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

===== 5.5.1.2.4 Land-sea integrated eco-engineering =====

Land-based nutrient management could, in theory, be used to enhance carbon storage in coastal seas and deeper waters, by increasing the amount of refractory dissolved organic carbon (Jiao et al., 2011 <sup>[[#fn:r1779|1779]]</sup> ; Jiao et al., 2014b <sup>[[#fn:r1780|1780]]</sup> ; Jiao et al., 2018b <sup>[[#fn:r1781|1781]]</sup> ). This idea is supported by a statistical analysis of the relationship between organic carbon and nitrate in various natural environments (Taylor and Townsend, 2010 <sup>[[#fn:r1782|1782]]</sup> ) as well as by experimental results in estuarine and offshore waters (Yuan et al., 2010 <sup>[[#fn:r1783|1783]]</sup> ; Jiao et al., 2011 <sup>[[#fn:r1784|1784]]</sup> ; Jiao et al., 2014b <sup>[[#fn:r1785|1785]]</sup> ). Delivery of nutrients from agricultural fertilisers and sewage discharge to coastal waters may currently promote the microbial breakdown of river-derived terrestrial dissolved organic carbon, reducing carbon storage (Liu et al., 2014 <sup>[[#fn:r1786|1786]]</sup> ). Thus reducing nutrient inputs in the future may expand carbon storage by favouring the microbial carbon pump, in addition to the multiple co-benefits of reduced nutrient loads related to HABs, oxygenation and ocean acidification (Miranda et al., 2013 <sup>[[#fn:r1787|1787]]</sup> ; Jiao et al., 2018a <sup>[[#fn:r1788|1788]]</sup> ; Zhang et al., 2018 <sup>[[#fn:r1789|1789]]</sup> ). Although there is some evidence for the impact of dissolved organic carbon variations on global scale climate (Rothman et al., 2003 <sup>[[#fn:r1790|1790]]</sup> ) the benefits of this approach have yet to be determined quantitatively and uncertainties remain regarding the longevity of removal and associated carbon accounting (measurement, reporting and verification). Until such issues are better resolved, there is ''low confidence'' that stimulation of refractory dissolved organic carbon production could provide an operational long-term mitigation measure.

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