Nitrate availability affects denitrification in Phragmites australis sediments

Abstract

Understanding relationships between an increase in nitrate (NO3−) loading and the corresponding effects of wetland vegetation on denitrification is essential to designing, restoring, and managing wetlands and canals to maximize their effectiveness as buffers against eutrophication. Although Phragmites australis (Cav.) Trin. ex Steud. is frequently used to remediate nitrogen (N) pollution, no information is available on how NO3− concentration may affect plant‐mediated denitrification. In the present study, denitrification was measured in outdoor vegetated and unvegetated mesocosms incubated in both summer and winter. After spiking the mesocosms with NO3− concentrations typical of agricultural drainage water (0.7−11.2 mg N L−1), denitrification was quantified by the simultaneous measurement of NO3− consumption and dinitrogen gas (N2) production. Although denitrification rates varied with vegetation presence and season, NO3− availability exerted a significant positive effect on the process. Vegetated sediments were more efficient than bare sediments in adapting their mitigation potential to an increase in NO3−, by yielding a one‐order‐of‐magnitude increase in NO3− removal rates, under both summer (743−6007 mg N m−2 d−1) and winter (43−302 mg N m−2 d−1) conditions along the NO3− gradient. Denitrification was the dominant sink for water NO3− in winter and only for vegetated sediments in summer. Nitrification likely contributed to fuel denitrification in summer unvegetated sediments. Since denitrification rates followed Michaelis–Menten kinetics, P. australis‐mediated depuration may be considered optimal up to 5.0 mg N L−1. The present outcomes provide experimentally supported evidence that restoration with P. australis can work as a cost‐effective means of improving water quality in agricultural watersheds.

A threshold‐like effect on the interaction between hydrological connectivity and dominant plant population in tidal marsh wetlands

“…In addition, TN and TP were also reported as determinants for the growth and community succession of P . australis (González‐Alcaraz et al, 2012; Soana, Gavioli, Vincenzi, Fano, & Castaldelli, 2020) but failed to show significant impacts here. Further analysis showed that TN ranged from 0.11 to 0.26 g kg −1 , and TP ranged from 0.41 to 0.70 g kg −1 in the experimental area.…”

“…For the spatial structures shown in Figure 7b, the first two and three dimensions accounted for 36.87 and 43.76% of the explainable variance, respectively, and only SWC was correlated to the plant traits' matrix at a 95% confidence level (p = 0.032). In addition, TN and TP were also reported as determinants for the growth and community succession of P. australis (Gonz alez- Alcaraz et al, 2012;Soana, Gavioli, Vincenzi, Fano, & Castaldelli, 2020) but failed to show significant impacts here. Further analysis showed that TN ranged from 0.11 to 0.26 g kg À1 , and TP ranged from 0.41 to 0.70 g kg À1 in the experimental area.…”

A Threshold-like Effect on the Interaction Between Hydrological Connectivity and Dominant Plant Population in Tidal Marsh Wetlands

“…For the spatial structures shown in Figure 7B, the first two and three dimensions accounted for 36.87 % and 43.76 % of the explainable variance, respectively, and only SWC was correlated to the plant traits' matrix at a 95 % confidence level (P = 0.032 ). In addition, TN and TP were also reported as determinants for the growth and community succession of P. australis (Gonzalez-Alcaraz et al, 2012;Soana et al, 2020) but failed to show significant impacts here. Further analysis showed that TN ranged from 0.11 g/kg to 0.26 g/kg, and TP ranged from 0.41 g/kg to 0.70 g/kg in the experimental area.…”

Aquatic Vegetation Loss and Its Implication on Climate Regulation in a Protected Freshwater Wetland of Po River Delta Park (Italy)

“…On the other hand, the analysis of water chemistry did not highlight any nutrient retention process due to P. australis presence. Even though phytodepuration function of common reed beds are widely documented [65], denitrification processes are not supported in absence of constant water fluxes [66], such as the case of Valle Santa wetland. The high concentration of NO 3 − is coherent with the diffuse agricultural pollution that occur in the surrounding land and within the basin of Idice stream.…”