The dynamics of dissolved organic nitrogen and dissolved organic carbon in a small watershed of established Japanese cedar [Cryptomeria japonica] and cypress [Chamaecyparis obtusa] 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, A sub0-percolation, soil water, spring water and stream water were investigated. DON and DOC in order of high concentrations were in A sub0-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 sup(-1) in throughfall, 11.1kgha sup(-1) in A sub0-percolation, and only a little (under 0.9kgha sup(-1) in stream water. Annual fluxes of DOC were 139, 185, and 6.4kgha sup(-1), respectively. From throughfall to A sub0-percolation, the percentage of DON to total dissolved nitrogen (TON = DON + DIN) and the amount of NH4-N decreased, and the amount of NO3-N increased. The amount of DOC flux increase in throughfall minus A sub0-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 sub0-layer were high. The annual output of TDN from watershed was 13. Skgha sup(-1), and the percentage of DON/TDN was lower than 7%. The annual output of DOC was 6.4kgha sup(-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."