title: Microbial nitrogen transformation in constructed wetlands treating contaminated groundwater.
abstract: Pathways of ammonium (NH4 (+)) removal were investigated using the stable isotope approach in constructed wetlands (CWs). We investigated and compared several types of CWs: planted horizontal subsurface flow (HSSF), unplanted HSSF, and floating plant root mat (FPRM), including spatial and seasonal variations. Plant presence was the key factor influencing efficiency of NH4 (+) removal in all CWs, what was illustrated by lower NH4 (+)-N removal by the unplanted HSSF CW in comparison with planted CWs. No statistically significant differences in NH4 (+) removal efficiencies between seasons were detected. Even though plant uptake accounted for 32-100 % of NH4 (+) removal during spring and summer in planted CWs, throughout the year, most of NH4 (+) was removed via simultaneous nitrification-denitrification, what was clearly shown by linear increase of δ(15)N-NH4 (+) with decrease of loads along the flow path and absence of nitrate (NO3 (-)) accumulation. Average yearly enrichment factor for nitrification was -7.9 ‰ for planted HSSF CW and -5.8 ‰ for FPRM. Lack of enrichment for δ(15)N-NO3 (-) implied that other processes, such as nitrification and mineralization were superimposed on denitrification and makes the stable isotope approach unsuitable for the estimation of denitrification in the systems obtaining NH4 (+) rich inflow water.
authors.affiliation: Department of Catchment Hydrology, UFZ - Helmholtz Centre for Environmental Research, Theodor-Lieser-Str. 4, 06120, Halle/Saale, Germany, oksana.voloshchenko@ufz.de.
authors.forename: Oksana
authors.initials: O
authors.lastname: Coban
authors.forename: Peter
authors.initials: P
authors.lastname: Kuschk
authors.forename: Naomi S
authors.initials: NS
authors.lastname: Wells
authors.forename: Gerhard
authors.initials: G
authors.lastname: Strauch
authors.forename: Kay
authors.initials: K
authors.lastname: Knoeller
mesh_terms: D064751:Ammonium Compounds / Q000302:isolation & purification / Q000378:metabolism*; D001673:Biodegradation, Environmental; D058440:Denitrification; D060587:Groundwater / Q000032:analysis* / Q000382:microbiology; D009566:Nitrates / Q000302:isolation & purification / Q000378:metabolism*; D058465:Nitrification; D018517:Plant Roots / Q000378:metabolism; D006109:Poaceae / Q000378:metabolism; D012621:Seasons; D014874:Water Pollutants, Chemical / Q000032:analysis / Q000378:metabolism*; D018508:Water Purification; D053833:Wetlands
chemical_list: D064751:Ammonium Compounds; D009566:Nitrates; D014874:Water Pollutants, Chemical