Nitrogen Distribution in Soils of Constructed Wetlands Treating Lagoon Wastewater

Abstract

Constructed wetlands have the potential to be used for treatment of N‐rich livestock wastewater. Our objectives were to evaluate both the time effect and increasing N loading rates on soil N distribution and NH+4–N concentration in surface‐pore water of constructed wetlands. A 5‐yr study in North Carolina investigated two wetland systems that treated swine lagoon wastewater. Wetland System 1 was planted to a Schoenoplectus americanus (Pers.) Volkart ex Schinz & R. Keller, S. tabernaemontani (K.C. Gmel.) Palla, Scirpus cyperinus (L.) Kunth, and Juncus effusus L. plant community, and Wetland System 2 was planted to a Typha angustifolia L., T. latifolia L., and Sparganium americanum Nutt. plant community. Nitrogen loading rates were increased annually from 0.6 to 2.7 g m−2 d−1 Soils were analyzed for total N annually. Surface‐pore water was sampled with equilibrators and analyzed for NH+4–N. Although the total N accumulation significantly increased with time in both systems, total soil N accumulation by depth did not differ significantly between systems. Distribution profiles in the surface‐pore water column showed that NH+4–N was transported upward into surface water at N loading rates from 1.2 to 2.7 g m−2 d−1 As total N loading rates increased annually in both wetland systems, soil pore water had higher levels of NH+4–N but N removal efficiency of the wetlands sharply decreased. Accumulation of high levels of NH+4–N (>200 mg L−1) in soil pore water could negatively affect long‐term ability of wetland systems to treat wastewater with high N levels.