a study on evaluation for the loads of notrogen and phosphorus in a small watershed covered with an artificail forest

To present proper methods for estimating output fluxes of nitrogen (T-N) and phosphorus (T-P) from the watershed, hydrological and hydrochemical survey was conducted in a small watershed covered with an artificial forest of Chamaecyparis Obtusa, Japanese Cypress, over a period of 2-year.<br>To evaluate the reliability of L-Q method during rain events, the fluxes calculated by the method were compared with the measured fluxes during rain events. The result shows that L-Q method underestimates the fluxes of T-P, which constituents most proportion of particulate phosphorus (PTP), during rain events while the calculated fluxes of T-N were fitted well with the measured fluxes. The higher concentration of PTP was, the significantly L-Q method underestimated the fluxes of T-P. Therefore, it is suggested that L-Q method does not properly evaluate the fluxes of PTP during rain events and thus underestimates the annual fluxes of T-P.<br>I developed 2-component model, which calculates each fluxes of dissolved constituent and particulate constituent separately and subsequently sums them, to evaluate proper output fluxes of T-P including runoff characteristics of PTP during rain events. The result shows that the fluxes calculate by the model are fitted better with the measured fluxes than those by L-Q model. Therefore, it is considered that 2-component model describes runoff characteristics of PTP and thus runoff characteristics of PTP need to be taken into account in order to evaluate the proper fluxes of T-P.