A model for the contribution of macrophyte-derived organic carbon in harvested tidal freshwater marshes to surrounding estuarine and oceanic ecosystems and its response to global warming

The tidal freshwater marshes dominated by Phragmites australis (common reed) in the Chongxi Wetland are important components of the Yangtze River estuary in China. The litter from P. australis is exported to the surrounding estuarine area and the sea with the tidal flushing in the form of plant residue, particulate organic matter, and dissolved organic matter and is an important organic carbon resource of the East China Sea. A model was constructed using STELLA® software (version 9.1.3) to simulate the contribution of macrophyte-derived organic carbon to surrounding estuary and ocean ecosystems. The model is based on the monitoring and observational data from field surveys and published information on the Chongxi Wetland from 2008 to 2011, and the response of the total organic carbon flowing out of the wetland to global changes was also predicted in conditions of plant shoots that were annually harvested in winter. The results demonstrate the following: (1) the annual contributed organic carbon is 891 g C m−2, of which 612 g C m−2 flows out of the wetland directly as plant residue; (2) total organic carbon continually increases after a short decrease at the start of April of 2010, retains a high value from mid-July to mid-November and rapidly decreases to approximately zero during the harvest of the aboveground plant organs; and (3) accumulated annual organic carbon contributions to the surrounding estuarine and oceanic ecosystems are predicted to increase as the global average temperature rises, and the sea level increases.