Different Denitrification Capacity in Phragmites australis and Typha latifolia Sediments: Does the Availability of Surface Area for Biofilm Colonization Matter?

Denitrification is a permanent nitrogen removal pathway; thus, it is a desirable ecosystem function in water bodies receiving agricultural runoff. Knowledge of denitrification capacity in response to vegetation type and varying NO3− loads is essential for designing effectively constructed wetlands to control eutrophication. The aim of this study was to compare the nitrogen removal efficiency of two common wetland macrophytes, i.e., Phragmites australis and Typha latifolia in a NO3− enrichment experiment (50−800 µM). Measurements of NO3− consumption, and N2 production were performed in vegetated and unvegetated mesocosms incubated in summer (26 °C) at biomass peak. Vegetated sediments demonstrated higher efficiency in converting NO3− to N2 via denitrification (<600–18,000 µmol N m−2 h−1) than bare sediments (300–3300 µmol N m−2 h−1). However, the denitrification stimulation effect from NO3− pulsing differed significantly between plant types. It can be hypothesized that P. australis played a more beneficial role than T. latifolia due to its greater submerged surface area, which facilitated enhanced opportunities for contact between NO3− and denitrifying bacteria. This ultimately resulted in an increased treatment performance. Understanding the interactions between plants and environmental drivers regulating denitrification is critical information for optimal wetland species selection. With an increasing global focus on sustainable water quality management, this research provides valuable insights into optimizing nature-based solutions.