森林立地学会誌 森林立地44（1），2002，11〜20
Jpn.J.For.Environment 44（1），11−20 2002
スギ・ヒノキ壮齢人工林小流域における降雨の移動に伴う溶存有機態窒素
および溶存有機態炭素の動態
小柳信宏＊・浦川梨恵子＊＊・生原喜久雄＊＊＊・戸田浩人＊＊＊
＊東京農工大学大学院連合農学研究科・＊＊東京農工大学大学院農学研究科・＊＊＊東京農工大学農学部
スギ・ヒノキ壮齢人工林小流域での降雨の移動に伴う溶存有機態窒素（DON）と溶存有機態炭素（DOC）の動態特性を明らかにするため，降雨，林内雨，樹幹流，A0層通過水，土壌水，湧水および渓流水に含まれるDON，無機態窒素（DIN）およびDOCを調査した。DONおよびDOCとも降雨＜林内雨＜A0層通過水の順に濃度が高まるが，土壌水で著しく低下した。DOCは湧水・渓流水で濃度がさらに低下した。年間のDONフラックスは林内雨で5.5kgha-1，A0層通過水で11.1kgha-1，渓流水で痕跡程度（0.9kgha-1以下）であった。DOCフラックスはそれぞれ139，185，6.4kgha-1であった。A0層通過後に全溶存態窒素（DON＋DIN）に対するDONの割合が低下し，DINではNH4-Nが減少し，NO3-Nが増加した。A0層通過後のDOCの付加量は林内雨に比べて少なかった。以上のことから．A0層におけるDONおよびDOCの生成とともに，活発な無機化と硝化による溶存有機物の消費が示唆された。渓流への窒素の年間流出量は13.8kgha-1であり，DONの割合は7％以下と推定された。年間のDOC流出量は欧米の森林流域に比べて少なかった。本調査地で代表されるような日本のスギ・ヒノキ壮齢人工林流域では，渓流への窒素と炭素の流出に対するDONとDOCの寄与は小さいと考えられた。
Nobuhliro
Oyanagi, Rieko Urakawa, Kikuo Haibara and Hiroto Toda : The dynamics of
dissolved organic nitrogen and dissolved organic carbon in a small watershed of
established Japanese cedar and cypress plantation.
To clarify the dynamics of dissolved
organic nitrogen (DON) and dissolved organic carbon (DOC) with vertical
movements of rainfall in a small watershed of established Japanese cedar (Cryptomeria japonica D. Don) and
Japanese cypress (Chamaecyparis obtusa
Sieb. and Zucc.) plantation, DON, dissolved inorganic N (DIN), DOC in
precipitation, throughfall, stemflow. A0-percolation, soil water, spring water
and stream water were investigated. DON and DOC in order of high concentrations
were in A A0-percolation>throughfall>precipitation,
and was rapidly in low concentration in soil water. The concentration of DOC
decreased more along spring water and stream water. Annual fluxes of DON were
5.5kgha-1 in
throughfall, 1l. 1kgha-1 in A0-percolation, and only a little (under
0.9kgha-1) in stream water. Annual fluxes of DOC were 139, 185, and
6.4kgha-1, respectively. From throughfall to A0-percolation, the percentage of DON to
total dissolved nitrogen (TDN= DON+ DIN) and the amount of NH4-N
decreased, and the amount of NO3-N increased. The amount of DOC flux
increase in throughfal1 minus A0-percolation was smaller than that in precipitation
minus throughfall. These results suggested that both the productivity of DON
and DOC, and the activity of microbes for decomposition and nitrification in A0-layer were high. The annual output of
TDN from watershed was 13.8kgha-1, and the percentage of DON/TDN was
lower than 7%. The annual output of DOC was 6.4kgha-1 , which was
smaller than those from the watersheds in Europe and North America. These
results suggested that DON and DOC do not play an important role in N and C
discharge from stream water in the established cedar and cypress plantation
forests in Japan.