Abstract: Wetland ecosystems have strong carbon storage and sequestration abilities, playing an important role in global carbon cycle. To understand the carbon sequestration capacity of salt marsh wetlands, we estimated net primary productivity based on field investigation and remote sensing in a typical tidal creek system in the southern Chongming Dongtan Wetland. The carbon sequestration potential of salt marsh wetlands under environmental change was also estimated. The results showed that net primary productivity of halophytes exhibited significant temporal and spatial variations. The temporal variations were mainly reflected in the interannual differences and seasonal differences. The total net primary productivity of salt marsh in 2013 and 2017 was 245.70 and 257.75 t C·a^-1, respectively, showing a slight increase. The net primary productivity in summer (97.70±69.31 g C m^-2·month^-1) was significantly higher than that in other seasons (P<0.05). At the spatial scale, net primary productivity decreased with elevation and Phragmites australis cohorts (1079.64±168.34 g C m^-2·a^-1) had significantly higher net primary productivity than other cover types (P<0.05). In 2017-2018, the carbon sequestration capacity of salt marshes in the study area was lower than the average level of carbon sequestration capacity of terrestrial vegetation in the same area. As the marsh matures gradually, carbon sequestration capacity can be further improved. Under the background of sea level rise, the positive succession of salt marsh vegetation compensates for the organic carbon loss caused by the erosion of salt marsh edge. The total carbon sequestration potential increased by 130.24-250.12 t·a^-1. The continuous rise of global temperature and the changes of estuarine environment, such as sea level rise, shoreline erosion, vegetation succession and human disturbance, increase the uncertainty of salt marsh carbon sequestration ability. Prediction of its contribution to carboncycle will provide scientific support for carbon sequestration and increasing carbon sinks.

Key words: salt marsh, net primary productivity, carbon sequestration ability.