Seagrass Carbon Methods

[jaxinewolfe]

This documents the case where there is a curious split when plotting organic matter against fraction carbon for seagrass cores. The methods for these studies are presently undocumented in the database (because most were brought in via the Fourqurean synthesis), but it is likely that some of these cores measured and reported total carbon instead of organic carbon. Makes sense that these (tropical) seagrass systems have a lot of carbonate, so it becomes obvious when reported C is total or organic.

The modeled values in the following figure are not included in the Data Library – they were calculated post-synth using the Blue Carbon Manual (Howard et al 2014):

For seagrass soils with % LOI < 0.20 % OC = -0.21 + 0.40 (% LOI);
For seagrass soils with % LOI > 0.20 % OC = -0.33 + 0.43 (% LOI)

The following studies were identified as the ones with cores that may be reporting measured TC instead of OC:

record	bibliography ID	URL
1	Alongi_et_al_2008_article_oct	https://doi.org/10.3354/meps07661
2	Alongi_et_al_2008_article_may	https://doi.org/10.3354/ame01191
3	Fourqurean_et_al_2012_article	https://doi.org/10.1038/ngeo1477
4	Danovaro_1996_article	https://doi.org/10.1007/bf00993638
5	Erftemeijer_and_Middelburg_1993_article	https://www.jstor.org/stable/24841993
6	Fourqurean_et_al_2010_article	https://doi.org/10.1016/j.marpolbul.2010.03.003
7	Kamp-Nielsen_et_al_2002_article	https://doi.org/10.1006/ecss.2001.0822
8	Koch_and_Madden_2001_article	https://doi.org/10.3354/meps219109
9	Orem_et_al_1999_article	https://www.jstor.org/stable/4299024
10	Rigollet_et_al_2004_article	https://doi.org/10.1016/j.biortech.2003.12.018

[jaxinewolfe]

If I ignore the reported carbon for these studies and model OC from the LOI-determined OM, the figure looks like this:

The outlier measured values that indicate high OM and carbon content (high for seagrass) may be from meadows that are established on mangrove peat (this is at least noted for a few of these from Beers et al 2023).

@HolmquistJ I don't know if you'd like us to address any of this before the end-of-June update, but I'm flagging it just in case.