Restoration practices and soil properties influence potential denitrification in agricultural floodplain wetlands

Riparian wetlands play a crucial role in nutrient retention and water quality maintenance in agricultural watersheds. Restoring wetland function in these systems is becoming increasingly important as negative impacts of eutrophication continue to increase in both local and downstream ecosystems. This study identified factors regulating wetland soil denitrification rates, a major nitrogen (N) removal pathway, across various wetland restoration practices (based on hydrology and plant structure) in restored agricultural bottomland hardwood forested wetlands. Soil cores from five distinct restoration practices, natural vegetation regeneration, remnant forest, tree planting areas, and constructed shallow water areas (wet and dry), were collected in 23 restored wetlands in Kentucky and Tennessee, USA. Flow-through soil core incubations were used to estimate denitrification as nitrogen gas (N ₂ ) flux during a simulated 2-day flood event. All restoration practices produced N ₂ at each timepoint, and the rates were greater at 48 h for all practices. Mean N ₂ production was highest in natural regeneration and lowest in shallow water-wet areas throughout the 48 h incubation period. However, shallow water-wet areas exhibited the greatest percentage increase between 24 and 48 h, increasing by 48%. The predicted N ₂ production was correlated with sediment oxygen demand (SOD), initial soil moisture, and extractable soil phosphorus (P). These results suggest that all restoration practices efficiently remove N over a 48 h flood period; however, the highest removal rates can depend on the vegetation type, flooding duration, and site-specific soil properties.