Abstract
1. IntroductionA lot of nitrogenous fertilizers are used for the rapid economic growth when farm mechanization of Japan was promoted, and the expanded farmland, and high concentration Nitrate nitrogen came to be checked from national groundwater after the 1970s. Although it entered in recent years, nitric acid and nitrite nitrogen were added to the environmental standards method and the water quality standard item and the clear index was able to be done, the area which exceeds a standard value also still exists. Although Gumma Prefecture is proud of the leading agricultural-products quantity of production also in the whole country, groundwater Nitrate nitrogen contamination is also remarkable, the excess rates classified by all prefectures of the underground-water-quality measurement result in the Heisei 22 fiscal year which the Ministry of Environment performed are 21.9% and the worst [ 1 ], and contamination is so serious that it always goes into a higher rank it or before. In the research on groundwater of the Omama fan, Ayuba (1970) was delayed in the influence of rain for about two months, and appeared in the groundwater level, it was shown that can also send water temperature for about two months, and it is reflected from the temperature of surface of the earth, and it was shown clearly that the cause that the chlorine ion concentration of the central part of fan is high is drainage of pickles. Sekiya (1996) showed that the water temperature of a Yabutsuka side was comparatively high through every year, and Iwata (2004) investigated him at Nitta-cho 123 points for a fan end, and he showed clearly that nitric acid and nitrite nitrogen are high concentration at the point of the majority. 2. method of research After arranging the results of an investigation of the past in the region and clarifying long-term environmental change, a network of observation is newly fixed, not only groundwater but the network of observation of a river and an irrigation canal is arranged, and exchange of river water and groundwater is also considered. Record is considered especially this time as compared with the field survey result and the past which went in June – August, 2012. After observing AT, WT, EC, pH, RpH, a water level, etc., and the main ingredient was analyzed. 3. result and consideration The groundwater of high salt concentration considered for the value of EC of the Omama fan to be high as usual, and to originate in the pickles drainage pointed [ especially ] out at several places around 1970 was observed, and the area where Nitrate nitrogen concentration is high was also shown. There are a high point of pH, etc. locally and the necessity for examination also in consideration of a flow or exchange with river water was suggested. 4. conclusion Since it became consideration only by the observation result of one time in June - August this time, the change by a season was not able to be considered. I would like to perform continuous observation from now on, to also unite change of the groundwater level, and the difference in the amount from an irrigation canal, to advance consideration, and to clarify the long-term changes also including seasonal change.
