title: Sources of hydroxyl radical in headwater streams from nitrogen-saturated forest.
abstract: Hydroxyl radical (HO) photoformation rate (RHO) was determined in headwater stream samples from nitrogen (N)-saturated forests, (1) to quantify the sources of HO in headwater streams and (2) to evaluate the nitrate NO3(-)-induced enhancement of HO formation in stream water caused by N saturation in forested watersheds. Stream water fulvic acid extracted from the forested watersheds was used to quantify the contribution of dissolved organic matter (DOM) to RHO. The results showed that almost all (97%; 81-109%) RHO sources in our headwater stream samples were quantitatively elucidated; the photolysis of NO3(-) (55%; 34-75%), nitrite [N(III)] (2%; 0.5-5.2%), and DOM-derived HO formation, from which photo-Fenton reactions (18%; 12-26%) and the direct photolysis of fluorescent dissolved organic matter (FDOM) (22%; 10-40%), was successfully separated. FDOM, which accounted for 53% (24-96%) of DOM in total organic carbon bases, was responsible for HO formation in our headwater streams. High NO3(-) leaching caused by N saturation in forested watersheds increased RHO in the headwaters, indicating that N-saturated forest could significantly change photoinduced and biogeochemical processes via enhanced HO formation in downstream water.
authors.affiliation: Kyushu University Forest, Kyushu University, 394 Tsubakuro, Sasaguri 811-2415, Japan. Electronic address: mchiwa@forest.kyushu-u.ac.jp.
authors.forename: Masaaki
authors.initials: M
authors.lastname: Chiwa
authors.affiliation: Kyushu University Forest, Kyushu University, 394 Tsubakuro, Sasaguri 811-2415, Japan.
authors.forename: Naoko
authors.initials: N
authors.lastname: Higashi
authors.affiliation: Kyushu University Forest, Kyushu University, 394 Tsubakuro, Sasaguri 811-2415, Japan.
authors.forename: Kyoichi
authors.initials: K
authors.lastname: Otsuki
authors.affiliation: Graduate School of Science and Engineering, Saga University, 1 Honjo-machi, Saga-city, Saga 840-8502, Japan.
authors.forename: Hiroki
authors.initials: H
authors.lastname: Kodama
authors.affiliation: Graduate School of Science and Engineering, Saga University, 1 Honjo-machi, Saga-city, Saga 840-8502, Japan.
authors.forename: Tohru
authors.initials: T
authors.lastname: Miyajima
authors.affiliation: Graduate School of Biosphere Science, Hiroshima University, 1-7-1 Kagamiyama, Higashi-Hiroshima, Hiroshima 739-8521, Japan.
authors.forename: Kazuhiko
authors.initials: K
authors.lastname: Takeda
authors.affiliation: Graduate School of Biosphere Science, Hiroshima University, 1-7-1 Kagamiyama, Higashi-Hiroshima, Hiroshima 739-8521, Japan.
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Sakugawa
mesh_terms: D001578:Benzopyrans / Q000032:analysis; D065928:Forests; D017665:Hydroxyl Radical / Q000032:analysis*; D009566:Nitrates / Q000737:chemistry; D009584:Nitrogen / Q000737:chemistry*; D045483:Rivers / Q000737:chemistry*
chemical_list: D001578:Benzopyrans; D009566:Nitrates; D017665:Hydroxyl Radical; D009584:Nitrogen; C005023:fulvic acid
keywords: Dissolved organic matter; Hydroxyl radical; Nitrate; Photo-Fenton reaction; Photoinduced processes; Stream