Abstract
Nutrient effluent load from paddy fields has a large impact on water quality in the downstream areas. The sediment in drainage canals can act as nutrient source by releasing nutrients to the overlying drainage water. In this study, we evaluated the effect of bioturbation caused by tubificid worms, which live commonly in paddy fields, on nutrient release from the sediment in drainage canals. We investigated a low-lying paddy field district adjacent to Lake Biwa. We also sampled drainage water and the sediment in the study site and conducted incubation experiment of the sediment for four weeks. In the sediment incubation experiment, we added different densities of tubificid worms to the sediment. The effect of tubificid worms on nitrogen release was much larger than that on phosphorus. Nitrogen was mainly released as ammonium nitrogen by the excretion of tubificid worms.
