Nitrogen Removal in a Small Constructed Wetland:  An Isotope Mass Balance Approach

• Published in: Environmental science & technology Vol. 40; no. 10; pp. 3313 - 3319
• Main Authors: Reinhardt, Miriam, Müller, Beat, Gächter, René, Wehrli, Bernhard
• Format: Journal Article
• Language: English
• Published: Washington, DC American Chemical Society 15-05-2006
• Subjects: Ammonia - analysis; Ammonia - metabolism; Applied sciences; Biodegradation, Environmental; Biological and medical sciences; Biological and physicochemical phenomena; Biological treatment of waters; Biotechnology; Biotransformation; Conservation of Natural Resources; Earth sciences; Earth, ocean, space; Ecosystem; Efficiency; Engineering and environment geology. Geothermics; Environment and pollution; Environmental monitoring; Exact sciences and technology; Fundamental and applied biological sciences. Psychology; Geologic Sediments - chemistry; Industrial applications and implications. Economical aspects; Isotopes; Mineralization; Minerals - chemistry; Minerals - metabolism; Natural water pollution; Nitrates; Nitrites - chemistry; Nitrites - metabolism; Nitrogen; Nitrogen - isolation & purification; Nitrogen - metabolism; Nitrogen Isotopes; Organic Chemicals - isolation & purification; Organic Chemicals - metabolism; Pollution; Pollution, environment geology; Seasons; Sediments; Switzerland; Temperature; Water - chemistry; Water Movements; Water Purification - methods; Water treatment and pollution; Wetlands; Switzerland; Europe; Isotopic analysis; Ammonium; Sediment water interaction; Nitrogen compounds; Nitrates; Coastal zone; Decontamination; Artificial medium; Mineralization; Surface water; Nitrification; Denitrification; Agriculture; Water pollution; Bioremediation; Wetland; Seawater
• ISSN: 0013-936X; 1520-5851
• DOI: 10.1021/es052393d

The nitrogen (N) removal potential of constructed wetlands is increasingly used to lower the N load from agricultural nonpoint sources to inland and coastal waters. To determine the removal efficiency and key factors limiting wetland N removal, N fluxes were studied in a small constructed wetland in Central Switzerland. With an isotope mass balance approach integrating the natural isotope signature of nitrate (NO3 -), ammonium (NH4 +), and particulate nitrogen (PN), the N transformations such as assimilation, mineralization, nitrification, and denitrification were quantified. On average, the wetland removed 45 g m-2 yr-1 N during the studied 2.5 years, corresponding to a removal efficiency of 27%. Denitrification contributed 94% to the N removal, while only 6% of the removed N accumulated in the sediments. Denitrification was most efficient during periods with an oxic water column overlying anoxic sediments, as NH4 + released during mineralization of sediment organic matter was completely nitrified and subsequently denitrified at the sediment−water interface. During water column anoxia, NH4 + accumulated in the water and fueled assimilation by duckweed and internal recycling. The NO3−N isotope signature in the wetland mainly reflected the mineralization of sediment organic matter and subsequent nitrification, while denitrification at the sediment−water interface produced no fractionation.