Carbon fluxes and stocks in a carbonate-rich chenier plain

Abstract

Coastal wetlands play an important role in the global carbon cycle because they have high ecosystem productivity and carbon sequestration capability. Previous research focused on the carbon dynamics of organic-rich ecosystems (e.g., salt marshes, mangroves), while little attention has paid to the carbon cycling of carbonate-rich ecosystems such as chenier plains, sandy or shelly beach ridges that are parts of strand plains. Here we examined the carbon stocks and fluxes of the poorly studied chenier plain in the Yellow River Delta, China. The inorganic and organic carbon pools in the top 1 m sediment were 444 ± 92 Mg C ha−1 and 89 ± 7 Mg C ha−1, respectively. The average CO2 net sequestration was −177 ± 51 Mg C ha−1, indicating that the chenier plain had a net CO2 evasion during the entire soil formation process. With plant growth, however, the chenier plain provided a significant carbon sink (395 g C m−2 a−1) on a per-unit area basis. The annual gross ecosystem productivity (GEP) and ecosystem respiration (Re) were 1067 and 672 g C m−2 a−1, respectively. The carbon sink strength of the chenier plain was comparable to that of organic-rich salt marshes on a per-unit area basis. The biomass carbon pool was 5.0 ± 1.4 Mg C ha−1 in the chenier plain. Moreover, the sediment inorganic carbon content in mudflats was significantly lower than that of vegetated habitats. Our results showed that plant grown in a chenier plain could significantly enhance carbon sequestration by increasing organic carbon storage. Inorganic carbon storage should be considered in blue carbon inventories because inorganic carbon dominates the carbon pool and is important in the carbon cycling in a chenier plain. Our findings can help us better understand the carbon cycling of carbonate-rich coastal ecosystems and can inform chenier plain conservation and restoration efforts.