Impact of Coastal Beach Reclamation on Seasonal Greenhouse Gas Emissions: A Study of Diversified Saline–Alkaline Land Use Patterns

Reclaiming coastal wetlands for agricultural purposes has led to intensified farming activities, which are anticipated to affect greenhouse gas (GHG) flux processes within coastal wetland ecosystems. However, how greenhouse gas exchanges respond to variations in agricultural reclamation activities across different years remains uncertain. To address this knowledge gap, this study characterized dynamic exchanges within the soil–plant–atmosphere continuum by employing continuous monitoring across four representative coastal wetland soil–vegetation systems in Jiangsu, China. The results show the carbon dioxide (CO2) and nitrous oxide (N2O) flux exchanges between the system and the atmosphere and soil–vegetation carbon pools, which revealed the drivers of carbon dynamics in the coastal wetland system. The four study sites, converted from coastal wetlands to agricultural lands at different times (years), generally act as CO2 sinks and N2O sources. Higher levels of CO2 sequestration occur as the age of reclamation rises. In terms of time scale, crops lands were found to be CO2 sinks during the growing period but became CO2 sources during the crop fallow period. Although the temporal trend of the N2O flux was generally smooth, reclaimed farmlands acted as net sources of N2O, particularly during the crop-growing period. The RDA and PLS-PM models illustrate that soil salinity, acidity, and hydrothermal conditions were the key drivers affecting the magnitude of the GHG flux exchanges under reclamation. This study demonstrates that GHG emissions from reclaimed wetlands can be effectively regulated through science-based land management, calling for prioritized attention to post-development practices rather than blanket restrictions on coastal exploitation.