Carbon density assessment of typical areas of muddy tidal flat in Tangshan City, Hebei Province

As a type of coastal wetland in the sea-land interaction zone, muddy tidal flats exhibit significant carbon sequestration potential and ecological functions. We focused on the muddy tidal flats of Tangshan City, Hebei Province to carry out on-site investigations. We selected 23 sampling points to determine the sediment bulk density, organic carbon content and other indicators, calculate the sediment carbon density of estuaries, aquaculture ponds, and unvegetated areas, estimate the sediment carbon stock, and propose targeted strategies for carbon sequestration and sink enhancement. The results showed that the estuary had the highest carbon density (50.12 g/m²), followed by the aquaculture pond (44.30 g/m²), while the unvegetated area had the lowest (2.42 g/m²). The total sediment carbon storage in the investigated areas was approximately 89 417.99 t C, of which the estuary areas contributed over 50% (about 45 306.54 t C), the Douhe Estuary is 22 657.1 t C, and the Shahe Estuary is 22 649.44 t C; the aquaculture ponds contributed 42 384.06 t C, and the unvegetated areas contributed the least (1 727.38 t C). Differences in carbon density values were primarily caused by inputs from land-based sources, biological activities, and tidal flushing. The carbon sequestration capacity of unvegetated areas was extremely weak due to the lack of vegetation fixation and organic matter sources. The study revealed that the carbon density of muddy tidal flats was significantly lower than that of typical coastal ecosystems, such as mangrove forests and salt marshes, and the carbon density in the studied estuaries was significantly lower than in large estuaries such as the Yangtze River and Pearl River estuaries. To enhance regional carbon sequestration capacity, it was recommended to implement measures to restoring aquaculture ponds to natural tidal flats and establish a regular monitoring system.