Characteristics of Phosphorus in Sediments in Drainage Canals in Paddy-Field Districts around Lake Biwa

概要

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Phosphorus (P) is a limiting factor of eutrophication in many lakes. Paddy-field districts are major non-point sources of P; water pollution prevention measures are to be implemented in these districts. However, sediment in drainage canals has a large P buffering capacity and can release P to the water column when input of P from paddy fields is reduced. Therefore, it is necessary to evaluate the amounts of P in the sediment in drainage canals. In this study, the sediments in drainage canals in paddy-field districts around Lake Biwa were investigated. The amounts and fractions of P in the sediments during both the irrigation period and the non-irrigation period were analyzed. Results showed that the mean value of total P in the sediment was 0.6 g/kg in both periods, but total P in non-irrigation periods tends to be greater than that during irrigation periods for each site in the study. Furthermore, over 70% of total P was inorganic on the average. Moreover, the fractions of organic and inorganic P exhibited seasonal variability. The potential contribution of water-extractable P in the sediment to total P in drainage water increased from June to November.