Characteristics of Load from Lotus Fields along Lake Kasumigaura by Irrigating from River

The shipment of lotus plants in Ibaraki Prefecture is the first of its kind in the entire country. About 90 % of the lotus plantation in Ibaraki Prefecture was distributed the town and villages along Lake Kasumigaura. In this study, we investigated the load that outflows to the lake from the irrigation and drainage pump station and gates via the lotus fields, and further inflows to the lotus fields from Kawajiri River. The mechanism of load and unit effluent load of the lotus fields were determined by estimating the water and mass balances. As a result, 95% of the drainage from the study area entered the lake, and 5% of that drainage was recirculated as irrigation water. The discharged loads of COD, T-N, and T-P in cultivating period were found to be maximum during the puddling and planting period. Based on the mass balances of COD, T-N, and T-P, deduction in inflow and outflow loads from Lake Kasumigaura were 45.59, 2.97, and 2.22 kg.km super(-2).d super(-1), respectively. It was concluded that the discharged load can be effectively reduced by improving the irrigation system during puddling and planting period.