The dynamics of dissolved organic nitrogen and dissolved organic carbon in a small watershed of established Japanese cedar and cypress plantation

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  • 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
  • スギ ヒノキ ソウレイ ジンコウリン ショウリュウイキ ニ オケル コウウ ノ イドウ ニ トモナウ ヨウゾン ユウキタイ チッソ オヨビ ヨウゾン ユウキタイ タンソ ノ ドウタイ

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Abstract

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. A_0-percolation, soil water, spring water and stream water were investigated. DON and DOC in order of high concentrations were in A_0-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, 11.1kgha^<-1> in A_0-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 A_0-percolation, the percentage of DON to total dissolved nitrogen (TDN=DON+DIN) and the amount of NH_4-N decreased, and the amount of NO_3-N increased. The amount of DOC flux increase in throughfall minus A_0-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 A_0-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.

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