the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 12 Dec 2025
Shoreline exposure controls teal carbon accumulation in boreal lakes
Abstract. Aquatic vegetated ecosystems play an important role in global carbon sequestration. While research on coastal marine environments has expanded in recent decades, freshwater vegetated shorelines remain understudied despite their potential for significant carbon burial. This is especially relevant in boreal landscapes with high numbers of small, shallow lakes. In this study, we quantify organic carbon stocks (mass of carbon per area) in boreal lacustrine vegetated shorelines, so-called teal carbon environments. Moreover, we identified the main environmental drivers of carbon storage in these areas. We took 27 sediment cores from three large lakes in Finland with available satellite data of macrophyte coverage. At each site, sediment cores were sampled along a depth transect through macrophyte zones, from the landside towards the waterside. Sedimentary organic carbon (SOC) stocks ranged from 0 to 40.8 kg m−2, and showed a large spatial variability among lakes, zones and type of vegetation. We identified grain size as the most significant parameter explaining variability in the size of SOC stocks. Sites dominated by silts and with large SOC stocks were found in sheltered embayments, independent of proximity to rivers, density of vegetation or slope of the shoreline, implying a strong control of exposure on SOC accumulation. In more exposed areas, vegetation density might play an additional controlling role in SOC accumulation. Accounting for shoreline exposure is crucial for improving regional carbon budget estimates. This study highlights the central role of teal carbon ecosystems in carbon cycling in the boreal zone, often characterized by very high densities of lakes.
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Status: final response (author comments only)
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RC1: 'Comment on egusphere-2025-5053', Anonymous Referee #1, 27 Jan 2026
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RC2: 'Reply on RC1', Anonymous Referee #2, 26 Feb 2026
This manuscript represents a timely contribution to the journal. Freshwater wetlands along shorelines (“teal carbon” ecosystems) remain underrepresented in continental carbon budgets, despite growing recognition of the importance of inland waters in global carbon cycling. By quantifying sediment organic carbon (SOC) stocks across boreal lake shorelines and identifying shoreline exposure (fetch length) and sediment grain size as primary controls, the study provides insight into the spatial variability in carbon storage.
While the dataset is geographically limited (three Finnish lakes), the study helps in understanding process-based controls and offers transferable implications for carbon budgeting in lake-rich boreal regions. The sampling framework (27 sediment cores across lakes, sites, and shoreline zones) is appropriate for examining small-scale spatial variability.
A notable strength is the explicit evaluation of environmental predictors (vegetation density, water depth, slope, fetch), with average fetch length emerging as the strongest predictor of SOC stocks. The discussion presents results in the context of existing literature on fine-grained sediment controls, wave energy, and wetland carbon storage. One limitation of the study was the inability to establish sediment accumulation rates because the ¹³⁷Cs profiles were unclear, leading to reliance on stock estimates rather than burial rates . The authors acknowledge this clearly and interpret shoreline zones as areas of temporary storage rather than permanent sinks, however, some additional discussion of temporal stability and implications for long-term sequestration would enhance the manuscript.
Other Improvements could include:
- Tightening the discussion to reduce repetition regarding grain-size controls.
- Clarifying the distinction between carbon “storage” and “long-term sequestration,” the latter may not be an appropriate term here given the lack of accumulation-rate estimates.
Because the ¹³⁷Cs profiles could not be used to estimate C accumulation rates and suggest sediment mixing, the authors should be clear that long-term accumulation is not reported (e.g., line 213).
Fetch length was found to be the strongest predictor of SOC stocks. The authors might consider including a simple conceptual diagram summarizing the exposure → wave energy → grain size → SOC pathway.
Finally, and in light of the goals of the paper, the authors might consider adding discussion on how these site-level findings scale to regional boreal carbon budgets, and whether sheltered shoreline areas can be mapped remotely to upscale SOC estimate
Citation: https://doi.org/10.5194/egusphere-2025-5053-RC2
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RC2: 'Reply on RC1', Anonymous Referee #2, 26 Feb 2026
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This study entitled “Shoreline exposure controls teal carbon accumulation in boreal lakes” presents valuable insights into soil carbon accumulation in teal carbon environments of boreal lakes. Through a large soil core sampling, the authors quantified sediment organic carbon stocks in shallow vegetated areas of Finland Lakes and identified the main biotic and abiotic parameters controlling these stocks. Additionally, authors compare lake SOC stocks with those of freshwater and marine environments to assess the relative contribution of boreal lakes in teal carbon accumulation. The introduction is logically constructed, and the study's objectives are clear. The authors have made efforts to use statistical tools to highlight the main biotic and abiotic drivers controlling SOC stocks. The manuscript is well written, the results are well presented, and the organization is coherent. The manuscript clearly falls within the scope of the target journal, but several aspects of the analysis, presentation, and interpretation require strengthening before it can be considered for publication.