Soil Organic Carbon in Mid-Atlantic Region Forest Soils: Stocks and Vertical Distribution

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

General

The manuscript is generally well written and the experimental approach is sound. The analyses are largely descriptive but deal with subject matter of high interest having to do with soil carbon and utilizing the primary soil database in this country for soil considerations. Tables and figures are appropriate, although font sizes and style for ‘readability’ are substandard for a final published paper. The authors can clarify some of the details of the methodology as noted in the comments below, and given the descriptive nature of this research, the methods are critical. The authors give almost no attention to coarse fragments in the sampled pedons, nor did they sample for them, which can be a major weakness in their analysis of carbon stocks and the conclusions drawn among the various contrasts tested. The authors also allude to the potential value of their sites for future repeat measurements to get at changes over time, but do not talk about the equivalent mass approach versus the traditional depth sampling in order to make those comparisons.

Line

28        Why ‘dry’? They literally fix it into a wet or fresh organic matter material of course, but the implication of ‘more’ is that we are talking about total carbon mass regardless of whether the organic matter is wet or dry.

125      It would be useful to know what the total area of forest that passed criteria for inclusion was to understand the relative intensity of the design for a 250 m grid.

137      It is a little difficult to follow the details of this design. We know here it is a 250 m grid on some unknown total area. Presumably the GRTS to pick sampling locations using grid points? Then how is 707 m2 formed within this design?

169      The O horizon was carefully removed, but how was the O horizon sampled? It seems like the description from lines 176 to 181 should be inserted here.

176      I may have missed it but still wondering where 707 m2 is from? If the soil plot has the longest radius of the transects at 12 m, the area of that as a circle is not 707 m2.

192      Db “core” samples includes both the O and mineral material core samples?

200      I am confused. This refers to the mineral horizon sample implying that the above description was for something else? The first paragraph in 2.3 is about the leaf litter. The next paragraph refers to the ‘core samples’ for which there are both O and mineral core samples so I assume both. Then the last paragraph specifically refers to mineral horizon sample that leaves me confused.

216      Is the center marker at the center of a block 250 m on a side, or at the intersections of the grid?

218      How did the sampler know what the ‘original’ condition of the soil was? This seems like a broad framework of disturbance. Does this equate to any current observable evidence of disturbance, since there could have been disturbance a century ago that would not be readily evident today.

238      Just to check, the authors define E, B, and C as subsoil because O horizons were present for those pedons, but the A horizon is considered a surface horizon because none existed with an overlying O horizon?

292      Instead of ‘decreased’ perhaps this should be worded that the probability of encountering a C horizon in this study was less because of the fixed 1 m sampling depth.

303      lal should be Lal

307      All true. It could be worth adding that if using the 2 m NRCS depth for pedons, even more SOC would be below the A horizon.

348      Period after groups?

360      comma after kaolinite?

370      I do not understand the phrasing here. “increases from” means from kaolinite to illite to smectite in sequence?

385      ridge and valley or valley and ridge? Both are stated in reverse here but is that intentional, and if so, to convey what meaning?

469      7.51?

546      Is this statement for subsoils only, since A horizons do not correlate?

 

 

Author Response

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Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

I reviewed the manuscript "Soil Organic Carbon in Mid-Atlantic Region Forest Soils: Stocks and Vertical Distribution " by Daniel J. Colopietro and Ray R. Weil. Overall the manuscript is well written and clear. However, I fell some revisions are necessary for finalization of your work. So, some improvements are need. Please consider my comments as given below.

 

L23–24: The final sentence of the Abstract. Results can be used to develop a theory.

 

L28-31, the background section lacks content, and you don’t lead to your question very well. How do you let readers understand that the SOC stocks of forest is so important in the area or site you are concerned about? Please rephrase.

 

L95-97: After a long description and introduction of the SOC stocks estimation method and sampling depth of soil, you find some knowledge gap that your study is prepared to solve? Please rephase.

 

 

L183: In the future, I recommend avoiding paper plate to store samples, as the paper is made of C, and could contaminate organic samples.

 

 

L309: Given the variability presented, rounding to a single decimal place would seems more reasonable. For example, use 2.9 ± 0.3 rather than 2.85 ± 0.33 for SOC stocks for each master horizon in the upper 1m of soil sampled at 11 US National Park forests within Table 1. The same change applies throughout Table 1 and to all the data within the text of the Results section.

 

L111-115: These two sentences have the same meaning, please rephrase.

 

L114-115: You need to add the importance or necessity of your research at the end of the last paragraph of the introduction section. This is not complete in the current version.

 

L272: I suggest you split the results and discussion sections.

 

L305-307 Perhaps the important point to emphasize here is that SOC stratification reveals a dominance of plant roots inputs over those from plant shoots.

 

L335: Having a pronoun such as “it” as the subject of a sentence makes the reader take time to retreat to the previous sentence to find the meaning.

 

L514: The conclusion should be highly generalized, not a long description, please rephrase.

 

L517: Better to spell soil organic carbon (SOC) out here, to remind the reader who skips to the Conclusion – likewise for Db.

L526-541: The interpretation concerning Db is reasonable but this item should be part of the Discussion section.

 

 

Author Response

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Author Response File: Author Response.pdf

Reviewer 3 Report

Comments and Suggestions for Authors

RE- Soil Organic Carbon in Mid

 

The rigor of writing, lack of clear methodology/statistical section did not allow me to accept the manuscript in current shape. I suggest major revision of the manuscript as per my comments given bellow  

 

Comments

In abstract, there is no conclusion and implication of the study, it is  not clear that whether the reported results is the average of 10 years or single year, this need to be clarify

 

In the introduction section, no hypothesis has been developed, as no research question was mentioned, it is strongly recommended to formulate hypothesis as per research gap in this section to make proper story of the manuscript. The last paragraph is very confusing, make it more simple to clearly state the objectives. Some of the reported references are very old, please update them

 

The methodology section is very boring and not clear, it is advised to clearly write what were the materials and how you have measured. It is better to show what was the location/cite  history, from how many soil series and horizon you have made samples, and what you have measured and how you have measured. The current shape of the methodology is not clear at all, and not understandable due to haphazard arrangement, redundancy, and variable terminology, sampling depth, and procedure, in abstract it was stated that site was monitored for 10 years, and sampling were made over few years. Understanding the series and horizon number will ease the statistical analysis section, the current statement of the statistical analysis is vague and not clear

 

Results and discussion, the first paragraph has defined the C stock/calculation, but have not referred to tables/figures, it is also not advisable to write what is there in the tables/figure we need to write cross comparison among the various soil series/horizon. The results section needs to be improved in term of clarity and comparison among the soil series/horizon/orders, a % increase/decrease of horizon over the other will be better to make a proper comparison. In reality, I have not seen any discussion, that where is the discussion, only some of the irrelevant literature has been cited, without providing proper justification and mechanism for traits been studied. This results/discussion section contain useless statement and some time has been mixed with methodology, this section needs to be proper improved in term of clarity and readability.  

 

The conclusion should be linked directly with set objective in the introduction section, should have a take home message. The current version is not conclusion but look an extended summary without any proper conclusion.

 

In table 1, the soil profile & Mean % of Total Soil Profile C Stocks terms are not clear, this needs to be clarify

Fig 3/4, the unit should be written in the parenthesis. Is this SOC or SOC stock, and what is the difference between fig 3 and fig 4, fig 3 and fig 4 should be combined, where as fig5 and 6 should also be combined

Fig 8 is not self-explanatory, what is WD, PWD and PD

  

The number of figures is much more than required for a regular manuscript. Old refences should be deleted, and the number should be reduced to around 40-45.

 

L16,  NRCS/SSURGO------------------ spell out when used for the fist time to clarify for all readers

L20,  A horizon to an average lower boundary of 18.8 cm ----------------- not clear please rephrase  

L45, The IPCC states in their 45 2006 Guidelines for National Greenhouse Gas Inventories 4.2.3.--------------- what does this mean, if it refences, please cite properly

L53, Foxx et al. (1984) [22]----------------- very old refence

L109, that 58% of OC is found below 20----------------- cross check with your hypothesis in line 106, why this ill be then hypothesis

L220, determine Db, sand percentage, SOM con-220 tent and total organic carbon (TOC).--------------- procedure is missing

L227, Linear regression 227 was conducted in the base environment of R version 4.1.2--------------- redundancy

L243, Carbon Calculations--------------- this section calculation is not clear please rephrase

 

L275, LL------------ also define here in this section

L330, significantly (p ≤ 0.002) different among soil orders---------------- where is the ANOVA

L365, differences in DOC--------------- have you measured this, no information is given in the M&M section

 

Comments on the Quality of English Language

The English language is fine and readable 

Author Response

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Author Response File: Author Response.pdf

Reviewer 4 Report

Comments and Suggestions for Authors

 

I reviewed the article "Soil Organic Carbon in Mid-Atlantic Region Forest Soils: 2 Stocks and Vertical Distribution" by Colopietro and Weil.

The article is well-written and understandable. In the introduction section, I suggest that the authors:

a) explain why IPCC prefer to estimate the SOC in the most superficial layers.

b) emphasize the importance of constraining the SOC at depth >0.3 cm.  The SOC under 0.3 cm is mainly composed of ROC (readily oxidized organic carbon), which has a high turnover (10 years to centuries) respect to the labile SOC (some years), mainly present in the superficial layers. Therefore, the estimation of SOC at depth >0.3 cm is also environmental, as it can give an idea of the potential effects on climate. In fact, the exposure of ROC to the air through unsustainable practices could increase the GHGs. But, on the other hand, the sequestration of carbon in depth could lead to the climate mitigation.

Some reference:

- IPCC Special Report on Climate Change and Land (2019)

- Lal, R. (2004). "Soil carbon sequestration impacts on global climate change and food security"

 

Author Response

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Author Response File: Author Response.pdf

Round 2

Reviewer 3 Report

Comments and Suggestions for Authors

The authors have incorporated most of my comments, I feel no hesitation to accept the manuscript in current form