Abstract
In an urbanized agricultural area near the center of Ha Noi City, pH, ORP, and ammonium-N and nitrate-N concentrations were monitored for the surface water (canal/pond) and groundwater (shallow/deep tubewell) used locally for irrigation and domestic purposes, respectively. Only vegetables were cultivated eleven times throughout the year in farmland, and the rate of annual fertilizer N application amounted to 960-1, 150kg/ha. The pH was in the neutral range. The ORP varied from reductive/intermediate to oxidative states. The ammonium-N concentration was high (1.3-15.1mg/L), while the nitrate-N concentration was low (0.09-2.2mg/L) . The effect of fertilizer N application on the ammonium-N concentration was recognized in the surface water. The presence of ammonium-N in the groundwater was due to the percolation of surface water contaminated with NH4+. The effect of fertilizer N application on the nitrate-N concentration was not recognized in either surface water or groundwater. In the canal water, the ammonium-N plus nitrate-N concentration reached a harmful level for irrigation use (>5mg/L) . In the groundwater, the ammonium-N concentration exceeded the critical level of drinking use for human health. Therefore, countermeasures should be urgently implemented.
