Japan Geoscience Union Meeting 2014

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Oral

Symbol M (Multidisciplinary and Interdisciplinary) » M-IS Intersection

[M-IS21_28AM2] Biogeochemistry

Mon. Apr 28, 2014 11:00 AM - 12:45 PM 511 (5F)

Convener:*Muneoki Yoh(Tokyo University of Agriculture and Technology), Hideaki Shibata(Field Science Center fot Northern Biosphere, Hokkaido University), Naohiko Ohkouchi(Japan Agency for Marine-Earth Science and Technology), Youhei Yamashita(Faculty of Environmental Earth Science, Hokkaido University), Chair:Yoshinori Takano(Institute of Biogeosciences, Japan Agency for Marine-Earth Science and Technology (JAMSTEC)), Seiya Nagao(Institute of Nature and Environmental Technology, Kanazawa University), Ichiro Tayasu(Center for Ecological Research, Kyoto University), Tomoya Iwata(Faculty of Life and Environmental Sciences, University of Yamanashi)

12:00 PM - 12:15 PM

[MIS21-P04_PG] Sources of hydroxyl radical photochemically produced in headwater streams from nitrogen-saturated forest

3-min talk in an oral session

*Masaaki CHIWA1, Naoko HIGASHI1, Kyoichi OTSUKI1, Hiroki KODAMA2, Tohru MIYAJIMA2, Kazuhiko TAKEDA3, Hiroshi SAKUGAWA3 (1.Kyushu University Forest, 2.Graduate School of Science and Engineering, Saga University, 3.Graduate School of Biosphere Science, Hiroshima University)

Keywords:hydroxyl radical, dissolved organic matter, nitrate, photo-Fenton reaction, stream, photoinduced processes

Hydroxyl radical (●OH) is the most oxidative reactant among the active oxygen species and oxidation reactions with ●OH are involved in important biogeochemical processes. In this study ●OH photoformation rate (ROH) was determined in headwater stream samples from nitrogen (N)-saturated forests, 1) to quantify the sources of ●OH in headwater streams and 2) to evaluate the nitrate (NO3-)-induced enhancement of ●OH 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 ROH. The results showed that almost all (97%; 81-109%) ROH 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 ●OH 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 ●OH formation in our headwater streams. High NO3- leaching caused by N saturation in forested watersheds increased ROH in the headwaters, indicating that N-saturated forest could significantly change photoinduced and biogeochemical processes via enhanced ●OH formation in downstream water.