Sources of hydroxyl radical in headwater streams from nitrogen-saturated forest

• Published in: Chemosphere (Oxford) Vol. 119; pp. 1386 - 1390
• Main Authors: Chiwa, Masaaki, Higashi, Naoko, Otsuki, Kyoichi, Kodama, Hiroki, Miyajima, Tohru, Takeda, Kazuhiko, Sakugawa, Hiroshi
• Format: Journal Article
• Language: English
• Published: England Elsevier Ltd 01.01.2015
• Subjects: Benzopyrans - analysis; Dissolved organic matter; Forests; Formations; Headwaters; Hydroxyl radical; Hydroxyl Radical - analysis; Hydroxyl radicals; Nitrate; Nitrates - chemistry; Nitrogen - chemistry; Photo-Fenton reaction; Photoinduced processes; Photolysis; Rivers - chemistry; Saturation; Stream; Streams; Watersheds; Stream; Dissolved organic matter; Nitrate; Photo-Fenton reaction; Hydroxyl radical; Photoinduced processes
• ISSN: 0045-6535; 1879-1298
• DOI: 10.1016/j.chemosphere.2014.02.046

•Almost all sources of HO photoformation in streams were quantitatively elucidated.•Photo-Fenton reactions and the direct photolysis of FDOM were successfully separated.•High nitrate leaching increased HO photoformation in streams.•NO3- was an important HO source in headwater streams in nitrogen-saturated forests. 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.