【Changeof nitrogen with years】

　Nitrogen concentration in rivers which causes generation of water bloom in Akanoy Bay is decreasing in upstream and midstream so long as these 4 years are concerned. 

　Various efforts of the members and the residents concerned to keep rivers and streams clean which include increasing houses connected to the sewer system and broadening activities to improve the water front environment have produced a good effect.

　It is, however, necessary to continue monitoring further in order to make long-term transition clear.

　Phosphorus concentration which is regarded as influencing water bloom generation more than nitrogen is decreasing as well but not so evidently as nitrogen. 

　Water quality ranking shows us that more river points are polluted during the rice growing period when rice fields are fed with water than during the remaining period.

　It is thought that the elusion of phosphorus component contained in chemical fertilizer spread in rice fields has influence on the fact that high concentration of phosphorus is detected at many river points despite that river water flows abundantly and does not stagnate much during the rice-growing period.