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Kohzu, A., National Institute for Environmental Studies, Tsukuba, Japan, kohzu@nies.go.jp
Watanabe, M., National Institute for Environmental Studies, Tsukuba, Japan
Hayashi, S., National Institute for Environmental Studies, Tsukuba, Japan
Imai, A., National Institute for Environmental Studies, Tsukuba, Japan
Nakajima, Y., National Institute for Agro-Environmental Sciences, Tsukuba, Japan
Osaka, K., The University of Shiga Prefecture, Hikone, Japan
Miura, S., National Institute for Environmental Studies, Tsukuba, Japan

NITRATE METABOLISM IN FOREST ECOSYSTEMS FROM THE ANALYSIS OF NITRATE 15N AND 18O NATURAL ABUNDANCES IN MOUNTAIN STREAMS AROUND MT. TSUKUBA, JAPAN

The isotopic signatures of nitrate in streams revealed the dominant processes associated with nitrogen (N) export from a forested watershed. We conducted two types of field sampling, that is, the synoptic survey at 40 sites around Mt. Tsukuba and highly frequent sampling during rain run-off. The result of the synoptic survey showed that both seasonality and geophysical characteristics of the watershed significantly affected the N export processes in the forest watershed. From the analysis of the run-off samples, we could classify the nitrate discharge processes during run-off event into four kinds of steps. The discovered facts were as follows: 1) At seven sites among the 40 sites, the isotopic signal (i.e., high delta18O) indicated that throughfall was one of the primary nitrate sources in winter. 2) The increased nitrate production and consumption activity during the summer and the increase in the relative contribution of nitrate derived from throughfall in winter were related to the geophysical/geological characteristics of the watershed. 3) At the beginning of the run-off, the contribution of nitrate derived from throughfall to the stream water was significantly increased.

Poster presentation

Session #:SS58
Date: 7/12/2012
Time: 18:00 - 20:00