Agricultural reclamation influence on ecosystem CO2 exchange in a coastal wetlands in the Yellow River Delta, China

Background/Question/Methods

As a typical coastal wetland, the Yellow River Delta is one of the most active regions of land-ocean interaction in the world. The vegetation in the coastal wetland exhibits a patchy distribution, and the natural vegetation is composed of Aquatic and halophytic plant communities predominated by herb and shrub species. As the Yellow River Delta is a significant food production base, it has been undergoing extensive and rapid development of agriculture over recent decades. However, few studies to date have focused on reclamation effect of the net ecosystem carbon exchange over coastal wetlands in Yellow River Delta. In this study, we set up a paired EC flux towers to measure NEE in two adjacent ecosystems, a natural coastal grassland (reed) and a reclaimed coastal grassland (cotton) in the Yellow River Delta, China. The objective of this study was to investigate the impact of reclamation of a natural wetland on ecosystem carbon flux dynamics.

Results/Conclusions

During the growing season from May to October, the number of net sink days in the wetland and the farmland were 157 and 164 days, resulting in respective cumulative NEE values of -237.4 g C m^-2 and -202.0 g C m^-2. Although both sites functioned as net CO₂ sink and the magnitudes of net CO₂ uptake were close, the cumulative NEE in the wetland always higher than that in the farmland through the entire growing season. Thus, the conversion from wetland to farmland caused an increase in net C emissions of approximately 35 g C m^-2 just during the growing season. Furthermore, the cumulative assimilation and respiration values in these two ecosystems showed distinctly different. Approximately 585.7 and 494.8 g C m^-2 were assimilated by gross primary production (GPP), and 348.3 and 292.7 g C m^-2 were released by ecosystem respiration (Re) at the wetland and farmland sites. GPP and Reco at the wetland site were both 1.2 times higher than those at the farmland, respectively. For the entire growing season, the ratio of Reco/GPP in wetland was 0.62 while it was 0.63 for the farmland, indicating these two ecosystems acting as net sink of carbon.