地形連鎖と水田潅がいを有する農業小集水域から流出する水質の特徴について

Abstract

Fertilizer which runs off from agricultural watershed was a big problem if the runoff flew into closed water body such as lakes and ponds.Therefore, many researches were performed to verify the characteristics of behevior for water quality in such the watershed. However, for a case where there is the irrigation intakes from outside of the watershed, it will give great affection on the runoff of the water quality. The authors selected a small agricultural watershed which had irrigation from outside and tophographical chain in the watershed. We have made servey for water quality, rainfall, and runoff water quality from August 3, 1992 till now. As the results we knew irrigation affected greatly on runoff water quality and load. And we know also the tophographical chain decrease T-N concentrations when springing water from upland was again irrigated into lowland paddy fields becase denitrofication occurred there. The sharp decrease in T-N concentration appeared during irrigation period. We knew, then, in order to estimate water quality, LQ equation such as L=aQb or L=aQ+b might be difficult to apply. We must think about other ideas where irrigation area spread widely in the watershed.