Editing IPCC:AR6/SROCC/Chapter-5 (section)

===== 5.5.1.2.1 Opportunities and challenges relating to coastal carbon =====

Estuaries, shelf seas and a wide range of other intertidal and shallow-water habitats (Section 5.3) play an important role in the global carbon cycle through their primary production by rooted plants, seaweeds (macroalgae) and phytoplankton, and also by processing riverine organic carbon. However, the natural carbon dynamics of these systems have been greatly changed by human activities (Regnier et al., 2013 <sup>[[#fn:r1648|1648]]</sup> ; Cloern et al., 2016 <sup>[[#fn:r16|16]]</sup> 49; Day and Rybczyk, 2019 <sup>[[#fn:r1650|1650]]</sup> ) ( ''high confidence'' ). Direct anthropogenic impacts include coastal land-use change (Ramesh et al., 2015 <sup>[[#fn:r1651|1651]]</sup> ; Li et al., 2018a <sup>[[#fn:r1652|1652]]</sup> ); indirect effects include increased nutrient delivery and other changes in river catchments (Jiao et al., 2011 <sup>[[#fn:r1653|1653]]</sup> ; Regnier et al., 2013 <sup>[[#fn:r1654|1654]]</sup> ), and marine resource exploitation in shelf seas (Bauer et al., 2013 <sup>[[#fn:r1655|1655]]</sup> ). There is ''high confidence'' that these human-driven changes will continue, reflecting coastal settlement trends and global population growth (Barragán and de Andrés, 2015 <sup>[[#fn:r1656|1656]]</sup> ) .

Policy recognition of the mitigation benefits of coastal ecosystems requires quantitative information on their actual and potential carbon uptake and storage at the local and national scale, within an international framework for carbon accounting (Crooks et al., 2011 <sup>[[#fn:r1657|1657]]</sup> ; Hejnowicz et al., 2015 <sup>[[#fn:r1658|1658]]</sup> ). Such methods are being developed for coastal habitats structured by rooted plants (Needelman et al., 2018 <sup>[[#fn:r1659|1659]]</sup> ; Troxler et al., 2018 <sup>[[#fn:r1660|1660]]</sup> ; Needelman et al., 2019 <sup>[[#fn:r1661|1661]]</sup> ), considered here as ‘coastal vegetation’, linked to protocols for verification of longterm carbon removal and financial incentives (Crooks et al., 2011 <sup>[[#fn:r1662|1662]]</sup> ; Hejnowicz et al., 2015 <sup>[[#fn:r1663|1663]]</sup> ) and building on techniques used for managing terrestrial carbon sinks (Ahmed and Glaser, 2016b <sup>[[#fn:r1664|1664]]</sup> ; Aziz et al., 2016 <sup>[[#fn:r1665|1665]]</sup> ). Proposals to apply carbon accounting to seaweeds, the water column and shelf sea sediments (Krause-Jensen and Duarte, 2016 <sup>[[#fn:r1666|1666]]</sup> ; Zhang et al., 2017 <sup>[[#fn:r1667|1667]]</sup> ) are less well-developed.

<div id="section-5-5-1-2climate-mitigation-in-the-coastal-ocean-block-2"></div>

<span id="coastal-vegetation-mangrove-salt-marsh-and-seagrass-ecosystems"></span>