Chapter 15: Tidal Wetlands and Estuaries
Overview/Main Issues
This chapter synthesizes the latest scientific information on the carbon budget and dynamics of estuaries and tidal wetlands. The chapter provides an excellent summary of the state of knowledge in these coastal systems and the significant challenges posed by knowledge gaps. The Committee provides several ways that the chapter could be improved, including balancing the chapter with more estuarine information, including methane fluxes where possible, and expanding to include information from Hawaii, Pacific Islands, and Puerto Rico. The Committee also recommends expansion of Key Findings to reflect estuarine information and gaps in knowledge.
Statement of Task Questions
- Are the goals, objectives and intended audience of the product clearly described in the document? Does the report meet its stated goals?
This chapter is in alignment with the overall goals and objectives of the report as stated in the Executive Summary and Report Preface. This chapter is generally well written, is scientifically sound, and provides an excellent, thorough review of carbon cycling in tidal wetlands and estuaries.
- Does the report accurately reflect the scientific literature? Are there any critical content areas missing from the report?
The chapter provides ample guidance on processes in tidal wetlands, but is in need of additional information on estuaries. For example,
- The majority of the “Findings” are focused on tidal wetlands, not estuaries
- Methane production is covered for tidal wetlands, but not estuaries – the chapter is in need of an introduction to processes that produce methane in estuaries and quantification of fluxes.
- Key Areas” on p. 612 (bulleted list) also focus primarily on tidal wetlands
The section on Pacific Coast estuaries needs a more thorough discussion of “low inflow” estuaries such as Tomales Bay, Elkhorn Slough, Newport Bay, that are very common on the West Coast of the U.S. The only really thorough treatment of methane source/sink is in the Pacific Coast Estuaries section; the Committee recommends the expansion of discussion of CH4 in other sections where possible.
While this chapter focuses on the continental U.S., the Executive Summary of the report indicates that Hawaii, Pacific Islands, and Puerto Rico are part of the report’s purview. If that is indeed the intended scope, the report should incorporate known information on tidal wetlands and estuaries from these locations in both the text and the figures.
The discussion on p. 597 about why estuaries are unique systems to understand carbon cycling and acidification provides the basis for why some scientists refer specifically to this problem as “estuarine acidification”. The authors may want to specifically use this term and explain why these processes are distinct from open ocean acidification that is dictated purely by influx of anthropogenic CO2.
- Are the findings documented in a consistent, transparent and credible way?
The Findings are generally appropriate and are in alignment with the supporting text. However, they are primarily focused on tidal wetlands.
Finding 4 could be expanded to two bullets, one for tidal wetlands and one for estuaries.
The chapter would benefit from an additional Key Finding focused on research needs/gaps (for example, as seen in Chapter16)
An additional finding could focus on the loss of these critical habitats and the importance that has for the magnitude of the coastal carbon sink.
It is unclear why the authors rate Key Finding 2 with “high confidence” but “likely”.
- Are the report’s key messages and graphics clear and appropriate? Specifically, do they reflect supporting evidence, include an assessment of likelihood, and communicate effectively?
Tables are effective and clear, and figures are appropriate. The addition of one figure showing an example observational dataset would be helpful.
In Table 15.1 it seems possible that Pacific Coast seagrass and tidal marsh extent have been underestimated. As this value is not well-established in the literature, we urge the authors to carefully review relevant databases to assure this is as robust an estimate as possible.9
Figure 15.2 is not consistent with the figure in the Executive Summary that indicates that Hawaii, Pacific Islands, and Puerto Rico will be considered.
Figure 15.1 is very complex, but is a useful and important figure.
The tables in the Appendix are important and provide valuable information to support the findings in the report. Can Table 15A.4 be expanded to include Pacific estuaries? (see text below about further underscoring research gaps and needs if this is the case)
- Are the research needs identified in the report appropriate?
Research needs should be highlighted as a Finding if possible. In general, while the Synthesis, Knowledge Gaps & Outlook section is well written, these needs could be more significantly emphasized in the report.
Additional information is needed on how sea level rise will impact carbon storage in these environments, and/or a discussion of the fact that this is a gap/need in knowledge.
Also in Section 15.7: protection of habitats that provide carbon storage potential shows up in both Chapter 17 and the Executive Summary. The Committee recommends providing a discussion here of the value of conserving tidal wetlands and estuaries given their carbon storage potential.
In general, because some “gaps” have been discussed in previous sections (which is appropriate), the Synthesis/Knowledge Gaps section (15.7) is slightly redundant. One way to streamline this section would be to provide a brief synthesis section and then bullet points for “gaps”.
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9 For example: http://portal.westcoastoceans.org/; http://www.westcoast.fisheries.noaa.gov/habitat/fish_habitat/seagrass_2.html.
- Are the data and analyses handled in a competent manner? Are statistical methods applied appropriately?
The authors appropriately summarize and cite published analyses.
- Are the document’s presentation, level of technicality, and organization effective? Are the questions outlined in the prospectus addressed and communicated in a manner that is appropriate and accessible for the intended audience?
The chapter is well written, very through, and a concise point of reference for the state of the science on Estuary/Tidal carbon cycle. The level of technicality is appropriate for an interested scientific audience (undergraduates, graduate students, or scientists from other fields).
Line-Specific Comments
P595, Line 1-3
This Key Finding could be split into two.
P601, Line 17-28
The “low inflow estuaries” that are commonly found on the U.S. West Coast are not described and discussed here.
P604, Line 18
This should be corrected to “organic rich” not “organics rich.”
P612, Line 18
Key Areas should be broadened to reflect the full chapter.
P641 Line 2
The map should reflect / align with Executive Summary in including Hawaii, Pacific Islands and Puerto Rico.
P596, Line 12
Replace “dropped” to “slowed” - to avoid ..”rise dropped..”
P596, Line 39-40
This topic - the loss of habitat that serves as carbon storage - could be quantified further and included as a key finding.
P597, Line 1-24
This discussion summarizes why some scientist specify “estuarine acidification” processes as unique and distinct from ocean acidification. Authors may want to incorporate and utilize that term into their explanation.
P597, Line 35
Also methane emissions could be discussed here?
P601, Line 3
All other sections in this part of the chapter use regional abbreviations (GMx, MAB, etc) but Pacific Coast does not.
P601, Line 17
What is a “large marine ecosystem”? Does large refer to area?
P602, Line 30-40
Thorough treatment of CH4 here, could be expanded to other sections.
P611, Line 12-39
Could an example dataset be included as a figure here to provide a time series of observational data?
P613, Line 32
Some of this section is redundant with previous material; may be able to streamline by providing a summary of “gaps” in bullets.
