The change in the quality of irrigation water in ten years in Fukuoka prefecture [Japan]

The chemical properties of irrigation waters in Fukuoka Prefecture were examined from 1986 to 1988. The irrigation waters were sampled at 46 place several times during the period from puddling of paddy fields to the ripening of rice plants. Among the 232 waters sampled, the waters showing a higher value than the standard for agricultural water in pH, EC, COD and T-N were 28%, 11%, 46% and 87%, respectively. These values were generally higher than those reported in other prefectures in Japan. COD values were higher in Chikugo and Iizuka-Yahata and T-N was higher in Chikugo, a rural area in Fukuoka Prefecture. These values declined at the time of rice-transplanting, suggesting the run off the water from the paddy fields. COD was highly correlated with T-P, showing that the water pollution by organic matters was caused by the discharge of waste water containing a high amount of P. It is considered that reduction of the discharge of waste water which contains P is especially necessary for preventing the pollution. Comparison of the values obtained in 1986 - 88 with those in 199l - 93 in Fukuoka Prefecture showed that pH, COD, T-N and T-P increased in almost all areas.