Denitrification of soil nitrogen in coastal and inland salt marshes with different flooding frequencies

Denitrification is an important process for removing nitrogen in wetlands, and it is influenced by many environmental factors. However, little information is available on the relationship between hydrologic conditions and denitrification. In this study three typical sampling sites with different flooding frequencies, including short-term flooding wetlands (STFW), seasonal-flooding wetlands (SFW) and tidal flooding wetlands (TFW) were chosen as the study sites in the Yellow River Delta. In contrast, five typical sampling sites with different flooding frequencies, including 100-year floodplain (H), 10-year floodplain (T), 5-year floodplain (F), 1-year floodplain (O) and permanently flooded floodplain (B) were chosen as the study sites in Xianghai wetlands. This study reflected that the denitrification rates decreased with depth along soil profiles in both inland and coastal salt marsh soils. Flooding periods, soil depth and their interaction showed significant effects on the denitrification processes. Generally, higher flooding frequencies will cause higher denitrification rates in salt marshes. Moreover, the denitrification rates were significantly positively correlated with soil moisture content in both wetlands. Additionally, the denitrification rates were significantly positively correlated with organic matter and NO3−_N content while negatively correlated with soil pH and salinity in inland salt marshes. Therefore, the changes in soil properties (e.g. SOM, TN, pH and salinity) can become an important way to control NO3− levels in inland salt marshes.