Water-saving irrigation of paddy field to reduce nutrient runoff.

The purpose of this work is to study the effect of a type of water-saving irrigation (WSI) on nutrient runoff of paddy field. The volume of surface drainage was maintained low by WSI. In particular, WSI effectively reduced surface drainage in rain events.

Scenario analysis for reduction of pollutant load discharged from a watershed by recycling of treated water for irrigation.

A model in which a river model was layered on a distributed model (double-layered model) was developed to analyse the transport of water and pollutants (nitrogen, phosphorus, and BOD as organic matter) in watersheds and rivers. The model was applied to the watershed of Abragafuchi Lake, Japan, where serious water pollution has occurred over three decades, and the applicability of the model was demonstrated. Scenarios of recycling of sewage treated-water into agriculture to reduce pollutant load discharged into the lake were analysed.

Estimation of the impact of particulate organic matter drained from a freshwater reservoir on the sea using diatom tracking.

We estimated the extent of suspended solids (SS) and particulate organic matter (POM) discharged from a freshwater reservoir, called the Isahaya Reservoir, into a sea area by tracking the diatom frustules produced in the reservoir. The estimation method is based on the fact that Skeletonema subsalsum and S. costatum, are the predominant diatoms in the reservoir and the sea, respectively, and the discharged SS and POM contain the freshwater diatom, S.

Surface discharge of heavy metals from low farmland.

Runoff heavy metals from farmland were examined using the field data for the summer of 2005. The observation farmland is located on lowland where the irrigation water was contaminated with the drained water from the upstream farmlands. The area of the farmland is 11.

Economic valuation of reduction in nitrogen outflow from a paddy field area equipped with a recycling irrigation facility.

We estimated the reduction in nitrogen outflow load from a paddy field that had a recycling irrigation facility and, by using a replacement cost method, evaluated the economic effect of nitrogen removal by the paddy field during the irrigation period in the Yoshinuma region of Tsukuba City, Japan. The recycling ratio of outflow water (proportion of outflow reused) was 13.5%.