title: Evaluation of wastewater nitrogen transformation in a natural wetland (Ulaanbaatar, Mongolia) using dual-isotope analysis of nitrate.
abstract: The Tuul River, which provides water for the daily needs of many residents of Ulaanbaatar, Mongolia, has been increasingly polluted by wastewater from the city's sewage treatment plant. Information on water movement and the transformation of water-borne materials is required to alleviate the deterioration of water quality. We conducted a synoptic survey of general water movement, water quality including inorganic nitrogen concentrations, and isotopic composition of nitrogen (δ(15)N-NO(3)(-), δ(18)O-NO(3)(-), and δ(15)N-NH(4)(+)) and water (δ(18)O-H(2)O) in a wetland area that receives wastewater before it enters the Tuul River. We sampled surface water, groundwater, and spring water along the two major water routes in the wetland that flow from the drain of the sewage treatment plant to the Tuul River: a continuous tributary and a discontinuous tributary. The continuous tributary had high ammonium (NH(4)(+)) concentrations and nearly stable δ(15)N-NH(4)(+), δ(15)N-NO(3)(-), and δ(18)O-NO(3)(-) concentrations throughout its length, indicating that nitrogen transformation (i.e., nitrification and denitrification) during transit was small. In contrast, NH(4)(+) concentrations decreased along the discontinuous tributary and nitrate (NO(3)(-)) concentrations were low at many points. Values of δ(15)N-NH(4)(+), δ(15)N-NO(3)(-), and δ(18)O-NO(3)(-) increased with flow along the discontinuous route. Our results indicate that nitrification and denitrification contribute to nitrogen removal in the wetland area along the discontinuous tributary with slow water transport. Differences in hydrological pathways and the velocity of wastewater transport through the wetland area greatly affect the extent of nitrogen removal.
authors.affiliation: Center for Ecological Research, Kyoto University, 2-509-3 Hirano, Otsu, Shiga, 520-2113, Japan. masayukiitoh@yahoo.co.jp
authors.forename: Masayuki
authors.initials: M
authors.lastname: Itoh
authors.forename: Yasuhiro
authors.initials: Y
authors.lastname: Takemon
authors.forename: Akiko
authors.initials: A
authors.lastname: Makabe
authors.forename: Chikage
authors.initials: C
authors.lastname: Yoshimizu
authors.forename: Ayato
authors.initials: A
authors.lastname: Kohzu
authors.forename: Nobuhito
authors.initials: N
authors.lastname: Ohte
authors.forename: Dashzeveg
authors.initials: D
authors.lastname: Tumurskh
authors.forename: Ichiro
authors.initials: I
authors.lastname: Tayasu
authors.forename: Naohiro
authors.initials: N
authors.lastname: Yoshida
authors.forename: Toshi
authors.initials: T
authors.lastname: Nagata
mesh_terms: D004784:Environmental Monitoring / Q000379:methods; D005618:Fresh Water / Q000737:chemistry; D007554:Isotopes / Q000032:analysis / Q000737:chemistry; D008986:Mongolia; D009566:Nitrates / Q000032:analysis / Q000737:chemistry*; D009584:Nitrogen / Q000032:analysis / Q000737:chemistry*; D014865:Waste Disposal, Fluid / Q000379:methods*; D014874:Water Pollutants, Chemical / Q000032:analysis / Q000737:chemistry*; D053833:Wetlands
chemical_list: D007554:Isotopes; D009566:Nitrates; D014874:Water Pollutants, Chemical; D009584:Nitrogen