Changes of Inorganic Nitrogen Concentrations of Groundwater in Farming Villages around Ha Noi during the Latest Few Years

摘要

Groundwater in farming villages in the Red River delta has been polluted seriously by inorganic-N. In order to clarify how the water is polluted with inorganic-N, how the level of pollution changes with time/commune, and what lies in the background ofthe pollution, the ammonium-N and nitrate-N concentrations of the groundwater were monitored in 3 communes around Ha Noi. In these communes, three times of cropping has been made annually with a huge amount of fertilizer application. Monitoring was done7 times during October 2002 and September 2005 with an interval of 6 months. The ammonium-N concentration was mostly exceeded the Vietnamese water standard for drinking use (Sa 0.039 mg/L), while the nitrate-N concentration was lower than the WHO drinking water standard and the Vietnamese water standard for drinking use (both Sj 10 mg/L). The ammonium-N concentration varied with monitoring times and with communes when the monitoring was restricted to the 1st through 5th measurements, where the temporalchange of the concentration did not show the monotonous increase but the concentration was the highest at the 2nd or 3rd monitoring. Concerning the spatial variation of the ammonium-N concentration, the effect of the amount of fertilizer N application,which was different with communes, was conceivable. At the 6th monitoring, the ammonium-N concentration became the highest with an irregular temporal pattern, showing a cautious aspect of the temporal variation. The nitrate-N concentration significantlyvaried with communes but did not with monitoring times throughout the monitoring. The nitrate-N concentration in communes of the low-lying area was maintained very low throughout the monitoring, showing that nitrification hardly occurrs in groundwater inthese communes.