Muddy Waters: Unintentional Consequences of Blue Carbon Research Obscure Our Understanding of Organic Carbon Dynamics in Seagrass Ecosystems

Abstract

The recent surge in research on organic carbon sequestration by seagrass ecosystems has begun to reveal the complexity of the carbon cycle within these ecosystems. In this prospective we discuss two areas of investigation that require further scrutiny: (1) why organic carbon is stabilized in seagrass sediments, and (2) how long organic carbon resides within these sediments. By delving into these topics, pointing out current pitfalls, and highlighting methodological advances, our motive is to focus future efforts and provide a frame work to manage the complexity found within the diverse seagrass bioregions. The high rate of seagrass degradation and loss, coupled with increasing atmospheric CO 2 concentrations gives precedence to these lines of research, which require rigorous reevaluation if we are to substantially advance our understanding of OC dynamics in seagrass ecosystems.

Seagrass community-level controls over organic carbon storage are constrained by geophysical attributes within meadows of Zanzibar, Tanzania

“…Once the flow-regime becomes energetic enough to create sediment 10 limitation, properties of the sediment can again outweigh plant traits to limit OC storage even under meadows with traits conducive to OC storage. Of course, this hypothesis needs to be rigorously tested but the modulation of trait effects by geophysical properties provides hints that different OC stabilization mechanisms are potentially operating within the different environments (Belshe et al, 2017;Burdige, 2007;Lutzow et al, 2006;Miyajima et al, 2017), and the persistence of seagrass sediment OC is a whole-ecosystem property (Lehmann and Kleber, 2015;Schmidt et al, 2011). 15…”

“…Seagrass biomass has been correlated to OC storage (Armitage and Fourqurean, 2016;Serrano et al, 2016). Belowground production of seagrass roots and rhizomes places OC directly into sediments, which can be stabilized on mineral surfaces, within aggregates, or if microbial activity is suppressed due to lack of oxygen (Belshe et al, 2017;Duarte et al, 2010). In addition, the binding of the sediment by the root-rhizome Biogeosciences Discuss., https://doi.org /10.5194/bg-2017-474 Manuscript under review for journal Biogeosciences Discussion started: 18 December 2017 c Author(s) 2017.…”

Reduced water motion enhances organic carbon stocks in temperate eelgrass meadows

“…Carbon storage in seagrass meadows depends on species composition, canopy complexity, water depth, turbidity, and biotic interactions, among other factors (Belshe et al 2018;Mazarrasa et al 2018). Furthermore, the molecular composition and recalcitrance of OC sources (litter quality), sediment mineralogy, temperature, and microbial community composition are also important in determining the quantity and quality of carbon sequestered in seagrass meadows (Belshe et al 2017;Trevathan-Tackett et al 2017). Benthic disturbances, such as shading, bioturbation by infauna, and wave action, can also influence OC stocks (Barañano et al 2017;Trevathan-Tackett et al 2018).…”

Impacts of land management practices on blue carbon stocks and greenhouse gas fluxes in coastal ecosystems—A meta‐analysis

“…These often quantify the amount of carbon sequestered as a result of protecting a BCE against ongoing loss from anthropogenic threats such as urbanization, reclamation, deforestation, eutrophication and pollution (Ahmed & Glaser, 2016;Alongi, 2011;Herr, Unger, Laffoley, & Mcgivern, 2017;Lovelock & Duarte, 2019). Adapting such terrestrial forest management strategies to BCEs may enhance carbon sequestration, although the complex and open nature of coastal ecosystems compared to their terrestrial counterparts raise challenges in accurately identifying the underlying mechanisms controlling fluxes of both carbon and greenhouse gases (GHGs; Belshe, Mateo, Gillis, Zimmer, & Teichberg, 2017;Johannessen & Macdonald, 2016;McLeod et al, 2011). Restoration management, for example, which utilizes reconstruction or rehabilitation of degraded areas, has long been one of the main approaches used in terrestrial systems to restore ecosystem function to natural areas which have been transformed by deforestation, land-use change and pollution (Camargo, Ferraz, & Imakawa, 2002;Lamb, Erskine, & Parrotta, 2005;Stanturf, Palik, & Dumroese, 2014).…”