

Minor comments:

Abstract: Though the main aim is the comparison of three simple and cost-effective soil pretreatments, it is not directly mentioned in the abstract section. e.g., which method is the best?

Changes have been made to Line 25-26 and 31 to clarify the aim to compare the effect of the pretreatment methods. Since all tested pretreatments stopped the release of P at this site, further studies on other soil types are required to be able to determine which method will be best suited under the prevailing conditions.

Line 106-114: The objects are not clearly stated. What is novelty of the work compared to the other studies? Why did not you mention the N and Fe in the abstract? I recommend to rewrite this section.

Changes have been made to the abstract where N and Fe are included in Line 25-26, and a sentence describing the aim of the pretreatments have been included in the section “These pretreatments were applied to decrease P release following flooding and investigate if these methods constitute tools able to alleviate rapid eutrophication of reservoirs and possibly avoid or postpone the need of lake restorations after establishment” Line 120-123).

Line 128: Please add the landuse map of study area.

The Land use of the catchment is now included in the revised Figure 1, and the information is stated in the method section 2.1. Line 140-142.

Figure 1: please re scale the y to allow representing the better figures.

We assume that the comment refers to Figure 3?
The y-axis of frame A of Figure 3 is now rescaled to allow better visualization of both the P-flux of the control and pretreatments

Figure 2: please move the figure after citation in the text

Figure 1, Figure 2 and Figure 3 are now inserted after the first citation

Please strengthen the conclusion. I believe there is much more to conclude from his work.

The conclusion is expanded to include the limited P release from the untreated soil and the pretreatments effect on Fe and N release “The P release of the untreated agricultural soil was limited to the first 100 days of inundation and only a small fraction of the potentially mobile-P pool of the soil was released indicating that some agricultural land could be inundated without posing a threat of severe nutrient release and that the potentially mobile-P pool may be overestimated by the extraction procedure. Moreover, dissolution of Fe from CFH-12 was limited, suggesting that the product could be applied to alleviate P release from shallow lakes without immediate risk of toxic effects. Soil pretreatment of all three methods affect the N exchange between soil and water, most likely by limiting the availability of labile organic compounds and CFH-12 may initially constitute an electron source increasing ammonification.” Line 558-566.

Review report 3

The comment has been taken into consideration and the title have been changed accordingly. New title “Reduction of Internal Phosphorus Load in New Lakes by Pretreatment of the Former Agricultural Soil – Methods, Ecological Results and Costs”.

2) I suggest that Figure 1 should be titled (e.g.) ‘The experimental site’ and the word ‘Explanations’ should precede the descriptions (lines 129-136). Include figure 1 in subsection 2.2.

The revised Figure 1 is now titled, as recommended, with the title “Lake Roennebaek overview” and Frame C) specifically views the experimental site.
Figure 1 is moved to Section 2.2. and ‘Explanations’ are added to the figure description (which is revised slightly due to changes of Figure 1) as suggested, Line 151.

3) Differences: Lake area 7.9 ha (table 1) or 8 ha (line 119)? What is correct?

The average lake area is 7.9, however the area will variate during the year due to large seasonal water influx differences. Line 134 is now changed to 7.9.

4) It should changed: … Pretreating Lake Roennebaek (Line 423) - … pretreating Lake Roennebaek

This typo is now changed

5) I express my doubt whether the Authors were able to thoroughly analyze 108 literature items.

we have not addressed this comment

Reviewer 3 Report

Comments and remarks for Authors can be found in the attached file.

Comments for author File: Comments.pdf

Author Response

Dear Reviewer, I hereby resubmit the revised manuscript titled:

“Reduction of Internal Phosphorus Load in New Lakes by Pretreatment of the Former Agricultural Soil – Methods, Ecological Results and Costs”.

The revised manuscript is attached

and below the reply to this reviewer report follow the replies to the other review reports, as a context to changes in the attached file. replies are colored red.

Reply Review report:

Review report 3

The comment has been taken into consideration and the title have been changed accordingly. New title “Reduction of Internal Phosphorus Load in New Lakes by Pretreatment of the Former Agricultural Soil – Methods, Ecological Results and Costs”.

2) I suggest that Figure 1 should be titled (e.g.) ‘The experimental site’ and the word ‘Explanations’ should precede the descriptions (lines 129-136). Include figure 1 in subsection 2.2.

The revised Figure 1 is now titled, as recommended, with the title “Lake Roennebaek overview” and Frame C) specifically views the experimental site.
Figure 1 is moved to Section 2.2. and ‘Explanations’ are added to the figure description (which is revised slightly due to changes of Figure 1) as suggested, Line 151.

3) Differences: Lake area 7.9 ha (table 1) or 8 ha (line 119)? What is correct?

The average lake area is 7.9, however the area will variate during the year due to large seasonal water influx differences. Line 134 is now changed to 7.9.

4) It should changed: … Pretreating Lake Roennebaek (Line 423) - … pretreating Lake Roennebaek

This typo is now changed

5) I express my doubt whether the Authors were able to thoroughly analyze 108 literature items.

we have not addressed this comment

Review report 2

Comments and Suggestions for Authors

Reviewer’s Comments on the Paper Entitled “Reduction of internal Phosphorus load in new lakes by pretreatment of the former agricultural soil”

Minor comments:

Abstract: Though the main aim is the comparison of three simple and cost-effective soil pretreatments, it is not directly mentioned in the abstract section. e.g., which method is the best?

Changes have been made to Line 25-26 and 31 to clarify the aim to compare the effect of the pretreatment methods. Since all tested pretreatments stopped the release of P at this site, further studies on other soil types are required to be able to determine which method will be best suited under the prevailing conditions.

Line 106-114: The objects are not clearly stated. What is novelty of the work compared to the other studies? Why did not you mention the N and Fe in the abstract? I recommend to rewrite this section.

Changes have been made to the abstract where N and Fe are included in Line 25-26, and a sentence describing the aim of the pretreatments have been included in the section “These pretreatments were applied to decrease P release following flooding and investigate if these methods constitute tools able to alleviate rapid eutrophication of reservoirs and possibly avoid or postpone the need of lake restorations after establishment” Line 120-123).

Line 128: Please add the landuse map of study area.

The Land use of the catchment is now included in the revised Figure 1, and the information is stated in the method section 2.1. Line 140-142.

Figure 1: please re scale the y to allow representing the better figures.

We assume that the comment refers to Figure 3?
The y-axis of frame A of Figure 3 is now rescaled to allow better visualization of both the P-flux of the control and pretreatments

Figure 2: please move the figure after citation in the text

Figure 1, Figure 2 and Figure 3 are now inserted after the first citation

Please strengthen the conclusion. I believe there is much more to conclude from his work.

The conclusion is expanded to include the limited P release from the untreated soil and the pretreatments effect on Fe and N release “The P release of the untreated agricultural soil was limited to the first 100 days of inundation and only a small fraction of the potentially mobile-P pool of the soil was released indicating that some agricultural land could be inundated without posing a threat of severe nutrient release and that the potentially mobile-P pool may be overestimated by the extraction procedure. Moreover, dissolution of Fe from CFH-12 was limited, suggesting that the product could be applied to alleviate P release from shallow lakes without immediate risk of toxic effects. Soil pretreatment of all three methods affect the N exchange between soil and water, most likely by limiting the availability of labile organic compounds and CFH-12 may initially constitute an electron source increasing ammonification.” Line 558-566.

Review report 3

Comments and Suggestions for Authors

However, there are 2 general issues which I believe the Authors should consider:

The term „new lakes” is confusing. I suggest „reservoirs” for newly created water bodies. This would be much more clear.

The designation “new lake” is retained since the study is performed as part of a project about new lakes established with a variety of purposes, not only as a water storage reservoir. Reservoir may refer to water storage facilities not characterized as lakes due to e.g. impermanent water coverage. The new lakes are reestablished where former reclaimed natural lakes were placed, some are established specifically to improve biodiversity, others are leftovers of mineral excavations or technical facilities and reservoirs with the aim to retain nutrients and to store water. “New lakes” are in this context used to broadly include these diverse manmade permanent waterbodies. “reservoir” is though included as a keyword Line 38.

2. The Authors should refer to potential toxicity of iron (or its lack).

References to the toxic effects of Fe is added to the introduction “Elevated Fe concentrations due to lake restoration measures can lead to toxic effects in both plants and animals (Bakker et al. 2016). Line 72-73.
The issue of potential toxicity of Fe is further discussed in the discussion ”The dissolved Fe could potentially lead to toxic effects, however, the low DFe release compared to control soil indicated no immediate risk of toxic effects to flora and fauna in the water column posed from pretreatment with CFH-12 (Bakker et al. 2016)” Line 464-466.

The designation “in situ soil-water flux” are changed into “inundated soil flux”/”inundated soil experiment” and the designation of “long-term incubation experiment” is changed to “flooding experiment” as recommended
Figure 1 is revised as recommended

I have number of detailed but "small" questions, mainly to the way the methods were described, and doubts which I listed below:

Line 29. Consider „land” instead of „soil”.

Revised as requested

Line 97. “Stability” instead of “capacity” would be more appropriate here.

Revised as requested

Line 98-100. Why is CFH-12 less redox sensitive? Please explain here. Please define what this material is. Is it amorphous Fe(OH)₃?

Lyngsie et al. (2014) found through X-ray diffraction analysis (XRD) CFH-12 to consist of poorly ordered Fe-oxides with a high proportion of oxalate extractable Fe. CFH-12 was also shown to contain considerable amounts of Ca and Mg carbonates. Fuchs et al. (2018) found CFH-12 to be less redox sensitive compared to Fe(OH)₃ since cores added CFH-12 did not release significantly more Fe compared to control sediment under anoxic conditions, while this was the case of Fe(OH)₃. They also found that CFH-12 does not release sorped P under anoxic conditions, however, no explanation concerning the composition of CFH-12 to explain the lower redox sensitivity was given.
The characterization from Lyngsie et al. 2014 of CFH-12 as “consisting of poorly ordered Fe oxides containing magnesium (Mg) and Ca carbonates” have been added to Line 106-107.

This comment has been considered and the statement is changed by adding “…limestone to effectively reduce P mobility under reduced conditions typically prevalent in flooded soils (Ann et al. 1999)” at Line 113-115.

Title of section 2.2. changed to “Experimental site and soil treatments” as recommended
In relation to the Fe content of the sand, this was measured during the sequential extraction in this study and is now stated in the results at Line 307. The grain size and information of specific surface area of CFH-12 is included in Line 169 as well as the information added in the introduction from Lyngsie et al. 2014, stating the composition of CFH-12 of poorly ordered Fe oxide and Mg and Ca carbonates.

Line 54 – Consider adding „metals” after „with” („strong association with metals, eg. …”)

Revised as requested

Line 61 – „hydr-” instead of „Hydr-”

Revised as requested

The recommendations are included in the revised Figure 1, which is split into 4 frames connected with arrows and information about water sampling at W is provided.

Fig 1 on the page 8 should be Figure 3.

Revised as requested

The amount of sand added is now included in Line 165. Corresponding to 99 kg m^-2

Line 169-173. Data on plant available P for this soil was not provided in the paper. It was mentioned again in line 429, but I could not find the values in the paper.

Data on plant available P was provided as the P number in Table 1 and is now included in the result section “The Olsen-P in the untreated soil of the plow layer was 0.013-0.029 mg P g DW^-1 within the experimental site.” Line 281.

Navigation to following sections are added as recommended

Temperatures of 15 C degree was used to approximate the average temperature of the summer season (1/5-30/9) where the efflux of P from the soil can be expected to be most important for the ecological state of the lake, this explanation is added in the method section Line 209.
Explanations of interval between flux sampling and calculation of the flux is extended “Soil-water fluxes of nutrients were measured at regular intervals 21 times during the experiment, initially measured 3-2 times a week gradually extended to approximately once every second week at the end of the experiment. The fluxes were calculated as the difference between initial amounts and amounts present at the following sampling, with each end amount serving as the initial amount of the following flux interval, constituting a continual flux corrected for amounts removed during sampling and added to keep the volume of water constant. The fluxes between each sampling was presented as cummulated fluxes of each core.” Line 211-216

Line 203. Please repeat again here, when the cores were taken for subsequent incubation experiment.

As recommended, it is indicated that the cores were collected prior to flooding and a citation to section 2.4.1. describing the core sampling is included.

The definition of mobile-P from Reitzel 2005 is used, defining the potentially mobile-P pool as the sum of H₂O-DIP, BD-DIP, H₂O-nrP, BD-nrP and NaOH-nrP. nrP is non-reactive to molybdate-complexing but consists of poly-P and labile organic compounds, some of which easily oxidizes releasing molybdate reactive DIP, thus considered easily decomposable and mobile in lake sediments. In the extraction procedure utilized mobile-P associated to reducible Fe was distinguished by the BD extraction from non-mobile Al bound P in the NaOH-DIP fraction.
An extended explanation of the determination of HA-P-NaOH is added “Then addition of NaOH extracted P associated to e.g. Al (P-NaOH) and P bound in humic acids (HA-P-NaOH), separated by acidification and filtration on Gf/C filters (1.2 µm) subsequently combusted and determined as TP” Line 240.

The aim of the water sampling is specified in section 2.6. “ … to characterize the water quality of Lake Roennebaek, see Table 1” Line 261.
Methods for determination of DOC, Chlorophyl-a, total alkalinity and sulphate is added as requested, Line 263-268.
As requested, it is stated that the water samples were collected from the bottom water and the depth at W is stated, Line 263

The one-way ANOVA was used to compare the cumulated fluxes after 207 days incubation (at the end of the experiment)
The average daily flux refers to the flux of the flooding experiment 180 days after flooding and the flux of the inundated experiment after 180 days inundation. The “average” is due to measurements on several cores not a daily flux averaged over the entire incubation of the flooding experiment. These fluxes are presented in table 2. The explanation of Section 2.7. is revised.

The determination of LOI in each depth interval is mentioned in Section 2.4.3. Line 247.
The designation “organic content” is changed to LOI in Line 302 and 303.

I am not completely sure what was meant by (1), but I have now designated statistical significant differences between treatments in the revised Figure 3 and added F, degrees of freedom and p-values in the Figure text.
A caveat is included in the Figure description of Figure 3 and Table 2 “TDP was not included since 99% of TDP was constituted by DIP and no extra information would follow from including TDP in the figure.”.

“estimated” is changed to “calculated” to avoid confusion
Yes, the average daily flux mentioned in Section 2.7. referred to this flux, which now is designated “daily flux 180 days after flooding”.

Line 327. Should it be “According to our results…”?

No, this was a mistake and now removed

Line 387. “P released” - should be removed.

Another typo, now removed