Historical reconstruction of mangrove expansion in the Gulf of Mexico: Linking climate change with carbon sequestration in coastal wetlands

There has been considerable interest in a recently recognized and important sink in the global carbon pool, commonly referred to as “blue carbon”. The major goal of this study was to determine the historical reconstruction of mangrove expansion (Avicennia germinans) into salt marshes (Spartina alterniflora) and its effects on carbon sequestration and soil chemistry in wetland soils of the northwestern Gulf of Mexico. We used bulk stable isotopic, chemical biomarker analyses, and aerial imagery analysis to identify changes in OC wetland sources, and radiotracers (137Cs and 210Pb) for chronology. Soil cores were collected at two sites at Port Aransas, Texas (USA), Harbor Island and Mud Island. isotopic values of δ13C and δ15N of all soil samples ranged from −26.8 to −15.6‰ and 1.8–10.4‰ and showed a significant trend of increasing depletion for each isotope from bottom to surface soils. The most depleted δ13C values were in surface soils at the Mud Island (Mangrove 2) location. Carbon sequestration rates were greater in mangroves and for the Mud Island Mangrove 1 and the Marsh 1 sites ranged from 253 to 270 and 101–125 g C m−2 yr−1, respectively. Lignin storage rates were also greater for mangrove sites and for the Mud Island Mangrove 1 and the Marsh 1 ranged from 19.5 to 20.1 and 16.5 to 12.8 g lignin m−2 yr−1, respectively. Τhe Λ8 and Λ6 values for all cores ranged from 0.5 to 21.5 and 0.4 to 16.5, respectively, and showed a significant increase from bottom to surface sediments. If regional changes in the Gulf of Mexico are to persist and much of the marsh vegetation was to be replaced by mangroves, there could be significant increases on the overall storage and sequestration of carbon in the coastal zone.