Geophysical Characterization in the Shallow Water Estuarine Lakes of the Southern Everglades, Florida

Round 1

Reviewer 1 Report

The purpose of this paper is to understand the temporal and spatial variation of surface water and shallow groundwater salinity in coastal lakes. The author adopts electrical resistivity and electromagnetic methods. Then, the effects of seasonal variation, precipitation and evapotranspiration on conductivity are obtained. Finally, it clearly describes the temporal and spatial changes of salinity. This paper makes a good application and expansion for geophysical methods in the spatial distribution of conductivity of surface and shallow groundwater. The overall logic of the article is clear and the content is detailed. I recommend acceptance of this manuscript. However, improvements are needed in individual areas.

• Some legends are too large, the picture is fuzzy, and the information is unclear.
• The conversion formula from conductivity to salinity can be listed.
• The statistical information of apparent conductivity can be explained by tables, but not in the article.
• For the lake name, the format should be unified before and after, and in line 370, Westlake should be West Lake.
• If possible, water borne electrical resistivity will be better for this kind of research. Why the authors does not prefer this method in the first place.

Author Response

Dear Reviewer,

Thank you for your review of our paper. We have carefully reviewed your comments and revised the manuscript accordingly. We appreciate the valuable editorial suggestions, and we included the comments in this revised version. Our response to the major comments is provided point-by-point below.

Response: Thank you for your feedback. We rearrange the introduction part, and added short note that highlight the research significance at line 127 to 156

Point 1: Some legends are too large, the picture is fuzzy, and the information is unclear.

Response 1: We edited figure number 1 and added a new figure 7. We changed the caption details in most of the figures for clarification.

Point 2: The conversion formula from conductivity to salinity can be listed.

Response 2: The conversion formula is an empirical equation which has 17 coefficients, that’s why we cited the reference only.

Point 3: The statistical information of apparent conductivity can be explained by tables, but not in the article.

Response 3: The statistical information is limited and may not be necessary to include a new table.

Point 4: For the lake name, the format should be unified before and after, and in line 370, Westlake should be West Lake.

Response 4: We have replaced Westlake with West Lake throughout.

Point 5: If possible, water borne electrical resistivity will be better for this kind of research. Why the authors does not prefer this method in the first place.

Response 5: We did not have access to a continuous resistivity profiling system. Our electrical resistivity system is a 1-channel system only has the capability of making a limited number of spot measurements. Thus, we explored using the EM ground conductivity meter to make continuous measurements.

Author Response File: Author Response.docx

Reviewer 2 Report

Dear Authors, from my poin of view you have to check better your paper because there are some strong error on some part of the paper. I suppose it is not clear the concept of "formation factor" and how you can estimate it. Moreover, how you made the electrical data inversion? You wrote about Sounding approach...but you used Dipole-Dipole and it is not a good way to make sounding!!

I thinl your work is not a scientific work and I suggest you to read some paper about.

 

Several considerations are in the attached file

Comments for author File: Comments.pdf

Author Response

Dear Reviewer,

Thank you for your review of our paper. We have carefully reviewed your comments and revised the manuscript accordingly. We appreciate the valuable editorial suggestions, and we included the comments in this revised version. Our response to the major comments is provided point-by-point below.

Comments and Suggestions for Authors

Dear Authors,

from my point of view you have to check better your paper because there are some strong error on some part of the paper. I suppose it is not clear the concept of "formation factor" and how you can estimate it. Moreover, how you made the electrical data inversion? You wrote about Sounding approach...but you used Dipole-Dipole and it is not a good way to make sounding!!

Response: We changed the wording we used for the formation factor. The formation factor is estimated from the correlation between the inverted bulk resistivity values and the water resistivity values measured in groundwater. Formation factor in the mangrove lakes refer to the formation factor of the subsurface formation of the study area. We rewrite the sentence as “One method of estimating the formation factor of the lake bottom formation is by comparing groundwater resistivity  measured in the shallow groundwater wells with nearby values of lake bottom resistivity  modeled from the geophysical data.….” at line 440 to 443

We added a paragraph that describes the methodology as   “ Different regularization optimization techniques have been developed to invert ….. ”at line 183 193.We used 1D VES data using a Dipole- dipole array. We rewrite the paragraph in the Data Collection section at line 224 to 236. The VES was inverted as a 2-layer model, and we added a new figure 7 that shows the inversion results. The detail of the inversion result is described at line 389 to 393.

 

Line 24:  I suggest to rewrite this part because it is not well done.

Response: We rewrite the sentence as   …region by comparing the lake bottom formation resistivity inverted electrical resistivity soundings with coincident pore water resistivity measured in groundwater wells. Co…’ at line 24- 25

Figure 2; The triangles are not indicted in the map.

Response: The triangles represent the EM profile line, but as the sampling interval was close it appears as a line in the map. The triangles were replaced by colored lines in figure 1

Line 194- 195: How you make the calibration? Usually, it is possible with operator and without operator, in your case the instrument was on a small boat. Did you check the EM values acquired by EMP- 400 taking in account the distance from the main boat with motor and operator? This aspect is very important in order to obtain correct data.

Response: We calibrate the instrument on the site with the operator. During data collection the kayak was 6 m away from the boat and there was no observable effect from the boat on the EM data. We added a short note as “… since the kayak contained no conducting materials and was towed 6 m behind the skiff, little if any external effects affected the data ….” at line 213-215. However, when the boat parked to measure the depth of the water column, conductivity and salinity of the surface water, the kayak approaches the boat, and we observed a dramatic increase in the conductivity of the EM data. That’s why we introduced a smoothing filtering technique to remove the noise (spikes) by filtering the nearest 100 sample points.

We rewrite the paragraph … “ EM data often contains noise which must be removed to produce consistent results….. ”at line 270-281.

Line 196- 197: How deep was the investigation? Did you tried to estimate it? How deep is the bottom of the lake? Do you have a topographic map (DEM) of the surface bottom of the investigated area?

Response:  The depth of the lake bottom varies between 1 to 2 m. We added a short note as  “…the relationship between freshwater input and hydrochemistry of surface waters and lake-bottom groundwater in shallow (1-2 m) brackish lakes within the southern Everglades known as the Mangrove Lakes (Figure 1)... ” at line 125-127.

We measured the depth using a calibrated rod at selected points and sonar system throughout the lake. We arranged the sentence and added a note as ……”During the EM survey, at different localities and different intervals of time, the surface water conductivity, temperature, pH, and salinity were measured using a YSI water quality data sonde. Water depths were measured continuously using a sonar transducer and at spot locations using a calibrated rod.…” at line 219-222.

Line 247: Why do you used this kind of filter? which are the advantages?

Response:  We added a short note as … “ Spikes in the data often occur near the beginning and ends of collection segment when the kayak drifts close to the boat. These outliers were removed by eliminating measurements differing by greater than 3 standard deviations from a 100-sample window (Figure 3). High frequency noise is produced by the roll and pitch of the kayak caused by waves. After outlier removal, this noise was removed with a 100-point moving average convolution filter (Figure 3)……” at line 270-276. This filtering approach can produce consistent results after noise reduction and smoothing.

Line 255: Why you are writing VES sounding? You used a DD approach, and it is not an electrical sounding method, such as Wenner and Schlumberger

Response:  Dipole-dipole can be used for VES. The Dipole-dipole array was chosen after we compared the Dipole-dipole and the schlumberger array (Kiflai 2020). The Dipole-dipole array was superior compared to the schlumberger array as mentioned above. We rewrite the paragraph on the Data collection section as …… “VES surveys were conducted at spot locations in the Seven Palm and West Lake systems in July 2019 using a floating 14-electrode cable with a 1 m electrode spacing (Figure 1)….” at line 224 to 237.

Line 266: For Dipole-Dipole method, the maximum level should be n=6...an increase of n value highlights noise acquired data.

Response: Potentially for DD with increase in n value noise can be collected in the data. This rule probably applies on land, but as seen from figure 7, we consistently recorded DD measurements out to n =10. This is probably because of the low contact resistance between the brackish water and the electrodes. During our data acquisition, we measured a reciprocal measurement, and the observed error in the data was less than 3%.  For few measurements, for n-10 and 11, we masked the outlier values. We added a short note on the caption of Figure 7.

Line 275- 280: The correlation between the DD and wells data is not well described. it is not clear how you make it. Are the wells data from the same site of geophysical acquisition? which one? How many data you used for that? Moreover, the DD was made by electrode on surface water...the wells data are below the water?

Response:  Yes, both the DD and Well data are collected at the same site (Figure 1; Table 2). We modified table 2 and added in Table 2, the exact distance of the VES from the Well data.

We measured the surface water and ground water conductivity from the shallow groundwater wells (table 2). We converted the daily average ground water conductivity from the Wells to resistivity. In addition, we inverted the VES as a 2-layer model that corresponds for surface water and groundwater resistivity. Then, we calculated the formation factor from the ratio of the groundwater resistivity from the well data and VES model.

We rewrite the sentence as “ …. The formation factor for the study area was estimated using the bulk resistivity measured by the floating VES and coincident resistivity (inversely proportional to conductivity) data measured in the groundwater wells. The average daily conductivity (µS/cm) measurement in the groundwater wells was converted to resistivity, where the resistivity (Ω⋅m) = 10000/ Conductivity water (µS/cm). Then, the formation factor was calculated from the average value of the ratio of bulk resistivity modeled from the geophysical data and the pore water resistivity measured in the shallow groundwater wells. …. at line 301 to 307

Line 305: Figure 4: what is the "star"? You have to indicate in the legend of figure. Moreover, you have to write some indication of the geographic site, in order to understand where we are comparing with the map on figure 1

Response:  We mentioned the name of the Lakes in the 1^st subplot. We added a caption for the location of the well (star) in the figure

Line 329-331: Before to make consideration on the variation in the time, you have to define the error range of each measurement and after to check the variation. How you described in the text it is not clear if the variations are in the data error range or not. This point is crucial to make some final comments.

Response:  We added a short on the data analysis section on the error range as “ ….This random high frequency noise was on the order of 2-4 mS/m which is less than 1% of the field values. .. “ at line 276-277.

Line 342 and 348: Figure 5 and 6: You have to write some indication of the geographic site, in order to understand where we are comparing with the map on figure 1. Moroever the Stars are?

Response:  We mentioned the name of the Lakes in the 1^st subplot and indicated the location of the well (star) in the caption.

Linee 359 and 369: What do you mean? What do you inverted? How you did it?

where is it? How you make it? Which kind of inversion you used?

Response Line 359 and 369: In the electrical and electromagnetic method section 2, we introduced the inversion method we used at line 183 to 192. The details of the inversion were explained on the data analysis section on line 283 to 289.. We added the results of the inverse model as Figure 7; added a short note on line 389 to 393 and updated the index map figure 1.

We rewrite the sentence as “….. VES soundings data were inverted to two-layer models (water column and lake bottom resistivity) by constraining the depth of the water column using IX1DV3 software [31] The VES data were inverted using a ridge regression algorithm [31,32]. In the inversion, the water layer thickness was constrained fixed using the measured depth by a calibrated rod. In addition, the resistivity measured using a YSI probe was used as a starting model for the surface water resistivity and the lake bottom resistivity value was assumed five times higher water column resistivity..” at line 283 to 289.

Line376-377: You have to explain this consideration? Which is the correlation between boat navigation, wind and wave action?

Response:  We rewrite the sentence as High frequency noise is produced by the roll and pitch of the kayak caused by waves..” at line 274

Line 380: Figure 7: This figure is not so clear. Why you are indicating only some points? May be they are the resistivity value obtained from an inversion approach, where is it?

Response:  We added the inversion result as figure number 7. We showed the VES spot location in Figure 1, and mentioned the name of the Lakes in the 1st subplot of Figure 8

Line 383-385: This graph should be with three axis: Longitude, latitude and resistivity. Why you make only Resistivity and longitude?

Response:  We changed the caption of figure 9 and explained why we plot resistivity vs latitude  …. “West-east profile showing the inverted lake-bottom resistivity from the VES surveys. Error bars indicate the lower and upper acceptable limits derived from equivalence analysis..”Our focus is to show the uncertainty on the inverse model and to show the spatial change. The resistivity value and error bars will be merged if represented with latitude and longitude

Line 390: I suggest to be more clear about this approach: what do you are comparing? The Fomation factor is correlate with a geological formation or kind of sediment. You wrote "formation factor for coastal lake"...what do you mean? The formation factor is correlated with the porosity of the rock. I don't understand "formation factor" of a lake!!!!!!

Response: The formation factor is estimated from the correlation between the inverted bulk resistivity values and the water resistivity values measured in groundwater. Formation factor in the mangrove lakes refer to the formation factor of the subsurface formation of the study area. We rewrite the sentence as….. “One method of estimating the formation factor of the lake bottom formation is by comparing groundwater resistivity  measured in the shallow groundwater wells with nearby values of lake bottom resistivity  modeled from the geophysical data. ….” at line 440 to 443

We compared the Dipole- Dipole array and the schlumberger array and found the Dipole-dipole was superior compared to the schlumberger array (Figure 1, response). The Dipole-dipole array was highly constrained and repeatable compared to the Schlumberger array. In addition, the Occam’s inversion result is closely aligned with the best fit model of the Dipole-dipole array compared to the Schlumberger array. (Kiflai 2020, Dissertation paper, available on request), the result from the dissertation chapter will be published soon). We evaluated the effectiveness of each array, and then selected Dipole- dipole for the regional study.

Author Response File: Author Response.pdf

Reviewer 3 Report

Dear Authors,

 

Thank you for giving me the opportunity to read the article titled “Geophysical Characterization in the Shallow Water Lakes of the Southern Everglades, Florida”.

The presented publication is a very interesting example of using geophysical methods to determine the salinity of shallow water bodies. Considering the increased demand for groundwater in many susceptible regions of the world - especially those located in coastal areas - the presented research is a very important contribution to ensuring sustainable development of many regions of the world. Therefore, the presented research. indirectly, fits into important global aspects related to climate change. For this reason, I believe that the topic of the research is very important for many scientists from different fields worldwide.

Overall, the manuscript was written correctly and is thematically coherent and linear. The conclusions presented are supported by the research conducted. The quality of the graphics is also satisfactory. I suggest only correcting minor editorial errors in the manuscript before it can be published.

I attach some detailed - but mostly technical - comments below.

Congratulation on your work!

 

Kind regards,

Reviewer

 

Detailed comments:

Abstract:

Line 24: Please, remove full stop.

 

Introduction:

Line 45: Please, specify what kind of Congress you refer to (I suppose the Congress of the US).

Lines 123-144: I would suggest removing the full links from the text and moving them to the reference section.

Figure 1: Could you please provide a scale bar and projection information to the Figure?

Lines 150-158: The goals of the article overall sound reasonable. Nonetheless, I would suggest that there be more presentation of what the novelty of your proposed research is. This is what is missing here.

 

Electrical and Electromagnetic methods

Line 176: Erase full stop before Figure 2.

 

Data and Methods of Analysis:

This chapter is written completely correctly and comprehensively treats the research question.

 

Results:

This chapter is written completely correctly and comprehensively treats the research question.

 

Discussion:

This chapter is written completely correctly and comprehensively treats the research question.

 

Conclusions:

This chapter is written completely correctly and comprehensively treats the research question.

Author Response

Dear Reviewer,

Thank you for your review of our paper. We have carefully reviewed your comments and revised the manuscript accordingly. We appreciate the valuable editorial suggestions, and we included the comments in this revised version. Our response to the major comments is provided point-by-point below.

Detailed comments:

Abstract:

Line 24: Please, remove full stop.

Response: Full stop removed, and we rewrite the sentence as well at line 24

Introduction:

Line 45: Please, specify what kind of Congress you refer to (I suppose the Congress of the US).

Response: included the US congress at line 46

Lines 123-144: I would suggest removing the full links from the text and moving them to the reference section.

Response: links removed from the text at line (131 and 134) and moved to the reference

Figure 1: Could you please provide a scale bar and projection information to the Figure?

Response: The figures have a scale bar, and we added the projection information in the caption.  Map coordinates are in UTM, Zone 17N in figure 1.

Lines 150-158: The goals of the article overall sound reasonable. Nonetheless, I would suggest that there be more presentation of what the novelty of your proposed research is. This is what is missing here.

Response:  A new paragraph has been added that highlights the novelty of this research work at  lines 143 to 150.

Electrical and Electromagnetic methods

Line 176: Erase full stop before Figure 2.

Response: Erased