Water Quality Monitoring at Lowland Creek Area by GIS and Improvement Trials Using Fallow Paddy Fields

Lowland area at seacoast of the Arikake Bay in Japan is famous for rotational use of creek water for rice production. About 40 years ago, almost whole area was covered with rice paddy in summer season. For the purpose of regulating the rice production, about 40 % of rice fields have been used for upland crop production. In addition to the changes of agricultural style, the inflow of the contaminated drainage water has been increased by the development of urbanization. To keep the sustainable agriculture in this area, it is requested to establish the regional control system to keep the creek water clean. The objective of this study is to evaluate the effect of the rice paddy, upland crop, and greenhouse cultivations on the water quality. First, the effects of water management, fertilizer management, crop management on the nitrogen and phosphate loads to creek water were studied experimentally at the study site about 10 ha. Water purification functions of rice paddy were evaluated quantitatively. From this result, it was advocated to prepare water ponded fallow fields through out the year for cleaning creek water. Additionally, the effectiveness for water purification by some vegetables planted in the fallow paddy are introduced. Second, daily changes of creek water qualities were monitored with the automatic sampler at the end of creek networks. Using the data, the relationships between land use condition and water quality along the main creek were simulated with the support of GIS.