Measurement of Turbidity and Total Suspended Matter in the Albufera of Valencia Lagoon (Spain) Using Sentinel-2 Images

Round 1

Reviewer 1 Report

This paper discusses the measurement of turbidity and TSS in the lagoon using Sentinel-2 images. This is a valuable study, as there are not many studies on the separation of organic and inorganic components of TSS. However, in the following points. The argument in this paper is judged to be very vague. Therefore, I regret to inform you that the application will be rejected.

1.      This research uses algorithms from past research, and its novelty is very weak. What is the novelty?

2.      If you assume that [POM] and [PIM] can be separated, we must explain what kind of optical background allows them to be separated. At the very least, it should be verified after proposing an optical algorithm. Your explanation is very vague.

3.      The Chla algorithm using around 705 nm has a lot of research. In particular, two-wavelength algorithms of 665nm and 705nm and three-band algorithm have been proposed. Why aren't such algorithms tried as indicators of organic matter?

4.      Isn't the 665nm single-band algorithm usually effective for turbidity estimation?

5.      Perhaps the important parameter is the backscattering coefficient (bb) for inorganic SS and the absorption coefficient (a) for organic SS. Therefore, it is necessary to quantitatively discuss the positions and intensities of wavelengths with respect to bb and a.

That’s all

Author Response

This paper discusses the measurement of turbidity and TSS in the lagoon using Sentinel-2 images. This is a valuable study, as there are not many studies on the separation of organic and inorganic components of TSS. However, in the following points. The argument in this paper is judged to be very vague. Therefore, I regret to inform you that the application will be rejected.

Thank you very much for your valuables comments and spending time in this review.

1. This research uses algorithms from past research, and its novelty is very weak. What is the novelty?

The novelty is that no one had ever before estimated suspended solids in the Albufera lagoon using sentinel-2 images, let alone separating the organic from the inorganic part. As explained in the manuscript, the development of these algorithms has powerful applications in a more efficient management of water quality by the Natural Park managers. This statement was included in section 1.

2. If you assume that [POM] and [PIM] can be separated, we must explain what kind of optical background allows them to be separated. At the very least, it should be verified after proposing an optical algorithm. Your explanation is very vague.

We have added a new paragraph in section 2.4  explaining the optical differences between organic and inorganic solids that support their separation in the present study.

2. The Chla algorithm using around 705 nm has a lot of research. In particular, two-wavelength algorithms of 665nm and 705nm and three-band algorithm have been proposed. Why aren't such algorithms tried as indicators of organic matter?

In the present study, the 705 nm band was tested for organic solids and also the other variables; the 665 nm band was not tested because, due to the trophic characteristics of the lagoon, it was decided to use the red-edge bands. This is explained also in section 2.4 and in discussion.

3. Isn't the 665 nm single-band algorithm usually effective for turbidity estimation?

We add a explain of this band in the first part of discussion.

5. Perhaps the important parameter is the backscattering coefficient (bb) for inorganic SS and the absorption coefficient (a) for organic SS. Therefore, it is necessary to quantitatively discuss the positions and intensities of wavelengths with respect to bband a.

 We have now explained in section 2.4 and discussion. The propose of discuss the response of backscattering is an interesting idea, and we will make more detailed study in other works, incorporating also results with Particulate Organic and Inorganic Carbon.

Reviewer 2 Report

Dear Author,

your work is interesting and reads rather well, so I do not have major concerns.

However, as you can see below, I think that there is some room for improvement, especially with respect to the Introduction and the Discussion sections. I hope that my comments will help you in further developing this manuscript.

Introduction

It might help expand this section by adding more details on what reasons are behind the selection of the Albufera case study (what are the major challenges in the area? what is understudied there, etc.). This will help in showing the novelty of this research, as well as its impact at the local scale. I understand that this point is somehow addressed in the description of the case study, but I suggest reporting a few comments also in the Introduction

Materials and Methods

In Figure 1, please use different colors for the National Park delineation, as green is not clearly recognizable. Where are P1 and P2 in this map?

What is the hypothesis behind selecting satellite images from 2018, 2021, 2022 and 2023? Maybe a short comment on that can help readers better understand the study rationale.

Results

I suggest creating a table to summarize data reported in lines 188-217, as this will improve the text readability.

Please improve the quality of the graphs.

Discussion

Please describe more in detail what could be the reasons behind the differences between your results and the available literature. This might help readers better understand what model performs better/worse in what conditions.

I would like to see some more comments on the quality of the dataset (e.g., do you have enough data? were they acquired with the same conditions, and following the same protocol? what quality control was performed?). As the results highly depend on this dataset, readers should be provided with as many details as possible. 

Conclusions

You stated "Our results also highlight the importance of further investigating the role of inorganic solids in the Albufera, especially in windy conditions that may affect the resuspension of solid material in the sediment." Please provide some comments on what might be the next steps to address this issue, apart from collaborating with other scholars (which is a rather vague statement).

Data availability

Please consider sharing the data associated with the study in an open repository, as this will guarantee the reproducibility of your work, which is paramount in science.

Suggested references (to be considered only if relevant)

Cavallo, C., Papa, M. N., Gargiulo, M., Palau-Salvador, G., Vezza, P., & Ruello, G. (2021). Continuous monitoring of the flooding dynamics in the Albufera Wetland (Spain) by Landsat-8 and Sentinel-2 datasets. Remote Sensing, 13(17), 3525.

Quang, N. H., Nguyen, M. N., Paget, M., Anstee, J., Viet, N. D., Nones, M., & Tuan, V. A. (2022). Assessment of Human-Induced Effects on Sea/Brackish Water Chlorophyll-a Concentration in Ha Long Bay of Vietnam with Google Earth Engine. Remote Sensing, 14(19), 4822.

English is fine

Author Response

Dear Author,

your work is interesting and reads rather well, so I do not have major concerns.

However, as you can see below, I think that there is some room for improvement, especially with respect to the Introduction and the Discussion sections. I hope that my comments will help you in further developing this manuscript.

Thank you very much for your detailed review. We have substantially improved the discussion and other points considered by the reviewer 1 also.

Introduction

It might help expand this section by adding more details on what reasons are behind the selection of the Albufera case study (what are the major challenges in the area? what is understudied there, etc.). This will help in showing the novelty of this research, as well as its impact at the local scale. I understand that this point is somehow addressed in the description of the case study, but I suggest reporting a few comments also in the Introduction.

We have added new information at the end of section 1 to explain the reasons for the choice of the study area.

Materials and Methods

In Figure 1, please use different colors for the National Park delineation, as green is not clearly recognizable. Where are P1 and P2 in this map?

We have changed the hue and colors of the figures to improve the quality. We add a explanation about sample point P1 & P2.

What is the hypothesis behind selecting satellite images from 2018, 2021, 2022 and 2023? Maybe a short comment on that can help readers better understand the study rationale.

We write a paper with previous data of other water bodies and obtain a preliminary equation that we revised now with more data for Albufera lagoon, an hypertrophic shallow lake. We add a explanation in the introduction.

Results

I suggest creating a table to summarize data reported in lines 188-217, as this will improve the text readability.

We added in section 3 Table 3 with the descriptive statistics.

Please improve the quality of the graphs.

We have changed the colors and improved the figures.

Discussion

Please describe more in detail what could be the reasons behind the differences between your results and the available literature. This might help readers better understand what model performs better/worse in what conditions. I would like to see some more comments on the quality of the dataset (e.g., do you have enough data? were they acquired with the same conditions, and following the same protocol? what quality control was performed?). As the results highly depend on this dataset, readers should be provided with as many details as possible. 

We modified the discussion according also with reviewer 1 and add more information about this aspects.

Conclusions

You stated "Our results also highlight the importance of further investigating the role of inorganic solids in the Albufera, especially in windy conditions that may affect the resuspension of solid material in the sediment." Please provide some comments on what might be the next steps to address this issue, apart from collaborating with other scholars (which is a rather vague statement).

We rewrite the conclusions section according to the new aspects presented in the manuscript.

Data availability

Please consider sharing the data associated with the study in an open repository, as this will guarantee the reproducibility of your work, which is paramount in science.

We agree with this suggestion, but we will publish the dataset when we have finished another works in process.

Suggested references (to be considered only if relevant)

Cavallo, C., Papa, M. N., Gargiulo, M., Palau-Salvador, G., Vezza, P., & Ruello, G. (2021). Continuous monitoring of the flooding dynamics in the Albufera Wetland (Spain) by Landsat-8 and Sentinel-2 datasets. Remote Sensing, 13(17), 3525.

Quang, N. H., Nguyen, M. N., Paget, M., Anstee, J., Viet, N. D., Nones, M., & Tuan, V. A. (2022). Assessment of Human-Induced Effects on Sea/Brackish Water Chlorophyll-a Concentration in Ha Long Bay of Vietnam with Google Earth Engine. Remote Sensing, 14(19), 4822.

Thank you, we have reviewed and the fist one is about the ricefields around the Albufera lagoon and have incorporated in another work focused on hydrology of ricefields.

The second one is related to pigments, and are not the scope of this manuscript.