title: The use of δ15N and δ18O tracers with an understanding of groundwater flow dynamics for evaluating the origins and attenuation mechanisms of nitrate pollution.
abstract: During early 2000, a new analytical procedure for nitrate isotopic measurement, termed the "denitrifier method", was established. With the development of the nitrate isotope tracer method, much research has been reported detailing sources of groundwater nitrate and denitrification mechanisms. However, a shortcoming of these tracer studies has been indicated owing to some overlapping of isotope compositions among different source materials and denitrification trends. In order to reduce these uncertainties, we examined nitrate isotope ratios within a frame of "regional groundwater flow dynamics" to eliminate unnecessary uncertainties in elucidating nitrate sources and behaviors. A total of 361 samples were collected from the Kumamoto area: the circulated groundwater system with a scale of 10(3) km(2) in southern Japan. Subsequently, the nitrate pollution was examined within the above-mentioned framework. As a result, a reasonable identification of the sources and attenuation behaviors (both denitrification and dilution) of groundwater nitrate pollution was obtained over the study area. This study demonstrates that the use of nitrate isotope tracers efficiently improves with a comprehensive understanding of groundwater flow dynamics. The approach emphasized in this study is important and should be applicable in other areas.
authors.affiliation: Priority Organization for Innovation and Excellence, Kumamoto University, 2-39-1 Kurokami, Kumamoto 860-8555, Japan. hosono@kumamoto-u.ac.jp
authors.forename: Takahiro
authors.initials: T
authors.lastname: Hosono
authors.forename: Takahiro
authors.initials: T
authors.lastname: Tokunaga
authors.forename: Makoto
authors.initials: M
authors.lastname: Kagabu
authors.forename: Haruhiko
authors.initials: H
authors.lastname: Nakata
authors.forename: Takanori
authors.initials: T
authors.lastname: Orishikida
authors.forename: In-Tian
authors.initials: IT
authors.lastname: Lin
authors.forename: Jun
authors.initials: J
authors.lastname: Shimada
mesh_terms: D002852:Chromatography, Ion Exchange; D058440:Denitrification; D004784:Environmental Monitoring / Q000379:methods*; D005308:Fertilizers / Q000032:analysis; D060587:Groundwater / Q000032:analysis*; D007564:Japan; D008372:Manure / Q000032:analysis; D013058:Mass Spectrometry; D060985:Natural Springs / Q000032:analysis*; D009566:Nitrates / Q000032:analysis* / Q000737:chemistry; D009587:Nitrogen Isotopes / Q000032:analysis / Q000737:chemistry; D045483:Rivers / Q000737:chemistry*; D012621:Seasons; D012722:Sewage / Q000032:analysis; D014872:Water Movements; D014874:Water Pollutants, Chemical / Q000032:analysis*
chemical_list: D005308:Fertilizers; D008372:Manure; D009566:Nitrates; D009587:Nitrogen Isotopes; D012722:Sewage; D014874:Water Pollutants, Chemical