title: Isotopic composition of nitrogenous compounds with emphasis on anthropogenic loading in river ecosystems.
abstract: Nitrogenous compounds with high delta(15)N values were recently found in human-dominated small rivers in the Lake Biwa area. A detailed survey was performed to determine the distribution and variation of delta(15)N values in nitrogenous compounds in a representative small river (Hebisuna River) that flows into Lake Nishinoko, an inner bay of Lake Biwa. A high delta(15)N value was detected in the lower reaches of the river and the inner bay, most likely due to denitrification. These results strongly suggest that denitrification in small river systems such as the Hebisuna watershed has contributed to (15)N enrichment in the Lake Biwa ecosystem during the past 40 years. We also observed a clear, stepwise, positive correlation between population density and delta(15)N values for particulate organic matter or sediments. These results demonstrate that delta(15)N (POM) and delta(15)N (sediment) are helpful indicators for assessing nitrogen loading from domestic sewage. Moreover, they will aid in the development of new concepts in the environmental capacity of river ecosystems and its relationship to redox conditions. Finally, our data suggest that a population density of 100-200 persons per km(2) is the upper limit for a watershed in which only simple conventional sewage treatment is in effect.
authors.affiliation: Center for Ecological Research, Kyoto University, Otsu, Shiga, Japan.
authors.forename: Junko
authors.initials: J
authors.lastname: Nishikawa
authors.forename: Ayato
authors.initials: A
authors.lastname: Kohzu
authors.forename: Narin
authors.initials: N
authors.lastname: Boontanon
authors.forename: Tomoya
authors.initials: T
authors.lastname: Iwata
authors.forename: Takuya
authors.initials: T
authors.lastname: Tanaka
authors.forename: Nanako O
authors.initials: NO
authors.lastname: Ogawa
authors.forename: Reiichiro
authors.initials: R
authors.lastname: Ishii
authors.forename: Eitaro
authors.initials: E
authors.lastname: Wada
mesh_terms: D002712:Chlorides / Q000032:analysis; D017753:Ecosystem; D004784:Environmental Monitoring; D006801:Humans; D007564:Japan; D009584:Nitrogen / Q000032:analysis* / Q000737:chemistry; D009587:Nitrogen Isotopes / Q000032:analysis; D011156:Population Density; D045483:Rivers / Q000737:chemistry*; D014874:Water Pollutants, Chemical / Q000032:analysis* / Q000737:chemistry; D014881:Water Supply
chemical_list: D002712:Chlorides; D009587:Nitrogen Isotopes; D014874:Water Pollutants, Chemical; D009584:Nitrogen