the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
UAV approaches for improved mapping of vegetation cover and estimation of carbon storage of small saltmarshes: examples from Loch Fleet, northeast Scotland
Lucy Catherine Miller
Craig Smeaton
William Edward Newns Austin
Abstract. Saltmarsh environments are recognised as key components of many biophysical and biochemical processes at the local and global scale. Accurately mapping these environments, and understanding how they are changing over time, is crucial for better understanding these systems. However, traditional surveying techniques are time-consuming and are inadequate for understanding how these dynamic systems may be changing temporally and spatially. The development of Uncrewed Aerial Vehicle (UAV) technology presents an opportunity for efficiently mapping saltmarsh extent. Here we develop a methodology which combines field vegetation surveys with multispectral UAV data collected at two scales to estimate saltmarsh area and organic carbon storage at three saltmarshes in Loch Fleet (Scotland). We find that the Normalised Difference Vegetation Index (NDVI) values for surveyed saltmarsh vegetation communities, in combination with local tidal data, can be used to reliably estimate saltmarsh area. Using these area estimates, together with known plant community and soil organic carbon relationships, saltmarsh soil organic carbon storage is modelled. Based on our most reliable UAV-derived saltmarsh area estimates, we find that organic carbon storage is 15–20 % lower than previous area estimates would indicate. The methodology presented here potentially provides a cheap, affordable, and rapid method for saltmarsh mapping which could be implemented more widely to test and refine existing estimates of saltmarsh extent and is particularly well-suited to the mapping of small areas of saltmarsh habitat.
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William Hiles et al.
Status: final response (author comments only)
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RC1: 'Comment on egusphere-2023-1185', Anonymous Referee #1, 15 Aug 2023
General comments:
The paper describes an approach combing vegetation survey, UAV data and tidal data to estimate saltmarsh extent and saltmarsh organic carbon storage. It is certainly intended to be a method development study but has significant amount of work on the effects of areal estimates on organic carbon storage estimates. Do the authors use the estimate of OC storage as a way to assess the reliability of different approaches in extracting saltmarsh extent? As a result, I am less certain of the paper's objective(s). In any case, I see some values of this work but would like to see some improvements.
I found the five parts in Results section confusing and not appropriate to respond to the three objectives the authors raised in Introduction section. Especially for section 3.1, the authors should explain why it was included in Results section. Section 3.2 and 3.3 should be moved to Methods section, as it describe how to classify vegetation communities and estimate areas.
Several major concerns:
- How do the authors define the saltmarsh environments? Does it mean saltmarsh ecosystems?
- There is a fundamental issue here that the paper did not explore. When classifying saltmarsh vegetation, the authors used the National Vegetation Classification (NVC) scheme. It seems not require training data and validation data as well, so how the mapping accuracy can be achieved? This relates to the following estimation of saltmarsh extent.
- In Introduction section, the authors point out the location (elevation) of saltmarshes, that is, saltmarshes form between the high astronomical tide (HAT) and mean tidal level (MTL). In section 2.5.1, the authors stated that the saltmarsh area was estimated by calculating the area that inundated under each tidal condition. In this context, the authors focused on three tidal contexts: High Astronomical Tide (HAT), Mean Low Water Springs (MLWS), Mean High Water Neaps (MHWN). What is the connection between MTL, MLWS, and MHWN? Why the authors recognize the saltmarshes are expected to always be inundated?
- Some paragraphs in Section 2.5 and Section 2.6 should be connected.
- How to classify the saltmarsh vegetation? By using NVC scheme or NDVI extraction values described in section 2.5.2? The authors should add more details about vegetation classification.
- For the first objective of this work, the authors stated to delineate saltmarsh habitats. Vegetation composition is a key component of saltmarsh habitats, however, the related content is not well depicted in this paper. Please change the objective 1 more precisely.
- Do the authors used the same OC storage estimation method with Haynes et al., 2016? Section 2.7 need more related descriptions.
Specific & minor concerns:
- Line 35: simple or straightforward?
- Line 61: saltmarshes are not always small features.
- Line 94-98: these three sentences are not suitable for the study area section.
- Section 2.3: this section only describes how to design and collect UAV data. Seems better to change to UAV data collection.
- Line 136-137: please state what parameter did the internal sunlight sensor process.
- Table 1: the tidal ranges are the mean values?
- Line 191: typo, rewrite this sentence.
- Figure 4: the Wick HAT in middle 2 figures is not identical to the legend color scheme.
- Table 2: keep the same decimal place.
- Figure 5: abbreviation of SM10,…SM8 should be clarified.
- The form of the tables (Table 1-5) are not appropriate.
Citation: https://doi.org/10.5194/egusphere-2023-1185-RC1 -
RC2: 'Comment on egusphere-2023-1185', Anonymous Referee #2, 07 Sep 2023
Overall, the manuscript is well written and an enjoyable read. The approach is novel and of interest to those working in saltmarshes and coastal wetlands. There are, however, a couple of limitations that need to be addressed by the authors. Having read the manuscript, I am left wondering why the authors did not use a classification method, such as the Random Forest approach used by Villoslada et al. (2020)? Further justification for not using an approach such this, especially when the authors have the available data, is required.
There is also a need to consider the wider context and implications of the work. For example, it would be interesting to see some discussion of application of the approach in other systems such as mangroves or even restored saltmarshes including managed realignment sites. There have been a number of studies into the use of UAS approaches and blue carbon in these settings, it would be beneficial to evaluate if the method developed in this study could be beneficial to these investigations. Other systems, beyond coastal environments, could also be evaluated here to increase the application of the work. With these additions, the manuscript would be considerably stronger and of wider appeal to those working in both UAS remote sensing and blue carbon.
Citation: https://doi.org/10.5194/egusphere-2023-1185-RC2
William Hiles et al.
William Hiles et al.
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