Ultra-High-Resolution Monitoring of the Catchment Response to Changing Weather Conditions Using Online Sediment Trapping

Round 1

Reviewer 1 Report

Manuscript review

            The manuscript entitled “Ultra-high resolution monitoring on catchment response to synoptic weather conditions using online sediment trapping” by Johansson et al. is a relevant contribution to the understanding of the catchment dynamics and it is a good example of bringing the sediment trapping study to the next level.

            The manuscript uses computer tomography methods for imaging the object's interior and thus, allow for measuring the in-lake production and the detrital delivery from the catchment on a daily basis. Although the manuscript is well-written and structured, I have several comments and suggestions and hope they will help Authors to improve their manuscript. I wish to read the answers for questions asked in this review.

            The language should be consistent through the text. Examples: “Figure 5” in line 351 vs. “Fig 5” in line 356, “Savilathti Bay” vs. “Savilahti bay” or “ultra-high resolution” vs. “ultra-high-resolution”. However, there are more inconsistencies like these. There is also a syntax error in lines 58-59  in the sentence “So far, …, has not been carried out”.I think that the presentation of the results can be improved, especially Figures 3-5.

            I am not convinced of the proper use of the word  “synoptic” in this study. I would like to suggest changing the title of the manuscript into “Ultra-high-resolution monitoring of catchment response to weather conditions using online sediment trapping”. Also, the use of “synoptic” should be considered carefully in expressions such a “single synoptic events”. Did Authors think of “single meteorological events”?

There are also several double-spacing within the text. Examples: lines 14, 21, 22.

I have some questions and suggestions for every chapter. They are as follow:

Abstract:

            This part nicely summarizes the paper. However, a more detailed description of results should appear. In the last sentence, the authors wrote that their findings will facilitate modeling detailed weather and erosion conditions that are related to climate change. The study site is located on the shore of the University of Western Finland campus with the city of Kuopio nearby. I can imagine that the erosion is (and was) caused not only by climate but also by human activity. Moreover, to observe the impact of climate change, long datasets are required. How the sediment trapping will allow distinguishing the drivers of erosion in the past? If authors think about modeling of future changes, why do they mention varve sediments?

1. Introduction:

a) Authors introduced annually laminated sediments and their relevance in paleoecological and environmental studies. However, neither results nor discussion justifies mentioning varves. I recommend to either show the broader view or elaborate more about the results (read more in Discussion part).

b) Please rephrase the last sentence (lines 80-83). In the present form, it is hard to follow. What is a synoptic event? Did Authors think of a meteorological event?

c) un-direct or indirect (line 55)?

2. Material and Methods:

a) Add the date of the Weichselian ice sheet retreat.

b) Add information about the slopes steepness and land cover in the catchment.

c) Explain what kind of materials are coarse and fine-grained or change the wording on the map.

d) Add explanation of what “+” means in Figure 1.

e) Although Authors wrote another manuscript about operating principle and detailed technical description of the sediment trap methodology, I recommend to include a short paragraph here too. It would be beneficial to present the graphic with the working scheme. These steps are necessary especially because the mentioned manuscript has not been published yet.

f) Why the boundary of 1 cm was chosen to distinguish frozen and unfrozen soil?

g) Remove “were” at the beginning of line 181.

3. Results:

a) Add “ml/day” after 0.11 in line 192.

b) Replace “table 2” with “Table 2” in line 210.

c) Remove double-spacing after “table 2.” in line 210.

d) What does mean “manual measurement”? Was the water removed first?

e) Table 2, “Unit” column, “Ice cover”, “Construction” and “Ground frost” rows: move “1” to the same line as “(yes)”.

f) How depth of ground frost from years 1971-2000 was plotted in the one-year time scale?

g) Remove “a” after “(Table 3),” in line 241.

h) R=0.2 is a small positive correlation, not the medium (line 248).

i) What do stars mean in Figure 7?

4. Discussion;

a) Parts of the text should be moved to the Results section. Examples: “The 3-day long precipitation event…, even under the detection limit” in lines 353-359, “The 2-long windy event…, which lasted up to 6 days” in lines 366-372 and “The 6-long day… in daily accumulation” in lines 379-381.

b) Is it possible that the difference between on-line measurements and manual measurements are caused by the compaction/spaces between particles while the sample is in water (computer scanning) and manual measurements (please add info about how the volume was measured)?

c) In the introductory part, Authors mentioned varved sediments. However, no word was said about varves through the whole manuscript. What information was obtained through monitoring? Is there anything relevant for the sedimentation scheme? I have an impression that “annually laminated sediments” expression was used to attract the readers only. I would love to read more about the implications of ultra-high-resolution trapping for recognition of the annual cycle and varve formation processes.

5. Conclusions:

a) The same comments as in the introductory and discussion sections. After elaborating on varves in the previous part, add the summary here.

References:

Please check the spelling and correct typos. Examples: Line 422 “besonen” and double spacing, line 434 “Bigler,C”, line 435 “1580inferred”, line 443 “Sci.Rev.” and so on.

Author Response

SUMMARY OF THE REVISION

The authors thank the Reviewer from valuable comment in order to improve the manuscript. The key points addressed by the reviewer were the lack in sufficient description of on-line trap use in order to improve interpretations made from high-resolution varved sediment archives which has been revised throughout the manuscript (Abstract, discussion, conclusions). Other points such as language check and use of word synoptic events has been revised as suggested. The authors request the Quaternary service for language editing. The more detailed comments are answered below. The Reviewer comment/questions are shown with bold and our answers are provided after each question.

Abstract:

This part nicely summarizes the paper. However, a more detailed description of results should appear.

The results are now described in more detail in abstract.

In the last sentence, the authors wrote that their findings will facilitate modeling detailed weather and erosion conditions that are related to climate change. The study site is located on the shore of the University of Western Finland campus with the city of Kuopio nearby. I can imagine that the erosion is (and was) caused not only by climate but also by human activity.

The Reviewer is right. The data show clear response to seasonal conditions and short term weather conditions, but the anthropogenic influence can not be excluded, and furthermore the influence of construction work is shown clearly in our measurement data. This is shortage is now revised

Moreover, to observe the impact of climate change, long datasets are required. How the sediment trapping will allow distinguishing the drivers of erosion in the past? If authors think about modeling of future changes, why do they mention varve sediments?

This is a key point and it was insufficiently described. Now it has been revised throughout the manuscript. It is absolutely critical to use on-line methods together with high resolution records such as varves, to better understand the climatic controls on catchment, sediment accumulation and varve formation through time and thus be able to understand the mechanisms mediating the climate changes in the lake records in past – and future.

1. Introduction:

a) Authors introduced annually laminated sediments and their relevance in paleoecological and environmental studies. However, neither results nor discussion justifies mentioning varves. I recommend to either show the broader view or elaborate more about the results (read more in Discussion part).

The discussion has been elaborated with respect of varve records e.g. the need for ultra-high resolution sediment flux data in order to better understand the climate, meteorological and hydrological short term events and their influence in varve thicknesses. Lines 441-448 at discussion and lines 455-448 at Conclusions.

b) Please rephrase the last sentence (lines 80-83). In the present form, it is hard to follow. What is a synoptic event? Did Authors think of a meteorological event?

Sentence is rephrased. Now lines 84-88.

c) un-direct or indirect (line 55)?

Corrected to indirect. Now line 60

2. Material and Methods:

a) Add the date of the Weichselian ice sheet retreat.

This information (more than 9 500 years ago) is now provided at line 97

b) Add information about the slopes steepness and land cover in the catchment.

This information is now provided at lines 112-113

c) Explain what kind of materials are coarse and fine-grained or change the wording on the map.

The coarse grained materials (sand deposits and sand moraines) and fine-grained materials (former lake deposits) are now described at line 111.

d) Add explanation of what “+” means in Figure 1.

This information lacked from the figure caption. The symbol (the study site at the deepest part of the basin) is now explained in the figure caption.

e) Although Authors wrote another manuscript about operating principle and detailed technical description of the sediment trap methodology, I recommend to include a short paragraph here too. It would be beneficial to present the graphic with the working scheme. These steps are necessary especially because the mentioned manuscript has not been published yet.

The figure, illustrating the on-line trap configuration and operation technique is now added, Figure 2. The tomographic method is shortly described at lines 153-168

f) Why the boundary of 1 cm was chosen to distinguish frozen and unfrozen soil?

This is how the Finnish environmental administration providing the frost measurement data defines the frost measuring accuracy. Measurement is not very accuracy it is about 1-2 cm. We excluded data points from the analysis, which are below of specified accuracy. The boundary is now described at lines 197-198

g) Remove “were” at the beginning of line 181.

This is now removed. Now line 214

 3. Results:

a) Add “ml/day” after 0.11 in line 192.

This is now added. Now line 225

b) Replace “table 2” with “Table 2” in line 210.

This is now corrected. Now line 243

c) Remove double-spacing after “table 2.” in line 210.

This is now corrected

d) What does mean “manual measurement”? Was the water removed first?

Manual measurement was carried out using the measuring cylinder were the volume of sediment can be measured in a very similar way than how it occurs in the trap tube. Water was not removed but the sediment from the trap tube was let to settle down at the measuring glass. Manual measurement process is now described at lines 176-181.

e) Table 2, “Unit” column, “Ice cover”, “Construction” and “Ground frost” rows: move “1” to the same line as “(yes)”.

This is corrected as suggested

f) How depth of ground frost from years 1971-2000 was plotted in the one-year time scale?

The depth of frost varies through the winter season and its depth is measured every tenth day. The average frost depth of each measurement from years 1971-2000 was used for plotting. This is now clarified in the figure caption.

g) Remove “a” after “(Table 3),” in line 241.

This is now corrected. Now line 274

h) R=0.2 is a small positive correlation, not the medium (line 248).

This is now corrected. Now line 280

i) What do stars mean in Figure 7?

Star indicates extreme outliers, this is now clarified in the figure caption. Now figure 8

 4. Discussion;

a) Parts of the text should be moved to the Results section. Examples: “The 3-day long precipitation event…, even under the detection limit” in lines 353-359, “The 2-long windy event…, which lasted up to 6 days” in lines 366-372 and “The 6-long day… in daily accumulation” in lines 379-381.

This has been revised as suggested. Moved to lines 279-313

b) Is it possible that the difference between on-line measurements and manual measurements are caused by the compaction/spaces between particles while the sample is in water (computer scanning) and manual measurements (please add info about how the volume was measured)?

This is possible but not very likely, because the sediment volume is measured using volume specific measurement cylinder, where the sediment sample is let to accumulate on the bottom in a same way that sediment accumulates in the trap tube bottom. The measurement is described at lines 176-181

c) In the introductory part, Authors mentioned varved sediments. However, no word was said about varves through the whole manuscript. What information was obtained through monitoring? Is there anything relevant for the sedimentation scheme? I have an impression that “annually laminated sediments” expression was used to attract the readers only. I would love to read more about the implications of ultra-high-resolution trapping for recognition of the annual cycle and varve formation processes.

The advantages of on-line trapping in understanding seasonal sediment cycle but also understanding the importance of climatic and hydrological events such as frost and wind or single rain events that are difficult to address in detail using varve records can be identified. These events and their importance has long been discussed in varve studies, however, on-line sediment trapping enable to measure and understand the importance of these events for sediment accumulation in detail. This was insufficiently discussed in the manuscript. The discussion is now improved at lines 441-451

 5. Conclusions:

a) The same comments as in the introductory and discussion sections. After elaborating on varves in the previous part, add the summary here.

The conclusions have been elaborated with respect of varve records.

 References:

Please check the spelling and correct typos. Examples: Line 422 “besonen” and double spacing, line 434 “Bigler,C”, line 435 “1580inferred”, line 443 “Sci.Rev.” and so on.

The references has been revised as suggested

Author Response File: Author Response.docx

Reviewer 2 Report

General comments to the Author:

Validating climate reconstructions from instrumental data are necessary for the advancement of climate researches. In this paper, Johansson et al. present an interesting methodology to investigate the sediment supplies vs meteorological data with a daily basis to lake systems.  Validation of the archived signals is generally investigated on a monthly, annual or decadal basis, but not on the daily resolution, which makes the study innovative. Overall the design and analysis are rigorous and the results support well the conclusion that automatic tomographic scanning of the sediment trap method developed by the Authors can well capture trends, variability, and volumes of daily sediment accumulation rates. This methodology will certainly facilitate the interpretation of seasonal sedimentary records and improve proxy based paleoclimatological records. Overall, the manuscript is comprehensive and seems suitable for publication. 

Remarks to improve the manuscript: 

1.    A description of the computer tomography installation on the trap is missing. I recommend that the Authors include a figure and/or picture to present the full design of the installation. 

2.    The Authors need to include a reference as regards the material used in the study, and name the company…

I have one concern to address: why the Authors have not measured the suspended sediment matter (SSM) in the river inlet? SSM can already provide daily data, so why is it necessary to develop the tap system – we need to verify if SSM & traps records are congruent or not? 

On a different note, the general patterns of the annual hydrology are well captured by the traps, but there is no clear relation for single hydrological events. The difference is probably related to the catchment (hydrological) response, linked to hydrological connectivity, soil retention, etc… but the Authors have not yet investigated the question. I feel like the Authors could have discussed further the dissimilarity between hydrological events recorded in the meteorological station and the sediment record via (e.g. why not using some GIS which could help to investigate the hydrological network on the catchment?). 

Author Response

SUMMARY OF THE REVISION

The authors thank the Reviewer from valuable comment in order to improve the manuscript. The key points addressed by the reviewer were the lack in sufficient description of on-line trap installation and the references regarding the materials used in this study. Other points such as language check was advised. During the revision, a figure was added to better illustrate the sediment trap installation and the tomography configuration. The components of the trap, tomography device and energy supply, however, were self-built, so no companies can be addressed. The authors ask for the Quaternary service for language editing. The more detailed comments are answered below. The Reviewer comment/questions are shown with bold and our answers are provided after each question.

General comments to the Author:

Validating climate reconstructions from instrumental data are necessary for the advancement of climate researches. In this paper, Johansson et al. present an interesting methodology to investigate the sediment supplies vs meteorological data with a daily basis to lake systems.  Validation of the archived signals is generally investigated on a monthly, annual or decadal basis, but not on the daily resolution, which makes the study innovative. Overall the design and analysis are rigorous and the results support well the conclusion that automatic tomographic scanning of the sediment trap method developed by the Authors can well capture trends, variability, and volumes of daily sediment accumulation rates. This methodology will certainly facilitate the interpretation of seasonal sedimentary records and improve proxy based paleoclimatological records. Overall, the manuscript is comprehensive and seems suitable for publication. 

Authors wish to tank reviewer for encouraging comments.

Remarks to improve the manuscript: 

1.    A description of the computer tomography installation on the trap is missing. I recommend that the Authors include a figure and/or picture to present the full design of the installation. 

A new figure illustrating the sediment trap installation and tomography configuration is now provided (Figure2) and operation technique is shortly described at lines 158-167

2.    The Authors need to include a reference as regards the material used in the study, and name the company…

The components of the trap, tomography device and energy supply were self-built, and thus no companies can be addressed.

I have one concern to address: why the Authors have not measured the suspended sediment matter (SSM) in the river inlet? SSM can already provide daily data, so why is it necessary to develop the tap system – we need to verify if SSM & traps records are congruent or not? 

The sediment trap technique is widely used to better understand the seasonal cycle of sedimentary material related to varved sediment records. The supply and sources of sedimentary material varies between the seasons. During spring floods the depositing material is mostly minerogenic particles eroded from the catchment, largely transported through rivers and streams. However, particles are also transported through surface run-off and resuspension of littoral sediments. During growing season, the sediment supply is dominated by the biogenic matter from autochthonous sources. From the perspective of varve studies such high-resolution on-line data can facilitate interpretation of the seasonal cycle and help to understand the influence of hydro-climate in varve formation. The link to varve studies was insufficiently explained and the discussion has been elaborated with respect of varve records e.g. the need for ultra-high resolution sediment flux data in order to better understand the climate, meteorological and hydrological short term events and their influence in varve thicknesses (Lines 441-451 at discussion and lines 453-456 at Conclusions).

The river SSM can not only explain the sediment accumulation on the lake basins. But the reviewer is right that this would be a source for interesting additional information of lake-catchment dynamics and the daily data from river sources coupled with daily data from lake basin would provide interesting information on driving mechanisms of sediment depositions and its hydroclimatic controls.

On a different note, the general patterns of the annual hydrology are well captured by the traps, but there is no clear relation for single hydrological events. The difference is probably related to the catchment (hydrological) response, linked to hydrological connectivity, soil retention, etc… but the Authors have not yet investigated the question. I feel like the Authors could have discussed further the dissimilarity between hydrological events recorded in the meteorological station and the sediment record via (e.g. why not using some GIS which could help to investigate the hydrological network on the catchment?). 

This study aims to test and report the new on-line trap method and its possibilities to provide more detailed information on the varying flux rates at a lake basin to better understand hydro-climatic conditions driving the varve formation. This goal was insufficiently explained and is now better addressed. The deployment time of the on-line trap was only for one year and the sediment flux record suggest that such on-line trapping could provide very useful information for high-resolution climate studies. The reviewer is right that, for example, the enhanced sediment supply for several days after the significant rainfall event is very likely related to catchment hydrological response and the further studies would benefit from detailed understanding of ground water levels, soil types and their hydrological connectivity. However we feel that this would be slightly out of the scope of this particular study aiming to report new method and its potential for sediment flux studies. Yet this is a very good point and the discussion is improved by stating to soil processes (Line  410-411). Furthermore, this is an excellent idea to elaborate the on-line trapping in order to better understand catchment processes as well as lags and their causes in response to certain meteorological events. This would require perhaps longer deployment time and more detailed analyses of the trapped sediments as well, not only flux rate (e.g. chemical composition, organic matter content, TOC, C/N etc).

Author Response File: Author Response.docx