抄録
Many water quality conservation measures have been implemented in agricultural areas to reduce pollutant loading. However, controlling discharged drainage water enhances sedimentation of suspended solids in drainage canals in those areas. The sediment, which has high concentrations of nitrogen (N) and carbon (C), may release N and C and lower the effect of the conservation measures. In this study, we clarified the characteristics of N and C in the sediment in drainage canals. We have investigated paddy field districts around Lake Biwa and measured N and C contents in the sediment. We also conducted incubation experiment of the sediments sampled in two different paddy field districts. Changes in N and C fractions in the sediments and in the overlying water during the incubation period were analyzed. As a result, concentrations of total N and total organic C in the overlying water of the incubated sediment were respectively about two and three times those of drainage water measured at the study points. Total N flux was 33.0 - 41.1 mgN/m2/day and total organic C flux was 25.3 - 48.4 mgC/m2/day. It was indicated that the sediments had enough N and C for determining the water quality of drainage water.
