Hydrological Control of SOC Dynamics via Particle Size Redistribution Along Elevation Gradients in the Water Level Fluctuation Zone of the Three Gorges Reservoir

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

Major Comments

While the study addresses an important question, the novelty should be stated more explicitly in the introduction and discussion. How does this work advance beyond previous studies (e.g., Ran et al. 2023; Wei et al. 2025)? Currently, the contribution is implied but not strongly emphasized.

The hypothesis is mentioned (particle size mediates SOC accumulation and mineralization), but it could be framed more clearly at the end of the introduction. A conceptual diagram summarizing the expected interactions among elevation, hydrology, particle size, and SOC would strengthen the paper.

The number of replicates is limited (n = 3 per elevation per depth). Please discuss whether this sample size sufficiently captures the heterogeneity of the WLFZ. Could vegetation differences among plots confound the results?

Clarify how “random” sampling was ensured in terraced landscapes where soils might have strong microsite variability.

The incubation was performed under constant conditions (25 °C, 60% WFPS). However, the WLFZ is defined by dynamic wet–dry cycles. The discussion acknowledges this but downplays the implications. This limitation needs deeper consideration. Would fluctuating conditions yield different results, especially regarding microbial priming and redox dynamics?

Results show that sand has lower SOC but higher turnover. This is well established, but the manuscript should better explain why this pattern is more pronounced in the TGR than in other ecosystems. Are microbial adaptations, sedimentation dynamics, or vegetation factors the cause?

The use of both linear regression and random forest is appropriate. However, please provide details on cross-validation (number of folds, repetitions) for the random forest. Were variable importance results stable across resampling?

Section 4.3 suggests management strategies such as modifying hydrology and introducing vegetation. This is an important applied angle but currently feels superficial. Please provide more context: Which strategies are realistic given the scale of the TGR?, Are there existing ecological engineering trials in the area?, and How might reservoir management policies constrain or support these recommendations?

Minor Comments

The abstract is too long. Consider condensing by focusing on the most critical findings (mid-elevation differences, sand fraction instability, TN as a control).

line 4: I suggest revising this as: “represents a distinctive ecotone with inverted hydrological regimes, where elevation gradients play a critical role…”

line 12: I suggest revising this as: “Random forest and linear regression analyses revealed that total nitrogen (TN) and sand content were the primary factors controlling SOC.”

Some figures (e.g., Figures 2, 6, 7, 8) are crowded. Consider simplifying or merging panels. For readability, increase font size of axes and legends.

Ensure consistent use of terms: “non-flooded zone,” “control soils,” and “>175 m zone” are used interchangeably. Pick one.

Define acronyms (e.g., WFPS, DOC) clearly at first use in abstract and main text.

Some references appear twice (e.g., Wei et al. 2025). Double-check for duplication.

Ensure all references cited in text appear in the list (e.g., check Ran et al. 2023, Bao et al. 2015).

The manuscript is mostly clear, but many sentences are long and wordy. Shortening them would improve readability.

line 40: I suggest revising this as: “The reversed seasonal hydrology—characterized by summer exposure and winter submergence—causes many native terrestrial plants to decline…”

line 90: I suggest revising this as: “Soil samples were obtained at four depth intervals (0–10, 10–20, 20–30, and 30–40 cm) and thoroughly mixed within each layer to ensure homogeneity.”

Figure 3 caption: I suggest revising this as: “SOC stocks at different elevations in the water-level fluctuation zones…”

line 220: I suggest revising this as: “Thus, alternating redox environments may enhance carbon inputs but simultaneously accelerate carbon losses…”

line 290: I suggest revising this as: “Our findings are consistent, showing elevated sand content and higher carbon turnover at mid-elevations, suggesting that prolonged sediment deposition has altered soil texture and reduced SOC stability.”

Author Response

Major Comments

 

While the study addresses an important question, the novelty should be stated more explicitly in the introduction and discussion. How does this work advance beyond previous studies (e.g., Ran et al. 2023; Wei et al. 2025)? Currently, the contribution is implied but not strongly emphasized.

Response: Thank you for your valuable comments. We have revised both the introduction and discussion to clarify the novelty of our study, emphasizing that it focuses on the role of hydrological fluctuations in shaping soil particle-size composition along elevation gradients and their subsequent effects on SOC accumulation and mineralization (Lines 75-77, 417-420, &451-455).

“However, how hydrological fluctuations in the WLFZ reshape the soil particle-size composition along elevational gradients and how these changes in turn mediate SOC accumulation and mineralization remain poorly understood.”

“Compared with previous studies that mainly described elevation–SOC patterns, our results further demonstrate that such patterns are mediated by hydrological fluctuations that reshape the soil particle-size composition, suggesting that elevation effects on SOC are expressed through changes in soil texture and associated stability.”

“Our results indicate that hydrological disturbances in the WLFZ affect sediment deposition and particle size composition, thereby increasing SOC instability in the sand fraction. These findings suggest that SOC stability in the TGR is shaped jointly by the particle size class and elevation-dependent hydrological conditions.”

 

The hypothesis is mentioned (particle size mediates SOC accumulation and mineralization), but it could be framed more clearly at the end of the introduction. A conceptual diagram summarizing the expected interactions among elevation, hydrology, particle size, and SOC would strengthen the paper.

Response: Thank you for your helpful comments. In the revised manuscript, we have rewritten the hypothesis at the end of the introduction to make it more concise and explicit. In addition, we have added a conceptual framework (Fig. 1) summarizing the expected interactions among elevation, hydrology, particle size, and SOC processes.

“We hypothesize that soil particle-size composition mediates the effects of hydrological fluctuations on SOC accumulation and mineralization, leading to elevation-dependent differences in SOC content and stability (Fig. 1).”

 

The number of replicates is limited (n = 3 per elevation per depth). Please discuss whether this sample size sufficiently captures the heterogeneity of the WLFZ. Could vegetation differences among plots confound the results?

Response: Thank you for your valuable comments. In this study, the sampling sites were located in the midstream section of the WLFZ, focusing on natural soils primarily covered by annual and biennial herbaceous vegetation. Representative plots were selected to minimize differences in soil properties, vegetation coverage, and microtopography within each elevation zone, ensuring that the samples reflected typical conditions of the WLFZ. We have now added a statement in the Limitations section to clarify this point and to acknowledge that, although the sampling design effectively captured the dominant elevation-dependent trends in SOC, the limited number of replicates constrains the generalization of our findings to the entire WLFZ (Lines 482-487).

“The sampling sites were located in the midstream section of the WLFZ and focused on natural soils primarily covered by annual and biennial herbaceous vegetation. Representative plots were selected to minimize variation in the soil properties, vegetation coverage, and microtopography within each elevation zone. Although the sampling design effectively captured the dominant elevation-dependent trends in SOC across the study area, we acknowledge that the limited number of replicates constrains the generalization of our findings to the entire WLFZ.”

 

Clarify how “random” sampling was ensured in terraced landscapes where soils might have strong microsite variability.

Response: Thank you for your important comments. To ensure random yet representative sampling in the terraced WLFZ landscape, soil sampling within each elevation zone was conducted using a stratified random approach. Specifically, within each elevation band, three plots were randomly selected from areas with similar slope, aspect, and vegetation coverage to minimize microsite variability. All plots were located in relatively uniform terraces with consistent landform and hydrological conditions to avoid systematic bias introduced by microtopography. This clarification has now been added to the Materials and Methods section (Lines 136-138).

“In each elevation band and in the reference soil located above 175 m, three 1 m × 1 m plots were randomly selected for sampling using a composite collection strategy across various depths, with plot locations chosen to ensure similar slopes, aspects, and vegetation cover to minimize microsite variability within the terrace landscape.”

 

The incubation was performed under constant conditions (25 °C, 60% WFPS). However, the WLFZ is defined by dynamic wet–dry cycles. The discussion acknowledges this but downplays the implications. This limitation needs deeper consideration. Would fluctuating conditions yield different results, especially regarding microbial priming and redox dynamics?

Response: Thank you for your valuable comments. We have expanded the discussion in Section 4.4 (Limitations) to more deeply address the implications of using constant incubation conditions (Lines 487-500). We now note that in the WLFZ, frequent wet–dry alternations can strongly influence SOC mineralization by altering oxygen availability, substrate diffusion, and microbial activity. Such hydrological fluctuations can induce microbial priming and redox transitions that are not captured under constant laboratory conditions, potentially leading to different mineralization patterns.

“The SOC mineralization experiments were performed at constant temperature and moisture to ensure comparability among the treatments. However, these static incubation conditions cannot fully represent the natural hydrological fluctuations characteristic of the WLFZ. In field environments, alternating wet–dry cycles can substantially modify the soil oxygen status, substrate availability, and microbial community composition [6,8,12]. These changes may trigger microbial priming effects and transient redox reactions that accelerate the decomposition of both labile and mineral-associated organic carbon. Consequently, SOC mineralization rates under fluctuating conditions could differ markedly from those observed under constant incubation. Future research should therefore aim to simulate dynamic moisture regimes or incorporate in situ monitoring to better capture the non-linear SOC responses to hydrological variability. Moreover, expanding the spatial coverage of sampling and integrating remote sensing and geochemical modeling approaches could improve the regional applicability of the findings. Such combined field–laboratory frameworks would help elucidate both the mechanistic and spatial controls of SOC stability in the WLFZ.”

 

Results show that sand has lower SOC but higher turnover. This is well established, but the manuscript should better explain why this pattern is more pronounced in the TGR than in other ecosystems. Are microbial adaptations, sedimentation dynamics, or vegetation factors the cause?

Response: Thank you for your valuable comments. We have expanded the discussion to clarify why the observed SOC instability in the sand fractions was more pronounced in the Three Gorges Reservoir (TGR) than in other ecosystems. Specifically, we now emphasize that this pattern likely results from the combined effects of hydrological disturbance, sedimentation dynamics, vegetation composition, and microbial adaptation unique to the WLFZ (Lines 429–439).

“However, the extent of SOC instability in the sand fractions in our study was even more pronounced than that in other ecosystems [23]. This may be related to the unique hydrological disturbance and sedimentation dynamics of the TGR. Previous research has indicated that sediment deposition rates in the WLFZ increase as elevation decreases [15,25], with lower elevation zones (e.g., 155–165 m) tending to accumulate a greater proportion of coarse particles due to hydrodynamic sorting. In addition, the WLFZ experiences periodic wet-dry alternations that cause strong redox fluctuations, increasing substrate availability and microbial decomposition, particularly in coarse-textured soils with high aeration [6,12]. The dominance of annual and biennial herbaceous vegetation with labile litter inputs may further contribute to rapid carbon turnover, while microbial communities adapted to such hydrological variability exhibit flexible metabolism that accelerates SOC mineralization [8,9].”

 

The use of both linear regression and random forest is appropriate. However, please provide details on cross-validation (number of folds, repetitions) for the random forest. Were variable importance results stable across resampling?

Response: Thank you for your helpful comments. In the revised Materials and Methods section, we have added details of the random forest procedure. Specifically, the analysis was conducted in R with the “randomForest” package, using 500 trees and the default mtry setting. Model performance was evaluated with 10-fold cross-validation repeated three times, and the ranking of key predictors remained consistent across resampling, indicating stable variable importance results (Lines 222-225).

“The relative importance of influencing factors was evaluated using a random forest model in R with the “randomForest” package, which uses 500 trees and the default mtry setting. Model performance was assessed with 10-fold cross-validation repeated three times.”

 

Section 4.3 suggests management strategies such as modifying hydrology and introducing vegetation. This is an important applied angle but currently feels superficial. Please provide more context: Which strategies are realistic given the scale of the TGR?, Are there existing ecological engineering trials in the area?, and How might reservoir management policies constrain or support these recommendations?

Response: Thank you for your important comments. In the revised Section 4.3, we expanded the discussion to provide more context on the feasibility and practical implementation of the proposed strategies (Lines 462-471). We clarified that adaptive hydrological regulation—such as seasonal water storage adjustment—can help mitigate sediment disturbance and promote fine-particle retention, though its large-scale application is constrained by the reservoir’s operational priorities of flood control and hydropower generation. We also elaborated on the long-term vegetation restoration initiatives across the TGR, including slope stabilization and vegetation reconstruction along the WLFZ, which have demonstrated positive effects on sediment retention and soil improvement.

“One potential management approach involves reducing sand accumulation through hydrological regulation, such as adaptive control of seasonal water storage during the winter impoundment period, which can mitigate sediment disturbance and promote the retention of fine particles [54]. However, large-scale hydrological adjustments in the TGR are constrained by its operational priorities of flood control and hydropower generation, which limits the feasibility of basin-scale interventions. The restoration and optimization of vegetation structure represent another ecological strategy to improve soil texture and SOC stability [5]. Over the past few decades, a series of ecological restoration initiatives have been implemented throughout the TGR, including slope stabilization and vegetation reconstruction along the WLFZ, which have significantly improved sediment retention, soil structure, and vegetation recovery [55].”

 

Minor Comments

 

The abstract is too long. Consider condensing by focusing on the most critical findings (mid-elevation differences, sand fraction instability, TN as a control).

Response: Thank you for your important comments. While the main findings in the original abstract already focused on mid-elevation differences, sand fraction instability, and TN as a control factor, we have further shortened the abstract by condensing the background and conclusion. The revised abstract now presents the key findings more concisely (Lines 22-35).

“The water level fluctuation zone (WLFZ) of the Three Gorges Reservoir (TGR) represents a distinctive ecotone with inverted hydrological regimes, where elevation gradients play a critical role  in determining the spatial distribution and stability of soil organic carbon (SOC). The objective of this study was to test whether soil particle size mediates the effects of hydrological fluctuations on SOC dynamics across elevation gradients. In this study, soils from three elevation zones (155–165 m, 165–175 m, and non-flooded zones) were collected, separated into bulk soil, sand, silt, and clay fractions and incubated for 60 days to assess SOC mineralization. The results indicated that the SOC stock in the main stream was greater at middle elevations (3.94 ±0.26 kg·m–2) than at high elevations (3.20 ±0.18 kg·m–2), whereas the SOC stock in the tributary was greater at high elevations (3.39 ±0.18 kg·m–2). Random forest and linear regression analyses revealed that total nitrogen (TN) and sand contents were the primary factors controlling SOC. Despite its lower SOC content, the sand fraction presented significantly higher turnover rates (102.14 ±36.13 μg CO2-C·g–1C·h–1) than the finer fractions, indicating lower carbon stability. These findings suggest that hydrological fluctuations regulate SOC by altering the soil particle-size composition across elevation gradients.”

 

line 4: I suggest revising this as: “represents a distinctive ecotone with inverted hydrological regimes, where elevation gradients play a critical role…”

Response: Thank you for your careful comments. We have revised the sentence in the Abstract accordingly to improve clarity (Lines 22-23).

“The water level fluctuation zone (WLFZ) of the Three Gorges Reservoir (TGR) represents a distinctive ecotone with inverted hydrological regimes, where elevation gradients play a critical role  in determining the spatial distribution and stability of soil organic carbon (SOC).”

 

line 12: I suggest revising this as: “Random forest and linear regression analyses revealed that total nitrogen (TN) and sand content were the primary factors controlling SOC.”

Response: Thank you for your comments. We have revised the sentence in the Abstract accordingly to improve clarity (Lines 33-34).

“Random forest and linear regression analyses revealed that total nitrogen (TN) and sand contents were the primary factors controlling SOC.”

 

Some figures (e.g., Figures 2, 6, 7, 8) are crowded. Consider simplifying or merging panels. For readability, increase font size of axes and legends.

Response: Thank you for your valuable comments. In response, Figures 2, 6, 7, and 8 have been revised to simplify the layouts by merging panels with similar or redundant elements. Furthermore, the font sizes of axes and legends have been enlarged to improve readability and ensure consistency across all figures.

 

Ensure consistent use of terms: “non-flooded zone,” “control soils,” and “>175 m zone” are used interchangeably. Pick one.

Response: Thank you for your careful comments. In the revised manuscript, we have standardized the terminology and consistently use “non-flooded zone” throughout the text to avoid confusion. All occurrences of “control soils” and “>175 m zone” have been replaced accordingly.

 

Define acronyms (e.g., WFPS, DOC) clearly at first use in abstract and main text.

Response: Thank you for your helpful comments. We have carefully reviewed the manuscript and confirmed that all abbreviations are now defined at their first occurrence in both the abstract and the main text. For instance, WFPS (water-filled pore space) and DOC (dissolved organic carbon) have been explicitly introduced when first mentioned to ensure clarity and consistency.

 

Some references appear twice (e.g., Wei et al. 2025). Double-check for duplication.

Response: Thank you for your comments. We have carefully reviewed and reorganized the reference list to remove duplicated entries (e.g., Wei et al., 2025) and ensure consistency in citation formatting throughout the manuscript.

 

Ensure all references cited in text appear in the list (e.g., check Ran et al. 2023, Bao et al. 2015).

Response: Thank you for your comments. All in-text citations have been systematically verified against the reference list. Missing references, including Ran et al. (2023) and Bao et al. (2015), have now been added, and the entire reference section has been checked for completeness and consistency.

 

The manuscript is mostly clear, but many sentences are long and wordy. Shortening them would improve readability.

Response: Thank you for your careful comments. In response, we have thoroughly revised the manuscript to enhance clarity and conciseness. The language has been professionally edited with assistance from a native English speaker to improve overall readability.

 

line 40: I suggest revising this as: “The reversed seasonal hydrology—characterized by summer exposure and winter submergence—causes many native terrestrial plants to decline…”

Response: Thank you for your careful comments. We have revised the sentence in the Introduction accordingly to improve clarity (Lines 61-62).

“The reversed seasonal hydrology—characterized by summer exposure and winter submergence—causes many native terrestrial plants to decline, paving the way for the establishment of new flood-tolerant communities.”

 

line 90: I suggest revising this as: “Soil samples were obtained at four depth intervals (0–10, 10–20, 20–30, and 30–40 cm) and thoroughly mixed within each layer to ensure homogeneity.”

Response: Thank you for your helpful comments. We have revised the sentence in the Materials and methods as suggested to improve clarity (Lines 138-139).

“Soil samples were obtained at four depth intervals (0–10, 10–20, 20–30, and 30–40 cm) and thoroughly mixed within each layer to ensure homogeneity.”

 

Figure 3 caption: I suggest revising this as: “SOC stocks at different elevations in the water-level fluctuation zones…”

Response: Thank you for your comments. We have revised the caption of Figure 3 accordingly. The new caption now reads:

“SOC stocks at different elevations in the water-level fluctuation zones of the main stream (a) and tributary regions (b) in the TGR (mean ±standard error, n = 3).”

 

line 220: I suggest revising this as: “Thus, alternating redox environments may enhance carbon inputs but simultaneously accelerate carbon losses…”

Response: Thank you for your helpful comments. We have revised the sentence in the Discussion accordingly (Lines 414-415).

“Thus, alternating redox environments may enhance carbon inputs but simultaneously accelerate carbon losses, leading to heightened SOC turnover and decreased carbon stability at lower elevations.”

 

line 290: I suggest revising this as: “Our findings are consistent, showing elevated sand content and higher carbon turnover at mid-elevations, suggesting that prolonged sediment deposition has altered soil texture and reduced SOC stability.”

Response: Thank you for your comments. We have revised the sentence in the Discussion accordingly (Lines 439-441).

“Our findings are consistent, showing elevated sand content and higher carbon turnover at mid-elevations, suggesting that prolonged sediment deposition has altered soil texture and reduced SOC stability.”

Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

1. Please clarify whether the soil physicochemical parameters, including soil organic carbon (SOC) content and stock, were determined based on measurements in dry matter. This information is important for the clarity of the results and their comparability with other studies.

2. Abstract: it might strengthen the abstract if the research objective were stated more clearly—ideally in a single, concise sentence. This could help guide the reader more smoothly through the study scope.

Comments on the Quality of English Language

• Some sentences in this manuscript are quite long and complex, which may make the text harder to follow. For example, the sentence starting with “To reduce potential artifacts introduced by pre-treatment processes such as drying, wet sieving, sonication, and centrifugation on microbial activity, 2 mL of microbial inoculum was added to each flask...” contains multiple ideas and could be broken into shorter, clearer sentences. Simplifying sentence structure would greatly improve readability and could help readers better understand the experimental procedure.

Author Response

1. Please clarify whether the soil physicochemical parameters, including soil organic carbon (SOC) content and stock, were determined based on measurements in dry matter. This information is important for the clarity of the results and their comparability with other studies.

Response: Thank you for your valuable comments. We have clarified the measurement basis of all soil parameters in the revised manuscript. Specifically, we added the following statement at the end of the section describing soil physicochemical analyses (Lines 162–164):

“Except for NH₄⁺-N, NO₃⁻-N, and DOC, which were determined on a fresh-weight basis, all other soil parameters were expressed on a dry-weight basis.”

 

2. Abstract: it might strengthen the abstract if the research objective were stated more clearly—ideally in a single, concise sentence. This could help guide the reader more smoothly through the study scope.

Response: Thank you for your important comments. To address it, we have added a clear and concise statement of the research objective in the abstract (Lines 24-26)

“The objective of this study was to test whether soil particle size mediates the effects of hydrological fluctuations on SOC dynamics across elevation gradients.”

 

Some sentences in this manuscript are quite long and complex, which may make the text harder to follow. For example, the sentence starting with “To reduce potential artifacts introduced by pre-treatment processes such as drying, wet sieving, sonication, and centrifugation on microbial activity, 2 mL of microbial inoculum was added to each flask...” contains multiple ideas and could be broken into shorter, clearer sentences. Simplifying sentence structure would greatly improve readability and could help readers better understand the experimental procedure.

Response: Thank you for your helpful comments. The example sentence and other complex expressions throughout the manuscript have been carefully revised for clarity and readability. In particular, the sentence beginning with “To reduce potential artifacts introduced by pre-treatment processes...” has been divided into shorter and clearer sentences to better convey the experimental steps. The language of the entire manuscript has been polished with the assistance of a native English editor.

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

Abstract Line 6: what does this mean? does it mean "soil particle size distribution"?

Introduction Line 1: remove "the". Remove “the” before special names throughout the paper not only this one

Introduction last paragraph Line 1-4: the author revises the introduction quite a bit. however, the introduction still does not provide lack of knowledge to support what justification make this study question valuable to conduct.

Material and Methods paragraph 1 Last line: This doesn’t make sense to me. 5891.4 Celsius?

Material and Methods section 2.2. paragraph 1 line 8-9: how many years of sampling has been done? how long this study length was?

Material and Methods section 2.2. paragraph 2 line 4: not sure what this method mean?

Material and Methods section 2.2. paragraph 2 line 11-12 from the end: the proportions of soil particles ...

Material and Methods section 2.2. paragraph 2 last two lines: please describe this better and provide more details what this mean?

Author Response

Reviewer #1:

Abstract Line 6: what does this mean? does it mean "soil particle size distribution"?

Response: Thank you for your important comments. Yes, it refers to the separation of soil based on particle size. To clarify this, we have revised the sentence in the Abstract (Lines 27–28) as follows:

“In this study, soils from three elevation zones (155–165 m, 165–175 m, and non-flooded zones) were collected, and bulk soil and particle-size fractions (sand, silt, and clay) were incubated for 60 days to assess SOC mineralization.”

 

Introduction Line 1: remove "the". Remove “the” before special names throughout the paper not only this one

Response: Thank you for your comments. We have removed “the” before “Three Gorges Reservoir” in Line 1 and carefully checked the entire manuscript to ensure that “the” was removed before other special names.

 

Introduction last paragraph Line 1-4: the author revises the introduction quite a bit. however, the introduction still does not provide lack of knowledge to support what justification make this study question valuable to conduct.

Response: Thank you for your valuable comments. To better highlight the knowledge gap and justify the importance of this study, we have revised the last paragraph of the Introduction to explicitly state the existing research limitations and the rationale of our study (Lines 99–107). The revised section now emphasizes that, although many studies have examined SOC variation across elevation gradients in riparian or WLFZ ecosystems, the mechanisms by which hydrological fluctuations reshape soil particle-size composition and consequently regulate SOC accumulation and mineralization remain unclear. The revised paragraph reads as follows:

“This study is designed to investigate the underlying mechanisms and key determinants of SOC variation across elevation gradients in the WLFZ of TGR, with a particular focus on how particle size composition influences SOC dynamics and mineralization patterns. Although previous studies have reported significant variations in SOC along elevational gradients in riparian zones and WLFZs, the mechanisms through which hydrological fluctuations reshape soil particle-size composition and, in turn, regulate SOC accumulation and mineralization remain poorly understood. Existing research has mainly focused on bulk soils, while the contribution and response of specific particle-size fractions to SOC stabilization and turnover under fluctuating hydrological conditions have received limited attention. Addressing this knowledge gap is essential for improving our understanding of carbon cycling processes and SOC stability in hydrologically disturbed ecosystems such as the WLFZ of the TGR.”

 

Material and Methods paragraph 1 Last line: This doesn’t make sense to me. 5891.4 Celsius?

Response: Thank you for your helpful comments. We have revised this section for clarity. The last sentence referring to “purple soil” has been removed, as it was not essential to the study objectives and could cause confusion for readers unfamiliar with the local soil classification. In addition, the description of the accumulated temperature has been corrected for precision. The term “accumulated temperature (> 10 °C)” represents the annual cumulative sum of daily mean temperatures exceeding 10 °C and is now expressed as “5891.4 °C · d,” which is the standard meteorological unit. The revised sentence now reads as follows:

“The area is characterized by a subtropical humid monsoon climate, with an average annual temperature of 18.5 °C, an accumulated temperature (> 10 °C) of 5891.4 °C · d, and an average yearly rainfall of about 1200 mm, most of which occurs between May and September.”

 

Material and Methods section 2.2. paragraph 1 line 8-9: how many years of sampling has been done? how long this study length was?

Response: Thank you for your important comments. The soil sampling in this study was conducted once during the dry season of 2023, when the water level of TGR was at its lowest and soils in the WLFZ were fully exposed. All laboratory analyses and incubation experiments were completed within the same year. To clarify this information, we have added the following sentence at the beginning of Section 2.2:

“Soil sampling was conducted in the dry season of 2023, when the water level of TGR was at its lowest and soils in the WLFZ were fully exposed.”

 

Material and Methods section 2.2. paragraph 2 line 4: not sure what this method mean?

Response: Thank you for your valuable comments. We have revised the description of the soil particle-size separation method to clarify the procedure and its purpose (Lines 167–175). In the revised manuscript, we now provide more detail regarding the ultrasonic dispersion, sieving, and centrifugation steps used to separate the soil fractions and to calculate their relative proportions.

“The soil particle-size fractions were separated following the method of Ding et al. [21], combining ultrasonic dispersion, wet sieving, and repeated centrifugation. Briefly, 20 g of air-dried soil was ultrasonically dispersed in ultrapure water to disrupt aggregates. The resulting suspension was passed through a 50 μm sieve to collect the sand fraction (> 50 μm). The silt (2–50 μm) and clay (< 2 μm) fractions were subsequently separated from the filtrate according to Stokes’ law by stepwise centrifugation. All fractions were dried at 40 °C to constant weight, gently ground, and weighed to calculate their mass percentages relative to the total soil sample. The processed samples were then stored for subsequent physicochemical and incubation analyses to assess SOC mineralization characteristics among different particle-size classes.”

 

Material and Methods section 2.2. paragraph 2 line 11-12 from the end: the proportions of soil particles ...

Response: Thank you for your important comments. The previous description was ambiguous, we have revised the sentence to clarify that the soil particle-size fractions were separated and then weighed to calculate their relative mass percentages (Lines 167–175).

“The soil particle-size fractions were separated following the method of Ding et al. [21], combining ultrasonic dispersion, wet sieving, and repeated centrifugation. Briefly, 20 g of air-dried soil was ultrasonically dispersed in ultrapure water to disrupt aggregates. The resulting suspension was passed through a 50 μm sieve to collect the sand fraction (> 50 μm). The silt (2–50 μm) and clay (< 2 μm) fractions were subsequently separated from the filtrate according to Stokes’ law by stepwise centrifugation. All fractions were dried at 40 °C to constant weight, gently ground, and weighed to calculate their mass percentages relative to the total soil sample. The processed samples were then stored for subsequent physicochemical and incubation analyses to assess SOC mineralization characteristics among different particle-size classes.”

 

Material and Methods section 2.2. paragraph 2 last two lines: please describe this better and provide more details what this mean?

Response: Thank you for your important comments. We have clarified the rationale behind expressing some soil parameters on a fresh-weight basis and others on a dry-weight basis (Lines 183-184).

“Except for NH4+-N, NO3−-N, and DOC, which were determined on a fresh-weight basis to reflect their in-situ concentrations in moist soils, all the other soil parameters were expressed on a dry-weight basis to ensure consistency and comparability across samples.”

Author Response File: Author Response.pdf