Removal of floodwater nitrogen in a cypress swamp receiving primary wastewater effluent

Abstract

Intact sediment-water columns from a flowing cypress swamp receiving primary wastewater effluent were used to evaluate inorganic N removal and to determine the fate of ¹⁵NH ^sup+_inf4 -N added to the floodwater. Treatments represented wetland sites which had received 0 (initial application), 2, and 50 years of primary wastewater application. The rate of inorganic-N decrease in the floodwater was greatest for the initial application columns, primarily due to sediment adsorption of NH ^sup+_inf4 , followed by 2-year and 50-yr-columns. Maximum removal rates were 318, 296, and 148 mg N m⁻² day⁻¹, respectively. At the end of the 21-day study period, only 0.5 to 2.3% of applied ¹⁵N was recovered in the floodwater and 11.4 to 17.3% was recovered in the sediment, with the remaining 82.2 to 86.3% being lost from the sediment-water system. Results of the study indicated that N removal efficiency did not decrease with prolonged wastewater application, despite reduced sediment adsorption capacity, because of the significance of gaseous N losses (nitrification-denitrification, NH₃ volatilization) as an N sink in the sediment-water system.