Impacts of plant (egeria densa) density and nutrient composition on nitrogen transformation mechanisms in laboratory microcosms

Abstract

The impacts of plant (Egeria densa) density and nutrient composition on nitrogen transformation mechanisms in laboratory microcosms were studied with a low plant density system (LPDS) and a high plant density system (HPDS). The NH4+-N removal efficiency increased with increasing concentration (2–8 mgL−1) at lower NO3-N concentrations (0–2 mgL−1), while it decreased at higher NO3-N concentrations in LPDS (>2 mgL−1). The NO3-N removal efficiency showed a positive correlation with initial NH4+-N concentration in both HPDS (R2=0.93) and LPDS (R2=0.88). The total nitrogen (TN) removal efficiency was positively affected by the initial NH4+-N concentration, while it was negatively affected by the NO3-N concentration in LPDS. TN removal efficiency was significantly different between HPDS and LPDS (p<0.01). The organic nitrogen concentration was higher in LPDS than that found in the initial solution. The mutual interactions among different forms of nitrogen affected their removal mechanisms more significantly in LPDS than HPDS. Further, the removal efficiencies varied with the predominant transformation mechanisms, and consequently the plant density and nutrient composition must be considered simultaneously when applying these results to nitrogen removal efficiencies in submersed plant wetland system. © 2009, Copyright Taylor & Francis Group, LLC.