森林小流域で測定した比流出量の収斂性の検証

概要

論文の詳細を見る
In the previous paper, the loading rates of TN and TP were measured in Aburahi-S Experimental Forested Watershed (AsEFW; 3.34 ha), and the specific loads (Lss) were evaluated to be 9.95 and 0.168 kg·ha-1·y-1, respectively. The Ls values should be verified to converge within AsEFW in order to be appreciable as parameters characterizing AsEFW. However, it is difficult to install a sufficient number of weirs in such a small watershed to prove directly such convergence. In this paper, water samples of the baseflow were taken up monthly at twelve sites (R0-R7 and L1-L4) located upstream of the weir (R0) of AsEFW for one year. The average concentrations of the nutrients at R0 did not significantly differ (p<0.01) from those at R1-R4 within a distance of 130 m. During two rainfall events (58.5 and 151 mm), the concentrations were observed at R0, R1 and R3. The concentration levels and changing patterns were similar between R0 and these upstream sites. It was concluded, from these results, that the Ls values converge within AsEFW. Since springs may affect significantly Ls values, especially in small watersheds, their existence and effect should be checked. A small spring (L5) was found in AsEFW, and its influence on the Ls values of the nutrients was confirmed to be negligible.