2020 Volume 43 Issue 4 Pages 133-139
The annual average chemical oxygen demand (COD) in the Lake Inbanuma is about 10 mg L-1 for recent years. The amounts of wastewater loads from households and industry have been decreasing. However, the percentage of the inflow load from nonpoint sources is increasing. The paddy fields situated in the Lake Inbanuma basin is one of these nonpoint sources for which the nonpoint load is still unknown. Throughout the year, the investigation of the emission load from paddy fields situated in the Lake Inbanuma basin was conducted at the irrigation and drainage pump station. The annual effluent loads of COD, total nitrogen (T-N) , and total phosphorus (T-P) were 47.8 kg ha-1 yr-1, 6.8 kg ha-1 yr-1, and 0.61 kg ha-1 yr-1, respectively. These values were smaller than data for other regions. The results suggested that the reduction in load in the Lake Inbanuma is due to water being partially circulated as a result of water being pumped up from the drainage canal. The annual balance loads of COD, T-N, and T-P were -107.3 kg ha-1 yr-1, -28.4 kg ha-1 yr-1, and -1.3 kg ha-1 yr-1, respectively, which show a reduction type.
